Understanding nutrition [4 Australian & New Zealand ed.] 9780170424431, 017042443X
551 17 60MB
English Pages [834] Year 2019
IFC
Prelims
Title Page
Imprint Page
Contents in brief
Contents
Guide to the text
Guide to the online resources
Preface
About the authors
Acknowledgements
Chapter 1: An overview of nutrition
1.1 Food choices
1.2 The nutrients
1.3 The science of nutrition
1.4 Nutrient Reference Values
1.5 Nutrition assessment
1.6 Diet and health
Chapter activities
Highlight1: 1.7 Nutrition information and misinformation – on the Net and in the news
Chapter 2: Planning a healthy diet
2.1 Principles and guidelines
2.2 Diet-planning guides
2.3 Food labels
Chapter activities
Highlight 2: Vegetarian diets
Chaper 3: Digestion, absorption and transport
3.1 Digestion
3.2 Absorption
3.3 The circulatory systems
3.4 The health and regulation of the GI tract
Chapter activities
Highlight3: 3.5 Common digestive problems
Chapter 4: The carbohydrates: sugars, starches and dietary fibre
4.1 The chemist’s view of carbohydrates
4.2 The simple carbohydrates
4.3 The complex carbohydrates
4.4 Digestion and absorption of carbohydrates
4.5 Glucose in the body
4.6 Health effects and recommended intakes of sugars
4.7 Alternative sweeteners
4.8 Health effects and recommended intakes of starch and dietary fibre
Chapter activities
Highlight4: 4.9 Carbs, kilojoules and controversies
Chapter 5: The lipids: triglycerides, phospholipids and sterols
5.1 The chemist’s view of fatty acids and triglycerides
5.2 The chemist’s view of phospholipids and sterols
5.3 Digestion, absorption and transport of lipids
5.4 Lipids in the body
5.5 Health effects and recommended intakes of saturated fats, trans fats and cholesterol
5.6 Health effects and recommended intakes of mono-unsaturated and polyunsaturated fats
5.7 From guidelines to groceries
Chapter activities
Highlight: High-fat foods – friend or foe?
Chapter 6: Protein: amino acids
6.1 The chemist’s view of proteins
6.2 Digestion and absorption of protein
6.3 Proteins in the body
6.4 Protein in foods
6.5 Health effects and recommended intakes of protein
Chapter activities
Highlight 6: 6.6 Nutritional genomics
Chapter 7: Metabolism: transformations and interactions
7.1 Chemical reactions in the body
7.2 Breaking down nutrients for energy
7.3 Energy balance
Chapter activities
Highlight: 7.4 Alcohol in the body
Chapter 8: Energy balance and body composition
8.1 Energy balance
8.2 Energy in: the kilojoules foods provide
8.3 Energy out: the kilojoules the body expends
8.4 Body weight, body composition and health
8.5 Health risks associated with body weight and body fat
Chapter activities
Highlight8: 8.6 Eating disorders
Chapter 9: Weight management: overweight, obesity and underweight
9.1 Overweight and obesity
9.2 Causes of overweight and obesity
9.3 Problems of overweight and obesity
9.4 Aggressive treatments for obesity
9.5 Weight-loss strategies
9.6 Underweight
Chapter activities
Highlight 9: 9.7 The latest and greatest weight-loss diet – again
Chapter 10: The water-soluble vitamins: B group vitamins and vitamin C
10.1 The vitamins – an overview
10.2 The B group vitamins – as individuals
10.3 The B group vitamins – in concert
10.4 Vitamin C
Chapter activities
Highlight 10: 10.5 Vitamin and mineral supplements
Chapter 11: The fat-soluble vitamins: A, D, E and K
11.1 Vitamin A and beta-carotene
11.2 Vitamin D
11.3 Vitamin E
11.4 Vitamin K
Chapter activities
Highlight 11: 11.5 Is it time to shine for vitamin D?
Chapter 12: Water and the major minerals
12.1 Water and the body fluids
12.2 The minerals – an overview
12.3 Sodium
12.4 Chloride
12.5 Potassium
12.6 Calcium
12.7 Phosphorus
12.8 Magnesium
12.9 Sulphate
Chapter activities
Highlight 12: 12.10 Osteoporosis and calcium
Chapter 13: The trace minerals
13.1 The trace minerals – an overview
13.2 Iron
13.3 Zinc
13.4 Iodine
13.5 Selenium
13.6 Copper
13.7 Manganese
13.8 Fluoride
13.9 Chromium
13.10 Molybdenum
13.11 Other trace minerals
Chapter activities
Highlight 13: 13.12 Phytochemicals and functional foods
Chapter 14: Fitness: physical activity, nutrients and body adaptations
14.1 Fitness
14.2 Energy systems and fuels to support activity
14.3 Vitamins and minerals to support activity
14.4 Fluids and electrolytes to support activity
14.5 Diets for physically active people
Chapter activities
Highlight 14: 14.6 Supplements as ergogenic aids
Chapter 15: Life cycle nutrition: pregnancy and lactation
15.1 Nutrition prior to pregnancy
15.2 Growth and development during pregnancy
15.3 Maternal weight
15.4 Nutrition during pregnancy
15.5 High-risk pregnancies
15.6 Nutrition during lactation
Chapter activities
Highlight 15: 15.7 Foetal alcohol syndrome
Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
16.1 Nutrition during infancy
16.2 Nutrition during childhood
16.3 Nutrition during adolescence
Chapter activities
Highlight 16: 16.4 Childhood obesity and the early development of chronic diseases
Chapter 17: Life cycle nutrition: adulthood and the later years
17.1 Nutrition and longevity
17.2 The ageing process
17.3 Energy and nutrient needs of older adults
17.4 Nutrition-related concerns of older adults
17.5 Food choices and eating habits of older adults
Chapter activities
Highlight 17: 17.6 Nutrient–drug interactions
Chapter 18: Diet-related disease
18.1 Nutrition and infectious diseases
18.2 Nutrition and chronic diseases
18.3 Cardiovascular disease
18.4 Hypertension
18.5 Diabetes mellitus
18.6 Cancer
18.7 Recommendations for chronic disease prevention
Chapter activities
Highlight 18: 18.8 Complementary and alternative medicine
Chapter 19: Consumer concerns about foods and water
19.1 Food safety and food-borne illnesses
19.2 Environmental contaminants
19.3 Natural toxins in foods
19.4 Pesticides
19.5 Food additives
19.6 Consumer concerns about water
Chapter activities
Highlight 19: 19.7 Food biotechnology
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Appendix G
Answers
Glossary
Index
IBC
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- Sharon Rady Rolfes
- Tim Crowe
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Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Body mass index
In the table below, find your height in the left-hand column and look across the row until you find the number that is closest to your weight. The number at the top of that column identifies your body mass index (BMI) (in kg/m2). To calculate BMI yourself, divide your weight in kilograms by the square of your height in metres. Chapter 8 describes how BMI correlates with disease risks and defines obesity, and Chapter 16 presents BMI for children and adolescents. The area shaded in blue represents healthy weight ranges. The figure below presents silhouettes of various BMI. WOMEN
17
18
20
21
23.5
22.5
24
32
35
31.5
37
MEN
18
24.5
26.5
The Body Test (1988). Copyright © 1988 Dietitians of Canada. Reprinted with permission.
BODY MASS INDEX (BMI) IN kg/m2 18
19
20
21
22
23
24
25
26
27
28
Height (cm)
29
30
31
32
33
34
35
36
37
38
39
40
Body weight (kg)
150.0
40
43
45
47
49
52
54
56
58
60
63
65
67
69
72
74
76
78
81
83
85
88
90
152.5
42
44
46
49
51
54
56
58
60
63
65
67
69
72
74
76
79
81
83
86
88
90
93
155.0
43
45
48
50
53
55
58
60
62
65
67
69
72
74
77
79
82
84
86
88
91
93
96
157.5
44
47
49
52
54
57
59
62
64
67
69
72
74
77
79
82
84
87
89
92
94
97
99
160.0
46
49
51
54
56
59
61
64
66
69
72
74
77
79
82
84
87
89
92
94
97
100
102
162.5
48
50
53
55
58
61
64
66
68
71
74
77
79
82
84
87
89
93
95
98
100
103
105
165.0
49
52
54
57
60
63
65
68
71
73
76
79
82
84
87
90
93
95
98
101
103
106
109
167.5
51
54
56
59
62
64
67
70
73
76
78
81
84
87
90
93
95
98
101
104
107
109
112
170.0
52
55
58
61
64
66
69
72
75
78
81
84
87
90
93
96
98
101
104
107
110
113
116
172.5
54
57
59
63
65
68
72
74
78
80
83
86
89
92
95
98
101
104
107
110
113
116
119
175.0
55
58
61
64
68
70
73
77
80
83
86
89
92
95
98
101
104
107
110
113
117
119
122
177.5
57
60
63
66
69
73
76
79
82
85
88
92
95
98
101
104
107
110
113
117
120
123
126
180.0
59
62
65
68
71
75
78
81
84
88
91
94
98
101
104
107
110
113
117
120
123
127
130
182.5
60
64
67
70
73
77
80
83
87
90
93
97
100
103
107
110
113
117
120
123
127
130
133
185.0
62
65
68
72
75
79
83
86
89
93
96
99
103
107
110
113
117
120
123
127
131
134
137
187.5
64
67
70
74
78
81
84
88
92
95
99
102
106
109
113
116
120
123
127
130
134
137
141
190.0
65
69
73
76
80
83
87
91
94
98
102
105
109
112
116
120
123
127
130
134
137
141
145
192.5
67
71
74
78
82
86
89
93
97
100
104
108
112
115
119
123
127
130
134
138
142
145
149
195.0
68
73
76
80
84
88
92
95
99
103
107
111
114
118
122
126
130
133
137
141
145
149
152
197.5
70
74
78
82
86
90
94
98
102
106
109
113
117
121
125
129
133
137
141
145
149
152
156
200.0
72
76
80
84
88
92
96
100
104
108
111
115
119
123
127
131
135
139
143
147
151
154
158
Underweight
Healthy weight
Overweight
Obese
(,18.5)
(18.5–24.9)
(25–29.9)
($30)
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
4th
Australian & New Zealand Edition
understanding nutrition Eleanor Whitney Sharon Rady Rolfes Tim Crowe Adam Walsh
Vitamin C aids with iron absorbtion Nitrogen fixing, environmentally sustainable crop
Niacin helps reduce production of triglycerides
Chop before cooking to release sulforaphane
Very low GI food
Folate-rich foods are important during pregnancy
Amino acid asparagine is a natural diuretic
Vitamin K is essential for blood clotting
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Understanding Nutrition
© 2019 Cengage Learning Australia Pty Limited
4th Edition Eleanor Whitney
Copyright Notice
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Authorised adaptation of Whitney & Rolfes, Understanding Nutrition 15e, 9781337392693, © 2019
Cengage Learning New Zealand Unit 4B Rosedale Office Park 331 Rosedale Road, Albany, North Shore 0632, NZ For learning solutions, visit cengage.com.au Printed in China by 1010 Printing International Limited. 1 2 3 4 5 6 7 23 22 21 20 19
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
iii
CONTENTS IN BRIEF
Guide to the text Guide to the online resources Preface About the authors Acknowledgements
viii xi xiii xv xvi
CHAPTER 1
An overview of nutrition
1
CHAPTER 2
Planning a healthy diet
39
CHAPTER 3
Digestion, absorption and transport
66
CHAPTER 4
The carbohydrates: sugars, starches and dietary fibre
95
CHAPTER 5
The lipids: triglycerides, phospholipids and sterols
134
CHAPTER 6
Protein: amino acids
177
CHAPTER 7
Metabolism: transformations and interactions
213
CHAPTER 8
Energy balance and body composition
253
CHAPTER 9
Weight management: overweight, obesity and underweight
287
CHAPTER 10 The water-soluble vitamins: B group vitamins and vitamin C
329
CHAPTER 11 The fat-soluble vitamins: A, D, E and K
377
CHAPTER 12 Water and the major minerals
406
CHAPTER 13 The trace minerals
452
CHAPTER 14 Fitness: physical activity, nutrients and body adaptations
491
CHAPTER 15 Life cycle nutrition: pregnancy and lactation
527
CHAPTER 16 Life cycle nutrition: infancy, childhood and adolescence
563
CHAPTER 17 Life cycle nutrition: adulthood and the later years
600
CHAPTER 18 Diet-related disease
629
CHAPTER 19 Consumer concerns about foods and water
669
Appendix A Cells, hormones and nerves Appendix B Basic chemistry concepts Appendix C Biochemical structures and pathways Appendix D Measures of protein quality Appendix E Nutrition assessment Appendix F Physical activity and energy requirements Appendix G Aids to calculation Answers Glossary Index
703 708 717 735 738 762 765 767 771 791
Copyright
High in lutein, a carotenoid that may help prevent Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or vision in part.loss WCN 02-200-202
Radishes can help allieviate jaundice
iv
CONTENTS Guide to the text viii Guide to the online resources xi Preface xiii About the authors xv Acknowledgements xvi CHAPTER 1 AN OVERVIEW OF NUTRITION
Contains three times as much carbohydrate as nonstarchy vegetables
1.1 Food choices 1.2 The nutrients 1.3 The science of nutrition 1.4 Nutrient Reference Values 1.5 Nutrition assessment 1.6 Diet and health CHAPTER ACTIVITIES
1 2 4 10 17 22 25 29
32
CHAPTER 2 PLANNING A HEALTHY DIET
39
2.1 Principles and guidelines 2.2 Diet-planning guides 2.3 Food labels CHAPTER ACTIVITIES
40 44 53 58
CHAPTER 3 DIGESTION, ABSORPTION AND TRANSPORT
4.1 The chemist’s view of carbohydrates 4.2 The simple carbohydrates 4.3 The complex carbohydrates 4.4 Digestion and absorption of carbohydrates 4.5 Glucose in the body 4.6 Health effects and recommended intakes of sugars 4.7 Alternative sweeteners 4.8 Health effects and recommended intakes of starch and dietary fibre CHAPTER ACTIVITIES HIGHLIGHT 4 4.9 Carbs, kilojoules and controversies
HIGHLIGHT 1 1.7 Nutrition information and misinformation – on the Net and in the news
HIGHLIGHT 2 Vegetarian diets
CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 95
61
66
3.1 Digestion 3.2 Absorption 3.3 The circulatory systems 3.4 The health and regulation of the GI tract CHAPTER ACTIVITIES
67 75 77 80 85
HIGHLIGHT 3 3.5 Common digestive problems
87
96 96 100 102 107 112 116 120 126 129
CHAPTER 5 THE LIPIDS: TRIGLYCERIDES, PHOSPHOLIPIDS AND STEROLS 134 5.1 The chemist’s view of fatty acids and triglycerides 5.2 The chemist’s view of phospholipids and sterols 5.3 Digestion, absorption and transport of lipids 5.4 Lipids in the body 5.5 Health effects and recommended intakes of saturated fats, trans fats and cholesterol 5.6 Health effects and recommended intakes of mono-unsaturated and polyunsaturated fats 5.7 From guidelines to groceries CHAPTER ACTIVITIES
156 160 166
HIGHLIGHT 5 High-fat foods – friend or foe?
169
CHAPTER 6 PROTEIN: AMINO ACIDS
177
6.1 The chemist’s view of proteins 6.2 Digestion and absorption of protein
178 182
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
135 142 144 151
154
Contents
6.3 Proteins in the body 6.4 Protein in foods 6.5 Health effects and recommended intakes of protein CHAPTER ACTIVITIES
184 194 195 203
HIGHLIGHT 6 6.6 Nutritional genomics
206
CHAPTER 7 METABOLISM: TRANSFORMATIONS AND INTERACTIONS 213 7.1 Chemical reactions in the body 7.2 Breaking down nutrients for energy 7.3 Energy balance CHAPTER ACTIVITIES
214 218 234 240
HIGHLIGHT 7 7.4 Alcohol in the body
242
CHAPTER 8 ENERGY BALANCE AND BODY COMPOSITION 8.1 Energy balance 8.2 Energy in: the kilojoules foods provide 8.3 Energy out: the kilojoules the body expends 8.4 Body weight, body composition and health 8.5 Health risks associated with body weight and body fat CHAPTER ACTIVITIES HIGHLIGHT 8 8.6 Eating disorders
253 254 255 260 265 271 274 277
CHAPTER 9 WEIGHT MANAGEMENT: OVERWEIGHT, OBESITY AND UNDERWEIGHT
287
9.1 Overweight and obesity 9.2 Causes of overweight and obesity 9.3 Problems of overweight and obesity 9.4 Aggressive treatments for obesity 9.5 Weight-loss strategies 9.6 Underweight CHAPTER ACTIVITIES
288 291 297 302 304 316 318
HIGHLIGHT 9 9.7 The latest and greatest weight-loss diet – again
321
CHAPTER 10 THE WATER-SOLUBLE VITAMINS: B GROUP VITAMINS AND VITAMIN C
329
10.1 The vitamins – an overview 330 10.2 The B group vitamins – as individuals 333 10.3 The B group vitamins – in concert 358 10.4 Vitamin C 360 CHAPTER ACTIVITIES 368 HIGHLIGHT 10 10.5 Vitamin and mineral supplements
371
CHAPTER 11 THE FAT-SOLUBLE VITAMINS: A, D, E AND K
377
11.1 Vitamin A and beta-carotene 11.2 Vitamin D 11.3 Vitamin E 11.4 Vitamin K CHAPTER ACTIVITIES
378 386 392 394 399
HIGHLIGHT 11 11.5 Is it time to shine for vitamin D?
401
CHAPTER 12 WATER AND THE MAJOR MINERALS
406
12.1 Water and the body fluids 12.2 The minerals – an overview 12.3 Sodium 12.4 Chloride 12.5 Potassium 12.6 Calcium 12.7 Phosphorus 12.8 Magnesium 12.9 Sulphate CHAPTER ACTIVITIES
407 419 420 425 426 428 435 437 440 442
HIGHLIGHT 12 12.10 Osteoporosis and calcium
445
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Capsicums offer a great source of beta-carotene
v
vi
Contents
CHAPTER 13 THE TRACE MINERALS 13.1 The trace minerals – an overview 13.2 Iron 13.3 Zinc 13.4 Iodine 13.5 Selenium 13.6 Copper 13.7 Manganese 13.8 Fluoride 13.9 Chromium 13.10 Molybdenum 13.11 Other trace minerals CHAPTER ACTIVITIES Peas are rich in antioxidants and add great texture to everything from salads to soups
452 453 454 464 468 470 472 473 474 475 476 477 480
HIGHLIGHT 13 13.12 Phytochemicals and functional foods 483 CHAPTER 14 FITNESS: PHYSICAL ACTIVITY, NUTRIENTS AND BODY ADAPTATIONS 14.1 Fitness 14.2 Energy systems and fuels to support activity 14.3 Vitamins and minerals to support activity 14.4 Fluids and electrolytes to support activity 14.5 Diets for physically active people CHAPTER ACTIVITIES HIGHLIGHT 14 14.6 Supplements as ergogenic aids CHAPTER 15 LIFE CYCLE NUTRITION: PREGNANCY AND LACTATION 15.1 Nutrition prior to pregnancy 15.2 Growth and development during pregnancy 15.3 Maternal weight 15.4 Nutrition during pregnancy 15.5 High-risk pregnancies 15.6 Nutrition during lactation CHAPTER ACTIVITIES
491 492 498 508 510 515 518 520
527 528 528 534 537 543 550 556
HIGHLIGHT 15 15.7 Foetal alcohol syndrome
558
CHAPTER 16 LIFE CYCLE NUTRITION: INFANCY, CHILDHOOD AND ADOLESCENCE
563
16.1 Nutrition during infancy 16.2 Nutrition during childhood 16.3 Nutrition during adolescence CHAPTER ACTIVITIES
564 576 588 592
HIGHLIGHT 16 16.4 Childhood obesity and the early development of chronic diseases
594
CHAPTER 17 LIFE CYCLE NUTRITION: ADULTHOOD AND THE LATER YEARS
600
17.1 Nutrition and longevity 17.2 The ageing process 17.3 Energy and nutrient needs of older adults 17.4 Nutrition-related concerns of older adults 17.5 Food choices and eating habits of older adults CHAPTER ACTIVITIES
602 605 609 612 617 621
HIGHLIGHT 17 17.6 Nutrient–drug interactions
623
CHAPTER 18 DIET-RELATED DISEASE
629
18.1 Nutrition and infectious diseases 18.2 Nutrition and chronic diseases 18.3 Cardiovascular disease 18.4 Hypertension 18.5 Diabetes mellitus 18.6 Cancer 18.7 Recommendations for chronic disease prevention CHAPTER ACTIVITIES HIGHLIGHT 18 18.8 Complementary and alternative medicine
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
630 632 635 642 646 652 656 658
660
Contents
CHAPTER 19 CONSUMER CONCERNS ABOUT FOODS AND WATER
669
19.1 Food safety and food-borne illnesses 19.2 Environmental contaminants 19.3 Natural toxins in foods 19.4 Pesticides 19.5 Food additives 19.6 Consumer concerns about water CHAPTER ACTIVITIES
671 680 682 683 686 690 694
HIGHLIGHT 19 19.7 Food biotechnology
696
Appendix A Cells, hormones and nerves
703
Appendix B Basic chemistry concepts 708 Appendix C Biochemical structures and pathways 717 Appendix D Measures of protein quality 735 Appendix E Nutrition assessment 738 Appendix F Physical activity and energy requirements 762 Appendix G Aids to calculation 765 Answers 767 Glossary 771 Index 791
Salmon is rich in the essential omega-3 fatty acids EPA and DHA
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
vii
viii
Guide to the text As you read this text you will find a number of features in every chapter to enhance your study of nutrition and help you understand how the theory is applied in the real world. CHAPTER OPENING FEATURES 1
CHAPTER
Connect Nutrition in your life with the essential chapter concepts right from the beginning of each chapter.
1
AN OVERVIEW OF NUTRITION
Think about your intuitive beliefs related to the nutrition topics covered in the chapter by taking the Common sense test at the start of every chapter. Check your answers in the margins when the topic is discussed, which are explained further in the end-ofchapter review.
Nutrition in your life
Believe it or not, you have probably eaten at least 20 000 meals in your life. Without any conscious effort on your part, your body uses the nutrients from those meals to make all its components, fuel all its activities and defend itself against diseases. How successfully your body handles these tasks depends, in part, on your food choices. Nutritious food choices support healthy bodies. PUTTING COMMON SENSE TO THE TEST Circle your answer
T
F
What we eat is largely driven by how hungry we are.
T
F
Fat has twice the number of kilojoules as carbohydrates or protein.
T
F
All published research should be treated with some level of critical appraisal.
T
F
An RDI for a nutrient is the amount that everyone needs to consume each day.
T
F
Changing our diet will do little to reduce the risk of many chronic diseases.
LEARNING OBJECTIVES 1.1 1.2
1.3
1.4
Identify the key concepts that the chapter will cover with the Learning objectives at the start of each chapter.
590
Understanding nutrition
590
Understanding nutrition
Describe how various factors influence personal food choices. Name six major classes of nutrients and identify which are organic and which yield energy. Explain the scientific method and how scientists use various types of research studies and methods to acquire nutritional information. Define the four categories of the Nutrient Reference Values (NRVs) and explain their purpose.
1.5
1.6 1.7
Explain how the four assessment methods are used to detect energy and nutrient deficiencies and excesses. Identify several risk factors and explain their relationships to chronic diseases. Recognise misinformation and describe how to identify reliable nutrition information.
Blackberries are a very good source of vitamin C and manganese
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FEATURES WITHIN CHAPTERS Calcium
Adolescence is a crucial time for bone development, and the requirement for Calcium Chapter 1: An overview of nutrition calcium reaches its peak during these years. Unfortunately, between 82 and 89 per Adolescence is a crucial time forcalcium bone development, and the requirement 61for cent of girls aged 12 to 16 have intakes below recommendations. Low calcium reaches peaktimes duringofthese Unfortunately, 82 and 89 per calcium intakes its during activeyears. growth, especially ifbetween paired with physical 61 cent of girlscan aged 12 to 16 have intakes recommendations. Low inactivity, compromise thecalcium development ofbelow peak bone mass. In fact, inactivity calcium during times ofimpact active growth, if poor pairedcalcium with physical may haveintakes a greater detrimental on boneespecially mass than intake inactivity, compromise the development of peakinbone mass. fact,calcium inactivity HOW TO: CALCULATE THE ENERGY AVAILABLE FROM FOODS during thecan pubertal years. Increasing milk products the diet toIn meet may have a greater greatly detrimental impact ondensity. bone mass than poor calciumteenage intake recommendations increases bone Once again, however, Practise calculating the energy available from foods during the pubertal years. Increasing milk products in the diet to meet calcium girls are most vulnerable, for their milk – and therefore their calcium – intakes Because their lunches rarely include fruits, recommendations greatly increases bone density. Once again, however, teenage vegetables or milk, many teens fail to get all 1. To calculate the energy available from a 16 g carbohydrate 3 17 kJ/g 5 272 kJ begin to decline at the time when their calcium needs are greatest. Furthermore, the vitamins and minerals they need each day. girls are have mostmuch vulnerable, their milkthan – and therefore Because their lunches rarely include fruits, 7 g protein 3 17 kJ/g 5 119 kJ food, multiply the number of grams of women greaterfor bone losses men in later their life. calcium – intakes vegetables or milk, many teens fail to get all begin to decline at the time when their calcium needs are greatest. Furthermore, 9 g fat 3 37 kJ/g 5 333 kJ carbohydrate, protein and fat by 17, 17 the vitamins and minerals they need each day. women have much greater bone losses than men in later life. Total 5 724 kJ and 37, respectively. Then add the results together. For example, 1 slice of bread with 1 tablespoon of peanut butter on it Teenagers like the freedom to come and go as they choose. They eat what they want if it PUTTING contains 16 grams carbohydrate, 7 grams is convenient and if they have the time. With a multitude of after-school, social and job COMMON SENSE protein and 9 grams fat. Teenagers like the freedom to come as they eating choose.habits. They eat what theytime wanton if any it TO THE TEST PUTTING activities, they almost inevitably falland intogo irregular At any given is convenient and if they the time. With aeating multitude of after-school, socialorand job COMMON SENSE given day, a teenager mayhave be skipping a meal, a snack, preparing a meal consuming From the information you calculated in step 1, you can determine the percentage of The THE calcium TO TEST activities, they by almost inevitably fall intoAdolescents irregular eating At any any food prepared a parent or restaurant. who habits. frequently eat given mealstime withon their kilojoules each of the energy nutrients contributes to the total. requirement for given day,however, a teenager may befruits, skipping a meal, eating aand snack, preparingfoods, a mealand or drink consuming families, eat more vegetables, grains calcium-rich fewer The calcium an adolescent is 2. To determine the percentage of kilojoules 333 fat kJ 4 724 total kJ 5 0.46 fooddrinks, prepared by athose parent orseldom restaurant. Adolescents who frequently eat meals with 62 requirement soft than who eat with their families. Many adolescents also their begin to reduced afterfor the from fat, for example, divide the 333 fat families, however, morebasis, fruits,missing vegetables, grains and calcium-rich foods, an adolescent is skip breakfast on aeat regular out on important nutrients that areand not drink made fewer up at age of 14. 62 kilojoules by the total 724 kilojoules. soft drinks, than those whoTeenagers seldom eat with families. Many adolescents also begin to reduced after the later meals during the day. who eattheir breakfast are more likely to meet their nutrient FALSE 3. Then multiply by 100 to get the skip breakfast on a regular basis, missing out on important nutrients that are not made up at 0.46 3 100 5 46% age of 14. intake recommendations. percentage. laterIdeally, meals in during day. Teenagers who eat breakfast are more likely to the meetadult theircontinues nutrient FALSE light the of adolescents’ busy schedules and desire for freedom, intake to play recommendations. the role of gatekeeper, controlling the type and availability of food in the teenager’s Dietary recommendations that urge people to limit fat intake to 20 to 35 per cent of Ideally, in light of adolescents’ busy schedules and desire for freedom, the adult continues home environment. Teenagers should find plenty of nutritious, easy-to-grab foods in the kilojoules refer to the day’s total energy intake, not to individual foods. Still, if the proportion to play the role of gatekeeper, controlling type and availability of foodand in the teenager’s refrigerator (meats for sandwiches; low-fatthe cheeses; fresh, raw vegetables fruits; fruit of fat in each food choice throughout a day exceeds 35 per cent of kilojoules, then the day’s home should find plenty of nutritious, easy-to-grab the juices; environment. and milk) andTeenagers more in the cupboards (wholegrain breads, nut pastes, foods nuts, in popcorn total surely will, too. Knowing that this snack provides 46 per cent of its kilojoules from fat refrigerator and cereal).(meats for sandwiches; low-fat cheeses; fresh, raw vegetables and fruits; fruit alerts a person to the need to make lower-fat selections at other times that day. juices; and milk) and more in the cupboards (wholegrain breads, nut pastes, nuts, popcorn and cereal).
Practise common nutrition tasks such as comparing nutrient density Food choices and healthy habits or calculating your energy Food choices and healthy habits requirements by working through the How to boxes throughout the book.
Snacks
AUSTRALIAN DIETARY GUIDELINES AUSTRALIAN 2013 DIETARY --------------GUIDELINES 2013 Eat a wide variety of --------------nutritious foods –
Eat wide variety milk,a yoghurt, of nutritious cheese and/orfoods their– milk, yoghurt,mostly alternatives, cheese and/or their reduced-fat. alternatives, mostly reduced-fat. Caffeinecontaining soft drinks Caffeinetypically deliver containing between 30soft anddrinks typically 55 mg ofdeliver caffeine per between 30 and can. For perspective, 55 mg of caffeine per a pharmacologically can. perspective, activeFor dose of caffeine ais pharmacologically defined as 200 mg. active dose of caffeine is defined as 200 mg.
Vitamins
Snacks typically provide at least a quarter of the average teenager’s daily food energy intake. Snacks Most often, favourite snacks are too high in saturated fat and sodium and too low in fibre to Snacks provide at least quarter of the average daily food energy supporttypically good future health. Tablea 16.6 on page 587 showsteenager’s how to combine foods fromintake. differentThe vitamins are also organic, but they do not provide energy. Instead, they facilitate the Mostgroups often, favourite snacks are too high in saturated fat and sodium and too low in fibre to release of energy from carbohydrate, fat and protein and participate in numerous other food to create healthy snacks. support good future health. Table 16.6 on page 587 shows how to combine foods from differentactivities throughout the body. food groups to create healthy snacks. Each of the 13 different vitamins has its own special role to play.* One vitamin enables Beverages the eyes to see in dim light, another helps produce functional red blood cells, and still another Most frequently, adolescents drink soft drinks instead of fruit juice or milk. About the only helps make the sex hormones – among other things. When you cut yourself, one vitamin Beverages time they select fruit juices is at breakfast. When teens drink milk, they are more likely to helps stop the bleeding and another helps repair the skin. Vitamins busily help replace old red Most frequently, adolescents drink soft drinks instead of fruit juice or milk. About the only consume it with a meal (especially breakfast) than as a snack. Soft drinks, when chosen time selectbeverage, fruit juices is affect at breakfast. When because teens drink theymilk are more to blood cells and the lining of the digestive tract. Almost every action in the body requires the as thethey primary may bone density theymilk, displace from likely the diet. assistance of vitamins. consumeofit their with greater a meal food (especially breakfast) a snack. when chosen Because intakes, boys are than moreas likely thanSoft girlsdrinks, to drink enough milk to Vitamins can function only if they are intact, but because they are complex organic as thetheir primary beverage, meet calcium needs.may affect bone density because they displace milk from the diet. Because food intakes, boys are more likely to drink enough milk tomolecules, they are vulnerable to destruction by heat, light and chemical agents. This is why Over of thetheir pastgreater three decades, teens (especially girls) havethan beengirls drinking more soft drinks meetless their calcium needs. who drink soft drinks regularly have a higher energy intake and a the body handles them carefully, and why nutrition-wise cooks do, too. The strategies of 63 and milk. Adolescents cooking vegetables at moderate temperatures for short times and using small amounts of water Over the past three decades, (especially havemore beenlikely drinking soft drinks 64 lower calcium intake than those teens who do not; theygirls) are also to bemore overweight. andSoft less drinks milk.63 containing Adolescentscaffeine who drink soft drinks regularly have aifhigher energyintake intake and a help to preserve the vitamins. present a different problem caffeine 64 lower calcium intakeCaffeine than those whotodobenot; they are also more likely to be becomes excessive. seems relatively harmless when used inoverweight. moderate doses drinks containing caffeine different problem if caffeine intake (theSoft equivalent of fewer than threepresent cans of acola beverages a day). In greater amounts, becomes excessive. Caffeine seems toassociated be relatively harmless in moderate doses however, it can cause the symptoms with anxiety,when such used as sweating, tenseness (the inability equivalent fewer than three cans of cola beverages a day). In greater amounts, In the body, some minerals are put together in orderly arrays in such structures as bones and and to of concentrate. however, it can cause the symptoms associated with anxiety, such as sweating, tenseness teeth. Minerals are also found in the fluids of the body, which influences fluid properties. and inability to concentrate. Whatever their roles, minerals do not yield energy.
Connect key Australian Dietary Guidelines to your understanding of the chapter. Extend your learning with the additional information notes highlighting Minerals about the topic being discussed. interesting or important information * The water-soluble vitamins are vitamin C and the eight B vitamins: thiamin, riboflavin, niacin, vitamins B6 and B12, folate, biotin and pantothenic acid. The fat-soluble vitamins are vitamins A, D, E and K. The water-soluble vitamins are the subject of Chapter 10 and the fat-soluble vitamins are discussed in Chapter 11.
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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Guide to the text 516
Understanding nutrition
need diets rich in carbohydrate, and of course, meats have none to offer. Legumes, whole grains and vegetables provide some protein with abundant carbohydrate. Table 14.5 (page 508) shows recommended protein intakes for active people.
A performance diet example
FEATURES WITHIN CHAPTERS
A person who engages in vigorous physical activity on a daily basis could easily require more than 12 000 kilojoules per day. To meet this need, the person can choose a variety of nutrientdense foods. Athletes who train exhaustively for endurance events may want to aim for somewhat higher carbohydrate intakes. Beyond these specific concerns of total energy, protein and carbohydrate, the diet most beneficial to athletic performance is remarkably similar to the diet recommended for most people.
CURRENT RESEARCH IN NUTRITION Athletes can excel on a vegetarian diet
Explore relevant and up-to-date nutrition research in the Current research in nutrition boxes.
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When it comes to strength and fitness, research studies find that vegetarian athletes can perform just as well as their omnivore opponents. In a new study, researchers recruited 27 vegetarian and 43 omnivore competitive endurance athletes.24 Each person in the vegetarian group had followed the diet for at least two years, and there was a mixture of vegan and lacto-ovo vegetarians amongst the group. Food intake, maximal oxygen uptake (VO2 max) during treadmill running and leg strength were all assessed. For the males, there was little difference in cardio-respiratory fitness or strength between the vegetarian and omnivores. The surprising finding though was in the women. Vegetarian women had a 13 per cent greater VO2 max scores than women eating an omnivore diet. There was no difference in protein intake according to body weight between vegetarians and omnivores. Although vegetarians ate more carbohydrates and fibre, they do have less vitamin B12, which is not so surprising. One interesting finding was that vegetarians had more iron in their diet than omnivores. But because plant-based iron is less bioavailable than animal-based iron, then this may bring the vegetarians back on par with omnivores. A well-planned and varied vegetarian diet can meet the nutritional needs of an athlete just as well as an omnivore diet. Such a diet poses little risk of sub-par performance, and for some athletes it may even spur them on to higher levels of achievement. Understanding nutrition
Meals before and after competition
Evaluate how current research in the field informs our practical health and food choices in the Applications of nutritional research boxes in every chapter.
No single food improves speed, strength or skill in competitive events, although some kinds of APPLICATIONS OF NUTRITIONAL foods do support performance better than RESEARCH others, as already explained. Still, a competitor may eat a particular food before or after an event for psychological reasons. One eats a steak the The key dietary patterns of long-term health night before wrestling. Another eats some honey just five minutes after diving. As long as these Diet plays a big part in health. As the typical Western diet moved to more overly refined practices remain harmless, they should be respected. and energy dense foods, rates of obesity and type 2 diabetes mirrored this change. A major scientific review has taken things back to basics to reinforce where the best health gains are Pre-game meals to be found with diet.18 Science indicates that theatpre-game snack disease should include plenty fluids and be and The review looked the dietmeal and or chronic links from 304ofmeta-analyses light and easyreviews to digest. It should 3300 kilojoules, primarily from systematic published in provide the last between 63 years.1200 Typeand 2 diabetes, overweight and obesity, carbohydrate-rich foods thatdisease are familiar and accounted well tolerated theof athlete. The meal should cancer and cardiovascular together for by most the chronic disease links end three to four hours before competition to allow time for the stomach to empty before found. As for dietary patterns,pasta the findings showed plant-based foods werefoods more low protective exertion. Breads, potatoes, and fruit juices –that that is, carbohydrate-rich in the risk of developing chronic disease comparedmeal with (see animal-based Among fatagainst and dietary fibre – form the basis of the best pre-game Figure 14.3 foods. for some plant foods, grain-based to have a small over fruits andalthough vegetables. examples). Bulky, fibre-richfoods foods seemed such as raw vegetables or edge wholegrain cereals, So much for theare anti-grain sentiment that is competition. popular at theDietary moment! usually desirable, best avoided just before fibre in the digestive tract Forwater animal-based foods,stomach dairy products overall wereperformance. considered neutral on health, attracts and can cause discomfort during Liquid meals areand easy fish was considered protective. Red and processed meats were linked to a higher to digest, and many such meals are commercially available. Alternatively, athletes candisease mix risk. For tea-lovers, research this popular drink as being the most protective fat-free milk or juice, the frozen fruits confirmed and flavourings in a blender. against disease risk. On the other end of the spectrum, to no-one’s surprise, soft drinks had few redeeming health benefits. The findings from this major review are close to a carbon copy of existing dietary guidelines that have changed little over decades. Eat more plant-based foods than animal foods, choose whole grains over refined grains, limit red and processed meat and choose other beverages in preference to soft drink. Such recommendations may not get media attention, or help sell books in numbers like the latest fad diet, but they are the cornerstone Chapter 3: Digestion, absorption and transport of long-term health.
Highcarbohydrate, liquid pre-game fruit smoothie ideas include: • apple juice, frozen banana and 1 tablespoon of plain yoghurt • pineapple juice, frozen strawberries and several mint leaves • reduced-fat milk, frozen banana and vanilla essence.
Other risk factors, such as genetics, gender and age, also play important roles in the and transport Chapter 3: Digestion, absorption development of chronic diseases, but they cannot be changed. Health recommendations acknowledge the influence of such factors on the development of disease, but they must focus on the factors that are changeable. For the two out of three Australians who do not smoke or drink alcohol excessively, the one choice that can influence long-term health prospects more than any other is diet.
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CHAPTER ACTIVITIES
CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1
The process of food digestion in athe mouth and of diet4influences The gastrointestinal tract is sterile FALSE Within the range set bybegins genetics, person’s choice long-term health. Diet has throughout. no TRUE proceeds all the wayon into the diseases large intestine. There are bacteria found throughout the gastrointestinal influence some but is linked closely to others. Personal life trillions choices,ofsuch as engaging in REVIEW IT
END-OF-CHAPTER FEATURES
PUTTING COMMON SENSE TO THE TEST: ANSWERStract. 1 2
Food digestion and absorption a process that occurs alongalso the affect health for the better or worse. physical activity isand using tobacco or right alcohol, 5 functions of thetract digestive tract are an example 4 The gastrointestinal is sterile throughout. FALSEof the process homeostasis. There areof trillions of bacteriaTRUE found throughout the gastrointestinal tract. FALSE digestive tract is regulated at many different levels, from endocrine Food digestionThe and next absorption is a process that provide occurs right along more the several chapters many detailsThe about nutrients and how they support
gastrointestinal The process tract. of food digestion begins in the mouth and Intestinal allcells all along the digestive TRUE tract. proceeds the are way uniform into the large intestine.
At the end of each chapter you’ll find several tools to help you review, practise and extend your knowledge of the key learning outcomes. 2 3
3
• Reflect on your own personal nutritional choices in the Nutrition portfolio.
• Review the major chapter concepts in preparation for exams by completing the Study questions.
to neural, to maintain itseach functions. gastrointestinal tract. Intestinal cells have varying degrees of specialisation depending onshows5how health. Whenever appropriate, the discussion diet influences of today’s The functions of the digestive tract major are an example of the where they are found along therecommendations digestive tract.the digestive Intestinal cells are uniform all along process homeostasis. diseases. Dietary appeartract. again and again, as of each nutrient’sTRUE relationships FALSE Veins and vessels leaving thepeople digestive withlymphatic health are explored. Most whotract follow the recommendations will benefit canlevels, from endocrine The digestive tract is regulated at many and different to neural, to maintain its functions. TRUE carry nutrients tovarying the body. enjoy good health into later years. Intestinal cells have degrees oftheir specialisation depending on where they are along the digestive tract. avenues of nutrient Both veins andfound lymph vessels are important transportand fromlymphatic the digestivevessels tract. leaving the digestive tract Veins
carry nutrients to the body. TRUE
Both veins and lymph vessels are important avenues of nutrient
transport from the digestive tract. NUTRITION PORTFOLIO
A healthy digestive system can adjust to almost any diet and can handle any combination of foods with ease. PORTFOLIO •NUTRITION Describe the physical and emotional environment that typically surrounds your meals, including how it A systemiscan adjust to almost any diet 3 healthy Whichdigestive of the following consistent with the Australian affects you and it might be improved. and Dietary can handle any how combination of foods with ease. Guidelines ? • Describe the physical and emotional environment a Choose a diet restricted in fat and cholesterol. that typically surrounds your meals, including how it STUDY QUESTIONS b Eat plenty of vegetables, legumes and fruits. affects you and how it might be improved. Multiple choice questions c Balance the food you eat with physical activity. Answers canan beabundance found at the book.nutrient d Eat of back foodsoftothe ensure QUESTIONS adequacy. 1STUDY A key secretion of the gall bladder is: Multiple choicetoquestions 4 a According the Australian Guide to Healthy Eating, trypsin Answers can be found at the back of the book. the for b number amylaseof serves of dairy foods recommended aged 12–13ofis:the gall bladder is: 1 boys A secretion c key bile d 3 insulin a trypsin amylase 2 b The 3.5 muscular contractions that move food through cthe GI 4 bile tract are called: d 4.5 a insulin hydrolysis 5 within acontractions given food group of the food Australian 2 Foods The sphincters muscular that move through b Guide to Healthy Eating are similar in their tract are called: cthe GI peristalsis contents of:movements d a bowel hydrolysis a b sphincters The energy main function of bile is to: b and fibre ca proteins peristalsis emulsify fats cd vitamins and minerals movements b bowel catalyse hydrolysis d carbohydrates and fats mainprotein functiondigestion of bile is to: cThe slow Which ingredient is exempt from being listed in d stomach acidity a neutralise emulsify fats descending order of predominance by weight on 4 b The catalyse pancreashydrolysis neutralises stomach acid in the small food labels? Why?digestion cintestine slow protein by secreting: a Vitamins d neutralise stomach acidity a bilestarvation, which of the following would you 9 During b 4 expect The Minerals pancreas b mucus to see?neutralises stomach acid in the small by secreting: cintestine enzymes a increased protein synthesis d bile bicarbonate a b elevated glycogen production NUTRITION CALCULATIONS b higher mucus levels of ketone bodies in the blood c These will give you practice in doing simple c problems enzymes d higher levels of insulinAlthough in the blood nutrition-related calculations. the situations d bicarbonate 10 hypothetical, During a fast,the thenumbers body produces ketone bodies by: are are real, and calculating the answers (see theglycogen Answers section at the back of this a hydrolysing book) a valuable lesson. Be sure to b provides condensing acetylnutrition CoA showc your calculations for each problem. transaminating keto acids d converting ammonia urea 1 Read a food label. Look attothe label in Figure 2.5 (seequestions p. 55) and answer the following questions: Review 3
3 6
• Master the common Nutrition calculations introduced in the How to chapter features.
1 2
a What is the size anabolism of a servingand of the product?give Define metabolism, catabolism; b How many kilojoules are 7.1) in a serving? an example of each. (Section cHowHow fat is as in a serving? doesmuch ATP work the high-energy currency of cells? (Section 7.1)
• Expand your knowledge by exploring the online resources listed in Nutrition on the net and by completing the Search me! nutrition research activity.
ON THE NET 3NUTRITION What are coenzymes, and what service do they provide metabolism? (Section 7.1) online: To Analyse the in nutrient composition of foods learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition NUTRITION ON THE NET Database provided by Food Standards Australia Analyse the nutrient composition of foods online:New To Zealand from http://www.foodstandards.gov.au/science/ learn more about the nutrient content of the foods you monitoringnutrients/pages/default.aspx eat, you can access the full NUTTAB Food Composition • Search for ‘foodbylabels’ at the FSANZ website: Database provided Food Standards Australia New http://www.foodstandards.gov.au Zealand from http://www.foodstandards.gov.au/science/
Chapter 2: Planning a healthy diet
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• • 7 • 5
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Detail any GI discomforts you may experience regularly and include suggestions to alleviate or prevent their occurrence (see Highlight 3). List any changes you can make in your eating habits Detail any GI discomforts you may experience c Water to promote overall GI health. regularly d Salt and include suggestions to alleviate or prevent their occurrence (see Highlight 3). ‘Low in salt’ is an example of a: List any changes you can make in your eating habits a promote health claim to overall GI health. The nutrition digestionfact and absorption of carbohydrate occurs b in the:claim cpredominantly nutrient content
a nutrition mouth advertising d 5 b The small digestion and absorption of carbohydrate occurs intestine Review questions in the: cpredominantly stomach 1 Name the diet-planning principles and briefly describe d a large mouthintestine how each principle helps in diet planning. (Section 2.1) small intestine 6 b Absorption occurs primarily in the: 2 What recommendation is modified in the Australian ca stomach mouth Dietary Guidelines d intestine for children under the age of two b large stomach years? Why? (Section 2.1) 6 cAbsorption occurs primarily in the: small intestine 3 What are the differences and similarities between the d mouth large intestine a Australian Guide to Healthy Eating plate and the Nutrition b 7 Australia The stomach specialised that increase gastrointestinal Healthycells Eating Pyramid ? How might any ctractsmall intestine absorption area are called: differences be confusing to the general public? (Section 2.2) d intestine a large pancreatic cells Dietary Guidelines. What types 4 Review the Australian 7 b The villi specialised cells that increase gastrointestinal of food selections would you make to achieve those absorption area are called: ctractcolonocytes recommendations? (Section 2.1) d 7: Metabolism: islet cells cells a pancreatic Chapter transformations and interactions 241 5 What do you think is the most helpful information you b villinutrients leave the GI tract by way of the 8 can Which expect to find on a food label? When comparing clymphatic colonocytes system? panels, how can this information nutrition information d cells a islet water and minerals help you choose between two products? (Section 2.3) 8 b Which nutrients the GI tract by way of the proteins andleave minerals 6 isthe a nutrient claim? doesfrom this differ 4 What Name four basic units,How derived foods,from that a system? clymphatic Allclaim? vitamins and minerals health (Section are used by the body in2.3) metabolic transformations. d and fat-soluble vitamins a fats water minerals How manyand carbons are in the ‘backbones’ of each? b proteins (Section 7.2) and minerals c All vitamins and minerals 5 d Describe howfat-soluble the body recycles glucose from lactate. How many kilojoules does this amount of fat fats and vitamins (Section 7.2) represent? 6 e WhatWhat are the differences between deamination and percentage of the kilojoules in this product transamination? (Section 7.2) comes from fat? What does tell you?in the metabolism 7 fSummarise thethis main steps g Does this product meet theand criteria foracids. a low-fat of glucose, glycerol, fatty acids amino product (Section 7.2) (refer to Table 2.7 on page 56)? What how is the predominant in the 8 h Describe a surplus of theingredient three energy nutrients product?to body fat stores. (Section 7.2) contributes i Have any nutrients been added to this product 9 What adaptations does the body make during a fast? (is it fortified)? What are ketone bodies? Define ketosis. (Section 7.3) 10 Distinguish between a loss of fat and a loss of weight, and describe how each might happen. (Section 7.3) •
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Learn more about the Australian Guide to Healthy Eating: https://www.eatforhealth.gov. au/guidelines/ Find New Zealand information on nutrition guidelines com.au/factsheets/diets-intolerances/lowand food labels at http://www.foodstandards.govt.nz carbohydrate-diets/ Learn the Healthy Eating Pyramid Learn more about about the effects of intermittent fasting :on http://www.nutritionaustralia.org metabolism: https://www.healthline.com/nutrition/ intermittent-fasting-metabolism
monitoringnutrients/pages/default.aspx • Assess the evidence for low-carbohydrate diet from Sports Dietitians Australia: https://www.sportsdietitians.
SEARCH ME! NUTRITION Keyword: intermittent fasting What is intermittent fasting and what health benefits have been linked to it? The article Intermittent fasting:
The science of going without will help answer these questions.
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Guide to the text
HIGHLIGHTS Every chapter is followed by a highlight that provides readers with an in-depth look at a current, and often controversial, topic that relates to its companion chapter • Develop your understanding of these key topics by responding to the critical thinking questions. • Research these thoughtprovoking topics further by exploring the weblinks listed in Nutrition on the net.
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Understanding nutrition
HIGHLIGHT
6
6.6 NUTRITIONAL GENOMICS
Imagine this scenario: A physician scrapes a sample of cells from inside your cheek and submits it to a genomics lab. The lab returns a report based on your genetic profile that reveals which diseases you are most likely to develop and makes recommendations for specific diet and lifestyle changes that can help you maintain good health. You may also be given a prescription for a dietary supplement that will best meet your personal nutrient requirements. Such a scenario may one day become reality as scientists uncover the genetic relationships between diet and disease.1 (Until then, however, consumers need to know that many current genetic test kits commonly available on the Internet are unproven and quite likely fraudulent.) Chapter 6: Protein: amino acids 211
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1
How might nutritional genomics influence healthcare in the future?
2
You may have heard about the diet that is based on a person’s blood type and claims to restore the body’s natural genetic rhythms and improve health. Research may one day reveal exactly which foods might best turn on and off specific genes to defend
against specific chronic diseases. No doubt marketers will rush to fill supermarket shelves with foods manufactured to match genetic profiles. Why do you think these genetic approaches to diet and health might be more or less appealing than eating patterns that include a variety of fruits, vegetables, whole grains, milk products and meats? Can your specific diet and lifestyle needs be decided in a laboratory? Shutterstock.com/Darren Baker
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NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx
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REFERENCES CHAPTER 1
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C. Taylor, P. Kavanagh, and B. Zuckerman, Sickle cell trait—neglected opportunities in the era of genomic medicine, Journal of the American Medical Association 311 (2014): 1495–6. Position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets, Journal of the American Dietetic Association 109 (2009): 1266–1282. World Hunger Education Services (WHES), Hunger notes (2015), available at http://www.worldhunger.org/articles/Learn/child_ hunger_facts.htm H. Kismul and co-authors, Diet and kwashiorkor: a prospective study from rural DR Congo, PeerJ 15 (2014): e350 https://dx.doi. org/10.7717/peerj.350 P. Guleria and co-authors, Genetic Engineering: A Possible Strategy for Protein-Energy Malnutrition Regulation, Molecular Biotechnology 59 (2017): 499–517. Committee on Dietary Reference Intakes, Dietary reference intakes: energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids (Washington, D.C.: National Academies Press, 2005), 694. U. N. Das, Nutritional factors in the prevention and management of coronary artery disease and heart failure, Nutrition 31 (2015): 283–91. J. E. Baggott and T. Tamura, Homocysteine, iron and cardiovascular disease: A hypothesis, Nutrients 7 (2015): 1108–18. J. D. Bihuniak and K. L. Insogna, The effects of dietary protein and amino acids on skeletal metabolism, Molecular and Cellular Endocrinology 410(2015): 78–86.
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How nutrients influence gene activity and how genes Get information about humaninfluence genomicthe discoveries activities of nutrients is the focus of a and how they can be used to improve health from the new field of study called nutritional genomics. Unlike Public Health Genomics site of the US Centers for sciences in the twentieth century, nutritional genomics Disease Control and Prevention: http://www.cdc.gov/ takes a comprehensive approach in analysing information genomics from several fields of study, providing an integrated understanding of the findings. Consider how multiple disciplines contributed to our understanding of vitamin A over the past several decades, for example. Biochemistry revealed vitamin A’s three chemical structures. Immunology identified the anti-infective properties of one of these structures, while physiology focused on another structure and its role in vision. Epidemiology has G. A. Bray and coauthors, Effect of dietary protein content on weight reported improvements in the death rates and vision of
malnourished children given vitamin A supplements, and biology has explored how such effects might be possible. The process was slow as researchers collected information on one gene, one action and one nutrient at a time. Today’s research in nutritional genomics involves all of the sciences coordinating their multiple findings and explaining the interactions among several genes, actions and nutrients in relatively little time. As a result, nutrition knowledge is growing at an incredibly fast pace. The recent surge in genomics research grew from the Human Genome Project, an international effort by industry and government scientists to identify and describe all of the genes in the human genome – that is, all the genetic information contained within a person’s cells. Completed in 2003, this project developed many of the research technologies needed to study genes and genetic variation. Scientists are now working to identify the individual proteins made by the genes, the genes associated with diseases, and the dietary and lifestyle choices that most influence the expression of those genes. Such information will have major implications for society in general, and for healthcare in particular.2
A genomics primer Figure H6.1 shows the relationships among the materials that comprise the genome. As the discussion of protein synthesis in Chapter 6 points out, genetic information is encoded in DNA molecules within the nucleus of cells. The DNA molecules and associated proteins are packed within 46 chromosomes. The genes are segments of a DNA strand that can eventually be translated into one or more proteins. The sequence of nucleotide bases within each gene determines the amino acid sequence of a particular protein. Scientists currently estimate that there are between 20 000 and 25 000 genes in the human genome. As Figure 6.7 (page 185) explained, when cells make proteins, a DNA sequence is used to make messenger RNA. The nucleotide sequence in messenger RNA then determines the amino acid sequence to make a protein. This process – from genetic information to protein synthesis – is known as gene expression. Gene expression can be determined by measuring the amounts of messenger RNA in a tissue sample.
gain, energy expenditure, and body composition during overeating: A randomized controlled trial, Journal of the American Medical Association 307 (2012): 47–55. A. Dougkas and E. Östman, Protein-enriched liquid preloads varying in macronutrient content modulate appetite and appetite-regulating hormones in healthy adults, Journal of Nutrition 146 (2016): 637–45. M. Cuenca-Sánchez, D. Navas-Carillo, and E. Orenes-Piñero, Controversies surrounding high-protein diet intake: Satiating effect and kidney and bone health, Advances in Nutrition 6 (2015): 260–6. Q. J. Lew and coauthors, Red meat intake and risk of ESRD, Journal of the American Society of Nephrology 28 (2016): 304–12. National Health and Medical Research Council, Nutrient reference values for Australia and New Zealand, Canberra: Commonwealth of Australia (2006). R. J. Maughan, Quality assurance issues in the use of dietary supplement, with special reference to protein supplements, Journal of Nutrition 143 (2013): 1843S–1847S. S. M. Robinson and co-authors, Does nutrition play a role in the prevention and management of sarcopenia?, Clinical Nutrition 37 (4) (2018): 1121–32. C Beaudart and co-authors, Nutrition and physical activity in the prevention and treatment of sarcopenia: systematic review, Osteoporosis International 28 (6) (2017): 1817–33.
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Guide to the online resources FOR THE INSTRUCTOR Cengage is pleased to provide you with a selection of resources that will help you to prepare your lectures and assessments, when you choose this textbook for your course. Log in or request an account to access instructor resources at cengage.com.au/instructors for Australia or cengage.co.nz/instructors for New Zealand. MINDTAP Premium online teaching and learning tools are available on the MindTap platform – the personalised eLearning solution.
MindTap is a flexible and easy-to-use platform that helps build student confidence and gives you a clear picture of their progress. We partner with you to ease the transition to digital – we’re with you every step of the way. The Cengage Mobile App puts your course directly into students’ hands with course materials available on their smartphone or tablet. Students can read on the go, complete practise quizzes or participate in interactive real-time activities.
MindTap for Whitney’s Understanding Nutrition is full of innovative resources to support critical thinking and help your students move from memorisation to mastery! Includes: • Whitney’s Understanding Nutrition eBook • Interactive nutrition calculations, Concept checks, Case activities, Videos, Quizzes and more
MindTap is a premium purchasable eLearning tool. Contact your Cengage learning consultant to find out how MindTap can transform your course.
INSTRUCTOR’S MANUAL The Instructor’s Manual includes: • Learning objectives
• Worksheets and handouts
• Lecture presentation outlines and enrichments
• Classroom activities • New Zealand instructor information
• Answers to study questions
COGNERO® TEST BANK A bank of questions has been developed in conjunction with the text for creating quizzes, tests and exams for your students. Create multiple test versions in an instant and deliver tests from your LMS, your classroom, or wherever you want using Cognero. Cognero test generator is a flexible online system that allows you to import, edit, and manipulate content from the text’s test bank or elsewhere, including your own favourite test questions. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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Guide to the online resources
POWERPOINT™ PRESENTATIONS Use the chapter-by-chapter PowerPoint presentations to enhance your lecture presentations and handouts to reinforce the key principles of your subject.
ARTWORK FROM THE TEXT Add the digital files of graphs, tables, pictures and flow charts into your course management system, use them in student handouts, or copy them in your lecture presentations.
FOR THE STUDENT MINDTAP MindTap is the next-level online learning tool that helps you get better grades! MindTap gives you the resources you need to study – all in one place and available when you need them. In the MindTap Reader, you can make notes, highlight text and even find a definition directly from the page. If your instructor has chosen MindTap for your subject this semester, log in to MindTap to: • Get better grades • Save time and get organised • Connect with your instructor and peers • Study when and where you want, online and mobile • Complete assessment tasks as set by your instructor When your instructor creates a course using MindTap, they will let you know your course key so you can access the content. Please purchase MindTap only when directed by your instructor. Course length is set by your instructor.
SEARCH ME! NUTRITION Search Me! is an online research library customised to your subject, that puts the information you need right at your fingertips. Content is updated daily from hundreds of scholarly and popular journals, eBooks and newspapers. Plus, 24-hour access means you won’t be limited by library opening times! Log in using the code on the card inside the front cover.
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PREFACE
A zucchini has more potassium than a banana
Nutrition is a science. The details of a nutrient’s chemistry or a cell’s biology can be overwhelming and confusing to some, but it needn’t be. When the science is explained step by step and the facts are connected one by one, the details become clear and understandable. That has been the goal since this book was first developed and as it has continued to be updated in this fourth edition: to reveal the fascination of science and share the excitement of nutrition with readers. We have learned from the hundreds of university teachers and nutrition professionals and more than a million students who have used previous editions of this book through the years that readers want to understand nutrition so that they can make healthy choices in their daily lives. With its focus on Australia and New Zealand, the text incorporates current nutrition recommendations and public health issues, and food culture relevant to those studying and working in nutrition in this region of the world. Because nutrition is an active science, staying current is paramount. To that end, this edition incorporates the latest in nutrition research. The connections between diet and disease have become more apparent – and our interest in making smart health choices has followed. More people are living longer and healthier lives. The science of nutrition has grown rapidly, with new research emerging daily. In this edition, as with previous editions, every chapter has been substantially revised to reflect the many changes that have occurred in the field of nutrition and in our daily lives over the years. We hope that this book serves you well.
THE CHAPTERS
Understanding Nutrition presents the core information of an introductory nutrition course. The early chapters introduce the nutrients and their work in the body, and the later chapters apply that information to people’s lives – describing the role of foods and nutrients in energy balance and weight control, in physical activity, in the life cycle and in disease prevention, and food safety. Each chapter also clearly flags for the reader practical applications of nutrition research and presents the most recent research in the topic area.
THE HIGHLIGHTS
Every chapter is followed by a highlight that provides readers with an in-depth look at a current, and often controversial, topic that relates to its companion chapter. Highlight 11 features vitamin D and the many health benefits now being linked to this ‘sunshine vitamin’. Each highlight closes with critical thinking questions designed to encourage readers to develop clear, rational, open-minded and informed thoughts based on the evidence presented in the text. New to this edition are clearly stated learning objectives at the beginning of every chapter to outline the key concept areas to be covered.
THE APPENDICES
The appendices are valuable references for a number of purposes. Appendix A summarises background information on the hormonal and nervous systems, complementing Appendices B and C on basic chemistry, the chemical structures of nutrients and major metabolic pathways. Appendix D describes measures of protein quality. Appendix E provides detailed coverage of nutrition assessment with updated infant and child growth charts, and Appendix F presents estimated energy requirements for men and women at various levels of physical activity. Appendix G presents common calculation and conversion tips.
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Preface
THE COVERS
The book’s inside covers put commonly used information at your fingertips, including current nutrient recommendations and suggested weight ranges for various heights. We have taken great care to provide accurate information and have included many references at the end of the book. However, to keep the number of references manageable, many statements appear without references. All statements reflect current nutrition knowledge and the authors will supply references upon request. In addition to supporting text statements, the references provide readers with resources for finding a good overview or more details on a subject. In this new edition, the art and layout have been carefully designed to be inviting while enhancing student learning. For all chapters and highlights, content has been reviewed and updated. Several new figures and tables have been created and others revised to enhance learning. Each chapter also features a true–false ‘common sense’ test presented at the beginning to allow students to test their core knowledge on practical nutrition concepts related to the topic. Answers to these commonsense questions are revealed throughout the chapter and a brief explanation is given at the end. This new edition has also been revised throughout to include more content and related nutrition issues that are specific to New Zealand. For example, Chapter 2 features the newly released Eating and Activity Guidelines for New Zealand Adults. And to acknowledge the growing interest in the gastrointestinal microbiome in health, an expanded section in Chapter 3 has been added as well as a research focus in Chapter 4. Nutrition is a fascinating subject, and we hope our enthusiasm for it comes through on every page. Tim Crowe Adam Walsh Ellie Whitney Sharon Rady Rolfes
Eggplant skin is rich in magnesium
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ABOUT THE AUTHORS
Eleanor Noss Whitney, PhD, received her BA in Biology from Radcliffe College in 1960 and her PhD in Biology from Washington University, St Louis, in 1970. Formerly on the faculties at Florida State University and Florida A&M University and a dietitian registered with the American Dietetic Association, Ellie now devotes full time to research, writing and consulting in nutrition, health and environmental issues. Her earlier publications include articles in science, genetics, and other journals. Her textbooks include Nutrition Concepts and Controversies 12th edn, Understanding Nutrition 12th edn, Understanding Normal and Clinical Nutrition 9th edn and Nutrition and Diet Therapy 7th edn, all with Cengage Wadsworth. She also recently co-authored Priceless Florida (Pineapple Press), a comprehensive text examining the ecosystems in her home state. Her additional interests include energy conservation, solar energy use, alternatively fuelled vehicles and ecosystem restoration. Sharon Rady Rolfes received her MS in nutrition and food science from Florida State University. She is a founding member of Nutrition and Health Associates, an information resource centre that maintains a research database on over 1000 nutrition-related topics. Sharon’s publications include the college textbooks Understanding Nutrition 12th edn and Nutrition for Health and Health Care 4th edn. In addition to writing and research, she occasionally teaches at Florida State University and serves as a consultant for various educational projects. Her volunteer work includes serving on the board of Working Well, a community initiative dedicated to creating a healthy workforce. Dr Tim Crowe is an Advanced Accredited Practising Dietitian who has spent most of his career in the world of university nutrition teaching and research. He now works chiefly as a health and medical writer and scientific consultant and speaks on many health topics to the public through both the media, social media and writing for consumer publications. Dr Adam Walsh is a Senior Lecturer in Nutrition and Dietetics in the School of Exercise and Nutrition Sciences at Deakin University in Melbourne and an Accredited Practising Dietitian. He teaches in the undergraduate and postgraduate nutrition and dietetics programs in the areas of clinical dietetics, nutritional physiology and paediatric health. Adam’s area of research is the influence of fathers on young children’s nutrition and physical activity behaviours.
The only fruit that provides heart-healthy monounsaturated fat
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ACKNOWLEDGEMENTS
The adaptation and updating of this textbook has been a team effort with us all focused on improving a book that has been well-received throughout nutrition courses in Australia and New Zealand. Many thanks must go to the team of external reviewers who gave valuable feedback and advice on each of the chapters in order to improve the relevance of the text to the teaching of nutrition in Australia and New Zealand. The team at Cengage have been instrumental in guiding us through the entire process and have been a pleasure to work with through all stages of development. It is rewarding to see the text now in print after all our hard work. From Tim Crowe: Many thanks go to my nutrition and dietetic friends and colleagues who have been down the publication path before and assured me that the late nights and long weekends of writing and proofing would be time well spent in producing a piece of work to be proud of. From Adam Walsh: Thanks to my two wonderful boys for keeping me grounded. They have, on more than one occasion, reminded me that even though I’m the dietitian in the house, I’m still just Dad. Substitute for rice to increase your fibre intake
The authors and Cengage Learning would like to thank our reviewers who provided incisive and helpful feedback: • Martin Stone – Australis College • Anthony Villani – University of the Sunshine Coast • Matt Sharman – University of Tasmania • Kathleen (Katie) Lacy – Deakin University • Preetha Thomas – The University of Queensland • Janet Weber – Massey University • Thea Werkhoven – The University of Sydney • Aimee Dordevic – Monash University • Jennifer McCann – Deakin University • Judith Myers – Victoria University • Karin Clark – Curtin University • Ramon Hall - Deakin University The authors and Cengage Learning would also like to thank the following supplementary resource authors for their contributions to the first edition: • Associate Professor Jack Antonas – Victoria University • Dr Clare Wall – University of Auckland • Dr Fiona Pelly – University of the Sunshine Coast • Victoria Logan – Otago University • Alisa Conlan – RMIT University.
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CHAPTER
1
AN OVERVIEW OF NUTRITION Nutrition in your life
Believe it or not, you have probably eaten at least 20 000 meals in your life. Without any conscious effort on your part, your body uses the nutrients from those meals to make all its components, fuel all its activities and defend itself against diseases. How successfully your body handles these tasks depends, in part, on your food choices. Nutritious food choices support healthy bodies. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F What we eat is largely driven by how hungry we are. T F Fat has twice the number of kilojoules as carbohydrates or protein. T F All published research should be treated with some level of critical appraisal. T F An RDI for a nutrient is the amount that everyone needs to consume each day. T F Changing our diet will do little to reduce the risk of many chronic diseases.
LEARNING OBJECTIVES 1.1 Describe how various factors influence personal food choices. 1.2 Name six major classes of nutrients and identify which are organic and which yield energy. 1.3 Explain the scientific method and how scientists use various types of research studies and methods to acquire nutritional information. 1.4 Define the four categories of the Nutrient Reference Values (NRVs) and explain their purpose.
1.5 Explain how the four assessment methods are used to detect energy and nutrient deficiencies and excesses. 1.6 Identify several risk factors and explain their relationships to chronic diseases. 1.7 Recognise misinformation and describe how to identify reliable nutrition information.
Blackberries are a very good source of vitamin C and manganese
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Understanding nutrition
In general, a chronic disease progresses slowly or with little change and lasts a long time. By comparison, an acute disease develops quickly, produces sharp symptoms and runs a short course. • chronos 5 time • acute 5 sharp
PUTTING COMMON SENSE TO THE TEST
What we eat is largely driven by how hungry we are. FALSE
Welcome to the world of nutrition. Although you may not always have been aware of it, nutrition has played a significant role in your life. And it will continue to affect you in major ways, depending on the foods you select. Every day, several times a day, you make food choices that influence your body’s health for better or worse. Each day’s choices may benefit or harm your health only a little, but when these choices are repeated over years and decades, the rewards or consequences become major. That being the case, paying close attention to good eating habits now can bring you health benefits later. Conversely, carelessness about food choices can contribute to many chronic diseases prevalent in later life, including heart disease and cancer. Of course, some people will become ill or die young no matter what choices they make, and others will live long lives despite making poor choices. For the majority of us, however, the food choices we make each and every day will benefit or impair our health in proportion to the wisdom of those choices. Although most people realise that their food habits affect their health, they often choose foods for other reasons. After all, foods bring to the table a variety of pleasures, traditions and associations as well as nourishment. The challenge, then, is to combine favourite foods and fun times with a nutritionally balanced diet.
1.1 Food choices
People decide what to eat, when to eat and even whether to eat in highly personal ways, often based on behavioural or social motives rather than on an awareness of nutrition’s importance to health. Many different food choices can support good health, and an understanding of nutrition will help you to make sensible selections more often.
Personal preference As you might expect, the primary reason people choose foods is taste – they like certain flavours. Two widely shared preferences are for the sweetness of sugar and for the savouriness of salt. Liking high-fat foods also appears to be a universally common preference. Other preferences might be for the hot chilli common in Mexican cooking or the curry spices of Indian cuisine. Some research suggests that genetics may influence people’s food preferences.1
Habit People sometimes select foods out of habit. They eat cereal every morning, for example, simply because they have always eaten cereal for breakfast. Eating a familiar food and not having to make any decisions can be comforting.
Ethnic heritage or tradition
Getty Images/Fuse
Among the strongest influences on food choices are ethnic heritage and tradition. People eat the foods they grew up eating. Every country – and, in fact, every region of a country – has its own typical foods and ways of combining them into meals. The ‘Australian diet’ includes many ethnic foods from various countries, such as Greece, Italy, Thailand and China, all adding variety to the diet. The New Zealand diet has been influenced by British, Pacific and, more recently, Asian migrants. Recent trends in the New Zealand diet include a reduction in beef, lamb and potatoes and an increase in poultry, pasta and rice, which is a reflection of international food trends, food prices and ease of preparation.2
Social interactions An enjoyable way to learn about other cultures is to taste their ethnic foods.
Most people enjoy companionship while eating. It’s fun to go out with friends for pizza or Thai. Meals are social events, and sharing food is part of hospitality. Social customs invite people to accept food or drink offered by a host or shared by a group
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regardless of hunger signals. Such social interactions can be a challenge for people trying to limit their food intake; Chapter 9 describes how people tend to eat more food when socialising with others. People also tend to eat the kinds of foods eaten by those in their social circles, thus helping to explain why obesity seems to spread in social networks and weight loss is easier with a partner.
Marketing The food industry competes for our food dollars, persuading consumers to eat more – more food, more often. These marketing efforts pay off well, generating billions of dollars in new sales each year. In addition to building brand loyalty, food companies attract busy consumers with their promises of convenience.
Availability, convenience and economy People eat foods that are accessible, quick and easy to prepare, and within their financial means. Today’s consumers value convenience and are willing to spend more than half of their food budget on meals that require little, if any, further preparation.3 They frequently eat out, bring home ready-to-eat meals or have food delivered. Even when they venture into the kitchen, they want to prepare a meal in 15 to 20 minutes, using fewer than half a dozen ingredients – and those ‘ingredients’ are often semiprepared foods, such as canned soups. This emphasis on convenience limits food choices to the selections offered on menus and products designed for quick preparation. Whether decisions based on convenience meet a person’s nutrition needs depends on the choices made. Eating a banana or a chocolate bar may be equally convenient, but the fruit offers more vitamins and minerals and less sugar and fat. Given the abundance of convenient food options, fewer adults are learning the cooking skills needed to prepare meals at home, which has its downside. They are more likely to eat out where the choice is often low-cost fast-food outlets. People who are competent in their cooking skills eat more of their meals at home and tend to make healthier food choices.
Positive and negative associations People tend to like particular foods associated with happy occasions – such as meat pies at football games or cake at birthday parties. By the same token, people can develop aversions and dislike foods that they ate when they felt sick or that were forced on them.4 By using foods as rewards or punishments, parents may inadvertently teach their children to like and dislike certain foods.
Emotions are another factor that guide food choices and eating behaviours. Some people cannot eat when they are emotionally upset. Others may eat in response to a variety of emotional stimuli – for example, to relieve boredom or depression, or to calm anxiety.5 A depressed person may choose to eat rather than to call a friend. A person who has returned home from an exciting evening out may unwind with a late-night snack. These people may find emotional comfort, in part, because foods can influence the brain’s chemistry and the mind’s response. Eating in response to emotions can easily lead to overeating and
Alamy/Wave Royalty Free
Emotional comfort
To enhance your health, keep nutrition in mind when selecting foods.
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Understanding nutrition
obesity, but it may be appropriate at times. For example, sharing food at times of grief serves both the giver’s need to provide comfort and the receiver’s need to be cared for and to interact with others, as well as to take nourishment.
Values Food choices may reflect people’s religious beliefs, political views or environmental concerns. For example, many Christians forgo meat during Lent (the period prior to Easter), Jewish law includes an extensive set of dietary rules that govern the use of foods derived from animals, and Muslims fast between sunrise and sunset during Ramadan (the ninth month of the Islamic calendar). A concerned consumer may boycott fruit picked by migrant workers who have been exploited. People may buy vegetables from local farmers to save the fuel and environmental costs of foods shipped in from far away. They may also select foods packaged in containers that can be reused or recycled. Some consumers accept or reject foods that have been irradiated or genetically modified, depending on their approval of these processes (see Chapter and Highlight 19 for a complete discussion).
Nutrition and health benefits Finally, of course, many consumers make food choices that will benefit health. Making healthy food choices 100 years ago was rather easy; the list of options was relatively short and markets sold mostly fresh, whole foods. Examples of whole foods include vegetables and legumes; fruits; seafood, meats, poultry, eggs, nuts, and seeds; milk; and whole grains. Today, tens of thousands of food items fill the shelves of super-grocery stores and most of those items are processed foods. Whether a processed food is a healthy choice depends, in part, on how extensively the food was processed. When changes are minimal, processing can provide an abundant, safe, convenient, affordable, and nutritious product.6 Examples of minimally processed foods include frozen vegetables, fruit juices, smoked salmon, cheeses, and breads. The nutritional value diminishes, however, when changes are extensive, creating ultra-processed foods. Ultra-processed foods no longer resemble whole foods. They are made from substances that are typically used in food preparation but not consumed as foods themselves (such as oils, fats, flours, refined starches and sugars). These substances undergo further processing by adding little, if any, processed foods, salt and other preservatives, and additives such as flavours and colours. Examples of ultra-processed foods include soft drinks, corn chips, confectionery, chicken nuggets, canned cheese spreads and pastries. Notably, these foods cannot be made in a home kitchen using common grocery ingredients. Dominating the global foods market, ultra-processed foods tend to be attractive, tasty and cheap – as well as high in fat and sugar. Consumers who want to make healthy food choices will select fewer ultra-processed foods and more whole foods and minimally processed foods.7 REVIEW IT
A person selects foods for a variety of reasons. Whatever those reasons may be, food choices influence health. Individual food selections neither make nor break a diet’s healthfulness, but the balance of foods selected over time can make an important difference to health. For this reason, people are wise to think ‘nutrition’ when making their food choices.
1.2 The nutrients
Biologically speaking, people eat to receive nourishment. Do you ever think of yourself as a biological being made of carefully arranged atoms, molecules, cells, tissues and organs? Are you aware of the activity going on within your body even as you sit still? The atoms, molecules and cells of your body continually move and change, even though the structures of your tissues and organs and your external appearance remain relatively constant. Your skin, which
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has covered you since your birth, is replaced entirely by new cells every seven years. The fat beneath your skin is not the same fat that was there a year ago. Your oldest red blood cell is only 120 days old, and the entire lining of your digestive tract is renewed every three to five days. To maintain your ‘self’, you must continually replenish, from foods, the energy and the nutrients you deplete as your body maintains itself.
Shutterstock/Maridav
Nutrients in foods and in the body Amazingly, our bodies can derive all the energy, structural materials and regulating agents we need from the foods we eat. This section introduces the nutrients that foods deliver and shows how they participate in the dynamic processes that keep people alive and well.
Composition of foods Chemical analysis of a food such as a tomato shows that it is composed primarily of water (95 per cent). Most of the solid materials are carbohydrates, lipids and proteins. If you could remove these materials, you would find a tiny residue of vitamins, minerals and other compounds. Water, carbohydrates, lipids, proteins, vitamins and some of the minerals found in foods are nutrients – substances the body uses for the growth, maintenance and repair of its tissues. This book focuses mostly on the nutrients; however, foods contain other compounds as well – fibre, phytochemicals, pigments, additives, alcohols and others. Some are beneficial, some are neutral and a few are harmful. Later sections of the book touch on these compounds and their significance.
FIGURE 1.1 Body composition of healthy-weight men and women The human body is made of compounds similar to those found in foods – mostly water (60 per cent) and some fat (13 to 21 per cent for young men, 23 to 36 per cent for young women who are of a healthy weight), with carbohydrate, protein, vitamins, minerals and other minor constituents making up the remainder. (Chapter 8 describes the health hazards of too little or too much body fat.)
A complete chemical analysis of your body would show that it is made of materials similar to those found in foods (see Figure 1.1). A healthy 70 kg body contains about 41 kg of water and about 9 to 21 kg of fat. The remaining kilograms are mostly protein, carbohydrate and the major minerals of the bones. Vitamins, other minerals and incidental extras constitute a fraction of a kilogram.
Chemical composition of nutrients The simplest of the nutrients are the minerals. Each mineral is a chemical element; its atoms are all alike.
Key: % Carbohydrates, proteins, vitamins, minerals in the body % Fat in the body % Water in the body
Getty Images/PhotoDisc
Composition of the body
As Chapter 5 explains, most lipids are fats.
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Understanding nutrition
As a result, its identity never changes. For example, iron may have different electrical charges, but the individual iron atoms remain the same when they are in a food, when a person eats the food, when the iron becomes part of a red blood cell, when the cell is broken down and when the iron is lost from the body by excretion. The next simplest nutrient is water, a compound made of two elements – hydrogen and oxygen. Minerals and water are inorganic nutrients, which means they do not contain carbon. The other four classes of nutrients (carbohydrates, lipids, proteins and vitamins) are more complex. In addition to hydrogen and oxygen, they all contain carbon, an element found in all living things. They are therefore called organic compounds (meaning, literally, alive). Protein and some vitamins also contain nitrogen and may contain other elements as well (see Table 1.1). The use of the term ‘organic’ when describing the chemistry of substances should not be confused with the use of this term in the farming and produce sense to describe how food is grown under a certification system.
TABLE 1.1 Elements in the six classes of nutrients Notice that organic nutrients contain carbon. CARBON
HYDROGEN
OXYGEN
NITROGEN
MINERALS
Inorganic nutrients Minerals
✓
Water
✓
✓
Organic nutrients Carbohydrates
✓
✓
✓
Lipids (fats)
✓
✓
✓
Proteinsa
✓
✓
✓
Vitaminsb
✓
✓
✓
a
Some proteins also contain the mineral sulphur.
b
Some vitamins contain nitrogen; some contain minerals.
✓
Essential nutrients The body can make some nutrients, but it cannot make all of them. Also, it makes some in insufficient quantities to meet its needs and, therefore, must obtain these nutrients from foods. The nutrients that foods must supply are essential nutrients. When used to refer to nutrients, the word essential means more than just ‘necessary’; it means ‘needed from outside the body’ – normally from foods.
Energy-yielding nutrients: carbohydrate, fat and protein In the body, three organic nutrients can be used to provide energy: carbohydrate, fat and protein. In contrast to these energy-yielding nutrients, vitamins, minerals and water do not yield energy in the human body. Carbohydrate, fat, and protein are sometimes called macronutrients because the body requires them in relatively large amounts (many grams daily). In contrast, vitamins and minerals are micronutrients, required only in small amounts (milligrams or micrograms daily). Table 1.2 summarises some of the ways the six classes of nutrients can be described.
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Chapter 1: An overview of nutrition
TABLE 1.2 The six classes of nutrients NUTRIENT
ORGANIC
INORGANIC
ENERGY-YIELDING
MACRONUTRIENT
Carbohydrates
✓
✓
✓
Lipids (fats)
✓
✓
✓
Proteins
✓
✓
✓
Vitamins
✓
MICRONUTRIENT
✓
Minerals
✓
Water
✓
✓
Energy measured in kilojoules
The energy released from carbohydrates, fats and proteins can be measured in joules. In some countries (particularly the United States), ‘calorie’ is still the preferred measure of food energy, though in this context it is actually kilocalories (or kcalories) that is the implied unit of energy measure for food and the prefix of ‘kilo’ is normally dropped in everyday speaking. When you read in popular books or magazines that an apple provides ‘100 calories’, it actually means 100 kcalories, which is the same as 420 kilojoules. This book uses the term kilojoules and its abbreviation kJ throughout.
Energy from foods The amount of energy a food provides depends on how much carbohydrate, fat and protein it contains. When completely broken down in the body, a gram of carbohydrate yields about 17 kilojoules (4 kcalories) of energy, a gram of protein also yields 17 kilojoules (4 kcalories) and a gram of fat yields 37 kilojoules (9 kcalories) (see Table 1.3). Fat, therefore, has a greater energy density than either carbohydrate or protein. The energy yield from carbohydrate of 17 kilojoules per gram (kJ/g) is considered an average figure as monosaccharides (such as glucose), disaccharides (such as sucrose) and starch all yield slightly different amounts of energy per gram. The ‘How to’ box on page 9 explains how to calculate the energy available from foods.
The international unit for measuring food energy is the joule, a measure of work energy. The energy in food is normally expressed in kilojoules. To convert kcalories to kilojoules, multiply by 4.2; to convert kilojoules to kcalories, multiply by 0.24.
TABLE 1.3 Kilojoule and kcalorie values of energy nutrients Nutrients
Energy (kJ/g)
Energy (kcal/g)
Carbohydrate
17
4
Protein
17
4
Fat
37
9
NOTE: Alcohol contributes 29 kilojoules per gram that can be used for energy, but it is not considered a nutrient because it interferes with the body’s growth, maintenance and repair.
One other substance contributes energy – alcohol. Alcohol is not considered a nutrient because it interferes with the growth, maintenance and repair of the body, but it does yield energy (29 kilojoules or 7 kcalories per gram) when metabolised in the body. (Highlight 7 and Chapter 18 present the potential harms and possible benefits of alcohol consumption.) Most foods contain all three energy-yielding nutrients as well as water, vitamins, minerals and other substances. For example, meat contains water, fat, vitamins and minerals as well as protein. Bread contains water, a trace of fat, a little protein and some vitamins and minerals
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PUTTING COMMON SENSE TO THE TEST
Fat has twice the number of kilojoules than carbohydrates or protein. TRUE
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Understanding nutrition
in addition to its carbohydrate. Only a few foods are exceptions to this rule, the common ones being sugar (pure carbohydrate) and oil (essentially pure fat).
CURRENT RESEARCH IN NUTRITION Healthy choices better than trying to eat less There has been a trend over the last 50 years for food to be served in larger portion sizes. This trend applies equally to food purchased out of the home and food served at home. As portion sizes go up, people can easily eat more than they intended. To help address ‘portion creep’, a research team designed a program to educate a group of people on controlling portion size as part of an ongoing weight loss intervention.8 Three groups of women, one of which had already completed a one-year weight loss trial that included portion-control strategies, visited a food lab once a week for four weeks. At each visit, the women were given the same foods to eat, but portion size varied. Each meal had a range of foods with a high kilojoule density, like chocolate-chip cookies, and lower kilojoule density foods, such as a salad. When larger meal portions were served, the women ate more food, which was not much of a new finding. For example, when the portion size was increased by 75 per cent, an average of 27 per cent more food was eaten. The novel finding of the research was how the food choices differed. Women who had already undertaken portion control training ate more of the lower kilojoule dense foods and less of the higher kilojoule food. So, compared to women who had no portion control training, even though the volume of food they ate was the same, their overall kilojoule intake was lower because of eating more of the less kilojoule-dense options. Choosing to eat greater amounts of healthier, lower kilojoule-dense foods such as fruits and vegetables is a more effective and sustainable approach to eating than just trying to resist or control portions of higher kilojoule foods.
Energy in the body The processes by which nutrients are broken down to yield energy or used to make body structures are known as metabolism (defined and described further in Chapter 7).
The body uses the energy-yielding nutrients to fuel all its activities. When the body uses carbohydrate, fat or protein for energy, the bonds between the nutrient’s atoms break. As the bonds break, they release energy. Some of this energy is released as heat, but some is used to send electrical impulses through the brain and nerves, to synthesise body compounds and to move muscles. Thus the energy from food supports every activity, from quiet thought to vigorous sports. If the body does not use these nutrients to fuel its current activities, it rearranges them into storage compounds (such as body fat), to be used between meals and overnight when fresh energy supplies run low. If more energy is consumed than expended, the result is an increase in energy stores and weight gain. Similarly, if less energy is consumed than expended, the result is a decrease in energy stores and weight loss. When consumed in excess of energy needs, alcohol, too, can be converted to body fat and stored. When alcohol contributes a substantial portion of the energy in a person’s diet, the harm it does far exceeds the problems of excess body fat. (Highlight 7 describes the effects of alcohol on health and nutrition.)
Other roles of energy-yielding nutrients In addition to providing energy, carbohydrates, fats and proteins provide the raw materials for building the body’s tissues and regulating its many activities. In fact, protein’s role as a fuel source is relatively minor compared with the other two nutrients and its other roles. Proteins are found in structures such as the muscles and skin and help to regulate activities such as digestion and energy metabolism.
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Chapter 1: An overview of nutrition
HOW TO:
CALCULATE THE ENERGY AVAILABLE FROM FOODS
Practise calculating the energy available from foods 1. To calculate the energy available from a food, multiply the number of grams of carbohydrate, protein and fat by 17, 17 and 37, respectively. Then add the results together. For example, 1 slice of bread with 1 tablespoon of peanut butter on it contains 16 grams carbohydrate, 7 grams protein and 9 grams fat.
16 g carbohydrate 3 17 kJ/g 5 272 kJ 7 g protein 3 17 kJ/g 5 119 kJ 9 g fat 3 37 kJ/g 5 333 kJ Total 5 724 kJ
From the information you calculated in step 1, you can determine the percentage of kilojoules each of the energy nutrients contributes to the total. 2. To determine the percentage of kilojoules from fat, for example, divide the 333 fat kilojoules by the total 724 kilojoules. 3. Then multiply by 100 to get the percentage.
333 fat kJ 4 724 total kJ 5 0.46 0.46 3 100 5 46%
Dietary recommendations that urge people to limit fat intake to 20 to 35 per cent of kilojoules refer to the day’s total energy intake, not to individual foods. Still, if the proportion of fat in each food choice throughout a day exceeds 35 per cent of kilojoules, then the day’s total surely will, too. Knowing that this snack provides 46 per cent of its kilojoules from fat alerts a person to the need to make lower-fat selections at other times that day.
Vitamins The vitamins are also organic, but they do not provide energy. Instead, they facilitate the release of energy from carbohydrate, fat and protein and participate in numerous other activities throughout the body. Each of the 13 different vitamins has its own special role to play.* One vitamin enables the eyes to see in dim light, another helps produce functional red blood cells, and still another helps make the sex hormones – among other things. When you cut yourself, one vitamin helps stop the bleeding and another helps repair the skin. Vitamins busily help replace old red blood cells and the lining of the digestive tract. Almost every action in the body requires the assistance of vitamins. Vitamins can function only if they are intact, but because they are complex organic molecules, they are vulnerable to destruction by heat, light and chemical agents. This is why the body handles them carefully, and why nutrition-wise cooks do, too. The strategies of cooking vegetables at moderate temperatures for short times and using small amounts of water help to preserve the vitamins.
Minerals In the body, some minerals are put together in orderly arrays in such structures as bones and teeth. Minerals are also found in the fluids of the body, which influences fluid properties. Whatever their roles, minerals do not yield energy.
* The water-soluble vitamins are vitamin C and the eight B vitamins: thiamin, riboflavin, niacin, vitamins B6 and B12, folate, biotin and pantothenic acid. The fat-soluble vitamins are vitamins A, D, E and K. The water-soluble vitamins are the subject of Chapter 10 and the fat-soluble vitamins are discussed in Chapter 11.
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Understanding nutrition
Only 16 minerals are known to be essential in human nutrition.* Others are being studied to determine whether they play significant roles in the human body. Still other minerals are environmental contaminants that displace the nutrient minerals from their workplaces in the body, disrupting body functions. The problems caused by contaminant minerals are described in Chapter 13. Because minerals are inorganic, they are indestructible and need not be handled with the special care that vitamins require. Minerals can, however, be bound by substances that interfere with the body’s ability to absorb them. They can also be lost during food-refining processes or during cooking when they leach into water that is discarded.
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Water
Water itself is an essential nutrient and carries many minerals naturally.
Water, indispensable and abundant, provides the environment in which nearly all the body’s activities are conducted. It participates in many metabolic reactions, and supplies the medium for transporting vital materials to cells and carrying waste products away from them. Water is discussed fully in Chapter 12, but is mentioned in every chapter.
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Without exaggeration, nutrients provide the physical and metabolic basis for nearly all that we are and all that we do. Foods provide nutrients – substances that support the growth, maintenance and repair of the body’s tissues. The six classes of nutrients are: • carbohydrates • lipids (fats) • proteins • vitamins • minerals • water. Foods rich in the energy-yielding nutrients (carbohydrates, fats and proteins) provide the major materials for building the body’s tissues and yield energy for the body’s use or storage. Energy is measured in kilojoules. Vitamins, minerals and water facilitate a variety of activities in the body.
1.3 The science of nutrition
The science of nutrition is the study of the nutrients and other substances in foods and the body’s handling of them. It has its foundation in several other sciences, including biology, biochemistry, and physiology. Nutrition is a relatively young science, but much has happened in its short life. And it is currently experiencing a tremendous growth spurt as scientists apply knowledge gained from sequencing the human genome. The integration of nutrition,
*The major minerals are calcium, phosphorus, potassium, sodium, chloride, magnesium and sulphate. The trace minerals are iron, iodine, zinc, chromium, selenium, fluoride, molybdenum, copper and manganese. Chapters 12 and 13 are devoted to the major and trace minerals, respectively.
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Chapter 1: An overview of nutrition
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genomics and molecular biology has opened a new world of study called nutritional genomics – the science of how nutrients affect the activities of genes and how genes affect the interactions between diet and disease. Highlight 6 describes how nutritional genomics is shaping the science of nutrition, and examples of nutrient–gene interactions appear throughout later sections of the book. What has the field of nutrition research achieved in the way of significant discoveries over the last 30 years? And what are the greatest challenges for the coming 30 years? These questions were debated by an eminent panel of nutrition experts at a symposium in Wageningen, the Netherlands, and their viewpoints (see Table 1.4) make for an interesting summary of the milestone discoveries in nutrition.9 As for future challenges, controlling obesity and insulin resistance, delaying cognitive decline by diet, and restoring the balance between private and public control of nutrition research are all considered top priorities.
TABLE 1.4 Greatest discoveries in nutrition research in the past 30 years RANK
DISCOVERY
1
Folic acid supplements reduce the risk of birth defects
2
Health effects of trans fatty acids
3
Nutritional regulation of gene transcription
4
Progress in measuring energy intake – from questionnaires to doubly labelled water
5
Fat tissue as an endocrine organ
6
The LDL-cholesterol receptor and its regulation by diet
7
Obesity is a normal response to an abnormal environment
8
Alcohol causes breast cancer
9
Body fatness is the second most avoidable cause of cancer
10
Plant stanols and sterols and their effects on lipid metabolism
11
Diabetes can be prevented by diet and lifestyle
12
Interaction of carbohydrate/glycaemic load with insulin resistance
13
Vitamin E supplements do not reduce the risk of cardiovascular disease
14
Long-chain polyunsaturated fatty acids reduce mortality in coronary heart disease patients
15
The multisystemic role of vitamin D
Adapted from M. B. Katan and co-authors, Which are the Greatest Recent Discoveries and the Greatest Future Challenges in Nutrition? European Journal of Clinical Nutrition 63 (2009): 2−10.
Conducting research Whether a person is trained in human nutrition or not, we all have a view of how food relates to health. Our views will have been shaped by our biological needs, our culture and the role food plays in it, as well as by knowledge that extends beyond our immediate culture. The difficulty for each of us is that we are likely to see nutrition information from our own perspective, and a great deal of intellectual discipline is required to see it from other perspectives.
A personal account of an experience or event is an anecdote and is not accepted as reliable scientific information.
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Understanding nutrition
In the Western scientific tradition a new idea or perspective is generated as an hypothesis that should be testable. As Figure 1.2 shows, research always begins with a problem or a question. For example, ‘What foods or nutrients might protect against the common cold?’ In search of an answer, scientists have an hypothesis such as ‘Foods rich in vitamin C reduce the number of common colds’. Then they systematically conduct research studies to collect data that will test the hypothesis (see the Glossary for definitions of research terms). Some examples of various types of research designs are presented in Figure 1.3. Each type of study has strengths and weaknesses (see Table 1.5 on page 14). Consequently, some provide stronger evidence than others.
FIGURE 1.2 The scientific method Research scientists follow the scientific method. Note that most research generates new questions, not final answers. Thus the sequence begins anew, and research continues in a somewhat cyclical way. OBSERVATION AND QUESTION Identify a problem to be solved or ask a specific question to be answered.
HYPOTHESIS AND PREDICTION Formulate a hypothesis – a tentative solution to the problem or answer to the question – and make a prediction that can be tested.
EXPERIMENT Design a study and conduct the research to collect relevant data.
RESULTS AND INTERPRETATIONS Summarise, analyse, and interpret the data; draw conclusions.
HYPOTHESIS SUPPORTED
THEORY Develop a theory that integrates conclusions with those from numerous other studies.
HYPOTHESIS NOT SUPPORTED
NEW OBSERVATIONS AND QUESTIONS
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Chapter 1: An overview of nutrition
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FIGURE 1.3 Examples of research designs North Atlantic Ocean
EPIDEMIOLOGICAL STUDIES France
Slovenia
Croatia
Black Sea
Bosnia Italy
Montenegro Albania
Spain
Greece
Morocco
Algeria
Mediterranean Sea Tunisia
Heart attacks
Science Photo Library/Dr M. A. Ansary
Libya
Turkey
Lebanon Israel Jordan
Cross-sectional Researchers observe how much and what kinds of foods a group of people eat and how healthy those people Syria are. Their findings identify factors that might influence the incidence of a disease in various populations.
Example: The people of the Mediterranean region drink lots of wine, eat plenty of fat from olive oil and have a lower incidence of heart disease than northern Europeans and Australians.
Egypt
Case-control Researchers compare people who do and do not have a given condition such as a disease, closely matching them in age, gender and other key variables so that differences in other factors will stand out. These differences may account for the condition in the group that has it.
Example: People with goitre lack iodine in their diets.
Cohort Researchers analyse data collected from a selected group of people (a cohort) at intervals over a certain period of time.
Example: Data collected periodically over the past several decades from over 5000 people randomly selected from the town of Framingham, Massachusetts, in 1948 have revealed that the risk of heart attack increases as blood cholesterol increases.
EXPERIMENTAL STUDIES
laboratory where all conditions can be controlled.
PhotoDisc
iStockphoto/Mediaphotos
Getty Images/Remi Benali
Blood cholesterol
Laboratory-based animal studies Researchers feed animals special diets that provide or omit specific nutrients and then observe any changes in health. Such studies test possible disease causes and treatments in a
Example: Mice fed a high-fat diet eat less food than mice given a lower-fat diet, so they receive the same number of kilojoules – but the mice eating the fat-rich diet become severely obese.
Laboratory-based in-vitro studies Researchers examine the effects of a specific variable on a tissue, cell or molecule isolated from a living organism.
Example: Laboratory studies find that fish oils inhibit the growth and activity of the bacteria implicated in ulcer formation.
Human intervention (or clinical) trials Researchers ask people to adopt a new behaviour (for example, eat a citrus fruit, take a vitamin C supplement or exercise daily). These trials help determine the effectiveness of such interventions on the development or prevention of disease.
Example. Heart disease risk factors improve when men receive fresh squeezed orange juice daily for two months compared with those on a diet low in vitamin C – even when both groups follow a diet high in saturated fat.
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Understanding nutrition
TABLE 1.5 Strengths and weaknesses of research designs TYPE OF RESEARCH
STRENGTHS
WEAKNESSES
Epidemiological studies determine the incidence and distribution of diseases in a population. Epidemiological studies include cross-sectional, case-control and cohort (see Figure 1.3).
• Can narrow down the list of possible causes • Can raise questions to pursue through other types of studies
• Cannot control variables that may influence the development or the prevention of a disease • Cannot prove cause and effect
Laboratory-based studies explore the effects of a specific variable on a tissue, cell or molecule. Laboratory-based studies are often conducted in test tubes (in vitro) or on animals.
• Can control conditions • Can determine effects of a variable
• Cannot apply results from test tubes or animals to human beings
Human intervention or clinical trials involve human beings who follow a specified regimen.
• Can control conditions (for the most part) • Can apply findings to some groups of human beings
• Cannot generalise findings to all human beings • Cannot use certain treatments for clinical or ethical reasons
In attempting to discover whether a nutrient relieves symptoms or cures a disease, researchers deliberately manipulate one variable (for example, the amount of vitamin C in the diet) and measure any observed changes (perhaps the number of colds). As much as possible, all other conditions are held constant. The following paragraphs illustrate how this is accomplished.
Controls
In studies examining the effectiveness of vitamin C, researchers typically divide the subjects into two groups. One group (the experimental group) receives a vitamin C supplement, and the other (the control group) does not. Researchers observe both groups to determine whether one group has fewer or shorter colds than the other. The following discussion describes some of the pitfalls inherent in an experiment of this kind and ways to avoid them. In sorting subjects into two groups, researchers must ensure that each person has an equal chance of being assigned to either the experimental group or the control group. This is accomplished by randomisation; that is, the subjects are chosen randomly from the same population by flipping a coin or some other method involving chance. Randomisation helps to ensure that results reflect the treatment and not factors that might influence the grouping of subjects. Importantly, the two groups of people must be similar and must have the same track record with respect to colds to rule out the possibility that observed differences in the rate, severity or duration of colds might have occurred anyway. If, for example, the control group would normally catch twice as many colds as the experimental group, then the findings prove nothing. In experiments involving a nutrient, the diets of both groups must also be similar, especially with respect to the nutrient being studied. If those in the experimental group were receiving less vitamin C from their usual diet, then any effects of the supplement may not be apparent.
Sample size To ensure that chance variation between the two groups does not influence the results, the groups must be large. For example, if one member of a group of five people catches a bad cold by chance, they will pull the whole group’s average towards bad colds; but if one member of a group of 500 catches a bad cold, they will not unduly affect the group average. Statistical methods are used to determine whether differences between groups of various sizes support a hypothesis.
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Chapter 1: An overview of nutrition
Placebos
If people who take vitamin C for colds believe it will cure them, their chances of recovery may improve. Taking anything believed to be beneficial may hasten recovery. This phenomenon, the result of expectations, is known as the placebo effect. In experiments designed to determine vitamin C’s effect on colds, this mind–body effect must be rigorously controlled. One way experimenters control for the placebo effect is to give pills to all participants. Those in the experimental group, for example, receive pills containing vitamin C, and those in the control group receive a placebo – pills of similar appearance and taste containing an inactive ingredient. This way, the expectations of both groups will be equal. It is not necessary to convince all subjects that they are receiving vitamin C, but the extent of belief or unbelief must be the same in both groups. A study conducted under these conditions is called a blind experiment – that is, the subjects do not know (are blind to) whether they are members of the experimental group (receiving treatment) or the control group (receiving the placebo).
Double blind When both the subjects and the researchers do not know which subjects are in which group, the study is called a double-blind experiment. Being fallible human beings and having an emotional and sometimes a financial investment in a successful outcome, researchers might record and interpret results with a bias in the expected direction. To prevent such bias, the pills would be coded by a third party, who does not reveal to the experimenters which subjects were in which group until all results have been recorded.
PUTTING COMMON SENSE TO THE TEST
All published research should be treated with some level of critical appraisal. TRUE
Analysing research findings Research findings must be analysed and interpreted with an awareness of each study’s limitations. Scientists must be cautious about drawing any conclusions until they have accumulated a body of evidence from multiple studies that have used various types of research designs. As evidence accumulates, scientists begin to develop a theory that integrates the various findings and explains the complex relationships.
Correlations and causes Researchers often examine the relationships between two or more variables – for example, daily vitamin C intake and the number of colds or the duration and severity of cold symptoms. Importantly, researchers must be able to observe, measure or verify the variables selected. Findings Knowledge about the nutrients and their effects on health comes from scientific study. sometimes suggest no correlation between variables (regardless of the amount of vitamin C consumed, the number of colds remains the same). Other times, studies find either a positive correlation (the more vitamin C, the more colds) or a negative correlation (the more vitamin C, the fewer colds). Correlational evidence proves only that variables are associated, not that one is the cause of the other. People often jump to conclusions when they notice correlations, but their conclusions are often wrong. To actually prove that A causes B, scientists have to find evidence of the mechanism – that is, an explanation of how A might cause B.
Cautious conclusions When researchers record and analyse the results of their experiments, they must exercise caution in their interpretation of the findings. For example, in an epidemiological study, scientists may use a specific segment of the population – for example, men aged 18–30 years. When the scientists draw conclusions, they are careful not to generalise the findings to all people. Similarly, scientists performing research studies using animals are cautious in applying their findings to human beings. Conclusions from any one research study are always tentative
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Understanding nutrition
and take into account findings from studies conducted by other scientists as well. As evidence accumulates, scientists gain confidence about making recommendations that affect people’s health and lives. Still, their statements are worded cautiously, such as ‘A diet high in fruits and vegetables may protect against some cancers’.
Evaluating the reliability of research Wherever or however nutrition information is presented, it pays to retain a healthy scepticism. However, there are some ways in which the question of evaluating reliability can be approached more systematically. For research published in a journal, the findings are evaluated by a board of reviewers composed of other scientists who rigorously evaluate the study to assure that the scientific method was followed – a process known as peer review. The reviewers critique the study’s hypothesis, methodology, statistical significance and conclusions. If the reviewers consider the conclusions to be well supported by the evidence – that is, if the research has validity – they endorse the work for publication in a scientific journal where others can read it. This raises an important point regarding information found on the Internet: much gets published without the rigorous scrutiny of peer review. Consequently, readers must assume greater responsibility for examining the data and conclusions presented – often without the benefit of journal citations. Highlight 1 gives guidance in determining whether website information is reliable. Table 1.6 describes the parts of a typical research article.
TABLE 1.6 Parts of a typical research article • Abstract: The abstract provides a brief overview of the article. • Introduction: The introduction clearly states the purpose of the current study and provides a comprehensive review of the relevant literature. • Methodology: The methodology section defines key terms and describes the study design, subjects, and procedures used in conducting the study. • Results: The results report the findings and may include tables and figures that summarise the information. • Discussion: The discussion draws tentative conclusions that are supported by the data and reflect the original purpose as stated in the introduction. Usually, it answers a few questions and raises several more. • References: The references reflect the investigator’s knowledge of the subject and should include an extensive list of relevant studies.
Even when a new finding is published or released to the media, it is still only preliminary and not very meaningful by itself. Other scientists will need to confirm or disprove the findings through replication. To be accepted into the body of nutrition knowledge, a finding must stand up to rigorous, repeated testing in experiments performed by several different researchers. What we ‘know’ in nutrition results from years of replicating study findings. Communicating the latest finding in its proper context without distorting or oversimplifying the message is a challenge for scientists and journalists alike. With each report from scientists, the field of nutrition changes a little – each finding contributes another piece to the whole body of knowledge. People who know how science works understand that single findings, like single frames in a movie, are just small parts of a larger story. Over time, nutrition knowledge gradually changes, and dietary recommendations change to reflect the current understanding of scientific research. Highlight 5 provides a detailed look at how dietary fat recommendations have evolved over the past several decades as researchers have uncovered the relationships between the various kinds of fat and their roles in supporting or harming health.
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© Cengage
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Chapter 1: An overview of nutrition
REVIEW IT
Scientists learn about nutrition by conducting experiments that follow the protocol of scientific research. Researchers take care to establish similar control and experimental groups, large sample sizes, placebos and blind treatments. Their findings must be reviewed and replicated by other scientists before being accepted as valid. The characteristics of well-designed research have enabled scientists to study the actions of nutrients in the body. Such research has laid the foundation for quantifying how much of each nutrient the body needs.
1.4 Nutrient Reference Values
Using the results of thousands of research studies, nutrition experts have produced a set of standards that define the amounts of energy, nutrients, other dietary components and physical activity that best support health. These recommendations are called Nutrient Reference Values (NRV) and they reflect the collaborative efforts of researchers in both Australia and New Zealand.10 The inside-cover pages of this book provide a handy reference for NRV.
Establishing nutrient recommendations The NRV Working Party consisted of highly qualified scientists who based their estimates of nutrient needs on careful examination and interpretation of scientific evidence. These recommendations apply to healthy people and may not be appropriate for people with diseases that increase or decrease nutrient needs. The next few paragraphs discuss specific aspects of how the committee went about establishing the values that make up the NRV: • Estimated Average Requirement (EAR) • Recommended Dietary Intake (RDI) • Adequate Intake (AI) • Upper Level of Intake (UL). A further set of values, termed Suggested Dietary Targets (SDTs), was also established. These relate to nutrients for which there was a reasonable body of evidence indicating a potential chronic disease preventive effect at levels substantially higher than the EAR, RDI or AI.
Estimated Average Requirement (EAR)
The NRV Working Party reviewed hundreds of research studies to determine the requirement for each nutrient – how much is needed in the diet. The working party selected a different criterion for each nutrient based on its various roles in performing activities in the body and in reducing disease risks. An examination of all the available data reveals that each person’s body is unique and has its own set of requirements. Men differ from women, and needs change as people grow from infancy to old age. For this reason, recommendations for people are clustered into groups based on age and gender. Even so, the exact requirements for people of the same age and gender are likely to be different. For example, person A might need 40 units of a particular nutrient each day, person B might need 35 and person C might need 57. Looking at enough people might reveal that their individual requirements fall into a symmetrical distribution, with most near the midpoint and only a few at the extremes (see the left-hand side of Figure 1.4). Using this information, the working party determined an Estimated Average Requirement (EAR) for each nutrient – the average amount that appears sufficient for half of the population. In Figure 1.4, the EAR is shown as 45 units.
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Understanding nutrition
FIGURE 1.4 Estimated Average Requirement (EAR) and Recommended Dietary Intakes (RDI) compared Each square in the graphs below represents a person with unique nutritional requirements. (The text discusses three of these people – A, B, and C.) Some people require only a small amount of nutrient X and some require a lot. Most people, however, fall somewhere in the middle.
B
20
PUTTING COMMON SENSE TO THE TEST
An RDI for a nutrient is the amount that everyone needs to consume each day. FALSE
30
EAR Number of people
Number of people
EAR
A
B
C 40
50
60
70
20
30
RDI
A C 40
50
60
70
Daily requirement for nutrient X (units/day)
Daily requirement for nutrient X (units/day)
The EAR for a nutrient is the amount that meets the needs of about half of the population (shown here by the red line).
The RDI for a nutrient (shown here in green) is set well above the EAR, meeting the needs of about 98 per cent of the population.
Recommended Dietary Intake (RDI)
Once a nutrient requirement is established, the working party had to decide what intake to recommend for everybody – the Recommended Dietary Intake (RDI). As you can see by the distribution in Figure 1.4, the EAR (shown in the figure as 45 units) is probably closest to everyone’s need. However, if people consumed exactly the average requirement of a given nutrient each day, half of the population would develop deficiencies of that nutrient – in Figure 1.4, for example, person C would be among them. Recommendations are therefore set high enough above the EAR to meet the needs of most healthy people. Small amounts above the daily requirement do no harm, whereas amounts below the requirement may lead to health problems. When people’s nutrient intakes are consistently deficient (less than the requirement), their nutrient stores decline, and over time this decline leads to poor health and deficiency symptoms. Therefore, to ensure that the nutrient RDI meet the needs of as many people as possible, the RDI are set near the top end of the range of the population’s estimated requirements. In this example, a reasonable RDI might be 63 units a day (see the right side of Figure 1.4). Such a point can be calculated mathematically so that it covers about 98 per cent of a population. Almost everybody – including person C, whose needs were higher than the average – would be covered if they met this dietary goal. Relatively few people’s requirements would exceed this recommendation, and even then, they wouldn’t exceed it by much.
Adequate Intake (AI) For some nutrients, there is insufficient scientific evidence to determine an EAR (which is needed to set an RDI). In these cases, the working party established an Adequate Intake (AI) instead of an RDI. An AI reflects the average amount of a nutrient that a group of healthy people consumes. Like the RDI, the AI may be used as nutrient goals for individuals.
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Chapter 1: An overview of nutrition
Although both the RDI and the AI serve as nutrient intake goals for individuals, their differences are noteworthy. An RDI for a given nutrient is based on enough scientific evidence to expect that the needs of almost all healthy people will be met. An AI, on the other hand, must rely more heavily on scientific judgements because sufficient evidence is lacking. The percentage of people covered by an AI is unknown; an AI is expected to exceed average requirements, but it may cover more or fewer people than an RDI would cover (if an RDI could be determined). For these reasons, AI values are more tentative than RDI. The table on the inside back cover identifies which nutrients have an RDI and which have an AI. Later chapters present the RDI and AI values for the vitamins and minerals.
Upper Level of Intake (UL) As mentioned earlier, the recommended intakes for nutrients are generous and do not necessarily cover every individual for every nutrient. Nevertheless, it is probably best not to exceed these recommendations by very much or very often. Individual tolerances for high doses of nutrients vary and somewhere above the recommended intake is a point beyond which a nutrient is likely to become toxic. This point is known as the Upper Level of Intake (UL). It is naive – and inaccurate – to think of recommendations as minimum amounts. A more accurate view is to see a person’s nutrient needs as falling within a range, with marginal and danger zones both below and above it (see Figure 1.5).
FIGURE 1.5 Inaccurate versus accurate view for nutrient intakes The RDI or AI for a given nutrient represents a point that lies within a range of appropriate and reasonable intakes between toxicity and deficiency. Both of these recommendations are high enough to provide reserves in times of short-term dietary inadequacies, but not so high as to approach toxicity. Nutrient intakes above or below this range may be equally harmful.
Danger of toxicity
Marginal Safety
Tolerable Upper Intake Level
Intake
Safety RDI or AI RDI Marginal Danger
Inaccurate view
Estimated Average Requirement
Danger of deficiency Accurate view
Paying attention to upper levels is particularly useful in guarding against the overconsumption of nutrients, which may occur when people use large-dose supplements and fortified foods regularly. Later chapters discuss the dangers associated with excessively high intakes of vitamins and minerals, and the inside cover presents tables that include the upperlevel values for selected nutrients.
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Understanding nutrition
Establishing energy recommendations In contrast to the RDI and AI values for nutrients, the recommendation for energy is not generous. Excess energy cannot be readily excreted and is eventually stored as body fat. These reserves may be beneficial when food is scarce, but they can also lead to obesity and its associated health consequences.
Estimated Energy Requirement (EER) FIGURE 1.6 Energy nutrient contributions to the total The three energy nutrients – carbohydrate, fat, and protein – all contribute to the total energy intake. Each of these three bars illustrates percentages that fall within the Acceptable Macronutrient Distribution Ranges (AMDR). Notice that whenever the percentage of any one of them increases or decreases, the contribution of the others shifts as well. 100 80
10%
15% 35%
25%
35% 60 40
20% 65%
50%
45%
20 0
Key: Protein Fat Carbohydrate
The energy recommendation – called the Estimated Energy Requirement (EER) – represents the average dietary energy intake (kilojoules per day) that will maintain energy balance in a person who has a healthy body weight and level of physical activity. Appendix F lists EER values for children and adults engaging in different levels of physical activity. Balance is the key to the energy recommendation. Enough energy is needed to sustain a healthy and active life, but too much energy can lead to weight gain and obesity. Because any amount in excess of energy needs will result in weight gain, no upper level for energy has been determined.
Acceptable Macronutrient Distribution Ranges (AMDR) People don’t eat energy directly; they derive energy from foods containing carbohydrate, fat and protein. Each of these three energyyielding nutrients contributes to the total energy intake, and those contributions vary in relation to each other. The NRV Working Party determined that the composition of a diet that provides adequate energy and nutrients, maintains current body weight and reduces the risk of chronic diseases is: • 45–65 per cent kilojoules from carbohydrate • 20–35 per cent kilojoules from fat • 15–25 per cent kilojoules from protein. These values are known as Acceptable Macronutrient Distribution Ranges (AMDR). Figure 1.6 illustrates that diets with varying amounts of carbohydrate, fat, and protein can all fall within the AMDR and when the contribution of any of the energy nutrients increases or decreases, the contribution of the others shifts as well.
Using nutrient recommendations Although the intent of nutrient recommendations seems simple, they are the subject of much misunderstanding and controversy. Perhaps the following facts will help put them in perspective: 1 Estimates of adequate energy and nutrient intakes apply to healthy people. They need to be adjusted for malnourished people or those with medical problems who may require supplemented or restricted intakes. 2 Recommendations are not minimum requirements, nor are they necessarily optimal intakes for all individuals. Recommendations can only target ‘most’ of the people and cannot account for individual variations in nutrient needs – yet. Given the recent explosion of knowledge about genetics, the day may be fast approaching when nutrition scientists will be able to determine an individual’s optimal nutrient needs.11 Until then, dietitians and other qualified health professionals can help determine if recommendations should be adjusted to meet individual needs. 3 Most nutrient goals are intended to be met through diets composed of a variety of foods whenever possible. Because foods contain mixtures of nutrients and non-nutrients,
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Chapter 1: An overview of nutrition
they deliver more than just those nutrients covered by the recommendations. Excess intakes of vitamins and minerals are unlikely when they come from foods rather than supplements. 4 Recommendations apply to average daily intakes. Trying to meet the recommendations for every nutrient every day is difficult and unnecessary. The length of time over which a person’s intake can deviate from the average without risk of deficiency or overdose varies for each nutrient, depending on how the body uses and stores the nutrient. For most nutrients (such as thiamin and vitamin C), deprivation would lead to rapid development of deficiency symptoms (within days or weeks); for others (such as vitamin A and vitamin B12), deficiencies would develop more slowly (over months or years). 5 Each of the NRV categories serves a unique purpose. For example, the EARs are most appropriately used to develop and evaluate nutrition programs for groups such as schoolchildren or military personnel. The RDI (or AI if an RDI is not available) can be used to set goals for individuals. The UL serves as a reminder to keep nutrient intakes below amounts that increase the risk of toxicity – not a common problem when nutrients derive from foods, but a real possibility for some nutrients if supplements are used regularly. With these understandings, professionals can use the NRV for a variety of purposes. Using the online NRV calculator at http://www.nrv.gov.au you can gain a practical understanding of your own requirements.
Comparing nutrient recommendations At least 80 different nations and international organisations have published nutrient standards similar to those used in Australia and New Zealand. Slight differences may be apparent, reflecting differences both in the interpretation of the data from which the standards were derived and in the food habits and physical activities of the populations they serve. Terminologies may also vary between countries. For example, North America uses the term Dietary Reference Intakes (DRI) in place of NRV and adopts the term Recommended Dietary Allowance (RDA) instead of RDI. In the United Kingdom, Dietary Reference Values (DRV) are used, with Reference Nutrient Intake (RNI) used in place of RDI. Many countries use the recommendations developed by two international groups: the FAO (Food and Agriculture Organization) and WHO (World Health Organization). The FAO/WHO recommendations are considered sufficient to maintain health in nearly all healthy people worldwide. REVIEW IT
The Nutrient Reference Values (NRV) are a set of nutrient intake values that can be used to plan and evaluate diets for healthy people. The Estimated Average Requirement (EAR) defines the amount of a nutrient that supports a specific function in the body for half of the population. The Recommended Dietary Intake (RDI) is based on the EAR and establishes a goal for dietary intake that will meet the needs of almost all healthy people. An Adequate Intake (AI) serves a similar purpose when an RDI cannot be determined. The Suggested Dietary Targets (SDT) is a daily average intake from food and beverages for certain nutrients that that may help in prevention of chronic disease. The Estimated Energy Requirement (EER) defines the average amount of energy intake needed to maintain energy balance, and the Acceptable Macronutrient Distribution Ranges (AMDR) define the proportions contributed by carbohydrate, fat and protein to a healthy diet. The Upper Level of Intake (UL) establishes the highest amount that appears safe for regular consumption.
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1.5 Nutrition assessment
What happens when a person doesn’t get enough or gets too much of a nutrient or energy? If the deficiency or excess is significant over time, the person will exhibit signs of malnutrition. With a deficiency of energy, the person may display the symptoms of undernutrition by becoming extremely thin, losing muscle tissue and becoming prone to infection and disease. With a deficiency of a nutrient, the person may experience skin rashes, depression, hair loss, bleeding gums, muscle spasms, night blindness or other symptoms. With an excess of energy, the person may become obese and vulnerable to diseases associated with overnutrition, such as heart disease and diabetes. With a sudden nutrient overdose, the person may experience hot flushes, yellowing skin, a rapid heart rate, low blood pressure or other symptoms. Similarly, over time, regular intakes in excess of needs may also have adverse effects. This discussion presents the basics of nutrition assessment; many more details are offered in later chapters and in Appendix E.
Nutrition assessment of individuals To prepare a nutrition assessment, a dietitian or other trained healthcare professional uses: • historical information • anthropometric data • physical examinations • laboratory tests. Each of these methods involves collecting data in various ways and interpreting each finding in relation to the others to create a total picture. Nutrition screening is often the first part of the process to help identify people who are already malnourished or at risk of becoming so. After nutritional screening, nutrition assessment can then be undertaken. Nutrition assessment differs from nutrition screening by its use of a comprehensive assessment of a person’s nutrition status through such measures as health, medication use, diet histories, anthropometric and laboratory tests.
Historical information One step in evaluating nutrition status is to obtain information about a person’s history with respect to health status, socioeconomic status, medication use and diet. The health history reflects a person’s medical record and may reveal a disease that interferes with the person’s ability to eat or the body’s use of nutrients. The person’s family history of major diseases is also noteworthy, especially for conditions such as heart disease that have a genetic tendency to run in families. Economic circumstances may show a financial inability to buy foods or inadequate kitchen facilities in which to prepare them. Social factors such as marital status, ethnic background and educational level also influence food choices and nutrition status. A drug history, including all prescribed and over-thecounter medications as well as narcotics, may highlight possible interactions that lead to nutrient deficiencies (as described in Highlight 17). A diet history that examines a person’s intake of foods, beverages and supplements may reveal either a surplus or inadequacy of nutrients or energy. To take a diet history, the assessor collects data about the foods a person eats. The data may be collected by recording the foods the person has eaten over a period of 24 hours, three days, or a week or more, or by asking what foods the person typically eats and how much of each. The days in the record must be fairly typical of the person’s diet, and portion sizes must be recorded accurately. To determine the amounts of nutrients consumed, the assessor usually enters the foods and their portion sizes into a computer using a diet analysis program. The assessor then compares the calculated nutrient intakes with the NRV to determine the probability of adequacy (see Figure 1.7). Alternatively, the diet history might be compared against standards such as the Australian Guide to Healthy Eating, the Australian Dietary Guidelines or the New Zealand Food and Nutrition Guidelines (described in Chapter 2).
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Chapter 1: An overview of nutrition
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FIGURE 1.7 Using the NRV to assess the dietary intake of a healthy individual High Usual intake of nutrient X (units/day)
Intake probably adequate
If a person’s usual intake falls above the RDI, the intake is probably adequate because the RDI covers the needs of almost all people.
RDI Intake possibly inadequate
A dual intake that falls between the RDI and the EAR is more difficult to assess; the intake may be adequate, but the chances are greater or equal that it is inadequate.
EAR Intake probably inadequate
If the usual intake falls below the EAR, it is probably inadequate.
Low
An estimate of energy and nutrient intakes from a diet history, when combined with other sources of information, can help confirm or rule out the possibility of suspected nutrition problems. A sufficient intake of a nutrient does not guarantee adequacy, and an insufficient intake does not always indicate a deficiency. Such findings, however, warn of possible problems.
Anthropometric data
A second technique that may help to reveal nutrition problems is taking anthropometric measures such as height and weight. The assessor compares a person’s measurements with standards specific for gender and age or with previous measures on the same individual. (Chapter 8 presents information on body weight and its standards.) Measurements taken periodically and compared with previous measurements reveal patterns and indicate trends in a person’s overall nutrition status, but they provide little information about specific nutrients. Instead, measurements out of line with expectations may reveal such problems as children’s failure to thrive, the wasting or swelling of body tissues in adults, and obesity – conditions that may reflect energy or nutrient deficiencies or excesses.
Physical examinations A third nutrition assessment technique is a physical examination looking for clues to poor nutrition status. Every part of the body that can be inspected may offer such clues: hair, eyes, skin, posture, tongue, fingernails and others. The examination requires skill because many physical signs reflect more than one nutrient deficiency or toxicity – or even non-nutrition conditions. Like the other assessment techniques, a physical examination alone does not yield firm conclusions. Instead, physical examinations reveal possible imbalances that must be confirmed by other assessment techniques, or they confirm results from other assessment measures.
Laboratory tests A fourth way to detect a developing deficiency, imbalance or toxicity is to take samples of blood or urine, analyse them in the laboratory and compare the results with normal values for a similar population. A goal of nutrition assessment is to uncover early signs of malnutrition before symptoms appear, and laboratory tests are most useful for this purpose. In addition, they can confirm suspicions raised by other assessment methods.
Assessment may one day depend on measures of how a nutrient influences genetic activity within the cells, instead of quantities in the blood or other tissues.
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Understanding nutrition
An example: iron The mineral iron can be used to illustrate the stages in the development of a nutrient deficiency and the assessment techniques useful in detecting them. The overt, or outward, signs of an iron deficiency appear at the end of a long sequence of events. Figure 1.8 describes what happens in the body as a nutrient deficiency progresses, and shows which assessment methods can reveal those changes.
FIGURE 1.8 Stages in the development of a nutrient deficiency Internal changes precede outward signs of deficiencies. However, outward signs of sickness need not appear before a person takes corrective measures. Laboratory tests can help determine nutrient status in the early stages. WHAT HAPPENS IN THE BODY
WHICH ASSESSMENT METHODS REVEAL CHANGES
Primary deficiency caused by inadequate diet or Secondary deficiency caused by problem inside the body
Diet history
Declining nutrient stores (subclinical) and Abnormal functions inside the body (covert)
Physical signs and symptoms (overt)
Health history
Laboratory tests
Physical examination and anthropometric measures
First, the body has too little iron – either because iron is lacking in the person’s diet (a
primary deficiency) or because the person’s body doesn’t absorb enough, excretes too much or uses iron inefficiently (a secondary deficiency). A diet history provides clues to primary deficiencies; a health history provides clues to secondary deficiencies. Next, the body begins to use up its stores of iron. At this stage, the deficiency might be described as subclinical. It exists as a covert condition, and although it might be detected by laboratory tests, no outward signs are apparent. Finally, the body’s iron stores are exhausted. Now it cannot make enough iron-containing red blood cells to replace those that are ageing and dying. Iron is needed in red blood cells to carry oxygen to all the body’s tissues. When iron is lacking, fewer red blood cells are made, the new ones are pale and small, and every part of the body feels the effects of oxygen shortage. Now the overt symptoms of deficiency appear – weakness, fatigue, pallor and headaches – reflecting the iron-deficient state of the blood. A physical examination will reveal these symptoms.
Nutrition assessment of populations To assess a population’s nutrition status, researchers conduct surveys using techniques similar to those used on individuals. The data collected are then used by various agencies for numerous purposes, including the development of national health goals.
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Chapter 1: An overview of nutrition
National nutrition surveys National nutrition surveys gather information about the population’s dietary, nutritional, and related health status. The United States, the United Kingdom and many continental European nations have had ongoing, systematic programs for monitoring the diet and nutritional status of their populations for many years. Australia has conducted only four national surveys of diet in the past 50 years: a national dietary survey of adults in 1983, one of children in 1985, the National Nutrition Survey in 1995 and the most recent National Health Survey in 2017–18.12 In the absence of a regular, comprehensive and coordinated national nutrition monitoring survey in Australia, several State and Territory governments have established monitoring systems that survey health behaviours, including food habits.13 In New Zealand, Adult Nutrition Surveys were carried out by the Ministry of Health in 1997 and 2008–09 and the National Children’s Nutrition Survey was carried out in 2002.14 The Ministry of Health also collects information as part of its ongoing Health Survey, which includes some dietary habits questions and self-reported weight and height. The information gained from national nutrition surveys is used for a variety of purposes. For example, the government uses this information to establish public policy on nutrition education, public health nutrition programs and the regulation of the food supply. Scientists use the information to establish research priorities. The food industry uses these data to guide decisions in public relations and product development. The NRV and other major reports that examine the relationships between diet and health depend on the information collected from these nutrition surveys. These data also provide the basis for developing and monitoring national health goals.
National trends What do we eat and how has it changed over the past 30 years? The short answer to both questions is ‘a lot’. We eat more meals away from home, particularly at fast-food restaurants. We eat larger portions. We drink more sweetened beverages and eat more energy-dense, nutrient-poor foods such as lollies and chips. We snack frequently. As a result of these dietary habits, our energy intake has risen and, consequently, so has the incidence of overweight and obesity. Overweight and obesity, in turn, profoundly influence our health – as the next section explains.
REVIEW IT
People become malnourished when they get too little or too much energy or nutrients. Deficiencies, excesses and imbalances of nutrients lead to malnutrition diseases. To detect malnutrition in individuals, healthcare professionals use four nutrition assessment methods. Reviewing dietary data and health information may suggest a nutrition problem in its earliest stages. Laboratory tests may detect it before it becomes overt, whereas anthropometrics and physical examinations pick up on the problem only after it causes symptoms. National surveys use similar assessment methods to measure people’s food consumption and to evaluate the nutrition status of populations.
1.6 Diet and health
Diet has always played a vital role in supporting health. Early nutrition research focused on identifying the nutrients in foods that would prevent such common diseases as rickets and scurvy, the vitamin D- and vitamin C-deficiency diseases. With this knowledge, industrialised countries have successfully defended against nutrient deficiency diseases. More recently, nutrition research has focused on chronic diseases associated with energy and nutrient excesses. Once thought to be ‘rich countries’ problems’, chronic diseases have now become epidemic in developing countries as well – contributing to three out of five deaths worldwide.15
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Chronic diseases Table 1.7 lists the 10 leading causes of death in Australia. These ‘causes’ are stated as if a single condition such as heart disease caused death, but most chronic diseases arise from multiple factors over many years. A person who dies of heart disease may have been overweight, had high blood pressure, been a cigarette smoker, and spent years eating a diet high in saturated fat and getting too little exercise.
TABLE 1.7 Leading causes of death in Australia (2017) PERCENTAGE OF TOTAL DEATHS 1 Ischaemic heart disease
11.6
2 Dementia including Alzheimer’s disease
8.5
3 Cerebrovascular disease (stroke)
6.3
4 Chronic lower respiratory diseases
5.2
5 Lung cancer
5.1
6 Colorectal cancer
3.3
7 Diabetes
3.0
8 Lymph and blood cancer
2.8
9 Influenza and pneumonia
2.7
10 Diseases of the urinary system
2.2
NOTE: The diseases highlighted in green have relationships with diet. Australian Bureau of Statistics, Causes of Death, Australia, ABS Catalogue Number 3303.0, (Canberra: ABS, 2010). CC BY 2.5 Australia
PUTTING COMMON SENSE TO THE TEST
Changing our diet will do little to reduce the risk of many chronic diseases. FALSE
Of course, not all people who die of heart disease fit this description, and nor do all people with these characteristics die of heart disease. People who are overweight might die from the complications of diabetes instead, or those who smoke might die of lung cancer. They might even die from something totally unrelated to any of these factors, such as a car accident. Still, statistical studies have shown that certain conditions and behaviours are linked to certain diseases. Notice that Table 1.7 highlights five of the top 10 causes of death as having a link with diet. Coronary heart disease, colorectal cancer, stroke and diabetes account for a quarter of all deaths each year. During the past 30 years, as knowledge about these diet and disease relationships grew, the death rates for three of these – heart disease, cancers and strokes – decreased.16 Death rates for diabetes – a chronic disease closely associated with obesity – increased.
Risk factors for chronic diseases Factors that increase or reduce the risk of developing chronic diseases can be identified by analysing statistical data. A strong association between a risk factor and a disease means that when the factor is present, the likelihood of developing the disease increases. It does not mean that all people with the risk factor will develop the disease. Similarly, a lack of risk factors does not guarantee freedom from a given disease. On the average, though, the more risk factors in a person’s life, the greater that person’s chances of developing the disease. Conversely, the fewer risk factors in a person’s life, the better the chances for good health.
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Chapter 1: An overview of nutrition
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Risk factors persist Risk factors tend to persist over time. Without intervention, a young adult with high blood pressure will most likely continue to have high blood pressure as an older adult, for example. Thus, to minimise the damage, early intervention is most effective.
Risk factors cluster
Risk factors in perspective
iStockphoto/Sportstock
Risk factors tend to cluster. For example, a person who is obese may be physically inactive, have high blood pressure and have high blood cholesterol – all risk factors associated with heart disease. Intervention that focuses on one risk factor often benefits the others as well. For example, physical activity can help reduce weight. The physical activity and weight loss will, in turn, help to lower blood pressure and blood cholesterol. Physical activity can be both fun and beneficial.
The most prominent factors contributing to death in Australia all have dietary and lifestyle causes (see Table 1.8).17 Risk factors such as smoking, poor dietary habits, physical inactivity and alcohol consumption are personal behaviours that can be changed. Decisions to not smoke, to eat a well-balanced diet, to engage in regular physical activity and to drink alcohol in moderation (if at all) improve the likelihood that a person will enjoy good health. For this reason, guidelines such as Australian Guide to Healthy Eating and Australian Dietary Guidelines (both described in Chapter 2) have been developed to help individuals and health authorities determine what constitutes a healthy diet that will help lower disease risk.
Cigarette smoking is responsible for over one in every 10 deaths each year.
TABLE 1.8 Factors contributing to deaths and disease burden in Australia RISK FACTOR
PERCENTAGE OF TOTAL DALYa
Tobacco
9.0
Alcohol
5.1
Physical inactivity
5.0
High body mass
5.5
High blood pressure
4.9
High plasma glucose
2.7
High cholesterol
2.4
Diet low in fruit
2.0
Diet low in vegetables
1.1
Diet low in whole grains
1.1
DALY: Disability-Adjusted Life Year. The DALY is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death. a
Australian Burden of Disease Study: impact and causes of illness and death in Australia 2011, Australian Institute of Health and Welfare, (2016). CC-BY 3.0 Licence. (https://www.aihw.gov.au/copyright). https://www.aihw.gov.au/reports/burden-of-disease/abds-impact-andcauses-of-illness-death-2011/contents/highlights
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APPLICATIONS OF NUTRITIONAL RESEARCH The key dietary patterns of long-term health Diet plays a big part in health. As the typical Western diet moved to more overly refined and energy dense foods, rates of obesity and type 2 diabetes mirrored this change. A major scientific review has taken things back to basics to reinforce where the best health gains are to be found with diet.18 The review looked at the diet and chronic disease links from 304 meta-analyses and systematic reviews published in the last 63 years. Type 2 diabetes, overweight and obesity, cancer and cardiovascular disease together accounted for most of the chronic disease links found. As for dietary patterns, the findings showed that plant-based foods were more protective against the risk of developing chronic disease compared with animal-based foods. Among plant foods, grain-based foods seemed to have a small edge over fruits and vegetables. So much for the anti-grain sentiment that is popular at the moment! For animal-based foods, dairy products overall were considered neutral on health, and fish was considered protective. Red and processed meats were linked to a higher disease risk. For tea-lovers, the research confirmed this popular drink as being the most protective against disease risk. On the other end of the spectrum, to no-one’s surprise, soft drinks had few redeeming health benefits. The findings from this major review are close to a carbon copy of existing dietary guidelines that have changed little over decades. Eat more plant-based foods than animal foods, choose whole grains over refined grains, limit red and processed meat and choose other beverages in preference to soft drink. Such recommendations may not get media attention, or help sell books in numbers like the latest fad diet, but they are the cornerstone of long-term health.
Other risk factors, such as genetics, gender and age, also play important roles in the development of chronic diseases, but they cannot be changed. Health recommendations acknowledge the influence of such factors on the development of disease, but they must focus on the factors that are changeable. For the two out of three Australians who do not smoke or drink alcohol excessively, the one choice that can influence long-term health prospects more than any other is diet. REVIEW IT
Within the range set by genetics, a person’s choice of diet influences long-term health. Diet has no influence on some diseases but is linked closely to others. Personal life choices, such as engaging in physical activity and using tobacco or alcohol, also affect health for the better or worse.
The next several chapters provide many more details about nutrients and how they support health. Whenever appropriate, the discussion shows how diet influences each of today’s major diseases. Dietary recommendations appear again and again, as each nutrient’s relationships with health are explored. Most people who follow the recommendations will benefit and can enjoy good health into their later years.
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Chapter 1: An overview of nutrition
CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 What we eat is largely driven by how hungry we are. FALSE Personal food preferences, habit, social interactions, availability,
4 An RDI for a nutrient is the amount that everyone needs to consume each day. FALSE An RDI is set at the level of meeting the needs of 98 per cent of the
2 Fat has twice the number of kilojoules as carbohydrates or protein. TRUE Fat has 37 kJ/g compared with 17 kJ/g for carbohydrate and protein.
5 Changing our diet will do little to reduce the risk of many chronic diseases. FALSE Diet plays a large role in causing many of the chronic diseases we are
emotional comfort and health benefits are just some of the many factors that affect what we eat.
population it is targeting. Most people require less than this, but a small number require more.
faced with today, such as cancer, heart disease, stroke and diabetes.
3 All published research should be treated with some level of critical appraisal. TRUE No one research study is perfect, so any interpretation of a study should be done within the context of the study design limitations.
NUTRITION PORTFOLIO Each chapter in this book ends with simple ‘Nutrition portfolio’ activities that invite you to review key messages and consider whether your personal choices are meeting the dietary goals introduced in the text. By keeping a journal of these ‘Nutrition portfolio’ assignments, you can examine how your knowledge and behaviours change as you progress in your study of nutrition. Your food choices play a key role in keeping you healthy and reducing your risk of chronic diseases.
• •
•
Identify the factors that most influence your food choices for meals and snacks. List the chronic disease risk factors and conditions (see Table 1.8 on p. 27) that you or members of your family have. Describe lifestyle changes you can make to improve your chances of enjoying good health.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1
5
essential nutrients conditionally essential nutrients non-essential nutrients organic nutrients
The organic nutrients are: a b c d
proteins, fats and vitamins vitamins and minerals minerals and water water and proteins
6
fats, minerals and water minerals, proteins and vitamins carbohydrates, fats and vitamins carbohydrates, fats and proteins
Studies of populations that reveal correlations between dietary habits and disease incidence are: a b c d
Nutrients the human body must obtain from the diet because they cannot be made internally are called: a b c d
3
habit ethnic heritage or tradition personal preference social interactions
The energy-yielding nutrients are: a b c d
When people eat the foods that are influenced by the companionship of friends and family in a group, their choices are influenced by: a b c d
2
4
clinical trials laboratory studies case-control studies epidemiological studies
An experiment in which the researchers know who is receiving the treatment but the subjects do not is known as: a b c d
single blind double control double blind placebo control
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An Upper Level of Intake (UL) represents:
Review questions
a
1
Give several reasons (and examples) why people make the food choices that they do. (Section 1.1)
2
What is a nutrient? Name the six classes of nutrients found in foods. What is an essential nutrient? (Section 1.2)
3
Which nutrients are inorganic and which are organic? Discuss the significance of that distinction. (Section 1.2)
4
Which nutrients yield energy and how much energy do they yield per gram? How is energy measured? (Section 1.2)
5
Describe the process for calculating the energy available from foods. (Section 1.2)
6
What is the science of nutrition? Describe the types of research studies and methods used in acquiring nutrition information. (Section 1.3)
7
Explain how variables might be correlational but not causal. (Section 1.3)
8
What are the NRV? Who developed the NRV? To whom do they apply? How are they used? In your description, identify the categories of NRV and indicate how they are related. (Section 1.4)
9
What judgement factors are involved in setting the energy and nutrient recommendations? (Section 1.4)
b c d
8
Historical information, physical examinations, laboratory tests and anthropometric measures are: a b c d
9
the average amount of a nutrient considered adequate to meet the known nutrient needs of practically all healthy people the lowest amount of a nutrient that will maintain a specified criterion of adequacy the highest amount of a nutrient that appears safe for most healthy people the daily nutrient level estimated to meet the requirements of half the healthy individuals in a particular life stage and gender group
techniques used in diet planning steps used in the scientific method approaches used in disease prevention methods used in a nutrition assessment
A deficiency caused by an inadequate dietary intake is a(n): a b c d
overt deficiency covert deficiency primary deficiency secondary deficiency
10 Behaviours such as smoking, dietary habits, physical activity and alcohol consumption that influence the development of disease are known as: a b c d
risk factors chronic causes preventive agents disease descriptors
10 What happens when people get either too little or too much energy or nutrients? Define malnutrition, undernutrition and overnutrition. Describe the four methods used to detect energy and nutrient deficiencies and excesses. (Section 1.5) 11 What methods are used in nutrition surveys? What kinds of information can these surveys provide? (Section 1.6) 12 Describe the leading causes of death and their relationships to diet and lifestyle factors. (Section 1.6)
NUTRITION CALCULATIONS Many chapters end with problems to give you practice in doing simple nutrition-related calculations. Although the situations are hypothetical, the numbers are real, and calculating the answers (see the answers section at the back of this book) provides a valuable nutrition lesson. Once you have mastered these examples, you will be prepared to examine your own food choices. Be sure to show your calculations for each problem. 1
Calculate the energy provided by a food’s energynutrient contents. A cup of fried rice contains 5 grams protein, 30 grams carbohydrate and 11 grams fat. a
How many kilojoules does the rice provide from these energy nutrients? 5 kJ protein 5 kJ carbohydrate 5 kJ fat kJ Total 5
b
c
What percentage of the energy in the fried rice comes from each of the energy-yielding nutrients? 5 % kJ from protein 5 % kJ from carbohydrate 5 % kJ from fat % Total 5 NOTE: The total should add up to 100%; 99% or 101% due to rounding is also acceptable. Calculate how many of the 613 kilojoules provided by a 375-millilitre can of beer come from alcohol, if the beer contains 1 gram protein and 13 grams carbohydrate. (NOTE: The remaining kilojoules derive from alcohol.) 1 g protein 5 kJ protein kJ carbohydrate 13 g carbohydrate 5 kJ alcohol 5 % Total 5 How many grams of alcohol does this represent? g alcohol
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2
31
20 grams of protein and 100 kilojoules per dose. Is this possible? Why or why not? 5 kJ
To apply your nutrition knowledge to identify bogus claims, consider an advertisement for a new ‘superfood supplement’ that claims to contain
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search for ‘nutrition’ at the National Health and Medical Research Council site: http://www.nhmrc.gov.au • Learn more about basic science nutrition research from the Nutrition Society of Australia: http://www.nsa.asn.au • Review the Nutrient Reference Values: http://www.nrv.gov.au
•
•
•
•
Review nutrition recommendations from the Food and Agriculture Organization of the United Nations and the World Health Organization: http://www.fao.org and http://www.who.org Read about the Selected Highlights from the 2017–18 National Health http://www.abs.gov.au/ausstats/[email protected]/ PrimaryMainFeatures/4364.0.55.001?OpenDocument Read about food and nutrition monitoring in New Zealand by searching ‘nutrition survey’ at http://www.health.govt.nz Visit the food and nutrition centre at the Mayo Clinic: http://www.mayohealth.org
SEARCH ME! NUTRITION Keyword: healthy food choices Read the article Nutrition and healthy living. What were some of the key topics discussed in regard to diet and disease risk?
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Understanding nutrition
1.7 NUTRITION INFORMATION AND MISINFORMATION – ON THE NET AND IN THE NEWS
HIGHLIGHT
1
How can people distinguish valid nutrition information from misinformation? One excellent approach is to notice who is providing the information. The ‘who’ behind the information is not always evident, though, especially in the world of electronic media. Keep in mind that people develop DVDs and create websites on the Internet, just as people write books and report the news. In all cases, consumers need to determine whether the person is qualified to provide nutrition information. This highlight begins by examining the unique potential as well as the problems of relying on the Internet and the media for nutrition information. It continues with a discussion of how to identify reliable nutrition information that applies to all resources, including the Internet and the news. (The Glossary defines related terms.) This discussion recognises that identifying nutrition misinformation requires more than simply gathering accurate information, although that is a good start; it requires critical thinking. Critical thinking allows a person who has gathered information to: • understand the connections between concepts • identify and evaluate the pros and cons of an argument • detect inconsistencies and errors • solve problems • identify the relevance of information. To that end, the questions at the end of the highlights that follow all chapters are intended to help develop critical thinking skills.
Nutrition on the net Got a question? The Internet has an answer. The Internet offers endless opportunities to obtain highquality information, but it also delivers an abundance of incomplete, misleading or inaccurate information.1 Simply put: anyone can publish anything.
With hundreds of millions of websites on the World Wide Web, searching for nutrition information can be an overwhelming experience – much like walking into an enormous bookstore with millions of books, magazines, newspapers and DVDs. And like a bookstore, the Internet offers no guarantees of the accuracy of the information found there – much of which is pure fiction. When using the Internet, keep in mind that the quality of health-related information available covers a broad range.2 You must evaluate websites for their accuracy, just like every other source. The ‘How to’ box (on page 33) provides tips for determining whether a website is reliable. One of the most trustworthy sites used by scientists and others is the US National Library of Medicine’s PubMed, which provides free access to over 10 million abstracts (short descriptions) of research papers published in scientific journals around the world. Many abstracts provide links to websites where full articles are available. Figure H1.1 introduces this valuable resource. Did you receive the email warning about the health dangers associated with reusing or freezing plastic water bottles? If so, you’ve been scammed by Internet misinformation. When nutrition information arrives in unsolicited emails, be suspicious if: • the person sending it to you didn’t write it and you cannot determine who did or if that person is a nutrition expert • the phrase ‘Forward this to everyone you know’ appears • the phrase ‘This is not a hoax’ appears; chances are that it is • the news is sensational and you’ve never heard about it from legitimate sources • the language is emphatic and the text is sprinkled with capitalised words and exclamation marks • no references are given or, if present, are of questionable validity when examined • the message has been debunked on websites such as http://www.quackwatch.org or http://www. urbanlegends.com.
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Chapter 1: An overview of nutrition
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FIGURE H1.1 PubMed: Internet resource for scientific nutrition references
Courtesy of U.S. National Library of Medicine, /www.ncbi.nlm.nih.gov/pubmed/
The US National Library of Medicine’s PubMed website offers tutorials to help teach beginners to use the search system effectively. Often, simply visiting the site, typing a query in the ‘Search for’ box and clicking ‘Go’ will yield satisfactory results. For example, to find research concerning calcium and bone health, typing ‘calcium bone’ nets over 30 0 00 results. Try setting limits on dates, types of articles, languages and other criteria to obtain a more manageable number of abstracts to peruse.
Type search terms here
Use tutorial resources to answer questions
HOW TO:
DETERMINE WHETHER A WEBSITE IS RELIABLE
To determine whether a website offers reliable nutrition information, ask the following questions: ›› Who? Who is responsible for the site? Is it staffed by qualified professionals? Look for the authors’ names and credentials. Have experts reviewed the content for accuracy? ›› When? When was the site last updated? Because nutrition is an ever-changing science, sites need to be dated, and updated frequently. ›› Where? Where is the information coming from? The three letters following the dot in a Web address identify the site’s affiliation. Addresses ending in ‘gov’ (government), ‘edu’ (educational institute) and ‘org’ (organisation) generally provide reliable information; ‘com’ (commercial) sites represent businesses and, depending on their qualifications and integrity, may or may not offer dependable information. ›› Why? Why is the site giving you this information? Is the site providing a public service or selling a product? Many commercial sites provide accurate information, but some do not. When money is the prime motivation, be aware that the infomation may be biased. If you are satisfied with the answers to all of the questions above, then ask this final question: ›› What? What is the message, and is it in line with other reliable sources? Information that contradicts common knowledge should be questioned. Many reliable sites provide links to other sites to facilitate your quest for knowledge, but this provision alone does not guarantee a reputable intention. Be aware that any site can link to any other site without permission.
Nutrition in the news Consumers get much of their nutrition information from television news, ‘current affairs’ programs and magazine reports, which have heightened awareness of how diet influences the development of diseases.
Sometimes, however, when magazine articles or television programs report nutrition trends, they can mislead consumers and create confusion. They often tell a lopsided story based on a few testimonials instead of presenting the results of research studies or a balance of expert opinions.
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Understanding nutrition
Tight deadlines and limited understanding sometimes make it difficult to provide a thorough report. Hungry for the latest news, the media often report scientific findings prematurely – without the benefit of careful interpretation, replication and peer review.3 As a result, ‘surprising new findings’ seem to contradict one another, and consumers feel frustrated and betrayed. Occasionally the reports are downright false, but more often the apparent contradictions are simply the normal result of science at work. A single study contributes to the big picture, but when viewed alone, it can easily distort the image. To be meaningful, the conclusions of any study must be presented cautiously within the context of other research findings. Televised talk shows frequently offer health advice – most commonly, dietary advice. Such advice may sound valid, especially when delivered by a doctor, but viewers need to remember that the primary purpose of these programs is entertainment and selling products. One study examining 160 episodes of two popular medical talk shows found that fewer than half of the recommendations were based on evidence.4
Identifying nutrition experts Regardless of whether the medium is electronic, print or video, consumers need to ask whether the person behind the information is qualified to speak on nutrition. If the creator of a website recommends eating three pineapples a day to lose weight, a trainer at the gym praises a high-protein diet or a health-store sales assistant suggests a herbal supplement, should you believe these people? Can you distinguish between accurate news reports and infomercials on television? Have you noticed that many televised nutrition messages are presented by celebrities, fitness experts, psychologists, food editors and chefs – that is, almost anyone except a qualified dietitian or nutritionist? When you are confused or need sound dietary advice, whom should you ask?
Doctors and other healthcare professionals Many people turn to doctors or other healthcare professionals for dietary advice, expecting them to know about all health-related matters. But are they the best sources of accurate and current information on nutrition? Doctors acknowledge that nutrition plays a crucial role in health and agree that providing nutrition advice is part of their role, but barriers such as lack of nutrition education training and time constraints during appointments can reduce their role.5 By comparison, most students reading this text are taking a dedicated nutrition subject that may also form part of a nutrition degree or nutrition major.
Most healthcare professionals appreciate the connections between health and nutrition. Those who have specialised in clinical nutrition are especially well qualified to speak on the subject. Few, however, have the time or experience to develop diet plans and provide detailed diet instructions for clients. Often they wisely refer clients to a qualified nutrition expert – in Australia that would be an accredited practising dietitian (APD), credentialled by the Dietitians Association of Australia (DAA), and in New Zealand it would be a registered dietitian who is a member of the New Zealand Dietetic Association (NZDA). While not directly involved with nutrition counselling, an accredited exercise physiologist (AEP), as credentialled by Exercise and Sports Science Australia (ESSA), can work in conjunction with a dietitian in the delivery of exercise for the prevention and management of chronic disease conditions.
Dietitians and nutritionists A person who calls themselves a ‘dietitian’ or a ‘nutritionist’ and is a member of a relevant dietetics or nutrition professional organisation has the educational background necessary to deliver reliable nutrition advice. Dietitians usually study for a minimum of four to five years at university (which includes a practical component of at least six months’ practice in clinical nutrition, medical nutrition therapy, community nutrition and food service management) and learn how to apply nutrition information to a range of individuals and medical conditions to improve health. This is compared with someone who is professionally recognised as a nutritionist, such as a registered nutritionist. Nutritionists may work in a number of roles, including research, nutrition consultants and advisors, public health and health promotion officers, community development officers, quality and nutrition coordinators, food technologists, media spokespeople and more. A person with a dietetics qualification could also work professionally as a nutritionist, though someone with a nutrition qualification would not be able to work professionally in all the areas covered by a dietitian. Public health nutritionists who work in governmentfunded agencies play a key role in delivering nutrition services to people in the community. Among their many roles, public health dietitians help plan, coordinate and evaluate nutrition health-promotion programs; act as consultants to other agencies; and manage finances.
Identifying fake credentials In contrast to dietitians, thousands of people obtain fake nutrition degrees and claim to be nutrition consultants or doctors of ‘nutrimedicine’. These and other such titles
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Chapter 1: An overview of nutrition
may sound meaningful, but most of these people lack the established credentials and training of a registered nutritionist or DAA- or NZDA-recognised dietitian. If you look closely, you can see signs of their fake expertise.6 Consider educational background, for example. The minimum standards of education for a dietitian specify a Bachelor of Science (BSc) degree in nutrition and/or dietetics or relevant postgraduate training in dietetics from an accredited university. Such a degree generally requires four to five years of study. In contrast, a fake
HOW TO:
35
nutrition expert may display a degree from a six-month correspondence course. Such a ‘degree’ simply falls short. In some cases, businesses posing as legitimate correspondence schools offer even less – they sell certificates to anyone who pays the fees. To obtain these ‘degrees’, a candidate need not attend any classes, read any books or pass any examinations. Knowing the qualifications of someone who provides nutrition information can help you determine whether that person’s advice might be harmful or helpful. Don’t be afraid to ask for credentials. The ‘How to’ box below lists credible sources of nutrition information.
FIND CREDIBLE SOURCES OF NUTRITION INFORMATION
Government agencies, volunteer associations, consumer groups and professional organisations provide consumers with reliable health and nutrition information. Credible sources of nutrition information include: ›› International Food Information Council ›› nutrition and food science departments at Foundation universities http://www.ific.org ›› government health agencies such as: ›› Australian Government Department of ›› professional health organisations such as: ›› Dietitians Association of Australia Health and Ageing http://www.daa.asn.au http://www.health.gov.au ›› New Zealand Dietetic Association ›› National Health and Medical Research http://www.dietitians.org.nz Council ›› Australian Medical Association http://www.nhmrc.gov.au http://www.ama.com.au ›› New Zealand Ministry of Health ›› Journals such as: http://www.moh.govt.nz ›› American Journal of Clinical Nutrition ›› Therapeutic Goods Administration http://www.ajcn.org http://www.tga.gov.au ›› British Medical Journal ›› non-government health agencies such as: http://www.bmj.com ›› Cancer Council ›› Journal of Human Nutrition and http://www.cancercouncil.com.au Dietetics ›› Cancer Society of New Zealand http://www3.interscience.wiley.com/ http://www.cancernz.org.nz journal/117979034/home ›› Diabetes Australia ›› New England Journal of Medicine http://www.diabetesaustralia.com. au http://www.nejm.org ›› Heart Foundation ›› Nutrition & Dietetics http://www.heartfoundation.org.au http://www3.interscience.wiley.com/ ›› National Heart Foundation of New journal/118523059/home Zealand › › Nutrition Reviews http://www.nhf.org.nz http://www.ilsi.org /Pages/Nutrition ›› reputable consumer groups such as: Reviews.aspx. ›› Choice http://www.choice.com.au ›› Consumer Affairs New Zealand http://www.consumeraffairs.govt.nz
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Understanding nutrition
Red flags of nutrition quackery Figure H1.2 features eight red flags consumers can use to identify nutrition misinformation. Sales of unproven and dangerous products have always been a concern, but the Internet now provides merchants with an easy and inexpensive way to reach millions of customers around the world. Because of the difficulty in regulating the Internet, fraudulent and illegal sales of medical products have hit a bonanza. As is the case with the air, no-one owns the Internet; similarly, no-one has control over pollution. Countries have different laws regarding sales of
drugs, dietary supplements and other health products, but applying these laws to the Internet marketplace is almost impossible. Even if illegal activities could be defined and identified, finding the person responsible for a particular website is not always possible. Websites can open and close in a blink of a cursor. Now more than ever, consumers must heed the caution, ‘Buyer beware’. In summary, when you hear nutrition news, consider its source. Ask yourself these two questions: Is the person providing the information qualified to speak on nutrition? Is the information based on valid scientific research? If not, find a better source. After all, your health depends on it.
FIGURE H1.2 Red flags of nutrition quackery
Satisfaction guaranteed
One product does it all
Time tested or newfound treatment
Marketers may make generous promises, but consumers won’t be able to collect on them.
No one product can possibly treat such a diverse array of conditions.
Such findings would be widely publicised and accepted by health professionals.
Paranoid accusations And this product’s company doesn’t want money? At least the drug company has scientific research proving the safety and effectiveness of its products.
Quick and easy fixes Even proven treatments take time to be effective.
Personal testimonials Hearsay is the weakest form of evidence.
Natural Natural is not necessarily better or safer; any product that is strong enough to be effective is strong enough to cause side effects.
Meaningless medical jargon Phony terms hide the lack of scientific proof.
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Chapter 1: An overview of nutrition
37
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1 2
How would you judge the accuracy or validity of nutrition information? You have just received a forwarded email from a friend warning that the artificial sweetener aspartame is a TOXIN that causes muscle spasms, leg numbness, stomach cramps, vertigo, dizziness, headaches, tinnitus, joint pain, depression, anxiety, slurred speech, blurred vision, and memory loss. It goes on
to say that this DEADLY POISON causes blindness, multiple sclerosis, brain tumours, and cancer! The message alleges that aspartame remains on the market because of a conspiracy between FSANZ and the manufacturer to keep these dangers hidden from the public. How can you determine whether these claims are legitimate warnings or an irresponsible hoax?
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand at http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Find an accredited practising dietitian in your area by consulting the Dietitians Association of Australia; also find out which nutrition and dietetics courses are accredited by the association: http://www.daa.asn.au • Learn about the Registered Nutritionist program at the Nutrition Society of Australia: http://www.nsa. asn.au
• Read about the professional registration of nutritionists in New Zealand: http://www. nutritionsociety.ac.nz/registration • For foods commonly eaten in New Zealand, you can analyse their nutrient content from the database maintained by Plant and Food New Zealand: http://www.foodcomposition.co.nz • Learn more about quackery from Stephen Barrett’s Quackwatch: http://www.quackwatch.org • Visit the National Council against Health Fraud: http://www.ncahf.org • Check out health-related hoaxes and urban legends: http://www.urbanlegends.about.com • Find reliable research articles: http://www.pubmed.gov
REFERENCES CHAPTER 1
2
3
4
5 6 7
8
B. Garcia-Bailo and co-authors, Genetic variation in taste and its influence on food selection, Omics: A Journal of Integrative Biology, 13 (2009): 69–80. C. Smith and co-authors, Secular changes in intakes of foods among New Zealand adults from 1997 to 2008/09, Public Health Nutrition (2015): doi: 10.1017/S1368980015000890. L. E. Thornton, D. A. Crawford and K. B. Ball, Who is eating where? Findings from the SocioEconomic Status and Activity in Women (SESAW) study, Public Health Nutrition 14 (2011): 523–31. S. L. Johnson, Developmental and environmental influences on young children’s vegetable preferences and consumption, Advances in Nutrition 7 (2016): 220S–213S. I. Ioakimidis and co-authors,. How eating affects mood, Physiology & Behaviour 103 (2011): 290–4. C. M. Weaver and coauthors, Processed foods: Contributions to nutrition, American Journal of Clinical Nutrition 99 (2014): 1525–42. E. M. Steele and coauthors, Ultra-processed foods and added sugars in the US diet: Evidence from a nationally representative cross-sectional study, BMJ Open 6 (2016): e009892. F.M. Zuraikat and co-authors. Comparing the portion size effect in women with and without extended training in portion control: A
follow-up to the Portion-Control Strategies Trial. Appetite 123 (2018): 334–42. 9 M. B. Katan and co-authors, Which are the greatest recent discoveries and the greatest future challenges in nutrition? European Journal of Clinical Nutrition 63 (2009): 2–10. 10 Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). 11 J. Hesketh, Pesonalised nutrition: how far has nutrigenomics progressed?, European Journal of Clinical Nutrition 67 (2013): 430–5. 12 Department of Community Services and Health, National dietary survey of adults, 1983. No. 2. Nutrient intakes, Canberra: AGPS (1987); Department of Community Services and Health, National dietary survey of schoolchildren (10–15 years): 1985. No. 2. Nutrient intakes, Canberra: AGPS (1989); Australian Bureau of Statistics, National Nutrition Survey: Nutrient intakes and physical measurements, Australia, 1995, ABS Catalogue Number 4805.0, Canberra: ABS
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13
14
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(1998). Australian Bureau of Statistics, National health survey: first results, 2017–2018, ABS Catalogue Number 4364.0.55.001, Canberra: ABS (2018). M. L. Booth and co-authors, Methods of the NSW Schools Physical Activity and Nutrition Survey (SPANS), Journal of Science and Medicine in Sport 8 (2005): 284–93; C. K. Booth and R. A. Coad, The 1998 army recruit health and diet survey, Australian Military Medicine 11 (2002): 63–70; R. A. Abbott and co-authors, Healthy kids Queensland survey 2006 – summary report, Brisbane: Queensland Health (2006). New Zealand Ministry of Health, Nutrition Survey, available at http:// www.health.govt.nz/nz-health-statistics/national-collections-andsurveys/surveys/current-recent-surveys/nutrition-survey R. S. Magnusson, Rethinking global health challenges: Towards a ‘global compact’ for reducing the burden of chronic disease,
16
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Public Health 123 (2009): 265–74; B. M. Popkin, Global nutrition dynamics: the world is shifting rapidly toward a diet linked with noncommunicable diseases, American Journal of Clinical Nutrition 84 (2006): 289–98. Australian Institute of Health and Welfare, Leading Causes of Death (2018). https://www.aihw.gov.au/reports/life-expectancy-death/ deaths-in-australia/contents/leading-causes-of-death Australian Institute of Health and Welfare, Australian Burden of Disease Study: Impact and causes of illness and death in Australia 2011 (2016). A. Fardet and Y. Boirie, Associations between food and beverage groups and major diet-related chronic diseases: an exhaustive review of pooled/meta-analyses and systematic reviews, Nutrition Reviews 72 (2014): 741–62.
HIGHLIGHT 1
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Pew Research Center, The social life of health information, http:// www.pewresearch.org/fact-tank/2014/01/15/the-social-life-ofhealth-information Practice paper of the Academy of Nutrition and Dietetics abstract: Communicating accurate food and nutrition information, Journal of the Academy of Nutrition and Dietetics 112 (2012): 759. S. Rowe and N. Alexander, Conflicted science: Can nutrition communicators be biased too? Nutrition Today 50 (2015): 8–11.
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C. Korownyk and coauthors, Televised medical talk shows – What they recommend and the evidence to support their recommendations: A prospective observational study, British Medical Journal 349 (2014): doi 10.1136/bmj.g7346. M. Adamski and co-authors, Are doctors nutritionists? What is the role of doctors in providing nutrition advice?, Nutrition Bulletin 43 (2018): 147–52. Nutritionist imposters and how to spot them, Nutrition and the M.D. 30 (2004): 4–6.
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CHAPTER
2
PLANNING A HEALTHY DIET Nutrition in your life
You make food choices – deciding what to eat and how much to eat – more than 1000 times every year. We eat so frequently that it’s easy to choose a meal or snack without giving any thought to its nutrient contributions or health consequences. Even when we want to make healthy choices, we may not know which foods to select or how much to consume. With a few tools and tips, you can learn to plan a healthy diet. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F The concept of nutrient density means eating more calories to get
more nutrients.
T F The Australian Guide to Healthy Eating prescribes a set diet. T F Food companies can put anything they like on their food labels.
LEARNING OBJECTIVES 2.1 Explain how each of the diet-planning principles can be used to plan a healthy diet. 2.2 Use the Australian Guide to Healthy Eating to put a diet plan into action.
2.3 Compare the information on food labels to make selections that meet specific dietary and health goals.
Coconut meat is high in fibre and potassium
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Understanding nutrition
Chapter 1 explained that the body’s many activities are supported by the nutrients delivered by the foods people eat. Food choices made over years influence the body’s health, and consistently poor choices increase the risks of developing chronic diseases. This chapter shows how a person can select from the tens of thousands of available foods to create a diet that supports health. Fortunately most foods provide several nutrients, so one trick for wise diet planning is to select a combination of foods that deliver a full array of nutrients. This chapter begins by introducing the diet-planning principles and dietary guidelines that assist in selecting foods that will deliver nutrients with the right amount of energy (kilojoules) for the individual.
2.1 Principles and guidelines Diet-planning principles: • Adequacy • Balance • Energy (kJ) Control • Nutrient Density • Moderation • Variety
How well you nourish yourself does not depend on the selection of any one food. Instead, it depends on the selection of many different foods at numerous meals over days, months and years. Diet-planning principles and dietary guidelines are key concepts to keep in mind whenever you are selecting foods – whether shopping at the supermarket, choosing from a restaurant menu or preparing a home-cooked meal.
Diet-planning principles Qualified nutrition professionals use a variety of guidelines to plan diets for people. Whatever guideline or combination of guidelines they use, they keep in mind six basic diet-planning principles listed in the margin.
Adequacy
Shutterstock.com/nadianb
Adequacy means that the diet provides sufficient energy and enough
To ensure an adequate and balanced diet, eat a variety of foods daily, choosing different foods from each food group.
of all the nutrients to meet the needs of healthy people. Take the essential nutrient iron, for example. Because the body loses some iron each day, people have to replace it by eating foods that contain iron. A person whose diet fails to provide enough iron-rich foods may develop the symptoms of iron-deficiency anaemia: the person may feel weak, tired and listless, have frequent headaches and find that even the smallest amount of muscular work brings fatigue. To prevent these deficiency symptoms, a person must include foods that supply adequate iron. The same is true for all the other essential nutrients introduced in Chapter 1.
Balance
Balance in the diet helps to ensure adequacy.
The art of balancing the diet involves consuming enough – but not too much – of each type of food. The essential minerals calcium and iron, taken together, illustrate the importance of dietary balance. Meats, fish and poultry are rich in iron but poor in calcium. Conversely, milk and milk products are rich in calcium but poor in iron. Use some meat or meat alternatives for iron; use some milk and milk products for calcium; and save some space for other foods, too, because a diet consisting of milk and meat alone would not be adequate. For the other nutrients, people need whole grains, vegetables and fruits.
Energy (kilojoule) control Designing an adequate diet without overeating requires careful planning. Once again, balance plays a key role. The amount of energy coming into the body from foods should
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Chapter 2: Planning a healthy diet
balance with the amount of energy being used by the body to sustain its metabolic and physical activities. Upsetting this balance leads to gains or losses in body weight. The discussions of energy balance and weight control in Chapters 8 and 9 examine this issue in more detail, but the key to kilojoule control is to select foods of high nutrient density.
Nutrient density To eat well without overeating, select foods that provide the most nutrients for the least food energy (kilojoules). Consider foods containing calcium, for example. You can get about 300 milligrams of calcium from either 40 grams of cheddar cheese or 1 cup of low-fat milk, but the cheese delivers about twice as much food energy (kilojoules) as the milk. The lowfat milk, then, is twice as calcium-dense as the cheddar cheese; it offers the same amount of calcium for half the kilojoules. Both foods are excellent choices for adequacy’s sake alone, but to achieve adequacy while controlling kilojoules, the low-fat milk is the better choice. (Alternatively, a person could select a low-fat cheddar cheese.) The many bar graphs that appear in Chapters 10–13 highlight the most nutrient-dense choices. The following ‘How to’ box describes how to compare foods based on nutrient density.
HOW TO:
Nutrient density promotes adequacy and kilojoule control.
COMPARE FOODS BASED ON NUTRIENT DENSITY
One way to evaluate foods is simply to notice their nutrient contribution per serving: 1 cup of milk provides about 300 milligrams of calcium, and ½ cup of cooked spinach provides about 120 milligrams. Thus, a serving of milk offers 2½ times as much calcium as a serving of cooked spinach. To obtain 300 milligrams of calcium, a person could choose either 1 cup of milk or 1¼ cups of cooked spinach. Another valuable way to evaluate foods is to consider their nutrient density – their nutrient contribution per kilojoule. Low-fat milk delivers about 480 kilojoules with its 300 milligrams of calcium. To calculate the nutrient density, divide milligrams by kilojoules:
300 mg calcium = 0.6 mg per kJ 480 kJ Do the same for the cooked spinach, which provides 85 kilojoules with the 120 milligrams of calcium:
120 mg calcium = 1.4 mg per kJ 85 kJ The more milligrams per kilojoule, the greater the nutrient density. Cooked spinach is more calcium-dense than milk. It provides more calcium per kilojoule than milk, but milk offers more calcium per serving. Both approaches offer valuable information, especially when combined with a realistic appraisal. What matters most is which are you more likely to consume – 1¼ cups of cooked spinach or 1 cup of milk? You can get 300 milligrams of calcium from either, but the spinach will save you about 400 kilojoules (the savings would be even greater if you usually use whole milk). Keep in mind, too, that calcium is only one of the many nutrients that foods provide. Similar calculations for protein, for example, would show that low-fat milk provides more protein both per kilojoule and per serving than cooked spinach – that is, milk is more protein-dense. Combining variety with nutrient density helps to ensure the adequacy of all nutrients.
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Understanding nutrition
Just like a person who has to pay for rent, food and clothes on a limited budget, we have to obtain iron, calcium and all the other essential nutrients on a limited energy allowance. Success depends on getting many nutrients for each kilojoule ‘dollar’. For example, a can of soft drink and a handful of grapes may both provide about the same number of kilojoules, but the grapes deliver many more nutrients. A person who makes nutrient-dense choices, such as fruit instead of soft drink, can meet daily nutrient needs on a lower energy budget. Such choices support good health. Foods that are notably low in nutrient density – such as potato chips, lollies and soft drinks – are sometimes called empty-kilojoule foods. The kilojoules these foods provide are called ‘empty’ because they deliver energy (from sugar, fat or both) with little or no protein, vitamins or minerals.
Moderation Moderation contributes to adequacy, balance and energy control.
PUTTING COMMON SENSE TO THE TEST
The concept of nutrient density means eating more calories to get more nutrients. FALSE
Foods rich in fat and sugar provide enjoyment and energy but relatively few nutrients. In addition, they promote weight gain when eaten in excess. A person practising moderation eats such foods occasionally and regularly selects foods low in saturated fats and added sugars, a practice that automatically improves nutrient density. Returning to the example of cheddar cheese versus low-fat milk, the low-fat milk not only offers the same amount of calcium for less energy, but also contains far less fat than the cheese.
Variety
A diet may have all of the virtues just described and still lack variety, if a person eats the same foods day after day. People should select foods from each of the food groups daily and vary their choices within each food group from day to day, for several reasons. First, different foods within the same group contain a different array of nutrients. Among the fruits, for example, strawberries are especially rich in vitamin C while apricots are rich in vitamin A. Variety improves nutrient adequacy.1 Second, no food is guaranteed to be entirely free of substances that, in excess, could be harmful. The strawberries might contain trace amounts of one contaminant, the apricots another. By alternating fruit choices, a person will ingest very little of either contaminant. (Contamination of foods is discussed in Chapter 19.) Third, as the adage goes, variety is the spice of life. A person who eats beans frequently can enjoy pinto beans in Mexican burritos today, chickpeas in Greek salad tomorrow and baked beans on toast on the weekend. Eating nutritious meals need never be boring.
The Australian Dietary Guidelines What should a person eat to stay healthy? The answers can be found in the National Health and Medical Research Council’s Australian Dietary Guidelines.2 These guidelines use sciencebased evidence to provide information about healthy food choices. The use of the guidelines will promote health and minimise the risk of diet-related diseases within the Australian population. Table 2.1 presents the Dietary Guidelines, which, when used in conjunction with the Australian Guide to Healthy Eating (discussed later in this chapter), point the way towards better health. Table 2.2 presents New Zealand’s eating and activity guidelines for New Zealand adults. Some people might wonder why dietary guidelines include recommendations for physical activity. The simple answer is that most people who maintain a healthy body weight do more than eat right. They also exercise, engaging in moderately intense physical activity daily. As you will see repeatedly throughout this text, food and physical activity choices are integral partners in supporting good health.
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Chapter 2: Planning a healthy diet
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TABLE 2.1 The Australian Dietary Guidelines GUIDELINE 1 TO ACHIEVE AND MAINTAIN A HEALTHY WEIGHT, YOU SHOULD BE PHYSICALLY ACTIVE AND CHOOSE AMOUNTS OF NUTRITIOUS FOOD AND DRINKS TO MEET YOUR ENERGY NEEDS. • Children and adolescents should eat sufficient nutritious foods to grow and develop normally. They should be physically active every day and their growth should be checked regularly. • Older people should eat nutritious foods and keep physically active to help maintain muscle strength and a healthy weight. GUIDELINE 2 ENJOY A WIDE VARIETY OF NUTRITIOUS FOODS FROM THESE FIVE GROUPS EVERY DAY. • Plenty of vegetables, including different types and colours, and legumes/beans • Fruit • Grain (cereal) foods, mostly wholegrain and/or high cereal fibre varieties, such as breads, cereals, rice, pasta, noodles, polenta, couscous, oats, quinoa and barley • Lean meats and poultry, fish, eggs, tofu, nuts and seeds, and legumes/ beans • Milk, yoghurt, cheese and/or their alternatives, mostly reduced fat (reduced fat milks are not suitable for children under the age of 2 years) • And drink plenty of water. GUIDELINE 3 LIMIT INTAKE OF FOODS CONTAINING SATURATED FAT, ADDED SALT, ADDED SUGARS AND ALCOHOL. a Limit intake of foods high in saturated fat, such as many biscuits, cakes, pastries, pies, processed meats, commercial burgers, pizza, fried foods, potato chips, crisps and other savoury snacks. - Replace high fat foods which contain predominantly saturated fats, such as butter, cream, cooking margarine, coconut and palm oil with foods which contain predominantly polyunsaturated and mono-unsaturated fats such as oils, spreads, nut butters/pastes and avocado. - Low fat diets are not suitable for children under the age of 2 years. b Limit intake of foods and drinks containing added salt. - Read labels to choose lower sodium options among similar foods. - Do not add salt to foods in cooking or at the table. c Limit intake of foods and drinks containing added sugars, such as confectionery, sugar-sweetened soft drinks and cordials, fruit drinks, vitamin waters, energy and sports drinks. d If you choose to drink alcohol, limit intake. For women who are pregnant, planning a pregnancy or breastfeeding, not drinking alcohol is the safest option. GUIDELINE 4 ENCOURAGE, SUPPORT AND PROMOTE BREASTFEEDING. GUIDELINE 5 CARE FOR YOUR FOOD; PREPARE AND STORE IT SAFELY. © National Health and Medical Research Council. Eat for Health: Australian Dietary Guidelines, (2013): 5. © Commonwealth of Australia 2016 reproduced by permission. CC BY 4.0 International Licence. (https://www.eatforhealth.gov.au/copyright-information).
TABLE 2.2 Eating and Activity Guidelines for New Zealand Adults EATING STATEMENTS 1 Enjoy a variety of nutritious foods every day including: - plenty of vegetables and fruit - grain foods, mostly whole grain and those naturally high in fibre - some milk and milk products , mostly low and reduced fat - some legumes, nuts, seeds, fish and other seafood, eggs, poultry (e.g. chicken) and/or red meat with the fat removed. 2 Choose and/or prepare foods and drink: - with unsaturated fats instead of saturated fats - that are low in salt (sodium); if using salt, choose iodised salt - with little or no added sugar - that are mostly ‘whole’ and less processed. 3 Make plain water your first choice over other drinks.
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TABLE 2.2
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Understanding nutrition
4 If you drink alcohol, keep your intake low. Stop drinking alcohol if you could be pregnant, are pregnant or are trying to get pregnant. 5 Buy or gather, prepare, cook and store food in ways that keep it safe to eat. ACTIVITY STATEMENTS 1 Sit less, move more! Break up long periods of sitting 2 Do at least 2½ hours of moderate or 1¼ hours of vigorous physical activity spread throughout the week 3 For extra health benefits, aim for 5 hours of moderate or 2½ hours of vigorous physical activity spread throughout the week 4 Do muscle strengthening activities on at least 2 days each week 5 Doing some physical activity is better than doing none BODY WEIGHT STATEMENT Making good choices about what you eat and drink and being physically active are also important to achieve and maintain a healthy body weight. Ministry of Health. Eating and Activity Guidelines for New Zealand Adults, Wellington: Ministry of Health (2015). CC BY 4.0 International License. (https://www.health.govt.nz/about-site/copyright)
REVIEW IT
A well-planned diet delivers adequate nutrients, a balanced array of nutrients and an appropriate amount of energy. It is based on nutrient-dense foods, moderate in substances that can be detrimental to health, and varied in its selections. The Australian Dietary Guidelines and the Eating and Activity Guidelines for New Zealand Adults apply these principles, offering practical advice on how to eat for good health.
2.2 Diet-planning guides
To plan a diet that achieves all of the dietary ideals just outlined, a person needs tools as well as knowledge. Among the most widely used tools for diet planning are food group plans that build a diet from clusters of foods that are similar in nutrient content. Thus, each group represents a set of nutrients that differ somewhat from the nutrients supplied by the other groups. Selecting foods from each of the groups eases the task of creating an adequate and balanced diet.
The Australian Guide to Healthy Eating The five food groups are: • breads, cereals, rice, pasta, noodles • vegetables and legumes • fruit • milk, yoghurt and cheese • meat, fish, poultry, eggs, nuts, legumes. (Note that legumes are in two groups.)
The 2013 Australian Dietary Guidelines (updated in 2015) encourage consumers to adopt a balanced eating plan. One such plan has been developed by the Department of Health and Ageing: The Australian Guide to Healthy Eating. Figure 2.1 combines some recommendations from the Australian Guide to Healthy Eating with those of the Australian Dietary Guidelines. It assigns foods to five major groups and recommends daily amounts of foods from each group to meet nutrient needs. In addition to presenting the food groups, the figure lists the most notable nutrients of each group, the serving equivalents and the foods within each group sorted by nutrient density. Chapter 16 provides a food guide for young children.
Recommended amounts All food groups offer valuable nutrients, and people should make selections from each group daily. Table 2.3 and Table 2.4 indicate the amounts of foods from each group needed daily to create a healthful diet for all age groups.
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Chapter 2: Planning a healthy diet
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FIGURE 2.1 Australian Dietary Guidelines: eat a wide variety of nutritious foods from these five groups every day
Shutterstock.com/Romariolen
FRUITS These foods contribute folate, vitamin A, vitamin C, potassium and fibre. • 1 medium piece (150 g) of fruit (apple, banana, orange, pear) • 2 small pieces (150 g) of fruit (apricots, kiwifruit, plums) • 1 cup (150 g) diced pieces or canned fruit • 1½ tablespoons sultanas, 4 dried apricot halves
Shutterstock.com/Karissaa
VEGETABLES AND LEGUMES/ BEANS These foods contribute folate, vitamin A, vitamin C, vitamin K, vitamin E, magnesium, potassium and fibre. • ½ cup (75 g) cooked vegetables • ½ cup (75 g) cooked dried beans, peas or lentils • 1 cup salad vegetables • 1 small potato These amounts supply about 75–250 kJ each. Examples: Dark green vegetables: Broccoli and leafy greens such as spinach, bok choy, lettuce, kale and silverbeet
iStockphoto/ranplett
GRAINS (CEREAL) FOODS These foods contribute folate, niacin, riboflavin, thiamin, iron, magnesium, selenium and fibre. • 1 slice (40 g) bread, ½ medium bread roll • ½ cup (90 g) cooked rice, pasta, noodles • ½ cup (115 g) cooked porridge, ²/³ cup (30 g) cereal flakes or readyto-eat cereal
Shutterstock/Hurst Photo
LEAN MEAT AND POULTRY, FISH, EGGS, NUTS AND SEEDS AND LEGUMES/BEANS Meat, poultry, fish and eggs contribute protein, niacin, thiamin, vitamin B6, vitamin B12, iron, magnesium, potassium and zinc; legumes and nuts are notable for their protein, folate, thiamin, vitamin E, iron, magnesium, potassium, zinc and fibre. Care needs to be taken to ensure an adequate intake of iron, zinc and vitamin B12 with vegetarian and vegan diets. • 65 g cooked meat: ½ cup of lean mince, 2 small chops, 2 slices of roast meat • 80 g of cooked poultry
• ½ cup (125 mL) fruit juice These amounts supply about 300 kJ each. Examples: Apples, apricots, avocados, bananas, blueberries, rockmelon, cherries, grapefruit, grapes, guava, kiwifruit, mango, oranges, papaya, peaches, pears, pineapples, plums, raspberries, strawberries, watermelon, dried fruit (dates, figs, raisins), unsweetened juices Orange and deep yellow vegetables: Carrots, pumpkin, sweet potatoes and squash Legumes: Black beans, black-eyed peas, chickpeas, kidney beans, lentils, navy beans, pinto beans, soybeans and soy products such as tofu, and split peas Starchy vegetables: Potatoes, corn and lima beans Other vegetables: Artichokes, asparagus, bean sprouts, brussels sprouts, cabbages, cauliflower, celery, cucumbers, eggplant, green beans, mushrooms, okra, onions, peppers, snow peas, tomatoes and zucchini
• ¼ cup flour • 1 crumpet (60 g) or 1 small English muffin (35 g) These amounts supply about 400 kJ each. Examples: Whole grains (barley, brown rice, buckwheat, bulgur, millet, oats, rye, wheat) and wholegrain breads, cereals, crackers and pastas
• 1 cup (170 g) cooked (dried) beans, lentils, chickpeas, split peas and canned beans • 100 g cooked fish fillet • 2 large eggs (120 g) • 30 g nuts or nut/seed paste These amounts supply about 600–850 kJ each. Examples: Poultry (no skin), fish, shellfish, legumes, eggs, lean meat (fat-trimmed beef, game, ham, lamb, pork); lowfat tofu, tempeh, peanut butter, nuts (almonds, peanuts, pistachios, walnuts) or seeds (flaxseeds, pumpkin seeds, sunflower seeds)
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Understanding nutrition
Shutterstock.com/Alexander Prokopenko
MILK, YOGHURT, CHEESE AND/ OR THEIR ALTERNATIVES These foods contribute protein, riboflavin, vitamin B12, calcium, magnesium, potassium and, when fortified, vitamin D. • 1 cup (250 mL) fresh, long-life or reconstituted dried milk • 1 cup (250 mL) soy milk • ½ cup (125 mL) evaporated milk • 2 slices (40 g) cheese
FATS AND OILS – USE SMALL AMOUNTS
Shutterstock.com/JPC-PROD
Limit intake of foods and drinks containing saturated and trans fats. These foods contribute vitamin E and essential fatty acids (see Chapter 5), along with abundant kilojoules. Choose polyunsaturated and monounsaturated margarines and oils.
‘EXTRA’ FOODS AND BEVERAGES
Cengage Learning/Ronald Chung
Limit intake of foods and drinks containing added salt, added sugars and alcohol. Extra foods should only be chosen sometimes and in small amounts. Most people can eat small amounts of extra foods as part of a healthy diet. A healthier alternative is to eat more food from the five food groups most of the time. Examples of extra foods (providing about 600 kJ each) include: • 1 (40 g) doughnut • 4 (35 g) plain sweet biscuits • 1 slice (40 g) cake
• 1 small carton (200 g) yoghurt • 1 cup (250 mL) custard These amounts supply about 375–730 kJ each (custard, 1100 kJ). Examples: Fat-free milk and fat-free milk products such as buttermilk, cheeses, cottage cheese, yoghurt; fat-free fortified soy beverage, low-fat milk and low-fat milk products such as cheeses, cottage cheese, yoghurt and custard Examples: Sunflower oil, safflower oil, corn oil, soybean oil, olive oil, peanut oil, canola oil and margarines derived from these products; unsaturated oils that occur naturally in foods such as avocados, fatty fish, nuts, olives, seeds (flaxseeds, sesame seeds) and shellfish
• 25 g (½ small bar) chocolate • 2 tablespoons (40 g) cream, mayonnaise • 1 tablespoon (20 g) butter, margarine, oil • 200 mL wine (2 standard drinks) • 60 mL spirits (2 standard drinks) • 600 mL light beer (approximately 1½ standard drinks) • 400 mL regular beer (approximately 1½ standard drinks) • 1 can (375 mL) soft drink • 1 small packet (30 g) potato crisps • ¹/³ (60 g) meat pie or pasty • 12 (60 g) hot chips • 1½ scoops (50 g scoop) ice-cream.
Adapted from National Health and Medical Research Council, Department of Health and Ageing, Australian Dietary Guidelines, Canberra: Commonwealth of Australia (2013). CC BY 4.0 International Licence (https://www.eatforhealth.gov.au/copyright-information)
Reminder: Phytochemicals are the non-nutrient compounds found in plant-derived foods that have biological activity in the body.
All vegetables provide an array of vitamins, fibre and the mineral potassium, but some vegetables are especially good sources of certain nutrients and beneficial phytochemicals. Dark green vegetables deliver the B group vitamin folate; orange vegetables provide vitamin A; legumes supply iron and protein; starchy vegetables contribute carbohydrate energy; and other vegetables fill in any gaps and add more of these same nutrients.
Notable nutrients
As shown in Figure 2.1, each food group contributes key nutrients. This feature provides flexibility in diet planning because a person can select any food from a food group and receive similar nutrients. For example, a person can choose milk, cheese or yoghurt and receive the same key nutrients.
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Chapter 2: Planning a healthy diet
47
TABLE 2.3 Recommended dietary patterns for men and women
Grain (cereal) foods, mostly wholegrain, such as breads, cereals, rice, pasta, noodles, polenta, couscous, oats, quinoa and barley
Lean meat and poultry, fish, eggs, nuts and seeds, and legumes/beans
Milk, yoghurt, cheese and/or alternatives (mostly reduced fat)
Approximate number of additional serves from the five food groups or discretionary choices
19–50
6
2
6
3
2½
0–3
51–70
5½
2
6
2½
2½
0–2½
70+
5
2
4½
2½
3½
0–2½
19–50
5
2
6
2½
2½
0–2½
51–70
5
2
4
2
4
0–2½
70+
5
2
3
2
4
0–2
Pregnant
(19–50)
5
2
8½
3½
2½
0–2½
Lactating
(19–50)
7½
2
9
2½
2½
0–2½
Age
Fruit
ADDITIONAL SERVES FOR TALLER OR MORE ACTIVE MEN AND WOMEN
Vegetables and legumes/ beans
RECOMMENDED AVERAGE DAILY NUMBER OF SERVES FROM EACH OF THE FIVE FOOD GROUPS*
Men
Women
*Includes an allowance for unsaturated spreads or oils, nuts or seeds (4 serves [28−40 g] per day for men less than 70 years of age; 2 serves [14−20 g] per day for women and older men) National Health and Medical Research Council, Eat for Health Australian Dietary Guidelines Summary, page 41. https://www.eatforhealth.gov.au/sites/default/ files/content/The%20Guidelines/n55a_australian_dietary_guidelines_summary_131014_1.pdf. © Commonwealth of Australia 2015, CC BY 3.0 Australia License.
Because legumes contribute the same key nutrients – notably, protein, iron and zinc – as meats, poultry and fish, they are included in the same food group. For this reason, legumes are useful as meat alternatives, and they are also excellent sources of fibre and the B group vitamin folate. To encourage frequent consumption, legumes are also included in the vegetable group. Thus, legumes count in either the vegetable group or the meat and legumes group. In general, people who regularly eat meat, poultry and fish count legumes as a vegetable, and vegetarians and others who seldom eat meat, poultry or fish count legumes in the meat and legumes group.
Nutrient density
The Australian Guide to Healthy Eating provides a foundation for a healthy diet by emphasising nutrient-dense options within each food group. By consistently selecting nutrient-dense foods, a person can obtain all the nutrients needed and still maintain an appropriate energy balance. In contrast, eating foods that are low in nutrient density makes it difficult to get enough nutrients without exceeding energy needs and gaining weight. For this reason, consumers should select low-fat foods from each group and foods without added fats or sugars – for example, low-fat milk instead of whole milk, chicken without the skin instead of with the skin, steamed or boiled potatoes instead of chips, and whole oranges instead of orange juice. Oil is a notable exception: even though oil is pure fat and therefore rich in kilojoules, a small amount of oil from sources such as nuts, fish or vegetable oils is necessary every day to provide nutrients lacking from other foods. Consequently, these high-fat foods are listed among the nutrient-dense foods (see Highlight 5 to learn why).
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Understanding nutrition
TABLE 2.4 Recommended dietary patterns for children, adolescents and toddlers
Lean meat and poultry, fish, eggs, nuts and seeds, and legumes/beans
Milk, yoghurt, cheese and/or alternatives (mostly reduced fat)
1–2
2–3
½
4
1
1–1½
–
Boys
2–3
2½
1
4
1
1½
0–1
4–8
4½
1½
4
1½
2
0–2½
9–11
5
2
5
2½
2½
0–3
12–13
5½
2
6
2½
3½
0–3
14–18
5½
2
7
2½
3½
0–5
2–3
2½
1
4
1
1½
0–1
4–8
4½
1½
4
1½
1½
0–1
9–11
5
2
4
2½
3
0–3
12–13
5
2
5
2½
3½
0–2½
14–18
5
2
7
2½
3½
0–2½
Pregnant
5
2
8
3½
3½
0–3
Lactating
5½
2
9
2½
4
0–3
Girls
Approximate number of additional serves from the five food groups or discretionary choices
Grain (cereal) foods, mostly wholegrain, such as breads, cereals, rice, pasta, noodles, polenta, couscous, oats, quinoa and barley
Toddlers
Age
Fruit
ADDITIONAL SERVES FOR MORE ACTIVE, TALLER OR OLDER CHILDREN AND ADOLESCENTS
Vegetables and legumes/ beans
RECOMMENDED AVERAGE DAILY NUMBER OF SERVES FROM EACH OF THE FIVE FOOD GROUPS*
*Includes an allowance for unsaturated spreads or oils, nuts or seeds (½ serve [4−5 g] per day for children 2−3 years of age, 1 serve [7−10 g] per day for children 3−12 years of age; 1½ serves [11−15 g] per day for children 12−13 years, and 2 serves [14−20 g] per day for adolescents 14−18 years of age and for pregnant and lactating girls) National Health and Medical Research Council. Eat for Health Australian Dietary Guidelines Summary, page 42. https://www.eatforhealth.gov.au/sites/default/files/content/The%20Guidelines/n55a_ australian_dietary_guidelines_summary_131014_1.pdf. © Commonwealth of Australia 2015, CC BY 3.0 Australia.
For quick and easy estimates, visualise each portion as being about the size of a common object: • 1 cup fruit or vegetables 5 a cricket ball • ¼ cup dried fruit 5 a golf ball • 100 g of meat 5 a deck of cards • 1 tsp peanut butter 5 a marshmallow • ½ cup ice-cream 5 a tennis ball.
Serving equivalents Recommended serving amounts for fruits, vegetables and milk are generally measured in cups and those for grains and meats in grams. Figure 2.1 provides equivalent measures among the foods in each group, specifying, for example, that a slice of bread or ½ cup of cooked rice is equivalent to approximately 300 kilojoules. A person using The Australian Guide to Healthy Eating can become more familiar with measured portions by determining the answers to questions such as these: What portion of a cup is a small handful of raisins? Is a ‘serving’ of mashed potatoes more or less than a half-cup? How many grams of breakfast cereal do you typically pour into the bowl? How many grams is the steak at your favourite restaurant? Figure 2.1 (pages 45–46) includes the serving sizes and equivalent amounts for foods within each group.
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Chapter 2: Planning a healthy diet
PUTTING COMMON SENSE TO THE TEST
The Australian Guide to Healthy Eating prescribes a set diet. Medical Research © Commonwealth of Australia, 2016. CC BY 4.0 International Licence.
FALSE The Australian Nutrition Foundation, Inc. (http://www.nutritionaustralia.org/)
Department of Health and Ageing, The Australian Guide to Healthy Eating, National Health and
FIGURE 2.2 The Australian Guide to Healthy Eating circle (plate) and the Nutrition Australia Healthy Eating Pyramid
49
Vegetarian food guide Vegetarian diets rely mainly on plant foods: grains, vegetables, legumes, fruits, seeds and nuts. Some vegetarian diets include eggs, milk products or both. People who do not eat meats or milk products can still use the Australian Guide to Healthy Eating to create an adequate diet.3 The food groups are similar, and the amounts for each serving remain the same. Highlight 2 defines vegetarian terms and provides details on planning healthy vegetarian diets.
The Australian Guide to Healthy Eating circle (plate) and the Nutrition Australia Healthy Eating Pyramid As can be seen in Figure 2.2, The Australian Guide to Healthy Eating uses a circle (often referred to as a plate) to illustrate how the recommendations within it can be implemented. Nutrition Australia explains how a healthy diet can be implemented using a pyramid. Each of these tools is a useful resource for people trying to plan healthy diets.
Putting the plan into action Familiarising yourself with each of the food groups is the first step in diet planning. Table 2.5 shows how to use The Australian Guide to Healthy Eating to plan an 8700-kilojoule diet. The amounts listed from each of the food groups are assigned to meals and snacks as an example only. Now, a person can begin to fill in the plan with real foods to create an eating pattern to sustain good health. For example, the breakfast calls for 30 grams of grain, ½ cup fruit and 1 cup milk. A person might select a bowl of cereal with banana slices and milk: • 1 cup cereal 5 30 grams grain • 1 small banana 5 ½ cup fruit • 1 cup fat-free milk 5 1 cup milk. The person can then continue to create a diet plan by establishing healthy eating patterns for lunch, dinner and other snacks. As you can see, we all make countless food-related decisions daily – whether we have a plan or not. Following a plan, such as the Australian Guide to Healthy Eating, that incorporates health recommendations and diet-planning principles helps a person make wise decisions.
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Understanding nutrition
TABLE 2.5 Example of a diet planned using the Australian Guide to Healthy Eating FOOD GROUP
AMOUNTS
BREAKFAST
SNACK
1 small piece
1 small piece
Fruits
2 serves
Vegetables and legumes
6 serves
Breads and cereals
6 serves
1−2 serves of breakfast cereal
Dairy foods
2½ serves
glass of milk
Meat and legumes
2–3 serves
Extra foods
up to 2½ serves
LUNCH
SNACK
DINNER AND DESSERT
1 medium piece
½ cup salad vegetables
1 cup salad vegetables
2 potatoes, ½ cup of legumes, 1 cup of cooked vegetables
1 serve of dry crackers
2 slices of bread
1 medium bread roll
1 slice of cheese
1 serve of yoghurt
Small tin of tuna
100 g of lean red meat
1 serve margarine
25 g chocolate bar
From guidelines to the shopping trolley Dietary recommendations emphasise nutrient-rich foods such as whole grains, fruits, vegetables, lean meats, fish, poultry and low-fat milk products. You can design such a diet for yourself, but how do you begin? Start with the foods you enjoy eating. Then try to make improvements, little by little. When shopping, think of the food groups and choose nutrientdense foods within each group. Be aware that many of the 50 000 food options available today are processed foods that have lost valuable nutrients and have had sugar, fat and salt added as they were transformed from farm-fresh foods to those found in the bags, boxes and cans that line supermarket shelves. Their value in the diet depends on the starting food and how it was prepared or processed. Sometimes these foods have been fortified to improve their nutrient contents.
Breads and cereals
Grain-enrichment nutrients include: • iron • thiamin • riboflavin • niacin • folate.
When shopping for bread and cereal products, you may find them described as refined, enriched or wholegrain. These terms refer to the milling process and the making of grain products, and they have different nutrition implications (see Figure 2.3). Refined foods may have lost many nutrients during processing, enriched products may have had some nutrients (generally vitamins and minerals) added back and wholegrain products may be rich in fibre and all the nutrients found in the original grain. Wholegrain products support good health and should comprise the majority of choices within this food group. Ready-to-eat breakfast cereals are the most commonly fortified foods on the market. A fortified food has had nutrients added during processing, but the added nutrients may not have been present in the original product. Caution should be used when selecting breakfast cereals made from refined grains and fortified with vitamins and minerals as, while these may appear a healthy choice because of the fortification, they may fail to provide the full spectrum of nutrients that a wholegrain food or a mixture of such foods might provide.
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Chapter 2: Planning a healthy diet
51
FIGURE 2.3 A wheat plant
The protective coating of bran around the kernel of grain is rich in nutrients and fiber. The endosperm contains starch and proteins. The germ is the seed that grows into a wheat plant, so it is especially rich in vitamins and minerals to support new life. The outer husk (or chaff) is the inedible part of a grain. Wholegrain products contain much of the germ and bran, as well as the endosperm; that is why they are so nutritious. Refined grain products contain only the endosperm. Even with nutrients added back, they are not as nutritious as wholegrain products.
The difference between white flour and white wheat is noteworthy. Typically, white flour refers to refined flour (as defined above). Most flour – whether refined, white, or whole wheat – is made from red wheat. Wholegrain products made from red wheat are typically brown and full-flavoured. To capture the health benefits of whole grains for consumers who prefer white bread, manufacturers use an albino variety of wheat called white wheat . Wholegrain products made from white wheat provide the nutrients and fibre of a whole grain with a light colour and natural sweetness. Read labels carefully – white bread is a wholegrain product only if it is made from whole white wheat.
Wholegrain breads generally provide more nutrition than other breads. However, due to legislation implemented through Food Standards Australia New Zealand (FSANZ), Australian flour millers are required to add the B group vitamin folic acid to all bread flours, except for flour to be used in breads listed as ‘organic’. The mandatory fortification of bread flour was implemented due to a significant public health need as folic acid is important in the healthy development of babies in early pregnancy to reduce the risk of neural tube defects. In New Zealand, a voluntary fortification standard exists.
Vegetables Choose vegetables often in the diet, either fresh, canned or frozen (taking care to avoid added salt, sugar and fat), especially dark green leafy and yellow-orange vegetables such as spinach, broccoli and sweet potatoes (see Figure 2.4). Cooked or raw, vegetables are good sources of vitamins, minerals and fibre. Frozen and canned vegetables without added salt are acceptable alternatives to fresh varieties. To control fat, energy and sodium intakes, limit butter and salt on vegetables.
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AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
© Thomas Harm & Tom Peterson/Quest Photographic, Inc.
Common types of flour are: refined flour: finely ground endosperm that is usually enriched with nutrients and bleached for whiteness; sometimes called white flour. wheat flour: any flour made from the endosperm of the wheat kernel. whole-wheat flour: any flour made from the entire wheat kernel.
Enjoy a wide variety of nutritious foods every day, including milk, plenty of fruits and vegetables of different types and colours and legumes/beans.
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Understanding nutrition
Shutterstock.com/gpointstudio
FIGURE 2.4 Go for 2 fruit and 5 veg
When shopping for bread, look for the descriptive words wholegrain or whole wheat and check the fibre content on the nutrition information panel of the label – the more fibre, the more likely the bread is to be a wholegrain product.
Choose often from the variety of legumes available. nutrient- and fibre-rich food choice.
They are an economical, low-fat,
Fruit
Combining legumes with foods from other food groups creates delicious meals.
Add rice to red beans for a hearty meal.
Enjoy a Greek salad topped with chickpeas for a little ethnic diversity.
iStockphoto/Raul Taborda
Shutterstock.com/Ffolas
Getty Images/Quentin Bacon
Choose fresh fruits often. Frozen, dried and canned fruits without added sugar are acceptable alternatives to fresh, but be cautious as these can be a concentrated form of energy and may contain less fibre. Fruits supply valuable vitamins, minerals, fibre and phytochemicals. They can add flavours, colours and textures to meals, and their natural sweetness makes them enjoyable as snacks or desserts. Fruit juices are healthy beverages but contain little dietary fibre compared with whole fruits. Whole fruits satisfy the appetite better than juices, thereby helping people to limit food energy intakes. For people who need extra food energy, however, juices are a good choice. Be aware that sweetened fruit ‘drinks’ contain mostly water, sugar and a little juice for flavour. Some may have been fortified with vitamin C or calcium but lack any other significant nutritional value.
1998 PhotoDisc, Inc.
Legumes comprise a variety of beans and peas including: • adzuki beans • black beans • black-eyed peas • chickpeas • fava beans • kidney beans • lentils • lima beans • navy beans • peanuts • pinto beans • soybeans • split peas.
http://www.gofor2and5.com.au/ © State of Western Australia 2016. Reproduced with permission.
A bit of meat and lots of spices turn kidney beans into chilli con carne.
Meat, fish and poultry AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Enjoy a wide variety of nutritious foods every day, including milk, yoghurt, cheese and/ or their alternatives, mostly reduced fat.
Meat, fish and poultry provide essential minerals, such as iron and zinc, and abundant B group vitamins as well as protein. To buy and prepare these foods without excess energy, fat and sodium takes a little knowledge and planning. When shopping, choose fish, poultry and lean cuts of pork or red meat. In general, 120 grams of raw meat is equal to about 100 grams of cooked meat. Some examples of 100-gram portions of meat include 1 medium lean pork chop, ½ chicken breast with skin removed or 1 steak about the size of a deck of cards. To keep fat intake moderate try to bake, roast, grill or braise meats (but do not fry them in fat); remove the skin from poultry
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after cooking; trim visible fat before cooking; and drain fat after cooking. Chapter 5 offers many additional strategies for moderating fat intake.
Be aware that not all soy milks have been fortified. Read labels carefully.
Milk You may find a variety of fortified foods in the dairy case. Examples are milk, to which vitamins A and D may have been added, and soy milk to which calcium, vitamin D and vitamin B12 may have been added. In addition, you may find functional foods (such as margarine with added plant sterols). As food technology advances, many such foods offer alternatives to traditional choices that may help people who want to reduce their fat and cholesterol intakes. Chapter 5 gives other examples. When shopping, choose low-fat milks , yoghurts and cheeses. Such selections help consumers meet their vitamin and mineral needs within their energy requirements.4 Milk products are important sources of calcium, but can provide too much sodium and fat if not selected with care.
REVIEW IT
Food group plans such as the Australian Guide to Healthy Eating help people select the types and amounts of foods to provide adequacy, balance and variety in the diet. They make it easier to plan a diet that includes a balance of grains, vegetables, fruits, meats and dairy products. In making any food choice, remember to view the food in the context of your total diet. The combination of many different foods provides the abundance of nutrients that is so essential to a healthy diet.
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Reminder: Functional foods contain physiologically active compounds that provide health benefits beyond basic nutrition. Milk descriptions: • fat-free milk may also be called non-fat, skim, zero-fat or no-fat. • low-fat milk contains approximately 1.5% fat (1.5 g/100 mL). • reduced-fat milk refers to milk containing approximately 2% fat (2 g/100 mL).
2.3 Food labels
Many consumers read food labels to help them make healthy choices. Food labels appear on virtually all packaged foods (see Figure 2.5). A few foods need not carry nutrition labels: fresh fruit, vegetables, nuts, lentils, beans, fresh meat and fish; those contributing few nutrients, such as plain coffee, tea and spices; those produced by small businesses; and those prepared and sold in the same establishment. Producers of some of these items, however, use labels voluntarily.
The ingredient list
Serving sizes Because labels present nutrient information per serving, they must identify the size of the serving. FSANZ has established that, along with serving size
Shutterstock.com/Monkey Business Images
All packaged foods must list all ingredients on the label in descending order of predominance by weight. The exception is water. Knowing that the first ingredient predominates by ingoing weight, consumers can glean much information. Compare these products, for example: • a beverage powder that contains ‘sugar, citric acid, natural flavours ...’ versus a juice that contains ‘water, tomato concentrate, concentrated juices of carrots, celery ...’ • a cereal that contains ‘puffed milled corn, sugar, corn syrup, molasses, salt ...’ versus one that contains ‘100 per cent rolled oats’ • a canned fruit that contains ‘sugar, apples, water’ versus one that contains simply ‘apples, water’. In each of these comparisons, consumers can see that the second product is the more nutrient dense.
Consumers read food labels to learn about the nutrient contents of a food or to compare foods.
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information, products must also list nutrition information for 100 grams (or 100 millilitres) of the food product. This facilitates the comparison of foods that are a different size or don’t fall within the same food group. Consumers can see at a glance which product has more or fewer kilojoules, grams of fat or calcium, for example (see Figure 2.5). Table 2.6 shows common household and metric measures.
TABLE 2.6 Household and metric measures • 1 teaspoon (tsp) 5 5 millilitres (mL) • 1 tablespoon (tbs) 5 20 mL • 1 cup (c) 5 250 mL
When examining the nutrition facts on a food label, consumers need to compare the serving size on the label with how much they actually eat, and adjust their calculations accordingly. For example, if the serving size is two breakfast wheat biscuits and you only eat one, then you need to cut the nutrient and kilojoule values in half; similarly, if you eat four, then you need to double the values. Notice, too, that small bags or individually wrapped items, such as chips or chocolate bars, may contain more than a single serving. The number of servings per package is listed in the nutrition information panel, generally just above the serving size. Be aware that serving sizes on food labels are not always the same as those in the Australian Guide to Healthy Eating. For example, a serving of rice on a food label may be 1 cup, whereas in the Australian Guide to Healthy Eating it is ½ cup. This discrepancy, coupled with each person’s own perception (often misperception) of standard serving sizes, sometimes creates confusion for consumers trying to follow recommendations.
Nutrition facts In addition to the serving size and the servings per container, FSANZ requires that the ingredients list on food packaging presents ingredient information as a percentage of the product (see Figure 2.5).
PUTTING COMMON SENSE TO THE TEST
Food companies can put anything they like on their food labels. FALSE
Nutrient claims Have you noticed phrases such as ‘contains fibre’ on a box of cereal or ‘reduced fat’ on a package of cheese? These and other nutrient claims may be used on labels as long as they meet FSANZ definitions, which include the conditions under which each term can be used. For example, a product claiming to be ‘low fat’ must contain no more than 1.5 grams of fat per 100 millilitres for drinks and other liquid foods and no more than 3 grams of fat per 100 grams for all other foods.
Health claims The FSANZ Food Standard (Standard 1.2.7) relating to nutrition, health claims and related claims provides consumers with more information for healthier food choices, and the food industry with greater incentives to develop healthier food products.5 Examples
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Chapter 2: Planning a healthy diet
© Food Standards Australia New Zealand. CC BY 3.0 (http://www.foodstandards.gov.au/pages/copyright.aspx).
FIGURE 2.5 Example of a food label
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of nutrition content terms you may find on food labels are shown in Table 2.7. Food businesses had three years to make changes to ensure the new standard was being met by January 2016.
TABLE 2.7 Examples of nutrition content terms you may find on food labels Low fat or low in fat: The food must not contain more than 3 g of fat per 100 g of solid food (or 1.5 g of fat per 100 mL of liquid food). Reduced fat or less fat: The food contains at least 25 per cent less fat than the same quantity of the reference food. Low cholesterol or low in cholesterol: The food must not contain more than 20 mg cholesterol per 100 g of solid food or 10 mg per 100 mL of liquid food and must meet the conditions for a nutrition content claim about low saturated fatty acids. Low sugar or low in sugar: The food must not contain more than 5 g of sugar per 100 g of solid food or 2.5 g of sugar per 100 mL of liquid food. Source of fibre or contains fibre: The food contains at least 2 g of dietary fibre per serving of food. Good source of fibre: The food must not contain less than 4 g of dietary fibre per serving of food. Reduced salt/sodium: The food must contain at least 25 per cent less sodium than the same quantity of reference food. Low in salt: Low in salt means the food contains less than 120 mg of sodium per 100 g or 100 mL. No artificial colourings or flavours: Negative claims are statements that claim the non-addition or absence of a substance in a food. Such claims, especially referring to food additives, are a quick and effective way of communicating to consumers. Negative claims are commonly made about no artificial colourings or flavourings, no flavour enhancers or preservatives, or no added sugar. © Food Standards Australia New Zealand. CC BY 3.0.
The health claims are categorised according to level of claim and must be substantiated by scientific evidence: • Nutrition content claims are statements regarding the amount of a nutrient, energy or a biologically active substance in the food. Manufacturers must have proof that the nutrient, substance or property that is the subject of the claim is present at levels referred to in the claim. • General level health claims can refer to the presence of a nutrient or substance in a food and to its effect on a health function. A general level health claim cannot refer to a serious disease or condition or to an indicator of a serious disease (for example, blood cholesterol). Manufacturers must use either the FSANZ Model List of pre-approved statements, provide suitable scientific texts or dietary guidelines to support the claim, or hold scientific evidence to substantiate such claims and produce this evidence, on request, for enforcement agencies. • High-level health claims are those claims that make reference to a serious disease or biomarker and will need to be pre-approved by FSANZ, with approved claims being listed in the standard. Examples of claims that may be used can be seen in Table 2.8.
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TABLE 2.8 Examples of the levels of health claims that may be made on food packaging DESCRIPTION OF CLAIM Nutrition content claims Nutrition content claims are claims about the content of certain nutrients or substances in a food. These claims will need to meet certain criteria set out in the Standard.
EXAMPLE
This food is high in calcium.
General level health claims General level health claims refer to a nutrient or substance in a food and its effect on a health function. They must not refer to a serious disease or to a biomarker of a serious disease. ... maintenance of good health
Helps keep you regular as part of a high fibre diet
... a component and its function in the body
Calcium is good for strong bones and teeth
... specific benefits for performance and wellbeing in relation to foods
Gives you energy
... how a diet, food or component can modify a function beyond its role in normal growth and development
Exercise and a diet high in calcium helps build stronger bones
... potential for a food or component to assist in reducing the risk of or helping to control a non-serious disease or condition
Yoghurt high in X and Y as part of a healthy diet may reduce your risk of stomach upsets
High level health claims High level health claims must be based on a food–health relationship pre-approved by FSANZ. All health claims are required to be supported by scientific evidence to the same degree of certainty, whether they are pre-approved by FSANZ or selfsubstantiated by food businesses. Food-health relationships derived from health claims approved in the European Union, Canada and the US have been considered for inclusion in the Standard. Claim refers to the potential for a food or component to assist in controlling a serious disease or condition by either reducing risk factors or improving health.
This food is high in calcium. Diets high in calcium may increase bone mineral density.
Claim refers to the potential for a food or component to assist in reducing the risk of a serious disease or condition.
This food is low in sodium. Diets low in sodium may reduce risk of elevated blood pressure. © Food Standards Australia New Zealand. CC BY 3.0.
REVIEW IT
Food labels provide consumers with information they need to select foods that will help them meet their nutrition and health goals. When labels contain relevant information presented in a standardised, easy-to-read format, consumers are well prepared to plan and create healthful diets.
This chapter provides the links to go from dietary guidelines to buying groceries, and offers helpful tips for selecting nutritious foods. For additional information on foods, including organic foods, irradiated foods, genetically modified foods and more, turn to Chapter 19.
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 The concept of nutrient density means eating more kilojoules to get more nutrients. FALSE
Sometimes we do eat more kilojoules to obtain more nutrients but the concept of nutrient density is where we obtain more nutrients (e.g. iron) but eat less kilojoules (e.g. 300 instead of 450).
2 The Australian Guide to Healthy Eating prescribes a set diet. FALSE
The guidelines recognise that not everybody has exactly the same needs and so dietary intake will vary from person to person.
3 Food companies can put anything they like on their food labels. FALSE
The Australian Guide to Healthy Eating provides a number of guidelines for each food group depending on life-stage.
Although many food companies try to make their products stand out from others, what is allowed on food labels is tightly regulated by FSANZ. This includes things such as health claims or benefits of the food product.
CRITICAL THINKING QUESTIONS 1
apply a critical eye to these guidelines. After researching this topic, what do you think?
The dietary guidelines of Australia and New Zealand sometimes come under fire for being too restrictive, too confusing or unobtainable. Nutrition scientists
NUTRITION PORTFOLIO Each chapter in this book ends with simple ‘Nutrition portfolio’ activities that invite you to review key messages and consider whether your personal choices are meeting the dietary goals introduced in the text. By keeping a journal of these ‘Nutrition portfolio’ assignments, you can examine how your knowledge and behaviours change as you progress in your study of nutrition. The secret to making healthy food choices is learning to incorporate the Australian Dietary Guidelines and the Australian Guide to Healthy Eating into your decisionmaking process. • Compare the foods you typically eat daily with the Australian Guide to Healthy Eating recommendations
•
•
•
for your energy needs (see Table 2.3 on p. 47), making note of which food groups are usually overor under-represented. Describe your choices within each food group from day to day and include realistic suggestions for enhancing the variety in your diet. Write yourself a letter describing the dietary changes you can make to improve your chances of enjoying good health. Try to implement the changes outlined in your letter and form good eating habits now.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1
The diet-planning principle that provides all the essential nutrients in sufficient amounts to support health is: a b c d
balance variety adequacy moderation
2
A person who eats a food that provides 250 milligrams of calcium and 500 kilojoules instead of a food that provides 200 milligrams of calcium and 650 kilojoules is using the principle of nutrient: a b c d
control density adequacy moderation
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Chapter 2: Planning a healthy diet
3
a b c d 4
3 3.5 4 4.5
Foods within a given food group of the Australian Guide to Healthy Eating are similar in their contents of: a b c d
6
Choose a diet restricted in fat and cholesterol. Eat plenty of vegetables, legumes and fruits. Balance the food you eat with physical activity. Eat an abundance of foods to ensure nutrient adequacy.
According to the Australian Guide to Healthy Eating, the number of serves of dairy foods recommended for boys aged 12–13 is: a b c d
5
c d
Which of the following is consistent with the Australian Dietary Guidelines?
energy proteins and fibre vitamins and minerals carbohydrates and fats
Which ingredient is exempt from being listed in descending order of predominance by weight on food labels? Why? a b
Vitamins Minerals
7
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Water Salt
‘Low in salt’ is an example of a: a b c d
health claim nutrition fact nutrient content claim nutrition advertising
Review questions 1 Name the diet-planning principles and briefly describe how each principle helps in diet planning. (Section 2.1) 2
What recommendation is modified in the Australian Dietary Guidelines for children under the age of two years? Why? (Section 2.1)
3
What are the differences and similarities between the Australian Guide to Healthy Eating plate and the Nutrition Australia Healthy Eating Pyramid? How might any differences be confusing to the general public? (Section 2.2)
4
Review the Australian Dietary Guidelines. What types of food selections would you make to achieve those recommendations? (Section 2.1)
5
What do you think is the most helpful information you can expect to find on a food label? When comparing nutrition information panels, how can this information help you choose between two products? (Section 2.3)
6
What is a nutrient claim? How does this differ from a health claim? (Section 2.3)
NUTRITION CALCULATIONS d
These problems will give you practice in doing simple nutrition-related calculations. Although the situations are hypothetical, the numbers are real, and calculating the answers (see the Answers section at the back of this book) provides a valuable nutrition lesson. Be sure to show your calculations for each problem. 1
e f g
Read a food label. Look at the label in Figure 2.5 (see p. 55) and answer the following questions: a b c
h
What is the size of a serving of the product? How many kilojoules are in a serving? How much fat is in a serving?
i
How many kilojoules does this amount of fat represent? What percentage of the kilojoules in this product comes from fat? What does this tell you? Does this product meet the criteria for a low-fat product (refer to Table 2.7 on page 56)? What is the predominant ingredient in the product? Have any nutrients been added to this product (is it fortified)?
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search for ‘food labels’ at the FSANZ website: http://www.foodstandards.gov.au
•
• •
Learn more about the Australian Guide to Healthy Eating: https://www.eatforhealth.gov. au/guidelines/ Find New Zealand information on nutrition guidelines and food labels at http://www.foodstandards.govt.nz Learn more about the Healthy Eating Pyramid: http://www.nutritionaustralia.org
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•
•
•
Understanding nutrition
Visit the Traditional Diet Pyramids for various ethnic groups at Oldways Preservation and Exchange Trust: http://www.oldwayspt.org Visit the United States Department of Agriculture website and view ‘My Plate’: http://www.cnpp.usda. gov/MyPlate and compare it to the Australian version Search ‘food labels’ at the International Food Information Council Foundation: https://www. foodinsight.org/
•
• •
Read about the Health Star Rating, which is now on many New Zealand and Australian packaged foods: http://healthstarrating.gov.au/internet/ healthstarrating/publishing.nsf/content/home Get healthy eating tips from the ‘Go for 2&5’ program: http://www.gofor2and5.com.au Learn more about the Australian Dietary Guidelines at: http://www.eatforhealth.gov.au
SEARCH ME! NUTRITION Keyword: food labels Interpreting food labelling can be a confusing task for most people trying to make sense of all the nutritional information. Read the article Australian consumers are
sceptical about but influenced by claims about fat on food labels. What food label claims do consumers find most and least useful?
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Chapter 2: Planning a healthy diet
HIGHLIGHT
VEGETARIAN DIETS
2
abundant complex carbohydrates and fibre, an assortment of vitamins and minerals, a mixture of phytochemicals and little fat. These diets reflect current dietary recommendations aimed at promoting health and reducing obesity. Each of these foods – whole grains, vegetables, legumes, nuts and fruits – independently reduces the risk for several chronic diseases.1 This highlight examines the health benefits and potential problems of vegetarian diets and shows how to plan a well-balanced vegetarian diet.
iStockphoto/cobraphotography
The waiter presents this evening’s specials: a fresh spinach salad topped with mandarin oranges, raisins and sunflower seeds, served with a bowl of pasta smothered in a mushroom and tomato sauce and topped with grated parmesan cheese. Then this one: a salad made of chopped parsley, shallots, celery and tomatoes mixed with couscous and dressed with olive oil and lemon juice, served with a spinach and feta cheese pie. Do these meals sound good to you? Or is something missing ... some lean chicken breast or a steak, perhaps? Would vegetarian fare be acceptable to you some of the time? Most of the time? Ever? Perhaps it is helpful to recognise that dietary choices fall along a continuum – from one end, where people eat no meat or foods of animal origin, to the other end, where they eat generous quantities daily. The place of meat in the diet has been the subject of much research and controversy, as this highlight will reveal. One of the reasons for this highlight, in fact, is to identify the range of meat intakes most compatible with health. The health benefits of a primarily vegetarian diet seem to have encouraged many people to eat more vegetarian meals. The popular press refers to these ‘parttime vegetarians’ who eat small amounts of meat from time to time as ‘flexitarians’ or ‘semi-vegetarians’. People who choose to exclude meat and other animalderived foods from their diets today do so for many of the same reasons the Greek philosopher Pythagoras cited in the sixth century BCE – physical health, ecological responsibility and philosophical concerns. They might also cite world hunger issues, economic reasons, ethical concerns or religious beliefs as motivating factors. Whatever their reasons – and even if they don’t have a particular reason – people who exclude meat are better prepared to plan well-balanced meals if they understand the nutrition and health implications of vegetarian diets. Vegetarians are generally categorised not by their motivations but by the foods they choose to exclude. Some people exclude red meat only, some also exclude chicken or fish, others also exclude eggs, and still others exclude milk and milk products as well. In fact, finding agreement on the definition of the term vegetarian is a challenge. However, the foods a person excludes are not nearly as important as the foods a person includes in the diet. Well-balanced vegetarian diets that include a variety of whole grains, vegetables, legumes, nuts and fruits offer
61
A vegetarian meal may contain vegetables, seeds and tofu.
Health benefits of vegetarian diets There has been a large amount of research on the health implications of vegetarian diets. Researchers must account for any lifestyle differences between vegetarian and nonvegetarian populations before they can determine which aspects of health correlate just with diet. Even then, correlations merely reveal what health factors go with the vegetarian diet, not what health effects may be caused by the diet. Despite these limitations, research findings suggest that well-planned vegetarian diets offer sound nutrition and health benefits to adults.2 Dietary patterns that include very little, if any, meat may even increase life expectancy.3
Weight control In general, vegetarians maintain a lower and healthier body weight than non-vegetarians.4 Vegetarians’ lower
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body weights correlate with their high intakes of fibre and low intakes of fat. Because obesity impairs health in a number of ways, this gives vegetarians a health advantage.
Blood pressure Vegetarians tend to have lower blood pressure and lower rates of hypertension than non-vegetarians. Appropriate body weight helps to maintain a healthy blood pressure, as does a diet low in total fat and saturated fat and high in fibre, fruits, vegetables and soy protein.5 Lifestyle factors also influence blood pressure: smoking and alcohol intake raise blood pressure, and physical activity lowers it.
Heart disease The incidence of ischaemic heart disease deaths is as much as 24 per cent lower for vegetarians than for meat eaters.6 The dietary factor most directly related to heart disease is saturated animal fat and, in general, vegetarian diets are lower in total fat, saturated fat and cholesterol than typical meat-based diets.7 The fats common in plant-based diets – the monounsaturated fats of olives, seeds and nuts and the polyunsaturated fats of vegetable oils – are associated with a decreased risk of heart disease.8 Furthermore, vegetarian diets are generally higher in dietary fibre, antioxidant vitamins and phytochemicals – all factors that help control blood lipids and protect against heart disease. Many vegetarians include soy products such as tofu in their diets. Soy products may help to protect against heart disease because they contain polyunsaturated fats, fibre, vitamins and minerals, and little saturated fat. Even when intakes of energy, protein, carbohydrate, total fat, saturated fat, unsaturated fat, alcohol and fibre are the same, people eating meals based on tofu have lower blood cholesterol and triglyceride levels than those eating meat. Some research suggests that soy protein and phytochemicals may be responsible for some of these health benefits (as Highlight 13 explains in greater detail).9
Cancer Vegetarians have a significantly lower rate of cancer than the general population. Their low cancer rates may be due to their high intakes of fruits and vegetables. In fact, the ratio of vegetables to meat may be the most relevant dietary factor responsible for cancer prevention.10 Some scientific findings indicate that vegetarian diets are associated not only with lower cancer mortality in general, but also with lower incidence of cancer at specific sites as well – most notably, colon cancer.11 People with colon cancer seem to eat more meat, more saturated fat and fewer vegetables than do people without colon cancer. High-protein, high-fat, low-fibre diets create an environment in the colon that promotes the development
of cancer in some people. A high-meat diet has been associated with stomach cancer as well.12
Other diseases In addition to obesity, hypertension, heart disease and cancer, vegetarian diets may help prevent diabetes, osteoporosis, diverticular disease, gall stones and rheumatoid arthritis.13 These health benefits of a vegetarian diet depend on wise diet planning.
Vegetarian diet planning The vegetarian has the same meal-planning task as any other person – using a variety of foods to deliver all the needed nutrients within an energy allowance that maintains a healthy body weight (as discussed earlier in Chapter 2). Vegetarians who include milk products and eggs can meet recommendations for most nutrients as easily as nonvegetarians. Such diets can provide enough energy, protein and other nutrients to support the health of adults. Vegetarians who exclude milk products and eggs can select legumes, nuts and seeds, and products made from them, such as peanut butter, tempeh and tofu, to replace products from the meat group. Those who do not use milk can use soy beverage – a product made from soybeans that provides similar nutrients as long as it is fortified with calcium and vitamin D (and sometimes vitamin B12). When selecting from vegetable and fruit groups, vegetarians should emphasise particularly good sources of calcium and iron, respectively. Green leafy vegetables, for example, provide almost five times as much calcium per serving as other vegetables. Similarly, dried fruits deserve special notice in the fruit group because they deliver six times as much iron as other fruits. Fortified soy products may be used to replace milk products for those who do not use milk, cheese or yoghurt. Meat products may be replaced by legumes, soy products, nuts and seeds. To ensure adequate intakes of vitamin B12, vitamin D and calcium, vegetarians need to select fortified foods or take supplements regularly. Most vegetarians easily obtain large quantities of the nutrients that are abundant in plant foods: thiamin, folate and vitamins B6, C, A and E. Good planning of vegetarian diets using the Australian Guide to Healthy Eating and Nutrition Australia’s Healthy Eating Pyramid (see Figure 2.2 on page 49) can help to ensure adequate intakes of the main nutrients vegetarian diets might otherwise lack: protein, iron, zinc, calcium, vitamin B12, vitamin D and omega-3 fatty acids.
Protein The protein RDI for vegetarians is the same as for others, although some have suggested that it should be higher because of the lower digestibility of plant proteins.14
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Chapter 2: Planning a healthy diet
Lacto-ovo-vegetarians, who use animal-derived foods such as milk and eggs, receive high-quality proteins and are likely to meet their protein needs. Even those who adopt only plant-based diets are likely to meet protein needs, provided that their energy intakes are adequate and the protein sources varied. The proteins of whole grains, legumes, seeds, nuts and vegetables can provide adequate amounts of all the amino acids. An advantage of many vegetarian sources of protein is that they are generally lower in saturated fat than meats, and are often higher in fibre and richer in some vitamins and minerals. Vegetarians sometimes use meat replacements made of textured vegetable protein (soy protein). These foods are formulated to look and taste like meat, fish or poultry. Many of these products are fortified to provide the vitamins and minerals found in animal sources of protein. A wise vegetarian learns to use a variety of whole, unrefined foods often, and commercially prepared foods less frequently. Vegetarians may also use soy products such as tofu to bolster protein intake.
Iron Getting enough iron can be a problem even for meat eaters, and those who eat no meat must pay special attention to their iron intake. The iron in plant foods such as legumes, dark green leafy vegetables, iron-fortified cereals and wholegrain breads and cereals is called non-haem iron and isn’t absorbed as well as haem iron found in animal products.15 Fortunately, the body adapts to a vegetarian diet by absorbing iron more efficiently, but vegetarians need to be thoughtful with their diet planning. Iron absorption is enhanced by vitamin C, and vegetarians typically eat many vitamin C–rich fruits and vegetables. Consequently, vegetarians tend to suffer no more iron deficiency than other people do.16
Zinc Zinc is similar to iron in that meat is its richest food source, and zinc from plant sources is not absorbed well.17 In addition, soy, which is commonly used as a meat alternative in vegetarian meals, interferes with zinc absorption. Nevertheless, most vegetarian adults are not zinc-deficient. Perhaps the best advice to vegetarians regarding zinc is to eat a variety of nutrient-dense foods; include whole grains, nuts and legumes such as blackeyed peas, pinto beans and kidney beans; and maintain an adequate energy intake. For those who include seafood in their diets, oysters, crabmeat and prawns are rich in zinc.
Calcium
The calcium intakes of lactovegetarians are similar to those of the general population, but people who use no milk products risk deficiency. Careful planners select
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calcium-rich foods, such as calcium-fortified juices, soy beverages and breakfast cereals, in ample quantities regularly. This advice is especially important for children and adolescents. Other good calcium sources include figs, some legumes, some green vegetables such as broccoli and spinach, some nuts such as almonds, certain seeds such as sesame seeds, and calcium-set tofu.* The choices should be varied because calcium absorption from some plant foods may be limited (as Chapter 12 explains).
Vitamin B12
The requirement for vitamin B12 is small, but this vitamin is found only in animal-derived foods. Consequently, vegetarians, in general, and vegans who eat no foods of animal origin, in particular, may not get enough vitamin B12 in their diets. Fermented soy products such as tempeh may contain some vitamin B12 from the bacteria, but unfortunately, much of the vitamin B12 found in these products may be an inactive form. Seaweeds such as nori and chlorella supply some vitamin B12, but not much, and excessive intakes of these foods can lead to iodine toxicity. To defend against vitamin B12 deficiency, vegans must rely on vitamin B12–fortified sources (such as soy beverages) or supplements. Without vitamin B12, the nerves suffer damage, leading to such health consequences as loss of vision.
Vitamin D People who do not use vitamin D–fortified foods and do not receive enough exposure to sunlight to synthesise adequate vitamin D may need supplements to defend against bone loss. This is particularly important for infants, children and older adults.
Omega-3 fatty acids Both Chapter 5 and Highlight 5 describe the health benefits of unsaturated fats, most notably the omega-3 fatty acids commonly found in fatty fish. To obtain sufficient amounts of omega-3 fatty acids, vegetarians (who don’t eat fish products either) need to consume flaxseed, walnuts, soybeans and products derived from these.
Healthy food choices In general, adults who eat vegetarian diets have lower risks of mortality and several chronic diseases, including obesity, high blood pressure, heart disease and cancer. But there is nothing mysterious or magical about the vegetarian diet; vegetarianism is not a religion like Buddhism or Hinduism, but merely an eating plan that selects plant foods to deliver needed nutrients. *Calcium salts are often added during processing to coagulate the tofu.
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The quality of the diet depends not on whether it includes meat but on whether the other food choices are nutritionally sound. A diet that includes ample fruits, vegetables, whole grains, legumes, nuts and seeds is higher in fibre, antioxidant vitamins and phytochemicals, and lower in saturated fats than meat-based diets. Variety is key to nutritional adequacy in a vegetarian diet. Restrictive plans, such as macrobiotic diets, that limit selections to a few grains and vegetables, cannot possibly deliver a full array of nutrients. If not properly balanced, any diet – vegetarian or otherwise – can lack nutrients. Poorly planned vegetarian diets typically lack iron, zinc, calcium, vitamin B12 and vitamin D; without planning, the meat eater’s diet may
lack vitamin A, vitamin C, folate and fibre, among others. Quite simply, the negative health aspects of any diet, including vegetarian diets, reflect poor diet planning. Careful attention to energy intake and specific problem nutrients can ensure adequacy. Keep in mind, too, that diet is only one factor influencing health. Whatever a diet consists of, its context is also important: no smoking, alcohol consumption in moderation, regular physical activity, adequate rest and medical attention when needed all contribute to a healthy life. Establishing these healthy habits early in life seems to be the most important step one can take to reduce the risks of later diseases (see Highlight 16).
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1
Why are vegetarian diets often considered healthier than non-vegetarian diets?
2
Your interest in nutrition has been piqued by the concept of a vegetarian diet, and you recognise that a well-planned vegetarian diet involves more than simply replacing a chicken sandwich with a large green salad.
Design and follow a vegetarian meal plan for three days, including at least one vegan day. Outline the social, personal, and nutritional challenges you faced and describe how you might partially or fully integrate vegetarian meals into your current meal plan.
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search for ‘vegetarian’ at the US Food and Drug Administration’s site: http://www.fda.gov
• •
Visit the site of the Australian Vegetarian and Vegan Society: http://www.vegsa.org.au Review another vegetarian diet pyramid developed by Oldways Preservation & Exchange Trust: http://www. oldwayspt.org
REFERENCES CHAPTER 1
2
3
Position of the Academy of Nutrition and Dietetics: Total diet approach to healthy eating, Journal of the Academy of Nutrition and Dietetics 113 (2013): 307–17. National Health and Medical Research Council, Australian Dietary Guidelines, Canberra: Commonwealth of Australia (2013), available at https://www.eatforhealth.gov.au/
Department of Health and Ageing, Australian Guide to Healthy Eating, Canberra: Commonwealth of Australia (2013), available at https://www.eatforhealth.gov.au/
4
5
R. Ranganathan and co-authors, The nutritional impact of dairy product consumption on dietary intakes of adults (1995–1996): The Bogalusa Heart Study, Journal of the American Dietetic Association 105 (2005): 1391–400. Food Standards Australia New Zealand, Standard 1.2.7 Nutrition, health & related claims, FSANZ, 2015, available at http://www. foodstandards.gov.au/publications/Pages/gettingyourclaimsright.aspx
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HIGHLIGHT 1
2 3 4 5 6 7
8
9
M. J. Orlich and co-authors, Vegetarian dietary patterns and mortality in Adventist Health Study 2, JAMA Internal Medicine 173 (2013): 1230–8. Craig, W.J. and A.R. Mangels, Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc., 2009. 109(7): p. 1266–82. A. Pan and coauthors, Red meat consumption and mortality, Archives of Internal Medicine 172 (2012): 555–63. P. N. Appleby and T. J. Key, The long-term health of vegetarians and vegans, Proceedings of the Nutrition Society 28 (2015): 1–7. Y. Yokoyama, Vegetarian diets and blood pressure: A meta-analysis, JAMA Internal Medicine 174 (2014): 577–87. P. Tuso, S. R. Stoll, and W. W. Li, A plant-based diet, atherogenesis, and coronary artery disease prevention, Permanente Journal 19 (2015): 62–7. D. C. Willcox and co-authors, The Okinawan diet: Health implications of a low-calorie, nutrient-dense, antioxidant-rich dietary pattern low in glycemic load, Journal of the American College of Nutrition 28 (2009): 500S–516S. T. Huang and coauthors, Cardiovascular disease mortality and cancer incidence in vegetarians: A meta-analysis and systematic review, Annals of Nutrition and Metabolism 60 (2012): 233–40. M. Messina, Insights gained from 20 years of soy research, Journal of Nutrition 140 (2010): 2289S–2295S.
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11 12
13
14 15 16
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K. E. Bradbury, P. N. Appleby, and T. J. Key, Fruit, vegetable, and fiber intake in relation to cancer risk: Findings from the European Prospective Investigation into Cancer and Nutrition (EPIC), American Journal of Clinical Nutrition 100 (2014): 394S–398S. M. J. Orlich and coauthors, Vegetarian dietary patterns and the risk of colorectal cancers, JAMA Internal Medicine 175 (2015): 767–76. D. Aune and co-authors, Dairy products and colorectal cancer risk: a systematic review and meta-analysis of cohort studies, Annals of Oncology 23(2012): 37–45. N. S. Rizzo and coauthors, Nutrient profiles of vegetarian and non vegetarian dietary patterns, Journal of the Academy of Nutrition and Dietetics 113 (2013): 1610–19. Marsh KA and co-authors, Protein and vegetarian diets, Med. J. Aust. 199 (4 Supplement), (2013): S7–S10. W. J. Craig, Nutrition concerns and health effects of vegetarian diets, Nutrition in Clinical Practice 25 (2010): 613–20. C. T. McEvoy, N. Temple, and J. V. Woodside, Vegetarian diets, lowmeat diets and health: a review, Public Health Nutrition 15 (2012): 2287–94. M. Foster and co-authors, Effect of vegetarian diets on zinc status: A systematic review and meta-analysis of studies in humans, Journal of the Science of Food and Agriculture 93 (2013): 2362–71.
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CHAPTER
3
DIGESTION, ABSORPTION AND TRANSPORT Nutrition in your life
Have you ever wondered what happens to the food you eat after you swallow it? Or how your body extracts nutrients from food? Have you ever marvelled at how it all just seems to happen? Follow foods as they travel through the digestive system. Learn how a healthy digestive system transforms whatever food you give it – whether T-bone steak and potatoes or tofu and brussels sprouts – into the nutrients that will nourish the cells of your body. In the ‘Nutrition portfolio’ at the end of the chapter, you can determine whether your current eating habits are supporting a healthy digestive system. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F The process of food digestion begins in the mouth and proceeds all the way into the
large intestine.
T F Intestinal cells are uniform all along the digestive tract. T F Veins and lymphatic vessels leaving the digestive tract carry nutrients to the body. T F The gastrointestinal tract is sterile throughout. T F The functions of the digestive tract are an example of the process of homeostasis.
LEARNING OBJECTIVES 3.1 Explain how foods move through the digestive system, describing the actions of the organs, muscles and digestive secretions along the way. 3.2 Describe the anatomical details of the intestinal cells that facilitate nutrient absorption. 3.3 Explain how nutrients travel in the circulatory systems from the GI tract into
the body and identify which nutrients enter the blood directly and which must first enter the lymph. 3.4 Describe how bacteria, hormones and nerves influence the health and activities of the GI tract. 3.5 Outline strategies to prevent or alleviate common GI problems.
Cherry juice can help with muscle soreness after exercise
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Each cell in the body needs a continuous supply of many specific nutrients to maintain itself and carry out its work. These nutrients derive from the foods consumed, but before the body’s cells can use the nutrients, foods must be broken down mechanically and chemically. This chapter follows the journey that breaks down foods into the nutrients featured in the later chapters. Then it follows the nutrients as they travel through the intestinal cells and into the body to do their work. As you read about the complexities and intricacies of these processes, take a moment to appreciate the beauty and wisdom of the body. Recognise that the activities of the digestive system are finely coordinated and fully integrated with those of the circulatory, nervous and hormonal systems. Then be thankful that your body can efficiently take care of its business without any direction from you, but know that it performs its best when you have given it optimal nourishment. This introduction presents a general overview of the processes common to all nutrients; later chapters discuss the specifics of digesting and absorbing individual nutrients.
3.1 Digestion
your part. Consider these challenges: 1 Human beings breathe, eat and drink through their mouths. Air taken in through the mouth must go to the lungs; food and liquid must go to the stomach. The throat must be arranged so that swallowing and breathing don’t interfere with each other. 2 Below the lungs lies the diaphragm, a dome of muscle that separates the upper half of the major body cavity from the lower half. Food must pass through this wall to reach the stomach. 3 The contents within the digestive tract should be kept moving forward, slowly but steadily, at a pace that permits all reactions to reach completion. 4 To move through the system, food must be lubricated with fluids. Too much would form a liquid that would flow too rapidly; too little would form a paste too dry and compact to move at all. The amount of fluids must be regulated to keep the intestinal contents at the right consistency to move smoothly along. 5 When the digestive enzymes break food down, they need it in a finely divided form, suspended in enough liquid so that every particle is accessible. Once digestion is complete and the needed nutrients have been absorbed out of the gastrointestinal (GI) tract and into the body, the system must excrete the remaining residue. Excreting all the water along with the solid residue, however, would be both wasteful and messy. Some water must be withdrawn to leave a paste just solid enough to be smooth and easy to pass. 6 The enzymes of the digestive tract are designed to digest carbohydrate, fat and protein. The walls of the tract, composed of living cells, are also made of carbohydrate, fat and protein. These cells need protection against the action of the powerful digestive juices that they secrete. 7 Once the residual matter has reached the end of the GI tract, it must be excreted, but it would be inconvenient and embarrassing if this function occurred continuously. Provision must be made for periodic, voluntary evacuation. The following sections show how the body elegantly and efficiently handles these challenges. Each section follows the GI tract from one end to the other – first describing its anatomy, then its muscular actions and finally its secretions.
Anatomy of the digestive tract The gastrointestinal (GI) tract is a flexible muscular tube that extends from the mouth, through the oesophagus, stomach, small intestine, large intestine
The process of digestion transforms all kinds of foods into nutrients.
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Hurst Photo/Shutterstock.com
Digestion is the body’s ingenious way of breaking down foods into nutrients in preparation for absorption. In the process, it overcomes many challenges without any conscious effort on
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and rectum to the anus. Figure 3.1 traces the path followed by food from one end to the other. In a sense, the human body surrounds the GI tract. The inner space within the GI tract, called the lumen, is continuous from one end to the other. Only when a nutrient or other substance finally penetrates the GI tract’s wall does it enter the body proper; many materials pass through the GI tract without being digested or absorbed.
FIGURE 3.1 The gastrointestinal tract Appendix Stores lymph cells
INGESTION Mouth Chews and mixes food with saliva
Small intestine Secretes enzymes that digest all energy-yielding nutrients to smaller nutrient particles; cells of wall absorb nutrients into blood and lymph
Salivary glands
Pharynx Directs food from mouth to oesophagus
Pharynx
Mouth
Epiglottis Upper oesophageal sphincter
Salivary glands Secrete saliva (contains starch-digesting enzymes) Epiglottis Protects airway during swallowing
Trachea (to lungs)
Oesophagus
Trachea Allows air to pass to and from lungs Oesophagus Passes food from the mouth to the stomach Oesophageal sphincters Allow passage from mouth to oesophagus and from oesophagus to stomach; prevent backflow from stomach to oesophagus and from oesophagus to mouth
Stomach Adds acid, enzymes, and fluid; churns, mixes and grinds food to a liquid mass Pyloric sphincter Allows passage from stomach to small intestine; prevents backflow from small intestine Liver Manufactures bile salts, detergent-like substances, to help digest fats
Lower oesophageal sphincter Liver
Ileocaecal valve (sphincter) Allows passage from small to large intestine; prevents backflow from large intestine Pancreas Manufactures enzymes to digest all energy-yielding nutrients and releases bicarbonate to neutralise acid chyme that enters the small intestine Pancreatic duct Conducts pancreatic juice from the pancreas to the small intestine Stomach
Gall bladder
Pancreas
Pyloric sphincter
Pancreatic duct
Bile duct
Small intestine (duodenum, jejunum, ileum)
Ileocaecal valve Appendix Large intestine (colon) Rectum Anus
Gall bladder Stores bile until needed Bile duct Conducts bile from the gallbladder to the small intestine
Large intestine (colon) Reabsorbs water and minerals; passes waste (fibre, bacteria and unabsorbed nutrients) along with water to the rectum Rectum Stores waste prior to elimination Anus Holds rectum closed; opens to allow elimination ELIMINATION
GI anatomy terms appear in boldface type and are defined in the Glossary.
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Chapter 3: Digestion, absorption and transport
Mouth
The process of digestion begins in the mouth. As you chew, your teeth crush large pieces of food into smaller ones, and fluids from foods, beverages and salivary glands blend with these pieces to ease swallowing. Fluids also help dissolve the food so that you can taste it; only particles in solution can react with taste buds. When stimulated, the taste buds detect one, or a combination, of the five basic taste sensations: sweet, sour, bitter, salty and umami, a savoury flavour commonly associated with monosodium glutamate. In addition to these chemical triggers, aroma, texture and temperature also affect a food’s flavour. In fact, the sense of smell is thousands of times more sensitive than the sense of taste. The tongue allows you not only to taste food, but also to move food around the mouth, facilitating chewing and swallowing. When you swallow a mouthful of food, it passes through the pharynx, a short tube that is shared by both the digestive system and the respiratory system. To bypass the entrance to your lungs, the epiglottis closes off your air passages so that you don’t choke when you swallow, thus resolving challenge 1. (Choking is discussed in Highlight 3.) After a mouthful of food has been swallowed, it is called a bolus.
The process of chewing is called mastication.
Oesophagus to the stomach
The oesophagus has a sphincter muscle at each end. During a swallow, the upper oesophageal sphincter opens. The bolus then slides down the oesophagus, which passes through a hole in the diaphragm (challenge 2) to the stomach. The lower oesophageal sphincter at the entrance to the stomach closes behind the bolus so that it proceeds forward and doesn’t slip back into the oesophagus (challenge 3). The stomach retains the bolus for a while in its upper portion. Little by little, the stomach transfers the food to its lower portion, adds juices to it and grinds it to a semiliquid mass called chyme. Then, bit by bit, the stomach releases the chyme through the pyloric sphincter, which opens into the small intestine and then closes behind the chyme.
Small intestine
At the beginning of the small intestine, the chyme bypasses the opening from the common bile duct, which is dripping fluids (challenge 4) into the small intestine from two organs outside the GI tract – the gall bladder and the pancreas. The chyme travels on down the small intestine through its three segments – the duodenum, the jejunum and the ileum – over three metres of tubing coiled within the abdomen.
Large intestine (colon) Having travelled the length of the small intestine, the remaining contents arrive at another sphincter (challenge 3 again): the ileocaecal valve, located at the beginning of the large intestine (colon) in the lower right side of the abdomen. Upon entering the colon, the contents pass another opening. Any intestinal contents slipping into this opening would end up in the appendix, a blind sac about the size of your little finger. The contents bypass this opening, however, and travel along the large intestine up the right side of the abdomen, across the front to the left side, down to the lower left side and finally below the other folds of the intestines to the back of the body, above the rectum. (See Figure 3.2.) As the intestinal contents pass to the rectum, the colon withdraws water, leaving semisolid waste (challenge 5). The strong muscles of the rectum and anal canal hold back this waste until it is time to defecate. Then the rectal muscles relax (challenge 7), and the two sphincters of the anus open to allow passage of the waste.
The muscular action of digestion In the mouth, chewing, the addition of saliva and the action of the tongue transform food into a coarse mash that can be swallowed. After swallowing, you are generally unaware of all the
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FIGURE 3.2 The colon The colon begins with the ascending colon rising upwards towards the liver. It becomes the transverse colon as it turns and crosses the body towards the spleen. The descending colon turns downwards and becomes the sigmoid colon, which extends to the rectum. Along the way, the colon mixes the intestinal contents, absorbs water and salts, and forms stools.
activity that follows. As is the case with so much else that happens in the body, the muscles of the digestive tract meet internal needs without any conscious effort on your part. They keep things moving at just the right pace, slow enough to get the job done and fast enough to make progress.
Segmentation and peristalsis Transverse colon
Ascending colon Opening from small intestine to large intestine
End of small intestine Appendix Rectum Anus
FIGURE 3.3 Stomach muscles Longitudinal
Two layers of muscles in the GI tract (the inner circular and outer longitudinal muscles) coordinate to produce two different kinds of action – segmentation and peristalsis (challenge 3 again). In segmentation, the inner circular muscles contract and relax in a way that churns the chyme. Unlike peristalsis, which predominates in the oesophagus, segmentation contractions occur in the small and large intestines. While peristalsis involves Descending colon one-way motion, segmentation contractions move chyme in both directions, which allows greater mixing with the secretions of the intestines. In peristalsis, the outer Sigmoid longitudinal muscles contract rhythmically colon in a way that moves chyme forward. These rhythmic contractions occur continuously at varying rates and intensities, depending on the section of the GI tract and on whether food is present. Factors such as stress, drugs and illness may interfere with normal GI tract contractions.
Stomach action Circular Diagonal
The ability of the GI tract muscles to move is called their motility.
The stomach has the thickest walls and strongest muscles of all the GI tract organs. In addition to the circular and longitudinal muscles, it has a third layer of diagonal muscles that also alternately contract and relax (see Figure 3.3). These three sets of muscles work to force the chyme downwards, but the pyloric sphincter usually remains tightly closed, preventing the chyme from passing into the duodenum of the small intestine. As a result, the chyme is churned and forced down; it hits the pyloric sphincter and remains in the stomach. Meanwhile, the stomach wall releases gastric juices. When the chyme is completely liquefied, the pyloric sphincter opens briefly, about three times a minute, to allow small portions of chyme to pass through. At this point, the chyme no longer resembles food at all.
Sphincter contractions Sphincter muscles periodically open and close, allowing the contents of the GI tract to move along at a controlled pace (challenge 3 again). At the top of the oesophagus, the upper oesophageal sphincter opens in response to swallowing. At the bottom of the oesophagus, the lower oesophageal sphincter (sometimes called the cardiac sphincter because of its proximity to the heart) prevents reflux of the stomach contents. At the bottom of the
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Chapter 3: Digestion, absorption and transport
stomach, the pyloric sphincter, which stays closed most of the time, holds the chyme in the stomach long enough for it to be thoroughly mixed with gastric juice and liquefied. The pyloric sphincter also prevents the intestinal contents from backing up into the stomach. At the end of the small intestine, the ileocaecal valve performs a similar function, allowing the contents of the small intestine to empty into the large intestine. Finally, the tightness of the rectal muscle is a kind of safety device; together with the two sphincters of the anus, it prevents elimination until you choose to perform it voluntarily (challenge 7). Figure 3.4 illustrates how sphincter muscles contract and relax to close and open passageways.
FIGURE 3.4 An example of a sphincter muscle Circular muscle
Oesophagus
Longitudinal muscle Oesophagus muscles relax, opening the passageway
Stomach
Diaphragm muscles relax, opening the passageway
Oesophagus muscles contract, squeezing on the inside Diaphragm muscles contract, squeezing on the outside
CURRENT RESEARCH IN NUTRITION Stomach hormones In addition to gastric juices, the stomach has a surprising role in secreting hormones that communicate with the brain. One hormone, ghrelin, is produced by stomach cells and functions to provide information on when the stomach is full. Before eating, the levels of ghrelin produced by the stomach rise, but once the stomach expands with food, ghrelin synthesis is stopped so blood ghrelin concentrations fall. Ghrelin receptors are found in the hypothalamus of the brain. Higher levels of ghrelin increase appetite, which is part of the complex way that the body regulates weight.1 Thus, an empty stomach is a powerful regulator to drive hunger cues in the brain. In addition to ghrelin’s effects on appetite and adiposity, ghrelin signalling also plays crucial roles in glucose and energy homeostasis, cardio-protection and muscle atrophy. Ghrelin also has a role in bone formation and metabolism and may also be a potential target for cancer, making future research into this hormone an exciting avenue.
The secretions of digestion The breakdown of food into nutrients requires secretions from five different organs: the salivary glands, the stomach, the pancreas, the liver (via the gall bladder) and the small intestine. These secretions enter the GI tract at various points along the way, bringing an abundance of water (challenge 3 again) and a variety of enzymes.
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Enzymes are formally introduced in Chapter 6, but for now a simple definition will suffice. An enzyme is a protein that facilitates a chemical reaction – making a molecule, breaking a molecule apart, changing the arrangement of a molecule or exchanging parts of molecules. As a catalyst, the enzyme itself remains unchanged. The enzymes involved in digestion facilitate a chemical reaction known as hydrolysis – the addition of water (hydro) to break (lysis) a molecule into smaller pieces. The Glossary includes some of the common digestive enzymes and related terms. When learning about enzymes, it helps to know that words ending in -ase denote an enzyme. Enzymes are often identified by the organ they come from and the compounds they work on. Gastric lipase, for example, is a stomach enzyme that acts on lipids, whereas pancreatic lipase comes from the pancreas (and also works on lipids). Because of all these secretions, the three energy-yielding nutrients – carbohydrate, fat and protein – are digested in the small intestine. (Table 3.1 provides a list of digestive secretions and their actions.)
TABLE 3.1 Summary of digestive secretions and their major actions ORGAN OR GLAND
TARGET ORGAN
SECRETION
ACTION
Salivary glands
Mouth
Saliva
Fluid eases swallowing; salivary enzyme breaks down some carbohydrate.*
Gastric glands
Stomach
Gastric juice
Fluid mixes with bolus; hydrochloric acid uncoils proteins; enzymes break down proteins; mucus protects stomach cells.*
Pancreas
Small intestine
Pancreatic juice
Bicarbonate neutralises acidic gastric juices; pancreatic enzymes break down carbohydrates, fats and proteins.
Liver
Gall bladder
Bile
Bile is stored until needed.
Gall bladder
Small intestine
Bile
Bile emulsifies fat so that enzymes can have access to break it down.
Intestinal glands
Small intestine
Intestinal juice
Intestinal enzymes break down carbohydrate, fat and protein fragments; mucus protects the intestinal wall.
*Saliva and gastric juice also contain lipases, but most fat breakdown occurs in the small intestine.
FIGURE 3.5 The salivary glands
Saliva
The salivary glands, shown in Figure 3.5, squirt just enough saliva to moisten each mouthful of food so that it can pass easily down the oesophagus (challenge 4). Digestive glands and their secretions are defined in the glossary. The saliva contains water, salts, mucus and enzymes that initiate the digestion of carbohydrates. Saliva also protects the teeth and the linings of the mouth, oesophagus and stomach from attack by substances that might harm them.
Gastric juice
Salivary glands
In the stomach, gastric glands secrete gastric juice, a mixture of water, enzymes and hydrochloric acid, which acts primarily in protein digestion. The acid is so strong that it causes the sensation of heartburn if it happens to reflux into the oesophagus. Highlight 3, at the end of this chapter, discusses heartburn, ulcers and other common digestive problems. The strong acidity of the stomach prevents bacterial growth and kills most bacteria that enter the body with food. It would destroy the cells of the stomach as well, but for their natural defences. To protect Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Chapter 3: Digestion, absorption and transport
themselves from gastric juice, the cells of the stomach wall secrete mucus, a thick, slippery, white substance that coats the cells, protecting them from the acid, enzymes and diseasecausing bacteria that might otherwise harm them (challenge 6). Figure 3.6 shows how the strength of acids is measured – in pH units. Note that the acidity of gastric juice registers below ‘2’ on the pH scale – stronger than vinegar. The stomach enzymes work most efficiently in the stomach’s strong acid, but the salivary enzymes, which are swallowed with food, do not work in acid this strong. Consequently, the salivary digestion of carbohydrate gradually ceases when the stomach acid penetrates each newly swallowed bolus of food. When they enter the stomach, salivary enzymes become just other proteins to be digested.
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The lower the pH, the higher the H+ ion concentration and the stronger the acid. A pH above 7 is alkaline, or base (a solution in which OH− ions predominate).
FIGURE 3.6 The pH scale
Pancreatic juice and intestinal enzymes By the time food leaves the stomach, digestion of all three energy nutrients (carbohydrates, fats and proteins) has begun, and the action gains momentum in the small intestine. There the pancreas contributes digestive juices by way of ducts leading into the duodenum. The pancreatic juice contains enzymes that act on all three energy nutrients, and the cells of the intestinal wall also possess digestive enzymes on their surfaces. In addition to enzymes, the pancreatic juice contains sodium bicarbonate, which is basic or alkaline – the opposite of the stomach’s acid (review Figure 3.6). The pancreatic juice thus neutralises the acidic chyme arriving in the small intestine from the stomach. From this point on, the chyme remains at a neutral or slightly alkaline pH. The enzymes of both the intestine and the pancreas work best in this environment.
pH of common substances: Basic
Concentrated lye
13
Oven cleaner
12 11
Household ammonia
10 9
6
Baking soda Bile Pancreatic juice Blood Water Saliva Urine
5
Coffee
4
Orange juice
3
Vinegar
2
Lemon juice Gastric juice
8 pH neutral
Bile
14
Bile also flows into the duodenum. The liver continuously produces bile, which is then concentrated and stored in the gall bladder. The gall bladder squirts the bile into the duodenum of the small intestine when fat arrives there. Bile is not an enzyme; it is an emulsifier that brings fats into suspension in water so that enzymes can break them down into their component parts.
The final stage At this point, the three energy-yielding nutrients – carbohydrate, fat and protein – have been disassembled and are ready to be absorbed. Most of the Acidic other nutrients – vitamins, minerals and water – need no such disassembly; some vitamins and minerals are altered slightly during digestion, but most are absorbed as they are. Undigested residues, such as some dietary fibre, are not absorbed. Instead, they continue through the digestive tract, providing a semisolid mass that helps exercise the muscles and keep them strong enough to perform peristalsis efficiently. Dietary fibre also retains water, accounting for the pasty consistency and adding bulk to the stools. By the time the contents of the GI tract reach the end of the small intestine, little remains but water, a few dissolved salts and body secretions, and undigested materials such as dietary fibre (with some fat, cholesterol and a few minerals bound to it). All of this remaining matter enters the large intestine (colon). In the colon, intestinal bacteria ferment some types of dietary fibre, producing water, gas and small fragments of fat that provide energy for the cells of the colon. The colon itself retrieves all materials that the body can recycle – water and dissolved salts (see Figure 3.7). The waste that is finally excreted has little or nothing of value left in it. The body has extracted all that it can use from the food. Figure 3.7 summarises digestion by following a sandwich through the GI tract and into the body.
7
1 0
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Battery acid
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Fat
tein Pro
Fib re
Carbohydrate digestion begins as the salivary enzyme starts to break down the starch from bread and peanut butter. Digestive fibre covering on the sesame seeds is crushed by the teeth, which exposes the nutrients inside the seeds to the digestive enzymes. Fat digestion is minimal. Some hard fats begin to melt as they reach body temperature. Protein foods are moistened by saliva.
Car
MOUTH: CHEWING AND SWALLOWING, WITH LITTLE DIGESTION
boh ydr ate
FIGURE 3.7 The digestive fate of a sandwich
STOMACH: COLLECTING AND CHURNING, WITH SOME DIGESTION Carbohydrate digestion continues until the mashed sandwich has been mixed with the gastric juices; the stomach acid of the gastric juices inactivates the salivary enzyme, and carbohydrate digestion ceases. Proteins from the bread, seeds and peanut butter begin to uncoil when they mix with the gastric acid, making them available to the gastric protease enzymes that begin to digest proteins. Fat from the peanut butter and seeds forms a separate layer on top of the watery mixture. SMALL INTESTINE: DIGESTING AND ABSORBING Carbohydrate digestion picks up when the pancreas sends pancreatic enzymes to the small intestine via the pancreatic duct to break down starch. Enzymes on the surfaces of the small intestinal cells complete the process of breaking down starch into small fragments that can be absorbed through the intestinal cell walls and into the hepatic portal vein. Sugars from the banana require so little digestion that they begin to traverse the intestinal cells immediately on contact. Fat from the peanut butter and seeds is emulsified with the watery digestive fluids by bile. Now the pancreatic and intestinal lipases can begin to break down the fat to smaller fragments that can be absorbed through the cells of the small intestinal wall and into the lymph. Protein digestion depends on the pancreatic and intestinal proteases. Small fragments of protein are liberated and absorbed through the cells of the small intestinal wall and into the hepatic portal vein. Vitamins and minerals are absorbed.
Note: Sugars and starches are members of the carbohydrate family. LARGE INTESTINE: ABSORBING AND ELIMINATING Fluids and some minerals are absorbed. Some digestive fibre from the seeds, whole-wheat bread, peanut butter and banana is partly digested by the bacteria living in the large intestine, and some of the products are absorbed. Most digestive fibre passes through the large intestine and is excreted as faeces; some fat, cholesterol and minerals bind to fibre and are also excreted.
ABSORPTION
EXCRETION
The process of food digestion begins in the mouth and proceeds all the way into the large intestine.
REVIEW IT
PUTTING COMMON SENSE TO THE TEST
As Figure 3.1 shows, food enters the mouth and travels through the upper oesophageal sphincter, down the oesophagus and through the lower oesophageal sphincter to the stomach, then through the pyloric sphincter to the small intestine, on through the ileocaecal valve to the large intestine, past the appendix to the rectum, ending at the anus. The wave-like contractions of peristalsis and the periodic squeezing of segmentation keep things moving at a reasonable pace. Along the way, secretions from the salivary glands, stomach, pancreas, liver (via the gall bladder), and small intestine deliver fluids and digestive enzymes.
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3.2 Absorption
Within three or four hours of having eaten a dinner of meat and vegetables with salad, a drink and dessert, your body must find a way to absorb the molecules derived from carbohydrate, protein and fat digestion – and the vitamin and mineral molecules as well. Most absorption takes place in the small intestine, one of the most elegantly designed organ systems in the body. Within its three-metre length, which provides a surface area equivalent to a tennis court, the small intestine engulfs and absorbs the nutrient molecules. To remove the molecules rapidly and provide room for more to be absorbed, a rush of circulating blood continuously washes the underside of this surface, carrying the absorbed nutrients away to the liver and other parts of the body. Figure 3.8 describes how nutrients are absorbed by simple diffusion, facilitated diffusion or active transport. Later chapters provide details on specific nutrients. Before following nutrients through the body, we must look more closely at the anatomy of the absorptive system.
FIGURE 3.8 Absorption of nutrients Carrier loads nutrient on outside of cell ...
Outside cell
Cell membrane
Carrier loads nutrient on outside of cell ...
En erg
y
... and then releases it on inside of cell.
Inside cell SIMPLE DIFFUSION
Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely.
FACILITATED TRANSPORT
Some nutrients (such as the water-soluble vitamins) are absorbed by facilitated transport. They need a specific carrier to transport them from one side of the cell membrane to the other. (Alternatively, facilitated transport may occur when the carrier changes the cell membrane in such a way that the nutrients can pass through.)
... and then releases it on inside of cell. ACTIVE TRANSPORT
Some nutrients (such as glucose and amino acids) are absorbed actively. These nutrients move against a concentration gradient, which requires energy.
The inner surface of the small intestine looks smooth and slippery, but when viewed through a microscope, it turns out to be wrinkled into hundreds of folds. Each fold is contoured into thousands of finger-like projections, as numerous as the hairs on velvet fabric. These small intestinal projections are the villi. A single villus, magnified still more, turns out to be composed of hundreds of cells, each covered with its own microscopic hairs, the microvilli (see Figure 3.9). In the crevices between the villi lie the crypts – tubular glands that secrete the intestinal juices into the small intestine. Nearby, goblet cells secrete mucus. The villi are in constant motion. Each villus is lined by a thin sheet of muscle, so it can wave, squirm and wriggle like the tentacles of a sea anemone. Any nutrient molecule small enough to be absorbed is trapped among the microvilli
Bill Crew/Super Stock
Anatomy of the absorptive system
If you have ever watched a sea anemone with its fingerlike projections in constant motion, you have a good picture of how the intestinal villi move.
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FIGURE 3.9 The small intestinal villi
Stomach Folds with villi on them
Small intestine
The wall of the small intestine is wrinkled into thousands of folds and is carpeted with villi. Circular muscles Microvilli
Lymphatic vessel (lacteal)
Longitudinal muscles
Science Photo Library/Eye of Science
Capillaries A villus Goblet cells
Crypts This is a photograph of part of an actual human intestinal cell with microvilli.
Each villus in turn is covered with even smaller projections, the microvilli. Microvilli on the cells of villi provide the absorptive surfaces that allow the nutrients to pass through to the body.
Artery Vein Lymphatic vessel
that coat the cells and then drawn into the cells. Some partially digested nutrients are caught in the microvilli, digested further by enzymes there and then absorbed into the cells.
A closer look at the intestinal cells The problem of food contaminants, which may be absorbed defencelessly by the body, is the subject of Chapter 19.
The cells of the villi are among the most amazing in the body, for they recognise and select the nutrients the body needs and regulate their absorption. As already described, each cell of a villus is coated with thousands of microvilli, which project from the cell’s membrane (review Figure 3.9). In these microvilli, and in the membrane, lie hundreds of different kinds of enzymes and ‘pumps’, which recognise and act on different nutrients. Descriptions of specific enzymes and ‘pumps’ for each nutrient are presented in the following chapters where appropriate; the point here is that the cells are equipped to handle all kinds and combinations of foods and nutrients.
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Specialisation cells A further refinement of the system is that the cells of successive portions of the intestinal tract are specialised to absorb different nutrients. The nutrients that are ready for absorption early are absorbed near the top of the GI tract; those that take longer to be digested are absorbed further down. Healthcare professionals who treat digestive disorders learn the specialised absorptive functions of different parts of the GI tract so that if one part becomes dysfunctional, the diet can be adjusted accordingly.
APPLICATIONS OF NUTRITIONAL RESEARCH The myth of ‘food combining’ The idea that people should not eat certain food combinations (for example, fruit and meat) at the same meal, because the digestive system cannot handle more than one task at a time, is a myth. The art of ‘food combining’ (which actually emphasises ‘food separating’) is based on this idea, and it represents faulty logic and a gross underestimation of the body’s capabilities. In fact, the contrary is often true; foods eaten together can enhance each other’s use by the body. For example, vitamin C in an orange or other citrus fruit can enhance the absorption of iron from a meal of chicken and rice or other iron-containing foods. Many other instances of mutually beneficial interactions are presented in later chapters.
PUTTING COMMON SENSE TO THE TEST
Intestinal cells are uniform all along the digestive tract.
Preparing nutrients for transport
FALSE
When a nutrient molecule has crossed the cell of a villus, it enters either the bloodstream or the lymphatic system. Both transport systems supply vessels to each villus, as shown in Figure 3.9. The water-soluble nutrients and the smaller products of fat digestion are released directly into the bloodstream and guided directly to the liver, where their fate and destination will be determined. The larger fats and the fat-soluble vitamins are insoluble in water, however, and blood is mostly water. The intestinal cells assemble many of the products of fat digestion into larger molecules. These larger molecules cluster together with special proteins, forming chylomicrons. Because chylomicrons carry fat, they are released into the lymphatic system. They move through the lymph until they can enter the bloodstream at a point near the heart, consequently bypassing the liver initially. (Chylomicrons are described in more detail further in this chapter and in Chapter 5.)
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The many folds and villi of the small intestine dramatically increase its surface area, facilitating nutrient absorption. Nutrients pass through the cells of the villi and enter either the blood (if they are watersoluble or small fat fragments) or the lymph (if they are fat-soluble).
3.3 The circulatory systems
Once a nutrient has entered the bloodstream, it may be transported to any of the cells in the body, from the tips of the toes to the roots of the hair. The circulatory systems deliver nutrients wherever they are needed.
The vascular system The vascular, or blood circulatory, system is a closed system of vessels through which blood flows continuously, with the heart serving as the pump (see Figure 3.10). As the blood circulates through this system, it picks up and delivers materials as needed.
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FIGURE 3.10 The vascular system
Head and upper body
2 Blood loses carbon dioxide and picks up oxygen in the lungs and returns to the left side of the heart by way of the pulmonary vein.
Lungs
Pulmonary vein
2 Pulmonary artery
Aorta
1 Blood leaves the right side of the heart by way of the pulmonary artery.
Left side
1
7 Lymph from most of the body’s organs, including the digestive system, enters the bloodstream near the heart.
7
Hepatic vein
Right side
4 4 Blood may leave the aorta to go to the upper body and head;
Heart
or
Hepatic artery Hepatic portal vein
Liver
Digestive tract
6 Blood returns to the right side of the heart. 6
Blood may leave the aorta to go to the lower body. 5 5 Blood may go to the digestive tract and then the liver; or
Lymph Key: Arteries
3 Blood leaves the left side of the heart by way of the aorta, the main artery that launches blood on its course through the body.
3
Entire body
Blood may go to the pelvis, kidneys and legs.
Capillaries Veins Lymph vessels
All the body tissues derive oxygen and nutrients from the blood and deposit carbon dioxide and other wastes back into the blood. The lungs exchange carbon dioxide (which leaves the blood to be exhaled) and oxygen (which enters the blood to be delivered to all cells). The digestive system supplies the nutrients to be picked up. In the kidneys, wastes other than carbon dioxide are filtered out of the blood to be excreted in the urine. Blood leaving the right side of the heart circulates through the lungs and then back to the left side of the heart. The left side of the heart then pumps the blood out of the aorta through arteries to all systems of the body. The blood circulates in the capillaries, where it exchanges material with the cells and then collects into veins, which return it again to the right side of the heart. In short, the simple route that blood travels is: • heart to arteries to capillaries to veins to heart. The route of the blood leaving the digestive system is a special feature. The blood is carried to the digestive system (as to all organs) by way of an artery, which (as in all organs) branches into capillaries to reach every cell. Blood leaving the digestive system, however, goes by way of a
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Chapter 3: Digestion, absorption and transport
vein. The hepatic portal vein directs blood not back to the heart, but to another organ – the liver. This vein again branches into capillaries so that every cell of the liver has access to the blood. Blood leaving the liver then again collects into a vein, called the hepatic vein, which returns blood to the heart. The route is: • heart to arteries to capillaries (in intestines) to hepatic portal vein to capillaries (in liver) to hepatic vein to heart. Figure 3.11 shows the liver’s key position in nutrient transport. An anatomist studying this system knows there must be a reason for this special arrangement. The liver’s placement ensures that it will be first to receive the nutrients absorbed from the GI tract. In fact, the liver has many jobs to do in preparing the absorbed nutrients for use by the body. It is the body’s major metabolic organ. In addition, the liver defends the body by detoxifying substances that might cause harm and preparing waste products for excretion. This is why, when people ingest poisons that succeed in passing the first barrier (the intestinal cells), the liver quite often suffers the damage – from viruses such as hepatitis, from drugs such as barbiturates or alcohol, from toxins such as pesticide residues and from contaminants such as mercury. Perhaps, in fact, you have been undervaluing your liver, not knowing what heroic tasks it quietly performs for you.
FIGURE 3.11 The liver Hepatic vein Capillaries 1
Vessels gather up nutrients from the digestive tract. Not shown here: Parallel to these vessels (veins) are other vessels (arteries) that carry oxygen-rich blood from the heart to the intestines.
2
The vessels merge into the hepatic portal vein, which conducts all absorbed materials to the liver.
3
The hepatic artery brings a supply of freshly oxygenated blood (not loaded with nutrients) from the lungs to supply oxygen to the liver’s own cells.
4
A network of large capillaries branch all over the liver, making nutrients and oxygen available to all its cells and giving the cells access to blood from the digestive system.
5
The hepatic vein gathers up blood in the liver and returns it to the heart.
In contrast, nutrients absorbed into lymph do not go to the liver first. They go to the heart, which pumps them to all the body’s cells. The cells remove the nutrients they need, and the liver handles the remnants.
Hepatic artery
5 4
Hepatic portal vein 3
2
Vessels
1
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The lymphatic system The lymphatic system provides a one-way route for fluid from the tissue spaces to enter the blood. Unlike the vascular system, the lymphatic system has no pump; instead, lymph circulates between the cells of the body and collects into tiny vessels. The fluid moves from one portion of the body to another as muscles contract and create pressure here and there. Ultimately, much of the lymph collects in the thoracic duct behind the heart. The thoracic duct opens into the subclavian vein, where the lymph enters the bloodstream. Thus, nutrients from the GI tract that enter lymphatic vessels (large fats and fat-soluble vitamins) ultimately enter the bloodstream, circulating through arteries, capillaries and veins like the other nutrients, with a notable exception – they bypass the liver. Once inside the vascular system, the nutrients can travel freely to any destination and can be taken into cells and used as needed. What becomes of them is described in later chapters.
The lymphatic vessels of the intestine that take up nutrients and pass them to the lymph circulation are called lacteals.
Veins and lymphatic vessels leaving the digestive tract carry nutrients to the body. TRUE
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PUTTING COMMON SENSE TO THE TEST
Nutrients leaving the digestive system via the blood travel directly to the liver before being transported to the body’s cells. Those leaving via the lymphatic system eventually enter the vascular system but bypass the liver at first.
3.4 The health and regulation of the GI tract
This section describes the bacterial conditions and hormonal regulation of a healthy GI tract, but many factors can influence normal GI function. For example, peristalsis and sphincter action are poorly coordinated in newborns, so infants tend to ‘spit up’ during the first several months of life. Older adults often experience constipation, in part because the intestinal wall loses strength and elasticity with age, which slows GI motility. Diseases can also interfere with digestion and absorption and often lead to malnutrition. Lack of nourishment in general, and lack of certain dietary constituents such as fibre, in particular, alter the structure and function of GI cells. Quite simply, GI tract health depends on adequate nutrition.
Gastrointestinal microbiome A healthy GI tract is home to a vibrant community of some 100 trillion microbes – bacteria, viruses, fungi, protozoa and other microorganisms, collectively known as the human microbiome. Weighing less than half a kilogram in total, these microbial cells outnumber the body’s cells tenfold. The bacteria alone represent more than 400 different species and subspecies. The prevalence of different microbes in various parts of the GI tract depends on such factors as pH, peristalsis, diet and other microbes. Relatively few microbes can live in the low pH of the stomach with its somewhat rapid peristalsis, whereas the neutral pH and slow peristalsis of the lower small intestine and the large intestine permit the growth of a diverse and abundant population. Recent research has revealed that a person’s health reflects the relative stability, disturbance, and resilience of the microbiome.2 Changes in the microbiota composition and activity are associated with dozens of common diseases, such as irritable bowel syndrome and obesity.3 Interestingly, similarities in microbiota composition are apparent in people who have the same disease, and differences are noted when their health status differs. For example, the number and kinds of GI microbes differ in non-obese and obese individuals; the population of microbes in obese people with more body fat and obesity-related diseases is less diverse than in non-obese people.4 Ongoing research is trying to determine exactly how the GI microbiota might contribute to the development of obesity and other metabolic diseases.5
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Chapter 3: Digestion, absorption and transport
The microbiome population and environment change dramatically in response to diet – in both the short term (daily meals) and the long term (habitual diet patterns).6 In fact, one of the ways diet may help manage diseases is by changing the microbiota. Consider, for example, that the most recommended diet strategy to improve health – plant-based eating patterns – promotes the most favourable changes in the GI microbiota.7 Such diets are high in fibres that cannot be digested by the human body but can provide a major source of energy for bacteria, fostering their growth. As GI bacteria digest and metabolise fibres, they produce short fragments of fat called short-chain fatty acids, which influence metabolism, inflammation and disease.8 Fibre and some other food components are called prebiotics because they encourage the growth and activity of bacteria. Research suggests that prebiotics might reduce the risk of GI infections, inflammation and disorders; increase the bioavailability of nutrients; and regulate appetite and satiety.9 Some foods contain probiotics, live microbes that change the conditions in the GI tract in ways that seem to benefit health. For example, yoghurt contains Lactobacillus and other living bacteria. The potential GI health benefits of probiotics or products of their metabolism include helping to alleviate diarrhoea, constipation, inflammatory bowel disease, ulcers, allergies, lactose intolerance and infant colic; enhance immune function; and protect against colon cancer.10 Research studies continue to explore how diet influences GI bacteria and which foods – with their prebiotics and probiotics – affect GI health. In addition, research studies are beginning to reveal several health benefits beyond the GI tract – such as lowering blood cholesterol, blood pressure and inflammation responses.11 Bacteria in the GI tract also produce several vitamins, including biotin, folate, pantothenic acid, riboflavin, thiamin, vitamin B6, vitamin B12 and vitamin K. Because the amounts produced of these vitamins are insufficient to meet the body’s needs or in the case of vitamin B12 it cannot be absorbed in the colon where it is produced, these vitamins are nevertheless considered essential nutrients that must be provided by the diet.
PUTTING COMMON SENSE TO THE TEST
The gastrointestinal tract is sterile throughout. FALSE
Gastrointestinal hormones and nerve pathways The ability of the digestive tract to handle its ever-changing contents routinely illustrates an important physiological principle that governs the way all living things function – the principle of homeostasis. Simply stated, survival depends on body conditions staying about the same; if they deviate too far from the norm, the body must ‘do something’ to bring them back to normal. The body’s regulation of digestion is one example of homeostatic regulation. The body also regulates its temperature, its blood pressure and all other aspects of its blood chemistry in similar ways. Two intricate and sensitive systems coordinate all the digestive and absorptive processes: the hormonal (or endocrine) system and the nervous system. Even before the first bite of food is taken, the mere thought, sight or smell of food can trigger a response from these systems. Then, as food travels through the GI tract, it either stimulates or inhibits digestive secretions by way of messages that are carried from one section of the GI tract to another by both hormones and nerve pathways. (Appendix A presents a brief summary of the body’s hormonal system and nervous system.) Notice that the kinds of regulation described next are all examples of feedback mechanisms. A certain condition demands a response. The response changes that condition, and the change then cuts off the response. Thus, the system is self-correcting. The following are examples of this: • The stomach normally maintains a pH between 1.5 and 1.7. How does it stay that way? Food entering the stomach stimulates cells in the stomach wall to release the hormone gastrin. Gastrin, in turn, stimulates the stomach glands to secrete the components of hydrochloric acid. When a pH of 1.5 is reached, the acid itself turns off the gastrin-producing cells. They stop releasing gastrin, and the glands stop producing hydrochloric acid. Thus, the system adjusts itself, as Figure 3.12 shows.
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In general, any gastrointestinal hormone may be called an enterogastrone, but the term refers specifically to any hormone that slows motility and inhibits gastric secretions.
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Nerve receptors in the stomach wall also respond to the presence of food and stimulate the gastric glands to secrete juices and the muscles to contract. As the stomach empties, the receptors are no longer stimulated, the flow of juices slows and the stomach quietens down. Acidity in the stomach causes the • The pyloric sphincter opens to let out a little chyme, then closes again. cells of the How does it know when to open and close? When the pyloric sphincter stomach wall to relaxes, acidic chyme slips through. The cells of the pyloric muscle stop releasing gastrin. on the intestinal side sense the acid, causing the pyloric sphincter to close tightly. Only after the chyme has been neutralised by pancreatic bicarbonate and the juices surrounding the pyloric sphincter have become alkaline can the muscle relax again. This process ensures that the chyme will be released slowly enough to be neutralised as it flows through the small intestine. This is important because the small intestine has less mucus coating than the stomach and so is not as well NEGATIVE protected from acid. FEEDBACK • As the chyme enters the intestine, the pancreas adds bicarbonate to it so that the intestinal contents always remain at a slightly alkaline pH. How does the pancreas know how much to add? The presence of chyme stimulates the cells of the duodenum wall to release the hormone secretin into the blood. When secretin reaches the pancreas, it stimulates the pancreas to release its bicarbonate-rich juices. Thus, whenever the duodenum signals that acidic chyme is present, the pancreas responds by sending bicarbonate to neutralise it. When the need has been met, the cells of the duodenum wall are no longer stimulated to release secretin, the hormone no longer flows through the blood, the pancreas no longer receives the message and it stops sending pancreatic juice. Nerves also regulate pancreatic secretions. • Pancreatic secretions contain a mixture of enzymes to digest carbohydrate, fat and protein. How does the pancreas know how much of each type of enzyme to provide? This is one of the most interesting questions physiologists have asked. Clearly, the pancreas does know what its owner has been eating, and it secretes enzyme mixtures tailored to handle the food mixtures that have been arriving recently (over the past several days). Enzyme activity changes proportionately in response to the amounts of carbohydrate, fat and protein in the diet. If a person has been eating mostly carbohydrates, the pancreas makes and secretes mostly carbohydrases; if the person’s diet has been high in fat, the pancreas produces more lipases; and so on. Presumably, hormones from the GI tract, secreted in response to meals, keep the pancreas informed about its digestive tasks. The day or two of lag between the time a person’s diet changes dramatically and the time digestion of the new diet becomes efficient explains why dietary changes can ‘upset digestion’ and should be made gradually. • Why don’t the digestive enzymes damage the pancreas? The pancreas protects itself from harm by producing an inactive form of the enzymes. It releases these proteins into the small intestine where they are activated to become enzymes. In pancreatitis, the digestive enzymes become active within the infected pancreas, causing inflammation and damage to the delicate pancreatic tissues. • When fat is present in the intestine, the gall bladder contracts to squirt bile into the intestine to emulsify the fat. How does the gall bladder get the message that fat is present? Fat in the intestine stimulates cells of the intestinal wall to release the hormone cholecystokinin (CCK). This hormone, travelling in the blood to the gall bladder, stimulates it to contract, releasing bile into the small intestine. Cholecystokinin also travels to the pancreas and stimulates it to secrete its juices, releasing bicarbonate and enzymes into the small intestine. Once the fat in the intestine is emulsified and enzymes have begun to work on it, the fat no longer provokes release of the hormone and the message to contract is cancelled. (Fat emulsification can continue even after
FIGURE 3.12 An example of a negative feedback loop Food in the stomach causes the cells of the stomach wall to start releasing gastrin.
Gastrin stimulates stomach glands to release the components of hydrochloric acid.
Stomach pH reaches 1.5 acidity.
The inactive precursor of an enzyme is called a proenzyme or zymogen: • pro 5 before • zym 5 concerning enzymes • gen 5 to produce.
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Chapter 3: Digestion, absorption and transport
a diseased gall bladder has been surgically removed because the liver can deliver bile directly to the small intestine.) • Fat and protein take longer to digest than carbohydrate does. When fat or protein is present, intestinal motility slows to allow time for its digestion. How does the intestine know when to slow down? Cholecystokinin is released in response to fat or protein in the small intestine. In addition to its role in fat emulsification and digestion, cholecystokinin slows GI tract motility. Slowing the digestive process helps to maintain a pace that allows all reactions to reach completion. Hormonal and nervous mechanisms like these account for much of the body’s ability to adapt to changing conditions. Table 3.2 summarises the actions of gastrin, secretin and cholecystokinin. These three hormones are among the most studied GI hormones, but the GI tract releases more than 20 hormones. In addition to assisting with digestion and absorption, many of these hormones regulate food intake and influence satiation. Current research is focusing on the roles these hormones may play in the development of obesity and its treatments. (More details are provided in Chapter 9.)
83
Satiation is the feeling of satisfaction and fullness that occurs during a meal and that halts eating.
TABLE 3.2 The primary actions of selected GI hormones HORMONE
RESPONDS TO
SECRETED FROM
STIMULATES
RESPONSE
Gastrin
Food in the stomach
Stomach wall
Stomach glands
Hydrochloric acid secreted into the stomach to maintain an acidic pH
Secretin
Acidic chyme in the small intestine
Duodenal wall
Pancreas
Bicarbonate-rich juices secreted into the small intestine to maintain a slightly alkaline pH
Cholecystokinin
Fat or protein in the small intestine
Intestinal wall
Gall bladder Pancreas
Bile secreted into the duodenum to emulsify fats. Bicarbonate- and enzyme-rich juices secreted into the small intestine to maintain a slightly alkaline pH, digest fats and proteins and slow GI tract motility
The system at its best This chapter describes the anatomy of the digestive tract on several levels: the sequence of digestive organs, the cells and structures of the villi, and the selective machinery of the cell membranes. The intricate architecture of the digestive system makes it sensitive and responsive to conditions in its environment. Several different kinds of GI tract cells confer specific immunity against intestinal diseases such as inflammatory bowel disease. In addition, secretions from the GI tract – saliva, mucus, gastric acid and digestive enzymes – not only help with digestion but also defend against many illnesses. One indispensable condition is good health of the digestive system itself. Like all the other organs of the body, the GI tract depends on a healthy supply of blood. The cells of the GI tract become weak and inflamed when blood flow is diminished, as may occur in heart disease when arteries become clogged or blood clots form. Just as a diminished blood flow to the heart or brain can cause a heart attack or stroke respectively, too little blood to the intestines can also be damaging – or even fatal. A diminished blood flow to the intestines – called intestinal ischaemia – is characterised by abdominal pain, forceful bowel movements, and blood in the stool. The health of the digestive system is also affected by such lifestyle factors as sleep, physical activity and state of mind. Adequate sleep allows for repair and maintenance of tissue and removal of wastes that might impair efficient functioning. Activity promotes healthy muscle tone. Stress alters GI motility, secretions, permeability, blood flow and bacteria. For healthy
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digestion, mealtimes should be relaxed and tranquil. Pleasant conversations and peaceful environments during meals ease the digestive process. Another factor in GI health is the kind of foods eaten. Among the characteristics of meals that promote optimal absorption of nutrients are those mentioned in Chapter 2: balance, moderation, variety and adequacy. Balance and moderation require having neither too much nor too little of anything. For example, too much fat can be harmful, but some fat is beneficial in slowing down intestinal motility and providing time for absorption of some of the nutrients that are slow to be absorbed. Variety is important for many reasons, but one is that some food constituents interfere with nutrient absorption. For example, some compounds common in high dietary fibre foods such as wholegrain cereals, certain leafy green vegetables, and legumes bind with minerals. To some extent, then, the minerals in those foods may become unavailable for absorption. These high-fibre foods are still valuable, but they need to be balanced with a variety of other foods that can provide the minerals. As for adequacy – in a sense, this entire book is about dietary adequacy. But here, at the end of this chapter, is a good place to emphasise the interdependence of the nutrients. It could almost be said that every nutrient depends on every other. All the nutrients work together, and all are present in the cells of a healthy digestive tract. To maintain health and promote the functions of the GI tract, you should make balance, moderation, variety and adequacy features of every day’s menus.
PUTTING COMMON SENSE TO THE TEST
The functions of the digestive tract are an example of the process of homeostasis. TRUE
REVIEW IT
A diverse and abundant bacteria population supports GI health. The regulation of GI processes depends on the coordinated efforts of the hormonal system and the nervous system. Together, digestion and absorption break down foods into nutrients for the body’s use. To function optimally, a healthy GI tract needs a balanced diet, adequate rest and regular physical activity
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 The process of food digestion begins in the mouth and proceeds all the way into the large intestine. TRUE
Food digestion and absorption is a process that occurs right along the gastrointestinal tract.
2 Intestinal cells are uniform all along the digestive tract. FALSE Intestinal cells have varying degrees of specialisation depending on
4 The gastrointestinal tract is sterile throughout. FALSE There are trillions of bacteria found throughout the gastrointestinal tract.
5 The functions of the digestive tract are an example of the process of homeostasis. TRUE The digestive tract is regulated at many different levels, from endocrine to neural, to maintain its functions.
where they are found along the digestive tract.
3 Veins and lymphatic vessels leaving the digestive tract carry nutrients to the body. TRUE Both veins and lymph vessels are important avenues of nutrient transport from the digestive tract.
NUTRITION PORTFOLIO A healthy digestive system can adjust to almost any diet and can handle any combination of foods with ease. • Describe the physical and emotional environment that typically surrounds your meals, including how it affects you and how it might be improved.
•
•
Detail any GI discomforts you may experience regularly and include suggestions to alleviate or prevent their occurrence (see Highlight 3). List any changes you can make in your eating habits to promote overall GI health.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book.
1
hydrolysis sphincters peristalsis bowel movements
7
emulsify fats catalyse hydrolysis slow protein digestion neutralise stomach acidity
The pancreas neutralises stomach acid in the small intestine by secreting: a b c d
bile mucus enzymes bicarbonate
mouth stomach small intestine large intestine
The specialised cells that increase gastrointestinal tract absorption area are called: a b c d
8
mouth small intestine stomach large intestine
Absorption occurs primarily in the: a b c d
The main function of bile is to: a b c d
4
6
The muscular contractions that move food through the GI tract are called: a b c d
3
trypsin amylase bile insulin
The digestion and absorption of carbohydrate occurs predominantly in the: a b c d
A key secretion of the gall bladder is: a b c d
2
5
pancreatic cells villi colonocytes islet cells
Which nutrients leave the GI tract by way of the lymphatic system? a b c d
water and minerals proteins and minerals All vitamins and minerals fats and fat-soluble vitamins
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Understanding nutrition
Digestion and absorption are coordinated by the: a b c d
pancreas and kidneys liver and gall bladder hormonal system and the nervous system vascular system and the lymphatic system
2
Describe the path food follows as it travels through the digestive system. Summarise the muscular actions that take place along the way. (Section 3.1)
3
Name five organs that secrete digestive juices. How do the juices and enzymes facilitate digestion? (Section 3.1)
4
Describe the problems associated with absorbing nutrients and the solutions offered by the small intestine. (Section 3.2)
5
How is blood directed through the digestive system? Which nutrients enter the bloodstream directly? Which are first absorbed into the lymph? (Section 3.3)
6
What role do microbes have in digestive processes? (Section 3.4)
7
Describe how the body coordinates and regulates the processes of digestion and absorption. (Section 3.4)
8
How does the composition of the diet influence the functioning of the GI tract? (Section 3.4)
•
Visit the Gastroenterological Society of Australia and highlight a section of the GI tract for further information: http://www.gesa.org.au For information on diseases of the GI tract, visit http://www.gastro-info.co.nz Visit the patient information section of the American College of Gastroenterology: http://www.acg.gi.org
10 One of the roles of gastrin is to: a b c d
increase salivary amylase production break down lactose promote stomach acid secretion increase bile secretion
Review questions These multiple choice questions will help you prepare for an exam. Answers can be found in the Answers section at the back of this book. 1
Describe the challenges associated with digesting food and the solutions offered by the human body. (Section 3.1)
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www. foodstandards.gov.au/science/monitoringnutrients/ pages/default.aspx
• •
SEARCH ME! NUTRITION Keyword: gut microbes The role of the gut microbiome in affecting health is getting more and more research attention. Read the
article Microbial ecology: Human gut microbes associated with obesity to appreciate how obesity is linked with a change in the microbial population of the gut.
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Chapter 3: Digestion, absorption and transport
3.5 COMMON DIGESTIVE PROBLEMS
HIGHLIGHT
3
Monkey Business Images/iStock/Getty Images
The facts of anatomy and physiology presented in Chapter 3 permit easy understanding of some common problems that occasionally arise in the digestive tract. Food may slip into the air passages instead of the oesophagus, causing choking. Bowel movements may be loose and watery, as in diarrhoea, or painful and hard, as in constipation. Some people complain about belching, while others are bothered by intestinal gas. Sometimes people develop medical problems such as an ulcer. This highlight describes some of the symptoms of these common digestive problems and suggests strategies for preventing them.
Choking Sometimes a sip of a beverage or a tiny bit of food ‘slips down the wrong pipe.’ The body’s first response is to cough, and quite often coughing clears the passage. When someone is truly choking, however, food has slipped into the trachea and completely blocked the air passageways (see Figure H3.1). Thus the person cannot cough – or even breathe. Without oxygen, the person may suffer brain damage within five minutes or even die. For this reason,
Healthy eating with some changes where needed can help avoid digestive problems.
it is imperative that everyone learns to recognise the universal distress signals for choking and to act promptly. To help a person who is choking, it is important to call for assistance and get this assisting person to dial 000 in Australia or 111 in New Zealand and request an ambulance. It is also important to first ask the person who
FIGURE H3.1 Normal swallowing and choking Tongue Food
Larynx rises Epiglottis closes over larynx
Oesophagus (to stomach) Trachea (to lungs)
Swallowing. The epiglottis closes over the larynx, blocking entrance to the lungs via the trachea. The red arrow shows that food is heading down the oesophagus normally.
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Choking. A choking person cannot speak or gasp because food lodged in the trachea blocks the passage of air. The red arrow points to where the food should have gone to prevent choking.
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is choking this critical question: Can you make any sound at all? If they can, you have time to decide what you can do to help. Encourage the person to relax and breathe deeply. Ask if they can cough. If they can cough, encourage them in a reassuring manner to do so. If they are unsuccessful, bend the choking person forward and give four sharp blows with the heel of your palm between the shoulder blades. This technique is called lateral chest thrusts and is carried out by using the heel of your hand in an upward movement between the shoulder blades. If this is still unsuccessful, place the person on their side on floor and wait for an ambulance. This advice is generic and in all cases, knowledge of first aid and regular training can save lives. Almost any food can cause choking, although some are cited more often than others: chunks of meat, hot dogs, nuts, whole grapes, raw carrots, marshmallows, hard or sticky candies, gum, popcorn and peanut butter. These foods are particularly difficult for young children to safely chew and swallow. Each year, approximately 500 children are admitted to hospitals in Australia for treatment of choking, of whom about 14 die.1 Inhaled food is the major cause of choking. Always remain alert to the dangers of choking whenever young children are eating. To prevent choking, cut food into small pieces, chew thoroughly before swallowing, don’t talk or laugh with food in your mouth and don’t eat when breathing hard.
Vomiting Vomiting can be a symptom of many different diseases or may arise in situations that upset the body’s equilibrium, such as air or sea travel. For whatever reason, the contents of the stomach are propelled up through the oesophagus to the mouth and expelled. Sometimes the muscular contractions will extend beyond the stomach and carry the contents of the duodenum, with its green bile, into the stomach and then up the oesophagus. Although certainly unpleasant and wearying for the nauseated person, vomiting is often not a cause for alarm. Vomiting is one of the body’s adaptive mechanisms to rid itself of something irritating. The best advice is to rest and drink small amounts of liquids as tolerated until the nausea subsides. Medical aid may be needed, however, when large quantities of fluid are lost from the GI tract, causing dehydration. With massive fluid loss from the GI tract, all the body’s other fluids redistribute themselves so that, eventually, fluid is taken from every cell of the body. Leaving the cells with the fluid are salts that are absolutely essential to the life of the cells, and they must be replaced. Replacement is difficult if the vomiting continues, and intravenous feedings of saline and glucose may be necessary while the medical practitioner
diagnoses the cause of the vomiting and begins corrective therapy. Self-induced vomiting, such as occurs in bulimia nervosa, also has serious consequences. In addition to fluid and salt imbalances, repeated vomiting can cause irritation and infection of the pharynx, oesophagus and salivary glands; erosion of the teeth and gums; and dental caries. The oesophagus may rupture or tear, as may the stomach. Sometimes the eyes become red from pressure during vomiting. Bulimic behaviour reflects underlying psychological problems that require intervention. (Bulimia nervosa is discussed fully in Highlight 8.)
Diarrhoea Diarrhoea is characterised by frequent, loose, watery stools. Such stools indicate that the intestinal contents have moved too quickly through the intestines for fluid absorption to take place, or that water has been drawn from the cells lining the intestinal tract and added to the food residue. Like vomiting, diarrhoea can lead to considerable fluid and salt losses, but the composition of the fluids is different. Stomach fluids lost in vomiting are highly acidic, whereas intestinal fluids lost in diarrhoea are nearly neutral. When fluid losses require medical attention, correct replacement is crucial. Diarrhoea is a symptom of various medical conditions and treatments. It may occur abruptly in a healthy person as a result of infections (such as food poisoning) or as a side effect of medications. When used in large quantities, food ingredients such as the sugar alternative sorbitol and the fat alternative olestra may also cause diarrhoea in some people. If a food is responsible, then that food must be omitted from the diet, at least temporarily. If medication is responsible, a different medicine, when possible, or a different form (injectable versus oral, for example) may alleviate the problem. Diarrhoea may also occur as a result of disorders of the GI tract, such as irritable bowel syndrome or colitis. Treatment for diarrhoea depends on cause and severity, but it always begins with rehydration. Mild diarrhoea may subside with simple rest and extra liquids (such as clear juices and soups) to replace fluid losses. If diarrhoea is bloody or if it worsens or persists – especially in an infant, young child, elderly person, or person with a compromised immune system – call a doctor. Severe diarrhoea can be life-threatening.
Irritable bowel syndrome Irritable bowel syndrome is one of the most common GI disorders and is characterised by frequent or severe abdominal discomfort and disturbance in the motility
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Chapter 3: Digestion, absorption and transport
Personal hygiene (such as regular hand washing with soap and water) and safe food preparation (as described in Chapter 19) are easy and effective steps to take in preventing diarrhoeal diseases.
of the GI tract.2 In most cases, GI contractions are stronger and last longer than normal, forcing intestinal contents through quickly and causing gas, bloating and diarrhoea. In some cases, however, GI contractions are weaker than normal, slowing the passage of intestinal contents and causing constipation. The exact cause of irritable bowel syndrome is not known, but researchers are actively investigating the role of the nervous system.3 The condition seems to worsen for some people when they eat certain foods or during stressful events. These triggers seem to aggravate symptoms but not cause them. Dietary treatment hinges on identifying and avoiding individual foods that aggravate symptoms; small meals may also be beneficial. Other treatments that may be effective include antispasmodic drugs and peppermint oil.
Colitis People with colitis, an inflammation of the large intestine, may also suffer from severe diarrhoea. They often benefit from complete bowel rest and medication. If treatment fails, surgery to remove the colon and rectum may be necessary.
Coeliac disease Coeliac disease is an autoimmune disease characterised by inflammation of the small intestine that occurs in response to foods that contain gluten, a protein commonly found in wheat, barley, rye, and possibly oats. Coeliac disease affects around 1 per cent of the population. In people with coeliac disease, gluten triggers an immune system reaction in the small intestine that causes inflammation, which damages the villi and decreases nutrient absorption. Signs of malnutrition – such as anaemia, weak and brittle bones, and dermatitis – may become apparent. Common
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symptoms include abdominal pains, bloating and flatulence, weight loss and chronic diarrhoea – making it challenging to diagnose. An accurate diagnosis depends on results from a blood test and a biopsy of the small intestine. Treatment focuses on a gluten-free diet, which allows the small intestine to heal. A gluten-free diet must eliminate not only wheat, barley, rye and, most often, oats but also many processed items made with these grains, such as bouillon cubes, hot dogs, gravies, salad dressings, soups and some dietary supplements. People with coeliac disease learn to read food labels and to ask specific questions at restaurants in order to determine what are gluten-free foods. Some people who do not test positive for coeliac disease seem to have similar symptoms that tend to diminish when on a gluten-free diet and return when gluten is reintroduced into the diet. These people may be described as having non-coeliac gluten sensitivity.4 Quite often, they tend to self-diagnose and self-treat, which presents a problem because a gluten-free diet interferes with an accurate diagnosis of coeliac disease.5 Whether the symptoms in non-coeliac gluten sensitivity are responding to gluten or FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) in similar foods is unclear.6 The popularity of gluten-free diets and products has grown dramatically in recent years, in part because of noncoeliac gluten sensitivity.7 In addition, some consumers seem slightly confused and mistakenly believe that if a product is free of something, then that missing something must be bad. Another common misconception is that a gluten-free diet is a weight-loss diet. Despite claims that eliminating gluten from the diet helps with a variety of ailments, there is no evidence to suggest that a gluten-free diet is beneficial for the general population, and it may even have unintended consequences.8
Constipation Like diarrhoea, constipation describes a symptom, not a disease. Each person’s GI tract has its own cycle of waste elimination, which depends on its owner’s health, the type of food eaten, when it was eaten and when the person takes time to defecate. What’s normal for some people may not be normal for others. Some people have bowel movements three times a day; others may have them three times a week. The symptoms of constipation include straining during bowel movements, hard stools and infrequent bowel movements (fewer than three per week). Abdominal discomfort, headaches, backaches and flatulence sometimes accompany constipation. Often, a person’s lifestyle may cause constipation. Being too busy to respond to the defecation signal is a common complaint. If a person receives the signal to defecate and ignores it, the signal may not return for several hours.
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In the meantime, water continues to be withdrawn from the faecal matter, so when the person does defecate, the stools are dry and hard. In such a case, a person’s daily regimen may need to be revised to allow time to have a bowel movement when the body sends its signal. Although constipation usually reflects lifestyle habits, in some cases it may be a side effect of medication or reflect a medical problem such as a bowel obstruction. If discomfort is associated with passing faecal matter, seek medical advice to rule out disease. Once this has been done, simple treatments, such as increased dietary fibre, fluids and exercise, are recommended before the use of medications. One dietary measure that may be appropriate is to increase dietary fibre to between 25 and 28 grams per day gradually over the course of a week or two. Dietary fibre found in fruits, vegetables and whole grains helps to prevent constipation by increasing faecal mass. In the GI tract, fibre attracts water, creating soft, bulky stools that stimulate bowel contractions to push the contents along. These contractions strengthen the intestinal muscles. The improved muscle tone, together with the water content of the stools, eases elimination, reducing the pressure in the rectal veins and helping to prevent haemorrhoids. (Chapter 4 provides more information on fibre’s role in maintaining a healthy colon and reducing the risks of colon cancer and diverticulitis.) Diverticulitis is a condition in which the intestinal walls develop bulges in weakened areas, most commonly in the colon (see Figure H3.2). These bulging pockets, known as diverticula, can worsen constipation, entrap faeces and become painfully infected and inflamed (diverticulitis). Treatment may require hospitalisation, antibiotics or surgery.
FIGURE H3.2 Diverticula in the colon Diverticula may develop anywhere along the GI tract, but they are most common in the colon.
Drinking plenty of water in conjunction with eating high-fibre foods also helps to prevent constipation. The increased bulk physically stimulates the upper GI tract, promoting peristalsis throughout. Similarly, physical activity improves the muscle tone and motility of the digestive tract. As little as 30 minutes of physical activity a day can help prevent or alleviate constipation. If these suggested changes in lifestyle or diet do not correct constipation, then a doctor might recommend the use of stool softeners, laxatives or mineral oil. These products are best used for brief periods. If needed for extended times, they should be used under physician supervision. Frequent use of laxatives can lead to dependency and upset the body’s fluid, salt, and mineral balances. Mineral oil interferes with the absorption of fat-soluble vitamins. One potentially harmful but currently popular practice is colonic irrigation – the internal washing of the large intestine with a powerful enema machine. Such an extreme cleansing is not only unnecessary but can be hazardous, especially for those with a history of digestive diseases. Side effects may be relatively minor (cramping, abdominal pain, bloating, nausea and vomiting) or quite severe (infections, kidney failure, pancreatitis and heart failure), sometimes leading to death.9 Common problems include equipment contamination, electrolyte abnormalities and intestinal perforation. Less extreme practices can cause problems, too.
Belching and flatulence Many people complain of problems that they attribute to excessive flatulence. For some, belching is the complaint. Others blame intestinal gas for abdominal discomforts and embarrassment.
Belching Belching results from swallowing air. Everyone swallows a little bit of air with each mouthful of food, but people who eat too quickly may swallow too much air. Ill-fitting dentures, carbonated beverages and chewing gum can also contribute to the swallowing of air with resultant belching. The best advice for belching seems to be to eat slowly, chew thoroughly and relax while eating.
Flatulence Diverticula (plural)
Diverticulum (singular)
Although flatulence can be an embarrassing experience, it is quite normal. (People who experience painful bloating from malabsorption diseases, however, require medical treatment.) Healthy people expel several hundred millilitres of intestinal gas several times a day. Almost all (99 per cent) of the gases expelled – nitrogen, oxygen, hydrogen, methane and carbon dioxide – are odourless. The remaining ‘volatile’ gases are the infamous ones.
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Chapter 3: Digestion, absorption and transport
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Foods that usually produce gas must be determined individually. The most common offenders are foods rich in the carbohydrates – sugars, starches and fibre. When partially digested carbohydrates reach the large intestine, bacteria digest them, giving off gas as a by-product. People can test foods suspected of forming gas by omitting them individually for a trial period to see if there is any improvement.
People troubled by flatulence need to determine which foods bother them and then eat those foods in moderation.
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Gastro-oesophageal reflux Almost everyone has experienced heartburn at one time or another, usually soon after eating a meal. Medically known as gastro-oesophageal reflux, heartburn is the painful sensation a person feels behind the breastbone (sternum) when the lower oesophageal sphincter allows the stomach contents to reflux into the oesophagus (see Figure H3.3). This may happen if a person eats or drinks too much (or both). Tight clothing and even changes of position (lying down, bending over) can cause it, too, as can some medications and smoking. Weight gain and overweight increase the frequency, severity and duration of heartburn symptoms. A defect of the sphincter muscle itself is a possible, but less common, cause. If the heartburn is not caused by an anatomical defect, treatment is fairly simple. To avoid such misery in the future, the person needs to learn to eat less at a sitting, chew food more thoroughly and eat it more slowly. Additional strategies are presented in Table H3.1. People who overeat or eat too quickly are likely to suffer from indigestion. The muscular reaction of the stomach to unchewed lumps or to being overfilled may be so intense that it upsets normal peristalsis. When this happens, overeaters may taste the stomach acid and feel pain. Over-the-counter antacids and acid controllers may provide relief but should be used
FIGURE H3.3 Gastro-oesophageal reflux Oesophagus Reflux Diaphragm Weakened lower oesophageal sphincter
Acidic stomach contents Stomach
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Understanding nutrition
only infrequently for occasional heartburn; they may mask or cause problems if used regularly. If problems continue, people who suffer from frequent and regular bouts of heartburn and indigestion may need to see a physician, who can prescribe specific medication to control gastro-oesophageal reflux. Without treatment, the repeated splashes of acid can severely damage the cells of the oesophagus, creating a condition known as Barrett’s oesophagus. At that stage, the risk of cancer in the oesophagus increases dramatically.10 To repeat, if symptoms persist, see a doctor – don’t self-medicate.
Ulcers Ulcers are another common digestive problem. An ulcer is a lesion (a sore), and a peptic ulcer is a lesion in the
lining of the stomach (gastric ulcers) or the duodenum of the small intestine (duodenal ulcers). The compromised lining is left unprotected and exposed to gastric juices, which can be painful. In some cases, ulcers can cause internal bleeding. If GI bleeding is excessive, iron deficiency may develop. Ulcers that perforate the GI lining can pose life-threatening complications. Many people naively believe that an ulcer is caused by stress or spicy foods, but this is not the case. The stomach lining in a healthy person is well protected by its mucus coat. What, then, causes ulcers to form? Three major causes of ulcers have been identified: bacterial infection with Helicobacter pylori (commonly abbreviated H. pylori); the use of certain antiinflammatory drugs such as aspirin, ibuprofen and naproxen; and disorders that cause excessive gastric acid
TABLE H3.1 Strategies to prevent or alleviate common GI problems GI PRODUCT
STRATEGIES
Choking
Take small bites of food. Chew thoroughly before swallowing. Don’t talk or laugh with food in your mouth. Don’t eat when breathing hard.
Diarrhoea
Avoid strenuous activity. Rest. Drink fluids to replace losses. Call for medical help if diarrhoea persists.
Constipation
Eat a high-fibre diet. Drink plenty of fluids. Exercise regularly. Respond promptly to the urge to defecate.
Belching
Eat slowly. Chew thoroughly. Relax while eating.
Intestinal gas/bloating
Eat troublesome foods in moderation.
Heartburn
Eat small meals. Drink liquids between meals. Sit up while eating; elevate your head when lying down. Wait three hours after eating before lying down. Wait two hours after eating before exercising. Refrain from wearing tight-fitting clothing. Avoid foods, beverages and medications that aggravate your heartburn. Common irritants include foods that are fried or high in fat; chocolate and peppermint; coffee, alcoholic beverages, and carbonated beverages; mustard, ketchup and tomato sauces; acidic substances such as vinegar, citrus juices and citrus fruits. Refrain from smoking cigarettes or using tobacco products. Lose weight if overweight.
Ulcer
Take medicine as prescribed by your doctor. Avoid coffee and caffeine- and alcohol-containing beverages. Avoid foods that aggravate your ulcer. Minimise aspirin, ibuprofen and naproxen use. Refrain from smoking cigarettes.
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Chapter 3: Digestion, absorption and transport
secretion. Most commonly, ulcers develop in response to H. pylori infection. This discovery was revolutionary as it had been long thought that no bacteria could live in the harsh acid environment of the stomach. Professor Robin Warren, a pathologist working at the Royal Perth Hospital, Western Australia, observed corkscrew-shaped bacteria in stomach samples he was examining. Despite his best efforts to convince colleagues and other scientists, it was a physician, Dr Barry Marshall, who took up the challenge and he, too, became convinced that many patients with stomach ulcers could be cured with a simple treatment of common antibiotics. It was a long road, with the turning point coming late in 1981 when Warren and Marshall succeeded in culturing the microbes and Marshall took the bold step of drinking some of them. Within days he was suffering the first signs of stomach ulcers, and the rest is now history – Warren and Marshall received the Nobel Prize for Medicine in 2005. Today, the standard treatment involves antibiotics that tackle the offending H. pylori bacteria, in conjunction with changes to lifestyle and diet that routinely cause indigestion or pain. This may include avoiding coffee and caffeine- and alcohol-containing beverages. Both regular and decaffeinated coffee stimulate acid secretion and so aggravate existing ulcers.
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Ulcers and their treatments highlight the importance of not self-medicating when symptoms persist. People with H. pylori infection often take over-the-counter acid controllers to relieve the pain of their ulcers when, instead, they need physician-prescribed antibiotics. Suppressing gastric acidity not only fails to heal the ulcer, but also actually worsens inflammation during an H. pylori infection. Furthermore, H. pylori infection has been linked with stomach cancer, making prompt diagnosis and appropriate treatment essential.
Summary Table H3.1 summarises strategies to prevent or alleviate common GI problems. Many of these problems reflect hurried lifestyles. For this reason, many of their remedies require that people slow down and take the time to eat leisurely; chew food thoroughly to prevent choking, heartburn and acid indigestion; rest until vomiting and diarrhoea subside; and heed the urge to defecate. In addition, people must learn how to handle life’s day-today problems and challenges without overreacting and becoming upset; learn how to relax, get enough sleep and enjoy life. Remember, ‘what’s eating you’ may cause more GI distress than what you eat.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1 2
Compare the energy, dietary fibre, added sugars, and saturated fat on the labels of two similar products – one wholegrain and the other glutenfree – and determine what benefits and risks might accompany a gluten-free diet for those with coeliac disease and for others. Which product would you now be more likely to buy? Why?
What strategies would be most helpful in preventing common digestive problems? The demand for gluten-free products has increased dramatically over the past decade as gluten-free diets have gained in popularity. Although a glutenfree diet is the best treatment for people with coeliac disease, it has been adopted by millions of other people for a variety of other reasons.
REFERENCES CHAPTER 1
2
G. Pradhan and co-authors, Ghrelin: Much more than a hunger hormone, Current Opinion in Clinical Nutrition and Metabolic Care 16 (2013): 619–24. S. V. Lynch and O. Pedersen, The human intestinal microbiome in health and disease, New England Journal of Medicine 375 (2016): 2369–79.
3
4
R. K. Singh and co-authors, Influence of diet on the gut microbiome and implications for human health, Translational Medicine 15 (2017): 73. E. LeChatelier and co-authors, Richness of human gut microbiome correlates with metabolic markers, Nature 500 (2013): 541–6.
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I. Moreno-Indias and co-authors, Impact of the gut microbiota on the development of obesity and type 2 diabetes mellitus, Frontiers in Microbiology 5 (2014): 1–10. L. A. David and co-authors, Diet rapidly and reproducibly alters the human gut microbiome, Nature 505 (2014): 559–63. V. A. do Rosario, R. Fernandes, and E. B. S. de M. Trindade, Vegetarian diets and gut microbiota: Important shifts in markers of metabolism and cardiovascular disease, Nutrition Reviews 74 (2016): 444–54. J. Tan and co-authors, The role of short-chain fatty acids in health and disease, Advances in Immunology 121 (2014): 91–119. J. Breton and co-authors, Gut commensal E. coli proteins activate host satiety pathways following nutrient-induced bacterial growth, Cell Metabolism 23 (2016): 324–34.
10 S. Lohner and co-authors, Prebiotics in healthy infants and children for prevention of acute infectious diseases: A systematic review and meta-analysis, Nutrition Reviews 72 (2014): 523–31; S. Hempel and co-authors, Probiotics for the prevention and treatment of antibioticassociated diarrhea: A systematic review and meta-analysis, Journal of the American Medical Association 307 (2012): 1959–69; B. C. Johnston and co-authors, Probiotics for the prevention of Clostridium difficileassociated diarrhea: A systematic review and meta-analysis, Annals of Internal Medicine 157 (2012): 878–88; M. Kumar and co-authors, Probiotic metabolites as epigenetic targets in the prevention of colon cancer, Nutrition Reviews 71 (2012): 23–34. 11 D. B. DiRienzo, Effect of probiotics on biomarkers of cardiovascular disease: Implications for heart-healthy diets, Nutrition Reviews 72 (2014): 18–29.
HIGHLIGHT 1 2 3
4
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B. J. Fotheringham, Alice in Blunderland, Medical Journal of Australia 173 (2000): 659–60. M. Halland and Y. A. Saito, Irritable bowel syndrome: new and emerging treatments, British Medical Journal 350 (2015): h1622. C. Stasi and co-authors, Serotonin receptors and their role in the pathophysiology and therapy of irritable bowel syndrome, Techniques in Coloproctology 18 (2014): 613–21. A. Fasano and co-authors, Nonceliac gluten sensitivity, Gastroenterology 148 (2015): 1195–1204; L. Elli, L. Roncoroni, and M. T. Bardella, Nonceliac gluten sensitivity: Time for sifting the grain, World Journal of Gastroenterology 21 (2015): 8221–6. M. El-Salhy and co-authors, The relation between celiac disease, nonceliac gluten sensitivity and irritable bowel syndrome, Nutrition Journal 14 (2015): 92–100.
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M. Vazquez-Roque and A. S. Oxentenko, Nonceliac gluten sensitivity, Mayo Clinic Proceedings 90 (2015): 1272–7. B. Lebwohl, J. F. Ludvigsson, and P. H. Green, Celiac disease and nonceliac gluten sensitivity, British Medical Journal 351 (2015): h4347. K. Stein, Severely restricted diets in the absence of medical necessity: The unintended consequences, Journal of the Academy of Nutrition and Dietetics 114 (2014): 986–94; G. A. Gaesser and S. S. Angadi, Glutenfree diet: Imprudent dietary advice for the general population? Journal of the Academy of Nutrition and Dietetics 112 (2012): 1330–3. R. Mishori, A. Otubu, A. A. Jones, The dangers of colon cleansing, Journal of Family Practice 60 (2011): 454–7. S. J. Spechler and R. F. Souza, Barrett’s esophagus, New England Journal of Medicine 371 (2014): 836–45.
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CHAPTER
4
THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE Nutrition in your life
Whether you are cramming for an exam or daydreaming about your next holiday, your brain needs carbohydrate to power its activities. Your muscles need carbohydrate to fuel their work, too, whether you are racing to get to class on time or enjoying a swim in the summer warmth. Where can you get carbohydrate? Are some foods healthier choices than others? As you will learn from this chapter, whole grains, vegetables, legumes and fruits naturally deliver ample carbohydrate and fibre with valuable vitamins and minerals and little or no fat. Milk products typically lack fibre, but they also provide carbohydrate along with an assortment of vitamins and minerals. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F Complex carbohydrates are long chains of monosaccharides joined together. T F The majority of carbohydrate digestion occurs in the large intestine. T F People who suffer lactose intolerance must avoid all dairy foods. T F Glucose fuels the majority of the body’s energy needs.
LEARNING OBJECTIVES 4.1 Identify the monosaccharides, disaccharides, and polysaccharides common in nutrition by their chemical structures and major food sources. 4.2 Identify the three important monosaccharides and three important disaccharides in the human diet. 4.3 Identify the three types of polysaccharides important in nutrition. 4.4 Summarise carbohydrate digestion and absorption. 4.5 Explain how the body maintains its blood glucose concentration and what happens
when blood glucose rises too high or falls too low. 4.6 Describe how added sugars can contribute to health problems. 4.7 Identify the three common types of alternative sweeteners and their chemical properties. 4.8 Identify the health benefits of, and recommendations for, starches and fibres. 4.9 Summarise the key scientific evidence behind some of the current controversies surrounding carbohydrates and their kilojoules.
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A student, quietly studying a textbook, is seldom aware that within their brain cells, billions of glucose molecules are splitting to provide the energy to permit learning. Yet glucose provides nearly all of the energy the human brain uses daily. Similarly, a marathon runner, bursting across the finish line in an explosion of sweat and triumph, seldom gives credit to the glycogen fuel that is devoured to help them finish the race. Yet, together, these two carbohydrates – glucose and its storage form, glycogen – provide about half of all the energy that muscles and other body tissues use. The other half of the body’s energy comes mostly from fat. People eat very little glucose and glycogen in their foods directly. When they eat foods rich in carbohydrates, their bodies receive glucose for immediate energy and convert the remainder into glycogen for reserve energy. All plant foods – whole grains, vegetables, legumes and fruits – provide carbohydrate. Dairy foods also contain carbohydrates. Many people mistakenly think of carbohydrates as ‘fattening’ and avoid them when trying to lose weight. Such a strategy may be helpful if the carbohydrates are the simple sugars of soft drinks, lollies and biscuits, but it is counterproductive if the carbohydrates are the complex carbohydrates of whole grains, vegetables and legumes. As the next section explains, not all carbohydrates are created equal.
FIGURE 4.1 Atoms and their bonds The four main types of atoms found in nutrients are hydrogen (H), oxygen (O), nitrogen (N) and carbon (C).
4.1 The chemist’s view of carbohydrates
The dietary carbohydrate family includes the simple carbohydrates (the sugars) and the complex carbohydrates (the starches and fibre). The simple carbohydrates are those that chemists describe as: • monosaccharides – single sugars O N C H • disaccharides – sugars composed of pairs of monosaccharides. 1 2 3 4 The complex carbohydrates are: Each atom has a characteristic number • polysaccharides – large molecules composed of chains of monosaccharides. of bonds it can form with other atoms. Each atom can form a certain number of chemical bonds with other atoms: • carbon atoms can form four bonds H H • nitrogen atoms, three H C C O H • oxygen atoms, two H H • hydrogen atoms, only one. Chemists represent the bonds as lines between the chemical symbols (such as Notice that in this simple molecule of ethyl alcohol, each H has one bond, C, N, O and H) that stand for the atoms (see Figure 4.1). O has two and each C has four. Atoms form molecules in ways that satisfy the bonding requirements of each atom. Figure 4.1 includes the structure of ethyl alcohol, the active ingredient of alcoholic beverages, as an example. The two carbons each have four bonds represented by lines, the oxygen has two, and each hydrogen has one bond connecting it to other atoms. Chemical structures bond according to these rules as dictated by nature.
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Most of the monosaccharides important in nutrition are hexoses, simple sugars with six atoms of carbon and the formula C6H12O6 • hex 5 six
The carbohydrates are made of carbon (C), oxygen (O) and hydrogen (H). Each of these atoms can form a specified number of chemical bonds: carbon forms four, oxygen forms two and hydrogen forms one.
4.2 The simple carbohydrates
The following list of the most important simple carbohydrates in nutrition symbolises them as hexagons and pentagons of different colours. Three are monosaccharides: • glucose • fructose • galactose
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Three are disaccharides: • maltose (glucose 1 glucose) • sucrose (glucose 1 fructose) • lactose (glucose 1 galactose) To understand the structure of carbohydrates, look at the units of which they are made. The monosaccharides most important in nutrition* each contain 6 carbon atoms, 12 hydrogens and 6 oxygen atoms (written in shorthand as C6H12O6).
Monosaccharides The three monosaccharides important in nutrition all have the same numbers and kinds of atoms, but in different arrangements. These chemical differences account for the differing sweetness of the monosaccharides. A pinch of purified glucose on the tongue gives only a mild sweet flavour, and galactose hardly tastes sweet at all. Fructose, however, is as intensely sweet as honey and, in fact, is the sugar primarily responsible for honey’s sweetness.
FIGURE 4.2 Chemical structure of glucose On paper, the structure of glucose has to be drawn flat, but in nature the five carbons and oxygen are roughly in a plane. The atoms attached to the ring carbons extend above and below the plane.
Glucose
Chemically, glucose is a larger and more complicated molecule than the ethanol H (alcohol) shown in Figure 4.1, but it obeys the same rules of chemistry: each carbon atom has four bonds; each oxygen, two bonds; and each hydrogen, one bond. Figure 4.2 H illustrates the chemical structure of a glucose molecule. C The diagram of a glucose molecule shows all the relationships between the atoms H O and proves simple on examination, but chemists have adopted even simpler ways to depict chemical structures. Figure 4.3 presents the chemical structure of glucose in a more simplified way by combining or omitting several symbols – yet it conveys the same information. Commonly known as blood sugar, glucose serves as an essential energy source for all the body’s activities. Its significance to nutrition is tremendous. Later sections explain that glucose is one of the two sugars in every disaccharide and the unit from which the majority of polysaccharides are made. One of these polysaccharides, starch, is the chief food source of energy for all the world’s people; another, glycogen, is an important storage form of energy in the body. Glucose reappears frequently throughout this chapter and all those that follow.
H C
O
C
H O
H
H O
H
C
H
C
C
H
O
O
H
H
FIGURE 4.3 Simplified diagrams of glucose CH2OH O H H H OH H HO OH H
OH
The lines representing some of the bonds and the carbons at the corners are not shown.
CH2OH O HO
OH
C C OH
OH Now the single hydrogens are not shown, but lines still extend upwards or downwards from the ring to show where they belong.
O
C
C C
C
Another way to look at glucose is to notice that its six carbon atoms are all connected.
In this and other illustrations throughout this book, glucose is represented as a blue hexagon.
* Fructose is shown as a pentagon, but like the other monosaccharides, it has six carbons (as you will see in Figure 4.4; see page 98).
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Fructose
Fructose is the sweetest of the sugars. Curiously, fructose has exactly the same chemical formula as glucose – C6H12O6 – but its structure differs (see Figure 4.4). The arrangement of the atoms in fructose stimulates the taste buds on the tongue to produce the sweet sensation. Fructose occurs naturally in fruits and honey; other sources include products such as some soft drinks, ready-toeat cereals and desserts, particularly those imported into Australia and New Zealand that have been sweetened with high-fructose corn syrup (defined in Table 4.1 on page 113).
Galactose
The monosaccharide galactose occurs naturally as a single sugar in only a few foods. Galactose has the same numbers and kinds of atoms as glucose and fructose in yet another arrangement. Figure 4.5 shows galactose beside a molecule of glucose for comparison.
FIGURE 4.5 Two monosaccharides: glucose and galactose
FIGURE 4.4 Two monosaccharides: glucose and fructose
Notice the similarities and the difference (highlighted in red) between glucose and galactose. Both have 6 carbons, 12 hydrogens and 6 oxygens, but the position of one OH group differs slightly.
Can you see the similarities? If you learned the rules in Figure 4.3, you will be able to ‘see’ 6 carbons (numbered), 12 hydrogens (those shown plus one at the end of each single line) and 6 oxygen atoms in both these compounds. 6
CH2OH 5
4 HO
OH 3
6 HOCH2
O
1
5
1 2
CH2OH
O
4
OH Glucose
OH
O
O
CH2OH
2 HO
OH
CH2OH
HO
OH
OH
3
HO OH
OH OH
OH Galactose
Glucose
Fructose
OH
Disaccharides The disaccharides are pairs of the three monosaccharides just described. Glucose occurs in all three; the second member of the pair is either fructose, galactose or another glucose. These carbohydrates – and all the other energy nutrients – are put together and taken apart by similar chemical reactions: condensation and hydrolysis.
Condensation
To make a disaccharide, a chemical reaction known as condensation links two monosaccharides together (see Figure 4.6). A hydroxyl (OH) group from one
FIGURE 4.6 Condensation of two monosaccharides to form a disaccharide iStockphoto/Ivan Bajic
CH2OH O HO Fruits package their simple sugars with fibre, vitamins and minerals, making them a sweet and healthy snack.
OH
CH2OH O OH
H
O
OH
OH
CH2OH O OH
OH H2O Water
Glucose + glucose An OH group from one glucose and an H atom from another glucose combine to create a molecule of H2O.
HO
CH2OH O
OH
OH OH
O +
OH OH
H2O Water Maltose The two glucose molecules bond together with a single O atom to form the disaccharide maltose.
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Chapter 4: The carbohydrates: sugars, starches and dietary fibre
monosaccharide and a hydrogen atom (H) from the other combine to create a molecule of water (H2O). The two originally separate monosaccharides link together with a single oxygen (O).
Reminder: A hydrolysis reaction splits a molecule into two, with H added to one and OH to the other (from water); Chapter 3 explained that hydrolysis reactions break down molecules during digestion.
Hydrolysis
To break a disaccharide in two, a chemical reaction known as hydrolysis occurs (see Figure 4.7). A molecule of water splits to provide the H and OH needed to complete the resulting monosaccharides. Hydrolysis reactions commonly occur during digestion.
FIGURE 4.7 Hydrolysis of a disaccharide
CH2OH O HO
Bond broken
OH
CH2OH O OH
OH
O Water H OH
CH2OH O OH
OH
HO
OH
99
CH2OH O + OH
HO
OH
OH
OH OH
Bond broken Maltose
Glucose + glucose
Polara Studios, Inc.
The disaccharide maltose splits into two glucose molecules with H added to one and OH to the other (from the water molecule).
Maltose
The disaccharide maltose consists of two glucose units. Maltose is produced whenever starch breaks down – as happens in human beings during carbohydrate digestion. It also occurs during the fermentation process that yields alcohol. Maltose is only a minor constituent of a few foods, most notably barley.
Sucrose
Major sources of starch include grains (such as rice, wheat, millet, rye, barley and oats), legumes (such as kidney beans, cannellini beans, peas, chickpeas and lentils), tubers (such as potatoes) and root crops (such as sweet potato and cassava).
Fructose and glucose together form sucrose. Because the fructose is accessible to the taste receptors, sucrose tastes sweet, accounting for some of the natural sweetness of fruits, vegetables and grains. To make table sugar, sucrose is refined from the juices of sugar cane and then granulated. Depending on the extent to which it is refined, the product becomes the familiar brown, white and powdered sugars available at supermarkets.
Lactose
The combination of galactose and glucose makes the disaccharide lactose, the principal carbohydrate of milk. Known as milk sugar, lactose contributes half of the energy (kilojoules) provided by fat-free milk.
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Six simple carbohydrates, or sugars, are important in nutrition. The three monosaccharides (glucose, fructose and galactose) all have the same chemical formula (C6H12O6), but their structures differ. The three disaccharides (maltose, sucrose and lactose) are pairs of monosaccharides, each containing a glucose paired with one of the three monosaccharides. These sugars derive primarily from plants, except for lactose and its component galactose, which come from milk and milk products. Two monosaccharides can be linked together by a condensation reaction to form a disaccharide and water. A disaccharide, in turn, can be broken into its two monosaccharides by a hydrolysis reaction using water.
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4.3 The complex carbohydrates
In contrast to the simple sugars just mentioned, complex carbohydrates contain many glucose units and, in some cases, a few other monosaccharides strung together as, firstly, oligosaccharides and, secondly, as the larger polysaccharides. Three types of polysaccharides are important in nutrition: glycogen, starches and fibre. Glycogen is a storage form of energy in the animal body; starches play that role in plants; and fibre provides structure in stems, trunks, roots, leaves and skins of plants. Both glycogen and starch are built of glucose units. Fibre is composed of a variety of monosaccharides and other carbohydrate derivatives.
Glycogen Glycogen is found to only a limited extent in meats and not at all in plants.* For this reason, food is not a significant source of glycogen. However, glycogen does perform an important role in the body. The human body stores glucose as glycogen – many glucose molecules linked together in highly branched chains (see the left-hand side of Figure 4.8). This arrangement permits rapid hydrolysis. When the hormonal message ‘release energy’ arrives at the glycogen storage sites in a liver or muscle cell, enzymes respond by attacking the many branches of glycogen simultaneously, making a surge of glucose available.** FIGURE 4.8 Glycogen and starch molecules compared (small segments) Notice that the more highly branched the structure, the greater the number of ends from which glucose can be released. (These units would have to be magnified millions of times to appear at the size shown in this figure. For details of the chemical structures, see Appendix C.)
Starch (amylopectin)
Glycogen A glycogen molecule contains hundreds of glucose units in highly branched chains. Each new glycogen molecule needs a special protein for the attachment of the first glucose (shown here in red).
Starch (amylose)
A starch molecule contains hundreds of glucose molecules in either occasionally branched chains (amylopectin) or unbranched chains (amylose).
Starches The human body stores glucose as glycogen, but plant cells store glucose as starches – long, branched or unbranched chains of hundreds or thousands of glucose molecules linked together (see the middle and right-hand side of Figure 4.8). These giant starch
* Glycogen in animal muscles rapidly hydrolyses after slaughter. ** Normally, only liver cells can produce glucose from glycogen to be sent directly to the blood; muscle cells can also produce glucose from glycogen, but must use it themselves. Muscle cells can restore the blood glucose level indirectly, however, as Chapter 7 explains.
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Chapter 4: The carbohydrates: sugars, starches and dietary fibre
molecules are packed side by side in grains such as wheat or rice, in root crops and tubers such as sweet potatoes and potatoes, and in legumes such as lentils and beans. When you eat the plant, your body hydrolyses the starch to glucose and uses the glucose for its own energy purposes. All starchy foods come from plants. Grains are the richest food source of starch, providing much of the food energy for people all over the world – rice in Asia; wheat in Australia, New Zealand, the United States and Europe; corn in much of Central and South America; and millet, rye, barley and oats elsewhere. Legumes and tubers are also important sources of starch.
101
PUTTING COMMON SENSE TO THE TEST
Complex carbohydrates are long chains of monosaccharides joined together. TRUE
Fibre Dietary fibre is the structural parts of plants and thus is found in all plant-derived foods – vegetables, fruits, whole grains and legumes. Most dietary fibre is made up of polysaccharides. As mentioned earlier, starches are also polysaccharides, but dietary fibre differs from starches in that the bonds between their monosaccharides cannot be broken down by digestive enzymes in the body. For this reason, dietary fibres are often described as non-starch polysaccharides.* Figure 4.9 illustrates the difference in the bonds that link glucose molecules together in starch with those found in the fibre cellulose. Because dietary fibre passes through the body, it contributes no monosaccharides, and therefore little or no energy. Even though most foods contain a variety of fibre, researchers often sort dietary fibre into two groups according to their solubility. Such distinctions help to explain their actions in the body.
Soluble fibre
Dietary fibre occurs naturally in intact plants. Functional fibre is sometimes used as a term to describe fibre that has been extracted from plants or manufactured and has beneficial effects in human beings. In manufactured foods, total fibre is the sum of dietary fibre and functional fibre.
Some dietary fibre dissolves in water (soluble fibre), forms gels (viscous) and is easily digested by bacteria in the colon (fermentable). Commonly found in oats, barley, legumes and citrus fruits, soluble fibre is most often associated with FIGURE 4.9 Starch and cellulose protecting against heart disease and diabetes by lowering blood cholesterol and molecules compared (small segments) glucose levels, respectively.1 The bonds that link the glucose
Insoluble fibre
Other fibre does not dissolve in water (insoluble fibre), does not form gels (non-viscous) and is less readily fermented. Found mostly in whole grains (bran) and vegetables, insoluble fibre promotes bowel movements and alleviates constipation.
molecules together in cellulose are different from the bonds in starch (and glycogen). Human enzymes cannot digest cellulose. See Appendix C for chemical structures and descriptions of linkages.
Resistant starches
A few starches are also classified as dietary fibre. Known as resistant starches, these starches escape digestion and absorption in the small intestine. Starch may resist digestion for several reasons, including the individual’s efficiency in digesting starches and the food’s physical properties. Resistant starch is common in whole legumes, raw potatoes and unripe bananas.
Starch
Cellulose
Phytic acid
Although not classified as a dietary fibre, phytic acid is often found accompanying them in the same foods. Because of this close association, researchers have been unable to determine whether it is the dietary fibre, the phytic acid or both that binds with minerals, preventing their absorption. This binding presents a risk of mineral deficiencies, but the risk is minimal
* The non-starch polysaccharide fibres include cellulose, hemicelluloses, pectins, gums and mucilages. Fibres also include some non-polysaccharides such as lignins, cutins and tannins.
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when total fibre intake is reasonable and mineral intake adequate. The nutrition consequences of such mineral losses are described further in Chapters 12 and 13.
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The short chains of glucose units that result from the breakdown of starch are known as dextrins. The word sometimes appears on food labels because dextrins can be used as thickening agents in processed foods. Reminder: A bolus is a portion of food swallowed at one time.
The complex carbohydrates are the polysaccharides (chains of monosaccharides): glycogen, starches and dietary fibre. Both glycogen and starch are storage forms of glucose – glycogen in the body, and starch in plants – and both yield energy for human use. Dietary fibre also contains glucose (and other monosaccharides), but its bonds cannot be broken by human digestive enzymes, so it yields little, if any, energy. The accompanying table summarises the carbohydrate family of compounds.
The carbohydrate family SIMPLE CARBOHYDRATES (SUGARS) Monosaccharides: • glucose • fructose • galactose.
COMPLEX CARBOHYDRATES Polysaccharides: • glycogen* • starches • fibres.
Disaccharides: • maltose • sucrose • lactose. * Glycogen is a complex carbohydrate (a polysaccharide) but not a dietary source of carbohydrate.
4.4 Digestion and absorption of carbohydrates
The ultimate goal of digestion and absorption of sugars and starches is to break them into small molecules – chiefly glucose – that the body can absorb and use. The large starch molecules require extensive breakdown; the disaccharides need only be broken once, and the monosaccharides not at all. The initial splitting begins in the mouth; the final splitting and absorption occur in the small intestine; and conversion to a common energy currency (glucose) takes place in the liver. The details follow.
Carbohydrate digestion Banana Stock
Figure 4.10 traces the digestion of carbohydrates through the GI tract. When a person eats foods containing starch, enzymes hydrolyse the long chains to shorter chains, the short chains to disaccharides and, finally, the disaccharides to monosaccharides. This process begins in the mouth. When a person eats carbohydrate-rich foods, the body receives a valuable commodity – glucose.
In the mouth
In the mouth, thoroughly chewing high-fibre foods slows eating and stimulates the flow of saliva. The salivary enzyme amylase starts to work, hydrolysing starch to shorter polysaccharides and to the disaccharide maltose. In fact, you can taste the change if you hold a piece of starchy food like a dry biscuit in your mouth for a few minutes without swallowing it – the dry biscuit begins tasting sweeter as the enzyme acts on it. Because food is in the mouth for only a short time, very little carbohydrate digestion takes place there; it begins again in the small intestine.
In the stomach The swallowed bolus mixes with the stomach’s acid and protein-digesting enzymes, which inactivate salivary amylase. Thus the role of salivary amylase in starch digestion is relatively minor. To a small extent, the stomach’s acid continues breaking down starch, but its juices
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FIGURE 4.10 Carbohydrate digestion in the GI tract STARCH
DIETARY FIBRE
Mouth and salivary glands The salivary glands secrete saliva into the mouth to moisten the food. The salivary enzyme amylase begins digestion: Starch
Amylase
Small polysaccharides, maltose
Mouth The mechanical action of the mouth crushes and tears dietary fibre in food and mixes it with saliva to moisten it for swallowing. Salivary glands
Mouth
Stomach Stomach Stomach acid inactivates salivary enzymes, halting starch digestion.
(Liver)
Stomach Dietary fibre is not digested, and it delays gastric emptying.
(Gall bladder)
Small intestine and pancreas The pancreas produces an amylase that is released through the pancreatic duct into the small intestine:
Starch
Pancreatic amylase
Small polysaccharides, maltose
Then disaccharidase enzymes on the surface of the small intestinal cells hydrolyse the disaccharides into monosaccharides: Glucose Maltose Maltase + Glucose Sucrose
Lactose
Sucrase
Lactase
Pancreas
Fructose + Glucose Galactose + Glucose
Small intestine Dietary fibre is not digested, and it delays absorption of other nutrients.
Small intestine Large intestine
Large intestine Most dietary fibre passes intact through the digestive tract to the large intestine. Here, bacterial enzymes digest dietary fibre: Some Bacterial Short-chain dietary enzymes fatty acids, fibre gas Dietary fibre holds water; regulates bowel activity; and binds substances such as bile, cholesterol and some minerals, carrying them out of the body.
Intestinal cells absorb these monosaccharides.
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contain no enzymes to digest carbohydrate. Dietary fibre lingers in the stomach and delays gastric emptying, thereby providing a feeling of fullness and satiety.
In the small intestine The small intestine performs most of the work of carbohydrate digestion. A major carbohydrate-digesting enzyme, pancreatic amylase, enters the intestine via the pancreatic duct and continues breaking down the polysaccharides to shorter glucose chains and maltose. The final step takes place on the outer membranes of the intestinal cells. There, specific enzymes break down specific disaccharides: • Maltase breaks maltose into two glucose molecules. • Sucrase breaks sucrose into one glucose and one fructose molecule. • Lactase breaks lactose into one glucose and one galactose molecule. At this point, all polysaccharides and disaccharides have been broken down to monosaccharides – mostly glucose molecules, with some fructose and galactose molecules as well.
Reminder: In general, the word ending -ase identifies an enzyme, and the beginning of the word identifies the molecule that the enzyme works on. Starches and sugars are called available carbohydrates because human digestive enzymes break them down for the body’s use. In contrast, dietary fibre is called unavailable carbohydrate because human digestive enzymes cannot break the bonds.
In the large intestine Within one to four hours after a meal, all the sugars and most of the starches have been digested. Only the dietary fibre remains in the digestive tract. Dietary fibre in the large intestine attracts water, which softens the stools for passage without straining. Also, bacteria in the GI tract ferment some dietary fibre. This process generates water, gas and short-chain fatty acids (described in Chapter 5).* The colon uses these small fat molecules for energy. Metabolism of short-chain fatty acids also occurs in the cells of the liver. Dietary fibre, therefore, can contribute some energy (6 to 10 kilojoules per gram), depending on the extent to which it is broken down by bacteria and the fatty acids are absorbed.
Carbohydrate absorption
PUTTING COMMON SENSE TO THE TEST
Glucose is unique in that it can be absorbed, to some extent through the lining of the mouth, but for the most part, nutrient absorption takes place in the small intestine. Glucose and galactose traverse the cells lining the small intestine by active transport; fructose is absorbed by facilitated diffusion, which slows its entry and produces a smaller rise in blood glucose. Likewise, unbranched chains of starch are digested slowly and produce a smaller rise in blood glucose than branched chains, which have many more places for enzymes to attack and release glucose rapidly. As the blood from the intestines circulates through the liver, cells there take up fructose and galactose and convert them to other compounds, most often to glucose, as shown in Figure 4.11. Thus, all disaccharides provide at least one glucose molecule directly, and they can provide another one indirectly – through the conversion of fructose and galactose to glucose.
The majority of carbohydrate digestion occurs in the large intestine. FALSE
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In the digestion and absorption of carbohydrates, the body breaks down starches into the disaccharide maltose. Maltose and the other disaccharides (lactose and sucrose) from foods are broken down into monosaccharides. Then monosaccharides are converted mostly to glucose to provide energy for the cells’ work. Dietary fibre helps to regulate the passage of food through the GI system and slows the absorption of glucose, but dietary fibre contributes little, if any, energy.
* The short-chain fatty acids produced by GI bacteria are primarily acetic acid, propionic acid and butyric acid.
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FIGURE 4.11 Absorption of monosaccharides 1 Monosaccharides, the end products of carbohydrate digestion, enter the capillaries of the intestinal villi.
3 In the liver, galactose and fructose are converted to glucose. Small intestine
Key: Glucose 2 Monosaccharides travel to the liver via the portal vein.
Fructose Galactose
Lactose intolerance Normally, the intestinal cells produce enough of the enzyme lactase to ensure that the disaccharide lactose found in milk is both digested and absorbed efficiently. Lactase activity is highest immediately after birth, as befits an infant whose first and only food for a while will be breast milk or infant formula. In the great majority of the world’s populations, lactase activity declines dramatically during childhood and adolescence to about 5–10 per cent of the activity at birth. Only a relatively small percentage (about 30 per cent) of the people in the world retain enough lactase to digest and absorb lactose efficiently throughout adult life.
Symptoms When more lactose is consumed than the available lactase can handle, lactose molecules remain in the intestine undigested, attracting water and causing bloating, abdominal discomfort and diarrhoea – the symptoms of lactose intolerance. The undigested lactose becomes food for intestinal bacteria, which multiply and produce irritating acid and gas, further contributing to the discomfort and diarrhoea.
Causes
Lactase activity commonly declines with age. Lactase deficiency may also develop when the intestinal villi are damaged by disease, certain medicines, prolonged diarrhoea or malnutrition. Depending on the extent of the intestinal damage, lactose malabsorption may be temporary or permanent. In extremely rare cases, an infant is born with a lactase deficiency.
Prevalence The prevalence of lactose intolerance varies widely among ethnic groups, indicating that the trait is genetically determined. The prevalence of lactose intolerance is lowest among Scandinavians and other northern Europeans and highest among native North Americans and South-East Asians.
Estimated prevalence of lactose intolerance: • .80% South-East Asians • 80% Native Americans • 75% African Americans • 70% Australian Aborigines • 70% Mediterranean and Middle Eastern people • 60% Inuit • 50% Hispanics • 20% Caucasians • ,10% Northern Europeans
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Dietary changes
Lactose in selected foods (per 100 g serving): • butter, regular 1 g • cheddar cheese 0.1 g • cottage cheese 2.7–3.4 g • ice-cream 4.7–5.9 g • milk (whole) 4.6 g • milk (skim) 5 g • Milo powder 12.7 g • plain or fruit buns 0–0.1 g • soy milk 0 g • wholegrain bread 0 g • yoghurt (natural, whole) 4.7 g. NOTE: Yoghurt is often enriched with nonfat milk solids, which increase its lactose content to a level higher than that of milk.
Managing lactose intolerance requires some dietary changes, although total elimination of milk products usually is not necessary. Excluding all milk products from the diet can lead to nutrient deficiencies because these foods are a major source of several nutrients, notably the mineral calcium, vitamin D and the B vitamin riboflavin. Fortunately, many people with lactose intolerance can generally consume foods containing up to 6 grams of lactose (½ cup milk) without symptoms. The most successful strategies are to increase the intake of milk products gradually, take them with other foods in meals and spread their intake throughout the day. A change in the GI bacteria, not the reappearance of the missing enzyme, accounts for the ability to adapt to milk products. Importantly, most lactose-intolerant individuals need to manage their dairy consumption rather than restrict it.2 In many cases, lactose-intolerant people can tolerate fermented milk products such as yoghurt. The bacteria in these products digest lactose for their own use, thus reducing the lactose content. Even when the lactose content is equivalent to that of milk, yoghurt produces fewer symptoms. Hard cheeses, such as cheddar, and cottage cheese are often well tolerated because most of the lactose is removed with the whey during manufacturing. Lactose continues to diminish as cheese ages. Many lactose-intolerant people use commercially prepared milk products that have been treated with an enzyme that breaks down the lactose. Alternatively, they take enzyme tablets with meals or add enzyme drops to their milk. The enzyme hydrolyses much of the lactose in milk to glucose and galactose, which lactose-intolerant people can absorb without ill effects. Because people’s tolerance to lactose varies widely, lactose-restricted diets must be highly individualised. A completely lactose-free diet can be difficult because lactose appears not only in milk and milk products but also as an ingredient in many non-dairy foods such as breads, cereals, breakfast drinks, salad dressings and cake mixes. People on strict lactose-free diets need to read labels and avoid foods that include milk, milk solids, whey (milk liquid) and casein (milk protein, which may contain traces of lactose). They also need to check all medications with the pharmacist because 20 per cent of prescription drugs and 5 per cent of over-thecounter drugs contain lactose as a filler. People who consume few or no milk products must take care to meet riboflavin, vitamin D and calcium needs. Later chapters on the vitamins and minerals offer help with finding good non-milk sources of these nutrients.
PUTTING COMMON SENSE TO THE TEST
People who suffer lactose intolerance must avoid all dairy foods. FALSE
CURRENT RESEARCH IN NUTRITION Fructose and FODMAPs FODMAPs are found in the foods we eat. The term FODMAP is an acronym for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols. When FODMAPs reach the large intestine, they become food for the bacteria living there. The bacterial digestion of FODMAPs produces additional symptoms of irritable bowel syndrome – intestinal gas and changes in bowel habits (diarrhoea, constipation or both). FODMAPs are only considered FODMAPs if people are sensitive to their effects in the digestive such as in irritable bowel syndrome. Fructose, a monosaccharide, can be a FODMAP (as can the disaccharide lactose). Fructose is commonly found in fruits and although a person needing a low-FODMAP diet may limit their intake of fruit, not all fruits have the same amount of fructose in them. This means, (much like lactose intolerance management), that being on a low-FODMAP diet is about managing exposure to FODMAPs for the individual.
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Lactose intolerance is a relatively common condition that occurs when there is insufficient lactase to digest the disaccharide lactose found in milk and milk products. Symptoms generally include GI distress. Because treatment requires limiting milk intake, other sources of calcium, riboflavin and vitamin D must be included in the diet.
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4.5 Glucose in the body
The primary role of the available carbohydrates in human nutrition is to supply the body’s cells with glucose for energy. Starch contributes most to the body’s glucose supply, but as explained earlier, any of the monosaccharides can also provide glucose. Scientists have long known that the primary role of glucose in the body is to provide energy, but they have only recently uncovered additional roles that glucose and other sugars perform in the body. Sugar molecules dangle from many of the body’s protein and fat molecules, with dramatic consequences. Sugars attached to a protein change the protein’s shape and function; when they bind to lipids in a cell’s membranes , sugars alter the way cells recognise each other.3 Cancer cells coated with sugar molecules, for example, are able to sneak by the cells of the immune system. Scientists are now trying to use sugar molecules to create an anticancer vaccine. Further advances in knowledge are sure to reveal numerous ways these simple, yet remarkable sugar molecules influence the health of the body.
The study of sugars is glycobiology. These combination molecules are known as glycoproteins and glycolipids, respectively.
A preview of carbohydrate metabolism Glucose plays the central role in carbohydrate metabolism. This brief discussion provides just enough information about carbohydrate metabolism to illustrate that the body needs and uses glucose as a chief energy nutrient. Chapter 7 provides a full description of energy metabolism.
Storing glucose as glycogen The liver stores about one-third of the body’s total glycogen and releases glucose into the bloodstream as needed. After a meal, blood glucose rises, and liver cells link the excess glucose molecules by condensation reactions into long, branching chains of glycogen. When blood glucose falls, the liver cells break glycogen by hydrolysis reactions into single molecules of glucose and release them into the bloodstream. Thus, glucose becomes available to supply energy to the brain and other tissues regardless of whether the person has eaten recently. Muscle cells can also store glucose as glycogen (the other two-thirds), but they hoard most of their supply, using it just for themselves during exercise. The brain maintains a small amount of glycogen, which is thought to provide an emergency energy reserve during times of severe glucose deprivation.4 Glycogen holds water and, therefore, is rather bulky. The body can store only enough glycogen to provide energy for relatively short periods of time – less than a day during rest and a few hours at most during exercise. For its long-term energy reserves – for use over days or weeks of food deprivation – the body uses its abundant, water-free fuel, fat, as Chapter 5 describes.
Glucose fuels the work of most of the body’s cells. Inside a cell, enzymes break glucose in half. These halves can be put back together to make glucose, or they can be further broken down into even smaller fragments (never again to be reassembled to form glucose). The small fragments can yield energy when broken down completely to carbon dioxide and water (see Chapter 7). The liver’s glycogen stores last only for hours, not days, so to keep providing glucose to meet the body’s energy needs, a person needs to eat dietary carbohydrate frequently. Yet people who do not always attend faithfully to their body’s carbohydrate needs still survive. How do they manage without glucose from dietary carbohydrate? Do they simply draw energy from the other two energy-yielding nutrients, fat and protein? The answer is a simple ‘yes’, but the process is far from simple.
Brian Leatart/Photolibrary/Getty Images
Using glucose for energy
The carbohydrates of grains, vegetables, fruits and legumes supply most of the energy in a well-balanced diet.
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Making glucose from protein Glucose is the preferred energy source for brain cells, other nerve cells and developing red blood cells. Body protein can be converted to glucose to some extent, but protein has a number of tasks that no other nutrient can do. Body fat cannot be converted to glucose to any significant extent. Thus, when a person does not replenish depleted glycogen stores by eating carbohydrate, body proteins are broken down to make glucose to fuel these special cells. The conversion of protein to glucose is called gluconeogenesis – literally, the making of new glucose. Only adequate dietary carbohydrate can prevent this use of protein for energy, and this role of carbohydrate is known as its protein-sparing action.
Making ketone bodies from fat fragments An inadequate supply of carbohydrate can shift the body’s energy metabolism in a precarious direction. With less carbohydrate providing glucose to meet the brain’s energy needs, fat takes an alternative metabolic pathway: instead of entering the main energy pathway, fat fragments combine with each other, forming ketone bodies. Ketone bodies provide an alternative fuel source during starvation, but when their production exceeds their use, they accumulate in the blood, causing ketosis, a condition that disturbs the body’s normal acid–base balance, as Chapter 7 describes. (Highlight 9 explores ketosis and the health consequences of lowcarbohydrate diets further.) To spare body protein and prevent ketosis, the body needs approximately 50 to 100 grams of carbohydrate a day. Dietary recommendations urge people to select abundantly from carbohydrate-rich foods to provide for considerably more.
Using glucose to make fat After meeting its energy needs and filling its glycogen stores to capacity, the body must find a way to handle any extra glucose. At first, energy metabolism shifts to use more glucose instead of fat. If that isn’t enough to restore glucose balance, the liver uses glucose to form the backbone of a triglyceride (glycerol), which allows a more permanent energy-storage compound – fat (as triglyceride) – to be stored. Thus, when carbohydrate is abundant, fat is stored. The fat then travels to the fatty tissues of the body for storage. Unlike the liver cells, which can store only enough glycogen to meet less than a day’s energy needs, fat cells can store seemingly unlimited quantities of fat. PUTTING COMMON SENSE TO THE TEST
Glucose fuels the majority of the body’s energy needs. TRUE Normal blood glucose (fasting): 4 to 6 mmol/L (published values vary slightly). Reminder: Homeostasis is the maintenance of constant internal conditions by the body’s control systems.
The constancy of blood glucose Every body cell depends on glucose for its fuel to some extent, and the cells of the brain and the rest of the nervous system depend almost exclusively on glucose for their energy. The activities of these cells never cease, and they have limited ability to store glucose. Day and night, they continually draw on the supply of glucose in the fluid surrounding them. To maintain the supply, a steady stream of blood moves past these cells bringing more glucose from either the intestines (food) or the liver (via glycogen breakdown or gluconeogenesis).
Maintaining glucose homeostasis To function optimally, the body must maintain blood glucose within limits that permit the cells to nourish themselves. If blood glucose falls below normal, a person may become dizzy and weak; if it rises above normal, a person may become fatigued. Left untreated, fluctuations to the extremes – either high or low – can be fatal.
The regulating hormones
Blood glucose homeostasis is regulated primarily by two hormones: insulin, which moves glucose from the blood into the cells, and glucagon, which brings glucose out of storage when necessary. Figure 4.12 depicts these hormonal regulators at work.
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FIGURE 4.12 Maintaining blood glucose homeostasis Blood vessel 1 When a person eats, blood glucose rises.
Intestine
1
4
4 As the body’s cells use glucose, blood levels decline.
Insulin 2 High blood glucose stimulates the pancreas to release insulin into the bloodstream.
2
5
5 Low blood glucose stimulates the pancreas to release glucagon into the bloodstream.
6
6 Glucagon stimulates liver cells to break down glycogen and release glucose into the blood.a
7
7 Blood glucose begins to rise.
Glucagon
Pancreas
Liver 3 Insulin stimulates the uptake of glucose into cells and storage as glycogen in the liver and muscles. Insulin also stimulates the conversion of excess glucose into fat for storage.
3
Key: Glucose 3
Insulin
Fat cell
Glucagon Glycogen Muscle
a The stress hormone epinephrine and other
hormones also bring glucose out of storage.
After a meal, as blood glucose rises, special cells of the pancreas respond by secreting
insulin into the blood.* In general, the amount of insulin secreted corresponds with the rise in glucose. As the circulating insulin contacts the receptors on the body’s other cells, the receptors respond by ushering glucose from the blood into the cells. Most of the cells take only the glucose they can use for energy right away, but the liver and muscle cells can assemble the small glucose units into long, branching chains of glycogen for storage. The liver cells can also convert glucose to fat for export to other cells. Thus, elevated blood glucose returns to normal levels as excess glucose is stored as glycogen and fat. When blood glucose falls (as occurs between meals), other special cells of the pancreas respond by secreting glucagon into the blood.** Glucagon raises blood glucose by signalling the liver to break down its glycogen stores and release glucose into the blood for use by all the other body cells. Another hormone that signals the liver cells to release glucose is the ‘fight-or-flight’ hormone, adrenaline (or epinephrine). When a person experiences stress, adrenaline acts quickly, ensuring that all the body cells have energy fuel in emergencies. Among its many roles in the body, adrenaline works to release glucose from liver glycogen to the blood.
Balancing within the normal range The maintenance of normal blood glucose ordinarily depends on two processes. When blood glucose falls below normal, food can replenish it, or, in the absence of food, glucagon can * The beta cells, one of several types of cells in the pancreas, secrete insulin in response to elevated blood glucose concentration. ** The alpha cells of the pancreas secrete glucagon in response to low blood glucose.
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signal the liver to break down glycogen stores. When blood glucose rises above normal, insulin can signal the cells to take in glucose for energy. Eating balanced meals at regular intervals helps the body maintain a happy medium between the extremes. Balanced meals that provide abundant complex carbohydrates, including dietary fibre and a little fat, help to slow down the digestion and absorption of carbohydrate so that glucose enters the blood gradually, providing a steady, ongoing supply.
Falling outside the normal range The influence of foods on blood glucose has given rise to the oversimplification that foods govern blood glucose concentrations. Foods do not; the body does. In some people, however, blood glucose regulation fails. When this happens, either of two conditions can result: diabetes or hypoglycaemia. People with these conditions often plan their diets to help maintain their blood glucose within a normal range.
Diabetes
Blood glucose (fasting): • prediabetes: 6.1 to 7 mmol/L • diabetes: greater than 7 mmol/L on two or more tests performed on different days The condition of having blood glucose levels higher than normal, but below the diagnosis of diabetes, is sometimes called prediabetes.
In diabetes, blood glucose surges after a meal and remains above normal levels because insulin is either inadequate or ineffective. Thus, blood glucose is central to diabetes, but dietary carbohydrates do not cause diabetes. There are two main types of diabetes. In type 1 diabetes, the less common type, the pancreas fails to produce insulin. Although the exact cause is unclear, some research suggests that in genetically susceptible people, certain viruses activate the immune system to attack and destroy cells in the pancreas as if they were foreign cells. In type 2 diabetes, the more common type of diabetes, the cells fail to respond to insulin. This condition tends to occur as a consequence of obesity. As the incidence of obesity in Australia and New Zealand has risen in recent decades, the incidence of diabetes has followed. Latest estimates show that nearly 0.9 million Australians have diabetes, but up to half of the people with type 2 diabetes remain undiagnosed.5 For New Zealand, diabetes rates are two to three times higher in Ma ¯ori and Pacific populations when compared with the entire population.6 This trend is most notable among children and adolescents, as obesity reaches epidemic proportions. Because obesity can precipitate type 2 diabetes, the best preventive measure is to maintain a healthy body weight. Sweets and lollies are not strictly excluded from the diabetic diet, as they once were; they can be eaten in limited amounts with meals as part of a healthy diet. Chapter 15 describes the type of diabetes that develops in some women during pregnancy (gestational diabetes), and Chapter 18 gives full coverage of type 1 and type 2 diabetes and their associated problems.
Hypoglycaemia In healthy people, blood glucose rises after eating and then gradually falls back into the normal range. The transition occurs without notice. Should blood glucose drop below normal, a person would experience the symptoms of hypoglycaemia: weakness, rapid heartbeat, sweating, anxiety, hunger and trembling. Most commonly, hypoglycaemia is a consequence of poorly managed diabetes. Too much insulin, strenuous physical activity, inadequate food intake or illness can cause blood glucose levels to plummet. Hypoglycaemia in healthy people is rare. Most people who experience hypoglycaemia need only adjust their diets by replacing refined carbohydrates with carbohydrates rich in dietary fibre and ensuring an adequate protein intake. In addition, smaller meals eaten more frequently may help. Hypoglycaemia caused by certain medications, pancreatic tumours, overuse of insulin, alcohol abuse, uncontrolled diabetes or other illnesses requires medical intervention.
The glycaemic response
The glycaemic response refers to how quickly glucose is absorbed after a person eats, how high blood glucose rises and how quickly it returns to normal. Slow absorption, a modest rise
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Chapter 4: The carbohydrates: sugars, starches and dietary fibre
in blood glucose and a smooth return to normal are desirable (a low glycaemic response). Fast absorption, a surge in blood glucose and an overreaction that plunges glucose below normal are less desirable (a high glycaemic response). Different foods have different effects on blood glucose. The rate of glucose absorption is particularly important to people with diabetes, who may benefit from limiting foods that produce too great a rise, or too sudden a fall, in blood glucose. To aid their choices, they may be able to use the glycaemic index (GI), a method of classifying foods according to their potential to raise blood glucose. Figure 4.13 ranks selected foods by their GI.7 Some studies have shown that selecting foods with a low GI is a practical way to improve glucose control.8
111
A related term, glycaemic load, reflects both the glycaemic index and the amount of carbohydrate.
LOW
White bread
Baked potato
Cornflakes
Pumpkin, doughnut Sports drinks, jelly beans
Watermelon, popcorn, bagel
Ice-cream Raisins, white rice Couscous
Yoghurt Tomato juice, navy beans, apples, pears Apple juice Bran cereals, black-eyed peas, peaches Chocolate, pudding Grapes Macaroni, carrots, green peas, baked beans Rye bread, orange juice Banana Wheat bread, corn, pound cake Brown rice Cola, pineapple
Butter beans
Barley Milk, kidney beans, chickpeas
Cashews, cherries
Soybeans
Peanuts
FIGURE 4.13 Glycaemic index of selected foods
HIGH
Lowering the glycaemic index of the diet may improve blood lipids and reduce the risk of heart disease as well.9 A low glycaemic index diet may also help with weight management, although research findings are mixed.10 Dietary fibre and other slowly digested carbohydrates prolong the presence of foods in the digestive tract, thus providing greater satiety and diminishing the insulin response, which can help with weight control. In contrast, the rapid absorption of glucose from a high glycaemic diet seems to increase the risk of heart disease and promote overeating in some overweight people.11 Despite these possible benefits, the usefulness of the glycaemic index is still being debated. Those opposing the use of the glycaemic index argue that it is not sufficiently supported by scientific research. The glycaemic index has been determined for relatively few foods, and when the glycaemic index has been established, it is based on an average of multiple tests with wide variations in their results. Values vary because of differences in the physical and chemical characteristics of foods, testing methods of laboratories and digestive processes of individuals.
APPLICATIONS OF NUTRITIONAL RESEARCH Diabetes and glycaemic index People with type 2 diabetes remain concerned about the role that carbohydrates have in regulating their blood glucose levels. Dietary advice is considered the most important lifestyle message that can positively affect blood glucose control. In recent years, the focus on the nutritional therapy for type 2 diabetes has changed from focusing on only the amount of carbohydrates to also include the importance of low glycaemic index foods to reduce the rise in blood glucose after a meal. Clinical research is demonstrating that low GI diets (and
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regular moderate exercise) can assist with the management of not only blood glucose but also blood lipids in people with type 2 diabetes. However, there is some debate about the usefulness of the glycaemic index as it has been determined for relatively few foods, and when the glycaemic index has been published, it has been based on an average of multiple tests with wide variations in the results. Some argue the practicality of the glycaemic index is limited because the information is seldom provided on food labels nor is it intuitive. Furthermore, the practical utility of the glycaemic index is limited because this information is neither provided on food labels nor intuitively apparent. Indeed, a food’s glycaemic index is not always what one might expect. Ice-cream, for example, is a high-sugar food but produces less of a glycaemic response than baked potatoes, a high-starch food. This effect is most likely because the fat in the ice-cream slows gastrointestinal motility, and thus the rate of glucose absorption. Mashed potatoes produce more of a response than honey, probably because the fructose content of honey has little effect on blood glucose. In fact, sugars such as fructose generally have a moderate to low glycaemic index and can have a positive effect on glycaemic control.12 Perhaps most relevant to real life, a food’s glycaemic effect differs depending on plant variety, food processing, cooking method and whether it is eaten alone or with other foods. Most people eat a variety of foods, cooked and raw, that provide different amounts of carbohydrate, fat and protein – all of which influence the glycaemic index of a meal. Paying attention to the glycaemic index may not be necessary because current guidelines already suggest many low glycaemic index choices: whole grains, legumes, vegetables, fruits and dairy products. In addition, eating frequent, small meals spreads glucose absorption across the day and thus offers similar metabolic advantages to eating foods with a low glycaemic response. People wanting to follow a low glycaemic diet should be careful not to adopt a low carbohydrate diet as well. The problems associated with a low carbohydrate diet are addressed in Highlight 9.
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As an additive, sugar: • enhances flavour • supplies texture and colour to baked goods • provides fuel for fermentation, causing bread to rise or producing alcohol • acts as a bulking agent in ice-cream and baked goods • acts as a preservative in jams • balances the acidity of tomatoand vinegar-based products.
Dietary carbohydrates provide glucose that can be used by the cells for energy stored by the liver and muscles as glycogen, or be converted into fat if intakes exceed needs. All of the body’s cells depend on glucose; those of the central nervous system are especially dependent on it. Without glucose, the body is forced to break down its protein tissues to make glucose and to alter energy metabolism to make ketone bodies from fats. Blood glucose regulation depends primarily on two pancreatic hormones: insulin to move glucose from the blood into the cells when levels are high, and glucagon to free glucose from glycogen stores and release it into the blood when levels are low. The glycaemic index measures how blood glucose responds to foods.
4.6 Health effects and recommended intakes of sugars
Ever since people first discovered honey and dates, they have enjoyed the sweetness of sugars. In Australia and New Zealand, the natural sugars of milk, fruits, vegetables and grains account for about half of the sugar intake; the other half consists of sugars that have been refined and added to foods for a variety of purposes. The use of added sugars has risen steadily over the past several decades, in Australia and New Zealand and around the world, with soft drinks and sugared fruit drinks accounting for most of the increase.13 These added sugars assume various names on food labels: sucrose, invert sugar, corn sugar, corn syrups and solids, highfructose corn syrup and honey. A food is likely to be high in added sugars if its ingredient list starts with any of the sugars named in Table 4.1 or if it includes several of them.
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TABLE 4.1 Examples of added sugars Brown sugar: refined white sugar crystals to which manufacturers have added molasses syrup with natural flavour and colour; 91 to 96 per cent pure sucrose Corn sweeteners: corn syrup and sugars derived from corn Corn syrup: a syrup made from cornstarch (cornflour) that has been treated with acid, high temperatures and enzymes that produce glucose, maltose and dextrins. See also high-fructose corn syrup (HFCS)
Dextrose: an older name for glucose Granulated sugar: crystalline sucrose; 99.9 per cent pure High-fructose corn syrup (HFCS): a syrup made from cornstarch that has been treated with an enzyme that converts some of the glucose to the sweeter fructose; made especially for use in processed foods and beverages, where it is the predominant sweetener. With a chemical structure similar to sucrose, HFCS has a fructose content of 42, 55 or 90 per cent, with glucose making up the remainder Honey: sugar (mostly sucrose) formed from nectar gathered by bees. An enzyme splits the sucrose into glucose and fructose. Composition and flavour vary, but honey always contains a mixture of sucrose, fructose and glucose Icing sugar: finely powdered sucrose, 99.9 per cent pure Levulose: an older name for fructose Molasses: the thick brown syrup produced during sugar refining. Molasses retains residual sugar and other by-products and a few minerals; blackstrap molasses contains significant amounts of calcium and iron Raw sugar: partially refined crystals harvested during sugar processing White sugar: pure sucrose or ‘table sugar’, produced by dissolving, concentrating and recrystallising raw sugar
Health effects of sugars In moderate amounts, sugars add pleasure to meals without harming health. In excess, however, they can be detrimental in two ways: sugars can contribute to nutrient deficiencies by supplying energy (kilojoules) without providing nutrients, and sugars contribute to tooth decay.
Obesity and chronic disease Over the past several decades, as obesity rates increased sharply, consumption of added sugars reached an all-time high. In Northern Hemisphere countries such as the US and Canada, this has been attributed to the use of high-fructose corn syrup. Compared with sucrose, high-fructose corn syrup is less expensive, easier to use and more soluble. Manufacturers prefer high-fructose corn syrup because it retains moisture, resists drying out, controls crystallisation, prevents microbial growth and blends easily with other sweeteners, acids and flavourings. In addition to being used in beverages, high-fructose corn syrup sweetens lollies, baked goods and hundreds of other foods. High-fructose corn syrup isn’t used prolifically in Australia or New Zealand, yet the obesity rates in those countries mirror those in other developed nations. In general, research findings tend to support an association between consuming sugary beverages and increases in energy intake and body weight. This is one of the reasons that health authorities such as the Australian Medical Association and research organisations such as the Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders are calling for a tax on sugar sweetened beverages. They believe that this will assist in the reduction of the rate of obesity as well as provide additional funding to treat obesity-related disease. Reducing the consumption of sugar-sweetened beverages or replacing them with beverages such as water or milk can help support a healthy body weight. Some research suggests that
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added sugars in general, and fructose in particular, favour the fat-making pathways and impair the fat-clearing pathways in the liver. The resulting blood lipid profile increases the risk of heart disease. As the liver busily makes lipids, its handling of glucose becomes unbalanced and insulin resistance develops – an indicator of prediabetes. All in all, research is finding links between added sugars and the risk of diabetes, inflammation, hypertension and heart disease. Importantly, moderate intakes of sugars do not cause these health problems. For this reason, researchers suggest replacing sugar-sweetened beverages with water.
Shutterstock.com/Kamil Macniak
Nutrient deficiencies Foods that contain large amounts of added sugar, such as cakes, lollies and soft drinks, deliver glucose and energy with few, if any, other nutrients. By comparison, foods such as whole grains, vegetables, legumes and fruits that contain some natural sugars and lots of starches and dietary fibre deliver protein, vitamins and minerals along with their glucose and energy. A person spending 800 kilojoules of a day’s energy allowance on a 650-millilitre soft drink gets little of value for those energy ‘dollars’. In contrast, a person using 800 kilojoules on three slices of wholegrain bread gets at least 9 grams of protein, 6 grams of fibre, plus several of the B vitamins with those kilojoules. For the person who wants something sweet, a reasonable compromise might be two slices of bread with a teaspoon of jam on each. The amount of sugar a person can afford to eat depends on how many kilojoules are available beyond those needed to deliver indispensable vitamins and minerals. Over half of the added sugars in our diet come from soft drinks and table sugar; however, baked goods, fruit drinks, ice-cream, Some people believe that because honey is a natural food, it lollies and breakfast cereals also make substantial contributions. is nutritious – or, at least, more nutritious than sugar.* A look at their chemical structures reveals the truth. Honey, like table sugar, contains glucose and fructose. The primary difference is that in table sugar, the two monosaccharides are bonded together as a disaccharide, whereas in honey some of them are free. Whether a person eats monosaccharides individually, as in honey, or linked together, as in table sugar, they end up the same way in the body: as glucose and fructose. Honey does contain a few vitamins and minerals, but not many. Honey is denser than crystalline sugar, too, so it provides more energy per spoonful. This is not to say that all sugar sources are alike, for some are more nutritious than others. Consider a fruit, such as an orange. The fruit may give you the same amounts of fructose and glucose and the same amount of energy as a spoonful of sugar or honey, but the packaging is more valuable nutritionally. The sugars in fruit arrive in the body diluted in a large volume of water, packaged in dietary fibre and mixed with essential vitamins, minerals and phytochemicals. As these comparisons illustrate, the significant difference between sugar sources is not between ‘natural’ honey and ‘purified’ sugar but between concentrated sweets and the diluted, naturally occurring sugars that sweeten foods. You can suspect an exaggerated nutrition claim when someone asserts that one product is more nutritious than another because it contains honey. Sugar can contribute to nutrient deficiencies only by displacing nutrients. For nutrition’s sake, the appropriate attitude to take is not that sugar is ‘bad’ and must be avoided, but that nutritious foods must come first. If nutritious foods crowd sugar out of the diet, that is fine – but not the other way around. As always, the goals to seek are balance, variety and moderation. * Honey should never be fed to infants because of the risk of botulism. Chapters 16 and 19 provide more details.
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Dental caries
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FIGURE 4.14 Dental caries
Dental caries begin when acid dissolves the Sugars from foods and from the breakdown of starches in the mouth can enamel that covers the tooth. If not repaired, contribute to tooth decay. Bacteria in the mouth ferment the sugars and, the decay may penetrate the dentine and in the process, produce an acid that erodes tooth enamel (see Figure 4.14), spread into the pulp of the tooth, causing causing dental caries, or tooth decay. People can eat sugar without this inflammation, abscess and possible loss of happening, though, because much depends on how long foods stay in the the tooth. mouth. Sticky foods stay on the teeth longer and continue to yield acid longer Enamel than foods that are readily cleared from the mouth. For that reason, sugar Caries in a juice consumed quickly, for example, is less likely to cause dental caries Crown Dentin than sugar in a pastry. By the same token, the sugar in sticky foods such as Gum dried fruits can be more detrimental than its quantity alone would suggest. Another concern is how often people eat sugar. The bacteria in the mouth Pulp (blood produce acid for 20 to 30 minutes after each exposure to sugar. If a person vessels, eats three lollies at one time, the teeth will be exposed to approximately nerves) 30 minutes of acid destruction. But if the person eats three lollies at halfhour intervals, the time of exposure increases to 90 minutes. Likewise, slowly sipping a sugary sports beverage may be more harmful than drinking Bone quickly and clearing the mouth of sugar. Non-sugary foods can help remove sugar from tooth surfaces; hence, it is better to eat sugar with meals than Root between meals.14 Foods such as milk and cheese may be particularly helpful canal in minimising the effects of the acids and in restoring the lost enamel. Beverages such as soft drinks, orange juice and sports drinks not only Nerve contain sugar but also have a low pH. These acidic drinks can erode tooth Blood vessel enamel and may explain why dental erosion is highly prevalent today. The development of caries depends on several factors: the bacteria that reside in dental plaque, the saliva that cleanses the mouth, the minerals that form the teeth and the foods that remain after swallowing. For most people, good oral To prevent dental hygiene will prevent dental caries. In fact, regular brushing (twice a day, with a fluoridecaries: containing toothpaste) and flossing may be more effective in preventing dental caries than • limit between-meal restricting sugary foods. snacks containing sugars and starches • brush and floss teeth regularly Because added sugars deliver energy but few or no nutrients, the National Health and Medical • if brushing and Research Council’s 2013 Australian Dietary Guidelines urge consumers to ‘limit intake of foods flossing are not and drinks containing added sugars’. Most people need to limit their use of added sugars. possible, at least rinse with water. Estimates indicate that, on average, each person in Australia consumes about 42 kilograms of sugar over a year, most as added cane sugar.15
Recommended intakes of sugars
HOW TO:
REDUCE THE INTAKE OF ADDED SUGARS
There are many ways to reduce the intake of added sugars: ›› Use less table sugar when preparing meals and at the table. ›› Drink fewer regular soft drinks, sports drinks, energy drinks, 100 per cent fruit juice and fruit drinks; choose water, low-fat milk, or unsweetened tea or coffee instead. If you do drink sugar sweetened beverages, have a small portion. ›› Select fruit for dessert. Eat less cake, biscuits, ice-cream, other desserts and lollies. If you do eat these foods, have a small portion. ›› The ingredients list also helps to identify foods with added sugars. A food is likely to be high in added sugars if its ingredient list starts with any of the sugars named in Table 4.1. or if it includes several of them. How many kilojoules from sugar does your favourite beverage or snack provide?
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REVIEW IT
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Limit intake of foods and drinks containing added sugars, such as confectionery, sugar-sweetened soft drinks and cordials, fruit drinks, vitamin waters and energy and sports drinks.
Sugars pose no major health threat except for an increased risk of dental caries. Excessive intakes, however, may displace needed nutrients and dietary fibre and may contribute to obesity when energy intake exceeds needs. A person deciding to limit daily sugar intake should recognise that not all sugars need to be restricted, just concentrated sweets, which are relatively empty of other nutrients and high in energy. Sugars that occur naturally in fruits, vegetables and milk are acceptable.
4.7 Alternative sweeteners
In an attempt to control weight gain, blood glucose and dental caries, many consumers turn to alternative sweeteners to help them limit kilojoules and minimise sugar intake. In doing so, they encounter three sets of alternative sweeteners: artificial sweeteners, herbal products and sugar alcohols. Table 4.2 provides general details about each of the sweeteners.
TABLE 4.2 Alternative sweeteners SWEETENER (ADDITIVE NUMBER)
CHEMICAL COMPOSITION
BODY’S RESPONSE
RELATIVE SWEETNESSa
ENERGY (kJ/g)
ACCEPTABLE DAILY INTAKE (ADI) (mg/kg BODY WEIGHT)b
APPROVAL STATUS
Artificial sweeteners Acesulfame potassium or
Potassium salt
Not digested or absorbed
200
0
15 mg/kg body weightd (30 cans diet soft drink)
Approved for use in Australia and New Zealand
Aspartamee (951)
Amino acids (phenylalanine and aspartic acid) and a methyl group
Digested and absorbed
200
16 f
40 mg/kg body weight (18 cans diet soft drink)g
Approved for use in Australia and New Zealand; warning for PKU
Cyclamate
Sodium or calcium salt of cyclamic acid
Incompletely absorbed; absorbed cyclamate is excreted unchanged; unabsorbed cyclamate may be metabolised by bacteria in the GI tract
30
0
11 mg/kg body weight (8 cans of diet soft drink)
Approved for use in Australia and New Zealand
Aspartame with an additional side group attached
Not digested or absorbed
8000
0
18 mg/day
Approved for use in Australia and New Zealand; no warning for PKU
Acesulfame Kc (950)
(952)
Neotame
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TABLE 4.2
Chapter 4: The carbohydrates: sugars, starches and dietary fibre
CHEMICAL COMPOSITION
SWEETENER (ADDITIVE NUMBER)
Saccharinh
BODY’S RESPONSE
RELATIVE SWEETNESSa
ENERGY (kJ/g)
ACCEPTABLE DAILY INTAKE (ADI) (mg/kg BODY WEIGHT)b
117
APPROVAL STATUS
Benzoic sulfimide
Rapidly absorbed and excreted
450
0
5 mg/kg body weight (10 packets of sweetener)
Approved for use in Australia and New Zealand; restricted use as a tabletop sweetener in Canada
Sucrose with chloride (Cl) atoms instead of OH groups
Not digested or absorbed
600
0
5 mg/kg body weight (6 cans diet soft drink)
Approved for use in Australia and New Zealand
Monosaccharide similar in structure to fructose; naturally occurring or derived from lactose
Mostly not absorbed; some short-chain fatty acids absorbed
0.8
1.5
7.5 g/day
GRASk approved; advice to avoid if fructosemalabsorptive
Glycosides found in the leaves of the Stevia rebaudiana herb
Digested and absorbed
300
0
4 mg/kg body weight
Approved for use in Australia and New Zealand
Erythritol (968)
Sugar alcohol
Partially absorbed in small intestine; unabsorbed sugar alcohols may be metabolised by bacteria in the GI tract
0.7
0.2
–m
Approved for use in Australia and New Zealand
Isomalt (953)
Sugar alcohol
Partially absorbed in small intestine; unabsorbed sugar alcohols may be metabolised by bacteria in the GI tract
0.5
8.0
–m
FSANZ approved
Lactitol (966)
Sugar alcohol
Partially absorbed in small intestine; unabsorbed sugar alcohols may be metabolised by bacteria in the GI tract
0.4
8.0
–m
FSANZ approved
Maltitol (965)
Sugar alcohol
Partially absorbed in small intestine; unabsorbed sugar alcohols may be metabolised by bacteria in the GI tract
0.9
8.5
–m
FSANZ approved
(954)
Sucralosei (955)
Tagatosej (no additive number)
Herbal sweeteners Stevial (960)
Sugar alcohols
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TABLE 4.2
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Understanding nutrition
SWEETENER (ADDITIVE NUMBER)
CHEMICAL COMPOSITION
BODY’S RESPONSE
RELATIVE SWEETNESSa
ENERGY (kJ/g)
ACCEPTABLE DAILY INTAKE (ADI) (mg/kg BODY WEIGHT)b
APPROVAL STATUS
Mannitol (421)
Sugar alcohol
Partially absorbed in small intestine; unabsorbed sugar alcohols may be metabolised by bacteria in the GI tract
0.7
6.7
–m
FSANZ approved
Sorbitol (420)
Sugar alcohol
Partially absorbed in small intestine; unabsorbed sugar alcohols may be metabolised by bacteria in the GI tract
0.5
11
–m
FSANZ approved
Xylitol (967)
Sugar alcohol
Partially absorbed in small intestine; unabsorbed sugar alcohols may be metabolised by bacteria in the GI tract
1.0
10
–m
FSANZ approved
PKU 5 phenylketonuria; GRAS 5 Generally recognised as safe Relative sweetness is determined by comparing the approximate sweetness of a sugar substitute with the sweetness of pure sucrose, which has been defined as 1.0. Chemical structure, temperature, acidity and other flavours of the foods in which the substance occurs all influence relative sweetness.
a
Based on a person weighing 70 kg.
b c
Marketed under the trade names Sunett, Sweet One. Recommendations from the World Health Organization limit acesulfame-K intake to 9 mg/kg of body weight per day.
d e
Marketed under the trade names NutraSweet, Equal. Aspartame provides 16 kJ/g, as does protein, but because so little is used, its energy contribution is negligible. In powdered form, it is sometimes mixed with lactose, however, so a 1 g packet may provide 16 kJ.
f
Recommendations from the World Health Organization and in Europe and Canada limit aspartame intake to 40 mg/kg of body weight per day.
g
h
Marketed under the trade names Sweet’N Low.
i
Marketed under the trade names Splenda.
j
Marketed under the trade names Nutralose, Nutrilatose. GRAS 5 food additives that are generally recognised as safe. First established by the FDA in 1958, the GRAS list is subject to revision as new facts become known.
k
l
Marketed under the trade names Sweetleaf, Purevia, Truvia, Honey Leaf. An ADI is ‘not specified’ for sugar alcohols, indicating the highest safety category. They require a warning label, however, that states ‘Excess consumption may have a laxative effect’ if reasonable consumption could result in the daily ingestion of 50 g of a sugar alcohol.
m
Artificial sweeteners Artificial sweeteners are sometimes called non-nutritive sweeteners because they provide virtually no energy. Table 4.2 provides general details about each of the sweeteners. Chapter 9 includes a discussion of their use in weight control, and Chapter 19 focuses on some of the safety issues surrounding their use. Considering that all substances are toxic at some dose, it is little surprise that large doses of artificial sweeteners (or their components or metabolic by-products) may have adverse effects. The question to ask is whether their ingestion is safe for human beings in quantities people normally use (and potentially abuse).
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Stevia – a herbal product The herb stevia derives from a plant whose leaves have long been used by the people of South America to sweeten their beverages. Until recently, stevia was sold in Australia and New Zealand only as a dietary supplement. In 2008, the Australian and New Zealand Food Authority (FSANZ) approved stevia as an ingredient in foods and beverages. The estimated amount of a sweetener that individuals can safely consume each day over the course of a lifetime without adverse effect is known as the Acceptable Daily Intake (ADI).
Sugar alcohols Some ‘sugar-free’ or reduced-kilojoule products contain sugar alcohols. The sugar alcohols (or polyols) provide bulk and sweetness in biscuits, hard candies, sugarless gums, jams and jellies. These products claim to be ‘sugar-free’ on their labels, but in this case, ‘sugar-free does not mean free of kilojoules. Sugar alcohols do provide kilojoules, but fewer than their carbohydrate cousins, the sugars. Because sugar alcohols yield energy, they are sometimes referred to as nutritive sweeteners. Table 4.2 includes their energy values. Sugar alcohols occur naturally in fruits and vegetables; manufacturers also use sugar alcohols in many processed foods to add bulk and texture, to provide a cooling effect or taste, to inhibit browning from heat and to retain moisture. Sugar alcohols evoke a low glycaemic response. The body absorbs sugar alcohols slowly; consequently, they are slower to enter the bloodstream than other sugars. Common side effects include intestinal gas, abdominal discomfort and diarrhoea. For this reason, regulations require food labels to state ‘Excess consumption may have a laxative effect’ if reasonable consumption of that food could result in the daily ingestion of 50 grams of a sugar alcohol. The real benefit of using sugar alcohols is that they do not contribute to dental caries. Bacteria in the mouth cannot metabolise sugar alcohols as rapidly as sugar. Sugar alcohols are therefore valuable in chewing gums, breath mints and other products that people keep in their mouths for a while. Figure 4.15 presents labelling information for products using sugar alternatives.
FIGURE 4.15 Sugar alternatives on food labels
Nutrition Facts Serving Size: 2 pieces (3 g) Servings: 6 Calories: 5
Amount per serving Total Fat 0 g
0%
Sodium 0 mg
0%
Total Carb. 2 g
1%
Sugars 0 g Sugar Alcohol 2 g Protein 0 g
*Per cent Daily Values (DV) are based on a 2000 calorie diet
% DV*
Not a significant source of other nutrients
35% FEWER CALORIES THAN SUGARED GUM
Products containing less than 0.5 g of sugar per serving can claim to be ‘sugarless’ or ‘sugar-free’.
Products that claim to be ‘reduced kcalories’ must provide at least 25% fewer kcalories per serving than the comparison item.
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DLibrary/The Wrigley Co Pty Ltd
Products containing aspartame must carry a warning for people with phenylketonuria.
This ingredient list includes both sugar alcohols and artificial sweetenters.
INGREDIENTS: SORBITOL, MALTITOL, GUM BASE, MANNITOL, ARTIFICIAL AND NATURAL FLAVORING, ACACIA, SOFTENERS, TITANIUM DIOXIDE (COLOR), ASPARTAME, ACESULFAME POTASSIUM AND CANDELILLA WAX. PHENYLKETONURICS: CONTAINS PHENYLALANINE
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Understanding nutrition
For consumers choosing to use alternative sweeteners, the Australian Diabetes Council advises artificial sweeteners can add variety and enjoyment to a low fat and high fibre eating plan although they are not a necessity.16 When used in moderation, these sweeteners will do no harm. In fact, they may even help, by providing an alternative to sugar for people with diabetes, by inhibiting caries-causing bacteria and by limiting energy intake. People may find it appropriate to use any of the sweeteners at times: artificial sweeteners, herbal products, sugar alcohols and sugar itself.
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Alternative sweeteners provide very few kilojoules, which make them a popular choice by consumers to use in place of sugar. The three main sets of alternative sweeteners are artificial sweeteners, herbal products and sugar alcohols. Alternative sweeteners can play a small role in controlling weight and diabetes and are considered safe to use.
4.8 Health effects and recommended intakes of starch and dietary fibre
Getty Images/The Image Bank/Rita Mass
Carbohydrates and fats are the two major sources of energy in the diet. When one is high, the other is usually low – and vice versa. A diet that provides abundant carbohydrate (45 to 65 per cent of energy intake) and some fat (20 to 35 per cent of energy intake) within a reasonable energy allowance best supports good health. To increase carbohydrate in the diet, focus on whole grains, vegetables, legumes and fruits – foods noted for their starch, dietary fibre and naturally occurring sugars.
Health effects of starch and dietary fibre In addition to starch, dietary fibre and natural sugars, whole grains, vegetables, legumes and fruits supply valuable vitamins and minerals, with little or no fat. The following paragraphs describe some of the health benefits of diets that include a variety of these foods daily. Foods rich in starch and dietary fibre offer many health benefits.
Consuming 5 to 10 g of soluble dietary fibre daily reduces blood cholesterol by 3 to 5%. For perspective, ½ cup dry rolled oats provides 8 g of dietary fibre, and ½ cup cooked legumes provides about 6 g of dietary fibre.
Heart disease
High-carbohydrate diets, especially those rich in whole grains, may protect against heart disease and stroke, although sorting out the exact reasons why can be difficult. Such diets are low in animal fat and cholesterol and high in dietary fibre, vegetable proteins and phytochemicals – all factors associated with a lower risk of heart disease. (The role of animal fat and cholesterol in heart disease is discussed in Chapter 5. The role of vegetable proteins in heart disease is presented in Chapter 6. The benefits of phytochemicals in disease prevention are featured in Highlight 13.) Foods rich in soluble dietary fibre (such as oat bran, barley and legumes) lower blood cholesterol by binding with bile acids and thereby increasing their excretion. Consequently, the liver must use its cholesterol to make new bile acids. In addition, the bacterial by-products of dietary fibre fermentation in the colon also inhibit cholesterol synthesis in the liver. The net result is lower blood cholesterol. Several researchers have speculated that dietary fibre may also exert its effect by displacing fats in the diet. Whereas this is certainly helpful, even when dietary fat is low, high intakes of dietary fibre exert a separate and significant cholesterol-lowering effect. In other words, a high-dietary fibre diet helps to decrease the risk of heart disease independent of fat intake.17
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Diabetes High-fibre foods – especially whole grains – play a key role in reducing the risk of type 2 diabetes.18 When soluble dietary fibre traps nutrients and delays their transit through the GI tract, glucose absorption is slowed, which helps to prevent the glucose surge and rebound that seem to be associated with diabetes onset.
Gastrointestinal health Dietary fibre enhances the health of the large intestine. The healthier the intestinal walls, the better they can block absorption of unwanted constituents. Fibre such as cellulose (as in cereal brans, fruits and vegetables) increases stool weight, easing passage and reducing transit time. In this way, dietary fibre helps to alleviate or prevent constipation. Taken with ample fluids, dietary fibre can help to prevent several GI disorders. Large, soft stools ease elimination for the rectal muscles and reduce the pressure in the lower bowel, making it less likely that rectal veins will swell (haemorrhoids). Dietary fibre prevents compaction of the intestinal contents, which could obstruct the appendix and permit bacteria to invade and infect it (appendicitis). In addition, dietary fibre stimulates the GI tract muscles so that they retain their strength and resist bulging out into pouches known as diverticula (illustrated in Figure H3.2 on page 90).19
Cancer Many, but not all, research studies suggest that increasing dietary fibre protects against colon cancer. When the EPIC study of diet and cancer examined the diets of over half a million people in 10 countries for four and a half years, the researchers found an inverse association between dietary fibre and colon cancer.20 People who ate the most dietary fibre (35 grams per day) reduced their risk of colon cancer by 40 per cent compared with those who ate the least fibre (15 grams per day). Importantly, the study focused on dietary fibre, not fibre supplements or additives, which lack valuable nutrients and phytochemicals that also help protect against cancer. Plant foods – vegetables, fruits and wholegrain products – reduce the risks of colon and rectal cancers.21 Dietary fibre may help prevent colon cancer by diluting, binding and rapidly removing potential cancer-causing agents from the colon. In addition, soluble dietary fibre stimulates bacterial fermentation, a process that produces short-chain fatty acids that lower the pH of the colon. These small fat molecules activate cancer-killing enzymes and inhibit inflammation in the colon.22
Weight management High-fibre and wholegrain foods help a person to maintain a healthy body weight. Foods rich in complex carbohydrates tend to be low in fat and added sugars and can therefore promote weight loss by delivering less energy per bite. In addition, as dietary fibre absorbs water from the digestive juices, it swells, creating feelings of fullness and delaying hunger. Many weight-loss products on the market today contain bulk-inducing dietary fibre such as methylcellulose, but buying purified fibre compounds like this is neither necessary nor advisable. Most experts agree that the health- and weight-management benefits attributed to dietary fibre may come from other constituents of fibre-containing foods, and not from dietary fibre alone. For this reason, consumers should select whole grains, legumes, fruits and vegetables instead of fibre-rich supplements. High-fibre foods not only add bulk to the diet but are economical and nutritious as well. Table 4.3 summarises dietary fibre and its health benefits.
Reminder: • carbohydrate: 17 kJ/g • fat: 37 kJ/g
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TABLE 4.3 Dietary fibre: Its characteristics, food sources and health effects in the body FIBRE CHARACTERISTICS
a
MAJOR FOOD SOURCES
ACTIONS IN THE BODY
HEALTH BENEFITS
Soluble, viscous, more fermentable • Gums and mucilages • Pectins • Psylliuma • Some hemicelluloses
Wholegrain products (barley, oats, oat bran, rye), fruits (apples, citrus), legumes, seeds and husks, vegetables; also extracted and used as food additives
• Lower blood cholesterol by binding bile • Slow glucose absorption • Slow transit of food through upper GI tract • Hold moisture in stools, softening them • Yield small fat molecules after fermentation that the colon can use for energy
• Lower risk of heart disease • Lower risk of diabetes
Insoluble, non-viscous, less fermentable • Cellulose • Lignins • Psylliuma • Resistant starch • Many hemicelluloses
Brown rice, fruits, legumes, seeds, vegetables (cabbage, carrots, brussels sprouts), wheat bran, whole grains; also extracted and used as food additives
• Increase faecal weight and speed faecal passage through colon • Provide bulk and feelings of fullness
• Alleviate constipation • Lower risks of diverticulosis, haemorrhoids and appendicitis • May help with weight management
Psyllium, a fibre laxative and cereal additive, has both soluble and insoluble properties.
Harmful effects of excessive dietary fibre intake
To maximise your dietary fibre intake: • eat wholegrain breakfast cereals • eat fruits (such as pears) and vegetables (such as potatoes) with their skins • choose wholegrain breads, brown rice and wholemeal pasta • add legumes to soups, salads and casseroles • eat fresh and dried fruit for snacks.
Despite the benefits of dietary fibre to health, a diet high in dietary fibre also has a few drawbacks. A person who has a small stomach capacity and eats mostly high-fibre foods may not be able to take in enough food to meet energy or nutrient needs. The malnourished, the elderly and young children adhering to all-plant (vegan) diets are especially vulnerable to this problem. Launching suddenly into a high-fibre diet can cause temporary bouts of abdominal discomfort, gas and diarrhoea. To prevent such complications, a person adopting a high-fibre diet can take the following precautions: • Increase dietary fibre intake gradually over several weeks to give the GI tract time to adapt. • Drink plenty of liquids to soften the dietary fibre as it moves through the GI tract. • Select fibre-rich foods from a variety of sources – fruits, vegetables, legumes and wholegrain breads and cereals. Some dietary fibre can limit the absorption of nutrients by speeding the transit of foods through the GI tract and by binding to minerals. When mineral intake is adequate, however, a reasonable intake of high-fibre foods does not seem to compromise mineral balance. Clearly, dietary fibre is like all the nutrients in that ‘more’ is ‘better’ only up to a point. Again, the key words are balance, moderation and variety.
Recommended intakes of starch and dietary fibre Dietary guidelines suggest that carbohydrates provide about half (45 to 65 per cent) of the energy requirement. A person consuming 8000 kilojoules a day should therefore have 3600 to 5200 kilojoules of carbohydrate, or about 200 to 325 grams. Because of the importance of carbohydrate as an essential energy source, there is no specific recommendation on amount required daily. The Australian Dietary Guidelines recommends eating plenty of cereals (including breads, rice, pasta and noodles), preferably wholegrain. Recommendations for dietary fibre suggest the same foods just mentioned: whole grains, vegetables, fruits and legumes, which also provide minerals and vitamins. The Nutrient Reference Values recommend eating 25 grams of dietary fibre per day for women and 30 grams
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for men. The average Australian currently eats around 20 grams of dietary fibre daily.23 One effective way to add fibre is to include plant sources of proteins (legumes) as part of a wellbalanced diet. Table 4.4 presents a list of dietary fibre sources.
TABLE 4.4 Dietary fibre in selected foods Grains Shutterstock.com/Billion Photos
Wholegrain products provide about 1 to 2 g (or more) of dietary fibre per serving: • 1 slice wholegrain or rye bread • 100 g rolled oats.
Vegetables Shutterstock.com/Shebeko
Most vegetables contain about 2 to 3 g of dietary fibre per serving: • ½ cup cooked broccoli, brussels sprouts, cabbage, carrots, cauliflower, sweet corn, eggplant, green beans, green peas, mushrooms, parsnips, pumpkin, spinach, sweet potatoes • ½ cup chopped raw carrots, capsicum.
Fruit Shutterstock.com/leonori
Fresh, frozen and dried fruits have about 2 g of fibre per serving: • 1 medium apple, banana, kiwifruit, nectarine, orange, pear • ½ cup blackberries, blueberries, raspberries, strawberries; fruit juices contain very little dietary fibre
Legumes
PhotoDisc
Many legumes provide about 6 to 8 g of dietary fibre per serving: • ½ cup cooked baked beans, black beans, black-eyed peas, kidney beans, navy beans. Some legumes provide about 5 g of dietary fibre per serving: • ½ cup cooked chickpeas, lentils, split peas.
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Adequate intake of dietary fibre: • fosters weight management • lowers blood cholesterol • may help prevent colon cancer • helps prevent and control diabetes • helps prevent and alleviate haemorrhoids • helps prevent appendicitis • helps prevent diverticulitis. Excessive intake of dietary fibre: • displaces energy- and nutrient-dense foods • causes intestinal discomfort and distension • may interfere with mineral absorption.
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From guidelines to groceries The Australian Guide to Healthy Eating recommends having several servings of fruits, vegetables or legumes, and of bread, cereals, rice, pasta or noodles daily as the best way to achieve the recommended amount of carbohydrates and dietary fibre. In selecting high-fibre foods, keep in mind the principle of variety. The dietary fibre in oats lowers cholesterol, whereas that in bran helps promote GI tract health.
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Enjoy a wide variety of nutritious foods, including grain (cereal) foods, mostly wholegrain and/or high cereal fibre varieties, such as breads, cereals, rice, pasta, noodles, polenta, couscous, oats, quinoa and barley.
Bread, cereals, rice, pasta and noodles Be aware that some foods in this group, especially baked goods such as biscuits, croissants and muffins, contain added sugars, added fat or both. Aim to select baked products that state they are ‘high-fibre’, ‘very high-fibre’, ‘a good source of fibre’, ‘have increased fibre’, ‘are fibreenriched’ or ‘have fibre added’. When selecting from this group of foods, be sure to choose at least half wholegrain products (see Figure 4.16).
FIGURE 4.16 Bread labels compared Food labels list the quantities of total carbohydrate, dietary fibre and sugars. A close look at these two labels reveals that bread made from whole-wheat flour provides almost three times as much dietary fibre as the one made mostly from refined flour.
Nutrition information
Nutrition information SERVINGS PER PACKAGE: 11 (20 SLICES 1 2 CRUSTS)
SERVINGS PER PACKAGE: 11 (20 SLICES 1 2 CRUSTS)
SERVING SIZE: 60 g (2 SLICES)
SERVING SIZE: 60 g (2 SLICES)
PER SERVING 60 g
PER SERVING 60 g
PER 100 g
PER 100 g
Energy
589 kJ
981 kJ
Energy
593 kJ
989 kJ
Protein
5.6 g
9.4 g
Protein
5.5 g
9.1 g
Fat:
Fat: • Total
1.7 g
2.9 g
• Total
2.3 g
3.9 g
• Saturated
0.2 g
0.4 g
• Saturated
0.3 g
0.5 g
• Trans
Less than 0.05 g
Less than 0.05 g
• Trans
Less than 0.05 g
Less than 0.05 g
• Polyunsaturated
0.7 g
1.1 g
• Polyunsaturated
9.8 g
1.4 g
• Mono-unsaturated
0.8 g
1.3 g
• Mono-unsaturated
1.1 g
1.9 g
Carbohydrate:
Carbohydrate: • Total
23.6 g
39.4 g
• Total
22.6 g
37.8 g
• Sugars
1.4 g
2.4 g
• Sugars
1.8 g
3.0 g
Dietary fibre
9g
15 g
Dietary fibre
1.8 g
6.1 g
Sodium
293 mg
489 mg
Sodium
238 mg
397 mg
Quantities stated above are averages only.
Quantities stated above are averages only. INGREDIENTS
INGREDIENTS Whole-wheat wheat flour, water, wheat flour, baker’s yeast, vinegar, gluten, salt, canola oil, emulsifiers (481, 472e, 471), soy flour, sugar, vitamin (thiamin).
Wheat flour, water, baker’s yeast, vinegar, salt, canola oil, gluten, emulsifiers (481, 472e, 471), soy flour, sugar, vitamin (thiamin).
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Chapter 4: The carbohydrates: sugars, starches and dietary fibre
Vegetables The amount of carbohydrate in a serving of vegetables depends primarily on its starch content. Starchy vegetables – ½ cup of cooked corn, peas or potatoes – provide about 15 grams of carbohydrate per serving. A serving of most other non-starchy vegetables – such as ½ cup of broccoli, green beans or tomatoes – provides about 5 grams.
Fruit A typical fruit serving – a small banana, apple or orange, or ½ cup of most canned or fresh fruit – contains an average of about 15 grams of carbohydrate, mostly as sugars, including the fruit sugar fructose. Fruits vary greatly in their water and dietary fibre contents and, therefore, in their sugar concentrations.
Milks, yoghurt and cheese A serving (1 cup) of milk or yoghurt provides about 12 grams of carbohydrate. Cottage cheese provides about 6 grams of carbohydrate per cup, but most other cheeses contain little, if any, carbohydrate.
Meat, fish, poultry, eggs, nuts and legumes With two exceptions, foods in the meats and meat alternatives group deliver almost no carbohydrate to the diet. The exceptions are nuts, which provide a little starch and dietary fibre along with their abundant fat, and legumes, which provide an abundance of both starch and dietary fibre. Just ½ cup serving of lentils provides about 20 grams of carbohydrate, of which one-third is from dietary fibre.
Read food labels
Food labels list the amount, in grams, of total carbohydrate – including starch – per serving and per 100 grams (review Figure 4.16). Dietary fibre (grams) is also listed separately, as are sugars (grams). Sugars reflect both added sugars and those that occur naturally in foods, which can make choosing products with low amounts of added sugars difficult.
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Clearly a diet rich in complex carbohydrates – starches and dietary fibre – supports efforts to control body weight and prevent heart disease, cancer, diabetes and GI disorders. For these reasons, recommendations urge people to eat plenty of whole grains, vegetables, legumes and fruits – enough to provide 45 to 65 per cent of the daily energy intake from carbohydrate.
In today’s world, there is one other reason why plant foods rich in complex carbohydrates and natural sugars are a better choice than animal foods or foods high in concentrated sweets: in general, less energy and fewer resources are required to grow and process plant foods than to produce sugar or foods derived from animals.
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Complex carbohydrates are long chains of monosaccharides joined together. TRUE
Complex carbohydrates contain many glucose units and, in some cases, a few other monosaccharides strung together as either oligosaccharides or larger polysaccharides.
2 The majority of carbohydrate digestion occurs in the large intestine. FALSE
Although some digestion occurs in the mouth, the majority of the digestion of carbohydrates occurs in the small intestine.
People who suffer lactose intolerance need to manage their dairy food intake so as to ensure adequate amounts of calcium in the diet. Choosing yoghurts and hard cheeses and spreading dairy intake across the day can assist in dietary management of lactose intolerance.
4 Glucose fuels the majority of the body’s energy needs. TRUE
3 People who suffer lactose intolerance must avoid all dairy foods. FALSE
Glucose fuels the work of most of the body’s cells. Fat and protein can be used as a fuel source but glucose is the body’s preferred form of fuel.
NUTRITION PORTFOLIO Foods derived from plants – whole grains, vegetables, legumes and fruits – naturally provide ample carbohydrates and dietary fibre with little or no fat. Refined foods often contain added sugars and fat. • List the types and amounts of grain products you eat daily, making note of which are wholegrain or refined foods and how your choices could include more wholegrain options.
•
•
List the types and amounts of fruits and vegetables you eat daily, making note of how many are dark green, orange or deep yellow, how many are starchy or legumes, and how your choices could include more of these options. Describe choices you can make in selecting and preparing foods and beverages to lower your intake of added sugars.
STUDY QUESTIONS c d
Multiple choice questions Answers can be found at the back of the book. 1
Carbohydrates are found in virtually all foods except: a b c d
2
4
c
maltose, fructose and galactose sucrose, maltose and fructose maltose, sucrose and lactose glucose, fructose and sucrose
d 6
The making of a disaccharide from two monosaccharides is an example of: a b c d
condensation gluconeogenesis digestion hydrolysis
Which carbohydrate is the most abundant in fruit? a b
Fructose Glycogen
The significant difference between starch and cellulose is that: a b
Disaccharides include: a b c d
3
5
milks meats breads fruits
starch is a polysaccharide, but cellulose is not animals can store glucose as starch, but not as cellulose hormones can make glucose from cellulose, but not from starch digestive enzymes can break the bonds in starch, but not in cellulose
The ultimate goal of carbohydrate digestion and absorption is to yield: a b c d
7
Lactose Starch
enzymes amylase dietary fibre glucose
Most carbohydrate digestion occurs in the: a b c d
mouth stomach pancreas small intestine
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Chapter 4: The carbohydrates: sugars, starches and dietary fibre
8
The human body stores glucose as: a b c d
9
dextrins starches fibre glycogen
Insulin; glycogen Glycogen; adrenaline Insulin; glucagon Glucagon; insulin
10 What percentage of the daily energy intake should come from carbohydrates? a b c d
15 to 20 25 to 30 45 to 50 45 to 65
Review questions 1 Which carbohydrates are described as simple and which as complex? (Section 4.1) 2
3
What happens in a condensation reaction? In a hydrolysis reaction? How are these reactions important in carbohydrates? (Section 4.2)
4
Describe the structure of polysaccharides, and name the ones important in nutrition. How are starch and glycogen similar, and how do they differ? How does dietary fibre differ from these polysaccharides? (Section 4.3)
5
Why does lactose intolerance occur? Do people with lactose intolerance need to avoid all dairy foods? If not, how can people with lactose intolerance manage their dairy food intake? (Section 4.4)
6
How is glucose made from protein? What is this process called? What is meant by the protein-sparing action of carbohydrate? (Section 4.5)
7
How does the body maintain its blood glucose concentration? What happens when the blood glucose concentration rises too high or falls too low? (Section 4.5)
8
What is meant by glycaemic index? How can this concept be used to improve health? (Section 4.5)
9
What are the health effects of starches and dietary fibre? What are the dietary recommendations regarding these complex carbohydrates? (Section 4.8)
What does the pancreas secrete when blood glucose rises and when blood glucose falls? a b c d
Describe the structure of a monosaccharide, and name the three monosaccharides important in nutrition. Name the three disaccharides commonly found in foods and their component monosaccharides. In what foods are these sugars found? (Section 4.2)
127
10 Which foods provide starches and dietary fibre? (Section 4.8)
NUTRITION CALCULATIONS These problems will give you practice in doing simple nutrition-related calculations. Although the situations are hypothetical, the numbers are real, and calculating the answers (see the Answers section at the back of this book) provides a valuable lesson. Be sure to show your calculations for each problem. Health recommendations suggest that 45 to 65 per cent of the daily energy intake comes from carbohydrates. Stating recommendations in terms of percentage of energy intake is meaningful only if energy intake is known. The following exercises illustrate this concept. 1
Calculating carbohydrate intakes: a
Calculate the carbohydrate intake (in grams) for a student who has a high carbohydrate intake (70 per cent of energy intake) and a moderate energy intake (8000 kJ/day).
b
c
2
Now consider a professor who eats half as much carbohydrate as the student (in grams) and has the same energy intake. What percentage does carbohydrate contribute to the daily intake? Now consider an athlete who eats twice as much carbohydrate (in grams) as the student and has a much higher energy intake (15 000 kJ/day). What percentage does carbohydrate contribute to this person’s daily intake?
In an attempt to lose weight, a person adopts a diet that provides 150 grams of carbohydrate per day and limits energy intake to 4000 kJ. What percentage does carbohydrate contribute to this person’s daily intake?
These exercises should convince you of the importance of examining actual intake as well the percentage of energy intake.
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NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search ‘lactose intolerance’ at the Victorian Government Better Health Channel: http://www.betterhealth.vic.gov.au • Search for ‘sugars’ and ‘fibre’ at the International Food Information Council Foundation site: https://www.foodinsight.org/
•
•
Learn more about dental caries from the HealthInsite webpages from the Australian Government Department of Health and Ageing: https://www.healthdirect.gov.au/ Learn more about diabetes from Diabetes Australia, Diabetes New Zealand and the US National Institute of Diabetes and Digestive and Kidney Diseases: http://www.diabetesaustralia.com.au, http://www.diabetes.org.nz and http://www.niddk. nih.gov
SEARCH ME! NUTRITION Keyword: carbohydrate weight loss To lose weight, is it more important to reduce carbohydrates or fat? The article Carbohydrates as macronutrients in relation to protein and fat for body
weight control addresses this question. Can weight be lost simply by restricting how much fat is eaten? What is the role of different sources of carbohydrate in weight loss?
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Chapter 4: The carbohydrates: sugars, starches and dietary fibre
4.9 CARBS, KILOJOULES AND CONTROVERSIES
Carbohydrates’ energy contributions The incidence of obesity in Australia and New Zealand, along with all industrialised and many developing countries, has risen dramatically over the past several decades.1 Popular diet books often blame carbohydrates for this increase in obesity. One way researchers can explore whether the amount of carbohydrate in the diet contributes to increases in body weight over time is by reviewing national food intake survey records, such as the United States National Health and Nutrition Examination Survey (NHANES) records. Figure H4.1 presents a summary of the energy nutrient data that has been compiled in the United States over the past three decades. These data show some remarkable trends. Over the past 30–40 years, energy from carbohydrates has increased from 42 to 49 per cent.2 At the same time, energy from fat dropped from 37 to 34 per cent. The percentage of protein intake
HIGHLIGHT
4
stayed about the same. Although these are data from the United States, many similarities will exist with Australia and New Zealand.
FIGURE H4.1 Energy nutrients over time Key: Carbohydrate Fat Protein 60 Daily intake (% kcal/day)
Carbohydrate-rich foods are easy to like. Mashed potatoes, warm muffins, blueberry pancakes, freshly baked bread, and tasty rice or pasta dishes tempt most people’s palates. In recent years, such foods have been blamed for causing weight gain and harming health. In contrast, the Australian Dietary Guidelines recommends eating plenty of vegetables, legumes, beans, fruit and grain (cereal foods) – all carbohydrate-rich foods. Do carbohydrate-rich foods cause obesity and related health problems? Should people ‘cut carbs’ to lose weight and protect their health? Many popular diet books espouse a carbohydrate-restricted or carbohydrate-modified diet. Some claim that all or some types of carbohydrates are bad. Others go so far as to equate carbohydrates with toxic poisons or addictive drugs. ‘Bad’ carbohydrates – such as sugar, white flour and potatoes – are considered evil because they are absorbed easily and raise blood glucose. The pancreas then responds by secreting insulin – and insulin is touted as the real villain responsible for an epidemic of obesity. Whether restricting overall carbohydrate intake or replacing certain ‘bad’ carbohydrates with ‘good’ carbohydrates, many of these popular diets tend to distort the facts. This highlight examines the scientific evidence behind some of the current controversies surrounding carbohydrates and their kilojoules.
129
50 40 30 20 10 0
1977–78
2011–12 Years
A closer look at the data reveals that, as the percentage of energy from the three energy nutrients shifted slightly, total daily energy intake increased significantly. In general, as food became more readily available, consumers began to eat more than they had in the past. Since the 1970s, total energy intakes per day have increased by about 1800 kilojoules.3 Almost all of the increase in energy came from an increase in carbohydrate intake. At the same time, most people were not active enough to use up the extra energy; in fact, estimated activity levels declined over the same period.4 Might too many carbohydrates in the diet be to blame for weight gains? Interestingly, epidemiological studies find an inverse relationship between carbohydrate intake and body weight.5 Those with the highest carbohydrate intake have the lowest body weight and vice versa. Dietary fibre, which favours a healthy body weight, explains some but not all of this relationship. Might a low-carbohydrate diet support weight losses? Studies report that people following low-carbohydrate diets do lose weight.6 In fact, they may lose more than people
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following conventional high-carbohydrate, low-fat diets – but generally only in the short term. Their later gains make up the difference, so total weight loss is no different after one year. For the most part, weight loss is similar for people following either a low-carbohydrate or a highcarbohydrate diet. This is an important point. Weight losses reflect restricted kilojoules – not the proportion of energy nutrients in the diet. Any diet can produce weight loss, at least temporarily, if energy intake is restricted.
Sugars’ share in the problem Over the past several decades, as obesity rates increased sharply, consumption of added sugars reached an alltime high. In the United States and Canada, much of the rising peak in added sweeteners has come from high-fructose corn syrup.7 High-fructose corn syrup is composed of fructose and glucose in a ratio of roughly 50:50. Compared with sucrose, high-fructose corn syrup in the United States is less expensive than cane-sugar, easier to use and more stable. In addition to being used in beverages, high-fructose corn syrup sweetens lollies and sweets, baked goods and hundreds of other foods. Fructose contributes about half of the added sugars in the United States food supply and accounts for about 10 per cent of the average energy intake in the United States. Estimates of the apparent consumption of high-fructose corn syrup in Australia and New Zealand suggest that intake remains low and represents less than 10 per cent of the total intake of additive sweeteners.8 Intakes may be higher in New Zealand as that country allows the importation of cola drinks manufactured in the United States. Although the use of high-fructose corn syrup sweetener parallels unprecedented increases in the incidence of obesity, particularly in the United States, does it mean that increasing sugar intakes are responsible for the increase in body fat and associated health problems?9 Excess sugar in the diet may be associated with more fat on the body. When eaten in excess of need, energy from added sugars contributes to body fat stores, just as excess energy from other sources does. Added sugars provide excess energy, raising the risk of weight gain. When total energy intake is controlled, however, moderate amounts of sugar do not cause obesity. Yet moderating sugar intake can be a challenge. Some claim sugar is addictive. Others assert sugary beverages are particularly easy to swallow and make it difficult for the body to regulate appetite control and energy metabolism.
Cravings and addictions Do sugars cause cravings and addictions? Foods in general, and carbohydrates and sugars more specifically, are not physically addictive in the ways that drugs are. Yet some
people describe themselves as having ‘carbohydrate cravings’ or being ‘sugar addicts’. One frequently noted theory is that people seek carbohydrates as a way to increase their levels of the brain neurotransmitter serotonin, which elevates mood. Interestingly, when those with self-described carbohydrate cravings indulge, they tend to eat more of everything; the percentage of energy from carbohydrates remains unchanged. One reasonable explanation for the carbohydrate cravings that some people experience involves the selfimposed labelling of a food as both ‘good’ and ‘bad’ – that is, one that is desirable but should be eaten with restraint. Restricting intake heightens the desire further (a ‘craving’). Then ‘addiction’ is used to explain why resisting the food is so difficult, and sometimes even impossible. But the ‘addiction’ is not physiological or pharmacological.
Simple to swallow In general, the energy intake of people who drink soft drinks, fruit punches and other sugary beverages is greater than those who choose differently. For example, people who drink as much as 600 millilitres or more of sugarsweetened soft drinks daily can consume 1000 kilojoules a day more than people who don’t. Not too surprisingly, they also tend to weigh more.10 Overweight children and adolescents tend to consume more sweet desserts and soft drinks than their normal-weight peers, with a review of the research confirming that consumption of sugary beverages correlates with both increased food energy and being overweight.11 The liquid form of sugar in soft drinks makes it especially easy to overconsume energy. Swallowing liquid energy requires little effort. These sweetened beverages are also cheap and widely available. The convenience, economy, availability and flavours of sugary foods and beverages make overconsumption especially likely. Limiting selections of foods and beverages high in added sugars can be an effective weight-loss strategy, especially when added sugars become an important energy source in their diets. Replacing a can of cola with a glass of water every day, for example, can help a person lose up to 2.5 per cent of their body weight.12 That may not sound like much, but it all adds up – and for very little effort.
Appetite control Recall that glucose stimulates the release of insulin from the pancreas. Insulin, in turn, sets off a sequence of hormonal actions that suppress the appetite. (Appetite regulation is discussed fully in Chapter 8.) Fructose, in contrast, does not stimulate the release of insulin, and therefore does not suppress appetite. Theoretically, then, eating lots of fructose would never satisfy a person’s
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Chapter 4: The carbohydrates: sugars, starches and dietary fibre
appetite. Although this idea sounds plausible, a major flaw exists: people don’t typically eat pure fructose – they eat sucrose or high-fructose corn syrup, and both of these sugars contain sufficient glucose to stimulate the release of insulin and suppress appetite accordingly. Whether the meal or snack is liquid or solid may also affect appetite. Even when energy intake is the same, a fresh apple suppresses appetite more than apple juice. Consequently, beverages can influence weight gains both by providing energy and by not satisfying hunger.
Energy regulation One explanation of why it is so easy to overconsume sugary beverages is, perhaps, that the body’s energy regulation system cannot detect the energy of sugar in liquid form. Consequently, a person would not compensate for energy excesses by reducing food intake at other times. A classic research study tested this hypothesis by giving students 450 kilojoules’ worth of either solid sugars (roughly 40 jelly beans) or liquid sugars (about three 375-millilitre cans of soft drinks) to consume daily whenever they chose.13 It showed that the energy intake from other foods during ‘jelly bean weeks’ was lower – the students ate less food to compensate for the energy received from the jelly beans. By comparison, energy intake from other foods during the ‘soft drink weeks’ did not decrease – the students ate their meals without compensating for the kilojoules in the beverages. Consequently, body weight increased during the beverage weeks, but not during the jelly bean weeks. Other studies, however, have found no differences between liquid and solid sugars when examining appetite, energy intake or body weight.14
Insulin’s response Several popular diet books hold insulin responsible for the obesity problem and advocate a low glycaemic diet as the weight-loss solution. Yet among nutrition researchers, controversy continues to surround the questions of whether insulin promotes weight gain or a low glycaemic diet fosters weight loss. Recall that just after a meal, blood glucose rises and insulin responds. How high the insulin levels surge may
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influence whether the body stores or uses its glucose and fat supplies. What does insulin do? Among its roles, insulin facilitates the transport of glucose into the cells, the storage of fatty acids as fat and the synthesis of cholesterol. It is an anabolic hormone that builds and stores, but there’s more to the story. Insulin is only one of many factors involved in the body’s metabolism of nutrients and regulation of body weight. Most importantly, insulin is critical to maintaining health, as any person with type 1 diabetes can attest. Insulin causes problems only when a person develops insulin resistance – that is, when the body’s cells do not respond to the large quantities of insulin that the pancreas continues to pump out in an effort to get a response. Insulin resistance is a major health problem – but it is not caused by carbohydrate, protein or fat. It results from being overweight. Importantly, when a person loses weight, insulin response improves, regardless of diet.
The glycaemic index and body weight The glycaemic index identifies foods that raise blood glucose and stimulate insulin secretion. What is the relationship between a diet’s glycaemic index and fat storage? Studies find that diets with a high glycaemic index are positively associated with body weight.15 Because fructose does not stimulate insulin secretion, it has a low glycaemic index. Yet some research suggests that fructose favours the fat-making pathways and impairs the fatclearing pathways in the body.16 As the liver busily makes lipids, its handling of glucose becomes unbalanced and insulin resistance develops.17 Research is beginning to find links between high fructose intake and prediabetes and the metabolic syndrome. Might a low glycaemic diet foster weight loss? When obese people followed one of three low-energy diets – high glycaemic diet, low glycaemic diet or high-fat diet – for nine months, they all lost about 9 kilograms.18 Furthermore, insulin sensitivity improved for all of them. Other studies confirm that overweight people experience similar weight losses on a low-energy diet regardless of whether it has a high or a low glycaemic index.19 In other words, all low-energy diets support weight loss; defining the type or amount of carbohydrate does not enhance losses.
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REVIEW IT
As might be expected, given the similarity in their chemical compositions, high-fructose corn syrup and sucrose produce similar effects in appetite control and energy metabolism. In fact, high-fructose corn syrup is more like sucrose than fructose. Furthermore, people don’t eat pure fructose; they eat foods and beverages that contain added sugars – either high-fructose corn syrup or sucrose. Limiting these sugars is a helpful strategy when trying to control body weight, but restricting all carbohydrates would be unwise. The quality of the diet suffers when carbohydrates are restricted. Without fruits, vegetables and whole grains, lowcarbohydrate diets lack not only carbohydrate but fibre, vitamins, minerals and phytochemicals as well – all dietary factors that are protective against disease. A healthy diet includes a variety of carbohydrate-rich sources: wholegrain cereals, vegetables, legumes and fruits.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS 1
Why should we include carbohydrates in the diet?
2
Why do diets low in carbohydrates appear to achieve good weight loss results in the short term? If you
were to exclude carbohydrates from the diet, what types of foods would you not eat? What types of foods would this leave you to select from?
REFERENCES CHAPTER 1
2 3
4
5
6
7
8
9
P. Gunness and co-authors, Mechanisms underlying the cholesterollowering properties of soluble dietary fibre polysaccharides. Food Funct. (2010 November) 1(2):149–55. NIH Consensus Development Conference: Lactose intolerance and health, http://consensus.nih.gov/2010/lactosestatement.htm K Furukawa and co authors, Glycolipids: Essential regulator of neuro-inflammation, metabolism and gliomagenesis, Biochimica et Biophysica Acta (BBA) – General Subjects 1861 (10) (2017): 2479–84. A. B. Walls & A. Schousboe, Brain glycogen: emergency fuel and dynamic function in neurotransmission, Metabolic Brain Disease 30 (2015): 249. E. L. M. Barr and co-authors, AusDiab 2005: The Australian Diabetes, Obesity and Lifestyle Study, Melbourne: International Diabetes Institute (2006). K. J. Coppell and co-authors, Prevalence of diagnosed and undiagnosed diabetes and prediabetes in New Zealand: findings from the 2008/09 Adult Nutrition Survey. NZ Med J 126.1370 (2013): 23–42. K. Foster-Powell, S. H. A. Holt and J. C. Brand-Miller, International table of glycemic index and glycemic load values: 2002, American Journal of Clinical Nutrition 76 (2002): 5–56. G. Livesey and co-authors, Is there a dose-response relation of dietary glycemic load to risk of type 2 diabetes? Meta-analysis of prospective cohort studies, American Journal of Clinical Nutrition 97 (2013): 584–596. L. M. Goff and co-authors, Low glycaemic index diets and blood lipids: a systematic review and meta-analysis of randomised controlled trials, Nutrition, Metabolism, and Cardiovascular Diseases 23 (2013): 1–10.
10
11
12
13
14
15
16 17
18
G. M. Turner-McGrievy and co-authors, Decreases in dietary glycemic index are related to weight loss among individuals following therapeutic diets for type 2 diabetes, Journal of Nutrition 141 (2011): 1469–74. M. L. Neuhouser and co-authors, A low-glycemic load diet reduces serum C-reactive protein and modestly increases adiponectin in overweight and obese adults, Journal of Nutrition 142 (2012): 369–74. A. I. Cozma and co-authors, Effect of fructose on glycaemic control in diabetes: a systematic review and meta-analysis of controlled feeding trials, Diabetes Care 35 (2012): 1611–20. B. M. Popkin and co-authors, The role of high sugar foods and sugar-sweetened beverages in weight gain and obesity, in T. Gill (ed), Managing and Preventing Obesity: Behavioural Factors and Dietary Interventions (2014), Cambridge, UK: Elsevier. A. Sheiham and W.P.T. James, Diet and dental caries: the pivotal role of free sugars reemphasized, Journal of Dental Research 94 (2015): 1341–7. T. J. McNeill & W.S. Shrapnel, Apparent consumption of refined sugar in Australia (1938–2011), European Journal of Clinical Nutrition 1 July 2015; doi:10.1038/ejcn.2015.105 Australian Diabetes Council. Alternative sweeteners. Talking Diabetes 2 (2012). L. Hartley and co authors, Dietary fibre to prevent cardiovascular disease, Cochrane Database of Systematic Reviews 1 (2016), Issue 1. Art. No.: CD011472. DOI:10.1002/14651858.CD011472.pub2. E. Q. Ye and co-authors, Greater whole-grain intake is associated with lower risk of type 2 diabetes, cardiovascular disease, and weight gain, Journal of Nutrition 142 (2012): 1304–13.
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Chapter 4: The carbohydrates: sugars, starches and dietary fibre
19
G. Maconi and co-authors, Treatment of diverticular disease of the colon and prevention of acute diverticulitis: a systematic review, Diseases of the Colon and Rectum 54 (2011): 1326–38. 20 S. A. Bingham and co-authors, Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study, Lancet 361 (2003): 1496–501.
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21
Q. J. Wu and co-authors, Cruciferous vegetables intake and the risk of colorectal cancer: a meta-analysis of observational studies, Annals of Oncology 24(4) (2013): 1079–87. 22 J. I. Barrasa and co-authors, Bile acids in the colon, from healthy to cytotoxic molecules, Toxicology in Vitro 27 (2013): 964–77. 23 Better Health Channel, Fibre in Food, http://www.betterhealth.vic. gov.au
HIGHLIGHT 1
2
3
4
5
6
7
8
9
10 11
B. Swinburn and A. Wood, Progress on obesity prevention over 20 years in Australia and New Zealand, Obesity Reviews 14 (2013): S60–S26. G Austin and co authors, Trends in carbohydrate, fat, and protein intakes and association with energy intake in normal-weight, overweight, and obese individuals: 1971–2006 The American Journal of Clinical Nutrition, 93 (4), (2011): 836–43. W. S. Yancy and co-authors, Trends in energy and macronutrient intakes by weight status over four decades, Public Health Nutrition 17 (2014): 256–65. Australian Bureau of Statistics, Profiles of Health, Australia 2011–13: overweight and obesity, ABS Catalogue Number 4338.0, Canberra: ABS, (2013). G. A. Gaesser, Carbohydrate quantity and quality in relation to body mass index, Journal of the American Dietetic Association 107 (2007): 1768–80. A. M. Johnstone, and co-authors, Effects of a high-protein, lowcarbohydrate v. high-protein, moderate-carbohydrate weight-loss diet on antioxidant status, endothelial markers and plasma indices of the cardiometabolic profile, British Journal of Nutrition 106 (2011): 282–91. V. S. Malik, M. B. Schulze and F. B. Hu, Intake of sugar-sweetened beverages and weight gain: a systematic review, American Journal of Clinical Nutrition 84 (2006): 274–88. T. J. McNeill & W. S. Shrapnel, Apparent consumption of refined sugar in Australia (1938–2011), European Journal of Clinical Nutrition (2015); doi:10.1038/ejcn.2015.105 J. M. Rippe and T. J. Angelopoulos, Sucrose, high-fructose corn syrup, and fructose, their metabolism and potential health effects: what do we really know? Advances in Nutrition 4 (2013): 236–245. B. Richelsen, Sugar-sweetened beverages and cardio-metabolic disease risks, Clinical Nutrition and Metabolic Care 16 (2013): 478–84. V. S. Malik, M. B. Schulze and F. B. Hu, Intake of sugar-sweetened beverages and weight gain: a systematic review, American Journal of Clinical Nutrition 84 (2006): 274–88.
12
13
14
15
16
17 18
19
D. F. Tate and co-authors, Replacing caloric beverages with water or diet beverages for weight loss in adults: main results of the Choose Healthy Options Consciously Everyday (CHOICE) randomized clinical trial, American Journal of Clinical Nutrition 95 (2012): 555–63. D. P. DiMeglio and R. D. Mattes, Liquid versus solid carbohydrate: Effects on food intake and body weight, International Journal of Obesity and Related Metabolic Disorders 24 (2000): 794–800. S. Soenen and M. S. Weterterp-Plantenga, No differences in satiety or energy intake after high-fructose corn syrup, sucrose, or milk preloads, American Journal of Clinical Nutrition 86 (2007): 1586–94. O. Gogebakan and co-authors, Effects of weight loss and long-term weight maintenance with diets varying in protein and glycemic index on cardiovascular risk factors: The Diet, Obesity, and Genes (DiOGenes) Study: a randomized, controlled trial, Circulation 124 (2011): 2829–38. E. J. Parks and co-authors, Dietary sugars stimulate fatty acid synthesis in adults, Journal of Nutrition 138 (2008): 1039–46. C. A. Lyssiotis and L. C. Cantley, Metabolic syndrome: F stands for fructose and fat, Nature 502 (2013): 181–2. S. K. Raatz and co-authors, Reduced glycemic index and glycemic load diets do not increase the effects of energy restriction on weight loss and insulin sensitivity in obese men and women, Journal of Nutrition 135 (2005): 2387–91. R. Sichieri and co-authors, An 18-mo randomized trial of a lowglycemic-index diet and weight change in Brazilian women, American Journal of Clinical Nutrition 86 (2007): 707–13; S. K. Das and co-authors, Long-term effects of 2 energy-restricted diets differing in glycemic load on dietary adherence, body composition, and metabolism in CALERIE: a 1-y randomized controlled trial, American Journal of Clinical Nutrition 85 (2007): 1023–30.
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CHAPTER
5
THE LIPIDS: TRIGLYCERIDES, PHOSPHOLIPIDS AND STEROLS Nutrition in your life
Most of us know what we don’t like about body fat, but we should all appreciate how it insulates us against the cold or powers us as we ride a bike around a lake. And what about food fat? It is right to credit fat for providing the delicious flavours and aromas of buttered popcorn and hamburgers – and to criticise it for contributing to the weight gain and heart disease so common today. The challenge is to strike a healthy balance of enjoying some fat, but not too much. Learning which kinds of fats are most harmful will help you make wise decisions. In the ‘Nutrition portfolio’ at the end of this chapter, you can examine whether your current fat choices are meeting dietary goals. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F Saturated and polyunsaturated fats have a different number of double bonds. T F Polyunsaturated fats can only be omega-3, not omega-6 fatty acids. T F Triglycerides are the major form of fats in the human diet. T F Fat and cholesterol are carried in the blood in special droplets. T F Saturated fats reduce the risk of heart disease.
LEARNING OBJECTIVES 5.1 Recognise the chemistry of fatty acids and triglycerides and differences between saturated and unsaturated fats. 5.2 Describe the chemistry, food sources, and roles of phospholipids and sterols. 5.3 Summarise fat digestion, absorption and transport. 5.4 Outline the major roles of fats in the body, including a discussion of essential fatty acids and the omega fatty acids.
5.5 Explain the relationships among saturated fats, trans fat, and cholesterol and chronic diseases, noting recommendations. 5.6 Explain the relationships between monounsaturated and polyunsaturated fats and health, noting recommendations. 5.7 Identify which fats support health and which impair it.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
No doubt you have heard that fats can contribute to the development of several chronic diseases, but did you realise that some fats are also essential to good health? Most people are surprised to learn that fat has virtues and that a well-balanced diet needs at least a little fat. Getting enough fat is rarely a problem. At least traces of fat can be found in almost all foods. In our society of abundance, people are more likely to consume too much fat, or too much of some kinds of fat – with consequent health problems. Learning which kinds of fats are harmful or helpful is key to healthy diet planning. Fat refers to the class of nutrients known as lipids. The lipid family includes triglycerides (fats and oils), phospholipids and sterols. Triglycerides are most abundant, both in foods and in the body. The following sections describe the similarities and differences among the remarkably diverse members of the lipid family.
5.1 The chemist’s view of fatty acids and triglycerides
Like carbohydrates, lipids are composed of carbon (C), hydrogen (H) and oxygen (O) atoms. Because these lipids have many more carbon and hydrogen atoms in proportion to oxygen atoms, they can supply more energy per gram than carbohydrates can (Chapter 7 provides details). The many names and relationships in the lipid family can seem overwhelming – like meeting a friend’s extended family for the first time. To ease the introductions, this chapter first presents each of the lipids from a chemist’s point of view using both words and diagrams. Then the chapter follows the lipids through digestion and absorption and into the body to examine their roles in health and disease. For people who think more easily in words than in chemical symbols, this preview of the upcoming chemistry may be helpful: 1 Every triglyceride contains one molecule of glycerol and three fatty acids (basically, chains of carbon atoms). 2 Fatty acids may be 4 to 24 (even numbers of) carbons long, the 18-carbon ones being the most common in foods and especially noteworthy in nutrition. 3 Fatty acids may be saturated or unsaturated. Unsaturated fatty acids may have one or more points of unsaturation – that is, they may be mono-unsaturated or polyunsaturated. 4 Of special importance in nutrition are the polyunsaturated fatty acids known as omega-3 fatty acids and omega-6 fatty acids. 5 The 18-carbon fatty acids are linolenic acid (omega-3) and linoleic acid (omega-6). Both are essential fatty acids that the body cannot make. Each is the primary member of a family of longer-chain fatty acids that help to regulate blood pressure, blood clotting, and other body functions important to health.
Fatty acids All fatty acids have the same basic structure – a chain of carbon and hydrogen atoms with an acid group (COOH) at one end and a methyl group (CH3) at the other end. Fatty acids may differ from one another, however, in the length of their carbon chains and in the number and location of their double bonds, as the following paragraphs describe.
The length of the carbon chain Most naturally occurring fatty acids contain even numbers of carbons in their chains – up to 24 carbons in length. This discussion begins with the 18-carbon fatty acids, which are
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abundant in our food supply. Stearic acid is the simplest of the 18-carbon fatty acids; the bonds between its carbons are all alike: H H
H H H
H
H H H
H
H H H H
H H H H O
C
C C
C
C
C C
C
C
C C C C
C C
H
H H H
H
H H H
H
H H H H
H H H H
C
C
C
O H
Stearic acid, an 18-carbon saturated fatty acid
Stearic acid, an 18-carbon saturated fatty acid
As you can see, stearic acid is 18 carbons long, and each atom meets the rules of chemical bonding described in Figure 4.1 on page 96. The following structure also depicts stearic acid, but in a simpler way, with each ‘corner’ on the zigzag line representing a carbon atom with two attached hydrogens: O H H
C
C
O
H
H Stearic acid (simplified structure)
Stearic acid (simplified structure)
As mentioned, the carbon chains of fatty acids vary in length. The long-chain (12–24 carbons) fatty acids of meats, fish and vegetable oils are most common in the diet. Smaller amounts of medium-chain (6 to 10 carbons) and short-chain (fewer than 6 carbons) fatty acids also occur, primarily in dairy products. (Tables C.1 and C.2 in Appendix C provide the names, chain lengths and sources of fatty acids commonly found in foods.)
The number of double bonds
Stearic acid (described and shown previously) is a saturated fatty acid. A saturated fatty acid is fully loaded with all its hydrogen atoms and contains only single bonds between its carbon atoms. If two hydrogens were missing from the middle of the carbon chain, the remaining structure might be:
H
H H H
H H H H O
H
H H H
H
H H H
C
C C
C
C
C C
C
C
C C C C
C C
H
H H H
H
H H H
H
H H H H
H H H H
C
C
C
O H
An impossible chemical structure
An impossible chemical structure
Notice that in the impossible chemical structure shown above, two of the carbons have only three bonds each. Such a compound cannot exist, because every carbon must have four bonds. To satisfy this rule, the two carbons form a double bond: H H
H H H
H
H H H
H
H H H
H H H O
C
C C
C
C
C C
C
C
C C
C C C
C C
H
H H H
H
H H H
H
H H
H H H
H H H
C
C
O H
Oleic acid, an 18-carbon mono-unsaturated fatty acid
Oleic acid, an 18-carbon monounsaturated fatty acid
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
Remember that each ‘corner’ on the zigzag line represents a carbon atom with two attached hydrogens.
The same structure drawn more simply looks like this:
H
H
O
C
C
137
O H
H Oleic acid (simplified structure)
Oleic acid (simplified structure)
Although drawn straight here (with zigzags), the actual shape bends at the double bond. The double bond is a point of unsaturation. A fatty acid like this – with two hydrogens missing and a double bond – is an unsaturated fatty acid. This one is the 18-carbon mono-unsaturated fatty acid oleic acid, which is abundant in olive oil and canola oil. A polyunsaturated fatty acid has two or more carbon-to-carbon double bonds. Linoleic acid, the 18-carbon fatty acid common in vegetable oils, lacks four hydrogens and has two double bonds: H H H
H
H H H
H H H
C C
C C
C
C
C C
C C
H H
H H H
H
H H
H H H H H
C C C
H H H H O C C
C
C
C
O H
H H H H
Linoleic acid, an 18-carbon polyunsaturated fatty acid
Linoleic acid, an 18-carbon polyunsaturated fatty acid
Drawn more simply, linoleic acid looks like this (though the actual shape would bend at the double bonds): H H
O
C
C
H
O H
Linoleic acid (simplified structure)
Linoleic acid (simplified structure)
A fourth 18-carbon fatty acid is linolenic acid, which has three double bonds. Table 5.1 presents the 18-carbon fatty acids.
PUTTING COMMON SENSE TO THE TEST
Saturated and polyunsaturated fats have differing numbers of double bonds. TRUE
TABLE 5.1 18-carbon fatty acids NAME
NUMBER OF CARBON ATOMS
NUMBER OF DOUBLE BONDS
SATURATION
COMMON FOOD SOURCES
Stearic acid
18
0
Saturated
Most animal fats
Oleic acid
18
1
Mono-unsaturated
Olive, canola oils
Linoleic acid
18
2
Polyunsaturated
Sunflower, safflower, corn and soybean oils
Alpha-linolenic acid
18
3
Polyunsaturated
Soybean and canola oils, flaxseed, walnuts
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Understanding nutrition
The location of double bonds Fatty acids differ not only in the length of their chains and their degree of saturation but also in the locations of their double bonds. Chemists identify polyunsaturated fatty acids by the position of the double bond nearest the methyl (CH3) end of the carbon chain, which is described by an omega number. A polyunsaturated fatty acid with its first double bond three carbons away from the methyl end is an omega-3 fatty acid. Similarly, an omega-6 fatty acid is a polyunsaturated fatty acid with its first double bond six carbons away from the methyl end. Figure 5.1 compares two 18-carbon fatty acids – linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).
FIGURE 5.1 Omega-3 and omega-6 fatty acids compared
PUTTING COMMON SENSE TO THE TEST
The omega number indicates the position of the double bond closest to the methyl (CH3) end. The fatty acids of an omega family may have different lengths and different numbers of double bonds, but the location of the double bond closest to the methyl end is the same in all of them. These structures are drawn linearly here to ease the counting of carbons and locating of double bonds, but their shapes actually bend at the double bonds.
Polyunsaturated fats can only be omega-3, not omega-6 fatty acids.
Linolenic acid, an 18-carbon, omega-3 fatty acid
FALSE
Omega carbon
O
H H
C
1
3
4
2
H
6
7
5
9
10
8
12 11
14
16 15
13
18 17
C
O
H
Acid end
Methyl end
Research scientists commonly use the term triacylglycerols; this book continues to use the more familiar term triglycerides, as do many other health and nutrition books and journals.
FIGURE 5.2 Glycerol When glycerol is free, an OH group is attached to each carbon. When glycerol is part of a triglyceride, each carbon is attached to a fatty acid (as shown in Figure 5.3).
H H C
O H
H C
O H
H C
O H
H
Linoleic acid, an 18-carbon, omega-6 fatty acid O Omega carbon
H H
C
1
2
H
6
4 3
5
7
9 8
10
12 11
14 13
16 15
18 17
C
O
H
Acid end
Methyl end
Mono-unsaturated fatty acids tend to belong to the omega-9 group, with their closest (and only) double bond nine carbons away from the methyl end. Oleic acid – the 18-carbon mono-unsaturated fatty acid common in olive oil mentioned earlier – is an omega-9 fatty acid. It is also the most predominant mono-unsaturated fatty acid in the diet.
Triglycerides Few fatty acids occur free in foods or in the body. Most often, they are incorporated into triglycerides – lipids composed of three fatty acids attached to a glycerol . Figure 5.2 presents a glycerol molecule. To make a triglyceride, a series of condensation reactions combine a hydrogen atom (H) from the glycerol and a hydroxyl (OH) group from a fatty acid, forming a molecule of water (H2O) and leaving a bond between the other two molecules (see the left side of Figure 5.3). Most triglycerides contain a mixture of more than one type of fatty acid (as shown on the right side of Figure 5.3).
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
139
FIGURE 5.3 Condensation of glycerol and fatty acids to form a triglyceride To make a triglyceride, three fatty acids attach to glycerol in condensation reactions. H
H
O
H C
O
H
H O
C
O
H
H C
O
H
H O
C
C H
H
H
O
H
C H
H C
O
C
H C
O
C
C H H
O
H C
O
H
C H
H2O
+
H2O
H
O
C H
H C
H
H
+
H
H
H O C
H2O
H
H O
+
O
C H
C
H
H
Glycerol + three fatty acids
Triglyceride + three water molecules
An H atom from glycerol and an OH group from a fatty acid combine to create water, leaving the O on the glycerol and the C at the acid end of each fatty acid to form a bond.
Three fatty acids attached to a glycerol form a triglyceride and yield water. In this example, the triglyceride includes (from top to bottom) a saturated fatty acid, a monounsaturated fatty acid and a polyunsaturated fatty acid.
Characteristics of solid fats and oils The chemistry of a fatty acid – whether it is short or long, saturated or unsaturated, with its closest double bond at carbon 3 or carbon 6 – influences the characteristics of foods and the health of the body. A later section in this chapter explains how these features affect health; this section describes how the degree of unsaturation influences the fats and oils in foods.
Firmness The degree of unsaturation influences the firmness of fats at room temperature (see Figure 5.4). Generally speaking, most polyunsaturated vegetable oils are liquid at room
FIGURE 5.4 Diagram of saturated and unsaturated fatty acids compared C C C Double bond
C
C
C
C
C
C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
C C C
Saturated fatty acids tend to stack together. Consequently, saturated fats tend to be solid (or more firm) at room temperature.
C
C
C
C
C
C
C C C
C C C
C C C
C C C
C C C
C C C
C C C C
C
C
C
C
C C
C C
This mixture of saturated and unsaturated fatty acids does not stack neatly because unsaturated fatty acids bend at the double bond(s). Consequently, unsaturated fats tend to be liquid (or less firm) at room temperature.
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C C
C
C
C
C C
C C
C
C
C
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Understanding nutrition
temperature, and the more saturated animal fats are solid. Some oils – notably, cocoa butter, palm oil, palm kernel oil and coconut oil – are saturated; they are firmer than most vegetable oils because of their saturation, but softer than most animal fats because of their shorter carbon chains (8 to 14 carbons long). Generally, the shorter the carbon chain, the softer the fat is at room temperature. Fatty acid compositions of selected fats and oils are shown in Figure 5.5, and Appendix H provides the fat and fatty acid contents of many other foods.
FIGURE 5.5 Fatty acid composition of common food fats Most fats are a mixture of saturated, mono-unsaturated, and polyunsaturated fatty acids. Key: Saturated fatty acids
Polyunsaturated, omega-6 fatty acids
Monounsaturated fatty acids
Polyunsaturated, omega-3 fatty acids
Animal fats and the tropical oils of coconut and palm contain mostly saturated fatty acids. Coconut oil Butter Beef tallow (beef fat) Palm oil Lard (pork fat) Chicken fat Some vegetable oils, such as olive and canola, are rich in monounsaturated fatty acids. Olive oil Canola oil Peanut oil Many vegetable oils are rich in polyunsaturated, omega-6 fatty acids. Safflower oil Sunflower oil Corn oil Soybean oil Walnut oil Cottonseed oil Only a few oils provide significant polyunsaturated, omega-3 fatty acids. Flaxseed oil Fish oil (salmon)
Stability The degree of unsaturation also influences stability. All fats become spoiled when exposed to oxygen. The oxidation of fats produces a variety of compounds that smell and taste rancid. (Other types of spoilage can occur due to microbial growth.) Polyunsaturated fats spoil most readily because their double bonds are unstable; mono-unsaturated fats are slightly less susceptible. Saturated fats are most resistant to oxidation and thus least likely to become rancid. Manufacturers can protect fat-containing products against rancidity in three ways – none of which are perfect. First, products may be sealed in air-tight, nonmetallic containers, protected from light, and refrigerated – an expensive and inconvenient storage system. Second, manufacturers may add antioxidants to compete for the oxygen and thus protect the oil; examples are the additives BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) and vitamin E. The advantages and disadvantages of antioxidant additives in food processing are presented in Chapter 19. Third, products may undergo a process known as hydrogenation.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
Hydrogenation During hydrogenation, some or all of the points of unsaturation are saturated by adding hydrogen molecules. Hydrogenation offers two advantages. First, it protects against oxidation (thereby prolonging shelf life) by making polyunsaturated fats more saturated. Second, it alters the texture of foods by making liquid vegetable oils more solid (as in margarine and shortening). Hydrogenated fats improve the texture of foods, making margarines spreadable, pie crusts flaky, and puddings creamy. Figure 5.6 illustrates the total hydrogenation of a polyunsaturated fatty acid to a saturated fatty acid. Total hydrogenation rarely occurs during food processing. Most often, a fat is partially hydrogenated, and some of the double bonds that remain after processing change their configuration from cis to trans.
FIGURE 5.6 Hydrogenation Double bonds carry a slightly negative charge and readily accept positively charged hydrogen atoms, creating a saturated fatty acid. Most often, fat is partially hydrogenated, creating a trans-fatty acid (shown in Figure 5.7).
O
H H
C O H
C H
H+ H+ H+ H+
O
H
C O H
H C H
Polyunsaturated fatty acid
Hydrogenated (saturated) fatty acid
Trans-fatty acids
In nature, most double bonds are cis – meaning that the hydrogens next to the double bonds are on the same side of the carbon chain. Only a few fatty acids (notably a small percentage of those found in milk and meat products) naturally occur as trans-fatty acids – meaning that the hydrogens next to the double bonds are on opposite sides of the carbon chain (see Figure 5.7). In the body, trans-fatty acids behave more like saturated fats, increasing blood cholesterol and the risk of heart disease (as a later section describes).
FIGURE 5.7 Cis- and trans-fatty acids compared This example compares the cis configuration for an 18-carbon mono-unsaturated fatty acid (oleic acid) with its corresponding trans configuration (elaidic acid).
H
H
H
H C
H C
O H
H C H
H
O C
O
H
H
O
H
cis -fatty acid A cis-fatty acid has its hydrogens on the same side of the double bond; cis molecules bend into a U-like formation. Most naturally occuring unsaturated fatty acids in foods are cis.
trans -fatty acid A trans -fatty acid has its hydrogens on the opposite sides of the double bond; trans molecules are more linear. The trans form typically occurs in partially hydrogenated foods when hydrogen atoms shift around some double bonds and change the configuration from cis to trans.
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Understanding nutrition
For example, most dairy products contain less than 0.5 grams of naturally occurring trans fat per serving.
Some research suggests that both naturally occurring and commercially created trans fats change blood lipids similarly; other research suggests that the negative effects are specific to only the commercial trans fats.1 In any case, the important distinction is that a relatively small amount of trans fat in the diet comes from natural sources. At current levels of consumption, natural trans fats have little, if any, effect on blood lipids. Some naturally occurring trans-fatty acids, known as conjugated linoleic acids, may even have health benefits.2 Conjugated linoleic acids are not counted as trans fats on food labels.
REVIEW IT
The predominant lipids both in foods and in the body are triglycerides: a molecule of glycerol with three fatty acids attached. Fatty acids vary in the length of their carbon chains, their degrees of unsaturation (number of double bonds), and the location of their double bond(s). Those that are fully loaded with hydrogens are saturated; those that are missing hydrogens and therefore have double bonds are unsaturated (mono-unsaturated or polyunsaturated). The vast majority of triglycerides contain more than one type of fatty acid. Fatty acid saturation affects fats’ physical characteristics and storage properties. Hydrogenation, which converts polyunsaturated fats to saturated fats, protects fats from oxidation and alters the texture by making liquid vegetable oils more solid. In the process, hydrogenation creates trans-fatty acids that damage health in ways similar to those of saturated fatty acids.
5.2 The chemist’s view of phospholipids and sterols
The preceding pages have been devoted to one of the classes of lipids, the triglycerides, and their component parts, glycerol and the fatty acids. The other lipids, the phospholipids and sterols, make up only 5 per cent of the lipids in the diet.
Phospholipids The best-known phospholipid is lecithin. A diagram of a lecithin molecule is shown in Figure 5.8. Notice that lecithin has a backbone of glycerol, with two of its three attachment sites occupied by fatty acids like those in triglycerides. The third site is occupied by a phosphate group and a molecule of choline. The hydrophobic fatty acids make phospholipids soluble in fat; the hydrophilic phosphate group allows them to dissolve in water. Such versatility enables the food industry to use phospholipids as an emulsifier to mix fats with water in such products as mayonnaise, salad dressings and snack bars.
Phospholipids in foods In addition to the phospholipids used by the food industry as emulsifiers, phospholipids are also found naturally in foods. The richest food sources of lecithin are eggs, liver, soybeans, wheat germ and peanuts.
Oil
© Matthew Farruggio
Roles of phospholipids Wa ter
Without help from emulsifiers, fats and water don’t mix.
The lecithins and other phospholipids are important constituents of cell membranes (see Figure 5.9). Because phospholipids are soluble in both water and fat, they can help fat-soluble substances, including vitamins and hormones, to pass easily in and out of cells. Phospholipids also act as emulsifiers in the body, helping to keep fats suspended in the blood and body fluids.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
FIGURE 5.8 Lecithin
FIGURE 5.9 Phospholipids of a cell membrane
Lecithin is similar to a triglyceride but contains only two fatty acids. The third position is occupied by a phosphate group and a molecule of choline. Other phospholipids have different fatty acids at the upper two positions and different groups attached to phosphate.
H C
H C
H
O
H O
C
C
O
From two fatty acids
H
A cell membrane is made of phospholipids assembled into an orderly formation called a bilayer. The fatty acid ‘tails’ orient themselves away from the watery fluid inside and outside of the cell. The glycerol and phosphate ‘heads’ are attracted to the watery fluid. Outside cell
H H
C
C
Hydrophobic tails H
H
H C
O
O
P
H
O
From glycerol
–
H
H
CH3
C
C
N
H
H
CH3
+
CH3
Watery fluid Hydrophilic heads
O
O
143
Inside cell
Watery fluid
The plus charge on the N is balanced by a negative ion – usually chloride. From choline
From phosphate
Sterols In addition to triglycerides and phospholipids, the lipids include the sterols, compounds with a multiple-ring structure . The most well-known sterol is cholesterol; Figure 5.10 shows its chemical structure.
Sterols in foods Foods derived from both plants and animals contain sterols, but only those from animals – meats, eggs, seafood, poultry and dairy products – contain significant amounts of cholesterol. Some people, confused about the distinction between dietary and blood cholesterol, have asked which foods contain the ‘good’ cholesterol. ‘Good’ cholesterol is not a type of cholesterol found in foods, but it refers to the way the body transports cholesterol in the blood, as explained in a later section of this chapter. Sterols other than cholesterol are found naturally in all plants. Being structurally similar to cholesterol, these plant sterols interfere with cholesterol absorption, thus lowering blood cholesterol levels.3 Food manufacturers have fortified foods such as margarine with plant sterols, creating a functional food that helps to reduce blood cholesterol.
FIGURE 5.10 Cholesterol Cholesterol is different from the triglycerides and phospholipids. The fat-soluble vitamin D is synthesised from cholesterol; they have many structural similarities. The only difference is that cholesterol has a closed ring (highlighted in red), whereas vitamin D’s is open, accounting for its vitamin activity. H3C CH3
CH3 CH3
CH3
HO
Roles of sterols Many vitally important body compounds are sterols. Among them are bile acids, the sex hormones (such as testosterone, androgen, and oestrogen), the adrenal hormones (such as cortisol, cortisone, and aldosterone) and vitamin D as well as cholesterol itself. Cholesterol in the body can serve as the starting material for the synthesis of these compounds or as a structural component of cell membranes; more than 90 per cent of all the body’s cholesterol resides in the cells. Unlike fatty acids, cholesterol cannot be used for energy.4 Despite popular impressions to the contrary, cholesterol
The four-ring core structure identifies a steroid; sterols are alcohol derivatives with a steroid ring structure.
Cholesterol H3C CH3 CH2
Vitamin D3
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CH3 CH3
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Understanding nutrition
is not a villain lurking in some evil foods – it is a compound the body makes and uses. The chemical structure is the same, but cholesterol that is made in the body is referred to as endogenous, whereas cholesterol from outside the body (from foods) is referred to as exogenous. Right now, as you read, your liver is manufacturing cholesterol from fragments of carbohydrate, protein, and fat. In fact, the liver makes about 800 to 1500 milligrams of cholesterol per day, thus contributing much more to the body’s total than does the diet. For perspective, the Daily Value on food labels for cholesterol is 300 milligrams per day. Cholesterol’s harmful effects in the body occur when it accumulates in the artery walls and contributes to the formation of plaque. These plaque deposits lead to atherosclerosis, a disease that causes heart attacks and strokes. Chapter 18 provides many more details.
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Phospholipids, including lecithin, have a unique chemical structure that allows them to be soluble in both water and fat. The food industry uses phospholipids as emulsifiers, and in the body phospholipids are part of cell membranes. Sterols have a multiple-ring structure that differs from the structure of other lipids. In the body, sterols include cholesterol, bile, vitamin D and some hormones. Animal-derived foods are rich sources of cholesterol.
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The members of the lipid family include the following: • triglycerides (fats and oils), which are made of glycerol (1 per triglyceride) and fatty acids (3 per triglyceride). Depending on the number of double bonds, fatty acids may be: - saturated (no double bonds) - mono-unsaturated (one double bond) - polyunsaturated (more than one double bond). Depending on the location of the double bonds, polyunsaturated fatty acids may be: • omega-3 (first double bond 3 carbons away from methyl end) • omega-6 (first double bond 6 carbons away from methyl end) • phospholipids (such as lecithin) • sterols (such as cholesterol).
5.3 Digestion, absorption and transport of lipids
Each day, the GI tract receives, on average from the food we eat, 50 to 100 grams of triglycerides, 4 to 8 grams of phospholipids and 200 to 350 milligrams of cholesterol. These lipids are hydrophobic, whereas the digestive enzymes are hydrophilic. As you read, notice how the body elegantly meets the challenges of keeping the lipids mixed in the watery fluids of the GI tract and facilitating the work of the lipases.
Lipid digestion Figure 5.11 traces the digestion of fat through the GI tract. The goal of fat digestion is to dismantle triglycerides into small molecules that the body can absorb and use – namely, monoglycerides, fatty acids and glycerol. The following paragraphs provide the details.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
FIGURE 5.11 Fat digestion in the GI tract FAT
Mouth and salivary glands Some hard fats begin to melt as they reach body temperature. The sublingual salivary gland in the base of the tongue secretes lingual lipase.
Mouth Salivary glands
Stomach The acid-stable lingual lipase initiates lipid digestion by hydrolysing one bond of triglycerides to produce diglycerides and fatty acids. The degree of hydrolysis by lingual lipase is slight for most fats but may be appreciable for milk fats. The stomach’s churning action mixes fat with water and acid. A gastric lipase accesses and hydrolyses (only a very small amount of) fat.
Tongue Sublingual salivary gland
Stomach Liver
Pancreatic duct
Gall bladder
Pancreas
Common bile duct Small intestine Bile flows in from the gall bladder (via the common bile duct): Fat
Bile
Emulsified fat
Pancreatic lipase flows in from the pancreas (via the pancreatic duct): Pancreatic (and intestinal) Monoglycerides, Emulsified fat lipase glycerol, fatty (triglycerides) acids (absorbed)
Small intestine Large intestine
Large intestine Some fat and cholesterol, trapped in fibre, exit in faeces.
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Understanding nutrition
In the mouth Fat digestion starts off slowly in the mouth, with some hard fats beginning to melt when they reach body temperature. A salivary gland at the base of the tongue releases lipase (an enzyme known as lingual lipase) that plays a minor role in fat digestion in adults and an active role in infants. In infants, this enzyme efficiently digests the short- and medium-chain fatty acids found in milk.
In the stomach In a quiet stomach, fat would float as a layer above the other components of swallowed food. But the strong muscle contractions of the stomach propel the stomach contents towards the pyloric sphincter. Some chyme passes through the pyloric sphincter periodically, but the remaining partially digested food is propelled back into the body of the stomach. This churning grinds the solid pieces to finer particles, mixes the chyme and disperses the fat into smaller droplets.5 These actions help to expose the fat for attack by the gastric enzyme lipase – an enzyme that performs best in the acidic environment of the stomach. Still, little fat digestion takes place in the stomach; most of the action occurs in the small intestine.
In the small intestine When fat enters the small intestine, it triggers the release of the hormone cholecystokinin (CCK), which signals to the gall bladder to release its stores of bile. (Remember that the liver makes bile, and the gall bladder stores it until it is needed.) Among bile’s many ingredients are bile acids, which are made in the liver from cholesterol and have a similar structure. In addition, they often pair up with an amino acid (a building block of protein). The amino acid end is attracted to water, and the sterol end is hydrophobic. This structure enables bile to act as an emulsifier, drawing fat molecules into the surrounding watery fluids. There, the fats are fully digested as they encounter lipase enzymes from the pancreas and small intestine. The process of emulsification is shown in Figure 5.12. Most of the hydrolysis of triglycerides occurs in the small intestine. The major fat-digesting enzymes are pancreatic lipases; some intestinal lipases are also active. These enzymes remove each of a triglyceride’s outer fatty acids one at a time, leaving a monoglyceride. Occasionally, enzymes remove all three fatty acids, leaving a free molecule of glycerol. Hydrolysis of a triglyceride is shown in Figure 5.13. Phospholipids are digested similarly – that is, their fatty acids are removed by hydrolysis. The two fatty acids and the remaining glycerol and phosphate fragments are then absorbed. Most sterols can be absorbed as is; if any fatty acids are attached, they are first hydrolysed off.
FIGURE 5.12 Emulsification of fat by bile Like bile, detergents are emulsifiers and work the same way, which is why they are effective in removing grease spots from clothes. Molecule by molecule, the grease is dissolved out of the spot and suspended in the water, where it can be rinsed away. Fat
Fat Enzyme
Watery GI juices
Bile Emulsified fat
Enzymes Fat and watery GI juices tend to separate; enzymes in the GI juices can’t get at the fat.
Emulsified fat
Emulsified fat When fat enters the small intestine, the gall bladder secretes bile. Bile has an affinity for both fat and water, so it can bring the fat into the water.
Bile’s emulsifying action converts large fat globules into small droplets that repel one another.
After emulsification, more fat is exposed to the enzymes, making fat digestion more efficient.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
147
FIGURE 5.13 Digestion (hydrolysis) of a triglyceride Bonds break
H O H H H C O
O
H C H
C
H H C O H
H C H
O H O C
H
H H C H
O H C
O
C
H H C H
O H C
O
C
H
H H O H
H
O H C
C H
O C
H H C H
O H C
O H
H O C
H
H
Bonds break Monoglyceride + two fatty acids
Triglyceride The triglyceride and two molecules of water are split. The H and OH from water complete the structures of two fatty acids and leave a monoglyceride.
These products may pass into the intestinal cells, but sometimes the monoglyceride is split with another molecule of water to give a third fatty acid and glycerol. Fatty acids, monoglycerides and glycerol are absorbed into intestinal cells.
The destination of bile After bile enters the small intestine and emulsifies fat, it has two possible destinations, illustrated in Figure 5.14. Most of the bile is reabsorbed from the intestine and recycled. The other possibility is that some of the bile can be trapped by dietary fibre in the large intestine and carried out of the body with the faeces. Because cholesterol is needed to make bile, the excretion of bile effectively reduces blood cholesterol. As Chapter 4 explains, the dietary fibres most effective at lowering blood cholesterol this way are the soluble dietary fibres commonly found in fruits, whole grains and legumes.
Lipid absorption
FIGURE 5.14 Enterohepatic circulation Most of the bile released into the small intestine is reabsorbed and sent back to the liver to be reused. This cycle is called the enterohepatic circulation of bile. Some bile is excreted. • enteron 5 intestine • hepat 5 liver In the gall bladder, bile is stored.
In the liver,
Figure 5.15 illustrates the absorption of lipids. Small molecules of digested bile is made from triglycerides (glycerol and short- and medium-chain fatty acids) can cholesterol. In the small intestine, diffuse easily into the intestinal cells; they are absorbed directly into the bile emulsifies fats. Bile bloodstream. Larger molecules (the monoglycerides and long-chain fatty into reabsorbed the blood acids) merge into spherical complexes known as micelles. The micelles diffuse into the intestinal cells, where the monoglycerides and long-chain In the colon, bile that has fatty acids are reassembled into new triglycerides. Within the intestinal cells, been trapped by soluble the newly made triglycerides and other lipids (cholesterol and phospholipids) fibres is excreted in faeces. are packed with protein into transport vehicles known as chylomicrons. The intestinal cells then release the chylomicrons into the lymphatic system.6 The chylomicrons glide through the lymph until they reach a point of entry into the bloodstream at the thoracic duct near the heart. (Recall from Chapter 3 that nutrients from the GI tract that enter the lymph system initially bypass the liver.) The blood carries these lipids to the rest of the body for immediate use or storage. A look at these lipids in the body reveals the kinds of fat the diet has been delivering. The blood, fat stores and muscle cells of people who eat a diet rich in unsaturated fats, for example, contain more unsaturated fats than those of people who select a diet high in saturated fats.
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FIGURE 5.15 Absorption of fat The end products of fat digestion are mostly monoglycerides, some fatty acids and very little glycerol. Their absorption differs depending on their size. (In reality, molecules of fatty acid are too small to see without a powerful microscope, whereas villi are visible to the naked eye.) Monoglyceride
Short-chain fatty acids
Small intestine Stomach
1
Medium-chain fatty acids
Micelle 2
Protein
Glycerol Triglyceride Chylomicrons Chylomicron
Capillary network
Lacteal (lymph)
Longchain fatty acids
2 Large lipids such as monoglycerides and long-chain fatty acids combine with bile, forming micelles that are sufficiently water soluble to penetrate the watery solution that bathes the absorptive cells. There the lipid contents of the micelles diffuse into the cells.
Blood vessels Via lymph to blood Via blood to liver 1 Glycerol and small lipids such as short- and medium-chain fatty acids can move directly into the bloodstream.
Chemists can identify the various lipoproteins by their density. They place a blood sample below a thick fluid in a test tube and spin the tube in a centrifuge. The most buoyant particles (highest in lipids) rise to the top and have the lowest density; the densest particles (highest in proteins) remain at the bottom. Others distribute themselves in between.
Lipid transport The chylomicrons are only one of several clusters of lipids and proteins that are used as transport vehicles for fats. As a group, these vehicles are known as lipoproteins, and they solve the body’s problem of transporting fat through the watery bloodstream. The body makes four main types of lipoproteins, distinguished by their size and density. Each type contains different kinds and amounts of lipids and proteins. The more lipids, the less dense: the more proteins, the denser. Figure 5.16 shows the relative compositions and sizes of the lipoproteins.
Chylomicrons
The chylomicrons are the largest and least dense of the lipoproteins. They transport dietderived lipids (mostly triglycerides) from the intestine (via the lymph system) to the rest of the body. Cells all over the body remove triglycerides from the chylomicrons as they pass by so the chylomicrons get smaller and smaller. Within 14 hours of absorption, most of the triglycerides have been depleted, and only a few remnants of protein, cholesterol and phospholipid remain. Special protein receptors on the membranes of the liver cells recognise and remove these chylomicron remnants from the blood.
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FIGURE 5.16 Sizes and compositions of the lipoproteins Protein
Phospholipid
A typical lipoprotein contains an interior of triglycerides and cholesterol surrounded by phospholipids. The phospholipids’ fatty acid ‘tails’ point towards the interior, where the lipids are. Proteins near the outer ends of the phospholipids cover the structure. This arrangement of hydrophobic molecules on the inside and hydrophilic molecules on the outside allows lipids to travel through the watery fluids of the blood.
Cholesterol Triglyceride
100 80
Protein
LDL
VLDL
Per cent
Chylomicron 60 40
Cholesterol
20
Phospholipid Triglyceride
0 Chylomicron HDL Notice how large the fat-filled chylomicron is compared with the others and how the others get progressively smaller as their proportion of fat declines and protein increases.
VLDL
LDL
HDL
Chylomicrons contain so little protein and so much triglyceride that they are the lowest in density. Very-low-density lipoproteins (VLDL) are half triglycerides, accounting for their very low density. Low-density lipoproteins (LDL) are half cholesterol, accounting for their implication in heart disease. High-density lipoproteins (HDL) are half protein, accounting for their high density.
VLDL (very-low-density lipoproteins) Meanwhile, in the liver – the most active site of lipid synthesis – cells are synthesising cholesterol, fatty acids and other lipid compounds. Ultimately, the lipids made in the liver and those collected from chylomicron remnants are packaged with proteins as a VLDL (verylow-density lipoprotein) and shipped to other parts of the body. As the VLDL travel through the body, cells remove triglycerides, causing the VLDL to shrink. As a VLDL loses triglycerides, the proportion of lipids shifts and the lipoprotein density increases. The remaining cholesterol-rich lipoprotein eventually becomes an LDL (lowdensity lipoprotein), loaded with cholesterol but containing relatively few triglycerides.
LDL (low-density lipoproteins) The LDL circulate throughout the body, making their contents available to the cells of all tissues – muscles (including the heart muscle), fat stores, the mammary glands and others. The cells take triglycerides, cholesterol and phospholipids to build new membranes, make hormones or other compounds, or store for later use. Special LDL receptors on the liver cells play a crucial role in the control of blood cholesterol concentrations by removing LDL from circulation.
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HDL (high-density lipoproteins)
The liver makes HDL (high-density lipoprotein) to remove cholesterol from the cells and carry it back to the liver for recycling or disposal. By efficiently clearing cholesterol, HDL lowers the risk of heart disease.7 In addition, HDL have anti-inflammatory properties that seem to keep artery-clogging plaque from breaking apart and causing heart attacks.8 Figure 5.17 summarises lipid transport via the lipoproteins.
FIGURE 5.17 Lipid transport via lipoproteins Intestine Intestinal cells form chylomicrons from dietary lipids.
Chylomicrons deliver dietary lipids to most of the body’s cells.
Liver cells receive small lipids directly from the intestine.
LDL deliver lipids to body cells or return to the liver.
HDL deliver cholesterol to the liver for excretion.
Fat cell Muscle
As cells remove lipids from the VLDL, it forms a smaller LDL.
As cells remove lipids from the chylomicron, it becomes a smaller chylomicron remnant.
Key: Chylomicron
LDL
Chylomicron remnant
HDL
Liver cells remove chylomicron remnants from the blood.
Liver cells synthesise lipids. Liver
Muscle Fat cell
Liver cells form VLDL, which deliver lipids to the body’s cells.
Liver cells form HDL, which pick up cholesterol from the body’s cells.
VLDL
PUTTING COMMON SENSE TO THE TEST
Fat and cholesterol are carried in the blood in special droplets. TRUE
Health implications The distinction between LDL and HDL has implications for the health of the heart and blood vessels. The blood lipid linked most directly to heart disease is LDL cholesterol. As mentioned, HDL also carry cholesterol, but elevated HDL represent cholesterol returning from the rest of the body to the liver for breakdown and excretion. The transport of cholesterol from the tissues back to the liver is sometimes called reverse cholesterol transport or the scavenger pathway. High LDL and low HDL cholesterol are both associated with a high risk of heart disease. Having adequate HDL is beneficial, but having high HDL is not necessarily more beneficial. Some people think of HDL as healthy and LDL as lousy, or refer to LDL as ‘bad’, and HDL as ‘good’, cholesterol. Keep in mind that the cholesterol itself is the same and that the differences between LDL and HDL reflect the proportions and types of lipids and proteins within them – not the type of cholesterol. The factors that help to lower LDL and/or raise HDL are: • weight control • mono-unsaturated or polyunsaturated, instead of saturated, fat in the diet • soluble dietary fibres • phytochemicals
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• moderate alcohol consumption • physical activity. Chapter 18 provides many more details. Not too surprisingly, numerous genes influence how the body handles the synthesis, transport, and degradation of lipids and lipoproteins. Much current research is focused on how nutrient–gene interactions may direct the progression of heart disease.
REVIEW IT
The body makes special arrangements to digest and absorb lipids. It provides the emulsifier bile to make them accessible to the fat-digesting lipases that dismantle triglycerides, mostly to monoglycerides and fatty acids, for absorption by the intestinal cells. Four types of lipoproteins transport all classes of lipids (triglycerides, phospholipids and cholesterol), but the chylomicrons are the largest and contain mostly triglycerides from the diet; VLDL are smaller and are about half triglycerides; LDL are smaller still and contain mostly cholesterol; and HDL are the densest and are rich in protein. High LDL cholesterol indicates increased risk of heart disease, whereas high HDL cholesterol has a protective effect.
5.4 Lipids in the body
In the body, lipids provide energy, insulate against temperature extremes, protect against shock and maintain cell membranes. This section provides an overview of the roles of triglycerides and fatty acids, and then of the metabolic pathways they can follow within the body’s cells.
Roles of triglycerides First and foremost, the triglycerides – either from food or from the body’s fat stores – provide the body with energy. When people dance all night, the triglycerides from their dinner provide some of the fuel that keeps them moving. When people lose their appetites, their stored triglycerides fuel much of their body’s work until they can eat again. Adipose tissue is more than just a storage depot for fat. Adipose tissue actively secretes several hormones known as adipokines – proteins that help regulate energy balance and influence several body functions. When body fat is markedly reduced or excessive, the type and quantity of adipokine secretions change, with consequences for the body’s health. Researchers are exploring how adipokines influence the links between obesity and chronic diseases such as type 2 diabetes, hypertension and heart disease.9 Obesity, for example, increases the release of the adipokine resistin that promotes inflammation and insulin resistance – factors that predict heart disease and diabetes. Similarly, obesity decreases the release of the adipokine adiponectin that protects against inflammation, diabetes and heart disease. Fat serves other roles in the body as well. Because fat is a poor conductor of heat, the layer of fat beneath the skin insulates the body from temperature extremes. Fat pads also serve as natural shock absorbers, providing a cushion for the bones and vital organs. Fat provides the structural material for cell membranes and participates in cell signalling pathways.
Essential fatty acids The human body needs fatty acids, and it can make all but two of them – linoleic acid (the 18-carbon omega-6 fatty acid) and linolenic acid (the 18-carbon omega-3 fatty acid). These two fatty acids must be supplied by the diet and are therefore essential fatty acids.
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PUTTING COMMON SENSE TO THE TEST
Triglycerides are the major form of fats in the human diet. TRUE
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FIGURE 5.18 The pathway from one omega-6 fatty acid to another
(18:3)
The cells do not possess the enzymes to make any of the omega-6 or omega-3 fatty acids from scratch, nor can they convert an omega-6 fatty acid to an omega-3 fatty acid or vice versa. Cells can, however, start with the 18-carbon member of an omega family and make the longer fatty acids of that family by forming double bonds (desaturation) and lengthening the chain two carbons at a time (elongation), as shown in Figure 5.18. This is a slow process because the omega-3 and omega-6 families compete for the same enzymes. Too much of a fatty acid from one family can create a deficiency of the other family’s longer fatty acids, which is critical only when the diet fails to deliver adequate supplies. Therefore, the most effective way to maintain body supplies of all the omega-6 and omega-3 fatty acids is to obtain them directly from foods – most notably, from vegetable oils, seeds, nuts, fish and other seafood.
(20:3)
Linoleic acid and the omega-6 family
The first number indicates the number of carbons and the second, the number of double bonds. Similar reactions occur when the body makes the omega-3 fatty acids EPA and DHA from linolenic acid. Linoleic acid
(18:2)
Desaturation creates double bond Elongation adds carbons Desaturation creates double bond Arachidonic acid
A non-essential nutrient (such as arachidonic acid) that must be supplied by the diet in special circumstances (as in a linoleic acid deficiency) is considered conditionally essential. This omega-3 linolenic acid is known as alpha-linolenic acid and is the fatty acid referred to in this chapter. Another fatty acid, also with 18 carbons and three double bonds, belongs to the omega-6 family and is known as gammalinolenic acid.
Linoleic acid is an essential fatty acid and the primary member of the omega-6 family. When the body receives linoleic acid from the diet, it can make other members of the omega-6 family – such as the 20-carbon (20:4) polyunsaturated fatty acid, arachidonic acid (as shown in Figure 5.18). Should a linoleic acid deficiency develop, arachidonic acid, and all other omega-6 fatty acids that derive from linoleic acid, would also become essential and have to be obtained from the diet. Normally, vegetable oils and meats supply enough omega-6 fatty acids to meet the body’s needs.
Linolenic acid and the omega-3 family Linolenic acid is the essential fatty acid and the primary member of the omega-3 family . Like linoleic acid, linolenic acid cannot be made in the body and must be supplied by foods. Given this 18-carbon fatty acid, the body can make small amounts of the 20- and 22-carbon members of the omega-3 series, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These omega-3 fatty acids play critical roles in the optimal structure and function of cells.10 Found abundantly in the eyes and brain, the omega-3 fatty acids are essential for normal growth, visual acuity and cognitive development. They may also play an important role in the prevention and treatment of heart disease, as later sections explain.
Eicosanoids
The body uses arachidonic acid and EPA to make substances known as eicosanoids. Eicosanoids are a diverse group of more than 100 compounds. Sometimes described as ‘hormone-like’, eicosanoids differ from hormones in important ways. For one, hormones are secreted in one location and travel to affect cells all over the body, whereas eicosanoids appear to affect only the cells in which they are made or nearby cells in the same localised environment. For another, hormones elicit the same response from all their target cells, whereas eicosanoids often have different effects on different cells. The actions of various eicosanoids sometimes oppose each other. For example, one causes muscles to relax and blood vessels to dilate, whereas another causes muscles to contract and blood vessels to constrict. Certain eicosanoids participate in the immune response to injury and infection, producing fever, inflammation and pain. One of the ways aspirin relieves these symptoms is by slowing the synthesis of these eicosanoids. Eicosanoids that derive from omega-3 fatty acids differ from those that derive from omega-6 fatty acids, with the omega-3 family providing greater health benefits. The omega-3 eicosanoids help lower blood pressure, prevent blood clot formation, protect against irregular heartbeats and reduce inflammation, whereas the omega-6 eicosanoids tend to promote clot formation, inflammation and blood vessel constriction.11
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
Omega-6 to omega-3 ratio Because omega-6 and omega-3 fatty acids compete for the same enzymes and their actions often oppose each other, researchers have studied whether there is an ideal ratio that best supports health.12 Suggested ratios range from 4:1 to 10:1. Although some researchers support such recommendations, others find the ratio of little value in improving health or predicting risk. Increasing the amount of omega-3 fatty acids in the diet is clearly beneficial, but reducing the amount of omega-6 fatty acids in the diet to improve the ratio may not be helpful. Omega-6 fatty acids protect heart health by lowering LDL cholesterol and improving insulin resistance.
Fatty acid deficiencies Most diets in Australia and New Zealand meet the minimum essential fatty acid requirements. Historically, deficiencies have developed only in infants and young children who have been fed fat-free milk and low-fat diets, or in hospital clients who have been mistakenly fed formulas that provided no polyunsaturated fatty acids for long periods of time. Classic deficiency symptoms include growth retardation, reproductive failure, skin lesions, kidney and liver disorders, and subtle neurological and visual problems.
A preview of lipid metabolism The blood delivers triglycerides to the cells for their use. This is a preview of how the cells store and release energy from fat; Chapter 7 provides details.
Storing fat as fat When meals deliver more energy than the body needs, the excess is stored as fat in the adipose cells for later use. An enzyme – lipoprotein lipase (LPL) – hydrolyses triglycerides from circulating lipoproteins, releasing fatty acids, diglycerides and monoglycerides into the adipose cells. Enzymes inside the adipose cells reassemble these fatty acids, diglycerides and monoglycerides into triglycerides again for storage. Triglycerides fill the adipose cells, storing a lot of energy in a relatively small space. This accumulation of fat in adipose tissue represents a key advantage that allows humans to survive through times when food is unavailable.13
Using fat for energy After meals, the blood delivers chylomicrons and VLDL loaded with triglycerides to the body’s cells for energy. Fat supplies about 60 per cent of the body’s ongoing energy needs during rest. During prolonged light to moderately intense exercise or extended periods of food deprivation, fat may make a slightly greater contribution to energy needs. During energy deprivation, several lipase enzymes (particularly hormone-sensitive lipase) inside the adipose cells respond by dismantling stored triglycerides and releasing the glycerol and fatty acids directly into the blood. Energy-hungry cells anywhere in the body can then capture these compounds and take them through a series of chemical reactions to yield energy, carbon dioxide, and water. A person who fasts (drinking only water) will rapidly metabolise body fat. Even with abundant body fat, the person has to obtain some energy from lean protein tissue because the brain, nerves and red blood cells need glucose – and without carbohydrate, only protein and the small glycerol molecule of a triglyceride can be converted to glucose; fatty acids cannot be. Still, in times of severe hunger and starvation, a fatter person can survive longer than a thinner person thanks to this energy reserve. But as Chapter 7 explains, fasting for too long will eventually cause death, even if the person still has ample body fat. In the body, triglycerides provide energy, insulate against temperature extremes, protect against shock, provide structural material for cell membranes and participate in cell signalling pathways. Linoleic acid (18 carbons, omega-6) and linolenic acid (18 carbons, omega-3) are essential fatty acids. They serve as structural parts of cell membranes and as
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precursors to the longer fatty acids that can make eicosanoids – powerful compounds that participate in blood pressure regulation, blood clot formation, and the immune response to injury and infection. Because essential fatty acids are common in the diet and stored in the body, deficiencies are unlikely. The body can easily store unlimited amounts of fat if given excesses, and this body fat is used for energy when needed. The role of fat in energy balance can be reviewed in Chapter 8.
REVIEW IT
The body can easily store unlimited amounts of fat if given excesses, and this body fat is used for energy when needed. (Remember that the liver can also convert a very small amount of excess carbohydrate and protein into fat.) Fat breakdown requires simultaneous carbohydrate breakdown for maximum efficiency; without carbohydrate, fats break down to ketone bodies.
5.5 Health effects and recommended intakes of saturated fats, trans fats and cholesterol
Some fats in the diet are essential for good health, but others can be harmful. The current Western diet delivers excessive amounts of solid fats , representing an average of almost one-fifth of the day’s total energy. Major sources of solid fats in our diet include desserts, pizza, pies and pastries, cheese, and processed and fatty meats (sausages, bacon, chops and ribs). Because foods made with solid fats provide abundant energy, but few if any essential nutrients, they contribute to weight gain and make it difficult to meet nutrient needs. Solid fats also provide abundant saturated fat, trans fat, and cholesterol. Even without overweight or obesity, high intakes of solid fats increase the risk of some chronic diseases. The easiest way to control saturated fat, trans fat, cholesterol, and energy is to limit solid fats in the diet.
Health effects of saturated fats, trans fats and cholesterol Hearing a doctor say ‘Your blood lipid profile looks fine’ is reassuring. Table 5.2 reveals the concentrations of various lipids in the blood, notably triglycerides and cholesterol and their lipoprotein carriers (VLDL, LDL and HDL). This information alerts people to possible disease risks and, perhaps, to a need for changing their exercise and eating habits. Both the amounts and types of fat in the diet influence people’s risk for disease.
TABLE 5.2 Desirable blood lipid profile The Heart Foundations of Australia and New Zealand recommendations for target lipid profile Total cholesterol
,4 mmol/L
LDL-cholesterol
,1.8 mmol/L (,2.0 mmol/L in New Zealand)
HDL-cholesterol
.1 mmol/L
Triglycerides
,2 mmol/L (,1.7 mmol/L in New Zealand) Reducing Risk in Heart Disease. An Expert Guide to Clinical Practice for Secondary Prevention of Coronary Heart Disease. Heart Foundation Australia (2012); Heart Foundation New Zealand, http://www.heartfoundation.org.nz/know-the-facts/conditions/high-cholesterol
Heart disease
Elevated LDL cholesterol is a major risk factor for cardiovascular disease (CVD).14 As LDL cholesterol accumulates in the arteries, blood flow becomes restricted and blood pressure rises. The consequences are deadly; in fact, heart disease is one of the nation’s leading causes
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
of death. LDL cholesterol is often used to predict the likelihood of a person’s suffering a heart attack or stroke; the higher the LDL, the earlier and more likely the tragedy. Much of the effort to prevent and treat heart disease focuses on lowering LDL cholesterol.15 Saturated fats are most often implicated in raising LDL cholesterol. In general, the more saturated fat in the diet, the more LDL cholesterol in the blood. Not all saturated fats have the same cholesterol-raising effect, however. Most notable among the saturated fatty acids that raise blood cholesterol are lauric, myristic, and palmitic acids (12, 14 and 16 carbons, respectively). In contrast, stearic acid (18 carbons) seems to have little or no effect on blood cholesterol. Making such distinctions may be impractical in diet planning, however, because these saturated fatty acids typically appear together in the same foods. In addition to raising blood cholesterol, saturated fatty acids contribute to heart disease by promoting blood clotting. Fats from animal sources (meats, milk and milk products) are the main sources of saturated fats in most people’s diets. Selecting lean cuts of meat, skinless poultry, and fat-reduced milk products helps to lower saturated fat intake and the risk of heart disease. Research also suggests an association between dietary trans fats and heart disease.16 In the body, trans fats alter blood cholesterol the same way some saturated fats do – they raise LDL cholesterol and lower HDL cholesterol. Limiting the intake of trans fats can improve blood cholesterol and lower the risk of heart disease.17 To that end, many restaurants and manufacturers have taken steps to eliminate or greatly reduce trans fats in foods, although there are no requirements regarding information on food labels unless the manufacturer makes a nutrition content claim about cholesterol or fatty acids.18 More information on labelling laws in Australia and New Zealand can be found in Chapter 2. The decrease in trans fatty acids in the food supply is apparent in a decrease in plasma concentrations of trans fatty acids in consumers.19 Unlike saturated fat and trans fat, dietary cholesterol raises blood cholesterol very little, if at all. Less clear is its role in heart disease.20
Cancer The links between dietary fats and cancer are not as evident as they are for heart disease. Dietary fat does not seem to initiate cancer development but, instead, may promote cancer once it has arisen. Stronger risk factors for cancer include smoking, alcohol and environmental contaminants. (Chapter 18 provides many more details about these risk factors and the development of cancer.) The relationship between dietary fat and the risk of cancer differs for various types of cancers. In the case of breast cancer, evidence has been weak and inconclusive. Some studies indicate an association between dietary fat and breast cancer; more convincing evidence indicates that body fatness contributes to the risk. In the case of colon cancer, limited evidence suggests a harmful association with foods containing animal fats. The relationship between dietary fat and the risk of cancer differs for various types and combinations of fats as well. The increased risk in cancer from fat appears to be due primarily to saturated fats or dietary fat from meats (which is mostly saturated). Fat from milk or fish has not been implicated in cancer risk. Olive oil seems to have a protective effect.
Obesity Fat contributes more than twice as many kilojoules per gram as either carbohydrate or protein. Consequently, people who eat high-fat diets regularly may exceed their energy needs and gain weight, especially if they are inactive. Because fat boosts energy intake, cutting fat from the diet can be an effective strategy in cutting energy intake. In some cases, though, choosing a fat-free food offers no energy savings. Fat-free frozen desserts and yoghurts, for example, often have so much sugar added that the kilojoule count can be as high as in the regular-fat product. In this case, cutting fat and adding carbohydrate offers no energy savings or weight-loss advantage. In fact, it may even raise energy intake and exacerbate weight problems. Later chapters revisit the role of dietary fat in the development of obesity.
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Recommended intakes of saturated fat, trans fat and cholesterol Defining the exact amount of saturated fat, trans fat or cholesterol that begins to harm health is difficult.25 For this reason, no RDI or upper limit has been set. Instead, the Australian Dietary Guidelines make the following recommendation: limit saturated fats and moderate total fat intake. When all fat types are considered, total fat intakes should be around 30 per cent of total daily energy intake. The proportion of energy in the diet from saturated and trans fats together in the range of 8 to 10 per cent of energy is recommended as prudent. For an average daily intake of around 8000 kilojoules, this represents 640 to 800 kilojoules (approximately 17.5 grams to 21 grams daily) from saturated and trans fats, combined. These recommendations recognise that diets with up to 35 per cent of kilojoules from fat can be compatible with good health if energy intake is reasonable and saturated fat, trans fat and cholesterol intakes are low. When total fat exceeds 35 per cent, however, saturated fat usually rises to unhealthy levels. For an 8000-kilojoule diet, 20 to 35 per cent represents 1600 to 2800 kilojoules from fat (roughly 45 to 75 grams). According to surveys, diets in the Australia and New Zealand provide about 32 to 34 per cent of their total energy from fat, with saturated fat contributing about 11 per cent of the total.21 The average daily intake of trans-fatty acids is about 0.5 to 0.6 grams per day – mostly from products that have been hydrogenated.22 Cholesterol intakes average around 219 milligrams a day for women and 316 for men.23 Although it is very difficult to do, some people actually manage to eat too little fat – to their detriment. Among them are people with eating disorders, described in Highlight 8, and athletes. Athletes following a diet too low in fat (less than 20 per cent of total energy) fall short on energy, vitamins, minerals and essential fatty acids as well as on performance.24 As a practical guideline, it is wise to include the equivalent of at least a teaspoon of fat in every meal – a little peanut butter on toast or mayonnaise in salad, for example. Dietary recommendations that limit fat were developed for healthy people over the age of 2 years; Chapter 16 discusses the fat needs of infants and young children.
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Enjoy lean meats and poultry, fish, eggs, tofu, nuts and seeds, and legumes/ beans.
REVIEW IT
Explain the relationships among saturated fat, trans fat, and cholesterol and chronic diseases, noting recommendations. Although some fat in the diet is necessary, too much fat adds energy without nutrients, which leads to obesity and nutrient inadequacies. Too much saturated fat, trans fat and cholesterol increases the risk of heart disease and possibly cancer. For these reasons, health authorities recommend a diet moderate in total fat and low in saturated fat, trans fat, and cholesterol.
5.6 Health effects and recommended intakes of mono-unsaturated and polyunsaturated fats
Whereas saturated fats, trans fats and cholesterol are implicated in chronic diseases, mono-unsaturated and polyunsaturated fats seem to offer health benefits. For this reason, dietary recommendations suggest replacing sources of saturated fats, trans fats and cholesterol with foods rich in mono-unsaturated and polyunsaturated fats – foods such as seafood, nuts, seeds and vegetable oils. Table 5.3 lists major food sources of these various lipids.
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TABLE 5.3 Major sources of various lipids POTENTIALLY HEALTHFUL LIPIDS Mono-unsaturated fats Avocado Nuts (almonds, cashews, filberts, hazelnuts, macadamia nuts, peanuts, pecans, pistachios) Oils (canola, olive, peanut, sesame) Olives Peanut butter Seeds (sesame)
Omega-6 polyunsaturated fats Margarine (non-hydrogenated) Mayonnaise Nuts (pine nuts, walnuts) Oils (corn, cottonseed, safflower, soybean) Salad dressing Seeds (pumpkin, sunflower)
Omega-3 polyunsaturated fats Fatty fish (herring, mackerel, salmon, sardines, tuna) Flaxseed, chia seed Marine algae Nuts (walnuts) Oils (canola, flaxseed) Yeast
POTENTIALLY HARMFUL LIPIDS
Trans fats
Saturated fats Bacon Butter Cheese Chocolate Coconut Cream cheese Cream, half-and-half Ice-cream Lard Meats (fatty cuts of pork and beef) Milk and milk products (whole) Oils (coconut, palm, palm kernel) and products containing them (such as lollies, biscuits, doughnuts, pastries, pies) Shortening Sour cream
Commercial baked goods (including doughnuts, cakes, biscuits, pastries) Fried foods (hydrogenated shortening) Many fast foods Many snack foods (including microwave popcorn, chips, crackers) Margarine (hydrogenated or partially hydrogenated) Non-dairy creamers Shortening
Cholesterol Eggs Meat, poultry, shellfish Milk and milk products
NOTE: Keep in mind that foods contain a mixture of fatty acids.
Researchers examining eating patterns from around the world have noted that some diets support good health despite being high in fat. As Highlight 5 explains, the type of fat may be more important than the amount of fat.
Health effects of mono-unsaturated and polyunsaturated fats Heart disease Replacing saturated fats with unsaturated fats reduces LDL cholesterol and lowers the risk of heart disease.25 To replace saturated fats with unsaturated fats, cook with olive oil instead of butter, snack on mixed nuts instead of potato chips, use avocado instead of cheese on a sandwich and eat salmon instead of steak. Table 5.4 shows how these simple substitutions can lower the saturated fat and raise the unsaturated fat in a meal. Highlight 5 provides more details about the benefits of healthy fats in the diet.
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PUTTING COMMON SENSE TO THE TEST
Saturated fats reduce the risk of heart disease. FALSE
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TABLE 5.4 Replacing saturated fat with unsaturated fat Portion sizes have been adjusted so that each of these foods provides approximately 420 kilojoules. Notice that for a similar number of kilojoules and total grams of fat, the second choices offer less saturated fat and more unsaturated fat. REPLACE THESE FOODS … Saturated fat (g)
… WITH THESE FOODS
Unsaturated fat (g)
Total fat (g)
Butter (1 tbs)
7
4
11
Bacon (2 slices)
3
6
Potato chips (10 chips)
2
Cheese (1 slice) Steak (45 g) Totals
Saturated fat (g)
Unsaturated fat (g)
Total fat (g)
Olive oil (1 tbs)
2
9
11
9
Sunflower seeds (2 tbs)
1
7
8
5
7
Mixed nuts (2 tbs)
1
8
9
4
4
8
Avocado (6 slices)
2
8
10
2
3
5
Salmon (45 g)
1
3
4
18
22
40
Totals
7
35
42
Research on the different types of fats has spotlighted the many beneficial effects of the omega-3 polyunsaturated fatty acids.26 Regular consumption of omega-3 fatty acids may help to prevent blood clots, protect against irregular heartbeats, improve blood lipids and lower blood pressure, especially in people with hypertension or atherosclerosis.27 In addition, omega-3 fatty acids support a healthy immune system and suppress inflammation.28
Cancer The omega-3 fatty acids of fatty fish may protect against some cancers as well, perhaps by suppressing inflammation.29 Even when omega-3 fats do not protect against cancer development, there seems to be a significant reduction in cancer-related deaths. Thus, dietary advice to reduce cancer risks parallels that given to reduce heart disease risks: reduce saturated fats and increase omega-3 fatty acids. Evidence does not support omega-3 supplementation.
Other diseases Limited research suggests that the omega-3 fatty acids of fish may protect against bone loss, asthma, periodontal diseases and eye diseases.30 Omega-3 fats also appear to play a role in improving memory and cognition, but not depression.31 Evidence on associations between fish consumption, omega-3 fatty acids and diabetes is inconsistent.
Omega-3 supplements Omega-3 fatty acids are available in capsules of fish oil supplements, although routine supplementation is not recommended. High intakes of omega-3 polyunsaturated fatty acids may increase bleeding time, interfere with wound healing, raise LDL cholesterol and suppress immune function.32 Such findings reinforce the concept that too much of a good thing can sometimes be harmful.33 People with heart disease, however, may benefit from doses greater than can be achieved through diet alone. Because high intakes of omega-3 fatty acids can cause excessive bleeding, supplements should be used only under close medical supervision.34 For those who decide to use fish oil supplements, Figure 5.19 explains how to read the label.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
FIGURE 5.19 How to read a fish oil supplement label
Supplement Facts Serving Size: 1 Softgel Servings Per Container: 120
1000 mg
Alex Mit/Shutterstock.com
Calories Total fat
Notice that this supplement offers 1000 mg of fish oil concentrate per capsule, but the oils offering the most health benefits are EPA and DHA. That information is in the Supplement Facts panel on the back.
Saturated fat Trans fat Polyunsaturated fat Monounsaturated fat Cholesterol Omega-3 fatty acids EPA (eicosapentaenoic acid) DHA (docosahexaenoic acid)
Amount Per Serving
% Daily Value
10 1
* 2%
0.5 g 0g 0.5g 0g 5 mg 300 mg
3% * * * 2% *
180 mg
*
120 mg
*
* Daily Value not established. Notice that one capsule of this supplement offers 180 mg of EPA and 120 mg of DHA, for a total of 300 mg of omega-3 oils – not 1000 mg. The recommended intake for omega-3 fatty acids is 500 mg per day. For heart health, consumers may need more, perhaps 2 to 4 grams (2000 to 4000 mg) per day.
CURRENT RESEARCH IN NUTRITION Omega-3s and brain development and function The actions of omega-3 fatty acids for the developing human brain is an area of major research interest. The omega-3 fats are essential in the development of the complex web of neurones necessary for optimal growth in a baby’s brain. Omega-3s are also important in neurotransmitter function. Understanding the role the mother plays in supplying optimal levels of omega-3s during pregnancy and the influence breast milk or infant formula has on the omega-3 levels in the brain during early life is critical to providing babies with an optimal start to life.35 At the other end of the life spectrum, there is growing research into the effects of omega-3s on the ageing brain and the potential for slowing of age-related cognitive decline, including Alzheimer’s disease.36 This includes research involving both omega-3 and B-group vitamin supplementation on reducing brain atrophy in people over the age of 70 years.37 Such research shows how important a well-balanced diet is across the lifespan.
REVIEW IT
In foods, triglycerides: • deliver fat-soluble vitamins, energy and essential fatty acids • contribute to the sensory appeal of foods and stimulate appetite. Some fat in the diet has health benefits, especially the mono-unsaturated and polyunsaturated fats that protect against heart disease and possibly cancer. For this reason, dietary guidelines recommend replacing saturated fats with mono-unsaturated and polyunsaturated fats, particularly omega-3 fatty acids from foods such as fatty fish, not from supplements. Many selection and preparation strategies can help bring these goals within reach, and food labels help to identify foods consistent with these guidelines.
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5.7 From guidelines to groceries
Fats accompany protein in foods derived from animals, such as meat, fish, poultry and eggs, and fats accompany carbohydrate in foods derived from plants, such as avocados and coconuts. Fats carry with them the four fat-soluble vitamins – A, D, E and K – together with many of the compounds that give foods their flavour, texture and palatability. Fat is responsible for the delicious aromas associated with sizzling bacon and hamburgers on the BBQ, onions being sautéed or vegetables in a stir-fry. Of course, these wonderful characteristics lure people into eating too much from time to time. With careful selections, a diet following the Australian Guide to Healthy Eating can support good health and still meet fat recommendations. As the photos in Figure 5.20 show, fat accounts for much of the energy in foods, and removing the fat from foods cuts energy and saturated fat intakes dramatically. To reduce dietary fat, eliminate fat as a seasoning and in cooking; remove the fat from high-fat foods; replace high-fat foods with low-fat alternatives; and emphasise whole grains, fruits and vegetables. The ‘How to’ feature on page 162 suggests additional heart-healthy choices by food group.
DLibrary/Murray Goulburn Co-Op Ltd.; Shutterstock/artphotoclub
Fat-free milk, 1 cup (378 kJ, ,1 g saturated fat)
© Matthew Farruggio
© Matthew Farruggio
Pork chop with fat trimmed off (966 kJ, 9 g fat, 3 g saturated fat)
Whole milk, 1 cup (630 kJ, 8 g fat, 5 g saturated fat)
© Matthew Farruggio
© Matthew Farruggio
Potato with 1 tbs butter and 1 tbs sour cream (1470 kJ, 14 g fat, 10 g saturated fat)
Pork chop with fat (1420 kJ, 19 g fat, 7 g saturated fat)
DLibrary/Murray Goulburn Co-Op Ltd.; Shutterstock/artphotoclub
FIGURE 5.20 Cutting fats cuts energy – and saturated fat
Plain potato (840 kJ, ,1 g fat, 0 g saturated fat)
In general, except for seafood, animal fats tend to have a higher proportion of saturated fatty acids. Except for the tropical oils, plant foods tend to have a higher proportion of mono-unsaturated and polyunsaturated fatty acids. Consumers can find an abundant array of fresh, unprocessed foods that are naturally low in saturated fat, trans fat, cholesterol and total fat. In addition, many familiar foods have been processed to provide less fat.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
For example, fat can be removed by skimming milk or trimming meats. Manufacturers can dilute fat by adding water or whipping in air. They can use fat-reduced milk in creamy desserts and lean meats in frozen meals. Sometimes manufacturers simply prepare the products differently. For example, fat-free potato chips may be baked instead of fried. Such choices make healthy eating easy.
Reducing fat intake Protein foods The fats in seafood, nuts, and seeds are considered oils, whereas the fats in meat, poultry, and eggs are considered solid fats because of their high fat, saturated fat and cholesterol content. Because these meats provide high-quality protein and valuable vitamins and minerals, however, they can be included in a healthy diet if a person makes lean choices (see Table 5.5), prepares them using the suggestions outlined in the ‘How to’ feature, and eats small portions. Selecting wild game or grass-fed cattle instead of grain-fed livestock offers the nutrient advantages of being lower in fat and higher in omega-3 polyunsaturated fatty acids. Another strategy to lower blood cholesterol is to prepare meals using soy protein instead of animal protein. When preparing meat, fish or poultry, consider grilling or baking, but not frying. Fried fish does not benefit heart disease. Fried fish from fast-food restaurants and frozen fried fish products are often low in omega-3 fatty acids and high in saturated fatty acids.
TABLE 5.5 Fat options among the protein foods Very lean options
Chicken (white meat, no skin) Cod, flounder, trout, tuna (fresh or canned in water) Legumes
Lean options
Beef or pork ‘round’ or ‘loin’ cuts Chicken (dark meat, no skin) Herring, salmon
Medium-fat options
Ground beef Eggs Tofu Tuna (canned in oil)
High-fat options
Bacon, hot dogs, luncheon meats, sausage Peanut butter Nuts
Table 5.5 includes sources of omega-3 and omega-6 fatty acids, and Table 5.6 sorts fish and seafood by their quantity of omega-3 fatty acids. Fatty fish are among the best sources of omega-3 fatty acids, and Highlight 5 features their role in supporting heart health. The Heart Foundations of Australia and New Zealand recommend eating at least two servings of fish a week, with an emphasis on fatty fish (salmon and sardines, some varieties of canned tuna, salmon and sardines, gemfish, blue-eye trevalla, blue mackerel and oysters, for example). Fish provides many minerals (except iron) and vitamins. Because fish is leaner than most other animal-protein sources it can help with weight-loss efforts. The combination of losing weight and eating fish improves blood lipids even more effectively than can be explained by either the weight loss or the omega-3 fats of the fish. Chapter 19 discusses the adverse consequences of mercury, an environmental contaminant common in some fish; in general, mercury is relatively high in swordfish, king mackerel and shark and relatively low in barramundi, snapper, salmon, flounder, sole and most shellfish. Most healthy people who eat two servings of fish a week can maximise the health benefits while incurring minimal risks. Non-fish sources of omega-3 fatty acids such as flaxseed may have less benefit.
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TABLE 5.6 Omega-3 fatty acids in fish and seafood 100 G OF OMEGA-3 FATTY ACID IS FOUND IN THE FOLLOWING AMOUNTS OF THE FOLLOWING SEAFOOD 500 mg
Herring, mackerel, oysters (Pacific wild), salmon (wild and farmed), sardines, toothfish, trout (wild and farmed)
150–500 mg
Catfish (wild and farmed), cod (Murray), crab (Alaskan king), flounder, haddock, hake, halibut, oysters (farmed), golden perch, scallops, shrimp (mixed varieties), sole, swordfish, barramundi
,150 mg
Lobster, mahi mahi, monkfish, red snapper, skate, tuna, wahoo
HOW TO:
MAKE HEART-HEALTHY CHOICES – BY FOOD GROUP
Breads and cereals ›› Select breads, cereals and biscuits that are low in saturated and trans fat (for example, bagels instead of croissants). ›› Prepare pasta with a tomato sauce instead of a cheese or cream sauce. Vegetables and fruits ›› Enjoy the natural flavour of steamed vegetables (without butter) for dinner and fruits for dessert. ›› Eat at least two vegetables (in addition to a salad) with dinner. ›› Snack on raw vegetables or fruits instead of high-fat items like potato chips. ›› Buy frozen vegetables without sauce. Milk and milk products ›› Switch from whole milk to reduced-fat, from reduced-fat to low-fat, and from low-fat to fat-free (non-fat). ›› Use fat-free and low-fat cheeses (such as part-skim ricotta and low-fat mozzarella) instead of regular cheeses. ›› Use fat-free or low-fat yoghurt or sour cream instead of regular sour cream. ›› Use evaporated fat-free milk instead of cream. ›› Enjoy fat-free frozen yoghurt, sherbet or ice milk instead of ice-cream. Meat and legumes ›› Remember that fat adds up quickly, even with lean meat. ›› Eat at least two servings of fish per week. ›› Choose fish, poultry or lean cuts of pork, lamb and beef; look for unmarbled meat and cuts with limited visible fat. ›› Choose processed meats such as luncheon meats and hot dogs that are low in saturated fat and cholesterol. ›› Trim the fat from pork, lamb and beef; remove the skin from poultry. ›› Grill, roast, broil, bake, stir-fry or stew meats; don’t fry. When possible, place food on a rack so that fat can drain. ›› Use lean minced pork or lean minced beef in recipes; brown minced meats without added fat, then drain off fat. ›› Consider low-fat meat sources including game such as kangaroo, venison and rabbit. ›› Select tuna, sardines and other canned meats packed in water; rinse oil-packed items with hot water to remove much of the fat.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
›› Fill kebab skewers with lots of vegetables and slivers of meat; create main dishes and casseroles by combining a little meat, fish or poultry with a lot of pasta, rice or vegetables. ›› Use legumes often. ›› Eat a meatless meal or two daily. ›› Use egg substitutes in recipes instead of whole eggs, or use two egg whites in place of each whole egg. Fats and oils ›› ›› ›› ››
Use butter or margarine sparingly. Use low-fat or fat-free mayonnaise and salad dressing instead of the regular form. Limit use of lard and meat fat. Limit use of products made with coconut oil, palm kernel oil and palm oil (read labels on bakery goods, processed foods, popcorn oils and non-dairy creamers). ›› Reduce use of hydrogenated shortenings and products that contain them (read labels on crackers, biscuits and other commercially prepared baked goods); use vegetable oils instead. Miscellaneous ›› Use a non-stick pan or coat the pan lightly with vegetable oil. ›› Refrigerate soups and stews; when the fat solidifies, remove it before re-heating. ›› Use wine; lemon, orange or tomato juice; herbs; spices; fruits; or broth instead of butter or margarine when cooking. ›› Stir-fry in a small amount of oil; add moisture and flavour with broth, tomato juice or wine. ›› Use variety to enhance enjoyment of the meal: vary colours, textures and temperatures – hot cooked versus cool raw foods – and use garnishes to complement food. ›› Omit high-fat meat gravies and cheese sauces. ›› Order pizzas with lots of vegetables, a little lean meat and half the cheese. Adapted from Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), NIH publication no. 02-5215, Bethesda, MD: National Heart, Lung, and Blood Institute (2002): V–8 and II–4.
Recall that cholesterol is found in all foods derived from animals. Consequently, eating fewer meats, eggs and milk products helps lower dietary cholesterol intake (as well as total and saturated fat intakes). Most foods that are high in cholesterol are also high in saturated fat, but eggs are an exception. An egg contains only 1 gram of saturated fat but has a little more than 200 milligrams of cholesterol – roughly two-thirds of the recommended daily limit. Still, for the general population, eating eggs does not seem to increase the risk of heart disease.38 For people with high blood cholesterol, however, limiting daily cholesterol intake to less than 200 milligrams may be beneficial. When eggs are included in the diet, other sources of cholesterol may need to be limited on that day. Eggs are a valuable part of the diet because they are inexpensive, useful in cooking, and a source of high-quality protein, other nutrients, and phytochemicals. To help consumers improve their omega-3 fatty acid intake, hens fed flaxseed, fish oil or marine algae produce eggs rich in omega-3 fatty acids (up to 200 milligrams per egg). Including even one enriched egg in the diet daily can significantly increase a person’s intake of omega-3 fatty acids.
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Milk and milk products Like meats, milks and milk products should also be selected with an awareness of their fat, saturated fat and cholesterol contents (see Table 5.7). Keep in mind that the fat in milk is a solid fat: that is apparent as butter, but less so when suspended in homogenised milk. Fat-free and low-fat milk products provide as much or more protein, calcium and other nutrients as their whole-milk versions – but with little or no saturated fat. Selecting fermented milk products, such as yoghurt, may also help to lower blood cholesterol. These foods increase the population and activity of bacteria in the colon that ferment dietary fibre. Interestingly, cheese does not seem to raise LDL cholesterol as its saturated fat content might predict, perhaps because its calcium promotes fat excretion in the GI tract. Such findings suggest that specific foods or nutrients within them influence the actions of their associated saturated fats.
TABLE 5.7 Fat options among milk and milk products Fat-free and low-fat options
Fat-free (skim) or 1% (low-fat) milk or yoghurt (plain)
Reduced-fat options
2% milk or yoghurt (plain)
High-fat options
Whole milk, yoghurt Most cheeses
Vegetables, fruits and grains Most vegetables and fruits naturally contain little or no fat. Although avocados and olives are exceptions, most of their fat is unsaturated, which is not harmful to heart health.39 Most grains contain only small amounts of fat. Consumers need to read food labels carefully, though, because many refined grain products such as corn chips, croissants and biscuits are high in saturated fat, and pastries and biscuits may contain trans fats. Similarly, many people add butter, margarine or cheese sauces to grains and vegetables, which raises the saturatedand trans-fat contents. Because fruits are often eaten without added fat, a diet that includes several servings of fruit daily can help a person meet the dietary recommendations for fat. A diet rich in vegetables, fruits, whole grains, and legumes also offers abundant vitamin C, folate, vitamin A, vitamin E, and dietary fibre – all important in supporting health. Consequently, such a diet protects against disease by reducing saturated fat, cholesterol and total fat as well as by increasing nutrients. It also provides valuable phytochemicals, which help defend against heart disease.
Solid fats and oils Solid fats include the fats in meat and poultry (as in poultry skin, processed meats, and sausage); the fats in whole milk, cheeses and butter; shortening (as in fried foods and baked goods); and margarine. Because solid fats deliver an abundance of saturated fatty acids, they are considered discretionary kJ. The fats of fish, nuts and vegetable oils are not counted as discretionary kJ because they provide valuable omega-3 fatty acids, essential fatty acids and vitamin E. When discretionary kJ are available, they may be used to add fats in cooking or at the table or to select higher fat items from the food groups. Some solid fats, such as butter and the fat trimmed from meat, are easy to see. Others – such as the fat that ‘marbles’ a steak or is hidden in foods such as cheese – are less apparent and can be present in foods in surprisingly high amounts. Any fried food contains abundant solid fats – potato crisps, chips and French fries, fried spring rolls and fried fish. Many baked goods, too, are high in solid fats – pie crusts, pastries, biscuits, doughnuts, sweet rolls and cakes.
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Chapter 5: The lipids: triglycerides, phospholipids and sterols
Read food labels Labels list total fat, saturated fat and cholesterol contents of foods. Because each package provides information for a single serving and because serving sizes are standardised, consumers can easily compare similar products. Total fat, saturated fat and cholesterol are also expressed as ‘% Daily Intake per serving’ for a person consuming 8700 kJ. Using 30 per cent of energy intake as the guideline for fat, the Daily Intake is 72.5 grams of fat; using 10 per cent for saturated fat, the Daily Intake is 20 grams of saturated fat. The Daily Value for cholesterol is 300 milligrams regardless of energy intake. There is no Daily Value for trans fat, but consumers should try to keep intakes as low as possible and within the 10 per cent allotted for saturated fat. People who consume more or less than 2800 kJ daily can calculate their personal Daily Intake for fat.
Fat replacers Some foods are made with fat replacers – ingredients that provide some of the taste and texture of fats, but with fewer kJ. Because the body may digest and absorb some of these fat replacers, they may contribute energy, although significantly less energy than fat’s 36 kJ per gram. Some fat replacers are derived from carbohydrate, protein or fat. Carbohydratebased fat replacers are used primarily as thickeners or stabilisers in foods such as soups and salad dressings. Protein-based fat replacers provide a creamy feeling in the mouth and are often used in foods such as ice-creams and yoghurts. Fat-based replacers act as emulsifiers and are heat stable, making them most versatile in shortenings used in cake mixes and biscuits. Fat replacers are common in the US, but rarely used in Australia and New Zealand. One product that is in use is olestra. Olestra’s chemical structure is similar to that of a triglyceride but with important differences. A triglyceride is composed of a glycerol molecule with three fatty acids attached, whereas Olestra is made of a sucrose molecule with six to eight fatty acids attached. Enzymes in the digestive tract cannot break the bonds of Olestra, so unlike sucrose or fatty acids, Olestra passes through the digestive system unabsorbed. Perhaps the best advice for consumers regarding fat in the diet would be to replace saturated fat with unsaturated fat. Sometimes these choices can be difficult, though, because fats make foods taste delicious. To maintain good health, must a person give up all high-fat foods forever – never again to eat steak, hollandaise sauce or gooey chocolate cake? Not at all! These foods bring pleasure to a meal and can be enjoyed as part of a healthy diet when eaten occasionally in small quantities; but they should not be everyday foods. The key dietary principle for fat is moderation, not deprivation. Appreciate the energy and enjoyment that fat provides, but take care not to exceed your needs.
REVIEW IT
Some fat in the diet has health benefits, especially the mono-unsaturated and polyunsaturated fats that protect against heart disease and possibly cancer. For this reason, dietary guidelines recommend replacing saturated fats with mono-unsaturated and polyunsaturated fats, particularly omega-3 fatty acids from foods such as fatty fish, not from supplements. Many selection and preparation strategies can help bring these goals within reach, and food labels help to identify foods consistent with these guidelines.
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Saturated and polyunsaturated fats have differing numbers of double bonds. TRUE
4 Fat and cholesterol are carried in the blood in special droplets. TRUE
Saturated fats have no double bonds whereas polyunsaturated fats have two or more double bonds. These double bonds occur at different places in different polyunsaturated fats.
2 Polyunsaturated fats can only be omega-3, not omega-6 fatty acids. FALSE What kind of ‘omega’ a polyunsaturated fatty acid is known as is
Fat and cholesterol are carried in the blood in special droplets known as chylomicrons. These droplets act as a transporter for cholesterol and fat taking it through the lymph system to the blood stream.
5 Saturated fats reduce the risk of heart disease. FALSE
dependent on where its first double bond occurs. If a double bond occurs at the third carbon in a polyunsaturated fat it is an ‘omega-3’ fatty acid. If it occurs at the sixth carbon it is an ‘omega-6’ fatty acid.
Saturated fats increase the risk of heart disease by promoting the formation of plaques in the blood vessels.
3 Triglycerides are the major form of fats in the human diet. TRUE
Few fatty acids occur free in foods or in the body. Most often, they are incorporated into triglycerides – lipids composed of three fatty acids attached to a glycerol.
NUTRITION PORTFOLIO To maintain good health, eat enough, but not too much, fat and select the right kinds. • List the types and amounts of fats and oils you eat daily, making note of which ones are saturated, monounsaturated or polyunsaturated and how your choices could include fewer saturated options.
•
•
List the types and amounts of milk products, red meat, seafood and chicken you eat daily, noting how your choices could include lower-fat options. Describe choices you can make in selecting and preparing foods to lower your intake of saturated fats.
STUDY QUESTIONS c d
Multiple choice questions Answers can be found at the back of the book. 1
Polyunsaturated fatty acids: a b c d
2
3
a b
5
only exist through hydrogenation have the hydrogens next to the double bonds on the same sides of the carbon chain
6
stearic acid and oleic acid oleic acid and linoleic acid palmitic acid and alpha-linolenic acid linoleic acid and alpha-linolenic acid
The adipokines do not include: a b c d
three fatty acids attached to a glucose three phospholipids attached to a cholesterol three fatty acids attached to a glycerol three glycerols attached to a lipid
Which of the following is true of trans fatty acids? Trans fatty acids:
The essential fatty acids include: a b c d
are always 22 carbons long have one or more double bond contribute to the development of heart disease are always liquid at room temperature
Triglycerides consist of: a b c d
4
are found naturally in some foods behave like unsaturated fat in the human body
adiponectin leptin resistin ghrelin
Chylomicrons are produced in the: a c b d
liver pancreas gall bladder small intestine
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Chapter 5: The lipids: triglycerides, phospholipids, and sterols
7
Transport vehicles for lipids are called: a b c d
8
The lipoprotein most associated with a reduced risk of heart disease is: a b c d
9
monoglycerides lipoproteins micelles blood vessels
CHD HDL LDL LPL
3
What does the term omega mean with respect to fatty acids? Describe the roles of the omega fatty acids in disease prevention. (Sections 5.1, 5.2)
4
Are there differences between alpha-linolenic acid and linoleic acid? If so, what are they? (Section 5.4)
5
What are trans-fatty acids, and how do they influence heart disease? How are trans-fatty acids created? (Sections 5.1, 5.5)
6
How do phospholipids differ from triglycerides in structure? How does cholesterol differ? How do these differences in structure affect function? (Sections 5.1, 5.2)
7
Differentiate between the roles of phospholipids and cholesterol in the body. (Section 5.1)
8
What are chylomicrons? Why is their role in the body so important? What happens to them once their task is complete? (Section 5.2).
9
What happens to bile once it is released into the small intestine? Why is bile recycled? (Section 5.3)
Which of the following is not true? Fats: a b c d
contain glucose provide energy protect against organ shock carry vitamins A, D, E and K
10 The hormone responsible for dismantling stored triglycerides and releasing the glycerol and fatty acids into the blood stream is: a b c d
167
10 What do lipoproteins do? What are the differences between VLDL, LDL and HDL? (Section 5.2)
ligual lipase hormone sensitive lipase gastric lipase pancreatic lipase
Review questions 1
Why are fats called fatty acids? (Section 5.1)
2
What chemical features distinguish fatty acids from each other? (Section 5.1)
NUTRITION CALCULATIONS These problems will give you practice in doing simple nutrition-related calculations (answers can be found in the back of this book). Show your calculations for each problem.
a
1
c
b
Be aware of the fats in milks. Following are four categories of milk: WT. (g)
FAT (g)
PROT. (g)
CARB. (g)
Milk A (1 cup)
244
8
8
12
Milk B (1 cup)
244
5
8
12
Milk C (1 cup)
244
3
8
12
Milk D (1 cup)
244
0
8
12
d e 2
Based on weight, what percentage of each milk is fat (round off to a whole number)? How much energy from fat will a person receive from drinking 1 cup of each milk? How much total energy will the person receive from 1 cup of each milk? What percentage of the energy in each milk comes from fat? How would each milk be labelled in the supermarket?
A new food product claims to be 97 per cent fatfree. The suggested serving size is 168 grams. How much fat is provided in this meal? What is the energy (kilojoules) supplied by fat in this meal?
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NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx
•
• •
Search ‘cholesterol’ and ‘dietary fat’ at the Australian and New Zealand Heart Foundation websites: http:// www.heartfoundation.org.au and https://www. heartfoundation.org.nz Search ‘fat’ at the International Food Information Council Foundation site: https://www.foodinsight.org/ Check out a Mediterranean food guide pyramid: http://www.oldwayspt.org
SEARCH ME! NUTRITION Keyword: omega-3s Read about some of the differing dietary sources of omega-3s. What are the benefits of omega-3s for heart
health? List the different mechanisms and pathways of action.
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Chapter 5: The lipids: triglycerides, phospholipids, and sterols
HIGH-FAT FOODS – FRIEND OR FOE? Eat less fat. Eat more fatty fish. Give up butter. Use margarine. Give up margarine. Use olive oil. Steer clear of saturated. Seek out omega-3. Stick with monounsaturated and polyunsaturated. Keep fat intake moderate. Today’s fat messages seem to be forever multiplying and changing. No wonder people feel confused about dietary fat. The confusion stems in part from the complexities of fat and in part from the nature of recommendations. As Chapter 5 explained, ‘dietary fat’ refers to several kinds of fats. Some fats support health whereas others damage it, and foods typically provide a mixture of fats in varying proportions. Researchers have spent decades sorting through the relationships among the various kinds of fat and their roles in supporting or harming health. Translating these research findings into dietary recommendations is challenging. Too little information can mislead consumers, but too much detail can overwhelm them. As research findings accumulate, recommendations slowly evolve and become more refined. Fortunately, that’s where we are with fat recommendations today – refining them from the general to the specific. Though they may seem to be ‘forever multiplying and changing’, in fact, they are becoming more meaningful. This highlight begins with a look at the dietary guidelines for fat intake. It continues by identifying which foods provide which fats and presenting the Mediterranean diet, an example of a food plan that embraces the heart-healthy fats. It closes with strategies
169
HIGHLIGHT
5
to help consumers choose the right amounts of the right kinds of fats for a healthy diet.
Guidelines for fat intake Dietary recommendations for fat have shifted in emphasis from lowering total fat in general, to limiting saturated and trans fat, specifically.1 Instead of urging people to cut back on all fats, recommendations suggest carefully replacing the ‘bad’ saturated fats with the ‘good’ unsaturated fats and enjoying them in moderation. The goal is to create a diet moderate in total energy that provides enough of the fats that support good health, but not too much of those that harm health. (Turn to Section 5.6 for a review of the health consequences of each type of fat.) Health authorities have concluded that a healthy range is 20 to 35 per cent of total energy intake from fat. This range appears to be compatible with low rates of heart disease, diabetes, obesity and cancer. Heart-healthy recommendations suggest that within this range, consumers should try to minimise their intakes of saturated fat, trans fat and cholesterol, and use mono-unsaturated and polyunsaturated fats instead.2 Asking consumers to limit their total fat intake was less than perfect advice, but it was straightforward – find the fat and cut back. Asking consumers to keep their intakes of saturated fats, trans fats and cholesterol low and to use mono-unsaturated and polyunsaturated fats instead may be more on-target with heart health, but it also makes diet planning more complicated. To make appropriate selections, consumers must first learn which foods contain which fats.
iStockphoto/Martin Firus
High-fat foods and heart health
Meat pies are a commonly eaten food at sporting events.
Avocados, bacon, walnuts, potato chips and mackerel are all high-fat foods, yet some of these foods have detrimental effects on heart health when consumed in excess, whereas others seem neutral or even beneficial. This section presents some of the accumulating evidence that helps to distinguish which high-fat foods belong in a healthy diet and which ones need to be kept to a minimum. As you will see, a little more fat in the diet may be compatible with heart health, but only if the great majority of it is the unsaturated kind.
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Cook with olive oil
high-fat diet rich in olive oil. Importantly, olive oil is not a magic potion; drizzling it on foods does not make them healthier. Like other fats, olive oil delivers 36 kilojoules per gram, which can contribute to weight gain in people who fail to balance their energy intake with physical activity. Its role in a healthy diet is to replace the saturated fats. Other vegetable oils, such as canola and safflower oil, are also generally low in saturated fats and high in unsaturated fats. For this reason, heart-healthy diets use these unsaturated vegetable oils to replace the more saturated fats of butter, hydrogenated hard margarine, lard or shortening. (Remember that the tropical oils – coconut, palm and palm kernel – are too saturated to be included with the heart-healthy vegetable oils.)
Nibble on nuts Tree nuts and peanuts are traditionally excluded from lowfat diets, and for good reasons. Nuts provide up to 80 per cent of their energy from fat, and ½ cup (about 75 grams) of mixed nuts provides over 1500 kilojoules. Frequent nut consumption, however, correlates with lower risk of mortality and chronic diseases, such as diabetes and heart disease.7 Benefits are seen for a variety of nuts, including almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pistachios, walnuts and peanuts. On average, these nuts contain mostly mono-unsaturated fat (59 per cent), some polyunsaturated fat (27 per cent) and little saturated fat (14 per cent). Nuts also provide valuable dietary fibre, vegetable protein, vitamin E, minerals and phytochemicals. Including nuts may be a wise diet strategy against heart disease. Nuts may protect against heart disease by:8 • lowering blood cholesterol • lowering blood pressure • limiting oxidative stress and inflammation. Some research suggests that a diet that includes nuts may benefit other diseases as well. Before advising consumers to
© Matthew Farruggio
© Matthew Farruggio
As it turns out, the traditional diets of Greece and other countries in the Mediterranean region offer an excellent example of eating patterns that use ‘good’ fats liberally. The primary fat in these diets is olive oil, which seems to play a key role in providing health benefits.3 A classic study of the world’s people, the Seven Countries Study, found that death rates from heart disease were strongly associated with diets high in saturated fats but only weakly linked with total fat.4 In fact, the two places with the highest fat intakes, Finland and the Greek island of Crete, had the highest (Finland) and lowest (Crete) rates of heart disease deaths. In both places, the people consumed 40 per cent or more of their kilojoules from fat. Clearly, a high-fat diet is not the primary problem.5 When researchers refocused their attention on type of fat, they began to notice the benefits of olive oil. A diet that uses olive oil instead of other fats, especially butter, margarine, and meat fats, offers numerous health benefits. Olive oil, canola oil and other oils rich in mono-unsaturated fatty acids help to protect against heart disease and stroke by:6 • lowering total and LDL cholesterol and not lowering HDL cholesterol or raising triglycerides • lowering LDL cholesterol susceptibility to oxidation • lowering blood-clotting factors • providing phytochemicals that act as antioxidants (see Highlight 11) • lowering blood pressure • interfering with the inflammatory response • providing antimicrobial actions. When compared with other fats, olive oil seems to be a wise choice, but controlled clinical trials are too scarce to support population-wide recommendations to switch to a
Olives and their oil may benefit heart health.
For heart health, snack on a few nuts instead of potato chips. Because nuts are energy-dense (high in energy per gram), it is especially important to keep portion size in mind when eating them.
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Chapter 5: The lipids: triglycerides, phospholipids, and sterols
include nuts in their diets, however, a caution is in order. As mentioned, most of the energy nuts provide comes from fats. Consequently, they deliver many kilojoules per bite. Incorporating nuts in the diet, however, does not necessarily lead to weight gains and may even help with weight control.9 Consumers can enjoy nuts without increasing total energy intake by using nuts instead of, not in addition to, other foods (such as meats, potato chips, oils, margarine and butter).
Feast on fish Research into the health benefits of the long-chain omega-3 polyunsaturated fatty acids began with a simple observation: the native peoples of Alaska, northern Canada and Greenland, who eat a diet rich in omega-3 fatty acids – notably, EPA and DHA – have a remarkably low rate of heart disease even though their diets are relatively high in fat. These omega-3 fatty acids help to protect against heart disease by:10 • reducing blood triglycerides • stabilising plaque • lowering blood pressure and resting heart rate • reducing inflammation • serving as precursors to eicosanoids. For people with hypertension or atherosclerosis, these actions can be life-saving. Research studies have provided strong evidence that increasing omega-3 fatty acids in the diet supports heart health and lowers the rate of deaths from heart disease.11 For this reason, the Heart Foundations of Australia and New Zealand recommend including fish in a heart-healthy diet. People who eat some fish each week can lower their risks of heart attack and stroke. Fish is the best source of EPA and DHA in the diet, but it is also a major source of mercury, an environmental contaminant. Most fish contain at least trace amounts of mercury, but shark species, swordfish, marlin, king mackerel and snapper have especially high levels. For this reason, Food Standards Australia New Zealand advises pregnant and lactating women, women of child-bearing age who may become pregnant, and young children to limit the intake of shark (flake) or billfish (swordfish/ broadbill and marlin) to one serve a fortnight. For other types of fish low in mercury, intake of two to three serves per week of any fish and seafood is recommended.12 Commonly eaten seafood relatively low in mercury include prawns, trout, salmon and canned tuna. In addition to the direct toxic effects of mercury, some research suggests that mercury may diminish the health benefits of omega-3 fatty acids. Such findings serve as a reminder that our health depends on the health of our planet. The protective effect of fish in the diet is available, provided that the fish and their surrounding waters are not heavily contaminated. (Chapter 19 discusses the adverse consequences of mercury, and
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Chapter 20 presents the relationships between diet and the environment in more detail.) In an effort to limit exposure to pollutants, some consumers choose farm-raised fish. Compared with fish caught in the wild, farm-raised fish tend to be lower in mercury, but they are also lower in omega-3 fatty acids. When selecting fish, keep the diet strategies of variety and moderation in mind. Varying choices and eating moderate amounts helps to limit the intake of contaminants such as mercury.
High-fat foods and heart disease The most important dietary determinant of LDL cholesterol is saturated fat. Each 1 per cent increase in energy from saturated fatty acids in the diet produces a 2 per cent jump in heart disease risk by elevating blood LDL cholesterol. Conversely, reducing saturated fat intake by 1 per cent can be expected to produce a 2 per cent drop in heart disease risk by the same mechanism. Even a 2 per cent drop in LDL represents a significant improvement for the health of the heart. Like saturated fats, trans fats also raise heart disease risk by elevating LDL cholesterol. A heart-healthy diet limits foods rich in these two types of fat. Figure H5.1 shows an example of a replacement meal.
Limit fatty meats, whole-milk products and tropical oil The major sources of saturated fats in the Australian and New Zealand diets are fatty meats, whole milk products, tropical oils and products made from any of these foods. To limit saturated fat intake, consumers must choose carefully among these high-fat foods. More than a third of the fat in most meats is saturated. Similarly, more than half of the fat is saturated in whole milk and other high-fat milk products, such as cheese, butter, cream, half-and-half, cream cheese, sour cream and ice-cream. The tropical oils of palm, palm kernel and coconut, which are rarely used by consumers in the kitchen, are used heavily by food manufacturers, and are commonly found in many commercially prepared foods. When choosing meats, milk products and commercially prepared foods, look for those lowest in saturated fat. Labels provide a useful guide for comparing products in this regard. Even with careful selections, a nutritionally adequate diet will provide some saturated fat. Zero saturated fat is not possible even when experts design menus with the mission to keep saturated fat as low as possible. Because most saturated fats come from animal foods, vegetarian diets can, and usually do, deliver fewer saturated fats than mixed diets.
The Mediterranean diet The links between good health and traditional Mediterranean eating patterns of the mid-1900s were introduced earlier
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FIGURE H5.1 Two meals compared: replacing saturated fat with unsaturated fat Examples of ways to replace saturated fats with unsaturated fats include sautéing vegetables in olive oil instead of butter, garnishing salads with avocado and sunflower seeds instead of bacon and blue cheese, and eating salmon instead of steak. Each of these meals provides roughly the same number of kcalories and grams of fat, but the one on the left has almost four times as much saturated fat and only half as many omega-3 fatty acids.
SATURATED FATS MEAL 1 c fresh broccoli topped with 1 tbs butter
© Matthew Farruggio
© Matthew Farruggio
To lower saturated fat and raise monounsaturated and polyunsaturated fats ...
UNSATURATED FATS MEAL 1 c fresh broccoli sautéed in 1 tbs olive oil
Unsaturated fat
1 c mixed baby greens salad with 2 strips bacon (crumbled) 30 g blue cheese crumble 1 tbs light Italian dressing 120 g grilled steak
1 c mixed baby greens salad with 2 avocado 2 tbs sunflower seeds 1 tbs light Italian dressing
Saturated fat
1
Total fat
120 g grilled salmon
Energy = 600 kcal
Energy = 600 kcal
© www.comstock.com
0
Fish is a good source of the omega-3 fatty acids.
10
20 30 GRAMS
40
50
with regard to olive oil. For people who eat these diets, the incidence of heart disease, some cancers, diabetes and other chronic inflammatory diseases is low, and life expectancy is high.13 Some research suggests that the health benefits of the Mediterranean eating pattern are partially due to its favourable effects on body weight.14 Although each of the many countries that border the Mediterranean Sea has its own culture, traditions and dietary habits, their similarities are much greater than the use of olive oil alone. In fact, no single factor can be credited with reducing disease risks – the association holds true only when the overall eating pattern is present. Apparently, each of the foods contributes small benefits that harmonise to produce either a substantial cumulative or synergistic effect. The Mediterranean eating pattern features fresh, whole foods. The people select crusty breads, whole grains, potatoes and pastas; a variety of vegetables (including wild greens) and legumes; feta and mozzarella cheeses and yoghurt; nuts; and fruits (especially grapes and figs). They eat some fish, other seafood, poultry, a few eggs and little meat. Along with olives and olive oil, their principal sources of fat are nuts and fish; they rarely use butter or encounter tropical fats. They commonly use herbs and spices instead of salt. Consequently, traditional Mediterranean diets are: • low in saturated fat • very low in trans fat • rich in mono-unsaturated and polyunsaturated fat
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APPLICATIONS OF NUTRITION RESEARCH Mediterranean diet and health Australia, particularly Melbourne, became home to a large southern European migrant population following the Second World War. These migrants have enriched Australian culture and cuisine with many foods and flavours. The beneficial health experienced by these migrants who stay true to their Mediterranean origins has been demonstrated through the Melbourne Collaborative Cohort Study. This study has followed this population carefully since the early 1990s, now demonstrating the long-term benefits of a Mediterranean diet in providing protection against cancer, heart disease and diabetes (http://www.cancervic.org. au). Additionally, recent Australian research has shown that a Mediterranean diet reduced the dietary inflammatory index score when compared to a low-fat diet. This has implications for dietary prescription for those who suffer from chronic non-communicable disease, such as heart disease and diabetes.16 following the traditional Mediterranean diet can receive as much as 40 per cent of a day’s energy intake from fat, but their limited consumption of milk and milk products and meats provides less than 10 per cent from saturated fats. In addition, because the animals in the
• rich in complex carbohydrate and dietary fibre • rich in nutrients and phytochemicals that support good health. As a result, lipid profiles improve, inflammation diminishes, and the risk of heart disease declines. People
FIGURE H5.2 Mediterranean diet pyramid
MEDITERRANEAN DIET PYRAMID A contemporary approach to delicious, healthy eating
Meats and sweets Sometimes (no more than a few times a month)
Wine
In moderation
Poultry, eggs, cheese and yoghurt Moderate portions, daily to weekly
Fish and seafood Drink water Throughout the day
Often, at least two times per week
Fruits, vegetables, whole grains, healthy fats such as olive oil, beans, nuts and peanuts, legumes and seeds, herbs and spices Every day
Be physically active Enjoy meals with others
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Understanding nutrition
Mediterranean region pasture-graze, the meat, milk and milk products, and eggs are richer in omega-3 fatty acids than those from animals fed grain. Other foods typical of the Mediterranean region, such as wild plants and snails, provide omega-3 fatty acids as well. All in all, the traditional Mediterranean diet has earned a reputation for its health benefits as well as its delicious flavours. By following a Mediterranean eating pattern, consumers improve their blood lipid profile, insulin resistance, blood pressure and body weight.15 Consumers need to beware that the typical Mediterranean-style cuisine available commercially, however, has been adjusted to popular tastes. Quite often, what is sold is much higher in saturated fats and meats – and much lower in the potentially beneficial constituents – than the traditional fare. Unfortunately, it appears that people in the Mediterranean region who are replacing some of their traditional dietary habits with those of Western foods are losing the health benefits enjoyed previously.
Conclusion Are some fats ‘good’ and others ‘bad’ from the body’s point of view? The saturated and trans fats indeed seem mostly bad for the health of the heart. Aside from providing energy, which unsaturated fats can do equally well, saturated and trans fats bring no indispensable benefits to the body. Furthermore, no harm can come from consuming diets low in them. Still, foods rich in these fats are often delicious, giving them an occasional
place in the diet. In contrast, the unsaturated fats are mostly good for heart health when consumed in moderation. To date, their one proven fault seems to be that they, like all fats, provide abundant energy to the body and so may promote obesity if they drive daily energy intakes higher than energy needs. Obesity, in turn, often begets many body ills, as Chapters 8 and 9 describe. Clearly, different fatty acids have different actions in the body and risks of chronic diseases. When judging foods by their fatty acids, keep in mind that the fat in foods is a mixture of ‘good’ and ‘bad’, providing both unsaturated and saturated fatty acids. Even predominantly mono-unsaturated olive oil delivers some saturated fat. Consequently, even when a person chooses foods with mostly unsaturated fats, saturated fat can still add up if total fat is too high. Focusing all efforts on simply lowering saturated fat in the diet may be narrow advice for heart health. Including vegetables, fruits, whole grains and legumes as part of a balanced daily diet is a good idea, as is replacing saturated fats such as butter, shortening and meat fat with unsaturated fats such as olive oil and the oils from nuts and fish.17 These foods provide beneficial fatty acids, dietary fibre, vitamins, minerals and phytochemicals as well as little (or no) salt, saturated fat and trans fat – all valuable in protecting the body’s health. In addition, take care to select portion sizes that will best meet energy needs. And enjoy some physical activity daily. Remember that even a healthy eating pattern can be detrimental if eaten in excess.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A What are the features of a healthy high-fat diet?
heart disease risk. People following the traditional Mediterranean diet, which emphasises fruits, vegetables, whole grains, beans, nuts and seeds, and olive oil, also enjoy good heart health. How are dietary fats related to heart health? How is it that such diverse diets can have such similar health outcomes?
B Heart disease is rare among the Inuit people of Alaska, who continue to eat their traditional diet of seal meat and blubber. A traditional Nordic diet of game meats, berries, root vegetables and legumes helps to lower blood cholesterol and reduce
REFERENCES CHAPTER 1
2
S. K. Gebauer and coauthors, Vaccenic acid and trans fatty acid isomers from partially hydrogenated oil both adversely affect LDL cholesterol: A doubleblind, randomized controlled trial, American Journal of Clinical Nutrition 102 (2015): 1339–46. H. S. Moon, Biological effects of conjugated linoleic acid on obesityrelated cancers, Chemico-Biological Interactions 224C (2014): 189–95.
3
4
D. S. Mackay and coauthors, Lathosterol-to-cholesterol ratio in serum predicts cholesterol-lowering response to plant sterol consumption in a dual-center, randomized single-blind placebo-controlled trial, American Journal of Clinical Nutrition 101 (2015): 432–9. V. A. Cortes and coauthors, Physiological and pathological implications of cholesterol, Frontiers in Bioscience 19 (2014): 416–28.
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5
A. Steingoetter and coauthors, Imaging gastric structuring of lipid emulsions and its effect on gastrointestinal function: A randomized trial in healthy subjects, American Journal of Clinical Nutrition 101 (2015): 714–24. 6 S. Dash and coauthors, New insights into the regulation of chylomicron production, Annual Review of Nutrition 35 (2015): 265–94. 7 D. Saleheen and coauthors, Association of HDL cholesterol efflux capacity with incident coronary heart disease events: A prospective casecontrol study, Lancet Diabetes and Endocrinology 3 (2015): 507–13. 8 W. Annema and A. von Eckardstein, High-density lipoproteins: Multifunctional but vulnerable protections from atherosclerosis, Circulation 77 (2013): 2432–48. 9 A. Rodriguez and coauthors, Revisiting the adipocyte: A model for integration of cytokine signaling in the regulation of energy metabolism, American Journal of Physiology: Endocrinolgy and Metabolism 309 (2015): E691–E714. 10 S. Rajaram, Health benefits of plant-derived a-linolenic acid, American Journal of Clinical Nutrition 100 (2014): 443S–448S; P. C. Calder, Mechanisms of action of (n-3) fatty acids, Journal of Nutrition 142 (2012): 592S–599S. 11 M. Dessi and coauthors, Atherosclerosis, dyslipidemia, and inflammation: The significant role of polyunsaturated fatty acids, ISRN Inflammation (2013): 191823 12 S. Marventano and coauthors, A review of recent evidence in human studies of n-3 and n-6 PUFA intake on cardiovascular disease, cancer, and depressive disorders: Does the ratio really matter? International Journal of Food Sciences and Nutrition 66 (2015): 611–22. 13 A. Caron, D. Richard, and M. Laplante, The roles of mTOR complexes in lipid metabolism, Annual Review of Nutrition 35 (2015): 321–48. 14 T. Ulven and E. Christiansen, Dietary fatty acids and their potential for controlling metabolic diseases through activation of FFA4/ GPR120, Annual Review of Nutrition 35 (2015): 239–63. 15 Position of the Academy of Nutrition and Dietetics: Dietary fatty acids for healthy adults, Journal of the Academy of Nutrition and Dietetics 114 (2014): 136–53. 16 I. A. Brouwer, A. J. Wanders, and M. B. Katan, Trans fatty acids and cardiovascular health: Research completed? European Journal of Clinical Nutrition 67 (2013): 541–7. 17 J. N. Kiage and coauthors, Intake of trans fat and all-cause mortality in the Reasons for Geographical and Racial Differences in Stroke (REGARDS) cohort, American Journal of Clinical Nutrition 97 (2013): 1121–8. 18 K. D. Brownell and J. L. Pomeranz, The trans-fat ban—Food regulation and long-term health, New England Journal of Medicine 370 (2014): 1773–5. 19 A. Baylin, Secular trends in trans fatty acids: Decreased trans fatty acids in the food supply are reflected in decreased trans fatty acids in plasma, American Journal of Clinical Nutrition 97 (2013): 665–6. 20 M. M. H. Abdullah, P. J. H. Jones, and P. K. Eck, Nutrigenetics of cholesterol metabolism: Observational and dietary intervention studies in the postgenomic era, Nutrition Reviews 73 (2015): 523–43. 21 University of Otago and Ministry of Health, A focus on nutrition: key findings of the 2008/09 New Zealand Adult Nutrition Survey, Wellington: Ministry of Health (2011); Australian Bureau of Statistics, Australian Health Survey: Usual Nutrient Intakes, 2011–12, http://www.abs.gov.au/ausstats/[email protected]/Lookup/4364.0.55.008mai n+features12011-12.
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22 G. Kaur, D. Cameron-Smith and A. J. Sinclair, Are trans fats a problem in Australia? Medical Journal of Australia 196 (2012): 666–7. 23 Australian Bureau of Statistics, National nutrition survey: nutrient intakes and physical measurements, Australia (1995), http://www. ausstats.abs.gov.au/ausstats/subscriber.nsf/0/CA25687100069892CA 25688900268A6D/$File/48050_1995.pdf 24 Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance, Journal of the American Dietetic Association 100 (2000): 1543–56. 25 U. Schwab and coauthors, Effect of the amount and type of dietary fat on cardiometabolic risk factors and risk of developing type 2 diabetes, cardiovascular diseases, and cancer: A systematic review, Food and Nutrition Research 58 (2014): 25145. 26 M. C. de Oliveira Otto and coauthors, Circulating and dietary omega-3 and omega-6 polyunsaturated fatty acids and incidence of CVD in the Multi-Ethnic Study of Atherosclerosis, Journal of the American Heart Association 2 (2013): e000506. 27 T. A. Mori, Dietary n-3 PUFA and CVD: A review of the evidence, Proceedings of the Nutrition Society 73 (2014): 57–4. 28 L. C. Del Gobbo and coauthors, v-3 Polyunsaturated fatty acid biomarkers and coronary heart disease, JAMA Internal Medicine 176 (2016): 1155–66. 29 A. Hidaka and coauthors, Fish, n-3 PUFA consumption, and pancreatic cancer risk in Japanese: A large, population-based, prospective cohort study, American Journal of Clinical Nutrition 102 (2015): 1490–7. 30 V. Oskarsson and coauthors, Fish consumption and risk of nongallstone related acute pancreatitis: A prospective cohort study, American Journal of Clinical Nutrition 101 (2015): 72–80. 31 K. Yurko-Mauro, D. D. Alexander, and M. E. Van Elswyk, Docosahexaenoic acid and adult memory: A systematic review and meta-analysis, PLoS One 10 (2015): e0120391. 32 Fish oil supplements, Journal of the American Medical Association 312 (2014): 839. 33 B. S. Peskin, Why fish oil fails: A comprehensive 21st century lipidsbased physiologic analysis, Journal of Lipids 2014 (2014): 495761. 34 B. Heydari and coauthors, Effect of omega-3 acid ethyl esters on left ventricular remodeling after acute myocardial infarction, Circulation 134 (2016): 378–91. 35 S. M. Innis, Dietary omega 3 fatty acids and the developing brain, Brain Research 1237 (2008): 35–43; J.T Brenna and S.E. Carlson, Docosahexaenoic acid and human brain development: evidence that a dietary supply is needed for optimal development, Journal of Human Evolution 77 (2014): 99–106. 36 R. Rathod and coauthors, Novel insights into the effect of vitamin B12 and omega-3 fatty acids on brain function, Journal of Biomedical Science 23 (2016): 17–23. 37 I. Blasko, Interaction of v-3 fatty acids with B vitamins in slowing the progression of brain atrophy: identifying the elderly at risk, The American Journal of Clinical Nutrition 102 (2015): 7–8. 38 S. C. Larsson, A. Akesson, and A. Wolk, Egg consumption and risk of heart failure, myocardial infarction, and stroke: Results from 2 prospective cohorts, American Journal of Clinical Nutrition 102 (2015): 1007–13. 39 S. Peou and coauthors, Impact of avocado-enriched diets on plasma lipoproteins: A meta-analysis, Journal of Clinical Lipidology 10 (2016): 161–71.
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HIGHLIGHT 1
2
3
4 5 6
7
8
9
D. Mozaffarian, R. Micha, and S. Wallace, Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials, PLoS Medicine 7 (2010): e10000252. M. Guasch-Ferré and coauthors, Dietary fat intake and risk of cardiovascular disease and all-cause mortality in a population at high risk of cardiovascular disease, American Journal of Clinical Nutrition 102 (2015): 1563–73. S. Bulotta and coauthors, Beneficial effects of the olive oil phenolic components oleuropein and hydroxytyrosol: Focus on protection against cardiovascular and metabolic diseases, Journal of Translational Medicine 12 (2014): 219. A. Keys, Seven Countries: A Multivariate Analysis of Death and Coronary Heart Disease (Cambridge: Harvard University Press, 1980). W. C. Willet, The great fat debate: total fat and health, Journal of the American Dietetic Association 111 (2011): 660–2. S. Martin-Paláez and coauthors, Health effects of olive oil polyphenols: Recent advances and possibilities for the use of health claims, Molecular Nutrition and Food Research 57 (2013): 760–1. H. N. Luu and coauthors, Prospective evaluation of the association of nut/peanut consumption with total and cause-specific mortality, JAMA Internal Medicine 175 (2015): 755–66. C. E. Berryman and co-authors, Effects of almond consumption on the reduction of LDL-cholesterol: a discussion of potential mechanisms and future research directions, Nutrition Reviews 69 (2011): 171–85. S. Y. Tan, J. Dhillion, and R. D. Mattes, A review of the effects of nuts on appetite, food intake, metabolism and body weight; American Journal of Clinical Nutrition 100 (2014): 412S–422S.
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A. C. Skulas-Ray and co-authors, Dose-response effects of omega-3 fatty acids on triglycerides, inflammation, and endothelial function in healthy persons with moderate hypertriglyceridemia, American Journal of Clinical Nutrition 93 (2011): 243–252D. 11 Mozaffarian and J. H. Y. Wu, Omega-3 fatty acids and cardiovascular disease: effects on risk factors, molecular pathways, and clinical events, Journal of the American College of Cardiology 58 (2011): 2047–67. 12 Food Standards Australia New Zealand, Food matters – mercury in fish, available at http;//www.foodstandards.gov.au/foodmatters/ mercuryinfish.cfm 13 T. Y. N. Tong and coauthors, Prospective association of the Mediterranean diet with cardiovascular disease incidence and mortality and its population impact in a non-Mediterranean population: The EPICNorfolk study, BMC Medicine 14 (2016): 135. 14 R. Estruch and coauthors, Effect of a high-fat Mediterranean diet on bodyweight and waist circumference: A prespecified secondary outcomes analysis of the PREDIMED randomised controlled trial, Lancet: Diabetes and Endocrinology (2016): S2213. 15 I. Castro-Quezada, B. Román-Vi.as, and L. Serra-Majem, The Mediterranean diet and nutritional adequacy: A review, Nutrients 6 (2014): 231–48. 16 H Mary and coauthors, Randomization to 6-month Mediterranean diet compared with a low-fat diet leads to improvement in Dietary Inflammatory Index scores in patients with coronary heart disease: the AUSMED Heart Trial, Nutrition Research 55 (2018): 94–107. 17 R. J. de Souza and S. S. Anand, Saturated fat and heart disease, British Medical Journal 355 (2016): i6257.
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CHAPTER
6
PROTEIN: AMINO ACIDS Nutrition in your life
Their versatility in the body is impressive. They help muscles to contract, blood to clot and eyes to see. They keep you alive and well by facilitating chemical reactions and defending against infections. Without them, your bones, skin and hair would have no structure. No wonder they were named proteins, meaning ‘of prime importance’. Does that mean proteins deserve top billing in your diet as well? Are the best sources of protein beef, beans or broccoli? Learn which foods will supply you with enough, but not too much, high-quality protein for health. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F Meat is the most important source of protein in the diet. T F When proteins are denatured they cease being proteins. T F Amino acids are the building blocks of proteins. T F Proteins have many roles in the body, including that of energy provision through glucose
production.
T F Foods derived from animals are considered high-quality proteins.
LEARNING OBJECTIVES 6.1 Recognise the chemical structures of amino acids and proteins. 6.2 Summarise protein digestion and absorption. 6.3 Describe how the body makes proteins and uses them to perform various roles. 6.4 Explain the differences between high‑quality and low-quality proteins, including notable food sources of each.
6.5 Identify the health benefits of, and recommendations for, protein. 6.6 Explain how nutrients influence gene activity (nutrigenomics) and how genes influence the activities of nutrients (nutrigenetics).
Spinach is an excellent source of vitamin K and iron
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Some misconceptions surround the roles of protein in the body and the importance of protein in the diet. For example, people who associate meat with protein and protein with strength may eat steak to build muscles. Their thinking is only partly correct, however. Protein is a vital structural and working substance in all cells – not just muscle cells. To build strength, muscle cells need physical activity and all the nutrients – not just protein. Furthermore, protein is found in milk, eggs, legumes and many grains and vegetables – not just meat. By overvaluing protein and overemphasising meat in the diet, a person may mistakenly crowd out other, equally important nutrients and foods. As this chapter describes the various roles of protein in the body and food sources in the diet, keep in mind that protein is one of many nutrients needed to maintain good health.
• • • •
Reminder: H forms 1 bond O forms 2 bonds N forms 3 bonds C forms 4 bonds
6.1 The chemist’s view of proteins
Chemically, proteins contain the same atoms as carbohydrates and lipids – carbon (C), hydrogen (H) and oxygen (O) – but proteins also contain nitrogen (N) atoms. These nitrogen atoms give the name amino (nitrogen containing) to the amino acids – the links in the chains of proteins.
PUTTING COMMON SENSE TO THE TEST
Amino acids All amino acids have the same basic structure – a central carbon (C) atom with a hydrogen atom (H), an amino group (NH2) and an acid group (COOH) attached to it. However, carbon atoms need to form four bonds, so a fourth attachment is necessary. This fourth site distinguishes each amino acid from the others. Attached to the carbon atom at the fourth bond is a distinct atom, or group of atoms, known as the side group or side chain (see Figure 6.1).
Meat is the most important source of protein in the diet. FALSE
Unique side groups
FIGURE 6.1 Amino acid structure
The side groups on amino acids vary from one amino acid to the next, making proteins more complex than both carbohydrates and lipids. A polysaccharide (starch, for example) may be several thousand units long, but each unit is a glucose molecule just like all the others. A protein, on the other hand, is made up of about 20 different amino acids, each with a different side group. Table 6.1 lists the amino acids most common in proteins.* The simplest amino acid, glycine, has a hydrogen atom as its side group. A slightly more complex amino acid, alanine, has an extra carbon with three hydrogen atoms. Other amino acids have more complex side groups (see Figure 6.2
Side group varies O Amino group
H N
C
H
H
C O
H
Acid group
FIGURE 6.2 Examples of amino acids Note that all amino acids have a common chemical structure, but that each has a different side group. Appendix C presents the chemical structures of the 20 amino acids most common in proteins. O H H
H
C
H
H N
C
C
H
H
O H N
C
H
H
C
Glycine
C
O
H
C
H
H N
C
C
H
H
O O H
Alanine
H H
C
H
H N
C
C
H
H
O O
H
O O
Aspartic acid
H
O H
Phenylalanine
* Besides the 20 common amino acids, which can all be components of proteins, others do not occur in proteins but can be found individually (for example, taurine and ornithine). Some amino acids occur in related forms (for example, proline can acquire an OH group to become hydroxyproline). Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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TABLE 6.1 Amino acids Proteins are made up of about 20 common amino acids. The first column lists the essential amino acids for human beings (those the body cannot make – that must be provided in the diet). The second column lists the non-essential amino acids. In special cases, some non-essential amino acids may become conditionally essential. In a newborn, for example, only five amino acids are truly non-essential; the other non-essential amino acids are conditionally essential until the body’s metabolic pathways are developed enough to make those amino acids in adequate amounts. NON-ESSENTIAL AMINO ACIDS
Histidine
(HISS-tuh-deen)
Alanine
(AL-ah-neen)
Isoleucine
(eye-so-LOO-seen)
Arginine
(ARJ-ih-neen)
Leucine
(LOO-seen)
Asparagine
(ah-SPAR-ah-geen)
Lysine
(LYE-seen)
Aspartic acid
(ah-SPAR-tic acid)
Methionine
(meh-THIGH-oh-neen)
Cysteine
(SIS-teh-een)
Phenylalanine
(fen-il-AL-ah-neen)
Glutamic acid
(GLU-tam-ic acid)
Threonine
(THREE-oh-neen)
Glutamine
(GLU-tah-meen)
Tryptophan
(TRIP-toe-fan, TRIP-toefane)
Glycine
(GLY-seen)
Valine
(VAY-leen)
Proline
(PRO-leen)
Serine
(SEER-een)
Tyrosine
(TIE-roe-seen)
© Cengage
ESSENTIAL AMINO ACIDS
NOTE: These 20 amino acids can all be commonly found in proteins. In addition, other amino acids do not occur in proteins but can be found individually (for example, taurine and ornithine). Some amino acids occur in related forms (for example, proline can acquire an OH group to become hydroxyproline).
for examples). Thus, although all amino acids share a common structure, they differ in size, shape, electrical charge and other characteristics because of differences in these side groups.
Non-essential amino acids
More than half of the amino acids are non-essential, meaning the body can synthesise them for itself. Proteins in foods usually deliver these amino acids, but it is not essential that they do so. The body can make all non-essential amino acids, given nitrogen to form the amino group and fragments from carbohydrate or fat to form the rest of the structure.
Essential amino acids There are nine amino acids that the human body either cannot make at all or cannot make in sufficient quantities to meet its needs. These nine amino acids must be supplied by the diet; they are essential. The first column in Table 6.1 presents the essential amino acids.
Conditionally essential amino acids Sometimes a non-essential amino acid becomes essential under special circumstances. For example, the body normally uses the essential amino acid phenylalanine to make tyrosine (a non-essential amino acid). But if the diet fails to supply enough phenylalanine, or if the body cannot make the conversion for some reason (as happens in the inherited disease phenylketonuria), then tyrosine becomes a conditionally essential amino acid.
Some researchers refer to essential amino acids as indispensable and to non-essential amino acids as dispensable.
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Proteins Cells link amino acids end to end in a variety of sequences to form thousands of different proteins. A peptide bond unites each amino acid to the next.
Amino acid chains Condensation reactions connect amino acids, just as they combine monosaccharides to form disaccharides and fatty acids with glycerol to form triglycerides. Two amino acids bonded together form a dipeptide (see Figure 6.3). By another such reaction, a third amino acid can be added to the chain to form a tripeptide. As additional amino acids join the chain, a polypeptide is formed. Most proteins are a few dozen to several hundred amino acids long; Figure 6.4 provides an example – insulin.
FIGURE 6.3 Condensation of two amino acids to form a dipeptide
H
H
H
C
H
H N
C
C
H
C
H
H N
C
C
O H
H
H
H
+
H
H
Amino acid
FIGURE 6.4 Amino acid sequence of human insulin Human insulin is a relatively small protein that consists of 51 amino acids in two short polypeptide chains. (For amino acid abbreviations, see Appendix C.) Two bridges link the two chains. A third bridge spans a section within the short chain. Known as disulphide bridges, these links always involve the amino acid cysteine (Cys), whose side group contains sulphur (S). Cysteines connect to each other when bonds form between these side groups.
Tyr
Phe Phe Gly Arg Glu Gly
H
H N
C
C
H
H
H
C
H
N
C
C
H
H
O O
An OH group from the acid end of one amino acid and an H atom from the amino group of another join to form a molecule of water.
Pro Lys Ala
C
O O
Amino acid
Thr
H
HOH
Water
O O
H
Dipeptide A peptide bond (highlighted in red) forms between the two amino acids, creating a dipeptide.
Amino acid sequences – primary structure
The primary structure of a protein is determined by the sequence of amino acids. If a person could walk along a carbohydrate molecule like starch, the first stepping stone would be a glucose. The next stepping stone would also be a glucose, and it would be followed by another glucose, and yet another glucose. But if a person were to walk along a Leu Ala Glu Val Leu His Ser Gly Cys Leu His Gln polypeptide chain, each stepping stone would be one Asn Tyr Val S Leu of 20 different amino acids. The first stepping stone Phe Val S might be the amino acid methionine. The second Cys might be an alanine. The third might be a glycine, Gly Ile Val Glu Gln Cys Cys S Ala the fourth a tryptophan, and so on. Walking along S Ser S another polypeptide path, a person might step on a S Val phenylalanine, then a valine and then a glutamine. Asn Cys Tyr Asn Glu Leu Gln Tyr Leu Ser Cys In other words, amino acid sequences within proteins vary. The amino acids can act somewhat like the letters in an alphabet. If you had only the letter G, all you could write would be a string of Gs: G-G-G-G-G-G-G. But with 26 different letters available, you can create poems, songs and novels. Similarly, the 20 amino acids can be linked together in a variety of sequences – even more than are possible for letters in a word or words in a sentence. Thus, the variety of possible sequences for polypeptide chains is tremendous.
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Polypeptide shapes – secondary structure The secondary structure of proteins is determined not by chemical bonds, as between the amino acids, but by weak electrical attractions within the polypeptide chain. As positively charged hydrogen atoms attract nearby negatively charged oxygen atoms, sections of the polypeptide chain twist into a helix or fold into a pleated sheet, for example. These shapes give proteins strength and rigidity.
Polypeptide tangles – tertiary structure The tertiary structure of proteins occurs as long polypeptide chains twist and fold into a variety of complex, tangled shapes. The unique side group of each amino acid gives it characteristics that attract it to, or repel it from, the surrounding fluids and other amino acids. Some amino acid side groups are attracted to water molecules; they are hydrophilic. Other side groups are repelled by water; they are hydrophobic. As amino acids are strung together to make a polypeptide, the chain folds so that its hydrophilic side groups are on the outer surface near water; the hydrophobic groups tuck themselves inside, away from water. Similarly, the disulphide bridges in insulin (see Figure 6.4) determine its tertiary structure. The extraordinary and unique shapes of proteins enable them to perform their various tasks in the body. Some form globular or spherical structures that can carry and store materials within them, and some, such as those of tendons, form linear structures that are more than 10 times as long as they are wide. The intricate shape a protein finally assumes gives it maximum stability.
Multiple polypeptide interactions – quaternary structures
FIGURE 6.5 The structure of haemoglobin Four highly folded polypeptide chains form the globular haemoglobin protein.
Iron
Haem, the non-protein portion of haemoglobin, holds iron.
The amino acid sequence determines the shape of the polypeptide chain.
Some polypeptides are functioning proteins just as they are; others need to associate with other polypeptides to form larger working complexes. The quaternary structure of proteins involves the interactions between two or more polypeptides. One molecule of haemoglobin – the large, globular protein molecule that, by the billions, packs the red blood cells and carries oxygen – is made of four associated polypeptide chains, each holding the mineral iron (see Figure 6.5).
When proteins are subjected to heat, acid or other conditions that disturb their stability, they undergo denaturation – that is, they uncoil and lose their shapes and, consequently, also lose their ability to function. Past a certain point, denaturation is irreversible. Familiar examples of denaturation include the hardening of an egg when it is cooked, the curdling of milk when acid is added, and the stiffening of egg whites when they are whipped.
© Matthew Farruggio
Protein denaturation
Cooking an egg denatures its proteins.
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Chemically speaking, proteins are more complex than carbohydrates or lipids, being made of some 20 different amino acids, nine of which the body cannot make. Each amino acid contains an amino group, an acid group, a hydrogen atom and a distinctive side group, all attached to a central carbon atom. Cells link amino acids together in a series of condensation reactions to create proteins. The distinctive sequence of amino acids in each protein determines the protein’s unique shape and function.
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PUTTING COMMON SENSE TO THE TEST
When proteins are denatured they cease being proteins. FALSE
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6.2 Digestion and absorption of protein
Proteins in foods do not become body proteins directly. Instead, they supply the amino acids from which the body makes its own proteins. When a person eats foods containing protein, enzymes break the long polypeptide strands into shorter strands, the short strands into tripeptides and dipeptides, and, finally, the tripeptides and dipeptides into amino acids.
Protein digestion Figure 6.6 illustrates the digestion of protein through the gastrointestinal (GI) tract. Proteins are crushed and moistened in the mouth, but the real action begins in the stomach.
In the stomach The inactive form of an enzyme is called a proenzyme or a zymogen.
The major event in the stomach is the partial breakdown (hydrolysis) of proteins. Hydrochloric acid uncoils (denatures) each protein’s tangled strands so that digestive enzymes can attack the peptide bonds. The hydrochloric acid also converts the inactive form of the enzyme pepsinogen to its active form, pepsin. Pepsin cleaves proteins – large polypeptides – into smaller polypeptides and some amino acids.
In the small intestine A string of four to nine amino acids is an oligopeptide. • oligo 5 few
When polypeptides enter the small intestine, several pancreatic and intestinal proteases hydrolyse them further into short peptide chains, tripeptides, dipeptides and amino acids. Then peptidase enzymes on the membrane surfaces of the intestinal cells split most of the dipeptides and tripeptides into single amino acids. Only a few peptides escape digestion and enter the blood intact. Figure 6.6 includes names of the digestive enzymes for protein and describes their actions.
Protein absorption A number of specific carriers transport amino acids (and some dipeptides and tripeptides) into the intestinal cells. Once inside the intestinal cells, amino acids may be used for energy or to synthesise needed compounds. Amino acids that are not used by the intestinal cells are transported across the cell membrane into the surrounding fluid where they enter the capillaries on their way to the liver. Consumers lacking nutrition knowledge may fail to realise that most proteins are broken down to amino acids before absorption. They may be misled by advertisements urging them to ‘Eat enzyme A. It will help you digest your food’. Or ‘Don’t eat food B. It contains enzyme C, which will digest cells in your body’. In reality, though, enzymes in foods are digested, just as all proteins are. Even the digestive enzymes – which function optimally at their specific pH – are denatured and digested when the pH of their environment changes. (For example, the enzyme pepsin, which works best in the low pH of the stomach, becomes inactive and digested when it enters the higher pH of the small intestine.) Another misconception is that eating pre-digested proteins (amino acid supplements) saves the body from having to digest proteins and keeps the digestive system from ‘overworking’. Such a belief grossly underestimates the body’s abilities. Actually, the digestive system handles whole proteins better than pre-digested ones because it dismantles and absorbs the amino acids at rates that are optimal for the body’s use. (The last section of this chapter discusses amino acid supplements further.)
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FIGURE 6.6 Protein digestion in the GI tract PROTEIN Mouth and salivary glands Chewing and crushing moisten protein-rich foods and mix them with saliva to be swallowed.
Mouth
Salivary glands
Stomach Hydrochloric acid (HCl) uncoils protein strands and activates stomach enzymes: Protein
(Oesophagus) (Liver)
Pepsin, HCl
Smaller polypeptides
Stomach Pancreatic duct
Small intestine and pancreas Pancreatic and small intestinal enzymes split polypeptides further:
Pancreas
(Gall bladder)
Polypeptides
Pancreatic and intestinal proteases
Tripeptides, dipeptides, amino acids
Then enzymes on the surface of the small intestinal cells hydrolyse these peptides and the cells absorb them: Intestinal tripeptidases and dipeptidases Amino acids Peptides (absorbed)
Small intestine
HYDROCHLORIC ACID AND THE DIGESTIVE ENZYMES In the stomach: Hydrochloric acid (HCl) Denatures protein structure Activates pepsinogen to pepsin Pepsin Cleaves proteins to smaller polypeptides and some free amino acids Inhibits pepsinogen synthesis In the small intestine: Enteropeptidasea Converts pancreatic trypsinogen to trypsin Trypsin Inhibits trypsinogen synthesis Cleaves peptide bonds next to the amino acids lysine and arginine Converts pancreatic procarboxypeptidases to carboxypeptidases Converts pancreatic chymotrypsinogen to chymotrypsin Chymotrypsin Cleaves peptide bonds next to the amino acids phenylalanine, tyrosine, tryptophan, methionine, asparagine and histidine Carboxypeptidases Cleave amino acids from the acid (carboxyl) ends of polypeptides Elastase and collagenase Cleave polypeptides into smaller polypeptides and tripeptides Intestinal tripeptidases Cleave tripeptides to dipeptides and amino acids Intestinal dipeptidases Cleave dipeptides to amino acids Intestinal aminopeptidases Cleave amino acids from the amino ends of small polypeptides (oligopeptides) aEnteropeptidase was formerly known as enterokinase .
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Digestion is facilitated mostly by the stomach’s acid and enzymes, which first denature dietary proteins, then cleave them into smaller polypeptides and some amino acids. Pancreatic and intestinal enzymes split these polypeptides further, to oligo-, tri- and dipeptides, and then split most of these to single amino acids. Then carriers in the membranes of intestinal cells transport the amino acids into the cells, where they are released into the bloodstream.
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6.3 Proteins in the body
The human body contains an estimated 30 000 different kinds of proteins. Of these, about 3000 have been studied, although, with the recent surge in knowledge gained from sequencing the human genome, this number is growing rapidly. Only about 10 are described in this chapter – but these should be enough to illustrate the versatility, uniqueness and importance of proteins. As you will see, each protein has a specific function, and that function is determined during protein synthesis.
The study of the body’s proteins is proteomics. The human genome is the full set of chromosomes, including all of the genes and associated DNA.
Protein synthesis Each human being is unique because of small differences in the body’s proteins. These differences are determined by the amino acid sequences of proteins, which, in turn, are determined by genes. The following paragraphs describe in words the ways cells synthesise proteins; Figure 6.7 provides a pictorial description. The instructions for making every protein in a person’s body are transmitted by way of the genetic information received at conception. This body of knowledge, which is filed in the DNA (deoxyribonucleic acid) within the nucleus of every cell, never leaves the nucleus.
Delivering the instructions This process of messenger RNA being made from a template of DNA is known as transcription. This process of messenger RNA directing the sequence of amino acids and synthesis of proteins is known as translation.
Anaemia is not a disease but a symptom of various diseases. In the case of sickle-cell anaemia, a defect in the haemoglobin molecule changes the shape of the red blood cells. Later chapters describe the anaemias of vitamin and mineral deficiencies. In all cases, the abnormal blood cells are unable to meet the body’s oxygen demands.
Transforming the information in DNA into the appropriate sequence of amino acids needed to make a specific protein requires two major steps. In the first step, a stretch of DNA is used as a template to make a strand of RNA (ribonucleic acid) known as messenger RNA. Messenger RNA then carries the code across the nuclear membrane into the body of the cell. There it seeks out and attaches itself to one of the ribosomes (a protein-making machine, which is itself composed of RNA and protein), where the second step takes place. Situated on a ribosome, messenger RNA specifies the sequence in which the amino acids line up for the synthesis of a protein.
Lining up the amino acids
Other forms of RNA, called transfer RNA, collect amino acids from the cell fluid and bring them to the messenger. Each of the 20 amino acids has a specific transfer RNA. Thousands of transfer RNA, each carrying its amino acid, cluster around the ribosomes, awaiting their turn to unload. When the messenger’s list calls for a specific amino acid, the transfer RNA carrying that amino acid moves into position. Then the next loaded transfer RNA moves into place and then the next and the next. In this way, the amino acids line up in the sequence that is called for, and enzymes bind them together. Finally, the completed protein strand is released, and the transfer RNA are freed to return for other loads of amino acids.
Sequencing errors The sequence of amino acids in each protein determines its shape, which supports a specific function. If a genetic error alters the amino acid sequence of a protein, or if a mistake is made in copying the sequence, an altered protein will result, sometimes with dramatic consequences. The protein haemoglobin offers one example of such a genetic variation. In a person with sickle-cell anaemia, two of haemoglobin’s four polypeptide chains (refer to Figure 6.5) have the normal sequence of amino acids, but the other two chains do not – they have the amino acid valine in a position that is normally occupied by glutamic acid (see Figure 6.8). This single alteration in the amino acid sequence changes the characteristics and shape of haemoglobin so much that it loses its ability to carry oxygen effectively. The red blood cells filled with this abnormal haemoglobin stiffen into elongated sickle, or crescent, shapes instead of maintaining their normal pliable disc shape – hence the name, sickle-cell anaemia. Sickle-cell anaemia raises energy needs, causes many medical problems and shortens life expectancy; genetic screening at birth identifies infants who have the disease or carry the trait.1 Caring for children with
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Chapter 6: Protein: amino acids
FIGURE 6.7 Protein synthesis Cell DNA
Nucleus
DNA
mR
NA
1 The DNA serves as a template to make strands of messenger RNA (mRNA). Each mRNA strand copies exactly the instructions for making some protein the cell needs. Ribosomes (protein-making machinery)
3 The mRNA attaches itself to the protein-making machinery of the cell, the ribosomes.
2 The mRNA leaves the nucleus through the nuclear membrane. DNA remains inside the nucleus.
Ribosome
A
mRN
4 Another form of RNA, transfer RNA (tRNA), collects amino acids from the cell fluid. Each tRNA carries its amino acids to the mRNA, which dictates the sequence in which the amino acids will be attached to form the protein strands. Thus, the mRNA ensures the amino acids are lined up in the correct sequence. Amino acid tRNA
A
mRN
5 As the amino acids are lined up in the right sequence, and the ribosome moves along the mRNA, an enzyme attaches one amino acid after another to the growing protein strand. The tRNA are freed to return for more amino acids. When all the amino acids have been attached, the completed protein is released.
Protein strand
A
mRN
6 Finally, the mRNA and ribosome separate. It takes many words to describe these events, but in the cell, 40 to 100 amino acids can be added to a growing protein strand in only a second. Furthermore, several ribosomes can simultaneously work on the same mRNA to make many copies of the protein.
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Understanding nutrition
FIGURE 6.8 Sickle cell compared with normal red blood cell
Sebastian Kaulitzki/ShutterStock.com
Normally, red blood cells are disc-shaped, but in the inherited disorder sickle-cell anaemia, they are sickle- or crescent-shaped. This alteration in shape occurs because valine replaces glutamic acid in the amino acid sequence of two of haemoglobin’s polypeptide chains. As a result of this one alteration, the haemoglobin has a diminished capacity to carry oxygen.
Normal red blood cell
Sickle-shaped blood cell
Amino acid sequence of normal haemoglobin: Val His Leu
Thr
Pro Glu Glu
Amino acid sequence of sickle-cell haemoglobin: Val His Leu
Nutrients can play key roles in activating or silencing genes. Switching genes on and off, without changing the genetic sequence itself, is known as epigenetics. • epi 5 among PUTTING COMMON SENSE TO THE TEST
Amino acids are the building blocks of proteins. TRUE Breaking-down reactions are catabolic; building-up reactions are anabolic. (Chapter 7 provides more details.)
Thr
Pro Val
Glu
sickle-cell anaemia includes diligent attention to their water needs, as dehydration can trigger a crisis.
Nutrients and gene expression When a cell makes a protein as described earlier, scientists say that the gene for that protein has been ‘expressed’. Cells can regulate gene expression to make the type of protein, and in the amounts and at the rate, they need. Nearly all of the body’s cells possess the genes for making all human proteins, but each type of cell makes only the proteins it needs. For example, cells of the pancreas express the gene for insulin; in other cells, that gene is idle. Similarly, the cells of the pancreas do not make the protein haemoglobin, which is needed only by the red blood cells. Recent research has unveiled some of the fascinating ways nutrients regulate gene expression and protein synthesis (see Highlight 6). Because diet plays an ongoing role in our lives from conception to death, it has a major influence on gene expression and disease development. The benefits of polyunsaturated fatty acids in defending against heart disease, for example, are partially explained by their role in influencing gene expression for lipid enzymes. Later chapters provide additional examples of relationships among nutrients, genes and disease development.
Roles of proteins Whenever the body is growing, repairing or replacing tissue, proteins are involved. Sometimes their role is to facilitate or to regulate; at other times it is to become part of a structure. Versatility is a key feature of proteins.
Building materials for growth and maintenance From the moment of conception, proteins form the building blocks of muscles, blood and skin – in fact, of most body structures. For example, to build a bone or a tooth, cells first lay down a matrix of the protein collagen and then fill it with crystals of calcium, phosphorus, magnesium, fluoride and other minerals. Collagen also provides the material of ligaments and tendons and the strengthening glue between the cells of the artery walls that enables the arteries to withstand the pressure of the blood surging through them with each heartbeat. Also made of collagen are scars that knit the separated parts of torn tissues together. Proteins are also needed for replacing dead or damaged cells. The life span of a skin cell is only about 30 days. As old skin cells are shed, new cells made largely of protein grow from underneath to replace them. Cells in the deeper skin layers synthesise new proteins to go into hair and fingernails. Muscle cells make new proteins to grow larger and stronger in response to exercise. Cells of the GI tract are replaced every few days. Both inside and outside, then, the body continuously deposits protein into the new cells that replace those that have been lost.
Enzymes
Some proteins act as enzymes. Digestive enzymes have appeared in every chapter since Chapter 3, but digestion is only one of the many processes facilitated by enzymes. Enzymes not only break down substances but also build substances (such as bone) and transform one substance into another (amino acids into glucose, for example). Figure 6.9 displays a synthesis reaction.
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FIGURE 6.9 Enzyme action Each enzyme facilitates a specific chemical reaction. In this diagram, an enzyme enables two compounds to make a more complex structure, but the enzyme itself remains unchanged. B
C
A
D A B
New compound
A B
Enzyme
The separate compounds, A and B, are attracted to the enzyme’s active site, making a reaction likely. Note that compounds C and D are not a good fit for the enzyme’s active site and would not trigger a reaction.
Enzyme
The enzyme forms a complex with A and B.
Enzyme
The enzyme is unchanged, but A and B have formed a new compound, AB.
An analogy may help to clarify the role of enzymes. Enzymes are comparable to the clergy and judges who make and dissolve marriages. When a minister marries two people, they become a couple, with a new bond between them. They are joined together – but the minister remains unchanged. The minister represents enzymes that synthesise large compounds from smaller ones. One minister can perform thousands of marriage ceremonies, just as one enzyme can perform billions of synthetic reactions. Similarly, a judge who lets married couples separate may decree many divorces before retiring. The judge represents enzymes that hydrolyse larger compounds to smaller ones; for example, the digestive enzymes. The point is that, like the minister and the judge, enzymes themselves are not altered by the reactions they facilitate. They are catalysts, permitting reactions to occur more quickly and efficiently than if substances depended on chance encounters alone.
Hormones
The body’s many hormones are messenger molecules, and some hormones are proteins. Various endocrine glands in the body release hormones in response to changes that challenge the body. The blood carries the hormones from these glands to their target tissues, where they elicit the appropriate responses to restore and maintain normal conditions. The hormone insulin provides a familiar example. When blood glucose rises, the pancreas releases its insulin. Insulin stimulates the transport proteins of the muscles and adipose tissue to pump glucose into the cells faster than it can leak out. (After acting on the message, the cells destroy the insulin.) Then, as blood glucose falls, the pancreas slows its release of insulin. Many other proteins act as hormones, regulating a variety of actions in the body (see Table 6.2 for examples).
Recall from Chapter 5 that some hormones, such as oestrogen and testosterone, derive from cholesterol.
Regulators of fluid balance
Proteins help to maintain the body’s fluid balance. Figure 12.1 (see page 407) illustrates a cell and its associated fluids. As the figure explains, the body’s fluids are contained inside the cells (intracellular) or outside the cells (extracellular). Extracellular fluids, in turn, can be found either in the spaces between the cells (interstitial) or within the blood vessels (intravascular). The fluid within the intravascular spaces is called plasma (essentially blood without its red blood cells). Fluids can flow freely between these compartments, but being large, proteins cannot. Proteins are trapped primarily within the cells and to a lesser extent in the plasma.
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TABLE 6.2 Examples of hormones and their actions HORMONES
ACTIONS
Oxytocin and prolactin
Support lactation (see Chapter 15)
Insulin and glucagon
Regulate blood glucose (see Chapter 4)
Thyroxine
Regulate the body’s metabolic rate (see Chapter 8)
Calcitonin and parathyroid hormone
Regulate blood calcium (see Chapter 12)
Antidiuretic hormone
Regulate fluid and electrolyte balance (see Chapter 12)
NOTE: Hormones are chemical messengers that are secreted by endocrine glands in response to altered conditions in the body. Each travels to one or more specific target tissues or organs, where it elicits a specific response. For descriptions of many hormones important in nutrition, see Appendix A.
The exchange of materials between the blood and the cells takes place across the capillary walls, which allow the passage of fluids and a variety of materials – but usually not plasma proteins. Still, some plasma proteins leak out of the capillaries into the interstitial fluid between the cells. These proteins cannot be reabsorbed back into the plasma; they normally re-enter circulation via the lymph system. If plasma proteins enter the interstitial spaces faster than they can be cleared, fluid accumulates (because plasma proteins attract water) and causes swelling. Swelling due to an excess of interstitial fluid is known as oedema. The proteinrelated causes of oedema include: • excessive protein losses caused by kidney disease or large wounds (such as extensive burns) • inadequate protein synthesis caused by liver disease • inadequate dietary intake of protein. Whatever the cause of oedema, the result is the same – a diminished capacity to deliver nutrients and oxygen to the cells and to remove wastes from them. As a consequence, cells fail to function adequately.
Acid–base regulators
Compounds that help keep a solution’s acidity or alkalinity constant are called buffers.
Proteins also help to maintain the balance between acids and bases within the body fluids. Normal body processes continually produce acids and bases, which the blood carries to the kidneys and lungs for excretion. The challenge is to do this without upsetting the blood’s acid– base balance. In an acid solution, hydrogen ions (H1) abound; the more hydrogen ions, the more concentrated the acid. Proteins, which have negative charges on their surfaces, attract hydrogen ions, which have positive charges. By accepting and releasing hydrogen ions, proteins maintain the acid–base balance of the blood and body fluids. The blood’s acid–base balance is tightly controlled. The extremes of acidosis and alkalosis lead to coma and death, largely because they denature working proteins. Disturbing a protein’s shape renders it useless. To give just one example, denatured haemoglobin loses its capacity to carry oxygen.
Transporters Some proteins move about in the body fluids, carrying nutrients and other molecules. The protein haemoglobin carries oxygen from the lungs to the cells. The lipoproteins transport lipids around the body. Special transport proteins carry vitamins and minerals. The transport of the mineral iron provides an especially good illustration of these proteins’ specificity and precision. When iron enters an intestinal cell after a meal has been digested and absorbed, it is captured by a protein. Before leaving the intestinal cell, iron is attached to
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another protein that carries it through the bloodstream to the cells. Once iron enters a cell, it is attached to a storage protein that will hold the iron until it is needed. When it is needed, iron is incorporated into proteins in the red blood cells and muscles that assist in oxygen transport and use. (Chapter 13 provides more details on how these protein carriers transport and store iron.) Some transport proteins reside in cell membranes and act as ‘pumps’, picking up compounds on one side of the membrane and releasing them on the other as needed. Each transport protein is specific for a certain compound or group of related compounds. Figure 6.10 illustrates how a membrane-bound transport protein helps to maintain the sodium and potassium concentrations in the fluids inside and outside cells. The balance of these two minerals is critical to nerve transmissions and muscle contractions; imbalances can cause irregular heartbeats, muscular weakness, kidney failure and even death.
FIGURE 6.10 An example of protein transport This transport protein resides within a cell membrane and acts as a two-door passageway. Molecules enter on one side of the membrane and exit on the other, but the protein doesn’t leave the membrane. This example shows how the transport protein moves sodium and potassium in opposite directions across the membrane to maintain a high concentration of potassium and a low concentration of sodium within the cell. This active transport system requires energy. Key: Sodium Potassium Cell membrane
Inside cell
Outside cell
Transport protein
The transport protein picks up sodium from inside the cell.
The protein changes shape and releases sodium outside the cell.
The transport protein picks up potassium from outside the cell.
The protein changes shape and releases potassium inside the cell.
Antibodies Proteins also defend the body against disease. A virus – whether it is one that causes flu, smallpox, measles or the common cold – enters the cells and multiplies there. One virus may produce 100 replicas of itself within an hour or so. Each replica can then burst out and invade 100 different cells, soon yielding 10 000 virus particles, which invade 10 000 cells. Left free to do their worst, they will soon overwhelm the body with disease. Fortunately, when the body detects these invading antigens, it manufactures antibodies, giant protein molecules designed specifically to combat them. The antibodies work so swiftly and efficiently that in a normal, healthy individual, most diseases never have a chance to get started. Without sufficient protein, though, the body cannot maintain its army of antibodies to resist infectious diseases. Each antibody is designed to destroy a specific antigen. Once the body has manufactured antibodies against a particular antigen (such as the measles virus), it ‘remembers’ how to make them. Consequently, the next time the body encounters that same antigen, it produces antibodies even more quickly. In other words, the body develops a molecular memory, known as immunity. (Chapter 16 describes food allergies – the immune system’s response to food antigens.)
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Source of energy and glucose
Reminder: Protein provides 17 kJ/g. Return to the ‘How to’ box on page 9 for a refresher on how to calculate the protein kilojoules from foods.
Without energy, cells die; without glucose, the brain and nervous system falter. Even though proteins are needed to do the work that only they can perform, they will be sacrificed to provide energy and glucose during times of starvation or insufficient carbohydrate intake. The body will break down its tissue proteins to make amino acids available for energy or glucose production. In this way, protein can maintain blood glucose levels, but at the expense of losing lean body tissue. Chapter 7 provides many more details on energy metabolism.
Reminder: The making of glucose from noncarbohydrate sources such as amino acids is gluconeogenesis.
Other roles As mentioned earlier, proteins form integral parts of most body structures such as skin, muscles and bones. They also participate in some of the body’s most amazing activities, such as blood clotting and vision. When a tissue is injured, a rapid chain of events leads to the production of fibrin, a stringy, insoluble mass of protein fibres that forms a solid clot from liquid blood. Later, more slowly, the protein collagen forms a scar to replace the clot and permanently heal the wound. The light-sensitive pigments in the cells of the eye’s retina are molecules of the protein opsin. Opsin responds to light by changing its shape, thus initiating the nerve impulses that convey the sense of sight to the brain.
PUTTING COMMON SENSE TO THE TEST
Proteins have many roles in the body, including that of energy provision through glucose production.
A preview of protein metabolism This section previews protein metabolism; Chapter 7 provides a full description. Cells have several metabolic options, depending on their protein and energy needs.
TRUE REVIEW IT
Cells synthesise proteins according to the genetic information provided by the DNA in the nucleus of each cell. This information dictates the order in which amino acids must be linked together to form a given protein. Sequencing errors occasionally occur, sometimes with significant consequences. The protein functions discussed here are summarised in the table below. They are only a few of the many roles proteins play but they convey some sense of the immense variety of proteins and their importance in the body. Growth and maintenance
Proteins form integral parts of most body structures such as skin, tendons, membranes, muscles, organs and bones. As such, they support the growth and repair of body tissues.
Enzymes
Proteins facilitate chemical reactions.
Hormones
Proteins regulate body processes. (Some, but not all, hormones are proteins.)
Fluid balance
Proteins help to maintain the volume and composition of body fluids.
Acid–base balance
Proteins help maintain the acid–base balance of body fluids by acting as buffers.
Transportation
Proteins transport substances, such as lipids, vitamins, minerals and oxygen, around the body.
Antibodies
Proteins inactivate foreign invaders, thus protecting the body against diseases.
Energy and glucose
Proteins provide some fuel, and glucose if needed, for the body’s energy needs.
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Chapter 6: Protein: amino acids
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Protein turnover and the amino acid pool
Nitrogen balance
Monkey Business Images/Shutterstock.com
Within each cell, proteins are continually being made and broken down, a process known as protein turnover. When proteins break down, they free amino acids. These amino acids mix with amino acids from dietary protein to form an ‘amino acid pool’ within the cells and circulating blood. The rate of protein degradation and the amount of protein intake may vary, but the pattern of amino acids within the pool remains fairly constant. Regardless of their source, any of these amino acids can be used to make body proteins or other nitrogen-containing compounds, or they can be stripped of their nitrogen and used for energy (either immediately or stored as fat for later use). Growing children end each day with more bone, blood, muscle and skin cells than they had at the beginning of the day.
Protein turnover and nitrogen balance go hand in hand. In healthy adults, protein synthesis balances with degradation, and protein intake from food balances with nitrogen excretion in the urine, faeces and sweat. When nitrogen intake equals nitrogen output, the person is in nitrogen equilibrium, or zero nitrogen balance. Researchers use nitrogen balance studies to estimate protein requirements. If the body synthesises more than it degrades and adds protein, nitrogen status becomes positive. Nitrogen status is positive in growing infants, children, adolescents, pregnant women and people recovering from protein deficiency or illness; their nitrogen intake exceeds their nitrogen output. They are retaining protein in new tissues as they add blood, bone, skin and muscle cells to their bodies. If the body degrades more than it synthesises and loses protein, nitrogen status becomes negative. Nitrogen status is negative in people who are starving or suffering other severe stresses such as burns, injuries, infections and fever; their nitrogen output exceeds their nitrogen intake. During these times, the body loses nitrogen as it breaks down muscle and other body proteins for energy.
Using amino acids to make proteins or non-essential amino acids As mentioned, cells can assemble amino acids into the proteins they need to do their work. If a particular non-essential amino acid is not readily available, cells can make it from another amino acid. If an essential amino acid is missing, the body may break down some of its own proteins to obtain it.
Amino acids (or proteins) that derive from within the body are endogenous. In contrast, those that derive from foods are exogenous. • endo 5 within • gen 5 arising • exo 5 outside (the body) Nitrogen balance: • nitrogen equilibrium (zero nitrogen balance): N in 5 N out • positive nitrogen: N in . N out • negative nitrogen: N in , N out
Using amino acids to make other compounds Cells can also use amino acids to make other compounds. For example, the amino acid tyrosine is used to make the neurotransmitters noradrenaline and adrenaline, which relay nervous system messages throughout the body. Tyrosine can also be made into the pigment melanin, which is responsible for brown hair, eye and skin colour, or into the hormone thyroxine, which helps to regulate the metabolic rate. For another example, the amino acid tryptophan serves as a precursor for the vitamin niacin and for serotonin, a neurotransmitter important in sleep regulation, appetite control and sensory perception.
Using amino acids for energy and glucose As mentioned earlier, when glucose or fatty acids are limited, cells are forced to use amino acids for energy and glucose. The body does not make a specialised storage form of protein as it does for carbohydrate and fat. Glucose is stored as glycogen in the liver and fat as triglycerides in adipose tissue, but protein in the body is available only from the working and structural components of the tissues. When the need arises, the body breaks down its tissue
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proteins and uses their amino acids for energy or glucose. Thus, over time, energy deprivation (starvation) always causes wasting of lean body tissue as well as fat loss. An adequate supply of carbohydrates and fats spares amino acids from being used for energy and allows them to perform their unique roles.
Using amino acids to make glycogen and fat The body does not have a specialised storage site for protein as it does for carbohydrate and fat. Recall that glucose is stored as glycogen in the liver and fat as triglycerides in adipose tissue, but protein is not stored as such. When energy intake exceeds demand, excess protein is converted to glucose (via gluconeogenesis) or ketone bodies, which are stored in the body as glycogen and fat, respectively.2
FIGURE 6.11 Deamination and synthesis of a non-essential amino acid
H C
When amino acids are broken down (as occurs when they are used for energy), they are first deaminated – stripped of their nitrogen-containing amino groups. Two products result from deamination: one is ammonia (NH3); the other is the carbon structure without its amino group – often, a keto acid. Keto acids may enter a number of metabolic pathways; for example, they may be used for energy or for the production of glucose, ketones, cholesterol or fat.* They may also be used to make non-essential amino acids.
Side group
Side group NH2
C
COOH
O
COOH NH3
Amino acid
Keto acid
The deamination of an amino acid produces ammonia (NH3) and a keto acid. Side group C
Using amino acids to make proteins and non-essential amino acids
Side group O
H C
COOH Keto acid
NH2
COOH NH3
Deaminating amino acids
Amino acid
Given a source of NH3, the body can make non-essential amino acids from keto acids.
As mentioned, cells can assemble amino acids into the proteins they need to do their work. If an essential amino acid is missing, the body may break down some of its own proteins to obtain it. If a particular non-essential amino acid is not readily available, cells can make it from a keto acid – if a nitrogen source is available. Ammonia provides some of the nitrogen needed for the synthesis of non-essential amino acids from keto acids (see Figure 6.11). Cells can also make a non-essential amino acid by transferring an amino group from one amino acid to its corresponding keto acid, as shown in Figure 6.12. Through many such transamination reactions, involving many different keto acids, the liver cells can synthesise the non-essential amino acids.
Converting ammonia to urea Ammonia is a toxic compound chemically identical to the strong-smelling ammonia in bottled cleaning solutions. Because ammonia is a base, the blood’s critical acid–base balance becomes upset if the cells produce larger quantities than the liver can handle.
FIGURE 6.12 Transamination and synthesis of a non-essential amino acid Side group C
Side group
O
H C
COOH Keto acid A
NH2
COOH
+
Amino acid B
Side group H C
Side group C
NH2
COOH Amino acid A
O
COOH
+
Keto acid B
The body can transfer amino groups (NH2) from an amino acid to a keto acid, forming a new non-essential amino acid and a new keto acid. Transamination reactions require the vitamin B6 coenzyme. * Chemists sometimes classify amino acids according to the destinations of their carbon fragments after deamination. If the fragment leads to the production of glucose, the amino acid is called glucogenic; if it leads to the formation of ketone bodies, fats and sterols, the amino acid is called ketogenic. There is no sharp distinction between glucogenic and ketogenic amino acids, however. A few are both, most are considered glucogenic, only one (leucine) is clearly ketogenic.
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Chapter 6: Protein: amino acids
FIGURE 6.13 Urea synthesis
FIGURE 6.14 Urea excretion
When amino acids are deaminated, ammonia is produced. The liver detoxifies ammonia before releasing it into the bloodstream by combining it with another waste product, carbon dioxide, to produce urea. See Appendix C for details. O
H H
C
+
N H
H
O
Ammonia
Bloodstream H
H
N
O
H
C
N
Amino acids
N H
Ammonia
Carbon dioxide
H
The liver and kidneys both play a role in disposing of excess nitrogen. Can you see why the person with liver disease has high blood ammonia, whereas the person with kidney disease has high blood urea? (Figure 12.2 on page 409 provides details of how the kidneys work.)
H
+
193
O H Water
Ammonia (NH3) + CO2 Liver
H
Urea Urea
To prevent such a crisis, the liver combines ammonia with carbon dioxide to make urea, a much less toxic compound. Figure 6.13 provides a greatly oversimplified diagram of urea synthesis; details are shown in Appendix C. The production of urea increases as dietary protein increases, until production hits its maximum rate at intakes approaching 250 grams per day.
Urea Bloodstream
Kidney
Urea
Excreting urea Liver cells release urea into the blood, where it circulates until it passes through the kidneys (see Figure 6.14). The kidneys then filter urea out of the blood for excretion in the urine. Normally, the liver efficiently captures all the ammonia, makes urea from it and releases the urea into the blood; then the kidneys clear all the urea from the blood. This division of labour allows easy diagnosis of diseases of both organs. In liver disease, blood ammonia will be high; in kidney disease, blood urea will be high. Urea is the body’s principal vehicle for excreting unused nitrogen, and the amount of urea produced increases with protein intake. To keep urea in solution, the body needs water. For this reason, a person who regularly consumes a highprotein diet (for example, 100 grams a day or more) must drink plenty of water to dilute and excrete urea from the body. Without extra water, a person on a high-protein diet risks dehydration because the body uses its water to rid itself of urea. This explains some of the water loss that accompanies high-protein diets. Such losses may make high-protein diets appear to be effective, but water loss, of course, is of no value to the person who wants to lose body fat (as Highlight 8 explains).
REVIEW IT
Proteins are constantly being synthesised and broken down as needed. The body’s assimilation of amino acids into proteins and its release of amino acids via protein degradation and excretion can be tracked by measuring nitrogen balance, which should be positive during growth and steady in adulthood. An energy deficit or an inadequate protein intake may force the body to use amino acids as fuel, creating a negative nitrogen balance. Protein eaten in excess of need is degraded and stored as body fat.
To bladder and out of body
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6.4 Protein in foods
In Australia and New Zealand, where nutritious foods are abundant, most people eat protein in such large quantities that they receive all the amino acids they need. In countries where food is scarce and people eat only marginal amounts of protein-rich foods, however, the quality of the protein becomes crucial.
Protein quality The protein quality of the diet determines, in large part, how well children grow and how well adults maintain their health. Put simply, high-quality proteins provide enough of all the essential amino acids needed to support the body’s work, and low-quality proteins don’t. Two factors influence protein quality – the protein’s digestibility and its amino acid composition.
Digestibility
As explained earlier, proteins must be digested before they can provide amino acids. Protein digestibility depends on such factors as the protein’s source and the other foods eaten with it. The digestibility of most animal proteins is high (90 to 99 per cent); plant proteins are less digestible (70 to 90 per cent for most, but over 90 per cent for soy and legumes).
Amino acid composition To make proteins, a cell must have all the needed amino acids available simultaneously. The liver can produce any non-essential amino acid that may be in short supply so that the cells can continue linking amino acids into protein strands. If an essential amino acid is missing, though, a cell must dismantle its own proteins to obtain it. Therefore, to prevent protein breakdown, dietary protein must supply at least the nine essential amino acids plus enough nitrogen-containing amino groups and energy for the synthesis of the others. If the diet supplies too little of any essential amino acid, protein synthesis will be limited. The body makes whole proteins only; if one amino acid is missing, the others cannot form a ‘partial’ protein. An essential amino acid supplied in less than the amount needed to support protein synthesis is called a limiting amino acid.
Reference protein In the past, egg protein was commonly used as the reference protein. Table D.1 in Appendix D presents the amino acid profile of egg. As the reference protein, egg was assigned the value of 100; Table D.3 includes several other food proteins for comparison.
The quality of a food protein is determined by comparing its amino acid composition with the essential amino acid requirements of preschool-age children. Such a standard is called a reference protein. The rationale behind using the requirements of this age group is that if a protein will effectively support a young child’s growth and development, then it will meet or exceed the requirements of older children and adults.
High-quality proteins A high-quality protein contains all the essential amino acids in relatively the same amounts and proportions that human beings require; it may or may not contain all the non-essential amino acids. Proteins that are low in an essential amino acid cannot, by themselves, support protein synthesis. Generally, foods derived from animals (meat, fish, poultry, cheese, eggs, yoghurt and milk) provide high-quality proteins, although gelatin is an exception. (It lacks tryptophan and cannot support growth and health as a diet’s sole protein.) Proteins from plants (vegetables, nuts, seeds, grains and legumes) have more diverse amino acid patterns and tend to be limiting in one or more essential amino acids. Some plant proteins are notoriously low quality (for example, corn protein). A few others are high quality (for example, soy protein). Researchers have developed several methods for evaluating the quality of food proteins and identifying high-quality proteins; Appendix D provides details.
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Chapter 6: Protein: amino acids
Complementary proteins In general, plant proteins are lower quality than animal proteins, and plants also offer less protein (per weight or measure of food). For this reason, many vegetarians improve the quality of proteins in their diets by combining plantprotein foods that have different but complementary amino acid patterns. This strategy yields complementary proteins that together contain all the essential amino acids in quantities sufficient to support health. The protein quality of the combination is greater than for either food alone (see Figure 6.15). Many people have long believed that combining plant proteins at every meal is critical for protein nutrition. For most healthy vegetarians, though, it is not necessary to balance amino acids at each meal if protein intake is varied and energy intake is sufficient. Vegetarians can receive all the amino acids they need over the course of a day by eating a variety of whole grains, legumes, seeds, nuts and vegetables. Protein deficiency will develop, however, when fruits and certain vegetables make up the core of the diet, severely limiting both the quantity and quality of protein. Highlight 2 describes how to plan a nutritious vegetarian diet.
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FIGURE 6.15 Complementary proteins In general, legumes provide plenty of isoleucine (Ile) and lysine (Lys) but fall short in methionine (Met) and tryptophan (Trp). Grains have the opposite strengths and weaknesses, making them a perfect match for legumes. Ile
Lys
Met
Trp
Legumes Grains Together
PUTTING COMMON SENSE TO THE TEST
Protein regulations for food labels All food labels must state the quantity of protein in grams. The ‘% RDI per serve’ for protein is not mandatory on labels, but is increasingly being used to highlight the contribution a food product can make to overall daily protein intake.
TRUE REVIEW IT
A diet that supplies all the essential amino acids in adequate amounts ensures protein synthesis. The best guarantee of amino acid adequacy is to eat foods containing high-quality proteins or mixtures of foods containing complementary proteins that can each supply the amino acids missing in the other. In addition to its amino acid content, the quality of protein is measured by its digestibility and its ability to support growth. Such measures are of great importance in dealing with malnutrition worldwide, but in Australia and New Zealand, where protein deficiency is not common, protein quality scores of individual foods deserve little emphasis.
Foods derived from animals are considered highquality proteins.
6.5 Health effects and recommended intakes of protein
Protein is indispensable to life. Consequently, it should come as no surprise that protein deficiency can have devastating effects on people’s health. But, like the other nutrients, protein in excess can also be harmful. This section examines the health effects and recommended intakes of protein.
Protein–energy malnutrition (PEM) When people are deprived of protein, energy or both, the result is protein–energy malnutrition (PEM). Although PEM touches many adult lives, it most often strikes early in childhood. It is one of the most prevalent and devastating forms of malnutrition in the world, afflicting one of every four children worldwide. In 2013 alone, the estimated number of children that died from hunger was 3.1 million.3 Inadequate food intake leads to poor growth in children and to weight loss and wasting in adults. Children who are thin for their height may be suffering from acute PEM (recent severe food deprivation), whereas children who are short for their age have experienced chronic PEM (long-term food deprivation). Poor growth due to PEM is easy to overlook
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Rice drinks are often sold as milk alternatives, but they fail to provide adequate protein, vitamins and minerals.
because a small child may look quite normal; however, it is the most common sign of malnutrition. PEM is most prevalent in Africa, Central America, South America and East and South-East Asia. In Australia and New Zealand, homeless people and those living in substandard housing in inner cities and rural areas have been diagnosed with PEM. In addition to those living in poverty, elderly people who live alone and adults who are addicted to drugs and alcohol are frequently victims of PEM. PEM can develop in young children when parents mistakenly provide ‘health-food beverages’ that lack adequate energy or protein instead of milk, most commonly because of nutritional ignorance, perceived milk intolerance or food faddism. Adult PEM is also seen in people hospitalised with infections such as AIDS or tuberculosis; these infections deplete body proteins, demand extra energy, induce nutrient losses and alter metabolic pathways. Furthermore, poor nutrient intake during hospitalisation worsens malnutrition and impairs recovery, whereas nutrition intervention often improves the body’s response to other treatments and the chances of survival. PEM is also common in those suffering from the eating disorder anorexia nervosa (discussed in Highlight 8). Prevention emphasises frequent, nutrient-dense, energy-dense meals and, equally importantly, resolution of the underlying causes of PEM – poverty, infections and illness.
Classifying PEM PEM occurs in two forms: marasmus and kwashiorkor, which differ in their clinical features (see Table 6.3). The following paragraphs present three clinical syndromes: marasmus, kwashiorkor and the combination of the two.
TABLE 6.3 Features of marasmus and kwashiorkor in children Separating PEM into two classifications oversimplifies the condition, but at the extremes, marasmus and kwashiorkor exhibit marked differences. Marasmus-kwashiorkor mix presents symptoms common to both marasmus and kwashiorkor. In all cases, children are likely to develop diarrhoea, infections and multiple nutrient deficiencies. MARASMUS
KWASHIORKOR
Infancy (65% lower cancer risk: Pooled analysis of randomized trial and prospective cohort study, PLoS One 11 (2016): e0152441. A. L. Creo and co-authors, Nutritional rickets around the world: an update, Paediatrics and International Child Health, 2 (2017): 84–98. B. Wheeler and co-authors, Incidence and characteristics of vitamin D deficiency rickets in New Zealand children: a prospective New Zealand paediatric surveillance unit study, International Journal of Pediatric
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8
9
10
11
12
Endocrinology 2015 Suppl. 1 (2015): P57; C. F. Munns and co-authors, Incidence of vitamin D deficiency rickets among Australian children: an Australian paediatric surveillance unit study, Medical Journal of Australia 196 (2012): 465–8. Osteoporosis Australia, Osteoporosis costing all Australians – a new burden of disease analysis, 2012–2022, available at https://www. osteoporosis.org.au/burdenofdisease Osteoporosis New Zealand, Osteoporosis in New Zealand 2007–2020, available at https://www.iofbonehealth.org/sites/default/files/PDFs/ white_paper_new_zealand_2007.pdf E. Degerud and co-authors, Plasma 25-hydroxyvitamin D and mortality in patients with suspected stable angina pectoris, Journal of Clinical Endocrinology & Metabolism 103 (2018): 1161–70. Q. Jiang, Natural forms of vitamin E: Metabolism, antioxidant, and anti-inflammatory activities and their role in disease prevention and therapy, Free Radical Biology and Medicine 72 (2014): 76–90. M. Rana and co-authors, Fat-soluble vitamin deficiency in children and adolescents with cystic fibrosis, Journal of Clinical Pathology 67 (2014): 605–8. M. Juanola-Falgarona and coauthors, Dietary intake of vitamin K is inversely associated with mortality risk, Journal of Nutrition 144 (2014): 743–50.
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Chapter 11: The fat-soluble vitamins: A, D, E and K
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4
5
6
I. D. Cameron and co-authors, Interventions for preventing falls in older people in nursing care facilities and hospitals, Cochrane Database of Systematic Reviews (2012): CD005465.pub3 T. L. Lenz, Vitamin D supplementation and cancer prevention, American Journal of Lifestyle Medicine 3 (2009): 365–8. B. Schöttker and co-authors, Strong associations of 25-hydroxyvitamin D concentrations with all-cause, cardio-vascular, cancer, and respiratory disease mortality in a large cohort study, American Journal of Clinical Nutrition 97 (2013): 782–793; A. C. Mamede and coauthors, The role of vitamins in cancer: a review, Nutrition and Cancer 63 (2011). G. Bjelakovic and co-authors, Vitamin D supplementation for prevention of cancer in adults Cochrane Database of Systematic Reviews 23 (2014): CD007469. J. F. Aloia and co-authors, A randomized controlled trial of vitamin D3 supplementation in African American women, Archives of Internal Medicine 165 (2005): 1618–23. D. A. Jolliffe, C. J. Griffiths and A. R. Martineau, Vitamin D in the prevention of acute respiratory infection: systematic review of clinical studies, Journal of Steroid Biochemistry and Molecular Biology 136 (2013): 321–9.
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8 9
10
11
12
M. Urashima and co-authors, Randomized trial of vitamin D supplementation to prevent seasonal influenza A in school children, American Journal of Clinical Nutrition 91 (2010): 1255–60. J. C. Temmerman, Vitamin D and cardiovascular disease, Journal of the American College of Nutrition 30 (2011): 167–70. B. Schöttker and co-authors, Strong associations of 25-hydroxyvitamin D concentrations with all-cause, cardiovascular, cancer, and respiratory disease mortality in a large cohort study, American Journal of Clinical Nutrition 97 (2013): 782–793; I. R. Reid and M. J. Bolland, Role of vitamin D deficiency in cardiovascular disease, Heart 98 (2012): 609–14. J. Y. Zong and co-authors, Vitamin D intake and risk of type 1 diabetes: a meta-analysis of observational studies, Nutrients 5 (2013): 3551–62. C. S. Zipitis and A. K. Akobeng, Vitamin D supplementation in early childhood and risk of type 1 diabetes: a systematic review and metaanalysis, Archives of Diseases in Childhood 93 (2008): 512–17. R. M. Greer and co-authors, Serum vitamin D levels are lower in Australian children and adolescents with type 1 diabetes than in children without diabetes. Pediatric Diabetes 14 (2013): 31–41.
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12
WATER AND THE MAJOR MINERALS Nutrition in your life
What’s your beverage of choice? If you said water, then congratulate yourself for recognising its importance in maintaining your body’s fluid balance. If you answered milk, then pat yourself on the back for taking good care of your bones. Faced with a lack of water, you would realise within days how vital it is to your very survival. The consequences of a lack of calcium-rich foods are also dramatic, but may not become apparent for decades. Water, calcium and all the other major minerals support fluid balance and bone health. Before getting too comfortable reading this chapter, you might want to get yourself a glass of water or milk. Your body will thank you. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F You need eight glasses of water a day to stay hydrated. T F Most of the salt we eat is added to food in its production, not at the table. T F Most of the body’s calcium is found in the bones. T F The calcium in milk is poorly absorbed. T F The phosphorus content of soft drinks is what makes them bad for the bones.
LEARNING OBJECTIVES 12.1 Explain how the body regulates fluid balance. 12.2 List some of the ways minerals differ from vitamins and other nutrients. 12.3 Identify the main roles, deficiency symptoms and food sources for sodium. 12.4 Identify the main roles, deficiency symptoms and food sources for chloride. 12.5 Identify the main roles, deficiency symptoms and food sources for potassium.
12.6 Identify the main roles, deficiency symptoms and food sources for calcium. 12.7 Identify the main roles, deficiency symptoms and food sources for phosphorus. 12.8 Identify the main roles, deficiency symptoms and food sources for magnesium. 12.9 Identify the main roles, deficiency symptoms and food sources for sulphate. 12.10 Describe factors that contribute to the development of osteoporosis and strategies to prevent it.
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Chapter 12: Water and the major minerals
Water is an essential nutrient, more important to life than any of the others. The body needs more water each day than any other nutrient. Furthermore, you can survive only a few days without water, whereas a deficiency of the other nutrients may take weeks, months or even years to develop. This chapter begins with a look at water and the body’s fluids. The body maintains an appropriate balance and distribution of fluids with the help of another class of nutrients – the minerals. In addition to introducing the minerals that help regulate body fluids, this chapter describes many of the other important functions minerals perform in the body. Chapter 19 revisits water as a beverage and addresses consumer concerns about its safety.
12.1 Water and the body fluids
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Water balance: intake 5 output The fluids in the body are: • intracellular (inside cells) • extracellular (outside cells) • interstitial (between cells) • intravascular (inside blood vessels).
Water constitutes about 60 per cent of an adult’s body weight and a higher percentage of a child’s (see Figure 1.1 on page 5). Because water makes up about three-quarters of the weight of lean tissue and less than one-quarter of the weight of fat, a person’s body composition The major influences how much of the body’s weight is water. The proportion of water is generally minerals are: • sodium smaller in females, obese people and the elderly because of their smaller proportion of • chloride lean tissue. • potassium In the body, water is the fluid in which all life processes occur. The water in the body fluids: • calcium • carries nutrients and waste products throughout the body • phosphorus • maintains the structure of large molecules such as proteins and glycogen • magnesium • participates in metabolic reactions • sulphur. • serves as the solvent for minerals, vitamins, amino acids, glucose and many other small molecules so that they can participate in metabolic activities FIGURE 12.1 One cell and its • acts as a lubricant and cushion around joints and inside the eyes, the spinal associated fluids cord and, in pregnancy, the amniotic sac surrounding the foetus in the Fluids are found within the cells womb (intracellular) or outside the cells • aids in the regulation of normal body temperature (as Chapter 14 explains, (extracellular). Extracellular fluids include evaporation of sweat from the skin removes excess heat from the body) plasma (the fluid portion of blood in the • maintains blood volume. intravascular spaces of blood vessels) and To support these and other vital functions, the body actively maintains an interstitial fluids (the tissue fluid that fills the intercellular spaces between the cells). appropriate water balance.
Distribution and movement of body fluids Every cell contains fluid of the exact composition that is best for that cell. Fluid inside cells is called intracellular fluid, whereas fluid outside of the cell is called extracellular fluid. The extracellular fluid that surrounds each cell is called interstitial fluid, whereas the extracellular fluid in the blood vessels is called intravascular fluid. Figure 12.1 illustrates a cell and its associated fluids. The compositions of intercellular and extracellular fluids differ from one another. They continuously lose and replace their components, yet the composition in each compartment remains remarkably constant under normal conditions. Maintaining a balance of about two-thirds of the body fluids inside the cells and one-third outside is vital to the life of the cells. If too much water were to enter the cells, they might rupture; if too much water were to leave, they would collapse. To control the movement of water, the cells direct the movement of the major minerals.
Electrolytes
When a mineral salt such as sodium chloride (NaCl) dissolves in water, it separates (dissociates) into ions – positively and negatively charged
Extracellular fluid between the cells (intercellular or interstitial)
Cell membrane
Nucleus
Intracellular fluid within the cell
Extracellular fluid (plasma) within the blood vessels (intravascular) Blood vessel
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particles (Na1 and Cl2). The positive ions are cations; the negative ones are anions. (To remember the difference between cations and anions, think of the ‘t’ in cations as a ‘plus’ sign and the ‘n’ in anions as ‘negative’.) Unlike pure water, which conducts electricity poorly, ions dissolved in water carry electrical current. For this reason, salts that dissociate into ions are called electrolytes, and fluids that contain them are electrolyte solutions. In all electrolyte solutions, anion and cation concentrations are balanced (the number of negative and positive charges are equal). If a fluid contains 1000 negative charges, it must contain 1000 positive charges, too. If an anion enters the fluid, a cation must accompany it or another anion must leave so that electrical neutrality will be maintained. Thus, whenever sodium (Na1) ions leave a cell, potassium (K1) ions enter, for example. In fact, it is usual that whenever Na1 and K1 ions are moving, they are going in opposite directions. Table 12.1 shows that the positive and negative charges inside and outside cells are indeed perfectly balanced even though the numbers of each kind of ion differ over a wide range. Inside the cells, the positive charges total 202 milliequivalents (mEq) and the negative charges balance these. Outside the cells, the amounts and proportions of the ions differ from those inside, but, again, the positive and negative charges balance.
TABLE 12.1 Important body electrolytes ELECTROLYTES
INTRACELLULAR (INSIDE CELLS) CONCENTRATION (mEq/L)
EXTRACELLULAR (OUTSIDE CELLS) CONCENTRATION (mEq/L)
Sodium (Na1)
10
142
Potassium (K1)
150
5
2
5
40
3
202
155
Chloride (Cl2)
2
103
Bicarbonate (HCO32)
10
27
Phosphate (HPO422)
103
2
Sulphate (SO422)
20
1
Organic acids (lactate, pyruvate)
10
6
Proteins
57
16
202
155
Cations (positively charged ions)
Calcium (Ca11) Magnesium (Mg ) 11
Total Anions (negatively charged ions)
Total
NOTE: The numbers of positive and negative charges in a given fluid are the same. For example, in extracellular fluid, the cations and anions both equal 155 milliequivalents per litre (mEq/L). Of the cations, sodium ions make up 142 mEq/L; and potassium, calcium and magnesium ions make up the remainder. Of the anions, chloride ions number 103 mEq/L, bicarbonate ions number 27, and the rest are provided by phosphate ions, sulphate ions, organic acids and protein.
A neutral molecule, such as water, that has opposite charges spatially separated within the molecule is polar. See Appendix B for more details.
Electrolytes attract water Whenever electrolytes move across the membrane, water follows because electrolytes attract water. Each water molecule has a net charge of zero, but the oxygen side of the molecule has a slight negative charge, and the hydrogens have a slight positive charge. Figure 12.2 shows
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Chapter 12: Water and the major minerals
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FIGURE 12.2 Water dissolves salts and follows electrolytes The structural arrangement of the two hydrogen atoms and one oxygen atom enables water to dissolve salts. Water’s role as a solvent is one of its most valuable characteristics.
Cl–
+ H
+
Na+
–
The negatively charged electrons that bond the hydrogens to the oxygen spend most of their time near the oxygen atom. As a result, the oxygen is slightly negative, and the hydrogens are slightly positive (see Appendix B).
© Cengage
Cl–
In an electrolyte solution, water molecules are attracted to both anions and cations. Notice that the negative oxygen atoms of the water molecules are drawn to the sodium cation (Na+), whereas the positive hydrogen atoms of the water molecules are drawn to the chloride ions (Cl–).
The word ending -ate denotes a salt of the mineral. Thus, phosphate is the salt form of the mineral phosphorus, and sulphate is the salt form of sulphur.
the result in an electrolyte solution: both positive and negative ions attract clusters of water molecules around them. This attraction dissolves salts in water and enables the body to move fluids into appropriate compartments.
Solutes attract water The concentration of a solution reflects the amount of a solute relative to its fluid volume. Consider saltwater, for example. One cup of water with one teaspoon salt dissolved in it has the same concentration as one-half cup water with one-half teaspoon salt dissolved in it; the proportions of salt to water are the same in the two solutions and they would taste the same with respect to their saltiness. Adding more water would dilute the solution, making it less concentrated; it wouldn’t taste as salty. Figure 12.3 shows, some electrolytes reside primarily outside the cells (notably, sodium and chloride), whereas others reside predominantly inside the cells (notably, potassium, magnesium, phosphate and sulphate). Cell membranes are selectively permeable, meaning that they allow the passage of some molecules, but not others. Whenever electrolytes move across the membrane, water follows. The movement of water across a membrane towards the more concentrated solutes is called osmosis. The amount of pressure needed to prevent the movement of water across a membrane is called the osmotic pressure. Figure 12.4 presents osmosis, and the photos of salted eggplant and rehydrated raisins provide familiar examples.
FIGURE 12.3 A cell and its electrolytes All of these electrolytes are found both inside and outside the cells, but each can be found mostly on one side or the other of the cell membrane.
Outside the cells
Chemical symbols: Ca = calcium Cl = chloride K = potassium Mg = magnesium Na = sodium P = phosphorus S = sulphate
Cell membrane
Ca K Mg S
P Within the cell
Na Cl
Key: Cations Blood vessel
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Anions
© Cengage
–
H O
Na+
Understanding nutrition
Reminder: Antidiuretic hormone (ADH) is a hormone secreted by the posterior pituitary gland in response to dehydration (or a high sodium concentration in the blood). It stimulates the kidneys to reabsorb more water and therefore to excrete less. Recall from Highlight 7 that alcohol depresses ADH activity, thus promoting fluid losses and dehydration. In addition to its antidiuretic effect, ADH elevates blood pressure and so is also called vasopressin. • vaso 5 vessel • press 5 pressure
FIGURE 12.4 Osmosis Water flows in the direction of the more highly concentrated solution. A
B
A
B
A
B
© Cengage
410
1 With equal numbers of solute particles on both sides of the semipermeable membrane, the concentrations are equal, and the tendency of water to move in either direction is about the same.
2 Now additional solute is added to side B. Solute cannot flow across the divider (in the case of a cell, its membrane).
3 Water can flow both ways across the divider, but has a greater tendency to move from side A to side B, where there is a greater concentration of solute. The volume of water becomes greater on side B, and the concentrations on side A and B become equal.
Proteins attract water Chapter 6 describes how proteins attract water and help to regulate fluid movement. In addition, transport proteins in the cell membranes regulate the passage of positive ions and other substances from one side of the membrane to the other. Negative ions follow positive ions, and water flows towards the more concentrated solution. A protein that regulates the flow of fluids and ions in and out of cells is the sodium–potassium pump. The pump actively exchanges sodium for potassium across the cell membrane, using ATP as an energy source. Figure 6.10 on page 189 illustrates this action.
© Craig M. Moore
Regulation of fluid balance
When immersed in water, raisins become plump because water moves towards the higher concentration of sugar inside the raisins.
Fluids maintain the blood volume, which in turn influences blood pressure. The kidneys are central to the regulation of blood volume and blood pressure. All day, every day, the kidneys reabsorb needed substances and water and excrete wastes with some water in the urine (see Figure 12.5). The kidneys meticulously adjust the volume and the concentration of the urine to accommodate changes in the body, including variations in the day’s food and beverage intakes. Instructions on whether to retain or release substances or water come from antidiuretic hormone (ADH), renin, angiotensin and aldosterone.
© Craig M. Moore
Antidiuretic hormone
When sprinkled with salt, eggplant and other vegetables ‘sweat’ because water moves towards the higher concentration of salt outside the vegetable.
Whenever blood volume or blood pressure falls too low, or whenever the extracellular fluid becomes too concentrated, the hypothalamus signals the pituitary gland to release ADH. ADH is a water-conserving hormone that stimulates the kidneys to reabsorb water. Consequently, the more water you need, the less your kidneys excrete. These events also trigger thirst. Drinking water and retaining fluids raise the blood volume and dilute the concentrated fluids, thus helping to restore homeostasis.
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Chapter 12: Water and the major minerals
FIGURE 12.5 A nephron, one of the kidney’s many functioning units A nephron (a working unit of the kidney). Each kidney contains more than 1 million nephrons. Blood vessel
Glomerulus 1
Kidney Ureter
1 Blood flows into the glomerulus, and some of its fluid, with dissolved substances, is absorbed into the tubule.
Capillaries of glomerulus
Tubule
Pelvis Bladder
To the body
2
2 The fluid and substances needed by the body are returned to the blood in vessels alongside the tubule.
Renal artery Renal vein
3
3 The tubule passes waste materials on to the bladder.
Kidney, sectioned to show location of nephrons
The cleansing of blood in the nephron is roughly analogous to the way you might clean your car. First 1 you remove all your possessions and trash so that the car can be vacuumed. Then 2 you put back in the car what you want to keep and 3 throw away the trash.
Renin
Cells in the kidneys respond to low blood pressure by releasing an enzyme called renin. Through a complex series of events, renin triggers the release of aldosterone, which causes the kidneys to reabsorb sodium. Sodium reabsorption, in turn, is always accompanied by water retention, which helps to restore blood volume and blood pressure.
Angiotensin In addition to its role in sodium retention, renin hydrolyses a protein from the liver called angiotensinogen to angiotensin I. Angiotensin I is inactive until another enzyme converts it to its active form – angiotensin II. Angiotensin II is a powerful vasoconstrictor that narrows the diameter of blood vessels, thereby raising the blood pressure.
Aldosterone In addition to acting as a vasoconstrictor, angiotensin II stimulates the release of the hormone aldosterone from the adrenal glands. Aldosterone signals the kidneys to retain more sodium, and therefore water, because when sodium moves, fluids follow. Again, the effect is that when more water is needed, less is excreted. All of these actions are presented in Figure 12.6 and help to explain why high-sodium diets aggravate conditions such as hypertension or oedema. Too much sodium causes water retention and an accompanying rise in blood pressure or swelling in the interstitial spaces. Chapter 18 discusses hypertension in detail.
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© Cengage
To the bladder
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FIGURE 12.6 How the body regulates blood volume The kidneys respond to reduced blood flow by releasing the enzyme renin.
The hypothalamus responds to a high-salt concentration in the blood by releasing ADH from the pituitary gland.
Renin
Renin converts angiotensinogen from the liver to angiotensin I.
Angiotensin I
The lungs, kidneys and brain activate angiotensin I to angiotensin II.
Angiotensin II
Angiotensin II causes the blood vessels to constrict, raising blood pressure. Angiotensin II stimulates release of aldosterone from the adrenal glands and ADH from the pituitary gland. Aldosterone ADH
Aldosterone signals the kidneys to excrete potassium, which causes the blood vessels to constrict.
ADH signals the kidneys to retain water, which increases blood volume.
Aldosterone signals the kidneys to retain sodium, which increases blood volume.
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In response to low blood volume, low blood pressure or highly concentrated body fluids, these actions combine to effectively restore homeostasis: • ADH retains water. • Renin retains sodium. • Angiotensin constricts blood vessels. • Aldosterone retains sodium. These actions can maintain water balance only if a person drinks enough water.
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Chapter 12: Water and the major minerals
413
Normally, the body defends itself successfully against fluid and electrolyte imbalances. With minor imbalances, people can replace the fluids and minerals lost in sweat or in a temporary bout of diarrhoea, for example, by drinking plain cool water and eating regular foods. Certain situations and some medications, however, may overwhelm the body’s ability to compensate. Severe, prolonged vomiting and diarrhoea as well as heavy sweating, burns, and traumatic wounds may incur such great fluid and electrolyte losses as to precipitate a medical emergency. Appropriate medical intervention depends on the circumstances surrounding the loss of fluids and their solutes. If fluid is lost by vomiting or diarrhoea, sodium is lost indiscriminately. If the adrenal glands oversecrete aldosterone, as may occur when a tumour develops, the kidneys may excrete too much potassium. A person with uncontrolled diabetes may lose glucose (a solute not normally excreted) and large amounts of fluid with it. Each situation results in dehydration, but drinking water alone will not restore balance; medical intervention is required to do this. Physically active people must remember to replace their body fluids. Situations that involve more severe fluid losses demand rapid replacement of fluids and electrolytes – for example, when diarrhoea Healthcare workers threatens the life of a malnourished child. Caregivers around the world use oral rehydration have learned to use simple formulae to treat mild-to-moderate cases of diarrhoea. These therapy (ORT) − a life-saving formulae do not require hospitalisation and can be prepared from ingredients simple solution of available locally. Caregivers need only learn to measure ingredients carefully and use sugar, salt and water sanitary water. Once rehydrated, a person can begin eating foods. (Chapter 14 presents a taken by mouth − to discussion of sport drinks.) treat dehydration
Acid–base balance The body uses its ions not only to help maintain fluid and electrolyte balance but also to regulate the acidity (pH) of its fluids . The pH scale (also discussed in Chapter 3) is shown in Figure 12.7, with the normal and abnormal pH ranges of the blood added. As you can see, the body must maintain the pH within a narrow range to avoid life-threatening consequences. Slight deviations in either direction can denature proteins, causing metabolic mayhem. Enzymes couldn’t catalyse reactions and haemoglobin couldn’t carry oxygen – to name just two examples. The acidity of the body’s fluids is determined by the concentration of hydrogen ions (H1). A high concentration of hydrogen ions is very acidic. Normal energy metabolism generates hydrogen ions, as well as many other acids, that must be neutralised. Three systems defend the body against fluctuations in pH – buffers in the blood, respiration in the lungs and excretion in the kidneys.
caused by diarrhoea. A simple ORT recipe (cool before giving) is: • 0.5 L boiling water • a small handful of sugar (4 tsp) • 3 pinches of salt (½ tsp).
Reminder: pH is the unit of measure expressing a substance’s acidity or alkalinity. The lower the pH, the higher the H1 ion concentration and the stronger the acid. A pH above 7 is alkaline, or base (a solution in which OH2 ions predominate).
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Fluid and electrolyte imbalance
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FIGURE 12.7 The pH Scale pH of common substances
Basic
14
Concentrated lye
Normal and abnormal pH ranges of blood 8.00
Death
13 12 11
Alkalosis
Household ammonia
10
pH-neutral
9
Baking soda
8
6
Pancreatic juice Blood Water Milk Urine
5
Coffee
4
Orange juice
3
Vinegar
2
Lemon juice Gastric juice
7
7.45 Normal 7.35
Acidosis
6.8
Death
1
Acidic
0
Battery acid
NOTE: Each step is 10 times as concentrated in base (one-tenth as much acid, or H1) as the one below it.
Reminder: Bicarbonate is an alkaline compound with the formula HCO32. It is produced in all cell fluids from the dissociation of carbonic acid to help maintain the body’s acid−base balance. (Bicarbonate is also secreted from the pancreas during digestion as part of the pancreatic juice.)
Regulation by the buffers
Bicarbonate (a base) and carbonic acid (an acid) in the body fluids (as well as some proteins) protect the body against changes in acidity by acting as buffers – substances that can neutralise acids or bases. Figure 12.8 presents the chemical reactions of this buffer system, which is primarily under the control of the lungs and kidneys. Carbon dioxide, which is formed all the time during energy metabolism, dissolves in water to form carbonic acid in the blood. Carbonic acid, in turn, dissociates to form hydrogen ions and bicarbonate ions. The appropriate balance between carbonic acid and bicarbonate is essential to maintaining optimal blood pH.
Regulation in the lungs The lungs control the concentration of carbonic acid by raising or slowing the respiration rate, depending on whether the pH needs to be increased or decreased. If too much carbonic acid builds up, the respiration rate speeds up; this hyperventilation increases the amount of carbon dioxide exhaled, thereby lowering the carbonic acid concentration and restoring homeostasis. Conversely, if bicarbonate builds up, the respiration rate slows; carbon dioxide is retained and forms more carbonic acid. Again, homeostasis is restored.
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FIGURE 12.8 Bicarbonate–carbonic acid buffer system The reversible reactions of the bicarbonate–carbonic acid buffer system help to regulate the body’s pH and maintain homeostasis. Recall from Chapter 7 that carbon dioxide and water are formed during energy metabolism. Carbon dioxide (CO2) is a volatile gas that quickly dissolves in water (H2O), forming carbonic acid (H2CO3), which lowers the body's pH: CO2
+
H2O
H2CO3
carbon dioxide
+
water
carbonic acid
Carbonic acid readily dissociates to a hydrogen ion (H+) and a bicarbonate ion (HCO3–), which raises the body's pH: H2CO3
H+
+
HCO3–
carbonic acid
hydrogen ion
+
bicarbonate ion
Excretion in the kidneys The kidneys control the concentration of bicarbonate by either reabsorbing or excreting it, depending on whether the pH needs to be increased or decreased, respectively. Their work is complex, but the net effect is easy to sum up. The body’s total acid burden remains nearly constant; the acidity of the urine fluctuates to accommodate that balance.
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Electrolytes (charged minerals) in the fluids help distribute the fluids inside and outside the cells, thus ensuring the appropriate water balance and acid–base balance to support all life processes. Excessive losses of fluids and electrolytes upset these balances, and the kidneys play a key role in restoring homeostasis.
Water balance and recommended intakes Because imbalances can be devastating, the body actively maintains an appropriate water balance between intake and output. Consequently, the entire system of cells and their fluids remains in a delicate, but controlled, state of homeostasis.
Water losses At the very least, the body must excrete a minimum of about 500 millilitres (about 2 cups) of water each day as urine – enough to carry away the waste products generated by a day’s metabolic activities. Above this amount, excretion adjusts to balance intake. If a person drinks more water, the kidneys excrete more urine and the urine becomes more diluted. In addition to urine, water is lost from the lungs as vapour and from the skin as sweat; some is also lost in faeces.* The amount of fluid lost from each source varies, depending on the environment (such as heat or humidity) and physical conditions (such as exercise or fever). On average, daily losses total about 2.2 litres. Table 12.2 shows how water excretion balances intake; maintaining this balance requires healthy kidneys and an adequate intake of fluids.
The amount of water the body has to excrete each day to dispose of its wastes is the obligatory water excretion − about 500 mL.
* Water lost from the lungs and skin accounts for almost half of the daily losses even when a person is not visibly perspiring; these losses are commonly referred to as insensible water losses.
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TABLE 12.2 Water balance WATER SOURCES
AMOUNT (mL)
WATER LOSSES
AMOUNT (mL)
Liquids
550 to 1500
Kidneys (urine)
500 to 1400
Foods
700 to 1000
Skin (sweat)
450 to 900
Metabolic water
200 to 300
Lungs (breath)
350
GI tract (faeces)
150
Total 1450 to 2800
Total 1450 to 2800
Water intake
Thirst and satiety influence water intake, apparently in response to changes sensed by the mouth, hypothalamus and nerves. When water intake is inadequate, the blood becomes concentrated (having lost water but not the dissolved substances within it), the mouth becomes dry and the hypothalamus initiates drinking behaviour. When water intake is excessive, the stomach expands and stretch receptors send signals to stop drinking. Similar signals are sent from receptors in the heart as blood volume increases. Thirst drives a person to seek water, but it lags behind the body’s need. When too much water is lost from the body and not replaced, dehydration develops. A first sign of dehydration is thirst, the signal that the body has already lost some of its fluid. If a person is unable to obtain fluid or, as in many FIGURE 12.9 The colour of urine in relation elderly people, fails to perceive the thirst message, the symptoms of to hydration dehydration may progress rapidly from thirst to weakness, exhaustion The colour of urine gives a hint to a person’s and delirium – and end in death if not corrected (see Table 12.3). hydration status, but cannot be used for diagnosis. Dehydration may easily develop with either water deprivation or In addition to dehydration, the colour of urine may excessive water losses. Figure 12.9 illustrates how the colour of urine indicate the presence of food dyes; blood; bladder, may indicate possible dehydration. (Chapter 14 revisits dehydration liver or kidney disease; and medications. and the fluid needs of athletes.) Reminder: The hypothalamus is a brain centre that controls activities such as maintenance of water balance, regulation of body temperature and control of appetite.
Transparent Possible over hydration
TABLE 12.3 Signs and symptoms of dehydration BODY WEIGHT LOST (%)
SYMPTOMS
1–2
Thirst, fatigue, weakness, vague discomfort, loss of appetite
Transparent yellow Normal
3–4
Dark yellow Normal, possible mild dehydration
Impaired physical performance, dry mouth, reduction in urine, flushed skin, impatience, apathy
5–6
Difficulty concentrating, headache, irritability, sleepiness, impaired temperature regulation, increased respiratory rate
7–10
Dizziness, spastic muscles, loss of balance, delirium, exhaustion, collapse
Pale straw Normal, well-hydrated
Deep amber or honey Normal, possible moderate dehydration Orange Possible severe dehydration
NOTE: The onset and severity of signs and symptoms at various percentages of body weight lost depend on the activity, fitness level, degree of acclimatisation, temperature and humidity. If not corrected, dehydration can lead to death.
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Water intoxication, on the other hand, is rare but can occur with excessive water ingestion and kidney disorders that reduce urine production. The symptoms may include confusion, convulsions and even death, in extreme cases. Excessive water ingestion (more than 4 litres) within a few hours in a well-hydrated person can contribute to the dangerous condition known as hyponatraemia, sometimes seen in endurance athletes. For this reason, guidelines suggest limiting fluid intake during times of heavy sweating to 1 to 1.5 litres per hour. (Chapter 14 revisits hyponatraemia.)
Water sources The obvious dietary sources of water are water itself and other beverages, but nearly all foods also contain water. Most fruits and vegetables contain up to Water is the most indispensable nutrient. 90 per cent water, and many meats and cheeses contain at least 50 per cent. (See Table 12.4 for the percentage of water in selected foods.) Also, water is generated during metabolism. Recall from Chapter 7 that when the energyyielding nutrients break down, their carbons and hydrogens combine with oxygen to yield carbon dioxide (CO2) and water (H2O). As Table 12.2 shows, the water derived daily from these three sources averages about 2.2 litres.
TABLE 12.4 Percentage of water in selected foods 100%
Water
90–99%
Milk, strawberries, watermelon, lettuce, cabbage, celery, spinach, broccoli
80–89%
Fruit juice, yoghurt, apples, grapes, oranges, carrots
70–79%
Prawns, bananas, corn, potatoes, avocados, cottage cheese, ricotta cheese
60–69%
Pasta, legumes, salmon, ice-cream, chicken breast
50–59%
Minced beef, hot dogs, feta cheese
40–49%
Pizza
30–39%
Cheddar cheese, bagels, bread
20–29%
Salami, cake, biscuits
10–19%
Butter, margarine, raisins
1–9% 0%
Biscuits, cereals, pretzels, taco shells, peanut butter, nuts Oils, sugar
Water recommendations Because water needs vary depending on diet, activity, environmental temperature and humidity, a general water requirement is difficult to establish. Recommendations are sometimes expressed in proportion to the amount of energy expended under average environmental conditions. The recommended water intake for a person who expends 8400 kilojoules a day, for example, is 2 to 3 litres. This recommendation is in line with the AI for total water as specified in the Nutrient Reference Values (NRVs). Total water includes not only drinking water but water in other beverages, such as milk, and in foods as well. In general, drinking water and other beverages contribute about 70 to 80 per cent to water intake, and foods contribute the remainder.
Water recommendation: • 0.24 mL/kJ expended (adults) • 0.36 mL/kJ expended (infants and athletes). AI for total water: • men: 3.4 L/day • women: 2.8 L/day.
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PUTTING COMMON SENSE TO THE TEST
You need eight glass of water a day to stay hydrated. FALSE
Because a wide range of water intakes will prevent dehydration and its harmful consequences, the AI is based on average intakes. People who are physically active or who live in hot environments may need more. Which beverages are best? Any beverage can readily meet the body’s fluid needs, but those with few or no kilojoules do so without contributing to weight gain. Given that obesity is a major health problem and that beverages, especially soft drink, are significant contributors to total energy intake in Australia, most people would do well to select water as their preferred beverage. Other choices include tea, coffee, reduced-fat milk and diet soft drinks. Because caffeine acts as a diuretic, people who drink caffeinated beverages may lose slightly more fluid than when drinking water, but the losses are relatively insignificant.1 There is little evidence, though, to support the view that caffeinated beverages contribute to chronic dehydration. Any diuretic effect of caffeine from a beverage is usually more than offset by the fluid in the beverage itself. As a rule of thumb, 1 milligram of caffeine can produce water losses of around 1.1 millilitres of water. A cup of instant coffee will contain around 80 milligrams of caffeine in approximately 250 millilitres of water, resulting in an overall net positive fluid balance. In other words, it doesn’t seem to matter whether people rely on caffeine-containing beverages or other beverages to meet some of their fluid needs. As Highlight 7 explains, alcohol acts as a diuretic, and it has many adverse effects on health and nutrition status. Alcohol should not be used to meet fluid needs.
APPLICATIONS OF NUTRITIONAL RESEARCH Do we really need ‘eight glasses of water’ each day? We have all heard the popular advice that we should drink at least eight glasses of water a day, so it may be a surprise that this is more myth than fact. Of course our bodies need water– without it, we would die from dehydration. But the amount needed is extremely variable and depends on a person’s body size, physical activity levels, climate and what types of food they are eating. It is believed that the ‘eight glasses’ myth was a US Recommended Dietary Allowance dating back to 1945. The guide said a suitable allowance of water for adults was 2.5 litres a day, but most of this water could be found in prepared foods. If that last, crucial, part is ignored, the statement could be interpreted as a clear instruction to drink eight glasses of water a day. Drinks such as soft drink, fruit juice, milk, and tea and coffee, and foods such as fruit, yoghurt, soups and stews all have appreciable amounts of water that contribute to fluid intake. Australian dietary recommendations also bust the eight-glass myth, as the official Nutrient Reference Values state ‘there is no single level of water intake that would ensure adequate hydration and optimal health for the apparently healthy people in the population’. So how do you know if you are drinking enough water? Well, you can check this for yourself every few hours. If your urine is lightly coloured or clear, you’re drinking enough. If it’s dark, then you should drink more.
Health effects of water Water supports good health. Physical and mental performances depend on it, as does the optimal functioning of the GI tract, kidneys, heart and other body systems. The kind of water a person drinks may also make a difference to health. Water is usually either ‘hard’ or ‘soft’. Hard water has high concentrations of calcium and magnesium; sodium or potassium is the principal mineral of soft water. In practical terms, soft water makes more bubbles with less soap; hard water leaves a ring on the bath, a crust of rock-like crystals in the kettle and a grey residue in the laundry. Soft water may seem more desirable around the house, and some home-owners purchase water softeners that replace magnesium and calcium with sodium. In the body, however, soft
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Chapter 12: Water and the major minerals
water with sodium may aggravate hypertension and heart disease. In contrast, the minerals in hard water may benefit these conditions. Many people select bottled water, believing it to be safer than tap water and therefore worth its substantial cost. Chapter 19 offers a discussion of bottled water safety and regulations.
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Water makes up about 60 per cent of an adult body’s weight. It assists with the transport of nutrients and waste products throughout the body, participates in chemical reactions, acts as a solvent, serves as a shock absorber and regulates body temperature. To maintain water balance, intake from liquids, foods and metabolism must equal losses from the kidneys, skin, lungs and GI tract. The amount and type of water a person drinks may have positive or negative health effects.
12.2 The minerals – an overview
Figure 12.10 shows the amounts of the major minerals found in the body and, for comparison, some of the trace minerals. The distinction between the major and the trace minerals does not mean that one group is more important than the other – all minerals are vital. The major minerals are so named because they are present, and needed, in larger amounts in the body. They are shown at the top of the figure and are discussed in this chapter. The trace minerals (shown at the bottom of the figure) are discussed in Chapter 13. A few generalisations pertain to all of the minerals and distinguish them from the vitamins. Especially notable is their chemical nature.
FIGURE 12.10 Minerals in a 60-kilogram human body Not only are the major minerals present in the body in larger amounts than the trace minerals, they are also needed by the body in larger amounts. Recommended intakes for the major minerals are stated in hundreds of milligrams or grams, whereas those for the trace minerals are listed in tens of milligrams or even micrograms. 1150
Calcium Phosphorus
600 210
Potassium 150
Sulphur Sodium
90
Chloride
90
Magnesium
MAJOR MINERALS The major minerals are those present in amounts larger than 5 g (a teaspoon).
30
Iron
2.4
Zinc
2.0
Copper
0.09
Manganese Iodine
0.02
Selenium
0.02
TRACE MINERALS There are more than a dozen trace minerals, although only six are shown here.
0.02 0
100
200
300
400
500
600
700
800
900 1000 1100 1200
Amount (g)
Inorganic elements Unlike the organic vitamins, which are easily destroyed, minerals are inorganic elements that always retain their chemical identity. Once minerals enter the body proper, they remain there until excreted; they cannot be changed into anything else. Iron, for example, may temporarily combine with other charged elements in salts, but it is always iron. Neither can minerals be
Reminder: An inorganic substance does not contain carbon.
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destroyed by heat, air, acid or mixing. Consequently, little care is needed to preserve minerals during food preparation. In fact, the ash that remains when a food is burned contains all the minerals that were in the food originally. Minerals can be lost from food only when they leach into cooking water that is then poured down the sink.
The body’s handling of minerals The minerals also differ from the vitamins in the amounts the body can absorb and in the extent to which they must be specially handled. Some minerals, such as potassium, are easily absorbed into the blood, transported freely and readily excreted by the kidneys, much like the water-soluble vitamins. Other minerals, such as calcium, are more like fat-soluble vitamins in that they must have carriers to be absorbed and transported. And, like some of the fat-soluble vitamins, minerals taken in excess can be toxic.
Variable bioavailability
The bioavailability of minerals varies. Some foods contain binders that combine chemically with minerals, preventing their absorption and carrying them out of the body with other wastes. Examples of binders include phytates, which are found primarily in legumes and grains, and oxalates, which are present in rhubarb and spinach, among other foods. These foods contain more minerals than the body actually receives for use.
Reminder: Bioavailability refers to the rate at and the extent to which a nutrient is absorbed and used.
Nutrient interactions Chapter 10 describes how the presence or absence of one vitamin can affect another’s absorption, metabolism and excretion. The same is true of the minerals. The interactions between sodium and calcium, for example, cause both to be excreted when sodium intakes are high. Phosphorus binds with magnesium in the GI tract, so magnesium absorption is limited when phosphorus intakes are high. These are just two examples of the interactions involving minerals featured in this chapter. Discussions in both this chapter and the next point out additional problems that arise from such interactions. Notice how often they reflect an excess of one mineral creating an inadequacy of another and how supplements – not foods – are most often to blame.
Varied roles Although all the major minerals help to maintain the body’s fluid balance as described earlier, sodium, chloride and potassium are most noted for that role. For this reason, these three minerals are discussed first here. Later sections describe the minerals most noted for their roles in bone growth and health – calcium, phosphorus and magnesium.
The key fluid balance nutrients are: • sodium • potassium • chloride. REVIEW IT
The major minerals are found in larger quantities in the body, whereas the trace minerals occur in smaller amounts. Minerals are inorganic elements that retain their chemical identities. They usually receive special handling and regulation in the body, and they may bind with other substances or interact with other minerals, thus limiting their absorption.
12.3 Sodium
People have held salt (sodium chloride) in high regard throughout recorded history. We describe someone we admire as ‘salt of the earth’ and someone we consider worthless as ‘not worth their salt’. Even the word ‘salary’ comes from the Latin word for salt, from the times when Roman soldiers were paid in salt for their service.
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Cultures vary in their use of salt, but most people find its taste innately appealing. Salt brings its own tangy taste and enhances other flavours, most likely by suppressing the bitter flavours. You can taste this effect for yourself: tonic water with its bitter quinine tastes sweeter with a little salt added.
Sodium roles in the body Sodium is the principal cation of the extracellular fluid and the primary regulator of its volume. Sodium also helps maintain acid–base balance and is essential to nerve impulse transmission and muscle contraction. One of the ways the kidneys regulate acid–base balance is by excreting hydrogen ions (H1) in exchange for sodium ions (Na1). Sodium is readily absorbed by the intestinal tract and travels freely in the blood until it reaches the kidneys, which filter all the sodium out of the blood. Then, with great precision, the kidneys return to the bloodstream the exact amount of sodium the body needs. Normally, the amount excreted is approximately equal to the amount ingested on a given day. When blood sodium rises, as when a person eats salted foods, thirst signals the person to drink until the appropriate sodium-to-water ratio is restored. Then the kidneys excrete both the excess water and the excess sodium together.
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Sodium and hypertension
For years, a high sodium intake was considered the primary factor responsible for high blood pressure. Then research pointed to salt (sodium chloride) as the dietary culprit. Salt has a greater effect on blood pressure than either sodium or chloride alone or in combination with other ions. For some individuals, blood pressure increases in response to excesses in salt intake. People most likely to have a salt sensitivity include those whose parents had high blood pressure, those with chronic kidney disease or diabetes and people over 50 years of age. Overweight people also appear to be particularly sensitive to the effect of salt on blood pressure. For them, a high salt intake correlates strongly with heart disease, and salt restriction helps to lower their blood pressure. In fact, a salt-restricted diet also lowers blood pressure in people without hypertension. Because reducing salt intake causes no harm and diminishes the risk of hypertension and heart disease, the Australian Dietary Guidelines advise choosing foods low in salt and to not add salt to foods in cooking or at the table. A daily salt intake of about 1 teaspoon is the equivalent of almost 2.3 grams, or 2300 milligrams of sodium, which is at the Upper Level of Intake (UL). Higher intakes seem to be well tolerated in most healthy people, however. The ‘How to’ box on page 422 offers strategies for cutting salt (and therefore sodium) intake.
Limit intake of foods and drinks containing added salt. Read labels to choose lower-sodium options among similar foods. Do not add salt to foods in cooking or at the table. Salt (sodium chloride) is about 40% sodium. • 1 g salt contributes 400 mg sodium • 5 g salt 5 1 tsp • 1 tsp salt contributes 2000 mg sodium
APPLICATIONS OF NUTRITIONAL RESEARCH A diet to lower blood pressure A diet plan known as the DASH (Dietary Approaches to Stop Hypertension) diet has been shown to lower blood pressure. The DASH approach emphasises fruits, vegetables and lowfat milk products; it includes whole grains, nuts, poultry and fish; and it calls for reduced intakes of red meat, butter and other high-fat foods. The DASH diet in combination with a reduced sodium intake is even more effective in lowering blood pressure than either strategy alone. The DASH diet has been modified to provide an appropriate diet for Australians – OZDASH.2 Chapter 18 offers a complete discussion of hypertension and the dietary recommendations for its prevention and treatment.
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Sodium and bone loss (osteoporosis)
ALEXSTAND/Shutterstock.com
A high salt intake is also associated with increased calcium excretion, but its influence on bone loss is less clear. In addition, potassium may prevent the increase in calcium excretion caused by a high-salt diet.3 For these reasons, dietary advice to prevent bone loss parallels those suggested for hypertension – a DASH-type diet such as OZDASH that is low in sodium and abundant in potassium-rich fruits and vegetables and calcium-rich low-fat milk products.
Sodium recommendations and sources Diets rarely lack sodium, and even when intakes are low, the body adapts by reducing sodium losses in urine and sweat, thus making deficiencies unlikely. Sodium recommendations are set low enough to protect against high blood pressure, but high enough to allow an adequate intake of other nutrients with a typical diet. Because high sodium intakes correlate with high blood pressure, the UL for adults was previously set at 2300 milligrams per day. This value was revised in 2017 to ‘not determined’ because a review failed to determine an identifiable point at which the relationship between higher sodium intakes and higher blood pressure did not occur. Recent estimates by Food Standards Australia New Zealand (FSANZ) show that one-third of Australians consume sodium at levels above the UL.4 In general, processed foods have the most sodium, whereas unprocessed foods such as fresh fruits, vegetables, milk and meats have the least. In fact, as much as 75 per cent of the sodium in people’s diets comes from salt added to foods by manufacturers; about 15 per cent comes from salt added during cooking and at the table, and only 10 per cent comes from the natural content in foods. Bread, processed meats, breakfast cereals, cheese and commercially produced condiments and sauces are some of the largest contributors to salt intakes for Australians and New Zealanders. Because processed foods may contain sodium without chloride, as in additives such as sodium bicarbonate, they do not always taste salty. The form of the food can also affect our perception of salty taste as the food matrix can suppress or augment sensations of saltiness. Most people are surprised to learn that a serving of cornflakes contains almost double the sodium of a similar serve of salted peanuts. (The peanuts taste saltier because the salt is all on the surface, where the tongue’s sensors immediately pick it up.) The total sodium content of packaged foods (including naturally occurring sodium, sodium from additives and added salt) must also be declared on the Nutrition Information Panel on the food label.
Fresh herbs add flavour to a recipe without adding salt.
AI for sodium: • 460−920 mg/day (adults).
PUTTING COMMON SENSE TO THE TEST
Most of the salt we eat is added to food in its production, not at the table. TRUE
HOW TO:
CUT SALT (AND SODIUM) INTAKE
Most people eat more salt (and therefore sodium) than they need. Some people can lower their blood pressure by avoiding highly salted foods and removing the salt shaker from the table. Foods eaten without salt may seem less tasty at first, but with repetition, people can learn to enjoy the natural flavours of many unsalted foods. Strategies to cut salt intake include the following: ›› Select fresh, unprocessed foods. ›› Cook with little or no added salt. ›› Prepare foods with sodium-free spices such as basil, bay leaves, curry, garlic, ginger, mint, oregano, pepper, rosemary and thyme; lemon juice; vinegar; or wine. ›› Add little or no salt at the table. Taste foods before adding salt.
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›› Read labels with an eye open for sodium. (See Table 2.7 on page 56 for terms used to describe the sodium contents of foods on labels.) ›› Select low-salt or salt-free products when available. Foods to use sparingly include: ›› foods prepared in brine, such as pickles and olives ›› salty or smoked meats, such as salami, corned beef, bacon, hot dogs, ham, luncheon meats, salted pork and sausages ›› salty or smoked fish, such as anchovies, caviar, salted and dried cod, herring, sardines and smoked salmon ›› snack items such as potato chips, pretzels, salted popcorn, salted nuts and biscuits ›› condiments such as stock cubes, seasoned salts, MSG and soy, teriyaki, Worcestershire and barbecue sauces ›› cheeses, especially processed types ›› canned and instant soups. Figure 12.11 shows that processed foods not only contain more sodium than their less processed counterparts but also have less potassium. Low potassium may be as significant as high sodium when it comes to blood pressure regulation, so processed foods have two strikes against them.
FIGURE 12.11 What processing does to the sodium and potassium content of foods People who eat foods high in salt often happen to be eating fewer potassium-containing foods at the same time. Notice how potassium is lost and sodium is gained as foods become more processed, causing the potassium-to-sodium ratio to fall dramatically. Even when potassium isn’t lost, the addition of sodium still lowers the potassium-to-sodium ratio. Limiting sodium intake may help in two ways, then – by lowering blood pressure in salt-sensitive individuals and by indirectly raising potassium intakes. Milks
Meats
Vegetables
Fruits
Grains
Milk (whole)
Roast beef
Fresh corn
Fresh peaches
Rolled oats
Instant chocolate pudding
Chipped beef
Canned cream corn
Peach pie
Oat cereal
Unprocessed
Key: Potassium Sodium
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Matthew Farruggio; Shutterstock
Processed
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Sodium deficiency and toxicity The consequences of sodium deficiency and toxicity are very different. For the average person, though, too much sodium in the diet presents the biggest health problem.
Sodium deficiency Sodium deficiency does not develop from an inadequate diet. The body only needs a small amount, and typical diets provide more than enough. If blood sodium drops, as may occur with vomiting, diarrhoea or heavy sweating, both sodium and water must be replenished. Under normal conditions of sweating due to physical activity, salt losses can easily be replaced later in the day with ordinary foods. Salt tablets are not recommended because too much salt, especially if taken with too little water, can induce dehydration. During intense activities, such as ultra-endurance events, athletes can lose so much sodium and drink so much water that they develop hyponatraemia – the dangerous condition of having too little sodium in the blood. Chapter 14 offers details about hyponatraemia and guidelines for ultra-endurance athletes.
Sodium toxicity and excessive intakes The immediate symptoms of acute sodium toxicity are oedema and hypertension, but such toxicity poses no problem as long as water needs are met. Prolonged excessive sodium intake may contribute to hypertension in some people, as explained earlier. In addition, a highsodium intake damages the blood vessels, kidneys, brain and heart, thus increasing the risk of death from heart disease as well as from other causes.5
REVIEW IT
Sodium is the main cation outside cells and one of the primary electrolytes responsible for maintaining fluid balance. Dietary deficiency is rare, and excesses may aggravate hypertension in some people. For this reason, health professionals advise a diet moderate in salt and sodium. The accompanying table summarises information about sodium.
Sodium ADEQUATE INTAKE (AI) Adults: 460–920 mg/day UPPER LEVEL (UL) Adults: Not determined CHIEF FUNCTIONS IN THE BODY Maintains normal fluid and electrolyte balance; assists in nerve impulse transmission and muscle contraction DEFICIENCY SYMPTOMS Muscle cramps, mental apathy, loss of appetite TOXICITY SYMPTOMS Oedema, acute hypertension SIGNIFICANT SOURCES Table salt, soy sauce; moderate amounts in meats, milks, breads and vegetables; large amounts in processed foods
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12.4 Chloride
The element chlorine (Cl2) is a poisonous gas. When chlorine reacts with sodium or hydrogen, however, it forms the negative chloride ion (Cl2). Chloride, an essential nutrient, is required in the diet.
Chloride roles in the body Chloride is the major anion of the extracellular fluids (outside the cells), where it occurs mostly in association with sodium. Chloride moves passively across membranes through channels and so also associates with potassium inside cells. Like sodium and potassium, chloride maintains fluid and electrolyte balance. In the stomach, the chloride ion is part of hydrochloric acid, which maintains the strong acidity of the gastric juice. One of the most serious consequences of vomiting is the loss of this acid from the stomach, which upsets the acid–base balance. Hydrochloric acid secretion into the stomach involves the addition of bicarbonate ions (base) to the plasma. These bicarbonate ions (HCO32) are neutralised by hydrogen ions (H1) from the gastric secretions that are reabsorbed into the plasma. When hydrochloric acid is lost during vomiting, these hydrogen ions are no longer available for reabsorption, and so, in effect, the concentration of bicarbonate ions in the plasma is increased. In this way, excessive vomiting of acidic gastric juices leads to metabolic alkalosis. Such imbalances are commonly seen in bulimia nervosa, as is described in Highlight 8.
Reminder: The loss of acid can lead to alkalosis, an abovenormal alkalinity in the blood and body fluids.
Chloride recommendations and intakes Chloride is abundant in foods (especially processed foods) as part of sodium chloride and other salts. The NRVs do not specify a recommended level of intake for chloride. Because of the amount of salt we eat in our diet, no one need ever be concerned that they are not consuming enough chloride.
Salt (sodium chloride) is about 60% chloride. • 1 g salt contributes 600 mg chloride • 5 g salt 5 1 tsp • 1 tsp salt contributes 3000 mg chloride
Chloride deficiency and toxicity Diets rarely lack chloride. Chloride losses may occur in conditions such as heavy sweating, chronic diarrhoea and vomiting. Consuming ordinary foods and beverages can restore chloride balance. The only known cause of high blood chloride concentrations is dehydration due to water deficiency. Toxicity causes vomiting. Consuming ordinary foods and beverages can restore chloride balance.
Chloride
REVIEW IT
Chloride is the major anion outside cells and it associates closely with sodium. In addition to its role in fluid balance, chloride is part of the stomach’s hydrochloric acid. The accompanying table summarises information on chloride.
ADEQUATE INTAKE (AI) None specified UPPER LEVEL (UL) None specified
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DEFICIENCY SYMPTOMS Does not occur under normal circumstances TOXICITY SYMPTOMS Vomiting CHIEF FUNCTIONS IN THE BODY Maintains normal fluid and electrolyte balance; part of hydrochloric acid found in the stomach, necessary for proper digestion SIGNIFICANT SOURCES Table salt, soy sauce; moderate amounts in meats, milks, eggs; large amounts in processed foods
12.5 Potassium
Like sodium, potassium is a positively charged ion. In contrast to sodium, potassium is the body’s principal intracellular cation, inside the body cells.
Potassium roles in the body
Polara Studios, Inc.
Potassium plays a major role in maintaining fluid and electrolyte balance and cell integrity. During nerve impulse transmission and muscle contraction, potassium and sodium briefly trade places across the cell membrane. The cell then quickly pumps them back into place. Controlling potassium distribution is a high priority for the body because this affects many aspects of homeostasis, including a steady heartbeat.
Potassium and hypertension Diets low in potassium, especially when combined with high sodium intakes, raise blood pressure and increase the risk of death from heart disease.6 In contrast, high potassium intakes reduce the risks of hypertension, heart disease, stroke, and related deaths.7 Potassiumrich fruits and vegetables also appear to reduce the risk of stroke – more so than can be explained by the reduction in blood pressure alone.
Fresh foods, especially fruits and vegetables, provide potassium in abundance.
Reminder: The DASH and OZDASH diets, used to lower blood pressure, emphasise potassiumrich foods such as fruits and vegetables.
Potassium recommendations and intakes Potassium is abundant in all living cells, both plant and animal. Because cells remain intact unless foods are processed, the richest sources of potassium are fresh foods – as Figure 12.12 shows. In contrast, most processed foods such as canned vegetables, ready-to-eat cereals and luncheon meats contain less potassium – and more sodium (recall Figure 12.11). To meet the AI for potassium, most people need to increase their intake of fruits and vegetables to five to nine servings daily.
Potassium deficiency and toxicity Potassium deficiency and toxicity have different causes, mostly unrelated to a person’s diet.
Potassium deficiency Potassium deficiency is characterised by an increase in blood pressure, salt sensitivity, kidney stones and bone turnover. As deficiency progresses, symptoms include irregular heartbeats,
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muscle weakness and glucose intolerance. Some diuretics can cause potassium loss from the body. Eating disorders, vomiting and laxative abuse, and a very low food intake can also result in potassium deficiency.
FIGURE 12.12 Potassium in selected foods See the ‘How to’ box on page 336 for more information on using this figure. Milligrams Food
Serving size (kilojoules)
Bread, whole wheat Cornflakes Spaghetti pasta Tortilla, flour
30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ) 1 25 cm-round (983 kJ) 1 ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ) 1 medium baked w/skin (559 kJ) 3 ⁄4 cup (130 kJ) 1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ)
Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg Excellent sources: Squash Soybeans Artichoke
1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ) 1 1
0
200
400
600
800
The AI for potassium is 3800 mg per day for men and 2800 mg per day for women.
POTASSIUM Fresh fruits (purple), vegetables (green), legumes (dark blue) and meats (brown) contribute potassium to the diet. Key: Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Best sources per kilojoule
⁄2 cup baked (290 kJ) ⁄2 cup cooked (626 kJ)
1 (252 kJ)
Potassium toxicity Potassium toxicity does not result from overeating foods high in potassium; therefore, a UL has not been set. Potassium toxicity can result from overconsumption of potassium salts or supplements (including some ‘energy fitness shakes’) and from certain diseases or treatments and crushing-type injuries. Given more potassium than the body needs, the kidneys accelerate their excretion. If the GI tract is bypassed, however, and potassium is injected directly into a vein, it can stop the heart.
REVIEW IT
Potassium, like sodium and chloride, is an electrolyte that plays an important role in maintaining fluid balance. Potassium is the primary cation inside cells; fresh foods, notably fruits and vegetables, are its best sources. The following table summarises facts about potassium.
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Potassium ADEQUATE INTAKE (AI) Men: 3800 mg/day Women: 2800 mg/day CHIEF FUNCTIONS IN THE BODY Maintains normal fluid and electrolyte balance; facilitates many reactions; supports cell integrity; assists in nerve impulse transmission and muscle contractions DEFICIENCY SYMPTOMSa Irregular heartbeat, muscular weakness, glucose intolerance TOXICITY SYMPTOMS Muscular weakness; vomiting; if given into a vein, can stop the heart SIGNIFICANT SOURCES All whole foods: meats, milks, fruits, vegetables, grains, legumes a
Deficiency accompanies dehydration.
12.6 Calcium
Calcium is the most abundant mineral in the body. It receives much emphasis in this chapter and in the highlight that follows because an adequate intake helps grow a healthy skeleton in early life and minimise bone loss in later life.
PUTTING COMMON SENSE TO THE TEST
Most of the body’s calcium is found in the bones TRUE
Calcium roles in the body Ninety-nine per cent of the body’s calcium is in the bones (and teeth), where it plays two roles. First, it is an integral part of bone structure, providing a rigid frame that holds the body upright and serves as attachment points for muscles, making motion possible. Second, it serves as a calcium bank, offering a readily available source of the mineral to the body fluids should a drop in blood calcium occur.
Calcium in bones
As bones begin to form, calcium salts form crystals, called hydroxyapatite, on a matrix of the protein collagen. During mineralisation, as the crystals become denser, they give strength and rigidity to the maturing bones. As a result, the long leg bones of children can support their weight by the time they have learned to walk. Many people have the idea that once a bone is built, it is inert like a rock. Actually, the bones are gaining and losing minerals continuously in an ongoing process of remodelling. Growing children gain more bone than they lose, and healthy adults maintain a reasonable balance. When withdrawals substantially exceed deposits, problems such as osteoporosis develop (as is described in Highlight 12). The formation of teeth follows a pattern similar to that of bones. The turnover of minerals in teeth is not as rapid as in bone, however; fluoride hardens and stabilises the crystals of teeth, opposing the withdrawal of minerals from them.
Calcium in body fluids Although only 1 per cent of the body’s calcium circulates in the extracellular and intracellular fluids, its presence there is vital to life. Many of its actions help to maintain normal blood pressure.
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Cells throughout the body can detect calcium in the extracellular fluids and respond accordingly. For example, when the extracellular fluid contains too little calcium, the parathyroid glands release parathyroid hormone and the kidneys reabsorb calcium – all in an effort to raise calcium levels. Extracellular calcium also participates in blood clotting. The calcium in intracellular fluids binds to proteins within the cells and activates them. These proteins participate in the regulation of muscle contractions, the transmission of nerve impulses, the secretion of hormones and the activation of some enzyme reactions.
Calcium balance Calcium homeostasis involves a system of hormones and vitamin D. Whenever blood calcium falls too low or rises too high, three organ systems respond: the intestines, the bones and the kidneys. Figure 12.13 illustrates how vitamin D and two hormones – parathyroid hormone and calcitonin – return blood calcium to normal.
An example of a protein that calcium binds with and activates is calmodulin. One of calmodulin’s roles is to activate the enzymes involved in breaking down glycogen, which releases energy for muscle contractions.
FIGURE 12.13 Calcium balance Blood calcium is regulated in part by vitamin D and two hormones: calcitonin and parathyroid hormone. Bone serves as a reservoir when blood calcium is high and as a source of calcium when blood calcium is low. Osteoclasts break down bone and release calcium into the blood; osteoblasts build new bone using calcium from the blood. Rising blood calcium signals the thyroid gland to secrete calcitonin.* 1
2
Calcitonin inhibits the activation of vitamin D.
Parathyroid (embedded in the thyroid)
Thyroid
Calcitonin Parathyroid hormone 1 Vitamin D 1 activation
Calcitonin prevents calcium reabsorption in the kidneys.
Kidneys
Calcitonin limits calcium absorption in the intestines.
Calcitonin inhibits osteoclast cells from breaking down bone, preventing the release of calcium. All these actions lower blood calcium levels, which inhibits calcitonin secretion.
2
Vitamin D and parathyroid hormone stimulate calcium reabsorption in the kidneys.
3
Vitamin D enhances calcium absorption in the intestines.
4
Vitamin D and parathyroid hormone stimulate osteoclast cells to break down bone, releasing calcium into the blood.
2
3
3 4
Parathyroid hormone stimulates the activation of vitamin D.
Vitamin D 2
3
Falling blood calcium signals the parathyroid glands to secrete parathyroid hormone. 1
Intestines 4
4
Bones
429
All these actions raise blood calcium levels, which inhibits parathyroid hormone secretion.
*Calcitonin plays a major role in defending infants and young children against the dangers of rising blood calcium that can occur when regular feedings of milk deliver large quantities of calcium to a small body. In contrast, calcitonin plays a relatively minor role in adults because their absorption of calcium is less efficient and their bodies are larger, making elevated blood calcium unlikely.
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FIGURE 12.14 Maintaining blood calcium from the diet and from the bones
© Permission by David Dempster from J. Bone Miner Res, 1986
With an adequate intake of calcium-rich food, blood calcium remains normal ...
With a dietary deficiency, blood calcium still remains normal ...
The calcium in bone provides a nearly inexhaustible bank of calcium for the blood. The blood borrows and returns calcium as needed so that even with a dietary deficiency, blood calcium remains normal – even as bone calcium diminishes (see Figure 12.14). Blood calcium changes only in response to abnormal regulatory control, not to diet. A person can have an inadequate calcium intake for years and suffer no noticeable symptoms. Only later in life does it become apparent that bone integrity has been compromised. Blood calcium above normal results in calcium rigor – the muscles contract and cannot relax. Similarly, blood calcium below normal causes calcium tetany – also characterised by uncontrolled muscle contraction. These conditions do not reflect a dietary excess or lack of calcium; they are caused by a lack of vitamin D or by abnormal secretion of the regulatory hormones. A chronic dietary deficiency of calcium, or a chronic deficiency due to poor absorption over the years, depletes the savings account in the bones. Again: the bones, not the blood, are robbed by a calcium deficiency.
Calcium absorption
... and bones deposit calcium. The result is strong, dense bones.
Factors that enhance calcium absorption are: • stomach acid • vitamin D • lactose (in infants only). Factors that inhibit calcium absorption are: • lack of stomach acid • vitamin D deficiency • high phosphorus intake • phytates (in seeds, nuts, grains) • oxalates (in beetroot, rhubarb, spinach, sweet potatoes).
Because many factors affect calcium absorption, the most effective way to ensure adequacy is to increase calcium intake. On average, adults absorb about 30 per cent of the calcium they ingest. The stomach’s acidity helps to keep calcium soluble, and vitamin D helps to make the calbindin needed for absorption. (This explains why calcium-rich milk is the best food for vitamin D fortification.) ... because bones Whenever calcium is needed, the body increases its production give up calcium to of calbindin to improve calcium absorption. The result is obvious the blood. The result in the case of a pregnant woman, who absorbs 50 per cent of the is weak, osteoporotic bones. calcium from the milk she drinks. Similarly, growing children and teens absorb 50 to 60 per cent of the calcium they consume. Then, when bone growth slows or stops, absorption falls to the adult level of about 30 per cent. In addition, absorption becomes more efficient during times of inadequate intakes. Many of the conditions that enhance calcium absorption inhibit its absorption when they are absent. For example, sufficient vitamin D supports absorption, and a deficiency impairs it. In addition, fibre in general, and the binders phytate and oxalate in particular, interfere with calcium absorption, but their effects are relatively minor in typical Australian diets. Vegetables with oxalates and whole grains with phytates are nutritious foods, of course, but they are not useful calcium sources. There are many factors that influence calcium balance.
Calcium recommendations and sources Calcium is unlike most other nutrients in that hormones maintain its blood concentration regardless of dietary intake. As Figure 12.13 shows, when calcium intake is high, the bones benefit; when intake is low, the bones suffer. Calcium recommendations are therefore based on the amount needed to retain the most calcium in bones. By retaining the most calcium possible, the bones can develop to their fullest potential in size and density – their peak bone mass – within genetic limits.
Calcium recommendations Because obtaining enough calcium during growth helps to ensure that the skeleton will be strong and dense, Nutrient Reference Values for Australia and New Zealand have been set high at 1300 milligrams daily for adolescents up to the age of 18 years. Between the ages of 19 and 50, recommendations are lowered to 1000 milligrams a day; for women over the
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age of 50 and men over the age of 70, recommendations are raised again to 1300 milligrams a day to minimise the bone loss that tends to occur later in life. Many people in Australia, particularly women, have calcium intakes far below current recommendations. High intakes of calcium from supplements may have adverse effects such as kidney stone formation. For this reason, a UL has been established (see the inside cover pages). A high-protein diet increases urinary calcium losses, but does not seem to impair bone health. In fact, protein may even improve calcium absorption and bone strength. The effects of protein on calcium loss may also be minimised by beneficial effects of other nutrients in the food and diet – for example, by the potassium in legumes and the calcium in milk.
Calcium food sources
Figure 12.15 shows that calcium is found most abundantly in a single class of foods – dairy products. The person who doesn’t like to drink milk may prefer to eat cheese or yoghurt. Alternatively, milk and milk products can be concealed in foods. Powdered fat-free milk can be added to casseroles, soups and other mixed dishes during preparation; five heaped tablespoons offer the equivalent of one glass of milk. This simple step is an excellent way for older women to obtain not only extra calcium but more protein, vitamins and minerals as well.
Suggested daily amounts of dairy products are: • young children (2 to 8 years): 2 serves • older children, teenagers and all adults: 3 serves.
FIGURE 12.15 Calcium in selected foods See the ‘How to’ box on page 336 for more information on using this figure. Milligrams Food
Serving size (kilojoules)
Bread, whole wheat Cornflakes Spaghetti pasta Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd)a Minced meat, lean Chicken breast
30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ) 1 25 cm-round (983 kJ) 1 ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ) 1 medium baked w/skin (559 kJ) 3 ⁄4 cup (130 kJ) 1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ)
Tuna, canned in water 85 g (416 kJ) Egg 1 hard boiled (328 kJ) Excellent sources: Sardines, with bonesb 85 g canned (739 kJ) 1 ⁄2 cup cooked (42 kJ) Bok choy (Chinese cabbage) Almonds 30 g (701 kJ)
0
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300
CALCIUM As in the riboflavin figure, milk and milk products (white) dominate the calcium figure. Most people need at least three selections from the milk group to meet recommendations. aValues
based on products containing added calcium salts; the calcium in 1⁄2 c soybeans is about 2⁄3 as much as in 1⁄2 c tofu. bIf bones are discarded, calcium declines dramatically.
Key: Breads and cereals Vegetables Fruits Milk and milk products
RDI for women 19–50
RDI for women 51+
RDI for men 19–70
RDI for men 71+
Legumes, nuts, seeds Meats Best sources per kilojoule
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It is especially difficult for children who don’t drink milk to meet their calcium needs. The consequences of drinking too little milk during childhood and adolescence persist into adulthood. Women who seldom drank milk as children or teenagers have lower bone density and greater risk of fractures than those who drank milk regularly. It is possible for people who do not drink milk to obtain adequate calcium, but only if they carefully select other calcium-rich foods. Many people, for a variety of reasons, cannot or do not drink milk. Some cultures do not use milk in their cuisines, some vegetarians exclude milk as well as meat and some people are People with lactose allergic to milk protein or are lactose intolerant. Others simply do not like the taste of milk. intolerance may be These people need to find non-milk sources of calcium to help meet their calcium needs or, able to consume small for those who are lactose intolerant, consider using lactose-free milk. Some brands of tofu, quantities of milk, as corn tortillas, some nuts (such as almonds) and some seeds (such as sesame seeds) can supply Chapter 4 explains. calcium for the person who doesn’t use milk products. Calcium-fortified soy milk is also an excellent substitute for cow’s milk in terms of providing an equivalent amount of calcium. A slice of most breads contains only about 5 to 10 per cent of the calcium found in milk, but it can be a major source for people who eat many slices, because the calcium is absorbed well. Among the vegetables, bok choy, kale, parsley, broccoli and watercress are good sources of PUTTING available calcium. So are some seaweeds such as the nori popular in Japanese cooking. Some COMMON SENSE TO THE TEST dark green leafy vegetables – notably spinach and silver beet – appear to be calcium-rich but actually provide little, if any, calcium to the body because the oxalate they contain can bind The calcium in milk is to divalent cations including calcium and iron. It would take 8 cups of spinach – containing poorly absorbed. six times as much calcium as 1 cup of milk – to deliver the equivalent in absorbable calcium. FALSE With the exception of foods such as spinach that contain calcium binders, the calcium content of foods is usually more important than bioavailability. Consequently, recognising that people eat a variety of foods containing calcium, the NRV Working Party FIGURE 12.16 Bioavailability of calcium did not consider calcium bioavailability when setting recommendations. from selected foods Figure 12.16 ranks selected foods according to their calcium bioavailability. Oysters are also a rich source of calcium, as are small fish eaten with their bones, such as canned sardines, tuna and salmon. Many Asian people prepare a stock from bones, which helps account for their adequate calcium intake Cauliflower, watercress, cabbage, brussels sprouts, without the use of milk. They soak the cracked bones from chicken, turkey, $50% rutabaga, kale, mustard absorbed pork or fish in vinegar and then slowly boil the bones until they become soft. greens, bok choy, broccoli, The bones release calcium into the acidic broth, and most of the vinegar boils turnip greens off. Cooks then use the stock, which contains more than 100 milligrams of 30% Milk, calcium-fortified soy calcium per tablespoon, in place of water to prepare soups, vegetables and rice. absorbed milk, calcium-set tofu, cheese, yogurt, calciumSome mineral waters provide as much as 500 milligrams of calcium per litre, fortified foods and beverages offering a convenient way to meet both calcium and water needs. Similarly, 20% Almonds, sesame seeds, calcium-fortified orange juice and other fruit and vegetable juices allow a person to absorbed pinto beans, sweet potatoes obtain both calcium and vitamins easily. Other examples of calcium-fortified foods include high-calcium milk (milk with extra calcium added) and calcium-fortified cereals and breads. The ‘How to’ box on page 433 describes a shortcut method for #5% Spinach, rhubarb, Swiss absorbed chard estimating your calcium intake. Highlight 12 discusses calcium supplements.
DASH eating plan is presented in Chapter 12.)
CURRENT RESEARCH IN NUTRITION Vegetarian eating in adolescence linked to good bone health Adolescence is an important time in laying the foundation for healthy bones that can protect a person from later osteoporosis risk. Calcium, of course, is one of the key nutrients that make up the bone matrix. Canadian researchers have recently looked at adolescent diets and later-life bone health in 125 males and females from the age of around 12 years to their later 20s.8 Bone health was assessed by measures of bone mineral content and bone mineral density.
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The research team identified five distinct patterns eaten. The first was a vegetarian-style diet that was high in dark green vegetables, eggs, whole grains, legumes, nuts and seeds, fruits and low-fat milk (including non-dairy milk). A Western-like diet was associated with higher intakes of fruit drinks, refined grains, cream, poultry and processed meats. The third type of diet was a high-fat, high-protein diet. The fourth was a mixed diet characterised by a high intake of yoghurt, cheese, desserts and sweets, fish and seafood, and fruit juice; the final type was, a snack dietary pattern high in dressings and sauces, chips and chicken and low in dark green vegetables and cheese. It was the vegetarian style that showed the clearest positive link with good bone health into adulthood and that was after allowing for confounding factors such as sex, physical activity, total energy intake and many other factors. None of the other dietary patterns appeared to be predictive of later-life bone health. Among those eating a vegetarian-style diet, adolescents eating most closely to the described pattern had the highest bone density and bone mineral content. The small sample size is an obvious limitation of this new study as too the accuracy of the diet records collected in adolescence which relied on a recall method. There are many positives to a vegetarian style eating on health. This new study supports the idea that a diverse and well-balanced mostly plant-based diet during adolescence has a beneficial impact on bone health during adolescence and this carries over into a positive consequence on bone accrual into young adulthood.
Calcium from supplements For people who cannot obtain adequate calcium from foods to meet their requirements, there is the option to consider taking calcium supplements. Most calcium supplements provide between 250 and 1000 milligrams of calcium. Calcium supplements are typically sold as compounds of calcium carbonate (common in antacids), citrate, gluconate, lactate, malate or phosphate. These supplements often include magnesium, vitamin D or both.
HOW TO:
ESTIMATE YOUR CALCIUM INTAKE
Most dietitians have developed useful shortcuts to help them estimate nutrient intakes and ‘see’ inadequacies in the diet. They can tell at a glance whether a day’s meals fall short of calcium recommendations, for example. To estimate calcium intakes, keep two bits of information in mind: ›› 1 cup of milk provides about 300 milligrams of calcium. ›› Adults need between 1000 and 1300 milligrams of calcium per day, which represents 3 to 4 cups of milk. If a person drinks 3–4 cups of milk a day, it’s easy to see that calcium needs are being met. If not, it takes some detective work to identify the other sources and estimate total calcium intake. To estimate a person’s daily calcium intake, use this shortcut, which compares the calcium in calcium-rich foods to the calcium content of milk. The calcium in 1 cup of milk is assigned 1 point, and the goal is to attain 3 to 4 points per day. Foods are given points as follows: ›› 1 cup milk, yoghurt or fortified soy milk, or 45 grams of cheese 5 1 point ›› 110 g canned fish with bones (such as sardines) 5 1 point ›› 1 cup ice-cream, cottage cheese or calcium-rich vegetable (see the text) 5 ½ point. Then, because other foods also contribute small amounts of calcium, together they are given a point. ›› A well-balanced diet containing a variety of foods 5 1 point. Now consider a day’s meals with calcium in mind. Cereal with 1 cup of milk for breakfast (1 point for milk), a chicken, salad and cheese sandwich for lunch (1 point for cheese), and
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a cup of broccoli and lasagne for dinner (½ point for calcium-rich vegetable and 1 point for cheese in lasagne) – plus 1 point for all other foods eaten that day – adds up to 4½ points. This shortcut estimate indicates that calcium recommendations have been met, and a diet analysis of these few foods reveals a calcium intake of over 1000 milligrams. By knowing the best sources of each nutrient, you can learn to scan the day’s meals and quickly see if you are meeting your daily goals. Unless the label states otherwise, supplements of calcium carbonate are 40 per cent calcium; those of calcium citrate are 21 per cent; lactate, 13 per cent; and gluconate, 9 per cent. Select a low-dose supplement and take it several times a day, rather than taking a large-dose supplement all at once. Taking supplements in doses of 500 milligrams or less improves absorption. Small doses also help ease the GI distress (constipation, intestinal bloating and excessive gas) that sometimes accompanies calcium supplement use. Supplements containing calcium carbonate require stomach acidity for optimal absorption and so are best taken with meals. People who suffer from reduced gastric acid production or are taking medications that inhibit gastric acid secretion are advised to take calcium citrate supplements rather than calcium carbonate. Calcium supplements are recommended for people over 65 years and for those with a poor dietary intake. A generalisation that has been gaining strength throughout this book is supported by the information given here about calcium. A balanced diet that supplies a variety of foods is the best plan to ensure adequacy for all essential nutrients. All food groups should be included, and none should be overemphasised. In our culture, calcium intake is usually inadequate wherever milk is lacking in the diet – whether through ignorance, poverty, simple dislike, fad dieting, lactose intolerance or allergy. By contrast, iron is usually lacking whenever milk is overemphasised, as Chapter 13 explains.
Calcium deficiency A low calcium intake during the growing years limits the bones’ ability to reach their optimal mass and density. Most people achieve a peak bone mass by their late twenties, and dense bones best protect against age-related bone loss and fractures (see Figure 12.17). All adults lose bone as they grow older, beginning between the ages of 30 and 40. When bone losses reach the point of causing fractures under common, everyday stresses, the condition is known as osteoporosis. One in two women and one in three men over 60 years of age in Australia will develop an osteoporotic fracture. Unlike many diseases that make themselves known through symptoms such as pain, shortness of breath, skin lesions, tiredness and the like, osteoporosis is silent. The body sends no signals saying bones are losing their calcium and, as a result, their integrity.
FIGURE 12.17 Phases of bone development throughout life The active growth phase occurs from birth to approximately age 20. The next phase of peak bone mass development occurs between the ages of 12 and 30. The final phase, when bone resorption exceeds formation, begins between the ages of 30 and 40 and continues through the remainder of life.
Peak bone mass Bone density
10 Active growth
20
30
40
50
60
70
Bone loss
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Blood samples offer no clues because blood calcium remains normal regardless of bone content, and measures of bone density are not routinely taken. Highlight 12 suggests strategies to protect against bone loss, of which eating calcium-rich foods is only one.
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Most of the body’s calcium is in the bones, where it provides a rigid structure and a reservoir of calcium for the blood. Blood calcium participates in muscle contraction, blood clotting and nerve impulses, and it is closely regulated by a system of hormones and vitamin D. Calcium is found predominantly in milk and milk products, but some other foods including certain vegetables and tofu also provide calcium. Even when calcium intake is inadequate, blood calcium remains normal, but at the expense of bone loss, which can lead to osteoporosis. Calcium’s roles, deficiency symptoms and food sources are summarised in the table below.
Calcium RDI Men: • 1000 mg/day (19–70 years) • 1300 mg/day (>70 years) Women: • 1000 mg/day (19–50 years) • 1300 mg/day (>50 years) UPPER LEVEL (UL) Adults: 2500 mg/day CHIEF FUNCTIONS IN THE BODY Mineralisation of bones and teeth; also involved in muscle contraction and relaxation, nerve functioning, blood clotting, blood pressure DEFICIENCY SYMPTOMS Stunted growth in children; bone loss (osteoporosis) in adults TOXICITY SYMPTOMS Constipation; increased risk of urinary stone formation and kidney dysfunction; interference with absorption of other minerals SIGNIFICANT SOURCES Dairy products, canned fish with bones, calcium-set tofu, calcium-fortified soy milk, greens (bok choy, broccoli, silverbeet, kale), legumes, almonds, sesame seeds
12.7 Phosphorus
Phosphorus is the second most abundant mineral in the body. About 85 per cent of it is found combined with calcium in the hydroxyapatite crystals of bones and teeth.
Phosphorus roles in the body Phosphorus salts (phosphates) are found not only in bones and teeth, but in all body cells as part of a major buffer system (phosphoric acid and its salts). Phosphorus is also part of DNA and RNA, and is therefore necessary for all growth. Phosphorus assists in energy metabolism. Many enzymes and the B vitamins become active only when a phosphate group is attached. ATP itself, the energy currency of the cells, uses three phosphate groups to do its work.
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Lipids containing phosphorus as part of their structures (phospholipids) help to transport other lipids in the blood. Phospholipids are also the major structural components of cell membranes, where they control the transport of nutrients into and out of the cells. Some proteins, such as the casein in milk, contain phosphorus as part of their structures (phosphoproteins).
Phosphorus recommendations and intakes PUTTING COMMON SENSE TO THE TEST
The phosphorus content of soft drinks is what makes them bad for the bones. FALSE
Because phosphorus is commonly found in almost all foods, dietary deficiencies are unlikely. As Figure 12.18 shows, foods rich in proteins are the best sources of phosphorus. In the past, researchers emphasised the importance of an ideal calcium-to-phosphorus ratio from the diet to support calcium metabolism, but there is little or no evidence to support this concept. The quantities of calcium and phosphorus in the diet are far more important than their ratio to each other. A high phosphorus intake has been blamed for bone loss when, in fact, a low calcium intake – not a phosphorus toxicity or an improper ratio – is responsible. Research shows that the displacement of milk in the diet by soft drinks, not the phosphoric acid content of the beverages, has adverse effects on bone. No adverse effects of high dietary phosphorus intakes have been reported; still, a UL has been established (see the inside cover).
FIGURE 12.18 Phosphorus in selected foods See the ‘How to’ box on page 336 for more information on using this figure. Milligrams Food
Serving size (kilojoules)
Bread, whole wheat Cornflakes Spaghetti pasta Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg Excellent sources: Liver Almonds Chocolate bar
30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ) 1 25 cm-round (983 kJ) 1 ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ) 1 medium baked w/skin (559 kJ) 3 ⁄4 cup (130 kJ) 1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ)
0
200
400
600
800
1000
RDI for adults
PHOSPHORUS Protein-rich sources, such as milk (white), meats (brown) and legumes (dark blue), provide abundant phosphorus.
Key: Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Miscellaneous Best sources per kilojoule
85 g (773 kJ) 30 g (693 kJ) 60 g (1168 kJ)
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Chapter 12: Water and the major minerals
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Refeeding syndrome Refeeding syndrome is a potentially fatal condition that results from a rapid shift in fluids and electrolytes that can occur in people who have undergone several days of starvation and are malnourished. Upon eating again, especially if the foods are high in carbohydrates, there is a rapid spike in insulin, which triggers rapid glucose and electrolyte uptake into the cells, causing a risk of electrolyte deficiencies, particularly phosphorus. Muscle pain, respiratory muscle weakness and cardiac arrhythmias from low blood phosphorus (which is needed for ATP production and cellular oxygen release) and a risk of Wernicke’s encephalopathy due to decreased thiamin stores are all potential consequences. Awareness of the risk of refeeding syndrome, combined with the slow reintroduction of food, replacement of thiamin and monitoring of blood electrolytes are the cornerstones of managing this condition.
Phosphorus
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Phosphorus accompanies calcium both in the crystals of bone and in many foods such as milk. Phosphorus is also important in energy metabolism, as part of phospholipids and as part of the genetic materials DNA and RNA. The summary table below lists functions of, and other information about, phosphorus.
RDI Adults: 1000 mg/day UPPER LEVEL (UL) Adults (19–70 years): 4000 mg/day CHIEF FUNCTIONS IN THE BODY Mineralisation of bones and teeth; part of every cell; important in genetic material, part of phospholipids, used in energy transfer and in buffer systems that maintain acid–base balance DEFICIENCY SYMPTOMS Muscular weakness, bone paina TOXICITY SYMPTOMS Calcification of non-skeletal tissues, particularly the kidneys SIGNIFICANT SOURCES All animal tissues (meat, fish, poultry, eggs, milk) Dietary deficiency rarely occurs, but some drugs can bind with phosphorus, making it unavailable and resulting in bone loss that is characterised by weakness and pain. a
12.8 Magnesium
Magnesium barely qualifies as a major mineral: only about 30 grams of magnesium is present in the body. Over half of the body’s magnesium is in the bones. Much of the rest is in the muscles and soft tissues, with only 1 per cent in the extracellular fluid. As with calcium, bone magnesium may serve as a reservoir to ensure normal blood concentrations.
Magnesium roles in the body In addition to maintaining bone health, magnesium acts in all the cells of the soft tissues, where it forms part of the protein-making machinery and is necessary for energy metabolism. It participates in hundreds of enzyme systems. A major role of magnesium is as a catalyst in the reaction that adds the last phosphate to the high-energy compound ATP, making it essential to the body’s use of glucose; the synthesis of protein, fat and nucleic acids; and the cells’ membrane transport systems. Together with calcium, magnesium is involved in muscle contraction and blood clotting: calcium promotes the processes, whereas magnesium inhibits them.
Reminder: A catalyst is a compound that facilitates chemical reactions without itself being changed in the process.
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This dynamic interaction between the two minerals helps regulate blood pressure and lung function. Like many other nutrients, magnesium supports the normal functioning of the immune system.
Magnesium intakes Average dietary magnesium estimates for Australian adults fall below recommendations. Dietary intake data, however, do not include the contribution made by water. In areas with hard water, the water contributes both calcium and magnesium to daily intakes. The mineral waters noted earlier for their calcium content may also be magnesium-rich and can be important sources of this mineral for those who drink them. The bioavailability of magnesium from mineral water is about 50 per cent, but it improves when the water is consumed with a meal. The dark blue bars in Figure 12.19 indicate that legumes, seeds and nuts make significant magnesium contributions. Magnesium is part of the chlorophyll molecule, so leafy green vegetables are also good sources.
FIGURE 12.19 Magnesium in selected foods See the ‘How to’ box on page 336 for more information on using this figure. Milligrams Food
Serving size (kilojoules)
Bread, whole wheat Cornflakes Spaghetti pasta Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg
30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ) 1 25 cm-round (983 kJ) 1 ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ) 1 medium baked w/skin (559 kJ) 3 ⁄4 cup (130 kJ) 1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ)
Excellent sources: Halibut Cashews Artichoke
85 g baked (836 kJ) 30 g (676 kJ) 1 (252 kJ)
0
50
100
150
200
250
300
350
400
RDI for men 19–30 MAGNESIUM Legumes (dark blue) are a rich source of magnesium. Key:
RDI for women 19–30
Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Best sources per kilojoule
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Chapter 12: Water and the major minerals
Magnesium deficiency and toxicity Even with average magnesium intakes below recommendations, deficiency symptoms rarely appear except with diseases.
Magnesium deficiency Average magnesium intakes typically fall below recommendations, which may exacerbate inflammation and contribute to chronic diseases such as heart disease, stroke, hypertension, diabetes and cancer.9 A severe magnesium deficiency causes a tetany similar to the calcium tetany described earlier. Magnesium deficiencies also impair central nervous system activity and may be responsible for the hallucinations experienced during alcohol withdrawal.
Magnesium and hypertension Magnesium is critical to heart function, and seems to protect against hypertension and heart disease.10 Interestingly, people living in areas with hard water, which contains high concentrations of calcium and magnesium, tend to have low rates of heart disease. With magnesium deficiency, the walls of the arteries and capillaries tend to constrict – a possible explanation for the hypertensive effect.
Magnesium toxicity Magnesium toxicity is rare, but it can be fatal. The UL for magnesium applies only to non-food sources such as supplements or magnesium salts.
Magnesium
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Like calcium and phosphorus, magnesium supports bone mineralisation. Magnesium is also involved in numerous enzyme systems and in heart function. It is found abundantly in legumes and leafy green vegetables and, in some areas, in water. The table below offers a summary.
RDI Men (19–30 years): 400 mg/day Women (19–30 years): 310 mg/day UPPER LEVEL (UL) Adults: 350 mg non-food magnesium/day CHIEF FUNCTIONS IN THE BODY Bone mineralisation, building of protein, enzyme action, normal muscle contraction, nerve impulse transmission, maintenance of teeth, and functioning of immune system DEFICIENCY SYMPTOMS Weakness; confusion; if extreme, convulsions, bizarre muscle movements (especially of eye and face muscles), hallucinations and difficulty in swallowing; in children, growth failurea TOXICITY SYMPTOMS From non-food sources only; diarrhoea, alkalosis, dehydration SIGNIFICANT SOURCES Nuts, legumes, whole grains, dark green vegetables, seafood, chocolate, cocoa A still more severe deficiency causes tetany, an extreme, prolonged contraction of the muscles similar to that caused by low blood calcium. a
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12.9 Sulphate
Sulphate is the oxidised form of the mineral sulphur, as it exists in food and water. The body’s need for sulphate is easily met by a variety of foods and beverages. In addition, the body receives sulphate from the amino acids methionine and cysteine, which are found in dietary proteins. These sulphur-containing amino acids help determine the contour of protein molecules. The sulphur-containing side chains in cysteine molecules can link to each other, forming disulphide bridges, which stabilise the protein structure. (See the drawing of insulin with its disulphide bridges in Figure 6.4 on page 180.) Skin, hair and nails contain some of the body’s more rigid proteins, which have a high sulphur content. Because the body’s sulphate needs are easily met with normal protein intakes, there is no recommended intake for sulphate. Deficiencies do not occur when diets contain protein. Only when people lack protein to the point of severe deficiency will they lack the sulphurcontaining amino acids.
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Like the other nutrients, minerals’ actions are coordinated to get the body’s work done. The major minerals, especially sodium, chloride and potassium, influence the body’s fluid balance; whenever an anion moves, a cation moves – always maintaining homeostasis. Sodium, chloride, potassium, calcium and magnesium are key members of the team of nutrients that directs nerve impulse transmission and muscle contraction. They are also the primary nutrients involved in regulating blood pressure. Phosphorus and magnesium participate in many reactions involving glucose, fatty acids, amino acids and the vitamins. Calcium, phosphorus and magnesium combine to form the structure of the bones and teeth. Each major mineral also plays other specific roles in the body. (See the summary table below.)
The major minerals MINERAL AND CHIEF FUNCTIONS
DEFICIENCY SYMPTOMS
TOXICITY SYMPTOMS
SIGNIFICANT SOURCES
Sodium Maintains normal fluid and electrolyte balance; assists in nerve impulse transmission and muscle contraction
Muscle cramps, mental apathy, loss of appetite
Oedema, acute hypertension
Table salt, soy sauce; moderate amounts in meats, milks, breads and vegetables; large amounts in processed foods
Do not occur under normal circumstances
Vomiting
Table salt, soy sauce; moderate amounts in meats, milks, eggs; large amounts in processed foods
Irregular heartbeat, muscular weakness, glucose intolerance
Muscular weakness; vomiting; if given into a vein, can stop the heart
All whole foods; meats, milks, fruits, vegetables, grains, legumes
Chloride Maintains normal fluid and electrolyte balance; part of hydrochloric acid found in the stomach, necessary for proper digestion Potassium Maintains normal fluid and electrolyte balance; facilitates many reactions; supports cell integrity; assists in nerve impulse transmission and muscle contractions
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Chapter 12: Water and the major minerals
MINERAL AND CHIEF FUNCTIONS
DEFICIENCY SYMPTOMS
TOXICITY SYMPTOMS
SIGNIFICANT SOURCES
Calcium Mineralisation of bones and teeth; also involved in muscle contraction and relaxation, nerve functioning, blood clotting and blood pressure
Stunted growth in children; bone loss (osteoporosis) in adults
Constipation; increased risk of urinary stone formation and kidney dysfunction; interference with absorption of other minerals
Dairy products, canned fish with bones, calciumfortified soy milk, tofu, greens (bok choy, broccoli, chard), legumes
Muscular weakness, bone paina
Calcification of non-skeletal tissues, particularly the kidneys
All animal tissues (meat, fish, poultry, eggs, milk)
Weakness; confusion; if extreme, convulsions, bizarre muscle movements (especially of eye and face muscles), hallucinations, and difficulty in swallowing; in children, growth failureb
From non-food sources only; diarrhoea, alkalosis, dehydration
Nuts, legumes, whole grains, dark green vegetables, seafood, chocolate, cocoa
None known; protein deficiency would occur first
Toxicity would occur only if sulphur-containing amino acids were eaten in excess; this (in animals) suppresses growth
All proteincontaining foods (meats, fish, poultry, eggs, milk, legumes, nuts)
Phosphorus Mineralisation of bones and teeth; part of every cell; important in genetic material, part of phospholipids, used in energy transfer and in buffer systems that maintain acid–base balance Magnesium Bone mineralisation, building of protein, enzyme action, normal muscle contraction, nerve impulse transmission, maintenance of teeth and functioning of immune system Sulphate As part of proteins, stabilises their shape by forming disulphide bridges; part of the vitamins biotin and thiamin and the hormone insulin
Dietary deficiency rarely occurs, but some drugs can bind with phosphorus, making it unavailable and resulting in bone loss that is characterised by weakness and pain.
a
b A still more severe deficiency causes tetany, an extreme, prolonged contraction of the muscles similar to that caused by low blood calcium.
With all of the tasks these minerals perform, they are of great importance to life. Consuming enough of each of them every day is easy given a variety of foods from each of the food groups. Wholegrain breads supply magnesium; fruits, vegetables and legumes provide magnesium and potassium; milks offer calcium and phosphorus; meats offer phosphorus and sulphate; all foods provide sodium and chloride, with excesses being more problematic than inadequacies. The message is quite simple and has been repeated throughout this text: for an adequate intake of all the nutrients, including the major minerals, choose different foods from each of the five food groups. And drink plenty of water.
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 You need eight glasses of water a day to stay hydrated. FALSE
4 The calcium in milk is poorly absorbed. FALSE
Because water requirements are so variable, there is no one set figure that would ensure everyone would be well hydrated. Body size, climate and physical activity levels, and what foods high in water content are eaten dictate how much additional water a person needs to drink.
Around 30 per cent of the calcium in milk is absorbed by the body. While the calcium in some green-leafy vegetables can be absorbed at higher rates of 50 per cent, the high amount of calcium found in milks still makes it an excellent dietary source.
2 Most of the salt we eat is added to food in its production, not at the table. TRUE
5 The phosphorus content of soft drinks is what makes them bad for the bones. FALSE
Foods such as bread, processed meat, breakfast cereals and cheese are the main contributors to a person’s salt intake.
It is displacement of milk from the diet that likely makes soft drinks harmful for bone health, not their phosphoric acid content.
3 Most of the body’s calcium is found in the bones. TRUE
Bones contain 99 per cent of the body’s calcium.
NUTRITION PORTFOLIO Many people may miss the mark when it comes to drinking enough water to keep their bodies well hydrated or obtaining enough calcium to promote strong bones; in contrast, sodium intakes often exceed those recommended for health. • Describe your strategy for ensuring that you drink plenty of water each day and how you would know if you were sufficiently hydrated.
• •
Explain the importance of selecting and preparing foods with less salt. Determine whether you drink at least three glasses of milk – or get the equivalent in calcium – every day.
STUDY QUESTIONS c d
Multiple choice questions Answers can be found at the back of the book. 1
The body generates water during the: a b c d
2
3
a b c d 4
ability of their ions to form salts amounts of their contents in the body importance of their functions in the body capacity to retain their identity after absorption
The principal cation in intracellular fluids is: a b
6
sodium chloride
7
Broccoli Eggs Cornflakes Whole-wheat bread
Calcium homeostasis depends on: a b c d
8
metabolise folate inhibit the absorption of vitamin B12 production of stomach acid assist in the production of aldosterone
Which food would provide the most potassium? a b c d
signal the kidneys to retain more sodium cause vasodilation cause water loss promote calcium update in the gut
The distinction between the major and trace minerals reflects the:
Which of the following is an important role of chloride? a b c d
buffering of acids dismantling of bone metabolism of minerals breakdown of energy nutrients
One of the functions of aldosterone is to: a b c d
5
potassium phosphorus
vitamin K, aldosterone and renin vitamin K, parathyroid hormone and renin vitamin D, aldosterone and calcitonin vitamin D, calcitonin and parathyroid hormone
Calcium absorption is improved by: a b c d
oxalates vitamin D low stomach acid phytates in nuts and seeds
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Chapter 12: Water and the major minerals
9
443
Which of the following factors would promote iron absorption?
6
Describe some characteristics of minerals that distinguish them from vitamins. (Section 12.2)
a b c d
7
What is the major function of sodium in the body? Describe how the kidneys regulate blood sodium. Is a dietary deficiency of sodium likely? Why or why not? (Section 12.3)
8
List calcium’s roles in the body. (Section 12.6)
9
How does the body keep blood calcium constant regardless of intake, and what are the roles of vitamin D and parathyroid hormone in the process? (Section 12.6)
Excess phytates in the diet Iron being in the ferrous form Following a vegetarian diet Consuming iron with calcium and fibre
10 Dietary sources with the highest concentration of magnesium are: a b c d
bottled mineral water animal foods fats and oils whole grains
Review questions 1 List the roles of water in the body. (Section 12.1) 2
What is ADH? Where does it exert its action? What is aldosterone? How does it work? (Section 12.1)
3
How do the concentrations of the main electrolytes differ between the intracellular and extracellular compartments? (Section 12.1)
4
List the sources of water intake and routes of water excretion. (Section 12.1)
5
What do the terms ‘major’ and ‘trace’ mean when describing the minerals in the body? (Section 12.2)
10 Name significant food sources of calcium. What are the consequences of inadequate intakes? (Section 12.6) 11 List the roles of phosphorus in the body. Discuss the relationships between calcium and phosphorus. Is a dietary deficiency of phosphorus likely? Why or why not? (Section 12.7) 12 State the major functions of chloride, potassium, magnesium and sulphur in the body. Are deficiencies of these nutrients likely to occur in your own diet? Why or why not? (Sections 12.4, 12.5, 12.8, 12.9)
NUTRITION CALCULATIONS These problems give you an appreciation for the minerals in foods. Be sure to show your calculations (answers can be found in the Answers section at the back of this book). 1
For each of these minerals, note the unit of measure: • • • • •
2
calcium magnesium phosphorus potassium sodium.
a The absorption of calcium from different foods can vary substantially. In this exercise, use Figure 12.16 on page 432 to determine how much calcium the body actually receives from the foods listed in the accompanying table by multiplying the milligrams of calcium in the food by the percentage absorbed. The first one is done for you.
FOOD
CALCIUM IN THE FOOD (mg)
ABSORPTION RATE (%)
CALCIUM IN THE BODY (mg)
Cauliflower, ½ cup cooked, fresh
10
$50
$5
Kale, ½ cup cooked, fresh
40
Milk, 1 cup full-fat
300
Sweet potatoes, 60 g
150
Spinach, 1 cup, raw
55
b
To appreciate how the absorption rate influences the amount of calcium available to the body, compare kale with sweet potatoes. Which provides more calcium in foods and to the body?
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Understanding nutrition
c
to receive an equivalent amount of calcium as from 1 cup of milk? How does your answer change when you account for differences in their absorption rates?
To appreciate how the calcium content of foods influences the amount of calcium available to the body, compare cauliflower with milk. How much cauliflower would a person have to eat
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search ‘minerals’ at the Dietitians Association of Australia site: http://www.daa.asn.au • Learn about sodium in foods and on food labels by searching ‘salt’ or ‘sodium’ at the
•
•
Food Standards Australia New Zealand website: http://www.foodstandards.gov.au Learn why Australians should reduce how much salt they are eating at the website of the Australian Division of World Action on Salt & Health: http://www.awash.org.au Learn about the benefits of calcium from Osteoporosis Australia: http://www.osteoporosis.org.au
SEARCH ME! NUTRITION Keyword: calcium osteoporosis Calcium and vitamin D play a vital role in bone health, especially in the elderly in long-term care. Read the
article Recommendations for preventing fracture in longterm care and list the recommendations made regarding calcium and vitamin D.
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Chapter 12: Water and the major minerals
12.10 OSTEOPOROSIS AND CALCIUM Osteoporosis becomes apparent during the later years,
PhotoDisc
but it develops much earlier – and without warning. Osteoporosis is rightly called a disease of older age that originates in youth. Few people are aware that their bones are being robbed of their strength. The problem often first becomes evident when someone’s hip suddenly gives way. People say, ‘She fell and broke her hip’, but in fact the hip may have been so fragile that it broke before she fell. Even bumping into a table may be enough to shatter a porous bone into fragments so numerous and scattered that they cannot be reassembled. Removing them and replacing them with an artificial joint requires major surgery. One in two women and one in three men over 60 years of age in Australia will develop an osteoporotic fracture. Of those suffering a hip fracture, one-quarter will die within 12 months and half of those surviving will not be able to walk without assistance, with many requiring full-time nursing care.
Obtaining plenty of calcium from the diet is important in maintaining healthy bones.
This highlight examines osteoporosis, one of the most prevalent diseases of ageing. Over 4 million people in Australia aged over 50 have osteoporosis or poor bone health.1 In New Zealand, 80 000 people break bones each year because of osteoporosis, and about three-quarters are women.2 This highlight reviews the many factors that contribute to a new hospitalisation every few minutes from breaks in the bones of the hips, vertebrae, wrists, arms and
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HIGHLIGHT
12
ankles. And it presents strategies to reduce the risks, paying special attention to the role of dietary calcium.
Bone development and disintegration Bone has two compartments: the outer, hard shell of cortical bone and the inner, lacy matrix of trabecular bone. Both can lose minerals, but in different ways and at different rates. The left-hand photograph in Figure H12.1 shows a human leg bone sliced lengthwise, exposing the lacy, calcium-containing crystals of trabecular bone. These crystals give up calcium to the blood when the diet runs short, and they take up calcium again when the supply is plentiful (review Figure 12.14 on page 430). For people who have eaten calcium-rich foods throughout the bone-forming years of their youth, these deposits make bones dense and provide a rich reservoir of calcium. Surrounding and protecting the trabecular bone is a dense, ivory-like exterior shell – the cortical bone. Cortical bone composes the shafts of the long bones, and a thin cortical shell caps the end of the bone, too. Both compartments confer strength on bone: cortical bone provides the sturdy outer wall, and trabecular bone provides support along the lines of stress. The two types of bone play different roles in calcium balance and osteoporosis. Supplied with blood vessels and metabolically active, trabecular bone is sensitive to hormones that govern day-to-day deposits and withdrawals of calcium. It readily gives up minerals whenever blood calcium needs replenishing. Losses of trabecular bone start becoming significant for men and women in their thirties, although losses can occur whenever calcium withdrawals exceed deposits. Cortical bone also gives up calcium, but slowly and at a steady pace. Cortical bone losses typically begin at about age 40 and continue slowly but surely thereafter. As bone loss continues, bone density declines, and osteoporosis becomes apparent (see Figure H12.1). Bones become so fragile that even the body’s own weight can overburden the spine – vertebrae may suddenly disintegrate and crush down, painfully pinching major nerves. Or the vertebrae may compress into wedge shapes, forming what is often called a ‘dowager’s hump’, the
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Understanding nutrition
© Permission by David Dempster from J. Bone Miner Res, 1986
© Permission by David Dempster from J. Bone Miner Res, 1986
Courtesy of Gjon Mili
FIGURE H12.1 Healthy and osteoporotic trabecular bones
Trabecular cular bone is bone theis lacy the network lacy of Electron Electron micrograph micrograph ofmicrograph healthy of healthy trabecular Electron Electron micrograph micrograph ofmicrograph trabecular of trabecular bone bone Trabecular bone is network theof lacy network of Electron oftrabecular healthy trabecular Electron of trabecular bone calcium-containing m-containing crystals crystals that fills that the fills that the fills the bone bone affected affected by osteoporosis by osteoporosis bone affected by osteoporosis calcium-containing crystals or. interior. Cortical Cortical bone is bone theis dense, the dense, interior. Cortical bone is the dense, ike ivorylike bone ivorylike that boneforms thatbone forms thethat exterior the exterior forms the exterior shell. shell.
posture many older people assume as they ‘grow shorter’. Figure H12.2 shows the effect of compressed spinal bone on a woman’s height and posture. Because both the cortical shell and the trabecular interior weaken, breaks most often occur in the hip. Physicians can diagnose osteoporosis and assess the risk of bone fractures by measuring bone density using dual-energy X-ray absorptiometry (DEXA scan) or ultrasound. They also consider risk factors that predict bone fractures, including age, personal and family history of fracture, BMI and physical inactivity. Table H12.1 summarises the major risk factors and protective factors for osteoporosis. The more risk factors that apply to a person, the greater the chances of bone loss. Notice that several risk factors that are influential in the development of osteoporosis – such as age, gender and genetics – cannot be changed. Other risk factors – such as diet, physical activity, body weight, smoking and alcohol use – are personal behaviours that can be changed. By eating a calcium-rich, well-balanced diet, being physically active, and abstaining from smoking and drinking alcohol in moderation (if at all), people can defend themselves against osteoporosis. These decisions are particularly important for those with other risk factors that cannot be changed. Whether a person develops osteoporosis seems to depend on the interactions of several factors, including nutrition. The strongest predictor of bone density is age: osteoporosis
is responsible for 90 per cent of the hip fractures in women and 80 per cent in men over the age of 65.
Age and bone calcium Two major stages of life are critical in the development of osteoporosis. The first is the bone-acquiring stage of childhood and adolescence. The second is the bone-losing decades of late adulthood (especially in women after menopause). The bones gain strength and density all through the growing years and into young adulthood. As people age, the cells that build bone gradually become less active, but those that dismantle bone continue working. The result is that bone loss exceeds bone formation. Some bone loss is inevitable, but losses can be curtailed by maximising bone mass.
Maximising bone mass To maximise bone mass, the diet must deliver an adequate supply of calcium during the first three decades of life. Children and teens who get enough calcium and vitamin D have denser bones than those with inadequate intakes. With little or no calcium from the diet, the body must depend on bone to supply calcium to the blood – bone mass diminishes, and bones lose their density and strength. When people reach the bone-losing years of middle age, those who formed dense bones during their
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Chapter 12: Water and the major minerals
FIGURE H12.2 Loss of height in a woman caused by osteoporosis The woman on the left is about 50 years old. The woman on the right is 80 years old. Her legs have not grown shorter. Instead, her back has lost length due to collapse of her spinal bones (vertebrae). Collapsed vertebrae cannot protect the spinal nerves from pressure that causes excruciating pain. 15 centimetres lost
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TABLE H12.1 Risk factors and protective factors for osteoporosis RISK FACTORS
PROTECTIVE FACTORS
• Older age (>50 yr)
• Younger age
• Small frame
• High BMI
• Caucasian, Asian or Hispanic heritage
• African–American heritage
• Cigarette smoking
• No smoking
• Alcohol consumption in excess
• Alcohol abstinence or consumption in moderation
• Sedentary lifestyle
• Regular weight-bearing exercise
• Use of glucocorticoids or anticonvulsants
• Use of diuretics
• Female gender
• Male gender
• Maternal history of osteoporosis fracture or personal history of fracture
• Bone density assessment and treatment (if necessary)
• Oestrogen deficiency in women (amenorrhoea or menopause, especially early or surgically induced); testosterone deficiency in men
• Use of oestrogen therapy
• Lifetime diet inadequate • Lifetime diet rich in calcium in calcium and vitamin D and vitamin D
80 years old Science Photo Library/Doncaster and Bassetlaw Hospitals
50 years old
youth have the advantage. They simply have more bone starting out and can lose more before suffering ill effects. Figure H12.3 demonstrates this effect.
Minimising bone loss Not only does dietary calcium build strong bones in youth, it remains important in protecting against losses in the later years. Unfortunately, calcium intakes of older adults are typically low, and calcium absorption declines after menopause. The kidneys do not activate vitamin D as well as they did earlier (recall that active vitamin D enhances calcium absorption). Also, sunlight is needed to form
Using a DEXA (dual-energy X-ray absorptiometry) scan to measure bone mineral density identifies osteoporosis, determines risks for fractures and tracks responses to treatment.
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Understanding nutrition
FIGURE H12.3 Bone losses over time compared Peak bone mass is achieved by age 30. Women gradually lose bone mass until menopause, when losses accelerate dramatically and then gradually taper off.
Bone mass
Woman A entered adulthood with enough calcium in her bones to last a lifetime.
Osteopenia
Woman B had less bone mass starting out, and so suffered ill effects from bone loss later on.
Osteoporosis Age 30
Menopause
Age 60
Time
a People with a moderate degree of bone mass reduction are said to have osteopenia and are at increased risk of fractures.
Data from Committee on Dietary Reference Intakes, Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride, Washington, DC: National Academy Press (1997): 71−145.
vitamin D, and many older people spend little or no time outdoors in the sunshine. For these reasons, and because intakes of vitamin D are typically low anyway, blood vitamin D declines. Some of the hormones that regulate bone and calcium metabolism also change with age and accelerate bone mineral withdrawal. Among the hormones suggested as influential are parathyroid hormone, calcitonin and oestrogen. Together, these age-related factors contribute to bone loss – inefficient bone remodelling, reduced calcium intakes, impaired calcium absorption, poor vitamin D status and hormonal changes that favour bone mineral withdrawal.
Gender and hormones After age, gender is the next strongest predictor of osteoporosis. Men have greater bone density than women at maturity, and women have greater losses than men in later life. Consequently, men develop bone problems about 10 years later than women, and women account for four out of five cases of osteoporosis. Menopause imperils women’s bones. Bone dwindles rapidly when the hormone oestrogen diminishes and menstruation ceases. Women may lose up to 20 per cent of their bone mass during the six to eight years following menopause. Eventually, losses taper off so
that women again lose bone at the same rate as men of their age. Losses of bone minerals continue throughout the remainder of a woman’s lifetime, but not at the free-fall pace of the menopause years (review Figure H12.3). Rapid bone losses also occur when young women’s ovaries fail to produce enough oestrogen, causing menstruation to cease. In some cases, diseased ovaries are to blame and must be removed; in others, the ovaries fail to produce sufficient oestrogen because the women suffer from anorexia nervosa and have unreasonably restricted their body weight (see Highlight 8). The amenorrhoea and low body weights explain much of the bone loss seen in these young women even years after diagnosis and treatment. Oestrogen therapy can help non-menstruating women prevent further bone loss and reduce the incidence of fractures. Because oestrogen therapy may increase the risks for breast cancer, women must carefully weigh any potential benefits against the possible dangers. Several drug therapies have been developed to inhibit bone loss and enhance bone formation. A combination of drugs or of hormone replacement and a drug may be most beneficial. Some women who choose not to use oestrogen therapy turn to soy as an alternative treatment. Interestingly, the phytochemicals commonly found in soy mimic the actions of oestrogen in the body. Research results have been mixed and controversial, but overall seem to indicate a lack of benefit for soy and its phytochemicals in helping to prevent the rapid bone losses of the menopause years.3 As is true of all dietary supplements and herbal products, there may be risks associated with their use; in the case of soy, research suggests relative safety with modest benefit.4 Because the risks and benefits vary depending on each person’s medical history, women should discuss soy options with their physicians. If oestrogen deficiency is a major cause of osteoporosis in women, what is the cause of bone loss in men? The male sex hormone testosterone appears to play a role. Men with low levels of testosterone, as occurs after removal of diseased testes or when testes lose function with ageing, suffer more fractures. Treatment for men with osteoporosis includes testosterone replacement therapy. Thus, both male and female sex hormones participate in the development and treatment of osteoporosis.
Genetics The role of genetics in osteoporosis is strong, although still unclear.5 Most likely, genes influence both the peak bone mass achieved during growth and the bone loss incurred during the later years. The extent to which a given genetic potential is realised, however, depends on many
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Chapter 12: Water and the major minerals
outside factors. Diet and physical activity, for example, can maximise peak bone density during growth, whereas alcohol and tobacco abuse can accelerate bone losses later in life. Importantly, these factors are within a person’s control.
Physical activity and body weight Physical activity may be the single most important factor supporting bone growth during adolescence.6 Muscle strength and bone strength go together. When muscles work, they pull on the bones, stimulating them to develop more trabeculae and grow denser. The hormones that promote new muscle growth also favour the building of bone. As a result, active bones are denser and stronger than sedentary bones. To keep bones healthy, a person should engage in weight training or weight-bearing endurance activities (such as tennis and jogging or vigorous walking) regularly. Regular physical activity combined with an adequate calcium intake helps to maximise bone density in adolescence. Adults can also maximise and maintain
449
bone density with a regular program of weight training. Even past menopause, when most women are losing bone, weight training improves bone density. Heavier body weights and weight gains place a similar stress on the bones and promote an increase in their density. In fact, weight loss reduces bone density and increases the risk of fractures – in part because energy restriction diminishes calcium absorption and compromises calcium balance. As is mentioned in Highlight 8, the combination of underweight, severely restricted energy intake, extreme daily exercise and amenorrhoea reliably predicts bone loss.
Smoking and alcohol Add bone damage to the list of ill consequences associated with smoking. The bones of smokers are less dense than those of non-smokers – even after controlling for differences in age, body weight and physical activity habits. Fortunately, the damaging effects can be reversed with smoking cessation. Blood indicators of beneficial bone activity are apparent six weeks after a person stops smoking. In time, the bone density of former smokers is similar to that of non-smokers. People who abuse alcohol often suffer from osteoporosis and experience more bone breaks than others. Several factors appear to be involved. Alcohol enhances fluid excretion, leading to excessive calcium losses in the urine; upsets the hormonal balance required for healthy bones; slows bone formation, leading to lower bone density; stimulates bone breakdown; and increases the risk of falling.
Dietary calcium
Catalin Petolea/Shutterstock.com
Bone strength later in life depends most on how well the bones were built during childhood and adolescence. Adequate calcium nutrition during the growing years is essential to achieving optimal peak bone mass. To that end, the Nutrient Reference Values for Australia and New Zealand recommend 1300 milligrams of calcium per day for everyone from 12 to 18 years of age. Unfortunately, few girls meet the recommendations for calcium during these bone-forming years. (Boys generally obtain intakes close to those recommended because they eat more food.) Consequently, most girls start their adult years with less-than-optimal bone density. As adults, women under the age of 50 rarely meet their recommended intakes of 1000 milligrams from food.
Other nutrients Strength training helps to build strong bones.
Much research has focused on calcium, but other nutrients support bone health, too. Adequate protein
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Understanding nutrition
protects bones and reduces the likelihood of hip fractures. As mentioned earlier, vitamin D is needed to maintain calcium metabolism and optimal bone health. Vitamin K regulates bone and cartilage mineralisation and decreases bone turnover.7 Vitamin C may slow bone losses. The minerals magnesium and potassium also help maintain bone mineral density. Vitamin A is needed in the boneremodelling process, but too much vitamin A may be associated with osteoporosis. Carotenoids may inhibit bone loss. Omega-3 fatty acids may help preserve bone integrity.8 Additional research points to the bone benefits not of a specific nutrient, but of a diet rich in fruits, vegetables, and whole grains. In contrast, diets containing too much salt are associated with bone losses. Similarly, diets containing too many soft drinks or commercially baked snack and fried foods are associated with low bone mineral density. Clearly, a well-balanced diet that depends on all the food groups to supply a full array of nutrients is central to bone health.
A perspective on supplements Bone health depends, in part, on calcium. People who do not consume milk products or other calcium-rich foods in amounts that provide even half the recommended calcium should consider, on consultation with a health professional, taking calcium supplements, which may help to enhance bone density and protect against bone loss. Calcium supplements are typically sold as compounds of calcium carbonate (common in antacids), citrate, gluconate, lactate, malate or phosphate. These supplements often include magnesium, vitamin D or both. In addition, some calcium supplements are made from bone meal, oyster shell or dolomite (limestone). Many calcium supplements, especially those derived from these natural products, contain lead – which impairs health in numerous ways, as Chapter 13 points out. Fortunately, calcium interferes with the absorption and action of lead in the body. The first question to ask is how much calcium the supplement provides. Most calcium supplements provide between 250 and 1000 milligrams of calcium. To be safe,
total calcium intake from both foods and supplements should not exceed 2500 milligrams a day. Read the label to find out how much a dose supplies. The next question to ask is how well the body absorbs and uses the calcium from various supplements. Most healthy people absorb calcium equally well from milk and from the supplements calcium carbonate, citrate and phosphate. More important than supplement solubility is tablet disintegration. When manufacturers compress large quantities of calcium into small pills, the stomach acid has difficulty penetrating the pill. To test a supplement’s ability to dissolve, drop it into a cup of vinegar and stir occasionally. A high-quality formulation will dissolve within half an hour. Supplements containing calcium carbonate require stomach acidity for optimal absorption and so are best taken with meals. People who suffer from reduced gastric acid production or are taking medications that inhibit gastric acid secretion are advised to take calcium citrate supplements rather than calcium carbonate. Calcium supplements are recommended for people over 65 years and for those with a poor dietary intake.
Some closing thoughts Unfortunately, many of the strongest risk factors for osteoporosis are beyond people’s control: age, gender and genetics. But several strategies are still effective for prevention. First, ensure an optimal peak bone mass during childhood and adolescence by eating a balanced diet rich in calcium and engaging in regular physical activity. Then maintain that bone mass by continuing those healthy diet and activity habits, abstaining from cigarette smoking and using alcohol only moderately, if at all. Finally, minimise bone loss by maintaining an adequate nutrition and exercise regimen, and, for women, consult a doctor about calcium supplements or other drug therapies that may be effective both in preventing bone loss and in restoring lost bone. The reward is the best possible chance of preserving bone health throughout life.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A Examine your own lifestyle behaviours and evaluate which ones are most likely to be protective against developing osteoporosis. B Osteoporosis typically develops in old age, yet the time to optimise bone density is during childhood and adolescence – decades away from the realities
of hip fractures and spinal collapses. What plan of action might you develop to encourage teens to adopt strategies that will enhance bone development? Be sure to address potential obstacles and the reluctance typical of that age group.
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NUTRITION ON THE NET Find out more information online. • Obtain additional information from Osteoporosis Australia: http://www.osteoporosis.org.au • Read about practical advice on maintaining healthy bones from the Jean Hailes organisation http://jeanhailes.org.au
• •
Search ‘falls and fractures’ at the National Ageing Research Institute: http://www.nari.net.au Visit the National Institutes of Health Osteoporosis and Related Bone Diseases National Resource Center: http://www.niams.nih.gov/Health_Info/Bone/
REFERENCES CHAPTER 1
2
3 4
5
Y. Zhang and co-authors, Caffeine and diuresis during rest and exercise: A meta-analysis, Journal of Science and Medicine in Sport 18 (2015): 569–74. C. A. Nowson and co-authors, Blood pressure response to dietary modifications in free-living individuals, Journal of Nutrition 134 (2004): 2322–9. M. C. Houston, The importance of potassium in managing hypertension, Current Hypertension Reports 13 (2011): 309–17. Food Standards Australia New Zealand: How much sodium and salt are we eating? (2015), available at http://www.foodstandards.gov.au/ scienceandeducation/factsheets/factsheets/howmuchsaltareweeating/ howmuchsaltandsodium4551.cfm N. R. Cook, L. J. Appel, and P. K. Whelton, Sodium intake and allcause mortality over 20 years in the trials of hypertension prevention, Journal of the American College of Cardiology 68 (2016): 1609–17; W. B. Farquhar and coauthors, Dietary sodium and health: More than just blood pressure, Journal of the American College of Cardiology 65 (2015): 1042–105.
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7
8
9
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Z. Zhang and coauthors, Association between usual sodium and potassium intake and blood pressure and hypertension among US adults: NHANES 2005-2010, PLoS One 8 (2013): e75289. A. Seth and coauthors, Potassium intake and risk of stroke in women with hypertension and nonhypertension in the Women’s Health Initiative, Stroke 45 (2014): 2874–80. E. Z. Movassagh, Vegetarian-style dietary pattern during adolescence has long-term positive impact on bone from adolescence to young adulthood: a longitudinal study. Nutrition Journal 17 (2018): 36. M. M. Joosten and co-authors, Urinary and plasma magnesium and risk of ischemic heart disease, American Journal of Clinical Nutrition 97 (2013): 1299–306. X. Zhang and co-authors, Effects of magnesium supplementation on blood pressure: A meta-analysis of randomized double-blind placebocontrolled trials, Hypertension 68 (2016): 324–33.
HIGHLIGHT 1
2
3
4
Osteoporosis Australia, Osteoporosis costing all Australians – a new burden of disease analysis, 2012–2022, available at https://www. osteoporosis.org.au/burdenofdisease Osteoporosis New Zealand, Osteoporosis in New Zealand 2007 – 2020, available at https://www.iofbonehealth.org/sites/default/files/PDFs/ white_paper_new_zealand_2007.pdf I. M. C. M. Rietjens, J. Louisse and K. Beekmann, The potential health effects of dietary phytoestrogens, British Journal of Pharmacology 174 (2017): 1263–80. D. L. Alekel and co-authors, Soy isoflavones for reducing bone loss study: Effects of a 3-year trial on hormones, adverse events, and endometrial thickness in postmenopausal women, Menopause 22 (2015): 185–97; J. W. Pawlowski and co-authors, Impact of equolproducing capacity and soy-isoflavone profiles of supplements on bone
5 6
7 8
calcium, retention in postmenopausal women: A randomized crossover trial, American Journal of Clinical Nutrition 102 (2015): 695–703. G. R. Clark and E. L. Duncan, The genetics of osteoporosis, British Medical Bulletin 113 (2015): 73–81. S. A. Jackowski and co-authors, Adolescent physical activity and bone strength at the proximal femur in adulthood, Medicine and Science in Sports and Exercise 46 (2014): 736–44. M. Fusaro, Vitamin K and bone, Clinical Cases in Mineral and Bone Metabolism, 14 (2017): 200–6. T. S. Orchard and co-authors, The association of red blood cell n-3 and n-6 fatty acids with bone mineral density and hip fracture risk in the women’s health initiative, Journal of Bone and Mineral Research 28 (2013): 505–15.
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13
THE TRACE MINERALS Nutrition in your life
Trace – a barely perceptible amount. But the trace minerals tackle big jobs. Your blood can’t carry oxygen without iron, insulin can’t deliver glucose without chromium and thyroid glands develop goitre without iodine. Together, the trace minerals – iron, zinc, iodine, selenium, copper, manganese, fluoride, chromium and molybdenum – keep you healthy and strong. Where can you get these amazing minerals? A variety of foods, especially those from the meat and meat alternative group, sprinkled with a little iodised salt will do the trick. It’s remarkable what your body can do with only a few milligrams – or even micrograms – of the trace minerals. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F Iron from animal foods is normally absorbed better than iron from plant foods. T F Vegetarians require the same amount of iron in their diet as meat eaters. T F Zinc deficiency is common in industrialised countries. T F Seafood is a good source of iodine. T F Bottled water is a good source of fluoride.
LEARNING OBJECTIVES 13.1 Summarise key factors unique to the trace minerals. 13.2 Identify the main roles, deficiency symptoms and food sources for iron. 13.3 Identify the main roles, deficiency symptoms and food sources for zinc. 13.4 Identify the main roles, deficiency symptoms and food sources for iodine. 13.5 Identify the main roles, deficiency symptoms and food sources for selenium. 13.6 Identify the main roles, deficiency symptoms and food sources for copper.
13.7 Identify the main roles, deficiency symptoms and food sources for manganese. 13.8 Identify the main roles, deficiency symptoms and food sources for fluoride. 13.9 Identify the main roles, deficiency symptoms and food sources for chromium. 13.10 Identify the main roles, deficiency symptoms and food sources for molybdenum. 13.11 Identify the importance of other trace minerals and describe the health effects of contaminant minerals. 13.12 Define phytochemicals and explain how they might defend against chronic diseases.
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This chapter features the essential trace minerals – iron, zinc, iodine, selenium, copper, manganese, fluoride, chromium and molybdenum. Figure 12.10 (page 419) shows the tiny quantities of trace minerals in the human body. The trace minerals are so named because they are present, and needed, in relatively small amounts in the body. All together, they would produce only a bit of dust, hardly enough to fill a teaspoon. Yet they are no less important than the major minerals or any of the other nutrients. Each of the trace minerals performs a vital role. A deficiency of any of them may be fatal, and an excess of many is equally deadly. Remarkably, people’s diets normally supply just enough of these minerals to maintain health. This chapter also mentions other trace minerals – such as arsenic, boron, nickel, bromine and vanadium – that are not considered nutrients. These minerals may have beneficial roles in the body, but research on them is insufficient to determine their essentialness. Also mentioned in this chapter are contaminant minerals that disrupt body processes and impair nutrition status. The highlight that follows examines phytochemicals – compounds that also are not essential nutrients but that have biological activity in the body. Again, a well-balanced diet – especially one abundant in fruits and vegetables – supplies a full array of phytochemicals to support good health.
13.1 The trace minerals – an overview
The body requires the trace minerals in minuscule quantities. They participate in diverse tasks all over the body, each having special duties that only it can perform.
Food sources The trace mineral contents of foods depend on soil and water composition and on how foods are processed. Furthermore, many factors in the diet and within the body affect the minerals’ bioavailability. Still, outstanding food sources for each of the trace minerals, just like those for the other nutrients, include a wide variety of foods, especially unprocessed whole foods.
Deficiencies Severe deficiencies of the better-known minerals are easy to recognise. Deficiencies of the others may be harder to diagnose, and for all minerals, mild deficiencies are easy to overlook. Because the minerals are active in all the body systems – the GI tract, cardiovascular system, blood, muscles, bones and central nervous system – deficiencies can have wide-reaching effects and can affect people of all ages. The most common result of a deficiency in children is failure to grow and thrive.
Reminder: Bioavailability refers to the rate at, and the extent to which, a nutrient is absorbed and used.
Toxicities Most of the trace minerals are toxic at intakes only two and a half to 11 times above current recommendations. Thus, it is important not to habitually exceed the Upper Level of Intake (UL). Many vitamin–mineral supplements contain trace minerals, making it easy for users to exceed their needs. Highlight 10 discusses supplement use and some of the regulations around their production and promotion. Individuals who take supplements must therefore be aware of the possible dangers and so select supplements that contain doses that would not mean they exceed the recommended UL. It would be easier and safer to meet nutrient needs by selecting a variety of foods than by combining an assortment of supplements (see Highlight 10).
Interactions Interactions among the trace minerals are common and often well-coordinated to meet the body’s needs. For example, several of the trace minerals support insulin’s work, influencing its synthesis, storage, release and action. At other times, interactions lead to nutrient imbalances. An excess of one may cause a deficiency of another (for example, a slight manganese overload may aggravate an iron
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deficiency). A deficiency of one may interfere with the work of another (for example, a selenium deficiency halts the activation of the iodine-containing thyroid hormones). A deficiency of a trace mineral may even open the way for a contaminant mineral to cause a toxic reaction (for example, iron deficiency makes the body vulnerable to lead poisoning). These examples reinforce the need to balance intakes and to use supplements wisely, if at all. A good food source of one nutrient may be a poor food source of another, and factors that enhance the action of some trace minerals may interfere with others. Red meat, for example, is a good source of iron but a poor source of calcium; vitamin C enhances the absorption of iron but hinders that of copper.
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Although the body uses only tiny amounts of the trace minerals, they are vital to health. Because so little is required, the trace minerals can be toxic at levels not far above estimated requirements – a consideration for supplement users. Like the other nutrients, the trace minerals are best obtained by eating a variety of whole foods.
13.2 Iron
Iron is an essential nutrient, vital to many of the cells’ activities, but it poses a problem for millions of people. Some people simply don’t eat enough iron-containing foods to support their health optimally, whereas others absorb so much iron that it threatens their health. Iron exemplifies the principle that both too little and too much of a nutrient in the body can be harmful. In its wisdom, the body has several ways to achieve iron homeostasis, protecting against both deficiency and overload. Iron’s two ionic states: • ferrous iron (reduced): Fe++ • ferric iron (oxidised): Fe+++
Iron roles in the body
Reminder: A cofactor is a substance that works with an enzyme to facilitate a chemical reaction. Reminder: Haemoglobin is the oxygen-carrying protein of the red blood cells that transports oxygen from the lungs to tissues throughout the body; haemoglobin accounts for 80% of the body’s iron. A mucous membrane such as the one that lines the GI tract is sometimes called the mucosa. The adjective of mucosa is mucosal.
Iron has the ability to switch back and forth between two ionic states. In the reduced state, iron has lost two electrons and therefore has a net positive charge of two; it is known as ferrous iron. In the oxidised state, iron has lost a third electron, has a net positive charge of three and is known as ferric iron. Ferrous iron can be oxidised to ferric iron, and ferric iron can be reduced to ferrous iron. Thus, iron can serve as a cofactor to enzymes involved in oxidation–reduction reactions – reactions so widespread in metabolism that they occur in all cells. Enzymes involved in making amino acids, collagen, hormones and neurotransmitters all require iron. (For details about ions, oxidation and reduction, see Appendix B.) Iron forms a part of the electron carriers that participate in the electron transport chain (discussed in Chapter 7). The iron-containing electron carriers of the electron transport chain are known as cytochromes (see Appendix C for details of this pathway). In this pathway, these carriers transfer hydrogens and electrons to oxygen, forming water, and in the process make ATP for the cells’ energy use. Most of the body’s iron is found in two proteins: haemoglobin in the red blood cells and myoglobin in the muscle cells. In both, iron helps accept, carry and then release oxygen.
Iron absorption and metabolism The body conserves iron. Because it is difficult to excrete iron once it is in the body, balance is maintained primarily through absorption. More iron is absorbed when stores are empty and less is absorbed when stores are full.
Iron absorption
Special proteins help the body absorb iron from food (see Figure 13.1). One protein, called mucosal ferritin, receives iron from food and stores it in the mucosal cells of the small intestine. When the body needs iron, mucosal ferritin releases some iron to another protein,
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FIGURE 13.1 Iron absorption
Iron in food
Mucosal cells in the intestine store excess iron in mucosal ferritin (a storage protein).
If the body does not need iron
Iron is not absorbed and is excreted in shed intestinal cells instead. Thus, iron absorption is reduced when the body does not need iron.
If the body needs iron Mucosal ferritin releases iron to mucosal transferrin (a transport protein), which hands off iron to another transferrin that travels through the blood to the rest of the body.
called mucosal transferrin. Mucosal transferrin transfers the iron to another protein, blood transferrin, which transports the iron to the rest of the body. If the body does not need iron, it is carried out when the intestinal cells are shed and excreted in the faeces; intestinal cells are replaced about every three to five days. By holding iron temporarily, these cells control iron absorption by either delivering iron when the day’s intake falls short or disposing of it when intakes exceed needs. This is an important regulatory process to prevent iron toxicity because, apart from blood loss, the body does not have a ready way to excrete excess iron once it has been absorbed.
Haem and non-haem iron Iron absorption depends in part on its dietary source. Iron occurs in two forms in foods: as haem iron, which is found only in foods derived from the flesh of animals, such as meats, poultry and fish, and as non-haem iron, which is found in both plant-derived and animalderived foods (see Figure 13.2). On average, haem iron represents about 10 per cent of the iron a person consumes in a day. Even though haem iron accounts for only a small proportion of the intake, it is so well absorbed that it contributes significant iron. About 25 per cent of haem iron and 17 per cent of non-haem iron is absorbed, depending on dietary factors and the body’s iron stores.1 In iron deficiency, absorption increases. In iron overload, absorption declines.
PUTTING COMMON SENSE TO THE TEST
Iron from animal foods is normally absorbed better than iron from plant foods. TRUE
Absorption-enhancing factors
Meat, fish and poultry contain not only the well-absorbed haem iron, but also MFP factor that promotes the absorption of non-haem iron from other foods eaten at the same meal. Vitamin C also enhances non-haem iron absorption from foods eaten in the same meal by capturing the iron and keeping it in the reduced ferrous form, ready for absorption. Some acids and sugars also enhance non-haem iron absorption.
Factors that enhance non-haem iron absorption are: • MFP factor • vitamin C (ascorbic acid) • gastric acidity.
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FIGURE 13.2 Haem and non-haem iron in foods About 40% of the iron in meat, fish, and poultry is bound into haem; the other 60% is non-haem iron. Key: Haem Non-haem
Factors that inhibit non-haem iron absorption are: • phytates (legumes, grains and rice) • vegetable proteins (soybeans, legumes, nuts) • tannic acid (and other polyphenols in tea and coffee) • reduced gastric acidity.
Haem accounts for about 10% of the average daily iron intake, but it is well absorbed (about 25%). Non-haem iron accounts for the remaining 90%, but it is less well absorbed (about 17%).
All of the iron in foods derived from plants is non-haem iron.
Absorption-inhibiting factors Some dietary factors bind with non-haem iron, inhibiting absorption. These factors include the phytates in legumes, whole grains and rice; the vegetable proteins in soybeans, other legumes and nuts; and the polyphenols (such as tannic acid) in tea, coffee, grain products, oregano and red wine.
CURRENT RESEARCH IN NUTRITION Probiotics boost iron absorption Iron deficiency is the most common and widespread nutritional disorder in the world, with the deficiency spanning both developing and industrialised countries. Strategies to increase the intake of foods rich in iron, as well as dietary factors that can enhance iron absorption, are therefore important to know about. One factor that is thought to increase iron absorption is lactic acid-fermented foods. A small number of single-meal studies using fermented vegetables have shown some promising results, but the research has so far yet to build a strong case for these foods being a useful dietary addition for someone with iron deficiency. Extending the research field, a Swedish study involving 22 healthy women gave each person either fruit juice containing 5 mg of iron alone or the same iron-fortified fruit juice drink but with the addition of one of two different probiotic strains of Lactobacillus plantarum.2 For drinks containing the bacterial strains, the average iron absorption went from 18.5 per cent with the control drink to 28.6 per cent with the probiotic drink. A similar result was seen using the second bacterial strain, with iron absorption rising from 20.1 to 29.1 per cent. Again, close to a 50 per cent increase in iron absorption compared to the control drink. How could a probiotic help with iron absorption? It may be related to the colonisation of the bacteria in the intestine with a subsequent decrease in colonic pH. As pH falls, iron can change its ionic state into the more absorbable ferrous iron form. The results from this small-scale study look impressive. Future work will certainly expand the evidence base for how best to use fermented foods or probiotic supplements to enhance absorption in vulnerable populations.
Individual variation Overall, about 18 per cent of dietary iron is absorbed from mixed diets and only about 10 per cent from vegetarian diets.3 As you might expect, vegetarian diets do not have the benefit of easy-to-absorb haem iron or the help of MFP in enhancing absorption. In addition to dietary
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influences, iron absorption also depends on an individual’s health, stage in the life cycle and iron status, as well as on genetic variations in the expression of the central iron regulatory hormone hepcidin.4 Produced by the liver, hepcidin helps to maintain blood iron within the normal range by limiting absorption from the small intestine and controlling release from the liver, spleen and bone marrow. Hepcidin production increases in iron overload and decreases in iron deficiency. Absorption of iron can be as low as 2 per cent in a person with GI disease or as high as 35 per cent in a rapidly growing, healthy child. The body adapts to absorb more iron when a person’s iron stores fall short or when the need increases for any reason (such as pregnancy). The body makes more mucosal transferrin to absorb more iron from the intestines and more blood transferrin to carry more iron around the body. Similarly, when iron stores are sufficient, the body adapts to absorb less iron.
Iron transport and storage The blood transport protein transferrin delivers iron to the bone marrow and other tissues. The bone marrow uses large quantities to make new red blood cells, whereas other tissues use less. Surplus iron is stored in the protein ferritin, primarily in the liver, but also in the bone marrow and spleen. When dietary iron has been plentiful, ferritin is constantly and rapidly made and broken down, providing an ever-ready supply of iron. When iron concentrations become abnormally high, the liver converts some ferritin into another storage protein called haemosiderin. Haemosiderin releases iron more slowly than ferritin does. By storing excess iron, the body protects itself: free iron acts as a free radical, attacking cell lipids, DNA and protein.
The average red blood cell lives about four months; then the spleen and liver cells remove it from the blood, take it apart and prepare the degradation products for excretion or recycling. The iron is salvaged – the liver attaches it to blood transferrin, which transports it back to the bone marrow to be reused in making new red blood cells. Thus, although red blood cells live for only about four months, the iron recycles through each new generation of cells (see Figure 13.3). The body loses some iron daily via the GI tract and, if bleeding occurs, in blood. Only tiny amounts of iron are lost in urine, sweat and shed skin. Adults lose about 1 milligram of iron per day. Women lose additional iron in menses. Menstrual losses vary considerably, but over a month they average about 0.5 milligrams per day.
Iron deficiency
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Iron recycling
This chilli dinner provides several factors that may enhance iron absorption: haem and non-haem iron and MFP from meat, non-haem iron from legumes, and vitamin C from tomatoes.
Iron deficiency is the most common and widespread nutritional disorder in the world. As well as affecting a large number of children and women in developing countries, it is the only nutrient deficiency that is also significantly prevalent in industrialised countries. The numbers are huge: almost two billion people – over 30 per cent of the world’s population – have anaemia, many due to iron deficiency, and in many developing areas of the world this is frequently exacerbated by infectious diseases.5 Iron deficiency is also relatively common among those who are overweight and obese. The association between iron deficiency and obesity has yet to be explained, but researchers are currently examining the relationships between the inflammation, hepcidin, and reduced iron absorption.6 Preventing and correcting iron deficiency are high priorities. Depletion of iron stores and iron deficiency occur in all age groups, particularly in groups of the population such as children, women after the onset of menstruation, elderly
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FIGURE 13.3 Iron recycled in the body Once iron enters the body, most of it is recycled. Some is lost with body tissues and must be replaced by eating iron-containing food. Some losses via sweat, skin, and urine
Transferrin carries iron in blood. Some iron delivered to myoglobin of muscle cells
Liver (and spleen) dismantles red blood cells, packages iron into transferrin, and stores excess iron in ferritin (and haemosiderin).
Some losses if bleeding occurs
Bone marrow incorporates iron into haemosiderin of red blood cells and stores excess iron in ferritin (and haemosiderin).
Iron-containing haemoglobin in red blood cells carries oxygen.
people, vegetarians (especially vegans) and in disadvantaged populations such as Indigenous Australians, refugees, recent migrants and institutionalised people. Preventing and correcting iron deficiency are high priorities. Groups with high risk for iron deficiency include: • women in their reproductive years • pregnant women • infants and young children • teenagers.
The iron content of blood is about 50 mg/100 mL blood. A person donating 500 mL of blood loses about 250 mg of iron. The stages of iron deficiency are: • iron stores diminish • transport iron decreases • haemoglobin production declines.
Vulnerable stages of life Some stages of life demand more iron but provide less, making deficiency likely. Women in their reproductive years are especially prone to iron deficiency because of repeated blood losses during menstruation. Pregnancy demands additional iron to support the added blood volume, growth of the foetus and blood loss during childbirth. Infants and young children receive little iron from their high-milk diets, yet need extra iron to support their rapid growth. The rapid growth of adolescence, especially for males, and the menstrual losses of females, also demand extra iron that a typical teen diet may not provide. An adequate iron intake is especially important during these stages of life.
Blood losses Bleeding from any site incurs iron losses. In some cases, such as an active ulcer, the bleeding may not be obvious, but even small chronic blood losses significantly deplete iron reserves. In developing countries, blood loss is often brought on by malaria and parasitic infections of the GI tract. People who donate blood regularly also incur losses and may benefit from iron supplements. As mentioned, menstrual losses can be considerable as they tap women’s iron stores regularly.
Assessment of iron deficiency Iron deficiency develops in stages. This section provides a brief overview of how to detect these stages, and Appendix E provides more details. In the first stage of iron deficiency, iron stores diminish. Measures of serum ferritin (in the blood) reflect iron stores and are most valuable in assessing iron status at this earliest stage.
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The second stage of iron deficiency is characterised by a decrease in transport iron: serum iron falls, and the iron-carrying protein transferrin increases (an adaptation that enhances iron absorption). Together, measurements of serum iron and transferrin can determine the severity of the deficiency – the more transferrin and the less iron in the blood, the more advanced the deficiency is. Transferrin saturation – the percentage of transferrin that is saturated with iron – decreases as iron stores decline. The third stage of iron deficiency occurs when the lack of iron limits haemoglobin production. Now the haemoglobin precursor, erythrocyte protoporphyrin, begins to accumulate as haemoglobin and haematocrit values decline. Haemoglobin and haematocrit tests are easy, quick and inexpensive, so they are the tests most commonly used in evaluating iron status. Their usefulness in detecting iron deficiency is limited, however, because they are late indicators. Furthermore, other nutrient deficiencies and medical conditions can influence their values.
Iron deficiency and anaemia
Iron deficiency and iron-deficiency anaemia are not the same: people may be iron-deficient without being anaemic. The term iron deficiency refers to depleted body iron stores without regard to the degree of depletion or to the presence of anaemia. The term iron-deficiency anaemia refers to the severe depletion of iron stores that results in a low haemoglobin concentration. In iron-deficiency anaemia, haemoglobin synthesis decreases, resulting in red blood cells that are pale (hypochromic) and small (microcytic), as shown in Figure 13.4. These cells can’t carry enough oxygen from the lungs to the tissues. Without adequate iron,
Iron-deficiency anaemia is a microcytic hypochromic anaemia. • micro = small • cytic = cell • hypo = too little • chrom = colour
FIGURE 13.4 Normal blood cells and blood cells in iron-deficiency anaemia compared Normal red blood cell production
In iron deficiency
DNA synthesis and cell division begins
Haemoglobin synthesis begins
Haemoglobin synthesis intensifies, slowing DNA synthesis and cell division
Without iron, haemoglobin synthesis is impaired
Nucleus migrates to cell wall
Nucleus and all cell organelles leave the cell
© Cengage
Mature red blood cells are small, containing only cytoplasm packed with haemoglobin
Red blood cells in iron-deficiency anaemia are relatively smaller (microcytic) and pale (hypochromic)
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energy metabolism in the cells falters. The result is fatigue, weakness, headaches, apathy, pallor and poor resistance to cold temperatures. Because haemoglobin is the bright red pigment of the blood, the skin of a fair person who is anaemic may become noticeably pale. In a darkskinned person, the tongue and eye lining, normally pink, are very pale. The fatigue that accompanies iron-deficiency anaemia differs from the tiredness a person experiences from a simple lack of sleep. People with anaemia feel fatigue only when they exert themselves. Iron supplementation can relieve the fatigue and improve the body’s response to physical activity. (The iron needs of physically active people and the special iron deficiency known as sports anaemia are discussed in Chapter 14.)
Iron deficiency and pica A curious behaviour seen in some iron-deficient people, especially in women and children of low-income groups, is pica – an appetite for ice, clay, paste and other non-food substances. These substances contain no iron and cannot remedy a deficiency; in fact, clay actually inhibits iron absorption, which may explain the iron deficiency that accompanies such behaviour. Pica is poorly understood. Its cause is unknown, but researchers hypothesise that it may be motivated by hunger, nutrient deficiencies, or an attempt to protect against toxins or microbes. The consequence of pica is anaemia.
Iron toxicity In general, even a diet that includes fortified foods poses no special risk for iron toxicity. The body normally absorbs less iron when its stores are full, but some individuals are poorly defended against excess iron. Once considered rare, iron overload has emerged as an important disorder of iron metabolism and regulation.
Iron overload
The iron overload disorder known as haemochromatosis is usually caused by a genetic failure to prevent unneeded iron in the diet from being absorbed. Haemochromatosis is one of the most common hereditary diseases. Around one in 300 people have a genetic predisposition to this disease. Recent research suggests that, just as insulin supports normal glucose homeostasis and its absence or ineffectiveness causes diabetes, the hormone hepcidin supports iron homeostasis and its absence or ineffectiveness causes haemochromatosis. Other causes of iron overload include repeated blood transfusions (which bypass the intestinal defence), massive doses of supplementary iron (which overwhelm the intestinal defence) and other rare metabolic disorders. Excess iron may cause haemosiderosis, a condition characterised by deposits of the iron storage protein haemosiderin in the liver, heart, joints and other tissues. Some of the signs and symptoms of iron overload are similar to those of iron deficiency: apathy, lethargy and fatigue. Therefore, taking iron supplements before assessing iron status is clearly unwise; haemoglobin tests alone would fail to make the distinction because excess iron accumulates in storage. Iron overload assessment tests measure transferrin saturation and serum ferritin. Iron overload is characterised by tissue damage, especially in iron-storing organs such as the liver. Infections are likely because bacteria thrive on iron-rich blood. Symptoms are most severe in alcohol abusers because alcohol damages the intestine, further impairing its defences against absorbing excess iron. Untreated haemochromatosis increases the risks of diabetes, liver cancer, heart disease and arthritis. Iron overload is more common in men than in women and is twice as prevalent among men as is iron deficiency. The widespread fortification of foods with iron makes it difficult for people with haemochromatosis to follow a low-iron diet, and greater dangers lie in the indiscriminate use of iron and vitamin C supplements. Vitamin C not only enhances iron absorption but also releases iron from ferritin, allowing free iron to wreak the damage typical of free radicals. Thus, vitamin C acts as a pro-oxidant when taken in high doses.
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Iron poisoning Large doses of iron supplements cause GI distress, including constipation, nausea, vomiting and diarrhoea. These effects may not be as serious as other consequences of iron toxicity, but they are consistent enough to establish an UL of 45 milligrams per day for adults. Ingestion of iron-containing supplements remains a leading cause of accidental poisoning in small children. Symptoms of toxicity include nausea, vomiting, diarrhoea, a rapid heartbeat, a weak pulse, dizziness, shock and confusion. As few as five iron tablets containing as little as 200 milligrams of iron have caused the deaths of dozens of young children. The exact cause of these deaths is uncertain, but excessive free-radical damage is thought to play a role in heart failure and respiratory distress. Autopsy reports reveal iron deposits and cell death in the stomach, small intestine, liver and blood vessels (which can cause internal bleeding). Keep iron-containing tablets out of the reach of children. If you suspect iron poisoning, call the nearest poison control centre or a doctor immediately.
Iron recommendations and sources To obtain enough iron, people must first select iron-rich foods and then take advantage of factors that maximise iron absorption. This discussion begins by identifying iron-rich foods and then reviews the factors affecting absorption.
Recommended iron intakes The recommended daily intake for men is 8 milligrams. Women in their reproductive years, however, need 18 milligrams a day. Because women have higher iron needs and lower energy needs, they sometimes have trouble obtaining enough iron. On average, Australian adult women consume only 10 milligrams of iron per day, which is not enough iron for women until after menopause.7 To meet their iron needs from foods, premenopausal women need to select iron-rich foods at every meal. Vegetarians need 80 per cent more iron in their diet than meat eaters to make up for the low bioavailability typical of their diets.8 To maximise iron absorption, vegetarians should incorporate iron-rich foods into their diet. Good food sources of iron include green leafy vegetables, peas and whole grains, enriched cereals, dried fruit (such as apricots and sultanas) and legumes. Combining these foods with foods high in vitamin C helps the body absorb the iron.
Iron in foods
Figure 13.5 shows the amounts of iron in selected foods. Meats, fish and poultry contribute the most iron per serving; other protein-rich foods such as legumes and eggs are also good sources. Although an indispensable part of the diet, foods in the milk group are notoriously poor in iron. Grain products vary, with wholegrain, enriched and fortified breads and cereals contributing significantly to iron intakes. Finally, dark greens (such as broccoli) and dried fruits (such as sultanas) contribute some iron.
Iron-fortified foods
PUTTING COMMON SENSE TO THE TEST
Vegetarians require the same amount of iron in their diet as meat eaters. FALSE
To calculate the RDI for vegetarians, multiply by 1.8: • 8 mg × 1.8 = 14 mg/day (vegetarian men) • 18 mg × 1.8 = 32 mg/day (vegetarian women, 19 to 50 years).
Iron is one of the fortification nutrients for grain products. One serving of fortified bread or cereal provides only a little iron, but because people eat many servings of these foods, the contribution can be significant. Iron added to foods is not absorbed as well as naturally occurring iron, but when eaten with absorption-enhancing foods, fortified iron can make a difference. In cases of iron overload, fortification may exacerbate the problem.
Maximising iron absorption In general, the bioavailability of iron is high in meats, fish and poultry, intermediate in grains and legumes, and low in most vegetables, especially those containing oxalates, such as spinach. The amount of iron ultimately absorbed from a meal depends on the combined effects of several enhancing and inhibiting factors. For maximum absorption of non-haem iron, eat
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FIGURE 13.5 Iron in selected foods See the ‘How to’ section on page 336 for more information on using this figure. Milligrams Food
Serving size (kilojoules)
Bread, whole wheat Cornflakes Spaghetti pasta Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg Excellent sources: Oysters, canned Beef liver Parsley
30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ) 1 25 cm-round (983 kJ) 1 ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ) 1 medium baked w/skin (559 kJ) 1 ⁄2 cup (130 kJ) 1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ)
0
2
4
6
8
10
12
14
16
18
RDI for women 19–50
RDI for women 51+
RDI for men IRON Meats (brown), legumes (dark blue) and some vegetables (green) make the greatest contributions of iron to the diet.
Key: Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Best sources per kilojoule
85 g (525 kJ) 85 g fried (773 kJ) 1 cup raw (92 kJ)
meat for MFP and fruits or vegetables for vitamin C. The iron of baked beans, for example, will be enhanced by the MFP in a slice of ham served with them. The iron of bread will be enhanced by the vitamin C in a slice of tomato on a sandwich.
Iron contamination and supplementation In addition to the iron from foods, contamination iron from non-food sources of inorganic iron salts can contribute to the day’s intakes. People can also get iron from supplements.
Contamination iron Foods cooked in iron cookware take up iron salts. The more acidic the food and the longer it is cooked in iron cookware, the higher the iron content. The iron content of eggs can triple in the time it takes to scramble them in an iron frying pan. Admittedly, the absorption of this iron may be poor (perhaps only 1 to 2 per cent), but every little bit helps a person who is trying to increase iron intake.
Iron supplements People who are iron deficient may need supplements as well as an iron-rich, absorption-enhancing diet. Many doctors routinely recommend iron supplements to pregnant women, infants and
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young children. Iron from supplements is less well absorbed than that from food, so the doses must be high. The absorption of iron taken as ferrous sulphate or as an iron chelate is better than that from other iron supplements. Absorption also improves when supplements are taken between meals, at bedtime on an empty stomach and with liquids (other than milk, tea or coffee, which inhibit absorption). Taking iron supplements in a single dose instead of several doses per day is equally effective and may improve a person’s willingness to take it regularly. There is no benefit to taking iron supplements with orange juice because vitamin C does not enhance absorption from supplements as it does from foods. (Vitamin C enhances iron absorption by converting insoluble ferric iron in foods to the more soluble ferrous iron, and supplemental iron is already in the ferrous form.) Constipation is a common side effect of iron supplementation; drinking plenty of water may help to relieve this problem.
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An old-fashioned iron skillet adds iron to foods.
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Most of the body’s iron is in haemoglobin and myoglobin where it carries oxygen for use in energy metabolism; some iron is also required for enzymes involved in a variety of reactions. Special proteins assist with iron absorption, transport and storage – all helping to maintain an appropriate balance, because both too little and too much iron can be damaging. Iron deficiency is most common among infants and young children, teenagers, women of child-bearing age and pregnant women. Symptoms include fatigue and anaemia. Iron overload is most common in men. Haem iron, which is found only in meat, fish and poultry, is better absorbed than non-haem iron, which occurs in most foods. Non-haem iron absorption is improved by eating iron-containing foods with foods containing the MFP factor and vitamin C; absorption is limited by phytates and oxalates. The summary table presents a few iron facts.
Iron RDI Men: 8 mg/day Women: • 18 mg/day (19–50 years) • 8 mg/day (51+ years) UPPER LEVEL (UL) Adults: 45 mg/day CHIEF FUNCTIONS IN THE BODY Part of the protein haemoglobin, which carries oxygen in the blood; part of the protein myoglobin in muscles, which makes oxygen available for muscle contraction; necessary for the utilisation of energy as part of the cells’ metabolic machinery SIGNIFICANT SOURCES Red meats, fish, poultry, shellfish, eggs, legumes, dried fruits DEFICIENCY SYMPTOMS Anaemia: weakness, fatigue, headaches; impaired work performance and cognitive function; impaired immunity; pale skin, nailbeds, mucous membranes and palm creases; concave nails; inability to regulate body temperature; pica TOXICITY SYMPTOMS GI distress Iron overload: infections, fatigue, joint pain, skin pigmentation, organ damage
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Reminder: A cofactor is a substance that works with an enzyme to facilitate a chemical reaction. Metalloenzymes that require zinc include those that: • help make parts of the genetic materials DNA and RNA • manufacture haem for haemoglobin • participate in essential fatty acid metabolism • release vitamin A from liver stores • metabolise carbohydrates • synthesise proteins • metabolise alcohol in the liver • dispose of damaging free radicals.
13.3 Zinc
Zinc is a versatile trace element required as a cofactor by more than 100 enzymes. Virtually all cells contain zinc, but the highest concentrations are found in muscle and bone.
Zinc roles in the body Zinc supports the work of numerous proteins in the body such as the metalloenzymes, which are involved in a variety of metabolic processes, including the regulation of gene expression. Among the metalloenzymes requiring zinc are carbonic anhydrase, deoxythymidine kinase, DNA and RNA polymerase, and alkaline phosphatase. In addition, zinc stabilises cell membranes, helping to strengthen their defence against free-radical attacks. Zinc also assists in immune function and in growth and development. Zinc participates in the synthesis, storage and release of the hormone insulin in the pancreas, although it does not appear to play a direct role in insulin’s action. Zinc interacts with platelets in blood clotting, affects thyroid hormone function, and influences behaviour and learning performance. It is needed to produce the active form of vitamin A (retinal) in visual pigments and the retinol-binding protein that transports vitamin A. It is essential for normal taste perception, wound healing, sperm production and foetal development. A zinc deficiency impairs all these and other functions, underlining the vast importance of zinc in supporting the body’s proteins.
Zinc absorption and metabolism The body’s handling of zinc resembles that of iron in some ways and differs in others. A key difference is the circular passage of zinc from the intestine to the body and back again.
Zinc absorption The rate of zinc absorption varies from about 15 to 40 per cent, depending on a person’s zinc status – if more is needed, more is absorbed. Also, dietary factors influence zinc absorption. For example, phytates bind zinc, thus limiting its bioavailability. Upon absorption into an intestinal cell, zinc has two options. It may become involved in the metabolic functions of the cell itself or, alternatively, it may be retained within the cell by metallothionein, a special binding protein similar to the iron storage protein, mucosal ferritin. Metallothionein in the intestinal cells helps to regulate zinc absorption by holding it in reserve until the body needs zinc. Then metallothionein releases zinc into the blood, where it can be transported around the body. Metallothionein in the liver performs a similar role, binding zinc until other body tissues signal a need for it.
Zinc transport After being absorbed, some zinc eventually reaches the pancreas, where it is incorporated into many of the digestive enzymes that the pancreas releases into the intestine at mealtimes. The intestine thus receives two doses of zinc with each meal – one from foods and the other from the zinc-rich pancreatic secretions. The recycling of zinc in the body from the pancreas to the intestine and back to the pancreas is referred to as the enteropancreatic circulation of zinc. As this zinc circulates through the intestine, it may be excreted in shed intestinal cells or absorbed into the body on any of its times around (see Figure 13.6). The body loses zinc primarily in faeces. Smaller losses occur in urine, shed skin, hair, sweat, menstrual fluids and semen. Zinc’s main transport vehicle in the blood is the protein albumin. Some zinc also binds to transferrin – the same transferrin that carries iron in the blood. In healthy individuals, transferrin is usually less than 50 per cent saturated with iron, but in iron overload, it is more
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FIGURE 13.6 Enteropancreatic circulation of zinc Some zinc from food is absorbed by the small intestine and sent to the pancreas to be incorporated into digestive enzymes that return to the small intestine. This cycle is called the enteropancreatic circulation of zinc.
Zinc in food
Mucosal cells in the intestine store excess zinc in metallothionein. The pancreas uses zinc to make digestive enzymes and secretes them into the intestine.
If the body does not need zinc
Zinc is not absorbed and is excreted in shed intestinal cells instead. Thus, zinc absorption is reduced when the body does not need zinc.
If the body needs zinc
Metallothionein releases zinc to albumin and transferrin for transport to the rest of the body.
saturated. Diets that deliver more than twice as much iron as zinc leave too few transferrin sites available for zinc. The result is poor zinc absorption. The converse is also true: large doses of zinc inhibit iron absorption.
Zinc deficiency Severe zinc deficiencies are not widespread in industrialised countries in the absence of other diseases, but they can still occur in vulnerable groups – pregnant women, young children, the elderly and the poor. Human zinc deficiency was first reported in the 1960s in children and adolescent boys in Egypt, Iran and Turkey. Children have especially high zinc needs because they are growing rapidly and synthesising many zinc-containing proteins, and the native diets among those populations were not meeting these needs. Middle Eastern diets are typically low in the richest zinc source, meats, and the staple foods are legumes, unleavened breads and other wholegrain foods – all high in fibre and phytates, which inhibit zinc absorption. Unleavened bread contains no yeast, which normally breaks down phytates during fermentation. Figure 13.7 shows the severe growth retardation and mentions the immature sexual development characteristic of zinc deficiency. In addition, zinc deficiency hinders digestion and absorption, causing diarrhoea, which worsens malnutrition not only for zinc but for all nutrients. It also impairs the immune response, making infections likely – among them GI tract infections, which worsen malnutrition, including zinc malnutrition (a classic downward spiral of events).9 Chronic zinc deficiency damages the central nervous system and brain and may lead to poor motor development and cognitive performance. Because zinc deficiency directly impairs vitamin A metabolism, vitamin A-deficiency symptoms often appear. Zinc deficiency also disturbs thyroid function and the metabolic rate. It alters taste, causes loss of appetite and slows wound healing – in fact, its symptoms are so pervasive that generalised malnutrition and sickness are more likely to be the diagnosis than simple zinc deficiency.
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PUTTING COMMON SENSE TO THE TEST
Zinc deficiency is common in industrialised countries. FALSE
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FIGURE 13.7 Zinc-deficiency symptom – stunted growth The growth retardation known as dwarfism is rightly ascribed to zinc deficiency because it is partially reversible when zinc is restored to the diet.
Zinc toxicity High doses (over 50 milligrams) of zinc may cause vomiting, diarrhoea, headaches, exhaustion and other symptoms. A UL for adults was set at 40 milligrams based on zinc’s interference in copper metabolism – an effect that, in animals, leads to degeneration of the heart muscle.
Zinc recommendations and sources Figure 13.8 shows zinc amounts in foods per serving. Zinc is highest in protein-rich foods such as shellfish (especially oysters), meats, poultry, milk and cheese. Legumes and wholegrain products are good sources of zinc if eaten in large quantities. The requirement for dietary zinc may be as much as 50 per cent greater for vegetarians, particularly strict vegetarians whose major staples are grains and legumes.
H. Sanstead, University of Texas at Galveston
Zinc supplementation
The Egyptian man on the right is an adult of average height. The Egyptian boy on the left is 17 years old but is only 4 feet tall, like a seven-year-old in the United States. His genitalia are like those of a six-year-old.
In industrialised countries, most people obtain enough zinc from the diet without resorting to supplements. In developing countries, zinc supplements play a major role in the treatment of childhood infectious diseases. Zinc supplements effectively reduce the incidence of disease and death associated with diarrhoea and pneumonia.10 The use of zinc lozenges to treat the common cold has been controversial and inconclusive, with some studies finding them effective and others not. Lozenges of zinc acetate or zinc gluconate seem to be the most effective, whereas other zinc compounds, including those with flavour enhancers, are much less effective. Common side effects of zinc lozenges include nausea and bad taste reactions.
APPLICATIONS OF NUTRITIONAL RESEARCH Despite the popularity of zinc supplements, controversy over their effectiveness in treating the common cold has raged for decades. In a recent systematic review and meta-analysis, researchers attempted to sort through the confusion. A review of data from seven clinical trials suggests that zinc supplements given within hours of onset of the symptoms of a cold can reduce the duration and severity of the illness by a third.11 There was no evidence that zinc doses over 100 mg/day can lead to greater benefit in the treatment of the common cold with most trials using doses in the range of 80 to 92 mg. Both zinc acetate and zinc gluconate formulations showed a benefit with a slight, nonsignificant greater benefit seen with the zinc acetate form. Even with the positive findings from this review, because of the differences in study populations, dosages, formulations and duration of treatment, it is difficult at this stage to make firm recommendations about the dose, formulation and duration that should be used for the general public.
Polara Studios, Inc.
Zinc and the common cold
Zinc is highest in protein-rich foods such as oysters, beef, poultry, legumes and nuts.
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FIGURE 13.8 Zinc in selected foods See the ‘How to’ box on page 336 for more information on using this figure. Milligrams Food
Serving size (kilojoules)
Bread, whole wheat Cornflakes Spaghetti pasta
30 g slice (294 kJ) 30 g (462 kJ) 1 ⁄2 cup cooked (416 kJ)
0
2
4
6
8
10
12
RDI for men
1 25 cm-round (983 kJ) ⁄2 cup cooked (92 kJ) 1 ⁄2 cup shredded raw (101 kJ)
Tortilla, flour Broccoli Carrots Potato Tomato juice Banana Orange Strawberries Watermelon Milk Yoghurt, plain Cheddar cheese Cottage cheese Pinto beans Peanut butter Sunflower seeds Tofu (soybean curd) Minced meat, lean Chicken breast Tuna, canned in water Egg
1 medium raw (458 kJ) 1 medium raw (260 kJ) 1 ⁄2 cup fresh (92 kJ) 1 slice (386 kJ) 1 cup reduced-fat 2% (508 kJ) 1 cup low-fat (651 kJ) 45 g (718 kJ) 1 ⁄2 cup low-fat 2% (424 kJ) 1 ⁄2 cup cooked (491 kJ) 2 tbs (790 kJ) 30 g dry (693 kJ) 1 ⁄2 cup (319 kJ) 85 g broiled (1025 kJ) 85 g roasted (588 kJ) 85 g (416 kJ) 1 hard boiled (328 kJ)
Excellent sources: Oysters Sirloin steak, lean Crab
85 g cooked (584 kJ) 85 g broiled (722 kJ) 85 g cooked (399 kJ)
1
1 medium baked w/skin (559 kJ) 3 ⁄4 cup (130 kJ)
14
RDI for women
ZINC Meat, fish and poultry (brown) are concentrated sources of zinc. Milk (white) and legumes (dark blue) contain some zinc. Key: Breads and cereals Vegetables Fruits Milk and milk products Legumes, nuts, seeds Meats Best sources per kilojoule
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Zinc-requiring enzymes participate in a multitude of reactions affecting growth, vitamin A activity and pancreatic digestive enzyme synthesis, among others. Both dietary zinc and zinc-rich pancreatic secretions (via enteropancreatic circulation) are available for absorption. Absorption is monitored by a special binding protein (metallothionein) in the intestine. Protein-rich foods derived from animals are the best sources of bioavailable zinc. Fibre and phytates in cereals bind zinc, limiting absorption. Growth retardation and sexual immaturity are hallmark symptoms of zinc deficiency. These facts and others are included in the following table.
Zinc RDI Men: 14 mg/day Women: 8 mg/day UPPER LEVEL (UL) Adults: 40 mg/day
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CHIEF FUNCTIONS IN THE BODY Part of many enzymes; associated with the hormone insulin; involved in making genetic material and proteins, immune reactions, transport of vitamin A, taste perception, wound healing, the making of sperm and the normal development of the foetus SIGNIFICANT SOURCES Protein-containing foods: red meats, shellfish, whole grains; some fortified cereals DEFICIENCY SYMPTOMSa Growth retardation, delayed sexual maturation, impaired immune function, hair loss, eye and skin lesions, loss of appetite TOXICITY SYMPTOMS Loss of appetite, impaired immunity, low HDL, copper and iron deficiencies
The ion form of iodine is called iodide. Thyroidstimulating hormone is also called thyrotropin. Examples of goitrogen-containing foods are: • cabbage, spinach, radishes, swedes • soybeans, peanuts • peaches, strawberries.
a
A rare inherited disease of zinc malabsorption, acrodermatitis, causes additional and more severe symptoms.
13.4 Iodine
Traces of the iodine ion (called iodide) are indispensable to life. In the GI tract, iodine from foods becomes iodide. This chapter uses the term iodine when referring to the nutrient in foods and iodide when referring to it in the body. Iodide occurs in the body in minuscule amounts, but its principal role in the body and its requirement are well established.
Iodide roles in the body
Iodide is an integral part of the thyroid hormones that regulate body temperature, metabolic rate, reproduction, growth, blood cell production, nerve and muscle function, and more. The thyroid gland releases tetraiodothyronine (T4), commonly known as thyroxine, to its target tissues. Upon reaching the cells, T4 is deiodinated to FIGURE 13.9 Iodine-deficiency symptom – triiodothyronine (T3) within cells by deiodinases. T3 is the active form of an enlarged thyroid the hormone and is three to four times more potent than T4.
Scott Camazine/Science Source
Iodine deficiency
In iodine deficiency, the thyroid gland enlarges – a condition known as simple goitre. Iodine toxicity also enlarges the thyroid gland, creating a similarlooking goitre.
The hypothalamus regulates thyroid hormone production by controlling the release of the pituitary’s thyroid-stimulating hormone (TSH). With iodine deficiency, thyroid hormone production declines and the body responds by secreting more TSH in a futile attempt to accelerate iodide uptake by the thyroid gland. If a deficiency persists, the cells of the thyroid gland enlarge to trap as much iodide as possible. Sometimes the gland enlarges until it makes a visible lump in the neck, a simple goitre (shown in Figure 13.9). Almost all cases of goitre are caused by iodine deficiency. A relatively small percentage of the world’s population have goitre because they regularly eat excessive amounts of foods that contain an antithyroid substance (goitrogen) whose effect is not counteracted by dietary iodine. The goitrogens present in plants remind us that even natural components of foods can cause harm when eaten in excess. Goitre may be the earliest and most obvious sign of iodine deficiency, but the most tragic and prevalent damage occurs in the brain. Children with even a mild iodine deficiency typically have goitres and perform poorly in school. With sustained treatment, however, mental performance in the classroom as well as thyroid function improve.
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Mild iodine deficiency has re-emerged in Australia and New Zealand as a major public health issue in the last 10 to 15 years. Even a mild form of iodine deficiency can give rise to hypothyroidism with symptoms of fatigue, goitre, mental impairment, depression, weight gain, and low basal body temperatures. The National Iodine Nutrition Study (a survey of iodine levels of 1709 children from 88 schools in Australia) indicated that, overall, Australian children were borderline iodine-deficient.12 There is also evidence that pregnant women are mildly iodine deficient in Australia.13 Likewise, evidence from a number of studies indicated that the iodine status of New Zealanders was declining to the point where intervention is required.14 Because of the re-emergence of iodine deficiency, from September 2009, Food Standards Australia New Zealand (FSANZ) introduced mandatory iodine fortification into the food supply using iodised salt in bread as the vehicle. Iodised salt is now added to all commercially sold bread in Australia and New Zealand, with the exception of organic and unleavened bread. A severe iodine deficiency during pregnancy causes the extreme and irreversible mental and physical retardation known as cretinism. Cretinism affects approximately 6 million people worldwide and can be averted by the early diagnosis and treatment of maternal iodine deficiency. A worldwide effort to provide iodised salt to people living in iodine-deficient areas has been dramatically successful. Because iron deficiency is common among people with iodine deficiency and because iron deficiency reduces the effectiveness of iodised salt, dual fortification with both iron and iodine may be most beneficial.
The underactivity of the thyroid gland is known as hypothyroidism and may be caused by iodine deficiency. Without treatment, an infant with congenital hypothyroidism will develop the physical and mental retardation of cretinism.
Iodine toxicity
PUTTING COMMON SENSE TO THE TEST
Excessive intakes of iodine can interfere with thyroid function and enlarge the glands, just as deficiency can. During pregnancy, exposure to excessive iodine from foods, prenatal supplements or medications is especially damaging to the developing infant. An infant exposed to toxic amounts of iodine during gestation may develop a goitre so severe as to block the airways and cause suffocation. The UL is over 1100 micrograms per day for an adult – several times higher than average intakes.
Seafood is a good source of iodine. TRUE On average, ½ teaspoon of iodised salt provides the RDI for iodine.
Iodine recommendations and sources
Craig M. Moore
The ocean is the world’s major source of iodine. In coastal areas, seafood, water and even iodine-containing sea mist are dependable iodine sources. Further inland, the amount of iodine in foods is variable and generally reflects the amount present in the soil in which plants are grown or on which animals graze. Landmasses that were once under the ocean have soils rich in iodine; those in flood-prone areas where water leaches iodine from the soil are poor in iodine. Most soils in New Zealand are low in iodine, resulting in low concentrations in locally grown foods. Some countries add iodine to bread, fish paste or drinking water instead. The recommended intake of iodine for adults is a minuscule amount. The need for iodine is easily met by consuming seafood, seaweed, dairy products, vegetables grown in iodine-rich soil and iodised salt. In Australia and New Zealand, labels indicate whether salt is iodised.
Only ‘iodised salt’ (right) has had iodine added.
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Iodide, the ion of the mineral iodine, is an essential component of thyroid hormone. An iodine deficiency can lead to simple goitre (enlargement of the thyroid gland) and can impair foetal development, causing cretinism. Iodine fortification has now been introduced into Australia and New Zealand to combat iodine deficiency. The following table provides a summary of iodine.
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Iodine RDI Adults: 150 µg/day UPPER LEVEL (UL) 1100 µg/day CHIEF FUNCTIONS IN THE BODY A component of two thyroid hormones that help to regulate growth, development and metabolic rate SIGNIFICANT SOURCES Iodised salt, seafood, seaweed, bread, dairy products, plants grown in iodine-rich soil and animals fed those plants DEFICIENCY DISEASE Simple goitre, cretinism DEFICIENCY SYMPTOMS Underactive thyroid gland, goitre, mental and physical retardation in infants (cretinism) TOXICITY SYMPTOMS Underactive thyroid gland, elevated TSH, goitre
13.5 Selenium
The essential mineral selenium shares some of the chemical characteristics of the mineral sulphur. This similarity allows selenium to substitute for sulphur in the amino acids methionine, cysteine and cystine.
Selenium roles in the body Key antioxidant nutrients are: • vitamin C, vitamin E, beta-carotene • selenium. The heart disease associated with selenium deficiency is named Keshan disease for one of the provinces of China where it was studied. Keshan disease is characterised by heart enlargement and insufficiency; fibrous tissue replaces the muscle tissue that normally composes the middle layer of the walls of the heart.
Selenium is one of the body’s antioxidant nutrients, working primarily as a part of proteins – most notably, the enzyme glutathione peroxidase. Glutathione peroxidase and vitamin E work in tandem. Glutathione peroxidase prevents free-radical formation, thus blocking the chain reaction before it begins; if free radicals do form and a chain reaction starts, vitamin E stops it. Another important role of selenium is in the conversion of thyroxine (T4) to triiodothyronine (T3) where selenium is a part of the deiodinases enzymes.
Selenium deficiency Selenium deficiency is associated with a heart disease that is prevalent in regions of China where the soil and foods lack selenium. Although the primary cause of this heart disease is probably a virus, selenium deficiency appears to predispose people to it, and adequate selenium seems to prevent it. Symptoms of selenium deficiency include impaired cognition and poor immunity. Selenium deficiency, though, is quite rare in healthy, well-nourished individuals. Deficiency has been seen in people with severely compromised intestinal function and in those of advanced age.
Selenium and cancer Some research suggests that selenium may protect against some types of cancers, though more recent findings do not support the use of this supplement in the primary prevention of cancer.15 However, given the potential for harm and the lack of conclusive evidence, recommendations to take selenium supplements would be premature – and perhaps ineffective
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Chapter 13: The trace minerals
as well. Selenium from foods appears to be more effective in inhibiting cancer growth than selenium from supplements. Such a finding reinforces a theme that has been repeated throughout this text – foods offer many more health benefits than supplements.
Selenium recommendations and sources Selenium is found in the soil, and therefore in the crops grown for consumption. Soil concentrations can range from less than 0.01 µg/g to more than 1000 µg/g with plant food content reflecting this range. People living in regions with selenium-poor soil may still get enough selenium, partly because they eat vegetables and grains transported from other regions, and partly because they eat meats and other animal products, which are reliable sources of selenium. In Australia and New Zealand, the main dietary sources of selenium are seafood, meat, poultry and eggs. New Zealand has a low soil selenium content, meaning that dietary intake of this nutrient is lower than in many other countries.
Selenium toxicity Because high doses of selenium are toxic, a UL has been set. Selenium toxicity causes loss and brittleness of hair and nails, garlic breath odour and nervous system abnormalities. Extreme cases of toxicity can result in cirrhosis of the liver, pulmonary oedema and death.
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Selenium is an antioxidant nutrient that works closely with the glutathione peroxidase enzyme and vitamin E. It is found in association with protein in foods. Deficiencies are associated with a predisposition to a type of heart abnormality known as Keshan disease. See the table below for a summary of selenium.
Selenium RDI Men: 70 µg/day Women: 60 µg/day UPPER LEVEL (UL) Adults: 400 µg/day CHIEF FUNCTIONS IN THE BODY Defends against oxidation; regulates thyroid hormone SIGNIFICANT SOURCES Seafood, meat, whole grains, fruits and vegetables (depending on soil content) DEFICIENCY SYMPTOMS Predisposition to heart disease characterised by cardiac tissue becoming fibrous (Keshan disease) TOXICITY SYMPTOMS Loss and brittleness of hair and nails; skin rash, fatigue, irritability and nervous system disorders; garlic breath odour
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13.6 Copper
The body contains about 100 milligrams of copper. It is found in a variety of cells and tissues.
Copper roles in the body Copper serves as a constituent of several enzymes. The copper-containing enzymes have diverse metabolic roles with one common characteristic: all involve reactions that consume oxygen or oxygen radicals. For example, copper-containing enzymes catalyse the oxidation of ferrous iron to ferric iron. Copper’s role in iron metabolism makes it a key factor in haemoglobin synthesis. Two copper- and zinc-containing enzymes participate in the body’s natural defence against free radicals. Still another copper enzyme helps to manufacture collagen and heal wounds. Copper, like iron, is needed in many of the metabolic reactions related to the release of energy.
Copper deficiency and toxicity Typical Australian and New Zealand diets provide adequate amounts of copper; deficiency is rare. In animals, copper deficiency raises blood cholesterol and damages blood vessels, raising questions about whether low dietary copper might contribute to cardiovascular disease in humans. Some genetic disorders create a copper toxicity, but excessive intakes from foods are unlikely. Excessive intakes from supplements may cause liver damage, and therefore a UL has been set. Two rare genetic disorders affect copper status in opposite directions. In Menkes disease, the intestinal cells absorb copper, but cannot release it into circulation, causing a lifethreatening deficiency. In Wilson disease, copper accumulates in the liver and brain, creating a life-threatening toxicity. Wilson disease can be controlled by reducing copper intake, using chelating agents such as penicillamine, and taking zinc supplements, which interfere with copper absorption. (The use of chelation in healthcare is mentioned in Highlight 18’s discussion of alternative therapies.)
Copper recommendations and sources The richest food sources of copper are legumes, whole grains, nuts, shellfish and seeds. Over half of the copper from foods is absorbed, and the major route of elimination appears to be bile. Water may also provide copper, depending on the type of plumbing pipe and the hardness of the water. The NRV Working Party found there was insufficient evidence to set a RDI for copper intake so it instead set an Adequate Intake (AI) based on median intake from Australian and New Zealand national dietary surveys.16
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Copper is a component of several enzymes, all of which are involved in some way with oxygen or oxidation. Some act as antioxidants; others are essential to iron metabolism. Legumes, whole grains and shellfish are good sources of copper. See the table below for a summary of copper facts.
Copper AI Men: 1.7 mg/day Women: 1.2 mg/day UPPER LEVEL (UL) Adults: 10 mg/day CHIEF FUNCTIONS IN THE BODY Necessary for the absorption and use of iron in the formation of haemoglobin; part of several enzymes
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Chapter 13: The trace minerals
SIGNIFICANT SOURCES Seafood, nuts, whole grains, seeds, legumes DEFICIENCY SYMPTOMS Anaemia, bone abnormalities TOXICITY SYMPTOMS Liver damage
13.7 Manganese
The human body contains a tiny 20 milligrams of manganese. Most of it can be found in the bones and metabolically active organs such as the liver, kidneys and pancreas.
Manganese roles in the body Manganese acts as a cofactor for many enzymes that facilitate the metabolism of carbohydrate, lipids and amino acids. In addition, manganese-containing metalloenzymes assist in bone formation and the conversion of pyruvate to a TCA cycle compound.
Manganese deficiency and toxicity Manganese requirements are low, and many plant foods contain significant amounts of this trace mineral, so deficiencies are rare. As is true of other trace minerals, however, dietary factors such as phytates inhibit its absorption. In addition, high intakes of iron and calcium limit manganese absorption, so people who use supplements of those minerals regularly may impair their manganese status. Toxicity is more likely to occur from an environment contaminated with manganese than from dietary intake. Miners who inhale large quantities of manganese dust over prolonged periods show symptoms of a brain disease, along with abnormalities in appearance and behaviour. The NRV Working Party did not specify a UL due to insufficient evidence to set a level with certainty.
Manganese recommendations and sources Grain products make the greatest contribution of manganese to the diet. With insufficient information to establish an RDI, an AI was set based on average intakes.
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Manganese-dependent enzymes are involved in bone formation and various metabolic processes. Because manganese is widespread in plant foods, deficiencies are rare, although regular use of calcium and iron supplements may limit manganese absorption. A summary of manganese appears in the table below.
Manganese AI Men: 5.5 mg/day Women: 5 mg/day UPPER LEVEL (UL) None specified CHIEF FUNCTIONS IN THE BODY Cofactor for several enzymes; bone formation
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SIGNIFICANT SOURCES Nuts, whole grains, leafy vegetables, tea DEFICIENCY SYMPTOMS Rare TOXICITY SYMPTOMS Nervous system disorders
13.8 Fluoride
The key bone nutrients are: • vitamin D, vitamin K, vitamin A • calcium, phosphorus, magnesium, fluoride.
Fluoride is present in virtually all soils, water supplies, plants and animals. Only a trace of fluoride occurs in the human body, but with this amount, the crystalline deposits in bones and teeth are larger and more perfectly formed.
Fluoride roles in the body
PUTTING COMMON SENSE TO THE TEST
Bottled water is a good source of fluoride. FALSE For perspective, 1 part per million (1 ppm) is approximately 1 mg/L.
To prevent fluorosis: • monitor the fluoride content of the local water supply • supervise toddlers when they brush their teeth, using only a small amount of toothpaste (pea-size amount) • use fluoride supplements only as prescribed by a doctor.
As Chapter 12 explains, during the mineralisation of bones and teeth, calcium and phosphorus form crystals called hydroxyapatite. Then fluoride replaces the hydroxyl (OH) portions of the hydroxyapatite crystal, forming fluorapatite, which makes the bones stronger and the teeth more resistant to decay. Dental caries, which can go on to progress to missing or filled teeth, rank as one of the most common and widespread health problems. By interfering with a person’s ability to chew and eat a wide variety of foods, these dental problems can quickly lead to a multitude of nutrition problems. Where fluoride is lacking, dental decay is common. Drinking water is usually the best source of fluoride. Most bottled waters lack fluoride. Fluoridation of drinking water (to raise the concentration to 1 part fluoride per 1 million parts water) offers the community, particularly children, a safe, economical, practical and effective way to defend against dental caries. The combined use of fluoride toothpaste and fluoridated water offers protection above using either separately. Both drinking water and toothpaste provide important and complementary benefits. The drinking water provides long low-level protection, but the fluoride in toothpaste is at a high enough concentration that it has additional properties. Because of the low natural levels of fluoride in some water supplies and high levels of dental caries, many authorities worldwide, including in Australia and New Zealand, have instigated fluoridation of water supplies. Concentrations in fluoridated areas are within the range identified as safe and effective, varying from 0.6 mg/L in Darwin to 1.1 mg/L in Hobart.17 In New Zealand, the Ministry of Health has recommended fluoridation of water supplies since the 1950s as the most effective and efficient way of preventing dental caries in communities receiving a reticulated water supply. In the Drinking Water Standards 2000, fluoridation is recommended at a level of 0.7–1 mg/L in drinking water. Around 85 per cent of the New Zealand population uses what the government considers to be satisfactorily safe community water supplies in terms of fluoride content.
Fluoride toxicity
Too much fluoride can damage the teeth, causing fluorosis. For this reason, a UL has been established. In mild cases, the teeth develop small white specks; in severe cases, the enamel becomes pitted and permanently stained (as shown in Figure 13.10). Fluorosis occurs only during tooth development and cannot be reversed, making its prevention a high priority. Fluorosis can also affect the skeleton, causing an increase in bone mass, joint pain and stiffness,
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Chapter 13: The trace minerals
and even deformities of the spine and major joints. To limit fluoride ingestion, take care not to swallow fluoride-containing dental products such as toothpaste and mouthwash.
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FIGURE 13.10 Fluoride-toxicity symptom – the mottled teeth of fluorosis
Fluoride recommendations and sources
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Fluoride makes bones stronger and teeth more resistant to decay. Fluoridation of public water supplies can significantly reduce the incidence of dental caries, but excess fluoride during tooth development can cause fluorosis – discoloured and pitted tooth enamel. The table below summarises fluoride information.
Dr. P. Marazzi/Science Source
Many people in Australia and New Zealand have access to water with an optimal fluoride concentration, which typically delivers about 1 milligram per person per day. Fish and most teas contain appreciable amounts of natural fluoride.
Fluoride AI Men: 4 mg/day Women: 3 mg/day UL Adults: 10 mg/day CHIEF FUNCTIONS IN THE BODY Maintains health of bones and teeth; helps to make teeth resistant to decay SIGNIFICANT SOURCES Drinking water (if fluoride-containing or fluoridated), tea, seafood DEFICIENCY SYMPTOMS Susceptibility to tooth decay TOXICITY SYMPTOMS Fluorosis (pitting and discoloration of teeth)
13.9 Chromium
Chromium is an essential mineral that participates in carbohydrate and lipid metabolism. Like iron, chromium assumes different charges. In chromium, the Cr+++ ion is the most stable and most commonly found in foods.
Chromium roles in the body Chromium helps maintain glucose homeostasis by enhancing the activity of the hormone insulin. When chromium is lacking, a diabetes-like condition may develop with elevated blood glucose and impaired glucose tolerance, insulin response and glucagon response. Some research suggests that chromium supplements lower blood glucose or improve insulin responses in type 2 diabetes, but findings have not been consistent.18
Small organic compounds that enhance insulin’s action are called glucose tolerance factors (GTF). Some glucose tolerance factors contain chromium.
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Chromium recommendations and sources Chromium is present in a variety of foods. The best sources are unrefined foods, particularly liver, brewer’s yeast and whole grains. The more refined foods people eat, the less chromium they ingest. No UL for chromium has been established.
Chromium supplements Supplement advertisements have succeeded in convincing consumers that they can lose fat and build muscle by taking chromium picolinate. Whether chromium supplements (either picolinate or plain) reduce body fat or improve muscle strength remains controversial. (Highlight 14 revisits chromium picolinate and other supplements athletes use in the hopes of improving their performance.)
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Chromium enhances insulin’s action. A deficiency can result in a diabetes-like condition. Chromium is widely available in unrefined foods including brewer’s yeast, whole grains and liver. The following table provides a summary of chromium.
Chromium AI Men: 35 µg/day Women: 25 µg/day UPPER LEVEL (UL) None specified CHIEF FUNCTIONS IN THE BODY Enhances insulin action and may improve glucose tolerance SIGNIFICANT SOURCES Meats (especially liver), whole grains, brewer’s yeast DEFICIENCY SYMPTOMS Diabetes-like condition (impaired glucose tolerance) TOXICITY SYMPTOMS None reported
13.10 Molybdenum
Molybdenum acts as a working part of several metalloenzymes. Dietary deficiencies of molybdenum are unknown because the amounts needed are minuscule – as little as 0.1 parts per million parts of body tissue. Legumes, breads and other grain products, leafy green vegetables, milk and liver are molybdenum-rich foods. Average daily intakes fall within the suggested range of intakes. Molybdenum toxicity in people is rare. It has been reported in animal studies, and an UL has been established. Characteristics of molybdenum toxicity include kidney damage and reproductive abnormalities. For a summary of molybdenum facts, see the accompanying table. REVIEW IT
Molybdenum RDI Adults: 45 µg/day
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UPPER LEVEL (UL) Adults: 2000 µg/day CHIEF FUNCTIONS IN THE BODY Cofactor for several enzymes SIGNIFICANT SOURCES Legumes, cereals, nuts DEFICIENCY SYMPTOMS Unknown TOXICITY SYMPTOMS None reported; reproductive effects in animals
13.11 Other trace minerals
Research to determine whether other trace minerals are essential is difficult because their quantities in the body are so small and also because human deficiencies are unknown. Guessing their functions in the body can be particularly problematic. Much of the available knowledge comes from research using animals. Some important trace minerals and their main functions include the following: • Nickel may serve as a cofactor for certain enzymes. • Silicon is involved in the formation of bones and collagen. FIGURE 13.11 Cobalt with vitamin B12 • Vanadium is necessary for growth and bone development and for The intricate vitamin B12 molecule contains normal reproduction. one atom of the mineral cobalt. The alternative • Cobalt is a key mineral in the large vitamin B12 molecule (see Figure name for vitamin B12, cobalamin, reflects the 13.11), but it is not an essential nutrient and no recommendation has presence of cobalt in its structure. been established. • Boron may play a key role in brain activities; in animals, boron NH2 strengthens bones. C O CN NH2 In the future, we may discover that many other trace minerals play key H N nutritional roles. Even arsenic – famous as a poison used by murderers and 2 CH2 C O NH2 CH3 known to be a carcinogen – may turn out to be essential for human beings O C CH2 H3C CH2 C O in tiny quantities. HC 2
Contaminant minerals
H3C H3C
N
N Co+
CH2 CH2 H H
N N Chapter 12 and this chapter have told of the many ways minerals serve H O CH3 the body – maintaining fluid and electrolyte balance, providing structural C H2C CH3 support to the bones, transporting oxygen and assisting enzymes. In CH2 CH2 CH2CH3 NH2 contrast to the minerals that the body requires, contaminant minerals CH3 CH C O 2 impair the body’s growth, work capacity and general health. Contaminant CH3 C O NH2 minerals include the heavy metals lead, mercury and cadmium that enter the food supply by way of soil, water and air pollution. This section CH CH2 NH focuses on lead poisoning because it is a serious environmental threat O O– to young children. Much of the information on lead applies to the other H P + CH3 N contaminant minerals as well – they all disrupt body processes and impair H O O OH nutrition status similarly. N H CH3 Lead typifies the ways all heavy metals behave in the body: they interfere H H H with nutrients that are trying to do their jobs. The ‘good guy’ nutrients are H CH2 O pushed aside by the ‘bad guy’ contaminants. Then, when the contaminants OH
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Understanding nutrition
cannot perform the roles of the nutrients, health diminishes. To safeguard our health, we must defend ourselves against contamination by eating nutrient-rich foods and preserving a clean environment.
Lead Like other minerals, lead is indestructible; the body cannot change its chemistry. Chemically similar to nutrient minerals such as iron, calcium and zinc (cations with two positive charges), lead displaces them from some of the metabolic sites they normally occupy, but is then unable to perform their roles. For example, lead competes with iron in haem, but it cannot carry oxygen. Similarly, lead competes with calcium in the brain, but it cannot signal messages from nerve cells. Excess lead in the blood also deranges the structure of red blood cell membranes, making them leaky and fragile. Lead interacts with white blood cells, too, impairing their ability to fight infection, and it binds to antibodies, thwarting their effort to resist disease. In addition to its effects on the blood, lead impairs many body systems, most notably causing irreversible damage to the central nervous system.19 In short, lead’s interactions in the body have profound adverse effects – the greater the exposure, the more damaging the effects. Table 13.1 lists symptoms of lead toxicity.
TABLE 13.1 Symptoms of lead toxicity IN CHILDREN • Learning disabilities (reduced short-term memory; impaired concentration) • Low IQ • Behaviour problems • Slow growth • Iron-deficiency anaemia • Dental caries • Sleep disturbances (night-waking, restlessness, head-banging) • Nervous system disorders, seizures • Slow reaction time, poor coordination • Impaired hearing IN ADULTS • Hypertension • Reproductive complications • Kidney failure
Closing thoughts on the nutrients This chapter completes the introductory lessons on the nutrients. Each nutrient from the amino acids to zinc has been described rather thoroughly – its chemistry, roles in the body, sources in the diet, symptoms of deficiency and toxicity, and influences on health and disease. Such a detailed examination is informative, but it can also be misleading. It is important to step back from the detailed study of the individual nutrients to look at them as a whole. After all, people eat foods, not nutrients, and most foods deliver dozens of nutrients. Furthermore, nutrients work cooperatively with each other in the body; their actions are most often interactions. This chapter alone mentioned how iron depends on vitamin C to keep it in its active form and on copper to incorporate it into haemoglobin, how zinc is needed to activate and transport vitamin A, and how both iodine and selenium are needed for the synthesis of thyroid hormone. The accompanying summary table condenses the information on the trace minerals for your review.
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Chapter 13: The trace minerals
MINERAL AND CHIEF FUNCTIONS
DEFICIENCY SYMPTOMS
TOXICITY SYMPTOMSa
SIGNIFICANT SOURCES
IRON Part of the protein haemoglobin, which carries oxygen in the blood; part of the protein myoglobin in muscles, which makes oxygen available for muscle contraction; necessary for energy metabolism
Anaemia: weakness, fatigue, headaches; impaired work performance; impaired immunity; pale skin, nail beds, mucous membranes and palm creases; concave nails; inability to regulate body temperature; pica
GI distress; iron overload: infections, fatigue, joint pain, skin pigmentation, organ damage
Red meats, fish, poultry, shellfish, eggs, legumes, dried fruits
Stunted growth, delayed sexual maturation, impaired immune function, hair loss, eye and skin lesions, loss of appetite
Loss of appetite, impaired immunity, low HDL, copper and iron deficiencies
Protein-containing foods: red meats, fish, shellfish, poultry, whole grains; fortified cereals
Underactive thyroid gland, goitre, mental and physical retardation (cretinism)
Underactive thyroid gland, elevated TSH, goitre
Iodised salt; seafood and seaweed; plants grown in iodine-rich soil and animals fed those plants
Associated with Keshan disease
Nail and hair brittleness and loss; fatigue, irritability and nervous system disorders; skin rash, garlic breath odour
Seafood, meat, whole grains, fruits and vegetables (depending on soil content)
Anaemia, bone abnormalities
Liver damage
Seafood, nuts, legumes, whole grains, seeds
Rare
Nervous symptom disorders
Nuts, whole grains, leafy vegetables, tea
Susceptibility to tooth decay
Fluorosis (pitting and discoloration) of teeth
Drinking water (if fluoridated), tea, seafood
Impaired glucose tolerance
None reported
Meats (liver), whole grains, brewer’s yeast
Unknown
None reported
Legumes, cereals, nuts
ZINC Part of insulin and many enzymes; involved in making genetic material and proteins, immune reactions, transport of vitamin A, taste perception, wound healing, sperm production and normal foetal development IODINE A component of the thyroid hormones that help to regulate growth, development and metabolic rate SELENIUM Part of an enzyme that defends against oxidation; regulates thyroid hormone COPPER Helps form haemoglobin; part of several enzymes MANGANESE Cofactor for several enzymes; bone formation FLUORIDE Maintains health of bones and teeth; confers decay resistance on teeth CHROMIUM Enhances insulin action, may improve glucose intolerance MOLYBDENUM Cofactor for several enzymes a
Acute toxicities of many minerals cause abdominal pain, nausea, vomiting and diarrhoea.
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The trace minerals
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Iron from animal foods is normally absorbed better than iron from plant foods. TRUE
Iron in the haem form, which is found in foods derived from the flesh of animals, is more absorbable than iron found in plant foods.
2 Vegetarians require the same amount of iron in their diet as meat eaters. FALSE
Because the overall bioavailability of iron from plant-based diets is less than that from mixed diets, vegetarians have 80 per cent higher requirements for dietary iron intake.
Zinc deficiency is not common in industrialised countries, but it can still occur in vulnerable groups such as infants, toddlers and the elderly.
4 Seafood is a good source of iodine. TRUE
The ocean is the world’s major source of iodine, so seafood and even seaweed are good sources of iodine.
5 Bottled water is a good source of fluoride. FALSE
Most bottled water lacks fluoride. Fluoridated drinking water is the best source of fluoride in our diet.
3 Zinc deficiency is common in industrialised countries. FALSE
NUTRITION PORTFOLIO Trace minerals from a variety of foods, especially those in the meat and meat alternative group, support many of the body’s activities. • Examine the variety in your food intake, taking particular notice of how often you include meats,
seafood, poultry or legumes, weekly. Estimate how much iron and zinc these foods provide for you. • Describe the advantages of using iodised salt. • Determine whether your community provides fluoridated water.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1
High fibre intake Iron being in a non-haem form Having low iron stores Drinking milk
7
Three-year-old boy 60-year-old woman 24-year-old woman 52-year-old man
Which provides the most absorbable iron? a b c d
85 g steak 30 g cheese 1 banana ½ cup spinach
anaemia goitre mottled teeth growth retardation
Cretinism is caused by a deficiency of: a b c d
8
albumin ferritin haemosiderin metallothionein
A classic sign of zinc deficiency is: a b c d
Which of these people has the highest requirement for iron? a b c d
4
6
Which of the following factors can enhance intestinal iron absorption? a b c d
3
haem phytates vitamin C MFP factor
The intestinal protein that helps to regulate zinc absorption is: a b c d
Iron absorption is impaired by: a b c d
2
5
iron zinc iodine selenium
Which of the following is the most important role of selenium? a b c d
Blood clotting Iron absorption Folate synthesis Antioxidant
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Chapter 13: The trace minerals
9
Fluorosis occurs when fluoride:
4
a b c d
Describe why iron recommendations vary among different age groups and sex groups? What is the rationale for these differences? (Section 13.2)
5
Describe the similarities and differences in the absorption and regulation of iron and zinc. (Sections 13.2, 13.3)
6
Describe how the symptoms of zinc deficiency in children are related to its functions. (Section 13.3)
7
Describe the principal functions of iodide, selenium, copper, manganese, fluoride, chromium and molybdenum in the body. (Sections 13.4–13.10)
8
What public health measure has been used in preventing simple goitre? What measure has been recommended for protection against tooth decay? (Sections 13.5, 13.11)
9
Discuss the importance of balanced and varied diets in obtaining the essential minerals and avoiding toxicities. (Section 13.11)
is excessive is inadequate binds with phosphorus interacts with calcium
10 Which of the following is the most important role of chromium? a b c d
Blood clotting Thiamin synthesis Enhancing insulin sensitivity Iron absorption
Review questions 1 Describe the key dietary factors that can affect iron absorption. (Section 13.2) 2
3
481
Distinguish between iron deficiency and iron-deficiency anaemia. What are the symptoms of iron-deficiency anaemia? (Section 13.2) Describe the main features of iron overload and toxicity and how these could arise. (Section 13.2)
NUTRITION CALCULATIONS Once you have mastered these examples, you will understand minerals slightly better and be prepared to examine your own food choices. Be sure to show your calculations for each problem. Answers can be found at the back of this book.
• • • • •
copper manganese fluoride chromium molybdenum.
1
2
The iron density of foods can vary widely. In the following table, calculate the iron density (divide milligrams by kilojoules) for each of the foods and rank them by their iron per 1000 kilojoule content.
For each of these minerals, note the unit of measure for recommendations: • • • •
iron zinc iodine selenium
IRON (mg)
ENERGY (kJ)
Milk, full-fat, 1 cup
0.10
357
Cheddar cheese, 30 g
0.19
479
Kale, cooked from fresh, chopped, 1 cup
1.31
184
Sweet potato, baked in skin, 1 whole
0.51
491
Lamb chop, 100 g
2.50
900
Carrots, fresh, ½ cup
0.48
147
Wholewheat bread, 1 slice
0.87
269
Green peas, cooked from frozen, ½ cup
1.26
260
Apple, 1 medium
0.38
525
Sirloin steak, lean, 115 g
3.81
958
IRON DENSITY (mg/1000 kJ)
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NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Learn more about iron and the diseases caused by over- or under consumption at the Australian Government healthdirect site: http://www.healthdirect. gov.au/iron
• Search ‘minerals’ at the Dietitians Association of Australia site: http://www.daa.asn.au • Learn more about iodine and thyroid disease from Thyroid Australian Thyroid Foundation Ltd and the Thyroid Association of New Zealand: http://www. thyroidfoundation.com.au and http://www.thyroid.org.nz/ • Learn more about lead in the environment and its effect on health from the Lead Group: http://www.lead.org.au
SEARCH ME! NUTRITION Keyword: iodine deficiency Read the article Dietary iodine: why are so many mothers not getting enough iodine? What are the consequences of iodine deficiency?
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Chapter 13: The trace minerals
13.12 PHYTOCHEMICALS AND FUNCTIONAL FOODS Chapter 13 completes the introductory discussions on the six classes of nutrients – carbohydrates, lipids, proteins, vitamins, minerals and water. In addition to these nutrients, foods contain thousands of non-nutrient compounds, including the phytochemicals. Chapter 1 introduced the phytochemicals as compounds found in plant-derived foods (phyto means plant) that have biological activity in the body. Research on phytochemicals is unfolding daily, adding to our knowledge of their roles in human health, but there are still many questions and only tentative answers. Just a few of the tens of thousands of phytochemicals have been researched at all, and only a sampling are mentioned in this Highlight – enough to illustrate their wide variety as food sources and roles in supporting health.
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HIGHLIGHT
13
example. This highlight begins with a look at some of these familiar functional foods, the phytochemicals they contain and their roles in disease prevention. Then the discussion turns to examine the most controversial of functional foods – novel foods to which phytochemicals have been added to promote health. How these foods fit into a healthy diet is still unclear.
The phytochemicals In foods, phytochemicals impart tastes, aromas, colours and other characteristics. They give chilli peppers their burning sensation, garlic its pungent flavour and tomatoes their dark red colour. In the body, phytochemicals can have profound physiological effects, acting as antioxidants, mimicking hormones and suppressing the development of diseases. Table H13.1 presents the names, possible effects and food sources of some of the better-known phytochemicals.
Tuzemka/Shutterstock.com
Defending against cancer
Vegetables are the best dietary sources of phytochemicals.
The concept that foods provide health benefits beyond those of the nutrients emerged from numerous epidemiological studies showing the protective effects of plant-based diets on cancer and heart disease. People have been using foods to maintain health and prevent disease for years, but now these foods have been given a name – they are called functional foods. As Chapter 1 explains, functional foods include all foods (whole, fortified or modified foods) that have a potentially beneficial effect on health. Much of this text touts the benefits of nature’s functional foods – grains rich in dietary fibres, fish rich in omega-3 fatty acids and fruits rich in phytochemicals, for
A variety of phytochemicals from a variety of foods appear to protect against DNA damage and defend the body against cancer. A few examples follow. Soybeans and products made from them correlate with low rates of some cancers.1 Soybeans – as well as other legumes, flaxseeds, whole grains, fruits and vegetables – are a rich source of an array of phytochemicals, among them the phytoestrogens. Because the chemical structure of these phytochemicals is similar to the steroid hormone oestrogen, they can weakly mimic or modulate the effects of oestrogen in the body. They also have antioxidant activity that appears to slow the growth of breast and prostate cancers. Soy foods appear to be most effective when consumed in moderation early and throughout life.2 However, the use of phytoestrogen supplements is ill-advised because of their much higher dosage of phytoestrogens, which may stimulate the growth of oestrogen-dependent cancers (such as breast cancer) and reduce the effectiveness of cancer treatments.3 Even the role of soy foods for breast cancer survivors is uncertain. The Cancer Council Australia does not recommend or support the use of phytoestrogen supplements for breast cancer survivors and advises that women with existing breast cancer or past breast cancer
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TABLE H13.1 Phytochemicals – their food sources and action NAME
POSSIBLE EFFECTS
FOOD SOURCES
Alkylresorcinols (phenolic lipids)
May contribute to the protective effect of grains in reducing the risks of diabetes, heart disease and some cancers
Whole-grain wheat and rye
Allicin (organosulphur compound)
Antimicrobial that may reduce ulcers; may lower blood cholesterol
Chives, garlic, leeks, onions
Capsaicin
Modulates blood clotting, possibly reducing the risk of fatal clots in heart and artery disease
Hot peppers
Carotenoids (include beta-carotene, lycopene, lutein and hundreds of related compounds)
Act as antioxidants, possibly reducing risks of cancer and other diseases
Deeply pigmented fruits and vegetables (apricots, broccoli, rockmelon, carrots, pumpkin, spinach, sweet potatoes, tomatoes)
Curcumin
Acts as an antioxidant and antiinflammatory agent; may reduce blood clot formation; may inhibit enzymes that activate carcinogens
Turmeric, a yellow-coloured spice
Flavonoids (include flavones, flavonols, isoflavones, catechins and others)
Act as antioxidants; scavenge carcinogens; bind to nitrates in the stomach, preventing conversion to nitrosamines; inhibit cell proliferation
Berries, black tea, celery, citrus fruits, green tea, olives, onions, oregano, purple grapes, purple grape juice, soybeans and soy products, vegetables, whole wheat, wine
Genistein and daidzein (isoflavones)
Phytoestrogens that inhibit cell replication in the GI tract; may reduce risk of breast, colon, ovarian, prostate and other oestrogen-sensitive cancers; may reduce cancer cell survival; may reduce risk of osteoporosis
Soybeans, soy flour, soy milk, tofu, textured vegetable protein, other legume products
Indoles (organosulphur compound)
May trigger production of enzymes that block DNA damage from carcinogens; may inhibit oestrogen action
Cruciferous vegetables such as broccoli, brussels sprouts, cabbage, cauliflower; horseradish, mustard greens, kale
Isothiocyanates (organosulphur compounds that include sulphoraphane)
Act as antioxidants; inhibit enzymes that activate carcinogens; activate enzymes that detoxify carcinogens; may reduce risk of breast cancer and prostate cancer
Cruciferous vegetables such as broccoli, brussels sprouts, cabbage, cauliflower; horseradish, mustard greens, kale
Lignans
Phytoestrogens that block oestrogen activity in cells possibly reducing the risk of cancer of the breast, colon, ovaries and prostate
Flaxseed and its oil, whole grains
Monoterpenes (including limonene)
May trigger enzyme production to detoxify carcinogens; inhibit cancer promotion and cell proliferation
Citrus fruit peels and oils
Phenolic acids
May trigger enzyme production to make carcinogens water soluble, facilitating excretion
Coffee beans, fruits (apples, blueberries, cherries, grapes, oranges, pears, prunes), oats, potatoes, soybeans
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Chapter 13: The trace minerals
TABLE H13.1
NAME
POSSIBLE EFFECTS
FOOD SOURCES
Phytic acid
Binds to minerals, preventing free-radical formation, possibly reducing cancer risk
Whole grains
Resveratrol
Acts as an antioxidant; may inhibit cancer growth; reduces inflammation, LDL oxidation and blood clot formation
Red wine, peanuts, grapes, raspberries
Saponins (glucosides)
May interfere with DNA replication, preventing cancer cells from multiplying; stimulate immune response
Alfalfa sprouts, other sprouts, green vegetables, potatoes, tomatoes
Tannins
Act as antioxidants; may inhibit carcinogen activation and cancer promotion
Black-eyed peas, grapes, lentils, red and white wine, tea
should be cautious in consuming large quantities of soy foods or phytoestrogen supplements.3 Limited evidence suggests that tomatoes may offer protection against cancers of the oesophagus, lungs, prostate and stomach. Among the phytochemicals responsible for this effect is lycopene, one of beta-carotene’s many carotenoid relatives. Lycopene is the pigment that gives apricots, guava, papaya, pink grapefruits and watermelon their red colour – and it is especially abundant in tomatoes and cooked tomato products. Lycopene is a powerful antioxidant that seems to inhibit the growth of cancer cells. Importantly, these benefits are seen when people eat foods containing lycopene. Soybeans and tomatoes are only two of the many fruits and vegetables credited with providing anticancer activity. Strong and convincing evidence shows that the risk of many cancers, and perhaps of cancer in general, decreases when diets include an abundance of fruits and vegetables.4 To that end, current recommendations urge consumers to eat five servings of vegetables and two servings of fruit a day.
Defending against heart disease Diets based primarily on unprocessed foods appear to support heart health better than those founded on highly refined foods – perhaps because of the abundance of nutrients, fibre or phytochemicals such as the flavonoids.5 Flavonoids, a large group of phytochemicals known for their health-promoting qualities, are found in whole grains, legumes, soy, vegetables, fruits, herbs, spices, teas, chocolate, nuts, olive oil and red wines. Flavonoids are powerful antioxidants that may help to protect LDL cholesterol against oxidation and reduce blood platelet stickiness, making blood clots less likely. In addition to flavonoids, fruits and vegetables are rich in carotenoids. Studies suggest that a diet rich in carotenoids may lower the risk of heart disease by decreasing inflammation and oxidative stress.6
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The phytosterols of soybeans and the lignans of flaxseed may also protect against heart disease.7 These cholesterol-like molecules are naturally found in all plants and inhibit cholesterol absorption in the body. As a result, blood cholesterol levels decline.8 These phytochemicals also seem to protect against heart disease by acting as antioxidants and lowering blood pressure.9
The phytochemicals in perspective Because foods deliver thousands of phytochemicals in addition to dozens of nutrients, researchers must be careful in giving credit for particular health benefits to any one compound. Diets rich in whole grains, legumes, vegetables, fruits and nuts seem to protect against heart disease and cancer, but identifying the specific foods or components of foods that are responsible is difficult. Each food possesses a unique array of phytochemicals – citrus fruits provide monoterpenes; grapes, resveratrol; cocoa, flavonoids; and flaxseed, lignans, to name just a few. (Review Table H13.1 for the possible effects and other food sources of these phytochemicals.) Broccoli may contain as many as 10 000 different phytochemicals – each with the potential to influence some action in the body. Beverages such as wine, spices such as oregano, and oils such as olive oil (especially virgin olive oil) contain many phytochemicals that may explain, in part, the observation that people who live in the Mediterranean region have reduced risks of heart disease and cancer. Even identifying all of the phytochemicals and their effects doesn’t answer all the questions because the actions of phytochemicals may be complementary or overlapping – which reinforces the principle of variety in diet planning. For an appreciation of the array of phytochemicals offered by a variety of fruits and vegetables, see Figure H13.1.
Functional foods Because foods naturally contain thousands of phytochemicals that are biologically active in the body,
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FIGURE H13.1 An array of phytochemicals in a variety of foods and beverages
Broccoli and broccoli sprouts contain an abundance of the cancer-fighting phytochemical sulforaphane.
An apple a day – rich in flavonoids – may protect against lung The phytoestrogens of soybeans seem to starve cancer cells and cancer. inhibit tumour growth; the phytosterols may lower blood cholesterol and protect cardiac arteries.
Garlic, with its abundant organosulphur compounds, may lower blood cholesterol and protect against stomach cancer.
The ellagic acid of strawberries may inhibit certain types of cancer.
The phytochemical resveratrol found in grapes (and nuts) protects against cancer by inhibiting cell growth and against heart disease by limiting clot formation and inflammation. The flavonoids in cocoa and chocolate defend against oxidation and reduce the tendency of blood to clot.
The monoterpenes of citrus fruits (and cherries) may inhibit cancer growth.
Flaxseed, the richest source of lignans, may prevent the spread of cancer. Spinach and other colourful vegetables contain the carotenoids lutein and zeaxanthin, which help protect the eyes against macular degeneration.
virtually all of them have some special value in supporting health. In other words, even simple, whole foods, in reality, are functional foods. Cranberries may help protect against urinary tract infections; garlic may lower blood cholesterol; and tomatoes may protect against some cancers, just to name a few examples. But that hasn’t stopped food manufacturers from trying to create functional foods as well. Functional foods rich in phytochemicals are easy to find in the fresh produce section of the supermarket; just look for the colourful fruits and vegetables (see Table H13.2). Many processed foods become functional foods when they are fortified with nutrients or enhanced with phytochemicals or herbs (sterol-enriched margarines, for example). Less frequently, an entirely new food is
Blueberries, a rich source of flavonoids, improve memory in animals.
© Courtesy of Brassica Protection Products; PhotoDisc; Eye Wire, Inc.; PhotoDisc; Shutterstock.com/Africa Studio; Shutterstock.com/Hadescom; PhotoDisc; Shutterstock; Shutterstock/Nattika; PhotoDisc; Shutterstock.com/Sarsmis; Courtesy of Flax Council of Canada; Matthew Farruggio
Craig M. Moore
Tomatoes, with their abundant lycopene, may defend against cancer by protecting DNA from oxidative damage.
The flavonoids in black tea may protect against heart disease; those in green tea may defend against cancer.
Nature offers a variety of functional foods that provide us with many health benefits.
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Chapter 13: The trace minerals
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TABLE H13.2 The colours of foods rich in phytochemicals GREEN
Alamy/D. Hurst
BLUE-PURPLE
Alamy/D. Hurst
Alamy/J.R. Bale
ORANGE-YELLOW
Alamy/D. Hurst
WHITE-BROWN
Alamy/foodfolio
RED
Anthocyanins Lycopene
Allicin Allyl sulfides
Beta-carotene Limonene
Anthocyanins Ellagic acid Phenolics
Beta-carotene Lutein Indoles
Beets Cherries Cranberries Pink grapefruit Pomegranates Radicchio Radishes Raspberries Red apples Red peppers Red potatoes Rhubarb Strawberries Tomatoes Watermelon
Bananas Brown pears Cauliflower Chives Dates Garlic Ginger Leeks Mushrooms Onions Parsnips Shallots Turnips
Apricots Carrots Lemons Mangoes Nectarines Oranges Papayas Peaches Persimmons Pineapple Pumpkin Rockmelon Squash Sweet potatoes Tangerines Yellow peppers
Black currants Blackberries Blueberries Dried plums Eggplant Elderberries Plums Purple figs Purple peppers Raisins Purple cabbage Purple grapes
Artichokes Asparagus Avocados Broccoli Brussels sprouts Cabbage Celery Cucumbers Endive Green apples Green beans Green grapes Green onions Green pears Green peppers Honeydew melon Kiwifruit Leafy greens Limes Okra Peas Rocket Snow peas Spinach Sugar snap peas Watercress Zucchini
created, as in the case of a meat substitute (trade name Quorn) made of mycoprotein – a protein derived from a fungus. This functional food not only provides dietary fibre, polyunsaturated fats and high-quality protein, but it lowers LDL cholesterol, raises HDL cholesterol, improves glucose response and prolongs satiety after a meal. Such a novel functional food raises the question – is it a food or a drug?
Foods as pharmacy Not too long ago, most of us could agree on what was a food and what was a drug. Today, functional foods blur the distinctions. They have characteristics similar to both foods and drugs, but do not fit neatly into either category.
Like drugs used to treat chronic diseases, functional foods may need to be eaten several times a day for several months or years to have a beneficial effect. Sporadic users may be disappointed in the results. Margarine enriched with 2 to 3 grams of phytosterols may reduce cholesterol by up to 15 per cent, much more than regular margarine does, but not nearly as much as the more than 30 per cent reduction seen with cholesterollowering drugs. For this reason, functional foods may be more useful for prevention and mild cases of disease than for intervention and more severe cases. Foods and drugs differ dramatically in cost as well. Functional foods such as fruits and vegetables incur no added costs, of course, but foods that have been manufactured with added phytochemicals can be expensive, costing up to six times as much as their conventional counterparts.
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The price of functional foods typically falls between that of traditional foods and medicines. In January 2013, FSANZ introduced new legislation regulating nutrition content claims and health claims on food labels and in advertisements.10 Health claims now fall into two categories. One is general level health claims that refer to a nutrient or substance in a food and its effect on a general health function – for example, calcium is good for bones and teeth. The other category is high level health claims, which refer to a nutrient or substance in a food and its relationship to a serious disease or to a biomarker of a serious disease – for example, ‘Diets high in calcium may reduce the risk of osteoporosis in people 65 years and over.’ An example of a biomarker health claim is, ‘Phytosterols may reduce blood cholesterol’. High-level health claims must be based on a food-health relationship pre-approved by FSANZ. There are currently 10 pre-approved food-health relationships for high-level health claims listed in the Standard.
Unanswered questions To achieve a desired health effect, which is the better choice: to eat a food designed to affect a body function or simply to adjust the diet? Does it make more sense to use a margarine enhanced with a phytosterol that lowers blood cholesterol or simply to limit the amount of takeaway food eaten? Is it smarter to eat eggs enriched with omega-3 fatty acids or to restrict egg consumption? Might functional foods offer a sensible solution for improving our nation’s health – if done correctly? Perhaps so, but the problem is that the food industry is moving too fast for either scientists or the Therapeutic Goods Administration to keep up. Research to determine the safety and effectiveness of these substances is still in progress. Until this work is complete, consumers are on their own in finding the answers to the following questions: • Does it work? Research is generally lacking and findings are often inconclusive. • How much does it contain? Food labels are not required to list the quantities of added phytochemicals. Even if they were, consumers have no standard for comparison and cannot deduce whether the amounts listed are a little or a lot. Most importantly, until research is complete, food manufacturers do not know what amounts (if any) are most effective – or most toxic.
• Is it safe? Functional foods can act like drugs. They contain ingredients that can alter body functions and cause allergies, drug interactions, drowsiness and other side effects. Yet, unlike drug labels, food labels do not provide instructions for the dosage, frequency or duration of treatment. • Is it healthy? Adding phytochemicals to a food does not magically make it a healthy choice. A chocolate bar may be fortified with phytochemicals, but it is still made mostly of sugar and fat. Critics suggest that the designation ‘functional foods’ may be nothing more than a marketing tool. After all, even the most experienced researchers cannot yet identify the perfect combination of nutrients and phytochemicals to support optimal health. Yet manufacturers are freely experimenting with various concoctions as if they possessed that knowledge. Is it okay for them to sprinkle phytochemicals on snack foods or confectionery and label them ‘functional’, thus implying health benefits?
Future foods Nature has elegantly designed foods to provide us with a complex array of dozens of nutrients and thousands of additional compounds that may benefit health – most of which we have yet to identify or understand. Over the years, we have taken those foods, deconstructed them and then reconstructed them in an effort to ‘improve’ them. With new scientific understandings of how nutrients – and the myriad other compounds in foods – interact with genes, we may some day be able to design foods to meet the exact health needs of each individual. Indeed, our knowledge of the human genome and of human nutrition may well merge to allow specific recommendations for individuals based on their predisposition to diet-related diseases. If the present trend continues, some day doctors or dietitians may be able to prescribe the perfect foods to enhance your health, and farmers will be able to grow them. As Highlight 19 explains, scientists have already developed gene technology to alter the composition of food crops. They can grow rice enriched with vitamin A and tomatoes containing a hepatitis vaccine, for example. It seems quite likely that foods can be created to meet every possible human need. But then, in a sense, that was largely true 100 years ago when we relied on the bounty of nature.
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HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A Which do you believe is the better choice – to eat highly processed foods that have been enhanced with phytochemicals that show evidence for a health benefit, or to choose foods that are minimally processed, close to their natural state and rich in chemicals?
(UTIs), but less is known about whether there is a good scientific case to support a similar benefit from cranberry supplements and it is unclear if there could be harm from taking such supplements. How can you determine whether a phytochemical and/or a functional food offers a safe and sensible solution to improving your health?
B There is research to support the claim that cranberries may help prevent urinary tract infections
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search ‘functional foods’ at the International Food Information Council Foundation website: http://www.foodinsight.org/
• Read about functional foods at the CSIRO Division of Food and Nutritional Sciences: http://www. foodscience.csiro.au/functional-foods.htm • Search ‘functional foods’ at the Dietitians Association of Australia site: http://www.daa.asn.au • Find out if warnings have been issued for any food ingredients at the TGA website: http://www.tga.gov.au
REFERENCES CHAPTER 1
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3
4
5 6
7
Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). M. Hoppe M, Probiotic strain Lactobacillus plantarum 299v increases iron absorption from an iron-supplemented fruit drink: a doubleisotope cross-over single-blind study in women of reproductive age, British Journal of Nutrition 14 (2015): 1195–202. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). S. Gulec, G. J. Anderson and J. F. Collins, Mechanistic and regulatory aspects of intestinal iron absorption, American Journal of Physiology – Gastrointestinal and Liver Physiology 307 (2014): G397–G409. World Health Organization, Micronutrient deficiencies, http://www. who.int/nutrition/topics/ida/en/index.html A. C. Cepeda-Lopez and co-authors, In overweight and obese women, dietary iron absorption is reduced and the enhancement of iron absorption by ascorbic acid is one-half that in normal-weight women, American Journal of Clinical Nutrition 102 (2015): 1389–97. Australian Health Survey: Nutrition first results – foods and nutrients, 2011–12 (2014), ABS Catalogue, no. 4364.0.55.007, Australian Government Publishing Service. Canberra.
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9 10 11
12
13
14 15 16
Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). H. Haase and L. Rink, Multiple impacts of zinc on immune function, Metallomics 6 (2014): 1175–80. M. E. Penny, Zinc supplementation in public health, Annals of Nutrition and Metabolism 62 (2013): 31–42. H. Hemilä, Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage, JSRM Open 8 (2017): 2054270417694291. M. Li and co-authors, Are Australian children iodine deficient? Results of the Australian National Iodine Nutrition Study, Medical Journal of Australia 184 (2006): 165–9. G. Gisselle, S. Goodall and C. J. Eastman, Iodine deficiency in Australia: is iodine supplementation for pregnant and lactating women warranted?, Medical Journal of Australia 192 (2010): 461–3. New Zealand Ministry of Health, Iodine, https://www.health.govt.nz/ our-work/preventative-health-wellness/nutrition/iodine M. Vinceti and co-authors, Selenium for preventing cancer, Cochrane Database of Systematic Reviews (2018): CD005195. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006).
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17 Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). 18 R. B. Costello, J. T. Dwyer, and R. L. Bailey, Chromium supplements for glycemic control in type 2 diabetes: Limited evidence of
effectiveness, Nutrition Reviews 74 (2016): 455–68; C. H. Bailey, Improved metanalytic methods show no effect of chromium supplements on fasting glucose, Biological Trace Element Research 157 (2014): 1–8. . 19 C. Cooksey, Health concerns of heavy metals and metalloids, Science Progress 95 (2012): 73–88.
HIGHLIGHT 1
2 3
4
5
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J. M. Pavese, S. N. Krishna, and R. C. Bergan, Genistein inhibits human prostate cancer cell detachment, invasion, and metastasis, American Journal of Clinical Nutrition 100 (2014): 431S–436S; X. O. Liu and co-authors, Association between dietary factors and breast cancer risk among Chinese females: Systematic review and metaanalysis, Asian Pacific Journal of Cancer Prevention 15 (2014): 1291–8. S. Ziaei and R. Halaby, Dietary isoflavones and breast cancer risk, Medicines 4 (2017): E18. The Cancer Council Australia, Position statement: Soy, phyto-estrogens and cancer prevention, available at https://wiki.cancer.org.au/policy/ Position_statement_-_Soy,_phyto-oestrogens_and_cancer_preventionSoy-Phyto-oestrogens-and-Cancer-Position-Statement.pdf K. E. Bradbury, P. N. Appleby, T. J. Key, Fruit, vegetable, and fiber intake in relation to cancer risk: findings from the European Prospective Investigation into Cancer and Nutrition (EPIC), American Journal of Clinical Nutrition 100 (2014): 394S–398S. C. P. Bondonno and co-authors, Dietary flavonoids and nitrate: Effects on nitric oxide and vascular function, Nutrition Reviews 73 (2015): 216–35. E. T. M. Leermakers and co-authors, The effects of lutein on cardiometabolic health across the life course: A systematic review and meta-analysis, American Journal of Clinical Nutrition 103 (2016):
481–94; L. Müller and co-authors, Lycopene and its antioxidant role in the prevention of cardiovascular diseases: A critical review, Critical Reviews in Food Science and Nutrition 56 (2016): 1868–79. 7 R. U. Almario and S. E. Karakas, Lignan content of the flaxseed influences its biological effects in healthy men and women, Journal of the American College of Nutrition 32 (2013): 194–9. 8 J. M. McKenney and co-authors, A softgel dietary supplement containing esterified plant sterols and stanols improves the blood lipid profile of adults with primary hypercholesterolemia: A randomized, double-blind, placebo-controlled replication study, Journal of the Academy of Nutrition and Dietetics 114 (2014): 244–9; M. A. Shaghaghi, S. S. Abumweis, and P. J. H. Jones, Cholesterol lowering efficacy of plant sterols/stanols provided in capsule and tablet formats: Results of a systematic review and meta-analysis, Journal of the Academy of Nutrition and Dietetics 113 (2013): 1494–1503. 9 D. Rodriguez-Leyva and co-authors, Potent antihypertensive action of dietary flaxseed in hypertensive patients, Hypertension 62 (2013): 1081–9. 10 Food Standards Australia New Zealand, Nutrition content claims and health claims (2016), http://www.foodstandards.gov.au/consumer/ labelling/nutrition/
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CHAPTER
14
FITNESS: PHYSICAL ACTIVITY, NUTRIENTS AND BODY ADAPTATIONS Nutrition in your life
Every day you choose to be physically active or inactive, and your choice can make a huge difference to how well you feel and how long you will live. Today’s world makes it easy to be inactive – too easy, in fact – but the many health rewards of being physically active make it well worth the effort. You may even discover how much fun it is to be active, and, with a little perseverance, you may become physically fit as well. As you become more active, you will find that the foods you eat can make a difference in how fast you run, how far you swim or how much weight you lift. It’s up to you; the choice is yours. As you read this chapter, consider whether your physical activities meet current recommendations and whether your daily food, fluid, and nutrient intakes are appropriate to support those activities. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F Regular exercise can reduce the risk of developing type 2 diabetes. T F Creatine phosphate is a reliable energy reserve for distance runners. T F As exercise intensity increases, glycogen utilisation also increases. T F Protein needs for endurance athletes are the same as those of sedentary people. T F Hypothermia is another name for heat stroke.
LEARNING OBJECTIVES 14.1 Describe the health benefits of being physically fit and explain how to develop the components of fitness. 14.2 Identify the factors that influence fuel use during physical activity and the types of activities that depend more on glucose or fat, respectively. 14.3 List which vitamin and mineral supplements, if any, athletes may need and why.
14.4 Identify the factors that influence an athlete’s fluid needs and describe the differences between water and sports drinks. 14.5 Discuss an appropriate daily eating pattern for athletes and list one example of a recommended pre-game and recovery meal. 14.6 Present arguments for and against the use of ergogenic aids.
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Are you physically fit? If so, the following description applies to you. Your joints are flexible, your muscles are strong and your body is lean with enough, but not too much, fat. You have the endurance to engage in daily physical activities with enough reserve energy to handle added challenges. Carrying heavy suitcases, opening a stuck window or climbing four flights of stairs, which might strain an unfit person, are easy for you. What’s more, you are prepared to meet mental and emotional challenges, too. All these characteristics of fitness describe the same wonderful condition of a healthy body. Or perhaps you are leading a sedentary life. Today’s world encourages inactivity, and people who go through life exerting minimal physical effort become weak and unfit, and may begin to feel unwell. In fact, a sedentary lifestyle fosters the development of several chronic diseases. Regardless of your level of fitness, this chapter is written for ‘you’, whoever you are and whatever your goals – whether you want to improve your health, lose weight, enhance your athletic skills, ensure your position on a sports team or simply adopt an active lifestyle. This chapter begins by discussing fitness and its benefits and then goes on to explain how the body uses energy nutrients to fuel physical activity. Finally, it describes diets to support fitness.
PUTTING COMMON SENSE TO THE TEST
Regular exercise can reduce the risk of developing type 2 diabetes. TRUE
14.1 Fitness
Fitness depends on a certain minimum amount of physical activity or exercise. Both physical activity and exercise involve body movement, muscle contraction and enhanced energy expenditure, but a distinction is made between the two terms. Exercise is often considered to be vigorous, structured and planned physical activity. This chapter focuses on how the active body uses energy nutrients – whether that body is pedalling a bike across town or spinning on a stationary bike in a gym. Thus, for our purposes, the terms physical activity and exercise are used interchangeably.
Benefits of fitness Each comparison influences the risks associated with chronic disease and death similarly: • vigorous exercise v minimal exercise • healthy weight v 20% overweight • non-smoking v smoking (one pack a day).
The health benefits of increasing physical activities and reducing sedentary times cannot be overemphasised. Extensive evidence confirms that regular physical activity promotes health and reduces the risk of developing a number of diseases.1 Still, despite an increasing awareness of the health benefits that physical activity confers, the 2014–15 Australian National Health Survey showed that only 55 per cent of adults aged 18 to 64 years exercised sufficiently to obtain benefits to their health, and in New Zealand the figure is similar, at 53 per cent.2 As a person becomes physically fit, the health of the entire body improves. In general, physically fit people enjoy the following: • Restful sleep: Rest and sleep occur naturally after periods of physical activity. During rest, the body repairs injuries, disposes of wastes generated during activity and builds new physical structures. • Nutritional health: Physical activity expends energy and thus allows people to eat more food. If they choose wisely, active people will consume more nutrients and be less likely to develop nutrient deficiencies. • Optimal body composition: A balanced program of physical activity limits body fat and increases or maintains lean tissue. Thus physically active people have relatively less body fat than sedentary people at the same body weight. • Optimal bone density: Weight-bearing physical activity builds bone strength and protects against osteoporosis.
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• Resistance to colds and other infectious diseases: Fitness enhances immunity.* • Low risks of some types of cancers: Lifelong physical activity may help to protect against colon cancer, breast cancer and some other cancers. • Strong circulation and lung function: Physical activity challenges the heart and lungs, and strengthens the circulatory system. • Low risk of cardiovascular disease: Physical activity lowers blood pressure, slows resting pulse rate and lowers blood cholesterol, thus reducing the risks of heart attack and stroke. Some research suggests that physical activity may reduce the risk of cardiovascular disease in another way as well – by reducing intra-abdominal fat stores. • Low risk of type 2 diabetes: Physical activity normalises glucose tolerance. Regular physical activity reduces the risk of developing type 2 diabetes and benefits those who already have the condition. • Reduced risk of gall bladder disease: Regular physical activity reduces the risk of gall bladder disease – perhaps by facilitating weight control and lowering blood lipid levels. • Low incidence and severity of anxiety and depression: Physical activity may improve mood and enhance the quality of life by reducing depression and anxiety. • Strong self-image: The sense of achievement that comes from meeting physical challenges promotes self-confidence. • Long life and high quality of life in the later years: Active people live longer healthier lives than sedentary people do. Even a 4-kilometre walk daily can add years to a person’s life. In addition to extending longevity, physical activity supports independence and mobility in later life by reducing the risk of falls and minimising the risk of injury should a fall occur. What does a person have to do to reap the health rewards of physical activity? Australia’s Physical Activity and Sedentary Behaviour Guidelines for Adults specify that being physically active and limiting sedentary behaviour every day is essential for health and wellbeing.3 The national physical activity guidelines for adults (aged 18–64 years) comprise a four-tier series of recommendations: 1 Doing any physical activity is better than doing none. If you currently do no physical activity, start by doing some, and gradually build up to the recommended amount. 2 Be active on most, preferably all, days every week. 3 Accumulate 150 to 300 minutes (2½ to 5 hours) of moderateintensity physical activity or 75 to 150 minutes (1¼ to 2½ hours) of Physical activity, or its lack, exerts a significant and vigorous intensity physical activity, or an equivalent combination of pervasive influence on everyone’s nutrition and overall health. both moderate and vigorous activities, each week. 4 Do muscle strengthening activities on at least two days each week. In addition to providing health benefits, physical activity helps to Reminder: Body develop and maintain fitness. Table 14.1 presents the American College of Sports Medicine composition refers to (ACSM) guidelines for physical activity.4 Following these guidelines will help adults improve the proportions of their cardiorespiratory endurance, body composition, strength and flexibility. At this level muscle, bone, fat and of fitness, a person can reap still greater health benefits (substantially lower risk of premature other tissue that make death compared with those who are inactive, improved cardiorespiratory fitness and improved up a person’s total body composition, for example). body weight.
*Moderate physical activity can stimulate immune function. Intense, vigorous, prolonged activity such as marathon running, however, may compromise immune function.
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David Hanover Photography
David Hanover Photography
David Hanover Photography
TABLE 14.1 Guidelines for physical fitness
Type of activity
Aerobic activity that uses largemuscle groups and can be maintained continuously
Resistance activity that is performed at a controlled speed and through a full range of motion
Stretching activity that uses the major muscle groups
Frequency
5 to 7 days per week
2 to 3 days per week
2 to 7 days per week
Intensity
Moderate (equivalent to walking at a pace of 5 to 6 kilometres per hour)a
Enough to enhance muscle strength and improve body composition
Enough to feel tightness or slight discomfort
Duration
At least 30 minutes per day
2 to 4 sets of 8 to 12 repetitions involving each major muscle group
2 to 4 repetitions of 15 to 30 seconds per muscle group
Examples
Running, cycling, swimming, in-line skating, aerobic classes, rowing, power walking, kickboxing, skipping; sports activities such as football, rugby, basketball, netball, soccer, squash, tennis, volleyball
Pull-ups, push-ups, weight-lifting, Pilates
Yoga
a For those who prefer vigorous-intensity aerobic activity such as walking at a very brisk pace (>6 km/h) or running (>8 km/h), a minimum of 20 minutes per day, three days per week is recommended.
American College of Sports Medicine position stand: Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults – guidance for prescribing exercise, Medicine and Science in Sports and Exercise 43 (2011): 1334–59.
The bottom line is that any physical activity, even moderate activity, provides some health benefits, and these benefits follow a dose–response relationship. Therefore, some activity is better than none, and more activity is better still – up to a point. Pursued in excess, intense physical activity, especially when combined with poor eating habits, can undermine health, as Highlight 8 explains.
Developing fitness A person who practises a physical activity adapts by becoming better able to perform that activity after each session. People shape their bodies by what they choose to do (and not do). Muscle cells and tissues respond to a physical activity overload by building, within genetic limits, the structures needed to perform it. Muscles are continuously under renovation. Every day, particularly during the fasting periods between meals, a healthy body degrades a small portion of its muscle protein and then rebuilds new muscle with available amino acids during feeding periods. This balance between protein degradation and synthesis maintains the body’s muscle tissue. To gain muscle tissue, protein synthesis must be greater than degradation, a condition called hypertrophy. When protein degradation is greater than synthesis, the result is atrophy. Physical activity tips the balance toward muscle hypertrophy. The opposite is also true: unused muscles diminish in size and weaken over time, tipping the balance towards muscle atrophy. The muscles adapt and build only the proteins they need to cope with the work performed. Muscles engaged in activities that require strength develop more of the proteins needed for greater muscle mass; body builders have large, well-developed muscles. By comparison, those engaged in endurance activities develop more of the proteins needed to combat muscle fatigue; distance cyclists can pedal for many hours before fatigue sets in.
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Strategies to build fitness and prevent injuries A variety of physical activities produces the best overall fitness and, to this end, people need to work different muscle groups from day to day. This strategy provides a day or two of rest for different muscle groups, giving them time to replenish nutrients and to repair any minor damage incurred by the activity. Other tips for building fitness and minimising the risk of overuse injuries are as follows: • Be active all week, not just on the weekends. • Use proper equipment and attire. • Perform exercises using proper form. • Include warm-up and cool-down activities in each session. Warming up helps to prepare muscles, ligaments and tendons for the upcoming activity and mobilises fuels to support strength and endurance activities. Cooling down reduces muscle cramping and allows the heart rate to slow gradually. • Train hard enough to challenge your strength or endurance a few times each week rather than every time you work out. Between challenges, do moderate work-outs and include at least one day of rest each week. • Pay attention to body signals. Symptoms such as abnormal heartbeats, dizziness, lightheadedness, cold sweat, confusion or pain or pressure in the middle of the chest, teeth, jaw, neck or arm demand immediate medical attention. • Work out wisely. Do not start with activities so demanding that pain stops you within a day or two. Learn to enjoy small steps towards improvement. Fitness builds slowly.
Major coronary risk factors are: • age (men $45 years or women $55 years) • family history of heart disease • cigarette smoking • hypertension • serum cholesterol • >5.5 mmol/L or HDL 30 kg/m2).
Cautions on starting a fitness program Before beginning a fitness program, make sure it is safe for you to do so. Most apparently healthy people can begin a moderate exercise program such as walking or increasing daily activities without a medical examination, but people with any major coronary risk factors may need medical advice.
To be physically fit, a person must develop enough flexibility, muscle strength and endurance, and cardiorespiratory endurance to meet the everyday demands of life with some to spare, and to achieve a reasonable body weight and body composition. Flexibility allows the joints to move freely, reducing the risk of injury. Muscle strength and muscle endurance enable muscles to work harder and longer without fatigue. Body composition improves as physical activity supports lean body tissues and reduces excess body fat. Although nutrition influences each component of fitness to some extent, its role in flexibility is not as apparent as for the others. For this reason, cardiorespiratory endurance and muscle strength and endurance are emphasised in the following sections. As the heart and lungs improve their capacity to sustain physical activity and the muscles become stronger and less readily fatigued, body composition improves: body fat decreases and lean body mass increases. Chapter 8 discusses body composition and the health risks of too much body fat.
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The components of fitness
Physical activity helps you look good, feel good and have fun, and it brings many long-term health benefits as well.
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Cardiorespiratory endurance
The key to regular physical activity is finding an activity that you enjoy.
Cardiorespiratory conditioning: • increases cardiac output and oxygen delivery • increases blood volume per heartbeat (stroke volume) • slows resting pulse • increases breathing efficiency • improves circulation • reduces blood pressure.
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Recall from Chapter 7 that aerobic means requiring oxygen.
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The length of time a person can remain active with an elevated heart rate – that is, the ability of the heart, lungs and blood to sustain a given demand – defines a person’s cardiorespiratory endurance. Cardiorespiratory endurance training improves a person’s ability to sustain vigorous activities such as running, brisk walking or swimming. Such training enhances the capacity of the heart, lungs and blood to deliver oxygen to, and remove waste from, the body’s cells. Cardiorespiratory endurance training, therefore, is aerobic. As the cardiorespiratory system gradually adapts to the demands of aerobic activity, the body delivers oxygen more efficiently. In fact, the accepted measure of a person’s cardiorespiratory fitness is maximal oxygen uptake (VO2max). The benefits of cardiorespiratory training are not just physical, though, because all of the body’s cells, including the brain cells, require oxygen to function. When the cells receive more oxygen more readily, both the body and the mind benefit.
People’s bodies are shaped by the activities they perform.
Cardiorespiratory conditioning
Cardiorespiratory conditioning occurs as aerobic work-outs improve heart and lung activities. Cardiac output increases, thus enhancing oxygen delivery. The heart becomes stronger, and each beat pumps more blood. Because the heart pumps more blood with each beat, fewer beats are necessary, and the resting heart rate slows down. The average resting pulse rate for adults is around 70 beats per minute, but people who achieve cardiorespiratory conditioning may have resting pulse rates of 50 or even lower. The muscles that work the lungs become stronger, too, so breathing becomes more efficient. Circulation through the arteries and veins improves. Blood moves easily, and blood pressure falls.5 Cardiorespiratory endurance reflects the health of the heart and circulatory system, on which all other body systems depend. Figure 14.1 shows the major relationships between the heart, circulatory system and lungs. To improve your cardiorespiratory endurance, the activity you choose must be sustained for 20 minutes or longer and use most of the large-muscle groups of the body (legs, buttocks and abdomen). You must also train at an intensity that elevates your heart rate. A person’s own perceived effort is usually a reliable indicator of the intensity of an activity. In general, when you’re working out, do so at an intensity that raises your heart rate but still leaves you able to talk comfortably. If you are more competitive and want to work to your limit on some days, a treadmill test can reveal your maximum heart rate. You can work out safely at up to 90 per cent of that rate. The ACSM guidelines for developing and maintaining cardiorespiratory fitness are given in Table 14.1 (on page 494).
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FIGURE 14.1 Delivery of oxygen by the heart and lungs to the muscles The cardiorespiratory system responds to the muscles’ demand for oxygen by building up its capacity to deliver oxygen. Researchers can measure cardiorespiratory fitness by measuring the maximum amount of oxygen a person consumes per minute while working out, a measure called VO2max.
1 The respiratory system delivers oxygen to the blood.
Air (O2, CO2), other gases O2
CO2
CO2
CO2 O2
O2
4 The blood carries the carbon dioxide back to the lungs.
CO2
2 The circulatory system carries oxygenated blood throughout the body.
O2
3 The muscles and other tissues obtain oxygen from the blood and release carbon dioxide into it.
Muscle conditioning One of the benefits of cardiorespiratory training is that fit muscles use oxygen efficiently, reducing the heart’s workload. An added bonus is that muscles that use oxygen efficiently can burn fat longer – a plus for body composition and weight control.
A balanced fitness program The intensity and type of physical activities that are best for one person may not be good for another. A person who has been sedentary will initially perform at a dramatically different level of intensity than a fit person. The type of physical activity that is best for you depends, too, on what you want to achieve and what you enjoy doing. Some people love walking, whereas others prefer to dance or ride
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AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
To achieve and maintain a healthy weight, be physically active and choose amounts of nutritious food and drinks to meet your energy needs.
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a bike. If you want to be stronger and firmer, lift weights. And remember, muscle is more metabolically active than body fat, so the more muscle you have, the more energy you’ll burn. In a balanced fitness program, aerobic activity improves cardiorespiratory fitness, stretching enhances flexibility, and resistance training develops muscle strength, muscle power and muscle endurance. Table 14.2 provides an example of a balanced fitness program.
TABLE 14.2 A sample balanced fitness program Monday, Tuesday, Wednesday, Thursday, Friday: • 5 minutes of warm-up activity • 45 minutes of aerobic activity • 10 minutes of cool-down activity and stretching Tuesday, Thursday, Saturday: • 5 minutes of warm-up activity • 30 minutes of weight training • 10 minutes of cool-down activity and stretching Saturday and/or Sunday: • Sports, walking, hiking, biking or swimming
Resistance training Resistance training has long been recognised as a means to build lean body mass and develop and maintain muscle strength and endurance. Additional benefits of resistance training, however, have emerged only recently. Progressive resistance training not only increases muscle strength and endurance, but it also prevents and manages several chronic diseases, including cardiovascular disease, and enhances psychological wellbeing.6 Resistance training can also help to maximise and maintain bone mass. Even in women past menopause (when most women are losing bone), resistance training can improve bone density, especially in combination with adequate dietary calcium and vitamin D intake.7 By promoting strong muscles in the back and abdomen, resistance training can improve posture and reduce the risk of back injury. Resistance training can also help prevent the decline in physical mobility that often accompanies ageing.8 Older adults, even those in their eighties, who participate in resistance training programs not only gain muscle strength but also improve their muscle endurance, which enables them to walk longer before exhaustion. Leg strength and walking endurance are powerful indicators of an older adult’s physical abilities. Resistance training builds muscle strength, muscle power and muscle endurance. To emphasise muscle strength, combine high resistance (heavy weight) with a low number (8 to 10) of repetitions.9 To emphasise muscle endurance, combine less resistance (lighter weight) with more (12 to 15) repetitions. Resistance training enhances performance in other sports, too. Swimmers can develop a more efficient stroke and tennis players a more powerful serve when they train with weights.
REVIEW IT
Physical activity brings positive rewards: good health and long life. To develop fitness – whose components are flexibility, muscle strength and endurance, and cardiorespiratory endurance – a person must condition the body, through training, to adapt to the activity performed.
14.2 Energy systems and fuels to support activity
Nutrition and physical activity go hand in hand. Activity demands carbohydrate and fat as fuel, protein to build and maintain lean tissues, vitamins and minerals to support both energy metabolism and tissue building, and water to help distribute the fuels and to dissipate
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the resulting heat and wastes. This section describes how nutrition supports a person who decides to get up and go.
The energy systems of physical activity – ATP and CP
The phosphagen system
Westend61/Westend61/Superstock
As Chapter 7 describes, all of the energy-yielding nutrients – carbohydrate, fat and protein – can enter metabolic pathways that make the high-energy compound ATP (adenosine triphosphate). ATP is present in small amounts in all body tissues all the time, and it can deliver energy instantly. In the muscles, ATP provides the chemical driving force for contraction. When an ATP molecule is split, its energy is released, and the muscle cells channel some of that energy into mechanical movement and most of it into heat. Three major energy systems enable muscle cells to regenerate ATP during different types of physical activity: • the phosphagen system (also called the creatine phosphate system) • the lactic acid system (anaerobic glycolysis) • the aerobic system (aerobic glycolysis, fatty acid oxidation, and TCA cycle) All three energy systems function at all times, but depending on the intensity of the activity and the conditioning of the athlete, one system will predominate at any given time. The following sections describe each of these systems. Split-second surges of power, as in the heave of a barbell or a jump of a basketball player,
Immediately after the onset of a demand, before muscle ATP pools dwindle, a involve anaerobic work. muscle enzyme begins to break down another high-energy compound that is stored in the muscle: CP, or creatine phosphate. CP is made from creatine, Recall from a compound commonly found in muscles, with a phosphate group attached, and it can split Chapter 7 that (anaerobically) to release phosphate and replenish ATP supplies. Supplies of CP in a muscle anaerobic means not requiring oxygen. last for only about 10 seconds, producing enough quick energy without oxygen for a 100-metre sprint. PUTTING When activity ceases and the muscles are resting, ATP feeds energy back to CP by giving COMMON SENSE up one of its phosphate groups to creatine. Thus, CP is produced during rest by reversing the TO THE TEST process that occurs during muscular activity. (Highlight 14 includes creatine supplements in Creatine phosphate its discussion of substances commonly used in the pursuit of fitness.) is a reliable energy reserve for distance The lactic acid system runners. After the first 10 seconds or so of intense activity, energy from the phosphagen system FALSE diminishes, so muscle cells call upon the lactic acid system to produce more ATP. As Chapter 7 describes, the lactic acid system involves the anaerobic breakdown of glucose to pyruvate (and During rest: then of pyruvate to lactate). The primary source of glucose is muscle glycogen. This system can • ATP 1 creatine generate a small amount of ATP quickly for high-intensity activity lasting up to three minutes. → CP. A later section describes the consequences of lactate accumulation. During activity:
The aerobic system
• CP → ATP 1 creatine.
To meet the more prolonged demands of sustained activity, the muscles rely on the aerobic system to provide ATP for muscle contraction. As Chapter 7 describes, carbohydrate, fat and some amino acids are continuously oxidised to ensure an uninterrupted supply of ATP. During rest, the body derives more than half of its ATP from the oxidation of fatty acids, most of the rest from the complete oxidation of glucose, and a small percentage from the oxidation of amino acids. During physical activity, the body adjusts its mixture of fuels. Muscles always use a mixture of fuels – never just one. How much of which fuel the muscles use during physical activity depends on an interplay among the fuels available from the diet, the intensity and duration of the activity, and the degree to which the body is conditioned to perform that activity. The next sections explain these relationships by examining each of the energy-yielding nutrients individually, but keep in mind that, although
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one fuel may predominate at a given time, the other two will still be involved. Table 14.3 shows how fuel use changes according to the intensity and duration of the activity.
TABLE 14.3 Primary fuels used for activities of different intensities and durations ACTIVITY INTENSITY
ACTIVITY DURATION
ENERGY SYSTEM
PREFERRED FUEL SOURCE
OXYGEN NEEDED?
ACTIVITY EXAMPLE
Extreme
5 to 10 sec
Phosphagen system
ATP-CP (immediate availability)
No
100-metre sprint, shot put, golf or baseball bat swing, tennis or volleyball serve
Very high
20 sec to 2 min
Lactic acid system
ATP from carbohydrate (anaerobic glycolysis)
No
400-metre run, 100-metre swim, gymnastic routines
High
2 min to 20 min
Aerobic system
ATP from carbohydrate (glycolysis and TCA cycle)
Yes
Cycling, swimming or running
Moderate
>20 min
Aerobic system
ATP from fat (fatty acidoxidation and TCA cycle)
Yes
Hiking
NOTE: All energy systems function at all times, but depending on the intensity of the activity and the conditioning of the athlete, one system will predominate at any given time.
Anaerobic versus aerobic Oxygen – or its lack – is central to the energy systems just described. The phosphagen and lactic acid systems are anaerobic – meaning without oxygen. As its name suggests, the aerobic system uses oxygen. As you read the following pages, notice how the fuel mixture shifts depending on whether the activity is anaerobic or aerobic. Anaerobic activities are associated with strength, agility, and split-second surges of power. The jump of a slam dunk, the power of a tennis serve and the heave of a bench press all involve anaerobic work. Such high-intensity, short-duration activities depend mostly on glucose as the chief energy fuel in the lactic acid system. Endurance activities of low to moderate intensity and long duration depend more on fat to provide energy through the aerobic system. The ability to continue swimming to the shore, to keep on hiking to the top of the mountain, or to continue pedalling all the way home reflects aerobic capacity. As mentioned earlier, aerobic capacity is also crucial to maintaining a healthy heart and circulatory system. Because various physical activities use different energy systems and quantities of nutrients to various degrees, a person’s food choices can greatly influence performance.
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Glucose use during physical activity
Sustained muscular efforts, as in a long-distance rowing event or a cross-country run, involve aerobic work.
Glucose, stored in the liver and muscles as glycogen, is vital to physical activity. During exertion, the liver breaks down its glycogen and releases the glucose into the bloodstream. The muscles use this glucose as well as their own private glycogen stores to fuel their work. Glycogen supplies can easily support everyday activities but are limited to less than 8000 kilojoules of energy, enough for about 40 kilometres of running. The more glycogen the muscles store, the longer the glycogen will last during physical activity, which in turn influences performance. When glycogen is depleted, the muscles become fatigued.
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Diet affects glycogen storage and use How much carbohydrate a person eats influences how much glycogen is stored. A classic study compared fuel use during activity between three groups of runners on different diets.10 For several days before testing, one group consumed a normal mixed diet, a second group consumed a high-carbohydrate diet and the third group consumed a nocarbohydrate diet (fat and protein diet). As Figure 14.2 shows, the high-carbohydrate diet allowed the runners to keep going longer before exhaustion. This study and many others that followed have confirmed that high-carbohydrate diets enhance endurance by ensuring ample glycogen stores.
To fill glycogen stores, eat plenty of carbohydrate-rich foods.
FIGURE 14.2 The effect of diet on physical endurance A high-carbohydrate diet can increase an athlete’s endurance. In the study described in the text, the fat and protein diet provided 94 per cent of energy from fat and 6 per cent from protein; the normal mixed diet provided 55 per cent of energy from carbohydrate; and the high-carbohydrate diet provided 83 per cent of energy from carbohydrate.
Maximum endurance time: Fat and protein diet 57 min Normal mixed diet
High-carbohydrate diet 167 min
Jupiter Images/Getty Images
114 min
Intensity of activity affects glycogen use How long an exercising person’s glycogen will last depends not only on diet but also on the intensity of the activity. Moderate activities, such as jogging, during which breathing is steady and easy, use glycogen slowly. The lungs and circulatory system have no trouble keeping up with the muscles’ need for oxygen. The individual breathes easily, and the heart beats steadily – the activity is aerobic. The muscles derive their energy from both glucose and fatty acids. By depending partly on fatty acids, moderate aerobic activity conserves glycogen. Intense activities – the kind that make it difficult ‘to catch your breath’ – use glycogen quickly. In such activities, the muscles break down glucose to pyruvate anaerobically, producing ATP quickly.
PUTTING COMMON SENSE TO THE TEST
As exercise intensity increases, glycogen utilisation also increases. TRUE
Lactate Lactate is the product of anaerobic glycolysis. When the rate of glycolysis exceeds the capacity of the mitochondria to accept hydrogens with their electrons for the electron transport chain, the accumulating pyruvate molecules are converted to lactate. At low intensities, lactate is readily cleared from the blood, but at higher intensities, lactate accumulates. When the rate of lactate production exceeds the rate of clearance, intense activity can be maintained for only one to three minutes (as in a 400- to 800-metre race or a boxing match). Lactate was long blamed for muscle fatigue, but recent research disputes this idea. Working muscles may produce lactate and experience fatigue, but the lactate does not cause the fatigue.11
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Reminder: Lactate is the product of anaerobic glycolysis.
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Lactate quickly leaves the muscles and travels in the blood to the liver. There, liver enzymes convert the lactate back into glucose. Glucose can then return to the muscles to fuel additional activity. (The recycling process that regenerates glucose from lactate is known as the Cori cycle, and is shown in Figure 7.6 on page 221.)
Duration of activity affects glycogen use Glycogen use depends not only on the intensity of an activity but also on its duration. Within the first 20 minutes or so of moderate activity, a person uses mostly glycogen for fuel – about one-fifth of the available glycogen. As the muscles devour their own glycogen, they become ravenous for more glucose. Glucagon signals the liver to empty out its glycogen Moderate- to high-intensity aerobic exercises that can be sustained for only a short time (less than 20 minutes) use some fat but more glucose for fuel. stores to provide the muscles with more glucose. After 20 minutes, a person who continues exercising moderately (mostly aerobically) begins to use less and less glycogen and more and more fat for fuel (review Table 14.3 on page 500). Still, glycogen use continues, and if the activity lasts long enough and is intense enough, blood glucose declines and muscle and liver glycogen stores are depleted. Physical activity can continue for a short time thereafter only because the liver scrambles to produce, from lactate and certain amino acids, the minimum amount of glucose needed to briefly forestall total depletion.
Training affects glycogen use
The mitochondria are the structures within a cell responsible for producing ATP (see Figure 7.1 on page 215).
Training, too, affects how much glycogen muscles will store. Muscle cells that repeatedly deplete their glycogen through hard work adapt to store greater amounts of glycogen to support that work. Conditioned muscles also rely less on glycogen and more on fat for energy, so glycogen breakdown and glucose use occur more slowly in trained than in untrained individuals at a given work intensity. A person attempting an activity for the first time uses much more glucose than an athlete who is trained to perform it. Oxygen delivery to the muscles by the heart and lungs plays a role, but equally importantly, trained muscles are better equipped to use the oxygen because their cells contain more mitochondria. Untrained muscles depend more heavily on anaerobic glucose breakdown, even when physical activity is just moderate.
Glucose before activity Most of an athlete’s glucose is provided by carbohydrate-rich meals consumed throughout the day. In addition, glucose consumed within a few hours before training or competition is thought to ‘top off’ the athlete’s glycogen stores, providing the greatest possible glucose supply to support sustained activity. The pre-game meal to provide glucose can take many forms, as a later section describes.
Glucose during activity Muscles can obtain the glucose they need not only from glycogen stores, but also from foods and beverages consumed during activity. Consuming carbohydrate is especially useful during exhausting endurance activities (lasting more than 60 minutes) and during games such as soccer or hockey, which last for hours and demand repeated bursts of intense activity.12 Interestingly, during high-intensity activity lasting less than an hour, some research suggests that merely rinsing the mouth with a carbohydrate solution may be enough to improve performance.13 In such instances, the benefit is not related to muscle glycogen availability, as
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Chapter 14: Fitness: physical activity, nutrients and body adaptations
when athletes ingest carbohydrate during prolonged events. Rather, researchers speculate that there may be receptors in the mouth that sense potential carbohydrate availability and relay this message to areas of the brain involved with reward and motor control. Endurance athletes often run short of glucose by the end of competitive events. To ensure optimal carbohydrate intake, sports nutrition experts recommend 30 to 60 grams of carbohydrate per hour during prolonged events.14 Carbohydrate-based sports drinks offer a convenient way to meet this recommendation and also help replace water and electrolyte losses. Thus, to ensure optimal hydration and carbohydrate intake, endurance athletes are advised to drink 0.5 to 1 L of a 4- to 8-per cent carbohydrate-based sports drink per hour, in small, frequent doses during activity. During the last stages of an endurance competition, when glycogen is running low, glucose consumed during the event can slowly make its way from the digestive tract to the muscles and augment the body’s supply of glucose enough to forestall exhaustion. Some researchers have questioned whether adding protein to carbohydrate-containing sports beverages would offer a performance advantage to endurance athletes.15 Evidence so far suggests that when carbohydrate intake is optimal, protein provides no additional performance benefit. Gluconeogenesis could support an activity of low intensity, such as walking, but cannot support continued strenuous activity. After a couple of hours of strenuous activity, glucose stores are depleted. When depletion occurs, it brings nervous system function to a near halt, making continued exertion at the same intensity almost impossible. Marathon runners refer to this point of glucose exhaustion as ‘hitting the wall.’ To avoid such debilitation, endurance athletes try to maintain their blood glucose for as long as they can. The following guidelines will help endurance athletes maximise glucose supply: • Eat a high-carbohydrate diet (approximately 8 grams of carbohydrate per kilogram of body weight, or about 70 per cent of energy intake) regularly. • Take glucose (usually in sports drinks) periodically during activities that last for 60 minutes or more. • Eat carbohydrate-rich foods (approximately 60 grams of carbohydrate) immediately following activity. To postpone fatigue and maximise performance, athletes must maintain available glucose supplies for as long as they can. To do so, athletes need abundant carbohydrate each day. Recent research supports a range of carbohydrate intakes for athletes based on the athlete’s total energy needs, training needs and performance (see Table 14.4).
A later section discusses fluid and electrolyte balance during activity.
TABLE 14.4 Guidelines for carbohydrate intake by athletes These general research-based guidelines should be adjusted to an athlete’s energy needs, training regimen and performance. DAILY NEEDS FOR FUEL AND RECOVERY SITUATION
CARBOHYDRATE NEEDS
Sedentary or low-intensity/skills-based training
3–5 g/kg/day
Moderate exercise program (~1 hour per day)
5–7 g/kg/day
Moderate-to-high intensity endurance training program (1–3 hours per day)
6–10 g/kg/day
Heavy endurance training (>4–5 hours per day) of moderate-to-high intensity training
8–12 g/kg/day
503
Source: Based on L. M. Burke et al., Carbohydrates for training and competition, Journal of Sports Science 29 (2011): S17–27.
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For perspective, snack ideas providing 60 g carbohydrate are: • 600 mL sports drink and a bread roll • 600 mL milk and four Anzac or oatmeal biscuits • 300 mL apple juice and a muesli bar.
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Section 14.5 discusses how to design a high-carbohydrate diet for performance, and the ‘How to’ box below describes carbohydrate loading – a technique used to maximise glycogen stores for long endurance competitions.
HOW TO:
MAXIMISE GLYCOGEN STORES: CARBOHYDRATE LOADING
Some athletes use a technique called ‘carbohydrate loading’ to trick their muscles into storing extra glycogen before a competition. Carbohydrate loading can nearly double muscle glycogen concentrations. In general, the athlete tapers training during the week before the competition and then eats a high-carbohydrate diet during the three days just prior to the event.a Specifically, the athlete follows the plan in the accompanying table. In this carbohydrate-loading plan, glycogen storage occurs slowly, and athletes must alter their training for several days before the event. In contrast, a group of researchers have designed a quick method of carbohydrate loading that has produced promising results. The researchers found that athletes could attain abovenormal concentrations of muscle glycogen by eating a high-carbohydrate diet (10 g/kg body weight) after a short (3 minutes) but very intense bout of exercise.b More studies are needed to confirm these findings and to determine whether an exercise session of less intensity and shorter duration would accomplish the same results. Extra glycogen gained through carbohydrate loading can benefit an athlete who must keep going for 90 minutes or longer. Those who exercise for shorter times simply need a regular high-carbohydrate diet. In a hot climate, extra glycogen confers an additional advantage: as glycogen breaks down, it releases water, which helps to meet the athlete’s fluid needs. BEFORE THE EVENT
Chapter 4 explains that the glycaemic index is a method of classifying foods according to their potential to raise blood glucose. Processed foods made from refined flour such as snack foods, breads and ready-to-eat cereals have a high glycaemic index. In popular magazine articles and on the Internet, foods with a high glycaemic index are sometimes called high-impact carbs, and foods with a low glycaemic index low-impact carbs.
TRAINING INTENSITY
TRAINING DURATION
DIETARY CARBOHYDRATE
6 days
Moderate (70% VO2max)
90 min
Normal (5 g/kg body weight)
4–5 days
Moderate (70% VO2max)
40 min
Normal (5 g/kg body weight)
2–3 days
Moderate (70% VO2max)
20 min
High-carbohydrate (10 g/kg body weight)
1 day
Rest
–
High-carbohydrate (10 g/kg body weight)
a E. Coleman, Carbohydrate and exercise, in Sports Nutrition: A Practice Manual for Professionals, 4th edn, ed. M. Dunford, Chicago: The American Dietetic Association (2006): 14–32.
T. J. Fairchild and co-authors, Rapid carbohydrate loading after a short bout of near maximal-intensity exercise, Medicine and Science in Sports and Exercise 34 (2002): 980–6.
b
Glucose after activity Muscles depleted of glycogen have greater insulin sensitivity, which enhances glucose uptake and promotes glycogen synthesis. Thus, eating high-carbohydrate foods after physical activity also enlarges glycogen stores. To accelerate the rate of glycogen storage, train normally; then, within two hours after physical activity, consume a high-carbohydrate meal, such as a glass of orange juice and some plain biscuits, toast, or cereal. After two hours, the rate of glycogen storage declines by almost half. This strategy is particularly important to athletes who train hard more than once a day. Chapter 4 introduces the glycaemic index and discusses the possible health benefits of eating a low-glycaemic diet. Such a diet may also benefit endurance performance.
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Some research indicates that foods with a low glycaemic index enhance fatty acid availability and use during subsequent activity, thereby reducing reliance on the muscles’ own lipid and glycogen stores.16 More research is needed to confirm these findings. For athletes wishing to maximise muscle glycogen synthesis after strenuous training, however, eating foods with a high glycaemic index may be more beneficial (see Figure 4.13 on page 111).
Sports nutrition experts recommend that endurance athletes consume 20 to 35 per cent of their energy from fat to meet nutrient and energy needs – the same recommendation as for others.17 Athletes who restrict fat below 20 per cent of total energy intake may fail to consume adequate energy and nutrients. Recommendations to include vegetable oils, nuts, olives, fatty fish, and other sources of health-promoting fats in the diet apply to athletes as well as to everyone else. Diets high in saturated fat carry risks of heart disease. Physical activity offers some protection against cardiovascular disease, but athletes may still suffer heart attacks and strokes. Limiting saturated fat intake to less than 10 per cent of total energy intake is another way athletes can protect themselves from heart disease. In contrast to dietary fat, body fat stores are extremely important during physical activity, as long as the activity is not too intense. Unlike glycogen stores, the body’s fat stores can usually provide more than 300 000 kilojoules and can fuel hours of activity without running out. The fat used in physical activity is liberated as fatty acids from the internal fat stores and from the fat under the skin. Areas that have the most fat to spare donate the greatest amounts (although they may not Abundant energy from the breakdown of fat can come only from aerobic metabolism. be the areas that appear fattest). Thus ‘spot reducing’ does not work because muscles do not ‘own’ the fat that surrounds them. Fat cells release fatty acids into the blood, not into the underlying muscles. Then the blood gives to each muscle the amount of fat that it needs. Proof of this is found in a tennis player’s arms – the skinfold measures of fat are the same in both arms, even though the muscles of one arm work much harder and may be larger than those of the other. A balanced fitness program that includes strength training, however, will tighten muscles underneath the fat, improving the overall appearance. Keep in mind that some body fat is essential to good health. (Chapter 8 discusses the health risks of too little body fat.)
PhotoDisc
Fat use during physical activity
Duration of activity affects fat use
SuperStock/Alamy Stock Photo
Early in an activity, as the muscles draw on fatty acids, blood levels fall. If the activity continues for more than a few minutes, the hormone adrenaline signals the fat cells to begin breaking down their stored triglycerides and liberating fatty acids into the blood. After about 20 minutes of physical activity, the blood fatty acid concentration surpasses the normal resting concentration. Thereafter, sustained moderate activity uses body fat stores as its major fuel.
Intensity of activity affects fat use The intensity of physical activity also affects fat use. As the intensity of activity increases, fat makes less and less of a contribution to the fuel mixture. Remember that fat can be broken down for energy only by aerobic metabolism. For fat to fuel activity, then, oxygen must be abundantly available. If a person is breathing easily during activity, the muscles are getting all the oxygen they need and are able to use more fat in the fuel mixture.
Low- to moderate-intensity aerobic exercises that can be sustained for a long time (more than 20 minutes) use some glucose, but more fat, for fuel.
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Training affects fat use Training – repeated aerobic activity – produces the adaptations that permit the body to draw more heavily on fat for fuel. Training stimulates the muscle cells to manufacture more and larger mitochondria, the ‘power house’ structures of the cells that produce ATP for energy. Another adaptation is that the heart and lungs become stronger and better able to deliver oxygen to muscles at high-activity intensities. Still another adaptation is that hormones in the body of a trained person slow glucose release from the liver and speed up the use of fat instead. These adaptations reward not only trained athletes but all active people; a person who trains by way of aerobic activities such as distance running or cycling becomes well suited to the activity.
Protein use during physical activity – and between times Table 14.3 on page 500 summarises the fuel uses discussed so far, but does not include the third energy-yielding nutrient, protein, because protein is not a major fuel used for physical activity. Nevertheless, physically active people use protein just as other people do – to build muscle and other lean tissues and, to some extent, to fuel activity. The body does, however, handle protein differently during activity than during rest.
Protein used in muscle building Synthesis of body proteins is suppressed during activity. In the hours of recovery following activity, though, protein synthesis accelerates beyond normal resting levels. As noted earlier, eating high-carbohydrate foods immediately after exercise accelerates muscle glycogen storage. Similarly, research shows that eating carbohydrate, together with protein, enhances muscle protein synthesis.18 Remember that the body adapts and builds the molecules, cells and tissues it needs for the next period of activity. Whenever the body remodels a part of itself, it also tears down old structures to make way for new ones. Repeated activity, with just a slight overload, triggers the protein-dismantling and protein-synthesising equipment of each muscle cell to make needed changes – that is, to adapt. The physical work of each muscle cell acts as a signal to its DNA and RNA to begin producing the kinds of proteins that will best support that work. Take jogging, for example. In the first difficult sessions, the body is not yet equipped to perform aerobic work easily, but with each session, the cells’ genetic material gets the message that an overhaul is needed. In the hours that follow the session, the genes send molecular messages to the protein-building equipment that tell it what old structures to break down and what new structures to build. Within the limits of its genetic potential, the body responds. An athlete may add between 7 and 28 grams of body protein to existing muscle mass each day during active musclebuilding phases of training. Also, more mitochondria are created to facilitate efficient aerobic metabolism. Over a few weeks’ time, remodelling occurs and jogging becomes easier. The body of a weight-lifter responds to training, as well, but the response differs from that of aerobic training. Weight-lifting stimulates synthesis of muscle fibre protein to enhance muscle mass and strength – with little change in mitochondrial protein.
Protein used as fuel
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Not only do athletes retain more protein in their muscles, they also use more protein as fuel. Muscles speed up their use of amino acids for energy during physical activity, just as they speed up their use of fat and carbohydrate. Still, protein contributes only about 10 per cent of the total fuel used, both during activity and during rest. The most active people of all, endurance athletes, use up large amounts of all energy fuels, including protein, during performance, but such athletes also eat more food and therefore usually consume enough protein.
Diet affects protein use during activity Protein not only builds muscle but also helps fuel exercise.
The factors that affect how much protein is used during activity seem to be the same three that influence the use of fat and carbohydrate – one factor is diet. People who consume diets adequate in energy and rich in carbohydrate use
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Chapter 14: Fitness: physical activity, nutrients and body adaptations
less protein than those who eat protein- and fat-rich diets. Recall that carbohydrates spare proteins from being broken down to make glucose when needed. Because physical activity requires glucose, a diet lacking in carbohydrate necessitates the conversion of amino acids to glucose. The same is true for a diet high in fat because fatty acids can never provide glucose.
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To conserve protein, eat a diet adequate in energy and rich in carbohydrate.
Intensity and duration of activity affect protein use during activity The intensity and duration of activity also modifies protein use. Endurance athletes who train for more than an hour a day, engaging in aerobic activity of moderate intensity and long duration, may deplete their glycogen stores by the end of their work-outs and become somewhat more dependent on body protein for energy. In contrast, anaerobic strength training does not use more protein for energy, but it does demand more protein to build muscle. Thus, the protein needs of both endurance and strength athletes are higher than those of sedentary people, but certainly not as high as the protein intakes many athletes consume. Another factor that influences a person’s use of protein during physical activity is the extent of training. Particularly in strength athletes, such as body builders, the higher the degree of training, the less protein a person uses during an activity.
Protein recommendations for active people As mentioned, all active people, and especially athletes in training, probably need more protein than sedentary people do. Endurance athletes, such as long-distance runners and cyclists, use more protein for fuel than strength or power athletes do, and they retain some, especially in the muscles used for their sport. Strength athletes, such as body builders, and power athletes, such as football players, use less protein for fuel, but they still use some and retain much more. Therefore, all athletes in training should attend to protein needs, but they should first meet their energy needs with adequate carbohydrate intakes. Without adequate carbohydrate intake, athletes will burn off as fuel the very protein that they wish to retain in muscle. How much protein, then, should an active person consume? Although the Nutrient Reference Values for Australia and New Zealand do not recommend greater than normal protein intakes for athletes, other authorities do.19 These recommendations specify different protein intakes for athletes pursuing different activities (see Table 14.5). Daily protein intake goals are best met by a meal plan that includes moderate amounts (20 to 30 grams) of highquality protein in 4 to 5 small meals throughout the day, including within two hours following strenuous training sessions. Table 14.6 presents foods and beverages that provide 20 grams of high-quality protein. Even the highest protein recommendations can be met without protein supplements, or even with excessive servings of meat. (Chapter 6 concludes that most people receive more than enough protein without supplements and reviews the potential dangers of using protein and amino acid supplements.)
TABLE 14.5 Recommended protein intakes for athletes RECOMMENDATIONS (g/kg/day)
RDI for adults Recommended intake for athletes
PROTEIN INTAKES (g/day) MALES
FEMALES
0.84 males 0.75 females
59
41
1.2−2.0
84−140
66−120
NOTE: Daily protein intakes are based on a 70-kg man and 55-kg woman. Adapted from National Health and Medical Research Council, Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia (2006): 35–9; Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28.
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PUTTING COMMON SENSE TO THE TEST
Protein needs for endurance athletes are the same as those of sedentary people. FALSE
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TABLE 14.6 Selected foods and beverages providing 20 grams of high-quality protein and varying amounts of energy as shown FOOD OR BEVERAGE
SERVING SIZE
ENERGY (kJ)
Almonds
85 grams
2100
Beef, cooked, lean
85 grams
609
Cheese, cheddar
85 grams
1450
Chicken, cooked, skinless breast
85 grams
550
Eggs (white)
6 large
420
Eggs (whole)
3 large
1130
Milk, low-fat
600 mL
Tofu
225 grams
Tuna, light, canned in water Yoghurt, Greek-style
1070 780
85 g
290
225 g
550
REVIEW IT
The mixture of fuels that the muscles use during physical activity depends on diet, the intensity and duration of the activity, and training. During intense activity, the fuel mix is mostly glucose, whereas during less intense, moderate activity, fat makes a greater contribution. With endurance training, muscle cells adapt to store more glycogen and to rely less on glucose and more on fat for energy. Athletes in training may need more protein than sedentary people do, but they typically eat more food as well, and therefore obtain enough protein.
14.3 Vitamins and minerals to support activity
Many vitamins and minerals assist in releasing energy from fuels and in transporting oxygen. This knowledge has led many people to believe, mistakenly, that vitamin and mineral supplements offer physically active people both health benefits and athletic advantages. (Review Highlight 10 for a discussion of vitamin and mineral supplements, and see Highlight 14, which explores supplements and other products people use in the hope of enhancing athletic performance.)
Dietary supplements Nutrient supplements do not enhance the performance of well-nourished people. Deficiencies of vitamins and minerals, however, do impede performance. In general, active people who eat enough nutrient-dense foods to meet energy needs also meet their vitamin and mineral needs. After all, active people eat more food; it stands to reason that with the right choices, they’ll get more nutrients. Athletes who lose weight to meet low body-weight requirements, however, may eat so little food that they fail to obtain all the nutrients they need. The practice of ‘making weight’ is opposed by many health and fitness organisations, but for athletes who choose this course of action, a single daily multivitamin–mineral supplement that provides no more than the NRVs for nutrients may be beneficial. Some athletes believe that taking vitamin or mineral supplements directly before competition will enhance performance. These beliefs are contrary to scientific reality. Most vitamins and minerals function as small parts of larger working units. After entering the blood, they have to wait for the cells to combine them with their appropriate other parts so that they can do their work. This takes time – hours or days. Vitamins or minerals taken right before an event are useless for improving performance, even if the person is actually suffering deficiencies of them.
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Nutrients of concern In general, then, most active people who eat well-balanced meals do not need vitamin or mineral supplements. Two nutrients, vitamin E and iron, do merit special mention here, however, each for a different reason. Vitamin E is discussed because so many athletes take vitamin E supplements. Iron is discussed because some athletes may be unaware that they need iron supplements.
During prolonged, high-intensity physical activity, the muscles’ consumption of oxygen increases tenfold or more, which increases the production of free radicals in the body. Vitamin E is a potent antioxidant that vigorously defends cell membranes against the oxidative damage of free radicals. Does vitamin E supplementation protect against exerciseinduced oxidative stress? Some studies find that it does; others show no effect, and still others report enhanced oxidative stress.20 Recent research may offer some insight into these inconsistencies. Although free radicals are usually damaging, during repeated episodes of endurance activities they may actually be beneficial. Free radicals activate powerful antioxidant enzymes, which may enhance the athlete’s tolerance to such oxidative stresses. Researchers speculate that antioxidant supplements such as vitamin E interfere with this adaptive response. This may explain why, in some studies, athletes taking vitamin E show signs of increased oxidative stress. The supplements interfere with protective adaptations. Clearly, more research is needed on supplements, but in the meantime, active people can benefit by using vegetable oils rich in vitamin E and eating generous servings of antioxidant-rich fruits and vegetables regularly.
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Vitamin E
For perfect functioning, every nutrient is needed.
Iron deficiency Physically active young women, especially those who engage in endurance activities such as distance running, are prone to iron deficiency.21 Habitually low intakes of iron-rich foods, high iron losses through menstruation, and the high demands of muscles for the iron-containing electron carriers of the mitochondria and the muscle protein myoglobin can cause iron deficiency in physically active young women. In addition, endurance activities temporarily increase the release of hepcidin, which limits iron absorption (see Chapter 13). Adolescent female athletes who eat vegetarian diets may be particularly vulnerable to iron deficiency. As Chapter 13 explained, the bioavailability of iron is often poor in vegetarian diets. To protect against iron deficiency, vegetarian athletes need to select good dietary sources of iron (fortified cereals, legumes, nuts and seeds) and include vitamin C-rich foods with each meal. As long as vegetarian athletes, like all athletes, consume enough nutrient-dense foods, they can perform as well as anyone.
Iron-deficiency anaemia Iron-deficiency anaemia impairs physical performance because the haemoglobin in red blood cells is needed to deliver oxygen to the cells for energy metabolism. Without adequate oxygen, an active person cannot perform aerobic activities and tires easily. Iron deficiency without clinical signs of anaemia may also impair physical performance.22
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Iron is an essential component of haemoglobin, the protein that transports oxygen throughout the body.
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Sports anaemia Early in training, athletes may develop low blood haemoglobin for a while. This condition, sometimes called sports anaemia, is not a true iron-deficiency condition. Strenuous aerobic activity promotes destruction of the more fragile, older red blood cells, and the resulting clean-up work reduces the blood’s iron content temporarily. Strenuous activity also expands the blood’s plasma volume, thereby reducing the red blood cell count per unit of blood. However, the red blood cells do not diminish in size or number as in anaemia, so their oxygen-carrying capacity is not hindered. Most researchers view sports anaemia as an adaptive, temporary response to endurance training. Iron-deficiency anaemia requires iron supplementation, but sports anaemia does not.
Iron recommendations for athletes The best strategy for maintaining adequate iron nutrition depends on the individual. Menstruating women may border on iron deficiency even without the iron losses incurred by physical activity. Active teens of both genders have high iron needs because they are growing. Especially for women and teens, then, prescribed supplements may be needed to correct iron deficiencies. Physicians use the results of blood tests to determine whether such supplementation is needed. (Review Chapter 13 for many more details about iron, and see Appendix E for a description of the tests used in assessing its status.) REVIEW IT
With the possible exception of iron, well-nourished active people and athletes do not need nutrient supplements. Female athletes need to pay special attention to their iron needs.
14.4 Fluids and electrolytes to support activity
The need for water far surpasses the need for any other nutrient. The body relies on watery fluids as the medium for all of its life-supporting activities, and if it loses too much water, its wellbeing will be compromised. Obviously, the body loses water via sweat. Breathing uses water, too, exhaled as vapour. During physical activity, water losses from both routes are significant, and dehydration becomes a threat. Dehydration’s first symptom is fatigue: a water loss of greater than 2 per cent of body weight can reduce a person’s capacity to do muscular work.23 With a water loss of about 7 per cent, a person is likely to collapse.
Samuel Borges Photography/Shutterstock.com
Temperature regulation As Chapter 7 discusses, working muscles produce heat as a by-product of energy metabolism. During intense activity, muscle heat production can be 15 to 20 times greater than at rest. The body cools itself by sweating. Each litre of sweat dissipates almost 2400 kilojoules of heat, preventing a rise in body temperature of almost 10ºC. The body routes its blood supply through the capillaries just under the skin, and the skin secretes sweat to evaporate and cool the skin and the underlying blood. The blood then flows back to cool the deeper body chambers.
Hyperthermia
To prevent dehydration and the fatigue that accompanies it, drink liquids before, during and after physical activity.
In hot, humid weather, sweat doesn’t evaporate well because the surrounding air is already laden with water. In hyperthermia, body heat builds up and triggers maximum sweating, but without sweat evaporation, little cooling takes place. In such conditions, active people must take precautions to prevent heat stroke. To reduce the risk of heat stroke, drink enough fluid before and during the activity, rest in the shade when tired and wear lightweight clothing that allows sweat to evaporate. (Hence the danger of rubber or heavy suits that supposedly promote weight loss during physical activity – they promote profuse sweating, prevent sweat
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evaporation and invite heat stroke.) If you ever experience any of the symptoms of heat stroke listed in Table 14.7, stop your activity, sip fluids, seek shade and ask for help. Heat stroke can be fatal – people sometimes die of it – and these symptoms demand attention.
Hypothermia
In cold weather, hypothermia, or low body temperature, can be as serious as heat stroke is in hot weather. Inexperienced, slow runners participating in long races on cold or wet, chilly days are especially vulnerable to hypothermia. Slow runners who produce little heat can become too cold if clothing is inadequate. Early symptoms of hypothermia include feeling cold, shivering, apathy, and social withdrawal. As body temperature continues to fall, shivering may stop, and disorientation, slurred speech, and change in behaviour or appearance set in (see Table 14.7). People with these symptoms soon become helpless to protect themselves from further body heat losses. Even in cold weather, however, the active body still sweats and still needs fluids. The fluids should be warm or at room temperature to help protect against hypothermia.
PUTTING COMMON SENSE TO THE TEST
Hypothermia is another name for heat stroke. FALSE
TABLE 14.7 Symptoms of heat stroke and hypothermia compared HEAT STROKE
HYPOTHERMIA
• Clumsiness, stumbling • Confusion, dizziness, other mental changes, loss of consciousness • Flushed skin (skin may turn red as body temperature rises) • Muscle cramping (early symptom) • Nausea and vomiting • Rapid breathing • Rapid heart rate • Sudden cessation of sweating (hot, dry, skin) • Throbbing headache
• Clumsiness, loss of coordination • Confusion, disorientation, other mental changes, loss of consciousness • Drowsiness • Shivering (early symptom) • Cessation of shivering (late symptom) • Slurred speech • Slow breathing • Slow heart rate
Adapted from United States Centers for Disease Control and Prevention, http://www.cdc.gov.
Fluid replacement via hydration Endurance athletes can easily lose 1.5 litres or more of fluid during each hour of activity. To prepare for fluid losses, a person must hydrate before activity. To replace fluid losses, the person must rehydrate during and after activity. (Table 14.8 presents one schedule of hydration for physical activity.) Even then, in hot weather, the GI tract may not be able to absorb enough water fast enough to keep up with sweat losses, and some degree of dehydration may be inevitable. Athletes who know their body’s hourly sweat rate can strive to replace the total amount of fluid lost during activity to prevent dehydration.
TABLE 14.8 A suggested hydration schedule for physical activity WHEN TO DRINK
AMOUNT OF FLUID
≥4 hours before activity
65 mL per 10 kilograms
2 hours before activity, if heavy sweating is expected
Add 40 mL per 10 kilograms
Every 15 minutes during activity
Drink enough to minimise loss of body weight, but don’t drink too much
After activity
≥100 mL for each 100 g of body weight losta
Drinking 500 mL (or 2 cups of fluid) every 20 to 30 minutes after exercise until the total amount required is consumed is more effective for rehydration than drinking the needed amount all at once. Rapid fluid replacement after exercise stimulates urine production and results in less body water retention.
a
C. A. Rosenbloom and E. J. Coleman, eds., Sports Nutrition: A Practice Manual for Professionals, Chicago: Academy of Nutrition and Dietetics (2012): 115; Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance, Journal of the American Dietetic Association 109 (2009): 509–27; American College of Sports Medicine, Position stand: Exercise and fluid replacement, Medicine and Science in Sports and Exercise 39 (2007): 377–90. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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Athletes who are preparing for competition are often advised to drink extra fluids in the days immediately before the event, especially if they are still training. The extra water is not stored in the body, but drinking extra water ensures maximum hydration at the start of the event. Full hydration is imperative for every athlete both in training and in competition. The athlete who arrives at an event even slightly dehydrated begins with a disadvantage. What is the best fluid for an exercising body? For non-competitive, everyday active people, plain, cool water is recommended, especially in warm weather, for two reasons – (1) water rapidly leaves the digestive tract to enter the tissues where it is needed, and (2) water cools the body from the inside out. For endurance athletes, carbohydrate-containing beverages may be appropriate. Fluid ingestion during the event has the dual purposes of replenishing water lost through sweating and providing a source of carbohydrate to supplement the body’s limited glycogen stores. Carbohydrate depletion brings on fatigue in the athlete, but as already mentioned, fluid loss and the accompanying build-up of body heat can be life-threatening. Thus, the first priority for endurance athletes should be to replace fluids. Many good-tasting drinks are marketed for active people; a later section compares them with water.
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Electrolyte losses and replacement
Water is the best fluid for most physically active people, but some consumers prefer the flavours of sports drinks.
When a person sweats, small amounts of electrolytes – the electrically charged minerals sodium, potassium, chloride and magnesium – are lost from the body along with water. Losses are greatest in beginners; training improves electrolyte retention. To replenish lost electrolytes, a person ordinarily needs only to eat a regular diet that meets energy and nutrient needs. In events lasting more than one hour, sports drinks may be needed to replace fluids and electrolytes. Salt tablets can worsen dehydration and impair performance; they increase potassium losses, irritate the stomach and cause vomiting.
APPLICATIONS OF NUTRITIONAL RESEARCH Hyponatraemia
Symptoms of hyponatraemia include: • severe headache • vomiting • bloating, puffiness from water retention (shoes tight, rings tight) • confusion • seizure.
When athletes compete in endurance sports lasting longer than three hours, replenishing electrolytes is crucial. If athletes sweat profusely over a long period of time and do not replace lost sodium, a dangerous condition known as hyponatraemia may result. Research shows that some athletes who sweat profusely may also lose more sodium in their sweat than others – and are prone to debilitating heat cramps. These athletes lose twice as much sodium in sweat as athletes who don’t cramp. Depending on individual variation, exercise intensity and changes in ambient temperature and humidity, sweat rates for these athletes can exceed 2 litres per hour. Hyponatraemia may also occur when endurance athletes drink such large amounts of water over the course of a long event that they overhydrate, diluting the body’s fluids to such an extent that the sodium concentration becomes extremely low. During long competitions, when athletes lose sodium through heavy sweating and consume excessive amounts of liquids, especially water, hyponatraemia becomes likely. Some athletes may still be vulnerable to hyponatraemia even when they drink sports drinks during an event. Sports drinks do contain sodium, but as a later section points out, the sodium content of sports drinks is low and, in some cases, too low to replace sweat losses. Still, sports drinks do offer more sodium than plain water. To prevent hyponatraemia, athletes need to replace sodium during prolonged events. They should favour sports drinks over water and eat pretzels in the last half of a long race. Some athletes may need beverages with higher sodium concentrations than commercial sports drinks. In the days before the event, especially an event in the heat, athletes should not restrict salt in their diets. The symptoms of hyponatraemia are similar to, but not the same as, those of dehydration (see the margin). Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Chapter 14: Fitness: physical activity, nutrients and body adaptations
HOW TO:
SPORTS DRINKS
Hydration is critical to optimal performance. Water best meets the fluid needs of most people, yet manufacturers market many good-tasting sports drinks for active people. The term ‘sports drink’ generally refers to beverages that contain carbohydrates and electrolytes in specific concentrations, and they are the focus of this discussion. What do sports drinks have to offer? Fluid Sports drinks offer fluids to help offset the loss of fluids during physical activity, but plain water can do this, too. Alternatively, diluted fruit juices or flavoured water can be used if preferred to plain water. Glucose Sports drinks offer simple sugars or glucose polymers that help maintain hydration and blood glucose and enhance performance as effectively as, or maybe even better than, water. Such measures are especially beneficial for strenuous endurance activities lasting longer than one hour, during intense activities or during prolonged competitive games that demand repeated intermittent activity. Sports drinks are also suitable for events lasting less than one hour, although plain water is appropriate as well. Fluid transport to the tissues from beverages containing up to 8 per cent glucose is rapid. Most sports drinks contain about 7 per cent carbohydrate (about half the sugar of ordinary soft drinks, or about 5 teaspoons in each 350 mL). Less than 6 per cent carbohydrate may not enhance performance, and more than 8 per cent may cause abdominal cramps, nausea and diarrhoea. Although glucose does enhance endurance performance in strenuous competitive events, for the moderate exerciser it can be counterproductive if weight loss is the goal. Glucose is sugar, and like candy, it provides only empty energy – no vitamins or minerals. Most sports drinks provide between 200 and 400 kJ per cup (250 mL). Sodium and other electrolytes Sports drinks offer sodium and other electrolytes to help replace those lost during physical activity. Sodium in sports drinks also helps to increase the rate of fluid absorption from the GI tract and maintain plasma volume during activity and recovery. Most physically active people do not need to replace the minerals lost in sweat immediately; a meal eaten within hours of competition replaces these minerals soon enough. Most sports drinks are relatively low in sodium, however, so those who choose to use these beverages run little risk of excessive intake. Good taste Manufacturers reason that if a drink tastes good, people will drink more, thereby ensuring adequate hydration. For athletes who prefer the flavours of sports drinks over water, it may be worth paying for good taste to replace lost fluids. For athletes who exercise for one hour or more, sports drinks provide an advantage over water. Sports drinks may also be beneficial for athletes who: › exercise on an empty stomach › do not consume enough carbohydrate › want to load carbohydrates › want to gain weight › train at altitude or in extreme weather › had diarrhoea (or vomiting) recently › do not drink adequate amounts of water. For most physically active people, though, water is the best fluid to replenish lost fluids. The most important thing to do is drink – even if you don’t feel thirsty.
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Enhanced water
Another beverage often marketed to athletes and active people is enhanced water. Enhanced waters are lightly flavoured waters with lower carbohydrate and electrolyte contents than traditional sports drinks. Marketers promote these beverages for the added vitamins, minerals and, in some cases, protein they contain. In fact, most enhanced waters contain small amounts of only a few minerals, some of the B vitamins and sometimes vitamin C or vitamin E. In the context of daily needs, the vitamins and minerals in these drinks do not add up to much. For example, it takes a quart of most of these beverages to provide only 10 per cent of the RDI for iron or calcium. Quite simply, enhanced waters are not a substitute for eating nutrient-rich fruits and vegetables. Enhanced waters may not be harmful (except maybe to the wallet), but most people do not need them. Plain water can meet fluid needs. If the flavour of enhanced waters encourages greater fluid intake, then they may offer some advantage. Serious endurance athletes need the carbohydrate–electrolyte sports drinks discussed earlier.
Poor beverage choices: caffeine and alcohol Athletes, like others, sometimes drink beverages that contain caffeine or alcohol. Each of these substances can influence physical performance.
Caffeine Caffeine is a stimulant, and athletes sometimes use it to enhance performance as Highlight 14 explains. Carbonated soft drinks, with or without caffeine, may not be a wise choice for athletes: bubbles make a person feel full quickly and so limit fluid intake. Some of the increasingly popular beverages, called energy drinks, contain amounts of caffeine equivalent to a cup or two of coffee. When used in excess or in combination with stimulants or other unregulated substances, energy drinks can hinder performance and are potentially dangerous. Another reason energy drinks should not be used for fluid replacement during athletic events is that the carbohydrate concentrations are too high for optimal fluid absorption.
Beer facts: • Beer is not carbohydrate-rich: Beer is kJ-rich, but only one-third of its energy is from carbohydrates. The other two-thirds are from alcohol. • Beer is mineral-poor: Beer contains a few minerals, but to replace the minerals lost in sweat, athletes need good sources, such as fruit juices. • Beer is vitaminpoor: Beer contains traces of some B vitamins, but it cannot compete with food sources. • Beer is a fluid, but alcohol is a diuretic and causes the body to lose valuable fluid.
Alcohol Some athletes mistakenly believe that they can replace fluids and load up on carbohydrates by drinking beer. A 350-mL beer provides 13 grams of carbohydrate – one-third the amount of carbohydrate in a glass of orange juice the same size. In addition to carbohydrate, beer also contains alcohol, of course. Energy from alcohol breakdown generates heat, but it does not fuel muscle work because alcohol is metabolised in the liver. It is difficult to overstate alcohol’s detrimental effects on physical activity. Alcohol’s diuretic effect impairs the body’s fluid balance, making dehydration likely; after physical activity, a person needs to replace fluids, not lose them by drinking beer. Alcohol also impairs the body’s ability to regulate its temperature, increasing the likelihood of hypothermia or heat stroke. Alcohol also alters perceptions; slows reaction time; reduces strength, power and endurance; and hinders accuracy, balance, eye–hand coordination and coordination in general – all opposing optimal athletic performance. In addition, it deprives people of their judgement, thereby compromising their safety in sports. Many sports-related fatalities and injuries involve alcohol or other drugs. Clearly, alcohol impairs performance; however, many physically active people do drink on occasion. A word of caution: do not drink alcohol before exercising, and drink plenty of water before drinking alcohol after exercising. REVIEW IT
Active people need to drink plenty of water; endurance athletes need to drink both water and carbohydrate-containing beverages, especially during training and competition. During events lasting longer than three hours, athletes need to pay special attention to the replacement of sodium losses to prevent hyponatraemia.
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14.5 Diets for physically active people No one diet best supports physical performance. Active people who choose foods within the framework of the diet-planning principles presented in Chapter 2 can design many excellent diets.
Choosing a diet to support fitness Above all, keep in mind that water is depleted more rapidly than any other nutrient. A diet to support fitness must provide water, energy and all the other nutrients.
Even casual exercisers must attend conscientiously to their fluid needs. Physical activity blunts the thirst mechanism, especially in cold weather. During activity, thirst signals come too late, so don’t wait to feel thirsty before drinking. To find out how much water is needed to replenish activity losses, weigh yourself before and after the activity – the difference is almost all water. One kilogram of weight lost should be replaced with an almost equivalent intake of fluid.
Polara Studios, Inc.
Water
A variety of foods is the best source of nutrients for athletes.
Nutrient density A healthful diet is based on nutrient-dense foods – foods that supply adequate vitamins and minerals for the energy they provide. Active people need to eat both for nutrient adequacy and for energy. A diet that is high in carbohydrate (60 to 70 per cent of total kilojoules), moderate in fat (20 to 30 per cent) and adequate in protein (10 to 20 per cent) ensures full glycogen and other nutrient stores.
Carbohydrate Full glycogen stores are critical to athletes and other highly active people. Guidelines to provide high carbohydrate availability for athletes are based on the athlete’s weight and the characteristics of training sessions and competitions. On two occasions, the active person’s regular high-carbohydrate, fibre-rich diet may require temporary adjustment. Both of these exceptions involve training for competition rather than for fitness in general. One special occasion is the pre-game meal, when fibre-rich, bulky foods are best avoided. The pre-game meal is discussed in a later section. The other occasion is during intensive training, when energy needs may be so high as to outstrip the person’s capacity to eat enough food to meet them. At that point, added sugar and fat may be needed. The athlete can add concentrated carbohydrate foods, such as dried fruits, sweet potatoes and white bread sandwiches, and even high-fat foods, such as avocados and nuts. Still, a nutrient-rich diet remains central for adequacy’s sake. Although vital, energy alone is not enough to support performance. Some athletes use commercial high-carbohydrate liquid supplements to obtain the carbohydrate and energy needed for heavy training and top performance. These supplements do not replace regular food; they are meant to be used in addition to it. Unlike the sports beverages discussed earlier, these high-carbohydrate supplements are too concentrated in carbohydrate to be used for fluid replacement.
Protein In addition to carbohydrate and some fat (and the energy they provide), physically active people need protein. Meats and milk products are rich protein sources, but recommending that active people emphasise these foods is narrow advice. As mentioned repeatedly, active people
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Carbohydrate recommendation for athletes in heavy training: 8 to 10 g/kg body weight
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need diets rich in carbohydrate, and of course, meats have none to offer. Legumes, whole grains and vegetables provide some protein with abundant carbohydrate. Table 14.5 (page 508) shows recommended protein intakes for active people.
A performance diet example A person who engages in vigorous physical activity on a daily basis could easily require more than 12 000 kilojoules per day. To meet this need, the person can choose a variety of nutrientdense foods. Athletes who train exhaustively for endurance events may want to aim for somewhat higher carbohydrate intakes. Beyond these specific concerns of total energy, protein and carbohydrate, the diet most beneficial to athletic performance is remarkably similar to the diet recommended for most people.
CURRENT RESEARCH IN NUTRITION Athletes can excel on a vegetarian diet When it comes to strength and fitness, research studies find that vegetarian athletes can perform just as well as their omnivore opponents. In a new study, researchers recruited 27 vegetarian and 43 omnivore competitive endurance athletes.24 Each person in the vegetarian group had followed the diet for at least two years, and there was a mixture of vegan and lacto-ovo vegetarians amongst the group. Food intake, maximal oxygen uptake (VO2 max) during treadmill running and leg strength were all assessed. For the males, there was little difference in cardio-respiratory fitness or strength between the vegetarian and omnivores. The surprising finding though was in the women. Vegetarian women had a 13 per cent greater VO2 max scores than women eating an omnivore diet. There was no difference in protein intake according to body weight between vegetarians and omnivores. Although vegetarians ate more carbohydrates and fibre, they do have less vitamin B12, which is not so surprising. One interesting finding was that vegetarians had more iron in their diet than omnivores. But because plant-based iron is less bioavailable than animal-based iron, then this may bring the vegetarians back on par with omnivores. A well-planned and varied vegetarian diet can meet the nutritional needs of an athlete just as well as an omnivore diet. Such a diet poses little risk of sub-par performance, and for some athletes it may even spur them on to higher levels of achievement.
Meals before and after competition
Highcarbohydrate, liquid pre-game fruit smoothie ideas include: • apple juice, frozen banana and 1 tablespoon of plain yoghurt • pineapple juice, frozen strawberries and several mint leaves • reduced-fat milk, frozen banana and vanilla essence.
No single food improves speed, strength or skill in competitive events, although some kinds of foods do support performance better than others, as already explained. Still, a competitor may eat a particular food before or after an event for psychological reasons. One eats a steak the night before wrestling. Another eats some honey just five minutes after diving. As long as these practices remain harmless, they should be respected.
Pre-game meals Science indicates that the pre-game meal or snack should include plenty of fluids and be light and easy to digest. It should provide between 1200 and 3300 kilojoules, primarily from carbohydrate-rich foods that are familiar and well tolerated by the athlete. The meal should end three to four hours before competition to allow time for the stomach to empty before exertion. Breads, potatoes, pasta and fruit juices – that is, carbohydrate-rich foods low in fat and dietary fibre – form the basis of the best pre-game meal (see Figure 14.3 for some examples). Bulky, fibre-rich foods such as raw vegetables or wholegrain cereals, although usually desirable, are best avoided just before competition. Dietary fibre in the digestive tract attracts water and can cause stomach discomfort during performance. Liquid meals are easy to digest, and many such meals are commercially available. Alternatively, athletes can mix fat-free milk or juice, frozen fruits and flavourings in a blender.
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FIGURE 14.3 Examples of high-carbohydrate pre-game meals
1200-kilojoule meal 1 large apple 4 plain biscuits 1½ tbs reduced-fat peanut butter
Matthew Farruggio
Matthew Farruggio
Matthew Farruggio
Pre-game meals should be eaten three to four hours before the event and provide 1200 to 3300 kJ, primarily from carbohydraterich foods. Each of these sample meals provides at least 65 per cent of total kilojoules from carbohydrate.
2100-kilojoule meal 1 large wholemeal bagel 2 tbs fruit jam 1½ c low-fat milk
3100-kilojoule meal 1 large baked potato 2 tsp margarine 1 c steamed broccoli 1 c mixed carrots and green peas 5 small vanilla biscuits 1½ c apple or pineapple juice
Recovery meals Athletes who perform intense practice sessions several times a day or compete for hours on consecutive days need to quickly replenish glycogen to be ready for the next activity. As mentioned earlier, eating high-carbohydrate foods after physical activity enhances glycogen storage, just as eating high-quality protein foods helps stimulate protein synthesis. Because people are usually not hungry immediately following physical activity, a carbohydratecontaining beverage such as low-fat milk may be preferred. A two-cup serving of chocolate milk, taken within an hour or two following exercise has been shown to both maintain muscle glycogen stores and increase muscle protein synthesis.25 If an active person does feel hungry after an event, then foods high in carbohydrate, moderate in protein, and low in fat and fibre are the ones to choose – similar to those recommended prior to competition.
REVIEW IT
The person who wants to excel physically will apply accurate nutrition knowledge along with dedication to rigorous training. A diet that provides ample fluid and includes a variety of nutrient-dense foods in quantities to meet energy needs will enhance not only athletic performance, but overall health as well. Carbohydrate-rich foods that are light and easy to digest are recommended for both the pre-game and the postgame meal. Training and genetics being equal, who will win a competition – the athlete who habitually consumes inadequate amounts of needed nutrients, or the competitor who arrives at the event with a long history of full nutrient stores and well-met metabolic needs?
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Regular exercise can reduce the risk of developing type 2 diabetes. TRUE
4 Protein needs for endurance athletes are the same as those of sedentary people. FALSE
Physical activity normalises glucose tolerance and reduces the risk of developing type 2 diabetes and benefits those who already have the condition.
2 Creatine phosphate is a reliable energy reserve for distance runners. FALSE
Creatine phosphate can only supply energy for around 10 seconds, and so is used in sprinting.
3 As exercise intensity increases, glycogen utilisation increases also. TRUE
The combination of the impact stress on the body and depletion of glycogen stores means endurance athletes have much higher protein requirements than a sedentary person.
5 Hypothermia is another name for heat stroke. FALSE
Hypothermia is seen in cold conditions and results in lowered body temperature. Heat stroke is a consequence of body heat build-up typically seen in hot and humid conditions combined with dehydration.
Anaerobic glycolysis becomes more important to meet ATP needs as exercise intensity increases to maximum.
NUTRITION PORTFOLIO The foods and beverages you eat and drink provide fuel and other nutrients to support your physical activity. • Describe your daily physical activities and how they compare with recommendations to be physically active for at least 30 minutes, and preferably 60 minutes, a day on most or all days of the week.
• Estimate your daily fluid intake, taking into account both liquids and an estimate of how much foods also contribute to this. • Evaluate the protein content of your diet and consider whether it would meet the needs of a physically active person.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1
2
The benefits of exercise include all of the following except: a flexibility c strength b fitness d digestion Use of creatine phosphate would be most important in which sport? a b
3
Road cycling Tennis
gluconeogenesis the ATP–CP cycle
c d
the TCA cycle the cardiac output cycle
Which of the following sources do not supply ATP during exercise? a b
5
c d
The process that regenerates glucose from lactate is known as: a b
4
Marathon running 100-metre sprinting
Glycogen Amino acids
c d
Triglycerides Insulin
The technique that endurance athletes use to maximise glycogen stores is called: a b
c d
carbohydrate loading progressive overloading
6 Conditioned muscles rely less on _____ and more on _____ for energy. a b c d
protein; fat fat; protein glycogen; fat fat; glycogen
7 An approximate target for protein intake for endurance athletes is: a b c d
0.8 g/kg/day 0.8–1.2 g/kg/day 1.2–2.0 g/kg/day 3.0 g/kg/day
8 Physically active young women, especially those who are endurance athletes, are prone to: a b c d
energy excess iron deficiency protein overload vitamin A toxicity
aerobic training muscle conditioning
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Chapter 14: Fitness: physical activity, nutrients and body adaptations
9 The body’s need for _____ far surpasses its need for any other nutrient. a b c d
water protein vitamins carbohydrate
10 A recommended pre-game meal includes plenty of fluids and provides between: a b c d
1200 and 3000 kJ, mostly from fat-rich foods 200 and 400 kJ, mostly from high-fibre foods 4000 and 8000 kJ, mostly from protein-rich foods 1200 and 3000 kJ, mostly from carbohydrate-rich foods
Review questions 1
Describe why physical activity complements a wellbalanced diet to improve health. (Section 14.1)
2
Explain the differences between strength and endurance exercise. (Section 14.1)
3
Define cardiorespiratory conditioning and list some of its benefits. (Section 14.1)
4
What types of activity are anaerobic? Which are aerobic? (Section 14.2)
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5
Describe the relationships among energy expenditure, type of activity and oxygen use. (Section 14.2)
6
What factors influence the body’s use of glucose during physical activity? How? (Section 14.2)
7
What factors influence the body’s use of fat during physical activity? How? (Section 14.2)
8
What factors influence the body’s use of protein during physical activity? How? (Section 14.2)
9
How do protein recommendations differ between athletes and the general population? (Section 14.2)
10 Why are some athletes likely to develop irondeficiency anaemia? Compare iron-deficiency anaemia and sports anaemia, explaining the differences. (Section 14.3) 11 Discuss the impact dehydration has on performance and strategies that can be used to prevent dehydration. (Section 14.4) 12 Describe the importance of carbohydrates as part of a healthy diet for athletic performance. (Section 14.5)
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Review the current lack of physical activity and awareness of the health benefits of physical activity; search ‘physical activity’ at http://www.aihw.gov.au
• Examine how physical activity can become a vital component of children’s education: http://www.achper.org.au • Learn about the activities of sports dietitians: http://www.sportsdietitians.com.au • Find fitness information at the Cooper Institute site: http://www.cooperinst.org • Find information on sports drinks and other nutrition and fitness topics at the Australian Institute of Sport Nutrition site: http://www.ausport.gov.au/ais/nutrition
SEARCH ME! NUTRITION Search me Keyword: sports nutrition Read the article Nutritional triggers to adaptation and performance and outline which nutritional strategies and
supplements have solid or emerging evidence to support a performance benefit in sport.
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14.6 SUPPLEMENTS AS ERGOGENIC AIDS
HIGHLIGHT
14
Athletes gravitate to promises that they can enhance their performance by taking pills, powders or potions. Unfortunately, they often hear such promises from their coaches and peers, who advise them to use nutrient supplements, take drugs or follow procedures that claim to deliver results with little effort. When such performanceenhancing aids are harmless, they are only a waste of money; when they impair performance or harm health, they waste athletic potential and cost lives. This highlight looks at scientific evidence for and against dietary supplements and hormonal preparations available to athletes.
For the vast majority of ergogenic aids, research findings do not support those claims.1 Athletes who hear that a product is ergogenic should ask who is making the claim and who will profit from the sale. Chapter 6 includes a discussion on protein powders and amino acid supplements. Athletes who supplement their diets with products promoted to improve athletic performance should be aware that some supplements are contaminated with illegal substances such as steroids that are not listed on the label.2 Supplements contaminated with illegal substances pose health risks to those who use them as well as the risk of positive drug testing for athletes subject to such tests.
Dietary supplements that perform as claimed Among the extensive array of dietary supplements and other ergogenic aids that athletes use, a few seem to live up to the claims made for them, based on research so far. Convenient dietary supplements, caffeine, creatine, sodium bicarbonate and beta-alanine are the examples discussed here.
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Convenient dietary supplements
Training hard is where most of the performance gains are made for athletes.
Ergogenic aids Many substances or treatments claim to be ergogenic, meaning work enhancing. In connection with athletic performance, ergogenic aids are substances or treatments that purportedly improve athletic performance above and beyond what is possible through training. For practical purposes, most ergogenic aids can be categorised as: • those that perform as claimed • those that may perform as claimed but for which there is insufficient evidence at this time • those that do not perform as claimed • those that are dangerous, banned or illegal, and therefore should not be used.
Ready-to-drink supplements such as liquid meal replacers and energy drinks, energy bars and energy gels are convenient dietary supplements for athletes and active people, especially when time is limited. Many such products appeal to athletes by claiming to provide ‘complete’ nutrition. These supplements usually taste good and provide extra carbohydrate and food energy, but they fall short of providing ‘complete’ nutrition. They can be useful as a pre-game meal or a between-meal snack, but they should not replace regular meals. Liquid meal replacers may help a nervous athlete who cannot tolerate solid food on the day of an event. A liquid meal two to three hours before competition can supply some of the fluid and carbohydrate needed in a pre-game meal, but a shake of fat-free milk or juice and frozen fat-free yoghurt or frozen fruit (such as strawberries or bananas) can do the same thing less expensively.
Caffeine
Some research supports the use of caffeine to enhance endurance and, to some extent, to enhance short-term, high-intensity exercise performance.3 Caffeine may
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stimulate fatty acid release during endurance activity, but in contrast to what was previously thought, caffeine does not slow muscle glycogen use.4 Light activity before a workout also stimulates fat release and, unlike caffeine, warms the muscles and connective tissues, making them flexible and resistant to injury. Caffeine is a stimulant that elicits a number of physiological and psychological effects in the body. It may enhance alertness and reduce the perception of fatigue.5 The possible benefits of caffeine use must be weighed against its adverse effects – stomach upset, nervousness, irritability, headaches and diarrhoea. Caffeine-containing beverages should be used in moderation, if at all, and in addition to other fluids, not as a substitute for them. In 2004, the World Anti-Doping Agency, established by the International Olympic Committee, removed caffeine from its list of prohibited substances.
Creatine
Interest in – and use of – creatine supplements to enhance performance during intense activity has grown dramatically in the last few years. Power athletes such as weight-lifters use creatine supplements to enhance stores of the high-energy compound creatine phosphate (CP) in muscles. Theoretically, the more creatine phosphate in muscles, the higher the intensity at which an athlete can train. High-intensity training stimulates the muscles to adapt, which, in turn, improves performance. The results of some studies suggest that creatine supplementation does enhance performance of short-term, repetitive, high-intensity activity such as weight-lifting and sprinting.6 Creatine may improve performance by increasing muscle strength and size, cell hydration or glycogen loading capacity. In contrast, creatine supplementation has not been shown to benefit endurance activity. The question of whether short-term use (up to a year) of creatine supplements (up to 5 grams per day) is safe continues to be studied, but so far, the supplements are viewed to be safe for healthy adults.7 More research is needed, however, to confirm the safety of larger doses and long-term creatine use. Creatine supplementation may pose risks to athletes with kidney disease or other conditions. One side effect of creatine supplementation that no one disputes is weight gain. For some athletes, weight gain, especially muscle gain, is beneficial, but for others, it is not. Some medical and fitness experts voice concern that, like many performance enhancement supplements before it, creatine is being taken in huge doses (up to 30 grams per day) before evidence of its value has been ascertained. Even people who eat red meat, which is a creatine-rich food, do not consume nearly the amount supplements provide. (Creatine content varies, but on average, pork, chicken and beef provide 250–650 milligrams per 100 grams.) Despite the uncertainties, creatine
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supplements are not illegal in international competition. The American Academy of Pediatrics strongly discourages the use of creatine supplements, as well as the use of any performance-enhancing substance in adolescents younger than 18 years old.
Sodium bicarbonate During short-term, high-intensity activity, acid and carbon dioxide accumulate in the blood and muscles. Sodium bicarbonate (0.3 grams per kilogram of body weight) ingested prior to high-intensity sports performance buffers the acid and neutralises the carbon dioxide, thereby maintaining muscle pH levels closer to normal and enhancing exercise capacity.8 Sodium bicarbonate supplementation may cause unpleasant side effects such as diarrhoea in some athletes.
Beta-alanine
Beta-alanine is a nonessential amino acid that has recently received much attention from exercise researchers. Beta-alanine is the rate-limiting precursor for the synthesis of the dipeptide carnosine. Carnosine occurs in high concentrations in skeletal muscle and is one of the primary buffering substances available in muscles. Supplementation with beta-alanine has been shown to raise the concentration of muscle carnosine, which enhances the muscles’ buffering capacity.9 This enhanced buffering is especially beneficial to high-intensity exercise performance such as sprinting. The only known adverse side effect of beta-alanine supplementation is a ‘pins and needles’ sensation that occurs with high (more than 800 milligrams) single doses. Additional research is needed to confirm the safety of beta-alanine supplementation.10
Dietary nitrate Nitrate is an inorganic compound present in both air and water, as well as in certain vegetables (spinach, beets, celery, radishes and lettuce). Nitrate is also a common food preservative added to processed meats such as bacon, bologna, hot dogs and lunch meats. As a supplement, dietary nitrate (either as beetroot juice or sodium nitrate) may improve athletic performance, which has sparked a flurry of intense, ongoing research.11 Once ingested, nitrate is converted to nitrite, which circulates in the blood. When oxygen availability is low (as can occur during exercise), nitrite can be converted to nitric oxide. Nitric oxide, an important signalling molecule, improves the muscles’ efficiency in using oxygen. By enhancing nitric oxide bioavailability, dietary nitrate supplementation reduces oxygen consumption; improves performance during moderate walking, running, rowing and cycling; and improves exercise tolerance at more
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vigorous intensities. Despite such findings, some studies of elite or highly trained athletes fail to show performance benefits following nitrate supplementation; such athletes may already be performing at their maximum oxygen efficiency, or perhaps they require larger doses of nitrate to elicit benefits.12 Additional research is needed to determine how age, health and fitness status, type of activity, and other factors influence the effects of nitrate supplementation on athletic performance. The safety of long-term nitrate supplementation also needs to be addressed.
Dietary supplements that may perform as claimed For some dietary supplements, it is just too early to tell whether they deliver on the promises made for them because research thus far is inconclusive. One example of a supplement that may perform as claimed, but for which there is insufficient evidence of efficacy is betahydroxymethylbutyrate. Beta-hydroxymethylbutyrate (HMB) is a metabolite of the amino acid leucine. Supplementing the diet with HMB during training has been shown to increase muscle mass and strength, especially among untrained individuals.13 Additional research is needed, however, to determine whether HMB supplementation in trained athletes enhances training adaptations.
Dietary supplements that do not perform as claimed Most of the dietary supplements promoted as ergogenic aids fall into the category of ‘those that do not perform as claimed.’ Carnitine is one example of an ineffective supplement discussed here, but others include boron, chromium picolinate, coenzyme Q10, ginseng and pyruvate. In the body, carnitine facilitates the transfer of fatty acids across the mitochondrial membrane. Supplement manufacturers suggest that with more carnitine available, fat oxidation will be enhanced, but this does not seem to be the case. Carnitine supplements neither raise muscle carnitine concentrations nor enhance exercise performance. Milk and meat products are good sources of carnitine, and supplements are not needed.
Dangerous, banned and illegal supplements The dietary supplements discussed this far may or may not help athletic performance, but in the doses commonly taken, they seem to cause little harm. The remaining discussion features hormonal preparations that are clearly damaging: anabolic steroids, DHEA
(dehydroepiandrosterone), androstenedione, and hGH (human growth hormone). All of these ergogenic aids are dangerous to use and are banned by most professional sports leagues and the World Anti-Doping Agency.
Anabolic steroids Among the most dangerous and illegal ergogenic practices is the taking of anabolic steroids. These drugs are derived from the male sex hormone testosterone, which promotes the development of male characteristics and lean body mass. The athletes who take steroids do so to stimulate muscle bulking. The known toxic side effects of steroids include, but are not limited to, extreme aggression and hostility, heart disease and liver damage. Taking these drugs is a form of cheating. The International Olympic Committee and almost all sporting agencies and governing organisations specifically ban the use of anabolic steroids. These authorities cite the known toxic side effects and maintain that taking these drugs is a form of cheating. Other athletes are put in the difficult position of either conceding an unfair advantage to competitors who use steroids or taking them and accepting the risk of harmful side effects (see Table H14.1). Young athletes should not be forced to make such a choice. The price for the potential competitive edge that steroids confer is high – sometimes it is life itself. Steroids are not simple pills that build bigger muscles. They are complex chemicals to which the body reacts in many ways, particularly when body builders and other athletes take large amounts. The safest, most effective way to build muscle has always been through hard training and a sound diet, and – despite popular misconceptions – it still is. Some manufacturers peddle specific herbs as legal substitutes for steroid drugs. They falsely claim that these herbs contain hormones, enhance the body’s hormonal activity, or both. In some cases, a herb may contain plant sterols, such as gamma-oryzanol, but these compounds are poorly absorbed. Even if absorption occurs, the body cannot convert herbal compounds to anabolic steroids. None of these products has any proven anabolic steroid activity, none enhances muscle strength and some contain natural toxins. In short, ‘natural’ does not mean ‘harmless’.
DHEA and androstenedione
Some athletes use DHEA (dehydroepiandrosterone) and androstenedione as alternatives to anabolic steroids. DHEA and androstenedione are hormones made in the adrenal glands that serve as precursors to the male hormone testosterone. Advertisements claim the hormones ‘burn fat’, ‘build muscle’ and ‘slow ageing’, but evidence to support such claims is lacking.
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TABLE H14.1 Anabolic steroids: side effects and adverse reactions MIND • Extreme aggression with hostility (‘steroid rage’), mood swings, anxiety, dizziness, drowsiness, unpredictability, insomnia, psychotic depression, personality changes, suicidal thoughts FACE AND HAIR • Swollen appearance, greasy skin, severe scarring acne, mouth and tongue soreness, yellowing of whites of eyes (jaundice) • In females: male-pattern hair loss and increased growth of face and body hair VOICE • In females: irreversible deepening of voice CHEST • In males: breathing difficulty, breast development • In females: breast atrophy HEART • Heart disease, elevated or reduced heart rate, heart attack, stroke, hypertension, increased LDL, reduced HDL ABDOMINAL ORGANS • Nausea, vomiting, bloody diarrhoea, pain, oedema, liver tumours (possibly cancerous), liver damage – disease or rupture leading to fatal liver failure, kidney stones and damage, gall stones, frequent urination, possible rupture of aneurysm or haemorrhage BLOOD • Blood clots, high risk of blood poisoning, those who share needles risk contracting HIV (the AIDS virus) or other diseasecausing organisms, septic shock (from injections) REPRODUCTIVE SYSTEM • In males: permanent shrinkage of testes, prostate enlargement with increased risk of cancer, sexual dysfunction, loss of fertility, excessive and painful erections • In females: loss of menstruation and fertility, permanent enlargement of external genitalia, foetal damage if pregnant MUSCLES, BONES AND CONNECTIVE TISSUES • Increased susceptibility to injury with delayed recovery times, cramps, tremors, seizure-like movements; injury at injection site • In adolescents: failure to grow to normal height OTHER • Fatigue, increased risk of cancer
Short-term side effects of DHEA and androstenedione may include oily skin, acne, body hair growth, liver enlargement, testicular shrinkage and aggressive behaviour. Long-term effects, such as serious liver damage, may take years to become evident. The potential for harm from DHEA and androstenedione supplements is great, and athletes, as well as others, should avoid them.
Human growth hormone A wide range of athletes, including weight-lifters, baseball players, cyclists, and track and field participants
use hGH (human growth hormone) to build lean tissue and improve athletic performance. The athletes experiment with hGH, believing the injectable hormone will provide the benefits of anabolic steroids without the dangerous side effects. Taken in large quantities, hGH causes the disease acromegaly, in which the body becomes huge and the organs and bones over-enlarge. Other effects include diabetes, thyroid disorder, heart disease, menstrual irregularities, diminished sexual desire and shortened life span. The International Olympic Committee, the Australian Sports Anti-Doping Authority and most
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professional sports leagues ban hGH use, but its use is difficult to detect. These organisations maintain that the use of hGH is a form of cheating that undermines the quest for physical excellence and that its use is coercive to other athletes.
A final word of caution Sometimes it is difficult to distinguish valid claims from bogus ones. Fitness magazines and Internet websites are particularly troublesome because many of them present both valid and invalid nutrition information along with slick advertisements for nutrition products. Advertisements often feature colourful anatomical figures, graphs and tables that appear scientific. Some ads even include references, citing or linking to such credible sources as the American Journal of Clinical Nutrition and the Journal of the American Medical Association. These ads create the illusion of endorsement and credibility to gain readers’ trust. Keep in mind, however, that the ads are created not to teach, but to sell. A careful reading of the cited research might reveal that the ads have presented the research findings out of context. For example, an ad might use a research article to conclude that its hGH supplement ‘increases lean body mass and bone mineral’ when, in fact, the researchers would conclude that ‘its general use
now or in the immediate future is not justified’. Scientific facts are often exaggerated and twisted to promote sales. Highlight 1 describes ways to recognise misinformation and quackery. The search for a single food, nutrient, drug or technique that will safely and effectively enhance athletic performance will no doubt continue as long as people strive to achieve excellence in sports. When athletic performance does improve after use of an ergogenic aid, the improvement can often be attributed to the placebo effect, which is strongly at work in athletes. Even if a reliable source reports a performance boost from a newly tried product, give the effect time to fade away. Chances are excellent that it simply reflects the power of the mind over the body. The overwhelming majority of performanceenhancing aids sold for athletes are frauds. Wishful thinking will not substitute for talent, hard training, adequate diet and mental preparedness in competition. But don’t discount the power of mind over body for a minute – it is formidable, and sports psychologists dedicate their work to harnessing it. You can use it by imagining yourself a winner and visualising yourself excelling in your sport. You don’t have to buy magic to obtain a winning edge; you already possess it – your physically fit mind and body.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A What are the moral implications of using ergogenic aids? B Because of serious doping violations, Lance Armstrong was stripped of his seven Tour de France titles and banned from cycling for life. For him, these actions are ‘equivalent to a death sentence’. What
is your opinion of Armstrong’s doping violations and the imposed consequences? If you were a member of world cycling’s governing body, how would you propose determining which, if any, substances to allow and/or ban?
NUTRITION ON THE NET Find out more information online. • Review the latest scientific evidence on supplements and sports nutrition at the nutrition page of the Australian Institute of Sport website: https://www.sportaus.gov.au/ais/nutrition
• Find information on sports drinks and other nutrition and fitness topics at the Gatorade Sports Science Institute site: https://www.gssiweb.org/en
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REFERENCES CHAPTER 1
U. Ekelund and co-authors, Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women, Lancet 388 (2016): 1302–10; D. Schmid and coauthors, Replacing sedentary time with physical activity in relation to mortality, Medicine and Science in Sports and Exercise 48 (2016): 1312–19. 2 Australian Bureau of Statistics, National Health Survey: First Results, 2014-15, ABS Catalogue Number 4364.0.55.001, Canberra: ABS (2015); New Zealand Ministry of Health, The Health of New Zealand Adults 2011/12 (2012), available at http://www.health.govt.nz/ publication/health-new-zealand-adults-2011-12 3 Department of Health, Australia’s Physical Activity and Sedentary Behaviour Guidelines (2017), available at http://www.health.gov.au/ internet/main/publishing.nsf/content/health-pubhlth-strateg-physact-guidelines 4 American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise, Medicine and Science in Sports and Exercise 43 (2011): 1334–59. 5 X. Lin and co-authors, Leisure time physical activity and cardiometabolic health: Results from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil), Journal of the American Heart Association 5 (2016): 6. 6 N. M. Johannsen and co-authors, Combined aerobic resistance training effects on glucose homeostasis, fitness, and other major health indices: A review of current guidelines, Sports Medicine, 46 (2016): 1809–18; C. K. Roberts and co-authors, Strength fitness and body weight status on markers of cardiometabolic health, Medicine and Science in Sports and Exercise 47 (2015): 1211–18. 7 V. P. Nicholson and co-authors, Low-load very high-repetition resistance training attenuates bone loss at the lumbar spine in active post-menopausal women, Calcified Tissue International, 96 (2015): 490–9. 8 B.J. Nicklas and co-authors, Effects of resistance training with and without caloric restriction on physical function and mobility in overweight and obese older adults: a randomized controlled trial, American Journal of Clinical Nutrition 101 (2015): 991–9. 9 American College of Sports Medicine, Position stand: Progression models in resistance training for healthy adults, Medicine and Science in Sports and Exercise 41, (2009): 687–708. 10 J. Bergstrom and co-authors, Diet, muscle glycogen and physical performance, Acta Physiologica Scandinavica 71 (1967): 140–50. 11 J. F. Moxnes and Ø. Sandbakk, The kinetics of lactate production and removal during whole-body exercise, Theoretical Biology and Medical Modeling 9 (2012): 7. 12 Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and American College of Sports Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28.
13 T. Stellingwerff and G. R. Cox, Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations, Applied Physiology, Nutrition, and Metabolism 39 (2014): 998–1011. 14 Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and American College of Sports Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28. 15 T. M. McLellan, S. M. Pasiakos, and H. R. Lieberman, Effects of protein in combination with carbohydrate supplements on acute or repeat endurance exercise performance: A systematic review, Sports Medicine 44 (2014): 535–50. 16 Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and American College of Sports Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28. 17 Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and American College of Sports Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28. 18 Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and American College of Sports Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28. 19 Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sport Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28. 20 R. T. Makowski and co-authors, Dietary antioxidants as modifiers of physiologic adaptations to exercise, Medicine and Science in Sports and Exercise 47 (2015): 1857–68. 21 G. Bruinvels and co-authors, The prevalence and impact of heavy menstrual bleeding (menorrhagia) in elite and non-elite athletes, PLoS One 11 (2016): e0149881; I. Alaunyte, V. Stojceska, and A. Plunkett, Iron and the female athlete: A review of dietary treatment methods for improving iron status and exercise performance, Journal of the International Society of Sports Nutrition 12 (2015): 38. 22 R. J. Burden and co-authors, Is iron treatment beneficial in irondeficient but non-anaemic (IDNA) endurance athletes? A systematic review and meta-analysis, British Journal of Sports Medicine 49 (2015): 1389–97. 23 Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sport Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28. 24 H. M. Lynch, C. M. Wharton and C. S. Johnstone, Cardiorespiratory fitness and peak torque differences between vegetarian and omnivore endurance athletes: a cross-sectional study, Nutrients 8 (2016): E726. 25 W. R. Lunn and co-authors, Chocolate milk and endurance exercise recovery: Protein balance, glycogen, and performance, Medicine and Science in Sports and Exercise 44 (2012): 682–91.
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HIGHLIGHT 1
2
3
4
5 6
7
8
Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance, Journal of the Academy of Nutrition and Dietetics 116 (2016): 501–28. P. A. Cohen, Hazards of hindsight—Monitoring the safety of nutritional supplements, New England Journal of Medicine 370 (2014): 1277–80. C. D. Black, D. E. Waddell, and A. R. Gonglach, Caffeine’s ergogenic effects on cycling: Neuromuscular and perceptual factors, Medicine and Science in Sports and Exercise 47 (2015): 1145–58; H. K. Stadheim and co-authors, Caffeine and performance over consecutive days of simulated competition, Medicine and Science in Sports and Exercise 46 (2014): 1787–96. M. Dunford and E. J. Coleman, Ergogenic aids, dietary supplements, and exercise, in sports nutrition: a practice manual for professionals, 5th ed., eds. C. A. Rosenbloom and E. J. Coleman, Chicago, IL: Academy of Nutrition and Dietetics (2012): 128–61. C. Rosenbloom, Energy drinks, caffeine, and athletes, Nutrition Today 49 (2014): 49–54. C. Lanhers and co-authors, Creatine supplementation and lower limb strength performance: A systematic review and meta-analysis, Sports Medicine 45 (2015): 1285–94. E. Galvan and co-authors, Acute and chronic safety and efficacy of dose dependent creatine nitrate supplementation and exercise performance, Journal of the International Society of Sports Nutrition, 13 (2016): 12. P. Krustrup, G. Ermidis and M. Mohr, Sodium bicarbonate intake improves high-intensity intermittent exercise performance in trained
young men, Journal of the International Society of Sports Nutrition, 12 (2015): 25; L. M. Burke, Practical considerations for bicarbonate loading and sports performance, Nestle’ Nutrition Institute Workshop Series 75 (2013): 15–26. 9 E. T. Trexler and co-authors, International society of sports nutrition position stand: Beta-alanine, Journal of the International Society of Sports Nutrition 12 (2015): 30; L. Junior and co-authors, Nutritional strategies to modulate intracellular and extracellular buffering capacity during high-intensity exercise, Sports Medicine 45 (2015): S71–S81. 10 J. J. Quesnele and co-authors, The effects of beta alanine supplementation on performance: a systematic review of the literature, International Journal of Sport Nutrition and Exercise Metabolism 24 (2014): 14–27. 11 N. F. McMahon, M. D. Leveritt and T. G. Pavey, The effect of dietary nitrate supplementation on endurance exercise performance in healthy adults: a systematic review and meta-analysis, Sport Medicine 47 (2017): 735–56. 12 S. Porcelli and co-authors, Aerobic fitness affects the exercise performance responses to nitrate supplementation, Medicine and Science in Sports and Exercise 47 (2015): 1643–51. 13 J. M. Wilson and co-authors, The effects of 12 weeks of betahydroxybeta- methylbutyrate free acid supplementation on muscle mass, strength, and power in resistance-trained individuals: A randomized, double-blind placebo-controlled study, European Journal of Applied Physiology 114 (2014): 1217–27; J. M. Wilson and co-authors, b-hydroxy-b-methylbutyrate free acid reduces markers of exercise-induced muscle damage and improves recovery in resistancetrained men, British Journal of Nutrition 110 (2013): 538–44.
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CHAPTER
15
LIFE CYCLE NUTRITION: PREGNANCY AND LACTATION Nutrition in your life
Food choices have consequences. Sometimes they happen immediately, as when you get heartburn after eating some pizza with extra chilli. Other times, these consequences can sneak up on you, as when you gain a few extra kilos after repeatedly overindulging in double-chocolate milkshakes. Quite often, the consequences are temporary and easily resolved, as when hunger pangs strike after you drink only a diet soft drink for lunch. During pregnancy, however, the consequences of a woman’s food choices are dramatic. They affect not just her health, but also the growth and development of another human being – and not just for today, but for years to come. Making smart food choices is a huge responsibility, but, fortunately, it’s reasonably simple. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F Being underweight but not overweight is associated with infertility. T F The neural tube development of a foetus occurs between 17 and 30 days gestation. T F The total folate requirement during pregnancy is 600 µg (0.6 mg)/day. T F Birth weight is the most reliable indicator of an infant’s health. T F The recommended weight gain for a woman who begins pregnancy at a healthy weight
and is carrying a single foetus is 11.5–16 kilograms.
LEARNING OBJECTIVES 15.1 List the ways men and women can prepare for a healthy pregnancy. 15.2 Describe foetal development from conception to birth and explain how maternal malnutrition can affect critical periods. 15.3 Explain how both underweight and overweight can interfere with a healthy pregnancy and how weight gain and physical activity can support maternal health and infant growth.
15.4 Summarise the nutrient needs of women during pregnancy. 15.5 Identify factors predicting low-risk and high-risk pregnancies and describe ways to manage them. 15.6 Summarise the nutrient needs of women during lactation. 15.7 Explain how drinking alcohol endangers the foetus and how women can prevent foetal alcohol syndrome.
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All people – pregnant and lactating women, infants, children, adolescents and adults – need the same nutrients, but the amounts they need vary depending on their stage of life. This chapter focuses on nutrition in preparation for, and support of, pregnancy and lactation. The next two chapters address the needs of infants, children, adolescents and older adults.
15.1 Nutrition prior to pregnancy
A section on nutrition prior to pregnancy must, by its nature, focus mainly on women. Both a man’s and a woman’s nutrition may affect fertility and, possibly, the genetic contributions they make to their children, but it is the woman’s nutrition that has the most direct influence on the developing foetus. Her body provides the environment for the growth and development of a new human being. Prior to pregnancy, a woman has a unique opportunity to prepare herself physically, mentally and emotionally for the many changes to come. In preparation for a healthy pregnancy, a woman can establish the following habits: • Achieve and maintain a healthy body weight: Both underweight and overweight are associated with infertility.1 Overweight and obese men have low sperm counts and hormonal changes that reduce fertility.2 Excess body fat in women disrupts menstrual regularity and ovarian hormone production. Should a pregnancy occur, mothers, both underweight and overweight, and their newborns, face increased risks of complications. • Choose an adequate and balanced diet: Malnutrition reduces fertility and impairs the early development of an infant should a woman become pregnant. • Be physically active: A woman who wants to be physically active when she is pregnant needs to become physically active beforehand. • Receive regular medical care: Regular healthcare visits can help ensure a healthy start to pregnancy. • Manage chronic conditions: Diseases such as diabetes, HIV/AIDS, phenylketonuria (PKU) and sexually transmitted infections can adversely affect a pregnancy and need close medical attention to help ensure a healthy outcome. • Avoid harmful influences: Both maternal and paternal ingestion of harmful substances (such as cigarettes, alcohol, drugs or environmental contaminants) can cause abnormalities, alter genes or their expression, and interfere with fertility.3 See Highlight 15 for the effects of excessive alcohol consumption during pregnancy. Young adults who nourish and protect their bodies do so not only for their own sake but also for future generations.
PUTTING COMMON SENSE TO THE TEST
Being underweight but not overweight is associated with infertility. FALSE
To meet additional energy needs, extra serves from the five food groups or unsaturated spreads and oils, or discretionary choices may be needed only by those women who are taller or more active but not overweight.
REVIEW IT
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Prior to pregnancy, the health and behaviours of both men and women can influence fertility and foetal development. In preparation, they can achieve and maintain a healthy body weight, choose an adequate and balanced diet, be physically active, receive regular medical care, manage chronic diseases and avoid harmful influences.
15.2 Growth and development during pregnancy
A whole new life begins at conception. Organ systems develop rapidly, and nutrition plays many supportive roles. This section describes placental development and foetal growth, paying close attention to times of intense developmental activity.
Placental development In the early days of pregnancy, a spongy structure known as the placenta develops in the uterus. Two associated structures also form (see Figure 15.1). One is the amniotic sac, a fluid-filled balloon-like structure that houses the developing foetus. The other is the umbilical cord, a rope-like structure containing foetal blood vessels that extends through
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FIGURE 15.1 The placenta and associated structures To understand how placental villi absorb nutrients without maternal and foetal blood interacting directly, think of how the intestinal villi work. The GI side of the intestinal villi is bathed in a nutrient-rich fluid (chyme). The intestinal villi absorb the nutrient molecules and release them into the body via capillaries. Similarly, the maternal side of the placental villi is bathed in nutrient-rich maternal blood. The placental villi absorb the nutrient molecules and release them to the foetus via foetal capillaries. The arrows indicate the direction of blood flow. Pool of mother’s blood
Foetal vein Foetal artery Fingerlike projections (called placental villi) contain foetal blood vessels and extend into the pool of mother’s blood. No actual mingling of foetal and maternal blood occurs, but substances pass back and forth.
Umbilical cord Uterine wall Placenta
Thus, oxygen and nutrients from the mother’s blood enter foetal vessels, and waste products are removed.
Umbilical cord Umbilical vein Umbilical arteries Amniotic sac
In the placenta, maternal blood vessels lie side by side with foetal blood vessels that reach the foetus through the umbilical cord.
Mother’s veins carry foetal wastes away.
Foetal portion Maternal portion of placenta of placenta
Mother’s arteries bring fresh blood with oxygen and nutrients to the foetus.
the foetus’s umbilicus to the placenta. These three structures (placenta, amniotic sac and umbilical cord) play crucial roles during pregnancy and are then expelled from the uterus during childbirth. The placenta develops as an interweaving of foetal and maternal blood vessels embedded in the uterine wall. The maternal blood transfers oxygen and nutrients to the foetus’s blood and receives foetal waste products. By exchanging oxygen, nutrients and waste products, the placenta performs the respiratory, absorptive and excretory functions that the foetus’s lungs, digestive system and kidneys will provide after birth. The placenta is a versatile, metabolically active organ. Like all body tissues, the placenta uses energy and nutrients to support its work. Like a gland, it produces an array of hormones that maintain pregnancy and prepare the mother’s breasts for lactation. A healthy placenta is essential for the developing foetus to attain its full potential.
Foetal growth and development Foetal development begins with the fertilisation of an ovum by a sperm. Three stages follow: the zygote, the embryo and the foetus (see Figure 15.2).
The zygote
The newly fertilised ovum, or zygote, begins as a single cell and divides to become many cells during the days after fertilisation. Within two weeks, the zygote embeds itself in the uterine wall – a process known as implantation. Cell division continues as each set of cells divides into many other cells. As development proceeds, the zygote becomes an embryo.
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Understanding nutrition
Petit Format/ Nestle/Science Source
1 A newly fertilized ovum is called a zygote and is about the size of the period at the end of this sentence. Less than one week after fertilisation, these cells have rapidly divided multiple times to become a blastocyst ready for implantation.
Petit Format/ Nestle/Science Source
FIGURE 15.2 Stages of embryonic and foetal development
4 A newborn infant after 9 months of development measures close to 50 centimetres in length. From 8 weeks to term, this infant grew 20 times longer and 50 times heavier.
Cindy Vannelli
Petit Format/ Nestle/Science Source
2 After implantation, the placenta develops and begins to provide nourishment to the developing embryo. An embryo 5 weeks after fertilisation is about 1.25 centimetres long.
3 A foetus after 11 weeks of development is just over 2.5 centimetres long. Notice the umbilical cord and blood vessels connecting the foetus with the placenta.
FIGURE 15.3 The concept of critical periods in foetal development Critical periods occur early in foetal development. An adverse influence felt early in pregnancy can have a much more severe and prolonged impact than one felt later on.
An adverse influence experienced late temporarily impairs development, but a full recovery is possible.
Normal development
The embryo
The embryo develops at an amazing rate. The number of cells in the embryo doubles approximately every 24 hours until the rate slows. At eight weeks, the 1.6-centimetre embryo has a complete central nervous system, a beating heart, a digestive system, well-defined fingers and toes, and the beginnings of facial features, and is known as a foetus.
The foetus
The foetus continues to grow during the next seven months. Each organ grows to maturity according to its own schedule, with greater intensity at some times than at others. As Figure 15.2 shows, foetal growth is phenomenal: weight increases from less than 30 grams to about 3.4 kilograms at birth. Most successful pregnancies last 38 to 42 weeks and produce a healthy infant weighing between 2.5 and 3.8 kilograms.
Critical periods Times of intense development and rapid cell division are called critical periods – critical in the sense that those cellular activities can occur only
Growth
An adverse influence experienced early permanently impairs development, and a full recovery never occurs.
Critical period
Time
at those times. If cell division and number are limited during a critical period, full recovery is not possible (see Figure 15.3). The development of each organ and tissue is most vulnerable to adverse influences (such as nutrient deficiencies or toxins) during its own critical period (see Figure 15.4). The critical period for neural tube development, for example, is from 17 to 30 days gestation. Consequently, neural tube development is most vulnerable to nutrient deficiencies, nutrient excesses or toxins during this critical time – when most women do not even realise they are pregnant. Any abnormal development of the neural tube or its failure to close completely can
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Chapter 15: Life cycle nutrition: pregnancy and lactation
FIGURE 15.4 Critical periods of development
The neural tube is the structure that eventually becomes the brain and spinal cord.
During embryonic development (from two to eight weeks), many of the tissues are in their critical periods (purple area of the bars); events that occur will have irreversible effects on the development of those tissues. In the later stages of development, the tissues continue to grow and change, but the events are less critical in that they are relatively minor or reversible. Central nervous system
PUTTING COMMON SENSE TO THE TEST
Heart Ears
The neural tube development of a foetus occurs between 17 and 30 days gestation.
Eyes
Tissue
531
Legs and arms Teeth
TRUE
Palate External genitalia
0
2
4 Embryo
8
12
16
Term
Foetus Weeks of gestation Adapted from K. L. Moore. and T. V. N. Persaud, Before We Are Born: Essentials of Embryology and Birth Defects, Philadelphia: Saunders (2003).
Reminder: A neural tube defect is a malformation of the brain, spinal cord or both during embryonic development. The two main types of neural tube defects are spina bifida (literally, ‘split spine’) and anencephaly (‘no brain’)
cause a major defect in the central nervous system. Figure 15.5 shows photos of neural tube development in the early weeks of gestation.
Neural tube defects In Australia (excluding the Northern Territory) and New Zealand, approximately 45 to 50 of every 100 000 newborns are born with a neural tube defect; roughly 108 or so infants are
FIGURE 15.5 Neural tube development
Science Photo Library/Edelmann
Science Photo Library/Steve Gschmeissner
The neural tube is the beginning structure of the brain and spinal cord. Any failure of the neural tube to close or to develop normally results in central nervous system disorders such as spina bifida and anencephaly. Successful development of the neural tube depends, in part, on the vitamin folate.
At 4 weeks, the neural tube has yet to close (notice the gap at the top).
At 6 weeks, the neural tube (outlined by the delicate red vertebral arteries) has successfully closed.
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Understanding nutrition
affected each year.4* Many other pregnancies with neural tube defects end in abortions or stillbirths. The two most common types of neural tube defects are anencephaly and spina bifida. In anencephaly, the upper end of the neural tube fails to close. Consequently, the brain is either missing or fails to develop. Pregnancies affected by anencephaly often end in miscarriage; infants born with anencephaly die shortly after birth. Spina bifida is characterised by incomplete closure of the spinal cord and its bony encasement (see Figure 15.6). The meninges membranes covering the spinal cord often protrude as a sac, which may rupture and lead to meningitis, a life-threatening infection. Spina bifida is accompanied by varying degrees of paralysis, depending on the extent of the spinal cord damage. Mild cases may not even be noticed, but severe cases often lead to death. Common problems include club foot, dislocated hip, kidney disorders, curvature of the spine, muscle weakness, mental handicaps, and motor and sensory losses. The cause of neural tube defects is unknown, but researchers are examining several gene– gene, gene–nutrient and gene–environment interactions. A pregnancy affected by a neural tube defect can occur in any woman, but factors that make it more likely are:5 • a previous pregnancy affected by a neural tube defect • maternal diabetes (type 1) • maternal use of anti-seizure medications • maternal obesity • exposure to high temperatures early in pregnancy (prolonged fever or hot-tub use) • race/ethnicity (more common among Anglo-Saxons than others) • low socioeconomic status. Folate supplementation reduces the risk.
FIGURE 15.6 Spina bifida Spina bifida, a common neural tube defect, occurs when the vertebrae of the spine fail to close around the spinal cord, leaving it unprotected. The B vitamin folate helps prevent spina bifida and other neural tube defects.
SPINA BIFIDA
Vertebra
NORMAL SPINE
Meninges Spinal cord Spinal fluid
Spine
Spine
*Worldwide, some 300 000 to 400 000 infants are born with neural tube defects each year.
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Folate supplementation Chapter 10 described how folate supplements taken one month before conception and continued throughout the first trimester can help support a healthy pregnancy, prevent neural tube defects and reduce the severity of those that do occur. For this reason, all women planning pregnancy, or of child-bearing age should consume an additional 400 micrograms (0.4 milligram) of folate daily beyond the RDI of 400 micrograms. During pregnancy, the RDI for folate is 600 micrograms. This means that during the first trimester of pregnancy, total intake, including supplements, should be approximately 1000 micrograms (dietary intake of 600 micrograms plus 400 micrograms as a supplement). In the second and third trimesters of pregnancy, women should continue to maintain an adequate folate intake and aim for the RDI for pregnancy of 600 micrograms. Because high doses of folate can mask the symptoms of pernicious anaemia associated with vitamin B12 deficiency, caution should be applied if taking higher than recommended doses of folate. Note that prenatal supplements contain varying amounts of folate per dose. The Nutrient Reference Values (NRVs) for Australia and New Zealand indicate that the RDI for pregnant women for folate is 600ug/day, but this does not take into consideration the additional supplemental folic acid required to prevent neural tube defects. Women capable of, or planning, pregnancies should consume additional folic acid as a supplement or in the form of fortified foods at a level of 400 µg/day folic acid for at least one month before and three months after conception, in addition to consuming food folate from a varied diet. Because approximately half of pregnancies each year are unplanned and because neural tube defects occur early in development before most women realise they are pregnant, bread flour in Australia is fortified with folate to help ensure an adequate intake. Labels on products containing additional folate may claim that an ‘adequate intake of folate has been shown to reduce the risk of neural tube defects’. In 2012, the New Zealand Government ruled against implementation of mandatory fortification, instead continuing with voluntary fortification of bread flour, which has been allowed in New Zealand since 1996.6
Folate RDI: (from dietary intake only) • for women: 400 µg (0.4 mg)/day • during pregnancy: 600 µg (0.6 mg)/ day.
CURRENT RESEARCH IN NUTRITION Folic acid in pregnancy A lack of folic acid early in pregnancy is known to cause neural tube defects such as spina bifida, but recent research shows a strong association between maternal folic acid intake and the risk of a baby developing cleft lip and cleft palate. The risk of having a cleft lip or palate appears to be more than four times higher if mothers do not take folic acid in the first three months of pregnancy than if they do take folic acid in the first three months.7
Chronic diseases Much research suggests that adverse influences at critical times during foetal development set the stage for the infant to develop chronic diseases in adult life. Poor maternal diet during critical periods may permanently alter body functions such as blood pressure, glucose tolerance and immune functions that influence disease development. For example, maternal diet may alter blood vessel growth and program lipid metabolism and lean body mass development in such a way that the infant will develop risk factors for cardiovascular disease as an adult. Malnutrition during the critical period of pancreatic cell growth provides an example of how type 2 diabetes may develop in adulthood.8 The pancreatic cells responsible for producing insulin (the beta cells) normally increase more than 130-fold between 12 weeks gestation and five months after birth. Nutrition is a primary determinant of beta cell growth, and infants who have suffered prenatal malnutrition have significantly fewer beta cells than well-nourished infants. They are also more likely to be low-birth-weight infants – and low birth weight and premature birth correlate with insulin resistance and type 2 diabetes later in life. One hypothesis suggests that diabetes may develop from the interaction of inadequate nutrition early in life with abundant nutrition later in life: the small mass of beta cells
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PUTTING COMMON SENSE TO THE TEST
The total folate requirement during pregnancy is 600 µg (0.6 mg)/day. FALSE
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Understanding nutrition
developed in times of undernutrition during foetal development may be insufficient in times of over-nutrition during adulthood when the body needs more insulin. Hypertension may develop from a similar scenario of inadequate growth during placental and gestational development followed by accelerated growth during early childhood: the small mass of kidney cells developed during malnutrition may be insufficient to handle the excessive demands of later life. Low-birth weight infants who gain weight rapidly as young children are likely to develop hypertension and heart disease as adults.
Foetal programming Recent genetic research may help to explain the phenomenon of substances such as nutrients influencing the development of diseases later on in adulthood – a process known as foetal programming. In the case of pregnancy, the mother’s nutrition can permanently change gene expression in the foetus with some research suggesting that foetal programming may influence several succeeding generations.9
REVIEW IT
PUTTING COMMON SENSE TO THE TEST
Because critical periods occur throughout pregnancy, a woman should continuously take good care of her health. That care should include achieving and maintaining a healthy body weight prior to pregnancy and gaining sufficient weight during pregnancy to support a healthy infant.
Birth weight is the most reliable indicator of an infant’s health. TRUE BMI was introduced in Chapter 8. • underweight 5 BMI 30 kg/m2 The term macrosomia describes high-birth-weight infants (approximately 4 kg or more); macrosomia can result from prepregnancy obesity, excessive weight gain during pregnancy or uncontrolled diabetes. • macro 5 large • soma 5 body
Maternal nutrition before and during pregnancy affects both the mother’s health and the infant’s growth. As the infant develops through its three stages – the zygote, embryo and foetus – its organs and tissues grow, each on their own schedule. Times of intense development are critical periods that depend on supply of nutrients to proceed smoothly. Without folate, for example, the neural tube fails to develop completely during the first month of pregnancy, prompting recommendations that all women of child-bearing age take folate daily.
15.3 Maternal weight
Birth weight is the most reliable indicator of an infant’s health. As a later section of this chapter explains, an underweight infant is more likely to have physical and mental defects, become ill and die than a normal-weight infant. In general, higher birth weights present fewer risks for infants. Two characteristics of the mother’s weight influence an infant’s birth weight: her weight prior to conception and her weight gain during pregnancy.
Weight prior to conception A woman’s weight prior to conception influences foetal growth. Even with the same weight gain during pregnancy, underweight women tend to have smaller babies than heavier women.
Underweight An underweight woman has a high risk of having a low-birth-weight infant, especially if she is malnourished or unable to gain sufficient weight during pregnancy. In addition, the rates of preterm births and infant deaths are higher for underweight women. An underweight woman improves her chances of having a healthy infant by gaining sufficient weight prior to conception or by gaining extra kilograms during pregnancy. To gain weight and ensure nutrient adequacy, an underweight woman can follow the dietary recommendations for pregnant women (described in Section 15.4).
Overweight and obesity An estimated one-third of all pregnant women in Australia and New Zealand are overweight or obese, which can create problems related to pregnancy and childbirth.10 Obese women have an
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especially high risk of medical complications such as hypertension, gestational diabetes and postpartum infections. Compared with other women, obese women are also more likely to have other complications of labour and delivery. Overweight women have the lowest rate of low-birth-weight infants. In fact, infants of overweight women are more likely to be born post-term and to weigh more than 4 kilograms. Large newborns increase the likelihood of a difficult labour and delivery, birth trauma and caesarean section. Consequently, these infants have a greater risk of poor health and death than infants of normal weight. Of greater concern than infant birth weight is the poor development of infants born to obese mothers.11 Obesity may double the risk for neural tube defects. The role of folate has been examined, but a more likely explanation seems to be poor glycaemic control. In addition, both overweight and obese women have a greater risk of giving birth to infants with heart defects and other abnormalities. Weight-loss dieting during pregnancy is never advisable. Overweight women should try to achieve a healthy body weight before becoming pregnant, avoid excessive weight gain during pregnancy and postpone weight loss until after childbirth.
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didesign021/Shutterstock.com
Chapter 15: Life cycle nutrition: pregnancy and lactation
Foetal growth and maternal health depend on a sufficient weight gain during pregnancy.
Weight gain during pregnancy All pregnant women must gain weight – foetal growth and maternal health depend on it. Maternal weight gain during pregnancy correlates closely with infant birth weight, which is a strong predictor of the health and subsequent development of the infant.
Recommended weight gains
Table 15.1 presents recommended weight gains for various pre-pregnancy weights. The recommended gain for a woman who begins pregnancy at a healthy weight and is carrying a single foetus is 11.5 to 16 kilograms. An underweight woman should gain between 12.5 to 18 kilograms, and an overweight woman between 7 to 11.5 kilograms.12 These gains will depend on individual circumstances. Some women should strive for gains at the upper end of the target range, such as adolescents who are still growing. Women who are carrying twins should aim for a weight gain of approximately 16 to 20 kilograms. If a woman gains more than is recommended early in pregnancy, she should not restrict her energy intake later in order to lose weight. A large weight gain over a short time, however, may indicate excessive fluid retention and may be the first sign of the serious medical complication pre-eclampsia, which is discussed later.
TABLE 15.1 Recommended weight gains based on pre-pregnancy weight PRE-PREGNANCY WEIGHT Underweight (BMI 30 kg/m2)
5 to 9 kg
2
Weight-gain patterns For the normal-weight woman, weight gain ideally follows a pattern of approximately 1 to 2 kilograms during the first trimester and around 400 grams per week thereafter. Healthcare professionals may monitor weight gain using a prenatal weight-gain grid (see Figure 15.7).
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PUTTING COMMON SENSE TO THE TEST
The recommended weight gain for a woman who begins pregnancy at a healthy weight and is carrying a single foetus is 11.5 to 16 kilograms. TRUE
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Understanding nutrition
Components of weight gain
FIGURE 15.7 Recommended prenatal weight gain based on pre-pregnancy weight
Women often express concern about the weight gain that accompanies a healthy pregnancy. They may find comfort by remembering that most of the gain supports the growth and development of the placenta, uterus, blood and breasts, the increase in blood supply and fluid volume, as well as an optimally healthy 3.4-kilogram infant. A small amount goes into maternal fat stores, and even that fat is there for a special purpose – to provide energy for labour and lactation. Figure 15.8 shows the components of a typical weight gain during pregnancy.
18 16 Kilograms gained
14 12 10 8 6 4
Weight loss after pregnancy
2 0
The pregnant woman loses some weight at delivery. In the following weeks, she loses more as her blood Weeks of gestation volume returns to normal and she sheds accumulated Healthy-weight women 1–2 kg gained at 12 weeks fluids. The typical woman does not, however, return with 10–13 kg at 40 weeks to her pre-pregnancy weight. In general, the more Underweight women Approx 1.5–2 kg at 12 weeks with 12–18 kg at 40 weeks weight a woman gains beyond the needs of pregnancy, Overweight women Approx 0.7–0.9 kg at 12 weeks the more she retains. Even with an average weight with 7–10 kg at 40 weeks gain during pregnancy, most women tend to retain a kilogram or two with each pregnancy. When those 1 or 2 kilograms become 3 or 4 or more and BMI increases by a unit or more, complications such as diabetes and hypertension in future pregnancies as well as chronic diseases in later life can increase – even for women who are not overweight.13 4
8
12
16
20
24
28
32
36
40
FIGURE 15.8 Components of weight gain during pregnancy Weight gain (kg)
1st trimester
2nd trimester
Increase in breast size
0.9
Increase in mother’s fluid volume
1.8
Placenta
0.7
Increase in blood supply to the placenta
1.8
Amniotic fluid
0.9
Infant at birth
3.4
Increase in size of uterus and supporting muscles
0.9
Mother’s necessary fat stores
3.2
3rd trimester
Exercise during pregnancy An active, physically fit woman experiencing a normal pregnancy can continue to exercise throughout pregnancy, adjusting the duration and intensity of activity as the pregnancy Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
13.6
Chapter 15: Life cycle nutrition: pregnancy and lactation
progresses. Staying active can improve fitness, prevent or manage gestational diabetes, facilitate labour and reduce stress. Women who exercise during pregnancy report fewer discomforts throughout their pregnancies. Regular exercise develops the strength and endurance a woman needs to carry the extra weight through pregnancy and to labour through an intense delivery. It also maintains the habits that help a woman lose excess weight and get back into shape after the birth. A pregnant woman should participate in ‘low-impact’ activities and avoid sports in which she might fall or be hit by other people or objects. For example, swimming is safer than a fast-moving game of squash in which competitors can collide. Swimming and water aerobics are particularly beneficial because they allow the body to remain cool and move freely with the water’s support, thus reducing back pain. Figure 15.9 provides some guidelines for exercise during pregnancy.14 Several of the guidelines are aimed at preventing excessively high internal body temperature and dehydration, both of which can harm foetal development. To this end, pregnant women should also stay out of saunas, steam rooms and hot tubs. Many forms of moderate intensity aerobic exercise such as swimming, running, aerobics and cycling (stationary, later in pregnancy) appear to be safe throughout pregnancy.15
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To achieve and maintain a healthy weight, be physically active and choose amounts of nutritious food and drinks to meet your energy needs.
FIGURE 15.9 Exercise guidelines during pregnancy DO
DON’T
Do begin to exercise gradually.
Don’t exercise vigorously after long periods of inactivity.
Do exercise regularly (most, if not all, days of the week).
Don’t exercise in hot, humid weather. Don’t exercise when sick with fever.
Do warm up with 5 to 10 minutes of light activity.
Tracy Frankel/Getty Images
Do 30 minutes or more of moderate physical activity. Do cool down with 5 to 10 minutes of slow activity and gentle stretching. Do drink water before, after and during exercise. Do eat enough to support the needs of pregnancy plus exercise.
Don’t participate in activities that may harm the abdomen or that involve jerky, bouncy movements. Don’t scuba dive.
Pregnant women can enjoy the benefits of exercise.
REVIEW IT
A healthy pregnancy depends on sufficient weight gain. Women who begin their pregnancies at a healthy weight should gain about 10–13 kilograms, which covers the growth and development of the placenta, uterus, breasts and infant, and increased blood volume. By remaining active throughout pregnancy, a woman can develop the strength she needs to carry the extra weight and maintain habits that will help her return to her pre-pregnancy weight after the birth.
Don’t exercise if you experience any pain, discomfort or fatigue.
Shutterstock.com/Monkey Business Images
Do rest adequately.
Don’t exercise while lying on your back after the first trimester of pregnancy or stand motionless for prolonged periods.
15.4 Nutrition during pregnancy
A woman’s body changes dramatically during pregnancy. Her uterus and its supporting muscles increase in size and strength; her blood volume increases by half to carry the additional nutrients and other materials; her joints become more flexible in preparation for childbirth; her feet swell in response to high concentrations of the hormone oestrogen, which promotes water retention and helps to ready the uterus for delivery; and her breasts enlarge in preparation for lactation. The hormones that mediate all these changes may influence her mood. She can best prepare to handle these changes given
A pregnant woman’s food choices support both her health and her infant’s growth and development.
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a nutritious diet, regular physical activity, plenty of rest and caring companions. This section highlights the role of nutrition.
The Nutrient Reference Values (NRV) table on the inside cover provides separate listings for women during pregnancy and lactation, reflecting their heightened nutrient needs. Chapters 10−13 present details on the vitamins and minerals.
Energy and nutrient needs during pregnancy From conception to birth, all parts of the infant – bones, muscles, organs, blood cells, skin and other tissues – are made from nutrients in the foods the mother eats. For most women, nutrient needs during pregnancy and lactation are higher than at any other time (see Figure 15.10). To meet the high nutrient demands of pregnancy, a woman will need to make careful food choices, but her body will also help by maximising absorption and minimising losses.
Energy The enhanced work of pregnancy increases the basal metabolic rate and requires extra energy. The energy needs of pregnant women are greater than those of non-pregnant women – an additional 1400 kilojoules per day during the second trimester and an extra 1900 kilojoules per day during the third trimester. A woman can easily get these additional kilojoules with nutrient-dense selections from the five food groups. See Table 15.2 for sample food choices for pregnant and lactating women. For an 8700-kilojoule daily intake, these added kilojoules represent about 15 to 20 per cent more food energy than before pregnancy. The increase in nutrient needs is often greater than the actual increase in energy, so nutrient-dense foods should be chosen to supply the extra kilojoules: foods such as wholegrain breads and cereals, legumes, dark green vegetables,
Energy requirement during pregnancy: • 2nd trimester: 11400 kJ/day • 3rd trimester: 11900 kJ/day.
FIGURE 15.10 Comparison of nutrient recommendations for non-pregnant, pregnant and lactating women For actual values, turn to the table on the inside cover. VITAMINS 0
50
Per cent 100 150
MINERALS 200
250
0
Biotin
Chromium
Choline
Copper
Folate
Iodine
Niacin
Iron
Pantothenic acid
Magnesium
Riboflavin
Manganese
Thiamin
Molybdenum
Vitamin A
Potassium
Vitamin B6
Selenium
Vitamin B12
Zinc
50
Per cent 100 150
200
250
The increased need for iron in pregnancy cannot be met by diet or by existing stores. Therefore, iron supplements are recommended.
Vitamin C Vitamin E
Key:
Non-pregnant (set at 100% for a woman 24 years old)
Pregnant
Lactating
a Energy allowance during pregnancy is for the second trimester; energy allowance during the third trimester is slightly higher; no additional allowance is provided during the first trimester. Energy allowance during lactation is for the first 6 months; energy allowance during the second 6 months is slightly higher.
No RDI is available – AI is given.
b
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Chapter 15: Life cycle nutrition: pregnancy and lactation
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TABLE 15.2 Minimum number of serves per day for women of different stages of life GRAINS (INCLUDING BREADS, RICE, PASTA, NOODLES)
VEGETABLES, FRUIT LEGUMES/ BEANS
MILK, YOGHURT, CHEESE OR ALTERNATIVES
LEAN MEAT, FISH, POULTRY, NUTS, LEGUMES
DISCRETIONARY FOODS (SUCH AS CAKES, PIES, SOFT DRINKS, LOLLIES)
WOMEN 19–50 years
6.0
5.0
2.0
2.5
2.5
0–2.5
51–70 years
4.0
5.0
2.0
4.0
2.0
0–2.5
70+ years
3.0
5.0
2.0
4.0
2.0
0–2.0
Pregnant (19+ years)
8.5
5.0
2.0
2.5
3.5
0–2.5
Breastfeeding (19+ years)
9.0
7.5
2.0
2.5
2.5
0–2.5
© National Health and Medical Research Council, Eat for Health: Australian Dietary Guidelines (Summary), 2013. https://www.nhmrc.gov.au/_files_nhmrc/publications/attachments/n55a_australian_dietary_guidelines_ summary_131014.pdf CC BY 3.0 Australia License.
citrus fruits, low-fat milk and milk products, and lean meats, fish, poultry and eggs. Ample carbohydrate is necessary to fuel the foetal brain. Sufficient carbohydrate ensures that the protein needed for growth will not be broken down and used to make glucose.
Protein The protein RDI for pregnancy is an additional 14 grams per day higher than for nonpregnant women during the second and third trimesters only.16 Pregnant women can easily meet their protein needs by selecting meats, milk products and protein-containing plant foods such as legumes, whole grains, nuts and seeds. Because the use of high-protein supplements during pregnancy may be harmful to the infant’s development, it is discouraged.
Protein RDI during second and third trimesters: 60 g/day (1g/kg)
Essential fatty acids The high nutrient requirements of pregnancy leave little room in the diet for excess fat, but the essential long-chain polyunsaturated fatty acids are particularly important to the growth and development of the foetus. The brain is largely made of lipid material, and it depends heavily on the long-chain omega-3 and omega-6 fatty acids for its growth, function and structure.17 (See Table 5.2 on page 154 for a list of good food sources of the omega fatty acids.)
Nutrients for blood production and cell growth New cells are laid down at a tremendous pace as the foetus grows and develops. At the same time, the mother’s red blood cell mass expands. All nutrients are important in these processes, but for folate, vitamin B12, iron and zinc, the needs are especially great due to their key roles in the synthesis of DNA and new cells. The requirement for folate increases dramatically during pregnancy. It is best to obtain sufficient folate from a combination of supplements, fortified foods and a diet that includes an additional serve each day of fruits and vegetables.18 The ‘How to’ box on page 349 of Chapter 10 describes how folate from each of these sources contributes to a day’s intake. Pregnant women also have a slightly greater need for the B vitamin that activates the folate enzyme – vitamin B12. Generally, even modest amounts of meat, fish, eggs or milk products together with body stores easily meet the need for vitamin B12. Vegans who exclude all foods of animal origin, however, need daily supplements of vitamin B12 or vitamin B12-fortified foods to prevent the neurological complications of a deficiency. Page 356 in Chapter 10 describes the functions and sources of vitamin B12 in more detail.
Folate RDI during pregnancy: • 600 µg/day (for dietary intake only) Vitamin B12 RDI during pregnancy: • 2.6 µg/day
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Iron RDI during pregnancy: 27 mg/day
Zinc RDI during pregnancy: • 10 mg/day (≤18 years) • 11 mg/day (19–50 years) Iodine RDI during pregnancy and lactation: • 220 µg during pregnancy • 270 µg during lactation
Pregnant women need iron to support their enlarged blood volume and to provide for placental and foetal needs.19 The developing foetus draws on maternal iron stores to create sufficient stores of its own to last through the first four to six months after birth. Even women with inadequate iron stores transfer significant amounts of iron to the foetus, suggesting that the iron needs of the foetus have priority over those of the mother. In addition, blood losses are inevitable at birth, especially during a caesarean section, and can further drain the mother’s supply.* During pregnancy, the body makes several adaptations to help meet the exceptionally high need for iron. Menstruation, the major route of iron loss in women, ceases, and iron absorption improves thanks to an increase in blood transferrin, the body’s iron-absorbing and iron-carrying protein. Without sufficient intake, though, iron stores would quickly dwindle. If women enter pregnancy with adequate iron stores, the increased absorptive capacity may be sufficient to meet increased requirements if dietary intake is around 12 to 16 mg/day. Haemoglobin levels of pregnant women should be checked at their first antenatal visit and again at 28 weeks. If low levels are present, this should be investigated and treated if needed. A daily iron supplement is generally not recommended unless anaemia is present or intake is inadequate so as to lead to anaemia.20 To enhance iron absorption, any supplements should be taken between meals or at bedtime and with liquids other than milk, coffee or tea, which inhibit iron absorption. Drinking orange juice tends not to enhance iron absorption from supplements as it does from foods; vitamin C enhances iron absorption by converting iron from its ferric form to its ferrous form – most supplemental iron is already in the ferrous form. Vitamin C is helpful, however, in preventing the premature rupture of amniotic membranes. Chapter 13 provides greater detail on iron balance, requirements and food sources. Zinc is required for DNA and RNA synthesis and thus for protein synthesis and cell development. Typical zinc intakes for pregnant women are lower than recommendations, but fortunately, zinc absorption increases when zinc intakes are low. Routine supplementation is not advised. Women taking iron supplements (more than 30 milligrams per day), however, may need zinc supplementation because large doses of iron can interfere with the body’s absorption and use of zinc. For an excellent overview of zinc, refer to Section 13.3 in Chapter 13. Iodine is found in food as iodide. Our bodies need it to make thyroid hormones. The thyroid is a gland in the throat that regulates many metabolic processes, such as growth and energy use. In the developing foetus, baby and young child, the effects of iodine deficiency are serious. They include stunted growth, diminished intelligence and retardation. In Australia, the presence of mild-to-moderate iodine deficiency has been seen in populations in New South Wales and Victoria. Western Australia and Queensland appear to have adequate intakes, with borderline intakes in South Australia.21 Iodine status in New Zealand populations has also been observed to be decreasing. Decreasing iodine intake is thought to be occurring due to a number of reasons. These include the use of non-iodised salt in processed foods, less iodine in milk because of changes in cleaning and treatment methods, a possible reduction of iodine levels in Australian soils, and a reduction in the use of salt in cooking and table salt (particularly iodised salt). Recent research suggests that even subclinical hypothyroidism may have clinical consequences, making it important to avoid iodine deficiency in pregnancy. In 2009, the mandatory fortification of bread flour with iodised salt commenced in Australia and New Zealand in an effort to reverse the current trend.22 Routine supplementation of iodine is not recommended unless living in regions of known deficiency; however, the NHMRC and the New Zealand Ministry of Health released a public statement in 2010 recommending that pregnant and lactating women and those considering pregnancy supplement their diet with
*On average, almost twice as much blood is lost during a caesarean delivery as during the average vaginal delivery of a single foetus.
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150 micrograms of iodine. The effects of iodine deficiency and toxicity are covered on Section 13.4 in Chapter 13.
Nutrients for bone development Vitamin D and the bone-building minerals calcium, phosphorus, magnesium and fluoride are in great demand during pregnancy. Insufficient intakes may produce abnormal foetal bones and teeth. Vitamin D plays a vital role in calcium absorption and utilisation. Consequently, severe maternal vitamin D deficiency interferes with normal calcium metabolism, resulting in rickets in the infant and osteomalacia in the mother.23 Regular exposure to sunlight and consumption of vitamin D-fortified foods are usually sufficient to provide the recommended amount of vitamin D during pregnancy, which is the same as for non-pregnant women. Routine supplementation is not recommended. Vegans who avoid milk, eggs and fish may receive enough vitamin D from regular exposure to sunlight and from fortified soy beverages. The importance of vitamin D is covered in Section 11.2 in Chapter 11. Calcium absorption and retention increases dramatically in pregnancy, helping the mother to meet the calcium needs of pregnancy. During the last trimester, as the foetal bones begin to calcify, over 300 milligrams a day are transferred to the foetus. Recommendations to ensure an adequate calcium intake during pregnancy help to conserve maternal bone while supplying foetal needs. Calcium is covered in more detail in Chapter 12, including in Highlight 12. Calcium intakes for pregnant women typically fall below recommendations. Because bones are still actively depositing minerals until about age 30, adequate calcium is especially important for young women. Pregnant women who receive less than 600 milligrams of dietary calcium daily should increase their intake of milk, cheese, yoghurt and other calcium-rich foods. Alternatively, they may need a daily calcium supplement to ensure that their needs and those of the foetus are met.
Other nutrients The nutrients mentioned here are those most intensely involved in blood production, cell growth and bone growth. Of course, other nutrients are also needed during pregnancy to support the growth and health of both foetus and mother. Even with adequate nutrition, repeated pregnancies less than a year apart deplete nutrient reserves. When this happens, foetal growth may be compromised and maternal health may decline. An interval between pregnancies of more than 18 months is suggested so that maternal health is maintained.
Nutrient supplements Pregnant women who make wise food choices can meet most of their nutrient needs, with the possible exception of iron. The use of daily multivitamin–mineral supplements for pregnant women is common. Prenatal supplements typically contain greater amounts of folate, iron and calcium than regular vitamin–mineral supplements, but investigation should occur as the amounts of each nutrient vary from brand to brand. Supplements are particularly beneficial for women who do not eat adequately and for those in high-risk groups: women carrying multiple foetuses, cigarette smokers, and alcohol and drug abusers. The use of prenatal supplements may help reduce the risks of preterm delivery, low infant birth weights and birth defects. Supplement use prior to conception also seems to reduce the risk of preterm births.24
Vegetarian diets during pregnancy and lactation In general, a vegetarian diet can support a healthy pregnancy and successful lactation if it provides adequate energy, includes dairy products and contains a wide variety of legumes, cereals, fruits and vegetables.25 Many vegetarian women are well-nourished, with nutrient
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The AI for vitamin D does not increase during pregnancy.
The RDI for calcium does not increase during pregnancy for those older than 18 years.
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intakes from diet alone often exceeding the RDI for all vitamins and minerals except iron, which is low for most women. In contrast, vegan women who restrict themselves to an exclusively plant-based diet generally have low food energy intakes and are thinner. For pregnant women, this can be a problem. Women with low pre-pregnancy weights and small weight gains during pregnancy jeopardise a healthy pregnancy. Vegan diets may require supplementation with vitamin B12, calcium, iron and vitamin D, or the addition of foods fortified with these nutrients. Infants of vegan parents may suffer spinal cord damage and develop severe psychomotor retardation due to a lack of vitamin B12 in the mother’s diet during pregnancy. Breastfed infants of vegan mothers have been reported to develop vitamin B12 deficiency and severe movement disorders. Giving the infants vitamin B12 supplements corrects the blood and neurological symptoms of deficiency, as well as the structural abnormalities, but cognitive and language development delays may persist. A vegan mother needs a regular source of foods fortified with vitamin B12 or a supplement that provides 2.6 micrograms of vitamin B12 daily. A pregnant woman who cannot meet her calcium needs through diet alone may need supplemental calcium daily, preferably taken with meals. Pregnant women who do not receive sufficient dietary vitamin D or enough exposure to sunlight may need a supplement that provides 5 micrograms of vitamin D daily.
Common nutrition-related concerns of pregnancy Nausea, constipation, heartburn and food sensitivities are common nutrition-related concerns during pregnancy. A few simple strategies can help alleviate maternal discomforts (see Table 15.3).
Nausea Not all women have queasy stomachs in the early months of pregnancy, but many do. The nausea of ‘morning sickness’ may actually occur at any time and ranges from mild queasiness to debilitating nausea and vomiting. Severe and continued vomiting may require hospitalisation if it results in acidosis, dehydration or excessive weight loss. The hormonal changes of early pregnancy seem to be responsible for a woman’s sensitivities to the appearance, texture or smell of foods. Traditional strategies for quelling nausea are listed in Table 15.3, but some women benefit most from resting when nauseated and simply eating the foods they want when they feel like eating.
Constipation and haemorrhoids As the hormones of pregnancy alter muscle tone and the growing foetus crowds intestinal organs, an expectant mother may experience constipation. She may also develop haemorrhoids
TABLE 15.3 Strategies to alleviate maternal discomforts TO ALLEVIATE THE NAUSEA OF PREGNANCY
TO PREVENT OR ALLEVIATE CONSTIPATION
TO PREVENT OR RELIEVE HEARTBURN
• On waking, arise slowly. • Eat dry toast or crackers. • Chew gum or suck hard lollies. • Eat small, frequent meals. • Avoid foods with strong odours. • When nauseated, drink carbonated beverages instead of citrus juice, water, milk, coffee or tea.
• Eat foods high in fibre (fruits, vegetables and wholegrain cereals). • Exercise regularly. • Drink at least eight glasses of water a day. • Respond promptly to the urge to defecate. • Use laxatives only as prescribed by a physician; do not use mineral oil, because it interferes with absorption of fat-soluble vitamins.
• Relax and eat slowly. • Chew food thoroughly. • Eat small, frequent meals. • Drink liquids between meals. • Avoid spicy or greasy foods. • Sit up while eating; elevate the head while sleeping. • Wait an hour after eating before lying down. • Wait two hours after eating before exercising.
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(swollen veins of the rectum). Haemorrhoids can be painful, and straining during bowel movements may cause bleeding. She can gain relief by following the strategies listed in Table 15.3.
Heartburn Heartburn is another common complaint during pregnancy. The hormones of pregnancy relax the digestive muscles, and the growing foetus puts increasing pressure on the mother’s stomach. This combination allows stomach acid back up into the lower oesophagus, creating a burning sensation near the heart. Tips to help relieve heartburn are included in Table 15.3.
Food cravings and aversions Some women develop cravings for, or aversions to, particular foods and beverages during pregnancy. Food cravings and food aversions are fairly common, but they do not seem to reflect real physiological needs or vitamin and mineral deficiencies. Cravings and aversions that arise during pregnancy are most likely due to hormone-induced changes in sensitivity to taste and smell. Reminder: Pica is the general term for eating non-food items. The specific craving for non-food items that come from the earth, such as dirt, is known as geophagia.
Non-food cravings Some pregnant women develop cravings for non-food items such as freezer frost, velcro, dirt or ice (commonly ‘crunchy’ items) – a practice known as pica.26 Pica is often associated with iron-deficiency anaemia, but whether iron deficiency leads to pica or pica leads to iron deficiency is unclear. Eating dirt may interfere with iron absorption and displace iron-rich foods from the diet.
15.5 High-risk pregnancies
Some pregnancies jeopardise the life and health of the mother and foetus. Table 15.4 identifies several characteristics of a high-risk pregnancy. A woman with none of these risk factors is said to have a low-risk pregnancy. The more factors that apply, the higher the risk to mother and foetus. All pregnant women, especially those in high-risk categories, need prenatal care, including dietary advice.
The infant’s birth weight A high-risk pregnancy is likely to produce an infant with low birth weight. Low-birthweight infants, defined as infants who weigh 2.5 kilograms or less, are classified according to their gestational age. Preterm infants are born before they are fully developed; they are often underweight and have trouble breathing because their lungs are immature. Preterm infants may be small, but if their size and weight are appropriate for their age, they can catch up in growth given adequate nutrition support. In contrast, small-for-gestational-age infants have suffered growth failure in the uterus and do not catch up as well. For the most part, survival improves with increased gestational age and birth weight. Low-birth-weight infants are more likely to experience complications during delivery than normal-weight babies. They also have a statistically greater chance of having physical and mental birth defects, contracting diseases and dying early in life. Of infants who die
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Energy and nutrient needs are higher during pregnancy. A balanced diet that includes extra servings from the five core food groups can usually meet these needs; with the possible exception of iron and folate (supplements are recommended). The nausea, constipation and heartburn that sometimes accompany pregnancy can usually be alleviated with a few simple strategies. Food cravings do not typically reflect physiological needs.
Nutrition advice in prenatal care: • Eat well-balanced meals. • Gain enough weight to support foetal growth. • Take prenatal supplements as prescribed. • Stop drinking alcohol. The weight of some preterm infants is appropriate for gestational age (AGA); others are small for gestational age (SGA), often reflecting malnutrition.
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TABLE 15.4 High-risk pregnancy factors FACTOR
CONDITION THAT RAISES RISK
Maternal weight: • Prior to pregnancy
Pre-pregnancy BMI either 25 kg/m2
• During pregnancy
Insufficient or excessive pregnancy weight gain
Maternal nutrition
Nutrient deficiencies or toxicities; eating disorders
Socioeconomic status
Poverty, lack of family support, low level of education, limited food available
Lifestyle habits
Smoking, alcohol or other drug use
Age
Teens, especially 15 years or younger; women 35 years or older
Previous pregnancies: • Number
Many previous pregnancies (three or more to mothers under age 20; four or more to mothers age 20 or older)
• Interval
Short or long intervals between pregnancies (59 months)
• Outcomes
Previous history of problems
• Multiple births
Twins or triplets
• Birth weight
Low- or high-birth-weight infants
Maternal health:
Reminder: Amenorrhoea is the temporary or permanent absence of menstrual periods. Amenorrhoea is normal before puberty, after menopause, during pregnancy and during lactation; otherwise it is abnormal.
• High blood pressure
Development of pregnancy-related hypertension
• Diabetes
Development of gestational diabetes
• Chronic diseases
Diabetes; heart, respiratory and kidney disease; certain genetic disorders; special diets and medications
before their first birthdays, about two-thirds are low-birth-weight newborns. Very-low-birthweight infants (1500 grams or less) struggle not only for their immediate physical health and survival but for their future cognitive development and abilities as well. A strong relationship is evident between socioeconomic disadvantage and low birth weight. Low socioeconomic status impairs foetal development by causing stress and by limiting access to medical care and to nutritious foods. Low socioeconomic status often accompanies teen pregnancies, smoking and alcohol and drug abuse – all predictors of low birth weight.
Malnutrition and pregnancy Good nutrition clearly supports a pregnancy. In contrast, malnutrition interferes with the ability to conceive, the likelihood of implantation and the subsequent development of a foetus should conception and implantation occur. Santibhavank P/Shutterstock.com
Malnutrition and fertility
Low-birth weight babies need special care and nourishment.
The nutrition habits and lifestyle choices people make can influence the course of a pregnancy they are not even planning at the time. Severe malnutrition and food deprivation can reduce fertility because women may develop amenorrhoea and men may be unable to produce viable sperm. Furthermore, both men and women lose sexual interest during times of starvation. Starvation arises predictably during famines, wars and droughts, but it can also occur amid peace and plenty. Many young women who diet excessively are starving and suffering from malnutrition (see Highlight 8).
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Malnutrition and early pregnancy If a malnourished woman does become pregnant, she faces the challenge of supporting both the growth of a baby and her own health with inadequate nutrient stores. Malnutrition prior to and around conception prevents the placenta from developing fully. A poorly developed placenta cannot deliver optimum nourishment to the foetus, and the infant will be born small and possibly with physical and cognitive abnormalities. If this small infant is a female, she may develop poorly and have an elevated risk of developing a chronic condition that could impair her ability to give birth to a healthy infant. Thus, a woman’s malnutrition can adversely affect not only her children but her grandchildren.
Malnutrition and foetal development Without adequate nutrition during pregnancy, foetal growth and infant health are compromised. In general, consequences of malnutrition during pregnancy include foetal growth retardation, congenital malformations (birth defects), spontaneous abortion and stillbirth, preterm birth and low infant birth weight. Preterm birth and low infant birth weight, in turn, predict the risk of stillbirth in a subsequent pregnancy. Malnutrition, coupled with low birth weight, are factors in more than half of all deaths of children under four years of age worldwide.
Maternal health Medical disorders can threaten the life and health of both mother and foetus. If diagnosed and treated early, many diseases can be managed to ensure a healthy outcome – another strong argument for early prenatal care. Furthermore, the changes in pregnancy can reveal disease risks, making screening important and early intervention possible.
Pre-existing diabetes Whether diabetes presents risks depends on how well it is controlled before and during pregnancy. Without proper management of maternal diabetes, women face high infertility rates, and those who do conceive may experience episodes of severe hypoglycaemia or hyperglycaemia, spontaneous abortions and pregnancy-related hypertension. Infants may be large, suffer physical and mental abnormalities, and experience other complications such as severe hypoglycaemia or respiratory distress, both of which can be fatal. Ideally, a woman with diabetes will receive the prenatal care needed to achieve glucose control before conception and continued glucose control throughout pregnancy.
Gestational diabetes Approximately 3–8 per cent of women entering pregnancy without diabetes will develop a condition known as gestational diabetes during pregnancy.27 Gestational diabetes usually develops during the second half of pregnancy with subsequent return to a non-diabetic state after childbirth. Some women with gestational diabetes, however, develop diabetes (usually type 2) after pregnancy, especially if they are overweight. For this reason, healthcare professionals strongly advise against excessive weight gain during pregnancy. The most common consequences of gestational diabetes are a high infant birth weight and complications during labour and delivery. Birth defects associated with gestational diabetes include heart damage, limb deformities and neural tube defects. To ensure that the problems of gestational diabetes are dealt with promptly, doctors screen for risk factors and test high-risk women for glucose intolerance immediately and average-risk women between 24 and 28 weeks gestation. Dietary recommendations should meet the needs of pregnancy and maternal blood glucose goals. To maintain normal blood glucose levels, carbohydrates should be restricted to 35–40 per cent of energy intake. To limit excessive weight gain, obese women should limit energy intake to about 100 kilojoules per kilogram
Risk factors for gestational diabetes are: • age 25 or older • BMI >25 kg/m2 or excessive weight gain • complications in previous pregnancies, including gestational diabetes or high-birthweight infant • pre-diabetes or symptoms of diabetes • family history of diabetes • South or East Asian, Pacific Islander or Indigenous Australian.
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body weight. Diet and moderate exercise may control gestational diabetes, but if blood glucose fails to normalise, insulin or other medications may be required. Importantly, treatment reduces birth complications, pre-eclampsia and infant deaths.28
Pre-existing hypertension Hypertension complicates pregnancy and affects its outcome in different ways, depending on when the hypertension first develops and on how severe it becomes. In addition to the threats hypertension always carries (such as heart attack and stroke), high blood pressure increases the risks of a low-birth-weight infant and the separation of the placenta from the wall of the uterus before the birth, resulting in stillbirth. Ideally, before a woman with hypertension becomes pregnant, her blood pressure is under control.
Transient hypertension of pregnancy The hypertensive diseases of pregnancy are sometimes called toxaemia.
Some women develop hypertension during the second half of pregnancy.* Most often, the rise in blood pressure is mild and does not affect the pregnancy adversely. Blood pressure usually returns to normal during the first few weeks after childbirth. This transient hypertension of pregnancy differs from the life-threatening hypertensive diseases of pregnancy – pre-eclampsia and eclampsia.
Pre-eclampsia and eclampsia The normal oedema of pregnancy responds to gravity; fluid accumulates around the ankles. The oedema of pre-eclampsia is a generalised oedema. The differences between these two types of oedema help with the diagnosis of pre-eclampsia. Warning signs of pre-eclampsia include: • hypertension • protein in the urine • upper abdominal pain • severe and constant headaches • swelling, especially of the face • dizziness • blurred vision • sudden weight gain (~500 g/day) • poor foetal growth.
Hypertension may signal the onset of pre-eclampsia, a condition characterised not only by high blood pressure but also by protein in the urine and fluid retention (oedema). The oedema of pre-eclampsia is a whole-body oedema, distinct from the localised fluid retention women normally experience late in pregnancy. The cause of pre-eclampsia remains unclear, but it usually occurs with first pregnancies and most often after 20 weeks gestation. Symptoms typically regress within two days of delivery. Both men and women who were born of pregnancies complicated by pre-eclampsia are more likely to have a child born of a pregnancy complicated by pre-eclampsia, suggesting a genetic predisposition. Pre-eclampsia affects almost all of the mother’s organs – the circulatory system, liver, kidneys and brain. Blood flow through the vessels that supply oxygen and nutrients to the placenta diminishes. For this reason, pre-eclampsia often retards foetal growth. In some cases, the placenta separates from the uterus, resulting in preterm birth or stillbirth. Pre-eclampsia can progress rapidly to eclampsia – a condition characterised by convulsive seizures and coma. Maternal death during pregnancy and childbirth is extremely rare in industrialised countries, but when it does occur, eclampsia is a common cause. Pre-eclampsia demands prompt medical attention. Treatment focuses on controlling blood pressure and preventing convulsions. If pre-eclampsia develops early and is severe, induced labour or caesarean section may be necessary, regardless of gestational age. The infant will be preterm, with all of the associated problems, including poor lung development and special care needs. Several dietary factors have been studied, but none have proved conclusive in preventing pre-eclampsia. Limited research suggests that exercise may protect against pre-eclampsia by stimulating placenta growth and vascularity and reducing oxidative stress.29
*Blood pressure of 140/90 millimetres mercury or greater during the second half of pregnancy in a woman who has not previously exhibited hypertension indicates high blood pressure. So does a rise in systolic blood pressure of 30 millimetres or in diastolic blood pressure of 15 millimetres on at least two occasions more than six hours apart. By this rule, an apparently ‘normal’ blood pressure of 120/85 is high for a woman whose normal value is 90/70.
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APPLICATIONS OF NUTRITIONAL RESEARCH Vitamin D deficiency in pregnancy Whether vitamin D deficiency in pregnancy is a cause of hypertension or pre-eclampsia is controversial but recent research points to its involvement in the development of hypertensive disorders. In one study, lower maternal vitamin D levels in the second trimester were associated with an increased risk of pre-eclampsia.30 Low levels of vitamin D during the third trimester of pregnancy have also been associated with small for gestational age, low birth weight and preterm delivery, whereas low levels of vitamin D were associated with pregnancy loss.31 While a growing area of research, the relationship between Vitamin D deficiency and unwanted pregnancy outcomes appears to exist and provides further reason to ensure good nutritional health prior to and during pregnancy.
The mother’s age Maternal age also influences the course of a pregnancy. Compared with women of the physically ideal child-bearing age of 20–25, both younger and older women face more complications of pregnancy.
Pregnancy in adolescents Many adolescents become sexually active before the age of 19 years. Approximately 13 births per 1000 adolescent women occur in Australia each year.32 The rate in New Zealand has been consistently dropping since 2008; it is now approximately 16 births per 1000 adolescent women each year.33 This does not take into account the actual number of pregnancies that occur. Nourishing a growing foetus adds to a teenage girl’s nutrition burden, especially if her growth is still incomplete. Simply being young increases the risks of pregnancy complications independently of important socioeconomic factors. Common complications among adolescent mothers include iron-deficiency anaemia (which may reflect poor diet and inadequate prenatal care) and prolonged labour (which reflects the mother’s physical immaturity). On a positive note, maternal death is lowest for mothers under age 20 years. Pregnant teenagers have higher rates of stillbirths, preterm births and low-birth-weight infants than do adult women. The care of infants born to teenagers places an additional burden on both the healthcare and welfare systems annually, as teenagers have fewer financial resources and rely on these systems. Furthermore, their low economic status contributes significantly to the complications surrounding their pregnancies. At a time when prenatal care is most important, it is less accessible. To support the needs of both mother and foetus, young teenagers (13–16 years old) are encouraged to strive for the highest weight gains recommended for pregnancy. For a teen who enters pregnancy at a healthy body weight, a weight gain of approximately 16 kilograms is recommended; this amount minimises the risk of delivering a low-birth-weight infant. Gaining less weight may limit foetal growth. Without the appropriate economic, social and physical support, a young mother will not be able to care for herself during her pregnancy, and for her child after the birth. To improve her chances for a successful pregnancy and a healthy infant, she must seek prenatal care.
Pregnancy in women over age 29 years In the last several decades, many women have delayed child-bearing while they pursue education and careers. As a result, the number of first births to women over the age of 29 has increased dramatically. Fertility rates for women aged 30–34 years are the highest of all age groups, at 120 babies per 1000 women in 2014.34 Fertility rates for women aged 35–39 years are also increasing: 68.9 births per 1000 women in 2014. The few complications associated with later child-bearing often reflect chronic conditions such as hypertension and diabetes, which can complicate an otherwise healthy pregnancy.
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These complications may result in a caesarean section, which is more common in women over 35 than younger women, although the reasons for this vary widely in the community. The babies of older mothers can face problems that include higher rates of preterm delivery and lower birth weight. The rates of birth defects of babies to older women are also higher. Approximately 2 per cent of pregnancies in older women result in an infant with genetic abnormalities. For a 40-year-old mother, the risk of having a child with Down syndrome, for example, is about 1 in 100, compared with 1 in 300 for a 35-year-old and 1 in 10 000 for a 20-year-old. In addition, foetal death is twice as high for women 35 years and older than for younger women. Why this is so remains undetermined. One possibility is that the uterine blood vessels of older women may not fully adapt to the increased demands of pregnancy.
Practices incompatible with pregnancy Besides malnutrition, a variety of lifestyle factors can have adverse effects on pregnancy, and some may be teratogenic. People who are planning to have children can make the choice to practise healthy behaviours.
Reminder: The word teratogenic describes a factor that causes abnormal foetal development and birth defects.
Alcohol Research has shown that approximately 35 per cent of women drink alcohol through pregnancy.35 Alcohol consumption during pregnancy can cause irreversible mental and physical retardation of the foetus – foetal alcohol syndrome (FAS). Of the leading causes of mental retardation, FAS is the only one that is totally preventable. Guidelines for alcohol consumption recommend that it is safest to not drink alcohol during pregnancy.36 Foetal alcohol syndrome is the topic of Highlight 15, which includes mention of how alcohol consumption by men may also affect fertility and foetal development.
Medicinal drugs Drugs other than alcohol can also cause complications during pregnancy, problems in labour, and serious birth defects. For these reasons, pregnant women should consult with their doctor prior to taking any prescribed or over-the-counter medications.
Herbal supplements Similarly, pregnant women should seek a doctor’s advice before using herbal supplements. Women sometimes seek herbal preparations during their pregnancies to quell nausea, induce labour, aid digestion, promote water loss, support restful sleep and fight depression. As Highlight 18 explains, some herbs may be safe, but many others are potentially harmful.
Illicit drugs Depending on the definition used, the word perinatal may refer to the time between the 20th week of gestation and up to one month after birth.
The recommendation to avoid drugs during pregnancy also includes illicit drugs. Unfortunately, use of illicit drugs, such as cocaine and marijuana, occurs in some pregnant women. Drugs of abuse, such as cocaine, easily cross the placenta and impair foetal growth and development. Furthermore, they are responsible for preterm births, low-birth-weight infants, perinatal deaths and sudden infant deaths. If these newborns survive, central nervous system damage is evident: their cries, sleep and behaviours early in life are abnormal, and their cognitive development later in life is impaired. They may be hypersensitive or underaroused; those who test positive for drugs suffer the greatest effects of toxicity and withdrawal.
Smoking Approximately 10 to 13 per cent of pregnant women in Australia and New Zealand smoke cigarettes during pregnancy.37 Smoking cigarettes at any time exerts harmful effects, and pregnancy dramatically magnifies the hazards of these practices. Smoking restricts the blood supply to the growing foetus and thus limits oxygen and nutrient delivery and waste removal.
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Chapter 15: Life cycle nutrition: pregnancy and lactation
A mother who smokes is more likely to have a complicated birth and a low-birth-weight infant. Indeed, of all preventable causes of low birth weight, smoking is the most common. Although, most infants born to cigarette smokers are of low birth weight, some are not, suggesting that the effect of smoking on birth weight also depends, in part, on genes involved in the metabolism of cigarette toxins. In addition to contributing to low birth weight, smoking interferes with lung growth and increases the risks of respiratory infections and childhood asthma.38 It can also cause death in an otherwise healthy foetus or newborn. A positive relationship exists between sudden infant death syndrome (SIDS) and both cigarette smoking during pregnancy and postnatal exposure to passive smoke.39 Smoking during pregnancy may even harm the intellectual and behavioural development of the child later in life. Smoking can also cause other complications during pregnancy.
Environmental contaminants Proving that environmental contaminants cause reproductive damage is difficult, but evidence in wildlife is established and seems likely for human beings. Infants and young children of pregnant women exposed to environmental contaminants such as lead show signs of delayed mental and psychomotor development. During pregnancy, lead readily moves across the placenta, inflicting severe damage on the developing foetal nervous system. In addition, infants exposed to even low levels of lead during gestation weigh less at birth and consequently struggle to survive. For these reasons, it is particularly important that pregnant women receive foods and beverages grown and prepared in environments free of contamination. A diet high in calcium will help to defend against lead contamination, and breastfeeding may help to counterbalance developmental damage incurred from other contaminants during pregnancy. Mercury is among the contaminants of concern. As Chapter 5 mentioned, fatty fish are a good source of omega-3 fatty acids, but some fish contain large amounts of the pollutant mercury, which can harm the developing brain and nervous system. Because the benefits of moderate fish consumption outweigh the risks, pregnant (and lactating) women should try to follow the recommendations for the number of serves of different types of fish that can be safely consumed: • one serve of fish such as orange roughy (deep sea perch) or catfish only once per week, and no other fish that week • one serve of fish such as shark (flake), billfish (swordfish, broadbill and marlin) and no other fish that fortnight • two to three serves of any other fish or seafood per week.40 There is no recommendation to restrict fish oil products and supplements on the basis of mercury content.
Food-borne illness As Chapter 19 explains, food-borne illnesses arise when people eat foods that contain infectious microbes or microbes that produce toxins. At best, the vomiting and diarrhoea associated with these illnesses can leave a pregnant woman exhausted and dehydrated; at worst, food-borne illnesses can cause meningitis, pneumonia or even foetal death. Pregnant women are about 20 times more likely than other healthy adults to get the food-borne illness listeriosis, although it should be noted that it is still an uncommon occurrence. The margin presents tips to prevent listeriosis, and Chapter 19 includes precautions to minimise the risks of other common food-borne illness.
Vitamin–mineral megadoses The pregnant woman who is trying to eat well may mistakenly assume that more is better when it comes to vitamin–mineral supplements. This is simply not true; many vitamins and minerals are toxic when taken in excess. Excessive vitamin A is particularly infamous for its role in malformations of the cranial nervous system. Intakes before the seventh week appear
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Complications associated with smoking during pregnancy include: • poor foetal growth • low birth weight • complications at birth (prolonged final stage of labour) • mislocation of the placenta • premature separation of the placenta • vaginal bleeding • spontaneous abortion • foetal death • sudden infant death syndrome (SIDS) • middle ear diseases • cardiac and respiratory diseases. Listeriosis can be prevented in the following ways: • Use only pasteurised dairy products. • Avoid soft cheeses such as feta, brie, camembert, ricotta and blue cheeses. • Avoid soft-serve ice-cream. • Thoroughly cook all meat, poultry, eggs and seafood. • Avoid pâté, meat spreads and smoked seafood such as salmon or trout. • Avoid hot dogs, luncheon meats and deli meats, including cured meats such as salami. • Avoid eating cooked chicken that has been cooled, and chilled seafood. • Wash all fruits and vegetables and avoid pre-prepared salads (both fruit and vegetable) from salad bars.
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to be the most damaging. (Review Figure 15.4 page 531 to see how many tissues are in their critical periods prior to the seventh week.) For this reason, vitamin A supplements are not given during pregnancy unless there is specific evidence of deficiency, which is rare. A pregnant woman can obtain all the vitamin A and most of the other vitamins and minerals she needs by making wise food choices. She should take supplements only on the advice of a qualified nutrition professional or doctor.
Caffeine Caffeine crosses the placenta, and the developing foetus has a limited ability to metabolise it. Research studies have not proved that caffeine (even in high doses) causes birth defects in human infants (as it does in animals), but some evidence suggests that heavy use may increase the risk of hypertension, miscarriage and stillbirth.41 (In these studies, heavy caffeine use is defined as the equivalent of eight or more cups of coffee a day.) General recommendations suggest that limiting caffeine consumption to the equivalent of 1 to 2 cups of coffee a day is safe.
Weight-loss dieting Weight-loss dieting, even for short periods, is hazardous during pregnancy. Low-carbohydrate diets or fasts that cause ketosis deprive the foetal brain of needed glucose and may impair cognitive development. Such diets are also likely to lack other nutrients vital to foetal growth. Regardless of pre-pregnancy weight, pregnant women should never intentionally lose weight.
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High-risk pregnancies, especially for teenagers, threaten the life and health of both mother and infant. Proper nutrition and abstinence from smoking, alcohol and other drugs can improve outcomes. Prenatal care includes monitoring pregnant women for gestational diabetes and pre-eclampsia. In general, the following guidelines will allow most women to enjoy a healthy pregnancy: Obtain prenatal care. Eat a balanced diet, safely prepared. Take prenatal supplements as prescribed. Gain a healthy amount of weight. Refrain from cigarettes, alcohol and drugs (including herbal remedies, unless prescribed by a doctor).42 Childbirth marks the end of pregnancy and the beginning of a new set of parental responsibilities – including feeding the newborn. • • • • •
To learn about breastfeeding, a pregnant woman has many resources she can consult. The ‘Nutrition on the Net’ section at the end of this chapter provides a list of resources, including La Leche League International.
15.6 Nutrition during lactation
Before the end of her pregnancy, a woman needs to consider whether to feed her infant breast milk, infant formula or both. These options are the only recommended foods for an infant during the first six months of life. Recent Australian breastfeeding data shows that approximately 74 per cent of newborns are breastfed in the first four months of life but this falls to around 50 per cent at six months of age and 29 per cent at age one year.43 In New Zealand, recent data show that approximately 84 per cent of newborns are breastfed in the first six weeks of life. This falls to approximately 60 per cent at six months of age and to less than 30 per cent at age one year.44 The Australian Dietary Guidelines recommend breastfeeding initiation rates of 90 per cent, with 80 per cent of infants being fed at six months for Australia.45 In New Zealand, the Food and Nutrition Guidelines for Healthy Infants and Toddlers recommend exclusive breast feeding targets of 74 per cent at six weeks of age, 57 per cent at three months of age and 27 per cent at six months of age.46 This section focuses on how the mother’s nutrition supports the making of breast milk, and the next chapter describes how the infant benefits from drinking breast milk.
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Chapter 15: Life cycle nutrition: pregnancy and lactation
In many countries around the world, a woman breastfeeds her newborn without considering the alternatives or making a conscious decision. In other parts of the world, a woman feeds her newborn formula simply because she knows so little about breastfeeding. She may have misconceptions or feel uncomfortable about a process she has never seen or experienced. Breastfeeding offers many health benefits to both mother and infant (see Table 15.5), and every pregnant woman should seriously consider it. Even so, there are sometimes valid reasons for not breastfeeding, and formula-fed infants grow and develop into healthy children.
TABLE 15.5 Benefits of breastfeeding FOR INFANTS • Provides the appropriate composition and balance of nutrients with high bioavailability • Provides hormones that promote physiological development • Improves cognitive development • Protects against a variety of infections • May protect against some chronic diseases later in life, such as diabetes (both types), obesity, atherosclerosis, asthma and hypertension • May protect against food allergies FOR MOTHERS • Contracts the uterus • Delays the return of regular ovulation, thus lengthening birth intervals (is not, however, a dependable method of contraception) • Conserves iron stores (by prolonging amenorrhoea) • May protect against breast and ovarian cancer and reduce the risk of diabetes (type 2) OTHER • Cost savings from not needing medical treatment for childhood illnesses or time off work for care • Cost savings from not needing to purchase formula (even after adjusting for added foods in the diet of a lactating mother)a • Environmental savings to society from not needing to manufacture, package and ship formula and dispose of the packaging • Convenience of not having to shop for and prepare formula A nursing mother produces more than 133 litres of milk during the first six months.
a
Lactation: a physiological process Lactation naturally follows pregnancy, as the mother’s body continues to nourish the infant. The mammary glands secrete milk for this purpose. The mammary glands develop during puberty but remain fairly inactive until pregnancy. During pregnancy, hormones promote the growth and branching of a duct system in the breasts and the development of the milkproducing cells. The hormones prolactin and oxytocin finely coordinate lactation. The infant’s demand for milk stimulates the release of these hormones, which signal the mammary glands to supply milk. Prolactin is responsible for milk production. As long as the infant is nursing, prolactin concentrations remain high, and milk production continues. The hormone oxytocin causes the mammary glands to eject milk into the ducts, a response known as the let-down reflex. The mother feels this reflex as a contraction of the breast, followed by the flow of milk and the release of pressure. By relaxing and eating well, the nursing mother promotes easy let-down of milk and greatly enhances her chances of successful lactation.
Breastfeeding: a learned behaviour Lactation is an automatic physiological process that virtually all mothers are capable of doing. Breastfeeding, on the other hand, is a learnt behaviour that not all mothers decide to do.
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A woman who decides to breastfeed offers her infant a full array of nutrients and protective factors to support optimal health and development.
Some hospitals employ certified lactation consultants who specialise in helping new mothers establish a healthy breastfeeding relationship with their newborn. These consultants are often registered nurses with specialised training in breast and infant anatomy and physiology.
Of women who do breastfeed, those who receive early and repeated information and support breastfeed their infants longer than others. Healthcare professionals play an important role in providing encouragement and accurate information on breastfeeding. Women who have been successful in breastfeeding can offer advice and dispel misperceptions about lifestyle issues. Table 15.6 lists 10 steps that maternity facilities can undertake to become accredited as Baby Friendly Hospitals and that health professionals can take to promote successful breastfeeding among new mothers. The mother’s partner also plays an important role in encouraging breastfeeding.47 When partners support the decision, mothers are more likely to start and continue breastfeeding. Educating those closest to the mother could change attitudes and promote breastfeeding. Most healthy women who want to breastfeed can do so with a little preparation. Physical obstacles to breastfeeding are rare, although most nursing mothers quit before the recommended six months because of perceived difficulties. Obese mothers seem to have a particularly difficult time, perhaps due to biological and sociocultural factors. Successful breastfeeding requires adequate nutrition and rest. This, plus the support of all who care, will help to enhance the wellbeing of mother and infant.
TABLE 15.6 Ten steps to successful breastfeeding To promote breastfeeding, every maternity facility should: • have a written breastfeeding policy that is routinely communicated to all healthcare staff • train all healthcare staff in the skills necessary to implement the breastfeeding policy • inform all pregnant women about the benefits and management of breastfeeding • place babies in skin-to-skin contact with their mothers immediately following birth for at least an hour and encourage mothers to recognise when their babies are ready to breastfeed, offering help if needed • show mothers how to breastfeed and how to maintain lactation, even if they should be separated from their infants • give newborn infants no food or drink other than breast milk, unless medically indicated • practise rooming-in, allowing mothers and infants to remain together 24 hours a day • encourage breastfeeding on demand • give no artificial teats or dummies to breastfeeding infants • foster the establishment of breastfeeding support and refer mothers on discharge from the facility. Reprinted from Protecting, Promoting and Supporting Breastfeeding: The Special Role of Maternity Services, a joint WHO/UNICEF statement published by the World Health Organization., 1989.
Maternal energy and nutrient needs during lactation Ideally, the mother who chooses to breastfeed her infant will continue to eat nutrient-dense foods throughout lactation. An adequate diet is needed to support the stamina, patience and self-confidence that nursing an infant demands.
Energy intake and exercise Energy requirement during lactation: • first 6 months: + 2000 kJ/day • second 6 months: + 2000 kJ/day
A nursing mother produces about 780 millilitres of milk per day, with considerable variation from woman to woman and in the same woman from time to time, depending primarily on the infant’s demand for milk. To produce an adequate supply of milk, a woman needs extra energy – approximately 2000 kilojoules a day above her regular need during the first six months of lactation (full breastfeeding). To meet this energy need, eating additional kilojoules each day and allowing the fat reserves she accumulated during pregnancy to provide energy is recommended. Table 15.2 on page 539 shows which food groups can contribute to these extra kilojoules. If breastfeeding continues in the second six months, despite the reduction in breast
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milk production, the additional energy requirement is approximately the same due to the depletion of maternal fat stores. After the birth of the infant, many women actively try to lose the extra weight and body fat they accumulated during pregnancy. Opinions differ as to whether breastfeeding helps with postpartum weight loss. Lactating women may lose body fat more slowly than non-lactating women, but the rate of weight loss is about the same.48 In general, most women lose 500 to 1000 grams a month during the first four to six months of lactation; some may lose more, and others may maintain or even gain weight. Neither the quality nor the quantity of breast milk is adversely affected by moderate weight loss, and infants grow normally. Gradual weight A jog through the park provides an opportunity for physical loss to pre-pregnancy weight is appropriate, while severe energy activity and fresh air. restriction may hinder milk production. Women often exercise to lose weight and improve fitness, and this is compatible with breastfeeding and infant growth. Because intense physical activity can raise the lactate concentration of breast milk and influence the milk’s taste, some infants may prefer milk produced prior to exercise. In these cases, mothers can either breastfeed before exercise or express their milk before exercise for use afterward.
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Chapter 15: Life cycle nutrition: pregnancy and lactation
Energy nutrients Recommendations for protein and fatty acids intakes remain about the same during lactation as during pregnancy, but they increase for carbohydrates and fibre. Nursing mothers need additional carbohydrate to replace the glucose used to make the lactose in breast milk. The fibre recommendation is 5 grams higher than for the general female population simply because it is based on increased energy needs during lactation (fibre needs during pregnancy are 3 grams higher than the general female population).
Vitamins and minerals A question often raised is whether a mother’s milk may lack a nutrient if she fails to get enough in her diet. The answer differs from one nutrient to the next, but in general, nutritional inadequacies reduce the quantity, not the quality, of breast milk. Women can produce milk with adequate protein, carbohydrate, fat and most minerals, even when their own supplies are limited. For these nutrients and for the vitamin folate as well, milk quality is maintained at the expense of maternal stores. This is most evident in the case of calcium: dietary calcium has no effect on the calcium concentration of breast milk, but maternal bones lose some density during lactation if calcium intakes are inadequate. Bone density increases again when lactation ends; breastfeeding has no long-term harmful effects on bones. The nutrients in breast milk that are most likely to decline in response to prolonged inadequate intakes are the vitamins – especially vitamins A, D, B6 and B12. Review Figure 15.10 (page 538) to compare a lactating woman’s nutrient needs with those of pregnant and non-pregnant women.
Most lactating women can obtain all the nutrients they need from a well-balanced diet without taking vitamin–mineral supplements. Nevertheless, some may need iron supplements – not to enhance the iron in their breast milk, but to refill their depleted iron stores. The mother’s iron stores dwindle during pregnancy as she supplies the developing foetus with enough iron to last through the first four to six months of the infant’s life. In addition, childbirth may have incurred blood losses. Thus, a woman may need iron supplements during lactation even though, until menstruation resumes, her iron requirement is about half that of other non-pregnant women her age.
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Nutrient supplements
Nutritious foods support successful lactation.
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Water Adequate Intake (AI) for total water (which includes 2.6 L from drinking fluid such as water and other beverages) during lactation: 3.5 L/day
Despite misconceptions, a mother who drinks more fluid does not produce more breast milk. To protect herself from dehydration, however, a lactating woman needs to drink plenty of fluids. Breastfeeding mothers need an additional 500 millilitres of fluid each day, of which water should provide the majority.
Particular foods Foods with strong or spicy flavours (such as garlic) may alter the flavour of breast milk. A sudden change in the taste of the milk may annoy some infants. Familiar flavours may enhance enjoyment. A nursing mother can usually eat whatever nutritious foods she chooses. If she suspects a particular food is causing the infant discomfort, her doctor may recommend a dietary challenge: eliminate the food from the diet to see if the infant’s reactions subside; then return the food to the diet and again monitor the infant’s reactions. If a food must be eliminated for an extended time, appropriate substitutions must be made to ensure nutrient adequacy. The advice of a qualified nutrition professional should be sought if this is the case.
Maternal health If a woman has an ordinary cold, she can continue nursing without worry. If susceptible, the infant will catch it from her anyway. (Thanks to the immunological protection of breast milk, the baby may be less susceptible than a formula-fed baby would be.) With appropriate treatment, a woman who has an infectious disease such as tuberculosis or hepatitis can breastfeed; transmission is rare.49 Women with HIV (human immunodeficiency virus) infections, however, should consider other options.
HIV infection and AIDS Mothers with HIV infections can transmit the virus (which causes AIDS) to their infants through breast milk, although rates of this occurring are 1 per cent or lower. Where safe alternatives are available, HIV-positive women should not breastfeed their infants. In developing countries, where the feeding of inappropriate or contaminated formulas causes 1.5 million infant deaths each year, the decision is less obvious. To prevent the mother-tochild transmission of HIV, WHO and UNICEF urge mothers in developing countries not to breastfeed. However, they stress the importance of finding suitable feeding alternatives to prevent the malnutrition, disease and death that commonly occur when women in these countries do not breastfeed.
Diabetes Women with diabetes (type 1) may need careful monitoring and counselling to ensure successful lactation. These women need to adjust their energy intakes and insulin doses to meet the heightened needs of lactation. Maintaining good glucose control helps to initiate lactation and support milk production.
Postpartum amenorrhoea
Women who breastfeed experience prolonged postpartum amenorrhoea. Absent menstrual periods, however, do not protect a woman from pregnancy. To prevent pregnancy, a couple must use some form of contraception. Breastfeeding women who use oral contraceptives should use progestin-only agents for at least the first six months. Oestrogen-containing oral contraceptives reduce the volume and the protein content of breast milk.
Breast health Some women fear that breastfeeding will cause their breasts to sag. The breasts do swell and become heavy and large immediately after the birth, but even when they produce enough milk to nourish a thriving infant, they generally shrink back to their pre-pregnant size. Given proper Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Chapter 15: Life cycle nutrition: pregnancy and lactation
support, diet and exercise, breasts often return to their former shape and size when lactation ends. Breasts change their shape as the body ages, but breastfeeding does not accelerate this process. Whether the physical and hormonal events of pregnancy and lactation protect women from later breast cancer is an area of active research.50 Some research suggests no association between breastfeeding and breast cancer, whereas other research suggests a protective effect. Protection against breast cancer is most apparent for premenopausal women who were young when they breastfed and who breastfed for a long time.
Practices incompatible with lactation Some substances impair milk production or enter breast milk and interfere with infant development. This section discusses practices that a breastfeeding mother should avoid.
Alcohol Alcohol easily enters breast milk, and its concentration peaks within an hour of ingestion. Infants drink less breast milk when their mothers have consumed even small amounts of alcohol. Three possible reasons, acting separately or together, may explain why. Alcohol may alter the flavour of the breast milk and thereby the infant’s acceptance of it. Because infants metabolise alcohol inefficiently, even low doses may be potent enough to suppress their feeding and cause sleepiness. Alcohol may interfere with lactation by inhibiting the hormone oxytocin. Recommendations for alcohol consumption during lactation are the same as those for pregnancy; avoidance of alcohol is the safest measure.
Medicinal drugs Most medicines are compatible with breastfeeding, but some are contraindicated, either because they suppress lactation or because they are secreted into breast milk and can harm the infant.95 As a precaution, a nursing mother should consult with her doctor prior to taking any medicine, including herbal supplements or over-the-counter preparations.
Illicit drugs Illicit drugs are harmful to the physical and emotional health of both the mother and the nursing infant. Breast milk can deliver such high doses of illicit drugs as to cause irritability, tremors, hallucinations and even death in infants.
Smoking Because cigarette smoking reduces milk volume, smokers may produce too little milk to meet their infants’ energy needs. The milk they do produce contains nicotine, which alters its smell and flavour. Consequently, infants of breastfeeding mothers who smoke gain less weight than infants of those who do not smoke. Furthermore, infant exposure to passive smoke negates the protective effect breastfeeding offers against SIDS and increases risk dramatically.
Caffeine Caffeine enters breast milk and may make an infant irritable and wakeful. As during pregnancy, caffeine consumption should be moderate – the equivalent of one to two cups of coffee a day. Larger doses of caffeine may interfere with the bioavailability of iron from breast milk and impair the infant’s iron status.
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The lactating woman needs extra fluid and enough energy and nutrients to produce about 750 millilitres of milk a day. Breastfeeding is contraindicated for those with HIV/AIDS. Alcohol, other drugs and smoking may reduce milk production or enter breast milk and impair infant development.
This chapter has focused on the nutrition needs of the mother during pregnancy and lactation. The next chapter explores the dietary needs of infants, children and adolescents. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Being underweight but not overweight is associated with infertility. FALSE
The RDI for folate during pregnancy is 600 µg (0.6 mg)/day from
dietary intake only. It is recommended that women planning pregnancy should consume an additional 400 micrograms (0.4 milligram) of folate daily beyond the RDI.
Being either underweight or overweight is associated with infertility. Extreme underweight or excess body fat in women can disrupt menstrual regularity and ovarian hormone production.
2 The neural tube development of a foetus occurs between 17 and 30 days gestation. TRUE
4 Birth weight is the most reliable indicator of an infant’s health. TRUE An underweight infant is more likely to have physical and mental
defects, become ill and die than a normal-weight infant. Generally, higher birth weight presents fewer risks for infants.
The critical period for neural tube development is between 17 and
30 days gestation. Neural tube development is most vulnerable to nutrient deficiencies during this time.
3 The total folate requirement during pregnancy is 600 µg (0.6 mg)/day. FALSE
5 The recommended weight gain for a woman who begins pregnancy at a healthy weight and is carrying a single foetus is 11.5 to 16 kilograms. TRUE Weight gains during pregnancy will depend on individual circumstances.
CRITICAL THINKING QUESTION Many infant formula companies have come under fire over recent decades about their marketing of infant formula in developing (and developed) nations. Some say this marketing has impacted on breastfeeding practices or
the decision to breastfeed of new mothers, while formula companies maintain they adhere to the WHO International Code of Marketing Breast-milk Substitutes. After researching this topic, what do you think?
NUTRITION PORTFOLIO The choices a woman makes in preparation for, and in support of, pregnancy and lactation can influence both her health and her infant’s development – today and for decades to come. • For women of child-bearing age, determine whether you consume at least 400 micrograms of dietary folate equivalents daily.
• For women who are pregnant, evaluate whether you are meeting your nutrition needs and gaining the amount of weight recommended. • For women who are about to give birth, carefully consider all the advantages of breastfeeding your infant and obtain the needed advice to support you.
STUDY QUESTIONS a b c d
Multiple choice questions Answers can be found at the back of the book. 1
The spongy structure that delivers nutrients to the foetus and returns waste products to the mother is called the: a b c d
2
4
beginning structure of kidneys beginning structure of the oesophagus beginning structure of the brain and spinal cord beginning structure of the heart
A reasonable weight gain during pregnancy for an overweight woman is about:
Energy needs during lactation increase by about: a b c d
The neural tube is the: a b c d
3
embryo uterus placenta amniotic sac
5
4.5 kg 9 kg 14 kg 18 kg 8400 kJ/day 1400 kJ/day 2000 kJ/day 2800 kJ/day
The RDI for folate from dietary sources during pregnancy is: a b c d
400 µg 500 µg 600 µg 700 µg
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6
Strategies to prevent constipation during pregnancy include: a eating dry toast b taking folate supplements c exercising regularly d avoiding spicy foods 7 The combination of high blood pressure, protein in the urine and oedema indicates: a jaundice b pre-eclampsia c gestational diabetes d gestational hypertension 8 Listeriosis can be prevented by: a using only pasteurised dairy products b eating soft cheeses such as brie c serving pâté and meat spreads d eating ready-made salads from salad bars 9 Approximately how much water should a breastfeeding woman drink each day? a 2000 ml b 2100 ml c 2400 ml d 2600 ml 10 The number of women affected by gestational diabetes is approximately: a 1 to 4 per cent b 2 to 6 per cent c 3 to 8 per cent d 4 to 10 per cent Review questions 1
How does parental weight status affect fertility? Is this the case for parents who are a healthy weight? What about overweight and underweight parents? (Section 15.3)
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2
Describe the normal events of foetal development. How does malnutrition or over-nutrition impact foetal development? (Section 15.2)
3
Define the term critical period. How do adverse influences during critical periods affect later health? (Section 15.2)
4
Explain why women of child-bearing age need folate in their diets. How much is recommended, and how can women ensure that these needs are met? (Section 15.2)
5
What is the recommended pattern of weight gain during pregnancy for a woman at a healthy weight? For an underweight woman? For an overweight woman? (Section 15.3)
6
Which nutrients are needed in greater amounts during pregnancy? Why are they so important? Describe wise food choices for the pregnant woman. (Section 15.4)
7
Define low-risk and high-risk pregnancies. What is the significance of infant birth weight in terms of the child’s future health? (Section 15.5)
8
What is pre-eclampsia? Why is pre-eclampsia an issue to an unborn child? (Section 15.5)
9
Which nutrients are needed in increased amounts in adolescent pregnancies? (Section 15.5)
10 What practices should be avoided during pregnancy? Why? (Section 15.5) 11 What are the 10 steps to successful breastfeeding promoted by baby-friendly hospitals? (Section 15.6) 12 What practices are incompatible with lactation? What are the possible reasons for any impact on breastfeeding? (Section 15.6)
NUTRITION ON THE NET Analyse the nutrient composition of foods online. To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Learn more about having a healthy baby and about birth defects from the Australian Government healthdirect site: https://www.healthdirect.gov.au/birth-defects • Learn more about neural tube defects from the Australian Government Healthdirect site: https://www.healthdirect.gov.au/spina-bifida
• Search ‘pregnancy’ at the Dietitians Association of Australia site: http://www.daa.asn.au • Visit the Royal Australian and New Zealand College of Obstetricians and Gynaecologists: http://www.ranzcog. edu.au • Learn more about gestational diabetes from the Diabetes Australia site: http://www.diabetesaustralia. com.au • Learn more about breastfeeding from La Leche League International: http://www.lalecheleague.org • Learn more about the Baby-friendly Hospital Initiative: http://www.who.int/nutrition/bfhi/en/
SEARCH ME! NUTRITION Keyword: fish pregnancy Women are advised to limit how much fish they eat during pregnancy to reduce the risk of mercury poisoning to the
foetus. However, can eating fish have health benefits that may outweigh this risk?
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HIGHLIGHT
15
15.7 FOETAL ALCOHOL SYNDROME
As mentioned earlier in Chapter 15, drinking alcohol during pregnancy endangers the foetus. Alcohol crosses the placenta freely and deprives the developing foetus of both nutrients and oxygen. The damaging effects of alcohol on the developing foetus cover a range of abnormalities referred to as foetal alcohol spectrum disorder. Those at the most severe end of the spectrum are described as having foetal alcohol syndrome (FAS), a cluster of physical, mental and neurobehavioural symptoms that includes: • prenatal and postnatal growth retardation • impairment of the brain and central nervous system, with consequent mental retardation, poor motor skills, poor coordination and hyperactivity • abnormalities of the face and skull (see Figure H15.1) • increased frequency of major birth defects: cleft palate, heart defects and defects in ears, eyes, genitals and urinary system. Tragically, the damage evident at birth persists: children with FAS never fully recover.1 The exact incidence of FAS in Australia and New Zealand is difficult to determine for a number of reasons, not least of which is the fact that alcohol is often not the only drug consumed during pregnancy. Evidence suggests that a woman who drinks while pregnant is also more likely to smoke cigarettes, use non-prescription and over-the-counter drugs, or take recreational drugs such as cannabis, all of which cross the placenta and affect a growing baby’s development. Australian and New Zealand studies in the area of FAS show: • continuing occurrence of FAS, with many sufferers in foster care and many with an affected sibling • a likely under-diagnosis of FAS due to a lack of knowledge among health professionals of the condition and criteria for its diagnosis • higher rates of FAS in some Indigenous communities compared with non-Indigenous communities2 • an identified need for research into the association between low to moderate alcohol consumption and foetal harm • a lack of data on rates of alcohol-related birth defects (ARBD) and alcohol-related neurodevelopmental disorder (ARND) in Australia and New Zealand.
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The effects of foetal alcohol syndrome are present from birth.
NHMRC guidelines suggest that it is safest for pregnant women to abstain from alcohol consumption. Abstinence from alcohol is the best policy for pregnant women both because alcohol consumption during pregnancy has such severe consequences and because FAS can only be prevented – it cannot be treated. Furthermore, because the most severe damage occurs around the time of conception – before a woman may even realise that she is pregnant – the warning to abstain includes women who are planning pregnancy.
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FIGURE H15.1 Typical facial characteristics of FAS Head Small head size Forehead Narrow, receding forehead Nose Short upturned nose Flattened nose bridge Jaw Underdeveloped jaw Receding chin Receding or flattened upper jaw Eyes Extra skin folds on eyelids Drooping eyelids Downward slant of eyes Unusually small openings between the upper and lower lids Short-sightedness Inability to focus (‘wandering eyes’) Ears Uneven in placement and size Poorly formed outer ear Backward curve Lips Absence of groove in upper lip; flat upper lip Thin upper lip
Stuart Wong/Newscom/Tribune News Service/Colorado Springs/CO/USA
Drinking during pregnancy
Characteristic facial features may diminish with time, but children with FAS typically continue to be short and underweight for their age.
When a woman drinks during pregnancy, she causes damage in two ways: directly, by intoxication, and indirectly, by malnutrition. Prior to the complete formation of the placenta (approximately 12 weeks), alcohol diffuses directly into the tissues of the developing embryo, causing incredible damage. (Review Figure 15.4 on page 531 and note that the critical periods for most tissues occur during embryonic development.) Alcohol interferes with the orderly development of tissues during their critical periods, reducing the number of cells and damaging those that are produced. The damage of alcohol toxicity during brain development is apparent in its reduced size and impaired function. When alcohol crosses the placenta, foetal blood alcohol rises until it reaches equilibrium with maternal blood alcohol. The mother may not even appear drunk, but the foetus may be poisoned. The foetus’s body is small, its detoxification system is immature and alcohol remains in foetal blood long after it has disappeared from maternal blood.
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How much is too much? A pregnant woman need not have an alcohol-abuse problem to give birth to a baby with FAS. She need only drink in excess of her liver’s capacity to detoxify alcohol. Even one standard drink a day may threaten neurological development and behaviours.3 Four standard drinks a day dramatically increases the risk of having an infant with physical malformations. In addition to total alcohol intake, drinking patterns play an important role. Most FAS studies report their findings in terms of average intake per day, but people usually drink more heavily on some days than on others. For example, a woman who drinks an average of two standard drinks a day may not drink at all during the week, but then have 10 standard drinks on Saturday night, exposing the foetus to extremely toxic quantities of alcohol. Whether various drinking patterns incur damage depends on the frequency of consumption, the quantity consumed and the stage of foetal development at the time of each drinking episode. An occasional drink may be innocuous, but researchers are unable to say how much alcohol is safe to consume during pregnancy. For this reason, healthcare professionals urge women to stop drinking alcohol as soon as they realise they are pregnant or, better, as soon as they plan to become pregnant. Why take any risk? Only the woman who abstains is sure of protecting her infant from FAS.
When is the damage done? The first month or two of pregnancy is a critical period of foetal development. Because pregnancy usually cannot be
Shutterstock/Rick’s Photography
A pregnant woman harms her unborn child not only by consuming alcohol but also by not consuming food. This combination enhances the likelihood of malnutrition and a poorly developed infant. It is impor tant to realise, however, that malnutrition is not the cause of FAS. It is true that mothers of FAS children often have unbalanced diets and nutrient deficiencies. It is also true that malnutrition may augment the clinical signs seen in these children, but it is the alcohol that causes the damage. An adequate diet alone will not prevent FAS if alcohol abuse continues. Children born with FAS must live with the long-term consequences of prenatal brain damage.
confirmed before five to six weeks, a woman may not even realise she is pregnant during that critical time. Therefore, it is advisable for women who are trying to conceive, or who suspect they might be pregnant, to abstain from alcohol to ensure a healthy start. The type of abnormality observed in an FAS infant depends on the developmental events occurring at the times of alcohol exposure. During the first trimester, developing organs such as the brain, heart and kidneys may be malformed. During the second trimester, the risk of spontaneous abortion increases. During the third trimester, body and brain growth may be retarded. Male alcohol ingestion may also affect fertility and foetal development. Animal studies have found smaller litter sizes, lower birth weights, reduced survival rates and impaired learning ability in the offspring of males consuming alcohol prior to conception. An association between paternal alcohol intake one month prior to conception and low infant birth weight is also apparent in human beings. (Paternal alcohol intake was defined as an average of two or more drinks daily or at least five drinks on one occasion.) This relationship was independent of either parent’s smoking and of the mother’s use of alcohol, caffeine or other drugs. In view of the damage caused by FAS, prevention efforts focus on educating women not to drink during pregnancy with everyone knowing of the potential dangers. Women who drink alcohol and who are sexually active may benefit from effective contraception to prevent pregnancy.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A What are the moral implications of using alcohol during pregnancy? B Clearly, drinking alcohol during pregnancy endangers the developing foetus, yet controversy surrounds the questions as to how much alcohol causes damage
and when the damage is done. What difficulties might researchers encounter in trying to determine the exact amount of alcohol and the timing during pregnancy that might be reasonably safe for foetal development?
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NUTRITION ON THE NET Analyse the nutrient composition of foods online. To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Visit the National Organisation for Foetal Alcohol Syndrome and Related Disorders: http://www.nofasd.org.au
• Search ‘foetal alcohol syndrome’ at the Australian Government’s Healthdirect website: https://www. healthdirect.gov.au/fetal-alcohol-spectrumdisorders • Gather facts on foetal alcohol syndrome from the University of New South Wales’s Embryology site: https:// embryology.med.unsw.edu.au/embryology/index.php/ Main_Page
REFERENCES CHAPTER 1
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A Mitchell & HC Fantasia, Understanding the Effect of Obesity on Fertility Among Reproductive-Age Women, Nursing for Women’s Health 20(4) (2016): 368–76. J. Feng and co-authors, Obesity impairs male fertility through longterm effects on spermatogenesis., BMC Urology 18(1) (2018): DOI 10.1186/s12894-018-0360-5. J. C. Sadeu and co-authors, Alcohol, drugs, caffeine, tobacco, and environmental contaminant exposure: Reproductive health consequences and clinical implications, Critical Reviews in Toxicology 40 (2010): 633–52. L. Hilder, Neural tube defects in Australia, 2007-2011: Before and after implementation of the mandatory folic acid fortification standard(UNSW National Perinatal Epidemiology and Statistics Unit, 2016); Ministry of Health, Improving folate intake in New Zealand: policy implications, Wellington: Ministry of Health (2003). A. J. Agopian and co-authors, Proportion of neural tube defects attributable to known risk factors, Birth Defects Research. Part A, Clinical and Molecular Teratology 97 (2013): 42–6. Ministry for Primary Industries, The future of folic acid fortification of bread in New Zealand. MPI Discussion Paper No: 2012/02, (Wellington: Ministry for Primary Industries, 2012). RF Figueiredo and authors, The role of the folic acid to the prevention of orofacial cleft: an epidemiological study., Oral Diseases s 21(2) (2015): 240–7. C. Fall, Fetal malnutrition and long-term outcomes, Nestle Nutrition Institute Workshop (2012): doi: 10.1159/000348384 B. Hocher, More than genes: the advanced fetal programming hypothesis, Journal of Reproductive Immunology 104-105 (2014): 8–11. L. K. Callaway and co-authors, The prevalence and impact of overweight and obesity in an Australian obstetric population, Medical Journal of Australia, 184 (2006): 56–9. P. van der Pligt and co-authors, Systematic review of lifestyle interventions to limit postpartum weight retention: Implications for future opportunities to prevent maternal overweight and obesity following childbirth, Obesity Reviews 14 (2013): 792–805. L. M. Szymanski and A. J. Satin, Exercise during pregnancy: foetal responses to current public health guidelines. Obstetrics and Gynecology 119 (2012): 603–10. Sports Medicine Australia, The benefits and risks of exercise during pregnancy (2002), available at http://sma.org.au/wp-content/ uploads/2009/05/pregnancystatement.pdf Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New
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18
19
20 21
22 23
24
25 26
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Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). A. S. de Souza, F. S. Fernandes, and M. das Graças Tavares do Carmo, Effects of maternal malnutrition and postnatal nutritional rehabilitation on brain fatty acids, learning, and memory, Nutrition Reviews 69 (2011): 132–44. National Health and Medical Research Council, Australian Dietary Guidelines, Canberra: Commonwealth of Australia (2013), available at https://www.eatforhealth.gov.au/guidelines A. Roy, S. E. Evers and M. K. Campbell, Dietary supplement use and iron, zinc and folate intake in pregnant women in London, Ontario. Chronic Diseases and Injuries in Canada 32 (2012): 76–83. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists, Position statement: Vitamin and mineral supplementation in pregnancy (2015), available at http:// www.ranzcog.edu.au/college-statements-guidelines.html C. M. Donangelo and co-authors, Zinc absorption and kinetics during pregnancy and lactation in Brazilian women, American Journal of Clinical Nutrition 82 (2005): 118–24. D. Shah and H. P. S. Sachdev, Zinc deficiency in pregnancy and foetal outcome, Nutrition Reviews 64 (2006): 15–30. Australian Population Health Development Principal Committee of the Australian Health Ministers Advisory Committee, The prevalence and severity of iodine deficiency in Australia (2007). Australian Health Ministers’ Advisory Council, 2017, The effectiveness and cost-effectiveness of mandatory folic acid and iodine fortification. A. Thorne-Lyman and W. W. Fawzi, Vitamin D during pregnancy and maternal, neonatal and infant health outcomes: a systematic review and meta-analysis. Paediatric Perinatal Epidemiology 26 (2012): 75–90. J. M. Catov and co-authors, Periconceptional multivitamin use and risk of preterm or small-for-gestational-age births in the Danish National Birth Cohort, American Journal of Clinical Nutrition 94 (2011): 906–12. Position of the American Dietetic Association: Vegetarian diets, Journal of the American Dietetic Association 109 (2009): 1266–82. E. J. Fawcett and co-authors, A meta-analysis of the world wide prevalence of pica during pregnancy and the postpartum period. International Journal of Gynaecololy and Obstertics 133(3) (2016): 277–83. Australian Institute of Health and Welfare, Australia’s health 2008, AIHW Catalogue Number AUS 73, Canberra: AIHW (2008). L. Hartling and co-authors, Benefits and harms of treating gestational diabetes mellitus: a systematic review and meta-analysis for the US Preventive Services Task Force and the National Institutes of Health
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31
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37
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Office of Medical Applications of Research, Annals of Internal Medicine 159 (2013): 123–9. C. G. Solomon and E. W. Seely, Preeclampsia – Searching for the cause, New England Journal of Medicine 350 (2004): 641–2. C. N. Spracken and co-authors, Physical activity during pregnancy and subsequent risk ofpreeclampsia and gestational hypertention: A case control study, Maternal and Child Health Journal 26 (6) (2016): 1193–202. S. Q. Wei and co-authors, Longitudinal vitamin D status in pregnancy and the risk of pre-eclampsia, British Journal of Obstetrics and Gynaecology. 119 (2012): 832–9. Australian Bureau of Statistics, Births Australia 2014, ABS Catalogue Number 3301.0, Canberra: ABS (2015). Stats NZ: New Zealand, 2017. Births and Deaths: Year ended December 2016 and March 2017. Australian Bureau of Statistics, Births Australia 2014, ABS Catalogue Number 3301.0, Canberra: ABS (2015). C. M. Cameron and co-authors, Changes in alcohol consumption in pregnant Australian women between 2007 and 2011, Medical Journal of Australia 199 (2013): 355–7. National Health and Medical Research Council, Australian guidelines to reduce the health risks from drinking alcohol,Canberra: Commonwealth of Australia (2009). Z. Li and coworkers, Australia’s mothers and babies 2011. Perinatal statistics series no. 28. Cat. no. PER 59. Canberra: AIHW National Perinatal Epidemiology and Statistics Unit (2013). C. C. Geerts and co-authors, Parental smoking and vascular damage in their 5-year-old children, Pediatrics 129 (2012): 45–54. J. R. DiFranza, C. A. Aligne and M. Weitzman, Prenatal and postnatal environmental tobacco smoke exposure and children’s health, Pediatrics 113 (2004): 1007–15.
40 A. Gomaa and co-authors, Maternal bone lead as an independent risk factor for fetal neurotoxicity: a prospective study, Pediatrics 110 (2002): 110–18. 41 Food Standards Australia New Zealand, Mercury in fish, Canberra/ Wellington: FSANZ (2011). 42 R. Bakker and co-authors, Maternal caffeine intake, blood pressure, and the risk of hypertensive complications during pregnancy: The Generation R Study, American Journal of Hypertension 24 (2011): 421–8. 43 Position of the American Dietetic Association: Use of nutritive and nonnutritive sweeteners, Journal of the American Dietetic Association 104 (2004): 255–75. 44 Australian Bureau of Statistics, Australian health survey: Health service usage and health related actions 2011–12, ABS Catalogue Number 4364.0.55.002, Canberra: ABS (2013). 45 Royal New Zealand Plunket Society: Breastfeeding data – analysis of 2004–2009 data (2010). 46 National Health and Medical Research Council, Australian Dietary Guidelines, Canberra: National Health and Medical Research Council (2013). 47 Ministry of Health, Food and nutrition guidelines for healthy infants and toddlers (aged 0–2): A background paper 4th ed., Wellington: Ministry of Health (2008). 48 N. Sherriff and co-authors, Engaging and supporting fathers to promote breastfeeding: A concept analysis, Midwifery 30(6) (2014): 667–77. 49 S. Tawia Mother to child transmission of HIV: What do we know in 2015? Australian Breastfeeding Association (2015. Available at: https://www.breastfeeding.asn.au/mother-to-child-transmission-ofhiv-what-do-we-know-in-2015 50 F. Meier-Abt and co-authors, Breast cancer prevention: lessons to be learned from mechanisms of early pregnancy-mediated breast cancer protection, Cancer Research 75 (2015): 803–7.
HIGHLIGHT 1
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K. Hellemans and co-authors, Prenatal alcohol exposure: Fetal programming and later life vulnerability to stress, depression and anxiety disorders, Neuroscience & Biobehavioural Reviews 34(6) (2010): 791–807. J. P. Fitzpatrick and co-authors, The Lililwan Project: Study protocol for a population-based active case ascertainment study of the
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prevalence of fetal alcohol spectrum disorders (FASD) in remote Australian Aboriginal communities, BMJ Open (2(3) (2012): doi:10.1136/bmjopen-2012-000968 I. Sarmon, Review shows that early foetal alcohol exposure may cause adverse effects even when the mother consumes low levels, Acta Pediatrics 107(6) (2018): 938–41.
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CHAPTER
16
LIFE CYCLE NUTRITION: INFANCY, CHILDHOOD AND ADOLESCENCE Nutrition in your life
Much of this book has focused on you – your food choices and how they might affect your health. This chapter shifts the focus from you the recipient to you the caregiver. One day (if not already), children may depend on you to feed them well and teach them wisely. The responsibility of nourishing children can seem overwhelming at times, but the job is fairly simple. Offer children a variety of nutritious foods to support their growth, and teach them how to make healthy food and activity choices. Presenting foods in a relaxed and supportive environment nourishes both physical and emotional wellbeing. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F An infant’s weight doubles every year of life up to five years of age. T F All infants require additional water irrespective of being breast-fed or formula-fed. T F Low-fat milks may be introduced to children from around 2 years of age. T F Infants require additional iron at around 6 months – more than body stores or breast-
feeding alone can provide.
T F Hyperactive children respond well to dietary modification. T F The calcium requirement for an adolescent is reduced after the age of 14.
LEARNING OBJECTIVES 16.1 List some of the components of breast milk and describe the appropriate foods for infants during the first year of life. 16.2 Explain how children’s appetites and nutrient needs reflect their stage of growth and why iron deficiency and obesity are often concerns during childhood.
16.3 Describe some of the challenges in meeting the nutrient needs of adolescents. 16.4 Describe the lifestyle factors that can help prevent childhood obesity and the development of type 2 diabetes and heart disease.
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The first year of life is a time of phenomenal growth and development. After the first year, a child continues to grow and change, but more slowly. Still, the cumulative effects over the first decade are remarkable. Then, as children enter their teens, the pace towards adulthood accelerates dramatically. This chapter examines the special nutrient needs of infants, children and adolescents.
16.1 Nutrition during infancy
Initially, the infant drinks only breast milk or formula but later begins to eat some foods, as appropriate. Commonsense in the selection of infant foods along with a nurturing, relaxed environment support an infant’s health and wellbeing.
FIGURE 16.1 Weight gains of infants in their first five years of life
15
An infant grows fast during the first year, as Figure 16.1 shows. Growth directly reflects nutrient intake and is an important parameter in assessing the nutrition status of infants and children. It is common for maternal and child health nurses to measure the height and weight of infants and children at intervals and compare the measurements with standard growth curves for gender and age, and with previous measures of each child (see the ‘How to’ box on page 565).
10
Energy intake and activity
In the first year, an infant’s birth weight may triple, but over the following several years, the rate of weight gain gradually diminishes. 20
Weight (kg)
Energy and nutrient needs
A healthy infant’s birth weight doubles by about five months of age and triples by approximately one year, typically reaching 9.5 to 5 10.5 kilograms. An infant’s length changes more slowly than its weight, increasing about 25 centimetres from birth to one year. By the end of the first year, infant growth slows considerably; during the second year, an 5 0 1 2 3 4 infant typically gains less than 2.5 kilograms and grows about Age (year) 10 centimetres in length. Not only do infants grow rapidly, their energy requirement is remarkably high – about twice that of an adult, based on body weight. While a newborn PUTTING baby requires about 1800–2000 kilojoules per day, compared to adults who require about COMMON SENSE 8500 kilojoules per day, in terms of body weight, the difference is remarkable: infants TO THE TEST require about 420–450 kilojoules per kilogram of body weight per day, whereas most adults An infant’s weight need fewer than 170 (see Table 16.1). If an infant’s energy needs were applied to an adult, a doubles every year 70-kilogram adult would require over 30 000 kilojoules a day. After six months, the infant’s of life up to five energy needs decline as growth rate slows, but some of the energy saved by slower growth is years of age. spent in increased activity. FALSE
TABLE 16.1 Infant and adult heart rate, respiration rate and energy needs compared Heart rate (beats/min) Respiration rate (breaths/min) Energy needs (kJ/kg body weight)
INFANTS
ADULTS
120 to 140
70 to 80
20 to 40
15 to 20
420 to 450
,170
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
PLOT MEASURES ON A GROWTH CHART
HOW TO:
You can assess the growth of infants and children by plotting their measurements on a growth chart. Growth charts divide the measures of a population into 100 equal divisions so that half of the population falls at or above the 50th percentile and half falls below. Using percentiles allows for comparisons among people of the same age and gender. To plot measures on a growth chart, follow these steps: › Select the appropriate chart based on age and gender. For this example, use the accompanying chart, which gives percentiles for weight for girls from birth to 24 months. (Appendix E provides other growth charts for both boys and girls of various ages.) ›› Locate the infant’s age along the horizontal axis at the bottom of the chart (in this example, six months). ›› Locate the infant’s weight in kilograms along the vertical axis of the chart (in this example, 8.3 kilograms). ›› Mark the chart where the age and weight lines intersect (shown here with a red dot), and follow the curved line to find the percentile. This 6-month-old infant is at the 85th percentile. Her maternal and child health nurse or doctor will weigh her again over the next few months and expect the growth curve to follow the same percentile throughout the first year. In general, dramatic changes or measures much above the 80th percentile or much below the 10th percentile may be cause for concern, but other factors need to be considered in determining whether this is the case. Weight-for-age percentiles Girls, birth to 36 months 15
97th
14 85th
13 12
50th
11 15th
Weight (kg)
10
3rd
9 8 7 6 5 4 3 2
Months
Birth
1
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1 year
1
2
3
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2 years
Age (completed months and years) WHO Child Growth Standards
Reprinted with permission from WHO Child Growth Standards (https://www.who.int/childgrowth/standards/en/)
Energy nutrients Recommendations for the energy nutrients – carbohydrate, fat and protein – during the first six months of life are based on the average intakes of healthy, full-term infants fed breast milk.1 During the second six months of life, recommendations reflect typical intakes from solid foods as well as breast milk. As discussed in Chapter 4, carbohydrates provide energy to all the cells of the body, especially those in the brain, which depend primarily on glucose to fuel activities. Relative to the size of the body, an infant’s brain is larger and uses relatively more glucose – about 60 per cent of the day’s total energy intake.
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Shutterstock.com/anek.soowannaphoom
566
After six months, energy saved by slower growth is spent in increased activity.
Fat provides most of the energy in breast milk and standard infant formula. Its high energy density supports the rapid growth of early infancy. No single nutrient is more essential to growth than protein. All of the body’s cells and most of its fluids contain protein; it is the basic building material of the body’s tissues. Chapter 6 detailed the problems inadequate protein can cause. Excess dietary protein can cause problems, too, especially in a small infant. Too much protein stresses the liver and kidneys, which have to metabolise and excrete the excess nitrogen. Signs of protein overload include acidosis, dehydration, diarrhoea, elevated blood ammonia, elevated blood urea and fever. Such problems are not common, but they have been observed in infants fed inappropriate foods, such as fat-free milk or concentrated formula.
Vitamins and minerals As with the energy nutrients, the recommendations for the vitamins and minerals are based on the average amount of nutrients consumed by thriving infants breastfed by well-nourished mothers. An infant’s needs for most of these nutrients, in proportion to body weight, are more than double those of an adult. Figure 16.2 illustrates this by comparing a 5-month-old infant’s needs per unit of body weight with those of an adult man. Some of the differences are extraordinary.
Water PUTTING COMMON SENSE TO THE TEST
All infants require additional water irrespective of whether they are breast-fed or formula-fed. FALSE
Chapter 15 discussed breastfeeding, breastfeeding support, reasons why some women choose not to breastfeed and contraindications to breastfeeding.
One of the most essential nutrients for infants, as for everyone, is water. The younger the infant, the greater the percentage of body weight is water. During early infancy, breast milk or infant formula normally provides enough water to replace fluid losses in a healthy infant. Even in hot, dry climates, breastfed infants don’t require additional water; however, on occasion, formula-fed infants may need supplemental water.2 Because much of the fluid in an infant’s body is located outside the cells – between the cells and in the blood vessels – rapid fluid losses and the resulting dehydration can be life-threatening. Conditions that cause rapid fluid loss, such as diarrhoea or vomiting, require treatment with an electrolyte solution designed for infants.
Breast milk In Australia and New Zealand, the two dietary practices that have the most significant effect on an infant’s nutrition are the type of milk the infant receives and the age at which solid foods are introduced. A later section discusses the introduction of solid foods, but as to the milk, the National Health and Medical Research Council (NHMRC) and the Royal Australasian College of Physicians (RACP) strongly recommend breastfeeding for healthy fullterm infants where possible due to the nutritional health it confers on the infant, as well as for the many other benefits it provides both infant and mother (review Table 15.5 on page 551).3 Breast milk excels as a source of nutrients for infants. Its unique nutrient composition and protective factors promote optimal infant health and development throughout the first year of life. Recommendations are for exclusive breastfeeding for about six months, and continued breastfeeding with complementary foods for as long as it is appropriate for the mother and infant.4 If breastfeeding isn’t possible, then an appropriate infant formula that imitates the nutrient composition of breast milk is an acceptable alternative. After all, the primary goal is to provide the infant nourishment in a relaxed and loving environment.
Frequency and duration of breastfeeding Breast milk is more easily and completely digested than formula, so breastfed infants usually need to feed more frequently than formula-fed infants do. During the first few weeks,
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
FIGURE 16.2 Recommended intakes of an infant and an adult compared on the basis of body weight Because infants are small, they need smaller total amounts of the nutrients than adults do, but when comparisons are based on body weight, infants need more than twice as much of many nutrients. Infants use large amounts of energy and nutrients, in proportion to their body size, to keep all their metabolic processes going. Recommendations for a 20-year-old male
Energy Protein Vitamin A
10 times as much per kilogram
5 times as much per kilogram as an adult male
Vitamin D recommendations for an infant are 10 times greater per kilogram of body weight than those for an adult male.
Vitamin D Vitamin E Vitamin C Folate Niacin Riboflavin Thiamin Vitamin B6 Vitamin B12 Calcium Phosphorus
Key: 20-year-old male (70 kg) 5-month-old boy (7 kg)
Magnesium Iodine Iron Zinc
approximately eight feeds a day, on demand, as soon as the infant shows early signs of hunger such as increased alertness, activity or suckling motions, promote optimal milk production and infant growth.5 Crying is a late indicator of hunger. An infant who nurses every two to three hours and displays appropriate growth on accepted growth charts is considered adequately nourished. As the infant gets older, stomach capacity enlarges and the mother’s milk production increases, allowing for longer intervals between feedings. Even though the infant obtains about half the milk from the breast during the first two or three minutes of sucking, breastfeeding is encouraged for about 10 to 15 minutes on each breast. The infant’s sucking, as well as the complete removal of milk from the breast, stimulates lactation.
Energy nutrients The energy–nutrient composition of breast milk differs dramatically from that recommended for adult diets (see Figure 16.3). For infants, breast milk is nature’s perfect food, providing the clear lesson that people at different stages of life have different nutrient needs.
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FIGURE 16.3 Percentages of energyyielding nutrients in breast milk and in recommended adult diets The proportions of energy-yielding nutrients in human breast milk differ from those recommended for adults. 6%
21% 26%
55%
53%
39% Breast milk
Recommended adult diets
Key: Protein Fat Carbohydrate
goodluz/Shutterstock.com
NOTE: The values listed for adults represent approximate midpoints of the acceptable ranges for protein (10 to 35 per cent), fat (20 to 35 per cent), and carbohydrate (45 to 65 per cent).
Women are encouraged to breastfeed whenever possible because breast milk provides infants with many nutrient and health advantages.
The carbohydrate in breast milk (and infant formula) is the disaccharide lactose. In addition to being easily digested, lactose enhances calcium absorption. The amount of protein in breast milk is less than in cow’s milk, but this quantity is actually beneficial because it places less stress on the infant’s immature kidneys to excrete the major end product of protein metabolism, urea. Much of the protein in breast milk is alpha-lactalbumin, which is efficiently digested and absorbed. As for the lipids, breast milk contains a generous proportion of the essential fatty acids linoleic acid and linolenic acid, as well as their longer-chain derivatives arachidonic acid (AA) and docosahexaenoic acid (DHA). Standard infant formula in Australia and New Zealand generally provides either linoleic acid or linolenic acid or both, in varying amounts, whereas AA and DHA are often included in infant formula marketed as ‘premium’ formula. These types of infant formula can be $5 to $7 per tin more expensive than standard infant formula, which substantially increases the cost of formula feeding an infant. Both AA and DHA are found abundantly in both the retina of the eye and the brain, and research has focused on the visual and mental development of breastfed infants and infants fed standard formula without DHA and AA added.6 Breastfed infants generally score higher on tests of mental development than formula-fed infants, and researchers are investigating whether this difference can be attributed to DHA and AA in breast milk.7 In one study, researchers found no developmental or visual differences between infants fed standard formula and those fed formula with added DHA and AA.8 In two other studies, however, infants fed the formula fortified with DHA and AA had sharper vision at one year of age than those who were fed standard formula.9 At longer-term follow-up (39 months) the evidence is inconclusive when comparing standard infant formula and infant formula with added DHA and AA. There currently appears to be no benefit to the infant in receiving these DHA- and AA-fortified, more expensive infant formula.10
Vitamins and minerals
The vitamin and mineral content of breast milk is ample to support infant growth. There has been some concern about the levels of vitamin D in breast milk and whether this is adequate. Vitamin D supplementation should only occur in at-risk populations such as infants of mothers who are vitamin D deficient.11 On the whole, the amount of vitamin D in the breast milk of non-deficient mothers, coupled with regular sunlight exposure, is sufficient to avoid the need for supplementation.12 The calcium content of breast milk is ideal for infant bone growth, and the calcium is well absorbed. Breast milk contains relatively small amounts of iron, but the iron has a high bioavailability. Zinc also has a high bioavailability, because of the presence of a zinc-binding protein. Breast milk is low in sodium, another benefit for immature kidneys. Table 16.2 highlights selected nutrients in breast milk and the average concentrations used to determine Adequate Intake for infants up to six months of age.
Immunological protection In addition to nutritional benefits, breast milk offers immunological protection. Not only is breast milk sterile, but it actively fights disease and protects infants from illnesses.13 Such protection is most valuable during the first year, when the infant’s immune system is not fully prepared to mount a response against infection.
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TABLE 16.2 Selected nutrients in breast milk ADEQUATE INTAKE FOR INFANTS 0–6 MONTHS (BASED ON MILK VOLUME OF 780 mL/day)
AVERAGE BREAST MILK CONCENTRATION USED IN ESTIMATIONS OF ADEQUATE INTAKE
Protein
10 g
12.7 g/L
Total fat
31 g
40 g/L
n-6 fats
4.4 g
5.6 g/L
n-3 fats
0.5 g
0.63 g/L
Carbohydrate
60 g
74 g/L
Water
0.7 L
Breast milk is 87% water
Vitamin C
25 mg
30 mg/L
Vitamin K
2 mg
2.5 mg/L
Calcium
210 mg
264 mg
Iron
0.2 mg
0.26 mg/L
Zinc
2 mg
2.5 mg/L (in early months)
NUTRIENT
Adapted from Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006).
During the first two or three days after delivery, the breasts produce colostrum, a pre-milk substance containing mostly serum with antibodies and white blood cells. Colostrum (like breast milk) helps protect the newborn from infections against which the mother has developed immunity. The maternal antibodies swallowed with the milk inactivate disease-causing bacteria within the digestive tract before they can start infections. This explains, in part, why breastfed infants have fewer intestinal infections than formulafed infants. In addition to antibodies, colostrum and breast milk provide other powerful agents that help to fight against bacterial infection. Among them are bifidus factors, which favour the growth of the ‘friendly’ bacterium Lactobacillus bifidus in the infant’s digestive tract, so that other, harmful bacteria cannot become established. An iron-binding protein in breast milk, lactoferrin, keeps bacteria from getting the iron they need to grow, helps absorb iron into the infant’s bloodstream and kills some bacteria directly.14 The protein lactadherin in breast milk binds to, and inhibits replication of, the virus that causes most infant diarrhoea.15 Breastfeeding also protects against other common illnesses of infancy such as middle ear infection and respiratory illness.16 In addition, a growth factor that is present in breast milk stimulates the development and maintenance of the infant’s digestive tract and its protective factors. Several breast milk enzymes, such as lipase, also help protect the infant against infection. Clearly, breast milk is a very special substance.
Allergy and disease protection In addition to protection against infection, breast milk may offer protection against the development of allergies. Compared with formula-fed infants, breastfed infants have a lower incidence of allergic reactions, such as asthma, recurrent wheezing and skin rash.17 This protection is especially noticeable among infants with a family history of allergies.18 Similarly, breast milk may offer protection against the development of cardiovascular disease. Compared with formula-fed infants, breastfed infants have lower blood pressure and lower blood cholesterol as adults.19
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Protective factors in breast milk are: • antibodies • bifidus factors • lactoferrin • lactadherin • growth factor • lipase enzyme.
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Other potential benefits
The infant thrives on infant formula offered with affection.
FIGURE 16.4 Percentages of energy-yielding nutrients in breast milk and in infant formula The average proportions of energyyielding nutrients in human breast milk and formula differ slightly. In contrast, cow’s milk provides too much protein (20%) and too little carbohydrate (29%). 6%
9%
55%
49%
39%
42%
Breast milk
Infant formula
20%
51%
Breastfeeding may also help protect against excessive weight gain in later life. A review of more than 60 published studies investigating the relationship between infant feeding and obesity suggests that initial breastfeeding protects against obesity in later life.20 A well-controlled survey of more than 15 000 adolescents and their mothers indicated that those who were mostly breastfed for the first six months of life were less likely to become overweight than those who were fed formula.21 A study of much younger children (three to five years of age), however, found no clear evidence that breastfeeding influences body weight.22 These researchers noted that other factors, especially the mother’s weight, strongly predict overweight in children. Many studies suggest a beneficial effect of breastfeeding on intelligence, but when subjected to strict standards of methodology (for example, large sample size and appropriate intelligence testing), the evidence is less convincing.23 Nevertheless, the possibility that breastfeeding may positively affect later intelligence is intriguing. It may be that some specific component of breast milk, such as DHA, stimulates brain development or that certain factors associated with the feeding process itself promote intellect. Most likely, a combination of factors is involved. More large, well-controlled studies are needed to confirm the effects, if any, of breastfeeding on intelligence.
Infant formula A woman who breastfeeds for a year can wean her infant to cow’s milk, bypassing the need for infant formula. However, a woman who decides to feed her infant formula from birth, to wean to formula after less than a year of breastfeeding, or to substitute formula for breastfeeding on occasion, must select an appropriate infant formula and learn to prepare it.
Infant formula composition Formula manufacturers attempt to mimic the nutrient composition of breast milk as closely as possible, but given that there are still many unknown constituents of breast milk, an identical product is impossible to manufacture. Figure 16.4 illustrates the energy–nutrient balance of breast milk, infant formula and cow’s milk.
Risks of formula feeding 29%
Key: Protein Fat Carbohydrate
Cow’s milk
Infant formulas contain no protective antibodies for infants, but in general, vaccinations, purified water and clean environments in industrialised countries help protect infants from infections. Formulas can be prepared safely by following proper food-handling techniques and by using water that is free of contamination. In developing countries, formula may be unavailable, prepared with contaminated water or over-diluted in an attempt to save money. Contaminated or incorrectly prepared formulas can cause infections, leading to diarrhoea, dehydration and malabsorption. Without sterilisation and refrigeration, formula is an ideal breeding ground for bacteria. Whenever such risks are present, breastfeeding can be a life-saving option: breast milk is sterile and its antibodies enhance an infant’s resistance to infections.
Infant formula standards National and international standards have been set for the nutrient contents of infant formulas. In Australia and New Zealand, FSANZ regulates infant formula composition through the Food Standards Code. In addition to this in Australia, the Marketing in Australia
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of Infant Formulas: Manufacturers and Importers Agreement 1992 (MAIF Agreement) exists. It is a voluntary, self-regulatory code of conduct between the manufacturers and importers of infant formula in Australia, and is Australia’s response to the World Health Organization’s International Code of Marketing of Breast-milk Substitutes 1981 (WHO Code). The MAIF Agreement applies only to those Australian manufacturers and importers of infant formula who are signatories. Formulas meeting the Food Standards Code have similar nutrient compositions but you may notice small differences among formulas. These are sometimes confusing, but usually unimportant.
Special formulas Standard formulas based on cow’s milk are inappropriate for some infants. Special formulas have been designed to meet the dietary needs of infants with specific conditions such as prematurity or inherited diseases. Infants allergic to milk protein can drink special hypoallergenic formulas or formulas based on soy protein.24 Soy formulas also use cornstarch and sucrose instead of lactose and so are recommended for infants with lactose intolerance as well. They are also useful as an alternative to milk-based formulas for vegan families. While soy formulas support the normal growth and development of infants, for infants who don’t need them, they offer no advantage over formulas based on cow’s milk.
Inappropriate formulas Caregivers must use only products designed for infants; cow’s milk, soy beverages or goat’s milk are nutritionally incomplete and inappropriate for infants – only infant formulas made to Australian standards are suitable as a breast milk substitute.
Nursing bottle tooth decay An infant should not be allowed to sleep with a bottle because of the potential damage to developing teeth. Salivary flow, which normally cleanses the mouth, diminishes as the infant falls asleep. Prolonged sucking on a bottle of formula, milk or juice bathes the upper teeth in a carbohydrate-rich fluid that nourishes decay-producing bacteria. (The tongue covers and protects most of the lower teeth, but they, too, may be affected.) The result is extensive and rapid tooth decay (see Figure 16.5). To prevent nursing bottle tooth decay, no infant should be put to bed with a bottle.
FIGURE 16.5 Nursing bottle tooth decay The terms preterm and premature imply incomplete foetal development, or immaturity, of many body systems. As might be expected, preterm birth is a leading cause of infant deaths. Preterm infants face physical independence from their mothers before some of their organs and body tissues are ready. The rate of weight gain in the foetus is greater during the last trimester of gestation than at any other time. Therefore, a preterm infant is most often a low-birthweight infant as well. A premature birth deprives the infant of the nutritional support of the placenta during a time of maximal growth. The last trimester of gestation is also a time of building nutrient stores. Being born with limited nutrient stores intensifies the already precarious situation for the infant. The physical and metabolic immaturity of preterm infants further compromises their nutrition status. Nutrient
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Ted Croll/Science Source
Special needs of preterm infants
This child was frequently put to bed sucking on a bottle filled with apple juice, so the teeth were bathed in carbohydrate for long periods of time – a perfect medium for bacterial growth. The upper teeth show signs of decay.
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Understanding nutrition
absorption, especially of fat and calcium, from an immature gastrointestinal (GI) tract is limited. Consequently, preterm, low-birth-weight infants are candidates for nutrient imbalances. Deficiencies of the fat-soluble vitamins, calcium, iron and zinc are common. Preterm breast milk is well suited to meet a preterm infant’s needs. During early lactation, preterm milk contains higher concentrations of protein and is lower in volume than term milk. The low milk volume is advantageous because preterm infants consume small quantities of milk per feeding, and the higher protein concentration allows for better growth. In many instances, supplements of nutrients specifically designed for preterm infants are added to the mother’s expressed breast milk and fed to the infant from a bottle. When fortified with a preterm supplement, preterm breast milk supports growth at a rate that approximates the growth rate that would have occurred within the uterus.
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Reduced-fat milks are not suitable for children under the age of 2 years.
Introducing cow’s milk The age at which whole cow’s milk should be introduced to the infant’s diet has long been a source of controversy. Cow’s milk is a poor source of iron and is never a substitute for breast milk or formula for babies under 12 months of age. Cow’s milk may be included from about seven months of age in small amounts as custard or yoghurt, or on breakfast cereals, but pasteurised whole cow’s milk shouldn’t be introduced as the main milk drink to a child’s diet until they’re about a year old. Children one to two years of age should not be given reduced-fat, low-fat or fat-free milk routinely; they need the fat of whole milk for their energy needs. After two years of age, the introduction of reduced-fat varieties of milks can occur.25 In some infants, particularly those younger than six months of age, whole cow’s milk may cause intestinal bleeding, which can lead to iron deficiency. Cow’s milk is also a poor source of iron. Consequently, it can cause both iron loss and failure to replace iron. Furthermore, the bioavailability of iron from infant cereal and other foods is reduced when cow’s milk replaces breast milk or iron-fortified formula during the first year. Compared with breast milk or ironfortified formula, cow’s milk is higher in calcium and lower in vitamin C, characteristics that reduce iron absorption. Furthermore, the higher protein concentration of cow’s milk can stress the infant’s kidneys. In short, cow’s milk is a poor choice during the first year of life; infants need breast milk or infant formula.
PUTTING COMMON SENSE TO THE TEST
Low-fat milks may be introduced to children from around 2 years of age. TRUE
Introducing solid foods The high nutrient needs of infancy are met first by breast milk or formula only, and then by the limited addition of selected foods over time. Infants gradually develop the ability to chew, swallow and digest the wide variety of foods available to adults. The caregiver’s selection of appropriate foods at the appropriate stages of development is a prerequisite for the infant’s optimal growth and health.
When to begin
Digestive secretions gradually increase throughout the first year of life, making the digestion of solid foods more efficient.
In addition to breast milk or formula, an infant can begin eating solid foods at around six months.26 The main purpose of introducing solid foods is to provide needed nutrients that are no longer supplied adequately by breast milk or formula alone. The foods chosen must be those that the infant is developmentally capable of handling both physically and metabolically. The exact timing depends on the individual infant’s needs and developmental readiness which vary from infant to infant because of differences in growth rates, activities and environmental conditions (see Table 16.3). In short, the addition of foods to an infant’s diet should be governed by three considerations: the infant’s nutrient needs, the infant’s physical readiness to handle different forms of foods, and the need to detect and control allergic reactions.
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TABLE 16.3 Infant development and recommended foods Because each stage of development builds on the previous stage, the foods from an earlier stage continue to be included in all later stages. AGE (MONTHS)
FEEDING SKILL
APPROPRIATE FOODS ADDED TO THE DIET
0–6
Turns head towards any object that brushes cheek Initially swallows using back of tongue; gradually begins to swallow using front of tongue as well Strong reflex (extrusion) to push food out during first two to four months
Feed breast milk or infant formula.
approx. 6
Extrusion reflex diminishes and the ability to swallow non-liquid foods develops Indicates desire for food by opening mouth and leaning forward Indicates satiety or disinterest by turning away and leaning back Sits erect with support at six months Begins chewing action Brings hand to mouth Grasps objects with palm of hand
Begin iron-fortified cereal mixed with breast milk, formula or water. Begin pureed vegetables and fruits.
approx. 8
Able to self-feed finger foods Develops pincer (finger to thumb) grasp Begins to drink from cup
Begin textured vegetables and fruits. Begin unsweetened, diluted fruit juices from cup.
8–10
Begins to hold own bottle Reaches for and grabs food and spoon Sits unsupported
Begin breads and cereals from table. Begin yoghurt. Begin pieces of soft, cooked vegetables and fruit from table. Gradually begin finely cut meats, fish, casseroles, cheese, eggs and mashed legumes.
10–12
Begins to master spoon, but still spills some
Add variety. Gradually increase portion sizes.
Adapted in part from Committee on Nutrition, American Academy of Pediatrics, Pediatric Nutrition Handbook, 6th edn, ed. R. E. Kleinman, Elk Grove Village, IL: American Academy of Pediatrics (2009): 113–42.
Food allergies When there is a family history of allergies, experts may recommend introducing singleingredient foods, one at a time, in small portions, and waiting a few days before introducing the next new food. This is so that the identification of a food causing an allergic reaction can occur. There is little evidence available to suggest that known allergenic foods should be avoided or any delay occur to their introduction. Considering the introduction of grains as an example, rice cereal is usually the first cereal introduced as it is iron-fortified. When it is clear that rice cereal is not causing an allergy, another grain, perhaps semolina or oats, is introduced. If a cereal causes an allergic reaction such as a skin rash, digestive upset or respiratory discomfort, it should be discontinued before introducing the next food. A later section in this chapter offers more information about food allergies.
Choice of infant foods Infant foods should be selected to provide variety, balance and moderation. Commercial baby foods offer a wide variety of palatable, nutritious foods in a safe and convenient form. Homemade infant foods can be as nutritious as commercially prepared ones, as long as
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the cook minimises nutrient losses during preparation. Ingredients for homemade foods should be fresh whole foods without added salt, sugar or seasonings. Pureed food can be frozen in ice cube trays, providing convenient-sized blocks of food that can be thawed, warmed and fed to the infant. To guard against food-borne illnesses, hands and equipment must be kept clean.
© Polara Studios, Inc.
Foods to provide iron Rapid growth demands iron. At about six months, the infant begins to need more iron than body stores plus breast milk or formula can provide. In addition to breast milk or formula, infants can receive iron from iron-fortified cereals and, once they readily accept solid foods, from meat or meat alternatives such as legumes. Iron-fortified cereals contribute a significant amount of iron to an infant’s diet, but the bioavailability of the iron is dependent upon the type of iron used to fortify the cereal.27
Foods to provide vitamin C The best sources of vitamin C are fruits and vegetables (see Section 10.4 in Chapter 10). It has been suggested that infants who are introduced to Foods such as iron-fortified cereals and formulas, fruits before vegetables may develop a preference for sweets and find the mashed legumes and soft meats provide iron. vegetables less palatable, but there is no evidence to support offering these foods in a particular order.28 Fruit juice is a good source of vitamin C, but drinking too much juice can lead to diarrhoea PUTTING in infants and young children.29 An infant’s fruit juice intake should be limited, to avoid COMMON SENSE TO THE TEST interfering with their intake of breast milk or infant formula. Infants require additional iron at around 6 months – more than body stores or breastfeeding alone can provide.
Foods to omit
TRUE To prevent choking, do not give infants or young children: • raw carrots • cherries • gum • lollies • sausages cut into ‘rings’ • marshmallows • nuts • whole beans • popcorn • raw celery • whole grapes. Keep all small nonfood items out of an infant’s reach.
Concentrated sweets, including baby food ‘desserts’, have no place in an infant’s diet. They provide minimal nutrients to support growth, and the extra food energy can promote obesity. Products containing sugar alcohols such as sorbitol should also be limited, as they may cause diarrhoea. Honey and corn syrup should never be fed to infants because of the risk of botulism.* Infants and young children are vulnerable to food-borne illnesses, and the Australian Dietary Guidelines address this risk. Infants and even young children cannot safely chew and swallow many foods; they can easily choke on these foods, a risk not worth taking. Non-food items may present even greater choking hazards to infants and young children.30 Parents and caregivers must pay careful attention to eliminate choking hazards in children’s environments.
Vegetarian diets during infancy As long as the infant has access to sufficient quantities of either infant formula or breast milk from a mother who eats an adequate diet, the infant will thrive during the early months. ‘Health-food beverages’, such as rice milk, are inappropriate choices because they lack the protein, vitamins and minerals infants and toddlers need; in fact, their use can lead to severe nutritional deficiencies. Infants beyond about six months of age present a greater challenge in terms of meeting nutrient needs by way of vegetarian and, especially, vegan diets. Continued breastfeeding or formula feeding is recommended, but supplementary feedings are necessary to ensure adequate energy and iron intakes. Infants and young children in vegetarian families should be provided with adequate sources of iron. Mashed or pureed legumes, tofu, dairy foods and cooked eggs can be added to their diets in place of meat as a source of protein. *In infants, but not in older individuals, ingestion of Clostridium botulinum spores can cause illness when the spores germinate in the intestine and produce a toxin, which is absorbed. Symptoms include poor feeding, constipation, loss of tension in the arteries and muscles, weakness and respiratory compromise.
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
The risks of undernutrition in infants increase with weaning and reliance on solid foods. Infants who receive a well-balanced vegetarian diet that includes milk products and a variety of other foods can easily meet their nutritional requirements for growth. This is not always true for vegan infants; the growth of vegan infants slows significantly around the time of transition from breast milk to solid foods. Protein–energy malnutrition and deficiencies of vitamin B12, iron and calcium have been reported in infants fed vegan diets.31 Vegan diets that are high in fibre, other complex carbohydrates and water will fill an infant’s stomach before meeting their energy needs. This problem can be partially alleviated by providing more energy-dense foods, such as nut butters, legumes, dried fruit spreads and mashed avocado. Using an infant formula beyond the age of 12 months can help prevent nutrient deficiencies in vegan diets. Parents or caregivers who choose to feed their infants vegan diets should consult with their paediatrician and a qualified nutrition professional regularly to ensure a nutritionally adequate diet that will support growth.
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Care for your food; prepare and store it safely.
Foods at one year
Mealtimes with toddlers The nurturing of a young child involves more than nutrition. Those who care for young children are responsible for providing not only nutritious foods but also a safe, loving, secure environment in which the children may grow and develop. In light of toddlers’ developmental and nutrient needs, and their often contrary and wilful behaviour, a few feeding guidelines may be helpful: • Discourage unacceptable behaviour, such as standing at the table or throwing food, by removing the young child from the table to wait until later to eat. Be consistent and firm, not punitive. The child will soon learn to sit Ideally, a one-year-old can enjoy the same and eat. meals as the rest of the family. • Let toddlers explore and enjoy food, even if this means eating with fingers for a while. Learning to use utensils will come in time. • Don’t force food on children. Rejecting new foods is normal, and acceptance is more likely as children become familiar with new foods through repeated opportunities to taste them. • Provide nutritious foods, and let children choose which ones, and how much, they will eat. Gradually, they will acquire a taste for different foods. • Limit sweets. Infants and young children have little room for empty-kilojoule foods in their daily energy allowance. Do not use sweets as a reward for eating other foods. • Don’t turn the dining table into a battleground. Make mealtimes enjoyable. Teach healthy food choices and eating habits in a pleasant environment.
REVIEW IT
The primary food for infants during the first 12 months is either breast milk or infant formula. In addition to nutrients, breast milk also offers immunological protection. At about six months, infants should gradually begin eating solid foods. By one year, they are drinking from a cup and eating most of the same foods as the rest of the family.
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At one year of age, whole cow’s milk can become the main milk drink in the infant’s diet; 2 to 3 cups a day (approximately 600 millilitres) is generally sufficient. Ingesting more milk than this can displace iron-rich foods, which can lead to milk anaemia. Other foods – meats, iron-fortified cereals, enriched or wholegrain breads, fruits and vegetables – should be supplied in variety and in amounts sufficient to round out total energy needs. Ideally, a one-year-old will sit at the table, eat most of the same foods everyone else eats and drink liquids from a cup, not a bottle.
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16.2 Nutrition during childhood
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Each year children grow, but their rate of growth slows after the age of one year until adolescence. Growth charts provide valuable clues to a child’s health. Weight gains out of proportion to height gains may reflect overeating and inactivity, whereas measures significantly below the standard suggest suboptimal nutrition. Increases in height and weight are only two of the many changes growing children experience (see Figure 16.6). At age one, children can stand alone and are beginning to toddle; by two years, they can walk and are learning to run; and by three years, they can jump and climb with confidence. Bones and muscles increase in mass and density to make these accomplishments possible. Thereafter, lengthening of the long bones and increases in musculature proceed unevenly and more slowly until adolescence.
Energy and nutrient needs Children’s appetites begin to diminish around one year, consistent with their slowing growth. Thereafter, children will generally spontaneously vary their food intakes to coincide with their growth patterns; they demand more food during periods of rapid growth than during slow growth. Sometimes they seem insatiable, and at other times they seem Toddlers can enjoy two to three glasses of milk each day. to live on air and water. Children’s energy intakes also vary widely from meal to meal. Even so, their total daily intakes remain remarkably constant.32 If children eat less at one meal, they typically eat more at the next, and vice versa. Overweight children are exceptions: they do not always adjust their energy intakes appropriately and may eat in response to external cues, disregarding hunger and satiety signals.
Individual children’s energy needs vary widely, depending on their growth and physical activity. A one-year-old child needs about 3300 kilojoules a day; an active six-year-old needs twice as many kilojoules a day. By age 10, an active child needs about 8500 kilojoules a day. Total energy needs increase slightly with age, but energy FIGURE 16.6 Body shape of one-year-old and two-year-old needs per kilogram of body weight actually decline compared gradually.33 The body shape of a 1-year-old (left) changes dramatically by age Physically active children of any age need more two years (right). The 2-year-old has lost much of the baby fat; the energy because they expend more, and inactive muscles (especially in the back, buttocks and legs) have firmed and children can become obese even when they eat strengthened, and the leg bones have lengthened. less food than average. Children who learn to enjoy physical play and exercise, both at home and at school, are best prepared to maintain active lifestyles as adults. Some children, notably those adhering to a vegan diet, may have difficulty meeting their energy needs. Grains, vegetables and fruits provide plenty of fibre, adding bulk, but may provide too few kilojoules to support growth. Soy products, other legumes and nut or seed butters offer more concentrated sources of energy to support optimal growth and development.34 © Anthony M. Vannelli
© Anthony M. Vannelli
Energy intake and activity
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Fibre Fibre recommendations are based on energy intakes. Consequently, fibre recommendations for younger children with low energy intakes are less than those for older ones with high energy intakes.
Fat and fatty acids
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Protein
Eat a wide variety of nutritious foods – grain (cereal) foods, mostly wholegrain, such as breads, cereals, rice, pasta, noodles, polenta, couscous, oats, quinoa and barley.
Like energy needs, total protein needs increase slightly with age, but when the child’s body weight is considered, the protein requirement actually declines slightly (see the inside cover). Protein recommendations must consider the requirements for maintaining nitrogen balance, the quality of protein consumed and the added needs of growth.
Fibre recommendations for children:
A Nutrient Reference Value for total fat has not been established, but there are recommendations of a fat intake of 50 per cent of energy for children up to one year of age, 40 per cent for children from one to two years of age, and 30 per cent for children two to 18 years of age.35 Children who eat low-fat diets tend to have low intakes of some vitamins and minerals. Recommended intakes of the essential fatty acids are based on average intakes (see the inside cover).
Age (yrs)
Vitamins and minerals The vitamin and mineral needs of children increase with age (see inside cover). A balanced diet of nutritious foods can meet children’s needs for these nutrients. Special consideration needs to be given to iron, however – iron-deficiency anaemia is a major problem worldwide.36 During the second year of life, toddlers progress from a diet of ironrich infant foods such as breast milk, or infant formula, and iron-fortified infant cereal to a diet of adult foods and iron-poor cow’s milk. In addition, their appetites often fluctuate – some become fussy about the foods they eat, and others prefer milk and juice to solid foods.37 All of these situations can interfere with children eating iron-rich foods at a critical time for brain growth and development. To prevent iron deficiency, children’s foods must deliver 4 to 6 milligrams of iron per day. To achieve this goal, snacks and meals should include iron-rich foods, and milk intake should be reasonable so that it will not displace lean meats, fish, poultry, eggs, legumes and whole-grain or enriched products. (Chapter 13 described iron-rich foods and ways to maximise iron absorption.)
AI (g/day)
1–3
14
4–8
8
boys 9–13
24
girls 9–13
20
boys 14–18
28
girls 14–18
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AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Hunger in children Hunger and behaviour
Even when hunger is temporary, as when a child misses one meal, behaviour and academic performance are affected. Associations exist between children who eat nutritious breakfasts and improved school performance and decreased behavioural problems.38 A nutritious breakfast is a central feature of a diet that meets the needs of children and supports their healthy growth and development.39 Children who skip breakfast typically do not make up the deficits at later meals – they simply have lower intakes of vitamins and minerals than those who eat breakfast. Without breakfast, children perform poorly in tasks requiring concentration, their attention spans are shorter and they score lower on intelligence tests than their breakfast-eating peers. Common sense dictates that it is unreasonable to expect anyone to learn and perform without fuel. For the child who hasn’t had breakfast, the morning’s lessons may be lost altogether. Healthy, well-nourished children are alert in the classroom and energetic at play.
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Limit intake of foods and drinks containing saturated and trans fats, added salt, added sugars.
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Iron deficiency and behaviour Iron deficiency has well-known and widespread effects on children’s behaviour and intellectual performance.40 In addition to carrying oxygen in the blood, iron transports oxygen within cells, which use it for energy metabolism. Iron is also used to make neurotransmitters – most notably, those that regulate the ability to pay attention, which is crucial to learning. Consequently, iron deficiency not only causes an energy crisis, but also directly impairs attention span and learning ability. Iron deficiency is often diagnosed by a quick, easy, inexpensive haemoglobin test that detects a deficit of iron in the blood. A child’s brain, however, is sensitive to low iron concentrations long before the blood effects appear. Iron deficiency lowers the motivation to persist in intellectually challenging tasks and impairs overall intellectual performance. Anaemic children perform poorly on tests and are disruptive in the classroom; iron supplementation improves learning and memory. When combined with other nutrient deficiencies, iron-deficiency anaemia has synergistic effects that are especially detrimental to learning. Furthermore, children who had iron-deficiency anaemia as infants can continue to perform poorly as they grow older, even if their iron status improves.41 The long-term damaging effects on mental development make prevention and treatment of iron deficiency during infancy and early childhood a high priority.
Other nutrient deficiencies and behaviour A child with any of several nutrient deficiencies may be irritable, aggressive and disagreeable, or sad and withdrawn. Such a child may be labelled ‘hyperactive’, ‘depressed’ or ‘unlikeable’, when in fact these traits may be due to simple, even marginal, malnutrition. Parents and medical practitioners often overlook the possibility that malnutrition may account for abnormalities of appearance and behaviour. Any departure from normal healthy appearance and behaviour is a sign of possible poor nutrition (see Table 16.4). In any such case, inspection of the child’s diet by a qualified nutrition professional or other qualified healthcare professional is in order. Any suspicion of dietary inadequacies, no matter what other causes may be implicated, should prompt steps to correct those inadequacies immediately.
TABLE 16.4 Physical signs of malnutrition in children WELL-NOURISHED
MALNOURISHED
POSSIBLE NUTRIENT DEFICIENCIES
Hair
Shiny, firm in the scalp
Dull, brittle, dry, loose; falls out
PEM
Eyes
Bright, clear pink membranes; adjust easily to light
Pale membranes; spots; redness; adjust slowly to darkness
Vitamin A, the B vitamins, zinc and iron
Teeth and gums
No pain or caries, gums firm, teeth bright
Missing, discoloured, decayed teeth; gums bleed easily and are swollen and spongy
Minerals and vitamin C
Face
Clear complexion without dryness or scaliness
Off-colour, scaly, flaky, cracked skin
PEM, vitamin A and iron
Glands
No lumps
Swollen at front of neck, cheeks
PEM and iodine
Tongue
Red, bumpy, rough
Sore, smooth, purplish, swollen
B vitamins
Skin
Smooth, firm, good colour
Dry, rough, spotty; ‘sandpaper’ feel or sores; lack of fat under skin
PEM, essential fatty acids, vitamin A, B vitamins and vitamin C
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TABLE 16.4
Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
WELL-NOURISHED
MALNOURISHED
579
POSSIBLE NUTRIENT DEFICIENCIES
Nails
Firm, pink
Spoon-shaped, brittle, ridged
Iron
Internal systems
Regular heart rhythm, heart rate and blood pressure; no impairment of digestive function, reflexes or mental status
Abnormal heart rate, heart rhythm or blood pressure; enlarged liver, spleen; abnormal digestion; burning, tingling of hands, feet; loss of balance, coordination; mental confusion, irritability, fatigue
PEM and minerals
Muscles and bones
Muscle tone; posture; long bone development appropriate for age
‘Wasted’ appearance of muscles; swollen bumps on skull or ends of bones; small bumps on ribs; bowed legs or knock-knees
PEM, minerals and vitamin D
Hyperactivity and ‘hyper’ behaviour Children are generally active, and many of them become overly active on occasion – for example, in anticipation of a birthday party. Such behaviour is markedly different from true hyperactivity.
Hyperactivity Hyperactive children have trouble sleeping, cannot sit still for more than a few minutes at a time, act impulsively and have difficulty paying attention. These behaviours interfere with social development and academic progress. The cause of hyperactivity remains unknown.42 To resolve the problems surrounding hyperactivity, doctors often recommend specific behavioural strategies, special educational programs and psychological counselling. In many cases, they prescribe medication.43 Parents of hyperactive children sometimes seek help from alternative therapies, including special diets. They mistakenly believe a solution may lie in manipulating the diet – most commonly, by excluding sugar or food additives. Adding carrots or eliminating lollies is such a simple solution that many parents eagerly give such dietary advice a try. However, these dietary changes are unlikely to solve the problem, and studies have consistently found no convincing evidence that sugar causes hyperactivity or worsens behaviour.
Misbehaving Even a child who is not truly hyperactive can be difficult to manage at times. Michael may be unruly from a desire for attention, Jessica may be cranky because of a lack of sleep, Christopher may react violently after watching too much television and Sheila may be unable to sit still in class due to a lack of exercise. All of these children may benefit from more consistent care – regular hours of sleep, regular mealtimes and regular outdoor activity.
Food allergy and intolerance Food allergy is frequently blamed for physical and behavioural abnormalities in children, but just 5 per cent of children are diagnosed with true food allergies.44 Food allergies tend to diminish with age, until in adulthood they affect only about 1 per cent of the population. A true food allergy occurs when fractions of a food protein are absorbed into the blood and elicit an immunologic response. (Recall that proteins are normally dismantled in the digestive tract to amino acids that are absorbed without such a reaction.) The body’s immune system reacts to these food proteins as it does to other antigens – by producing antibodies, histamines or other defensive agents. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
PUTTING COMMON SENSE TO THE TEST
Hyperactive children respond well to dietary modification. FALSE
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Science Photo Library/Sheila Terry
Detecting food allergy Allergies may have one or two components. They always involve antibodies, but they may or may not involve symptoms. This means that allergies can be diagnosed only by testing for antibodies. Even symptoms exactly like those of an allergy may not be caused by an allergy. However, once a food allergy has been diagnosed, the required treatment is strict elimination of the offending food. Children with allergies, like all children, need all their nutrients, so it is important to include other foods that offer the same nutrients as the omitted foods.45 Allergic reactions to food may be immediate or delayed. In both cases, the antigen interacts immediately with the immune system, but the timing of symptoms varies from minutes to hours after consumption of the antigen. These normally wholesome foods may cause Identifying the food that causes an immediate allergic reaction is fairly easy symptoms in people with allergies. because the symptoms appear shortly after the food is eaten. Identifying the food that causes a delayed reaction is more difficult because the symptoms A person who may not appear until much later. By this time, many other foods may have been eaten, produces antibodies complicating the picture. without having any symptoms has an Anaphylaxis asymptomatic allergy; a The life-threatening food allergy reaction of anaphylaxis is most often (but not always) person who produces caused by peanuts. Children are more likely to outgrow allergies to eggs, milk and soy than antibodies and has symptoms has a allergies to peanuts. Families of children with a life-threatening food allergy and school staff symptomatic allergy. who supervise them must protect them against any exposure to the allergen. The child must learn to identify which foods pose a problem and then learn and use refusal skills for all foods Symptoms of that may contain the allergen. anaphylaxis include: Parents of children with allergies can pack safe foods for lunches and snacks and ask • tingling sensation in school teachers to strictly enforce a ‘no swapping’ policy. The child must be able to recognise mouth the symptoms of anaphylaxis, such as a tingling of the tongue, throat or skin, or difficulty • swelling of the breathing. Any person with food allergies severe enough to cause anaphylactic shock should tongue and throat wear a medical alert bracelet or necklace and have an EpiPen (an adrenaline injection ) with • irritated, reddened them at all times. eyes • difficulty breathing, asthma Food intolerances • hives, swelling, Not all adverse reactions to foods are food allergies, although even doctors may describe rashes them as such. Signs of adverse reactions to foods include stomach aches, headaches, rapid • vomiting, abdominal pulse rate, nausea, wheezing, hives, bronchial irritation, coughs and other such discomforts. cramps, diarrhoea Among the causes may be reactions to chemicals in foods, such as the flavour enhancer • drop in blood monosodium glutamate (MSG), the natural laxative in prunes or the mineral sulphur; pressure digestive diseases, such as obstructions or injuries; enzyme deficiencies, such as lactose • loss of intolerance; and even psychological aversions. These reactions involve symptoms but no consciousness. antibody production. Therefore, they are food intolerances, not allergies. Reminder: Hunger, hyperactivity and allergic reactions can all adversely affect a child’s nutrition Adrenaline is a status and health. Fortunately, each of these problems has solutions. They may not be easy hormone of the solutions, but at least we have a reasonably good understanding of the problems and ways adrenal gland that to correct them. Such is not the case with the most pervasive health problem for children in modulates the stress Australia – obesity. response; it is also known as epinephrine. When administered by injection, adrenaline counteracts The number of overweight children has increased dramatically over the past three decades anaphylaxis by (see Figure 16.7). Like their parents, children in Australia are affected by overweight. An estimated opening the airways 25 per cent of Australian children are overweight or obese.46 These numbers aren’t dissimilar and maintaining in New Zealand where approximately 29 per cent of children are overweight or obese.47 Based heartbeat and blood on data from the Body Mass Index (BMI)-for-age growth charts, children and adolescents are pressure.
Childhood obesity
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Per cent
categorised as at risk of overweight above the 85th FIGURE 16.7 Trends in childhood overweight and obesity in Australia percentile and as overweight at the 95th percentile Key: and above. It must be noted that prevalence Boys data reflect only children and adolescents in the overweight category. Figure 16.8 presents the BMI Girls for children and adolescents, indicating cut-off points for overweight and at risk of overweight. 25 The use of the term overweight instead of obese when referring to children with a 20 BMI above the age- and gender-specific 95th percentiles is controversial. Some experts think 15 it is best not to label children as obese, whereas others think it important to recognise the full extent of the problem. 10 The problem of obesity in children is especially troubling because overweight children 5 are more likely to become overweight adults with all the social, economic and medical 0 implications that often accompany overweight Overweight Obese Overweight Obese Overweight Obese and obesity. They have additional problems, 1985 1995 2007 too, arising from differences in their growth, Boys 7–15 Boys 7–15 Boys 9–16 Girls 7–15 Girls 7–15 Girls 9–16 physical health and psychological development. In trying to explain the rise in childhood obesity, researchers point to both genetic and environmental factors.
FIGURE 16.8 BMI-for-age percentiles: boys and girls, age two to 20 36
36 Boys, 2 to 20 years
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30 28
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Key: Overweight $95th percentile
Normal 10th to 85th percentile
At risk of overweight .85th percentile
Underweight ,10th percentile
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18
20
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CURRENT RESEARCH IN NUTRITION Fruit juice and childhood adiposity Research is at loggerheads with itself when it comes to fruit juice intake and childhood adiposity. Some research indicates that fruit juice intake predicts increased adiposity gain in children, while there is also evidence of there being little effect. Researchers of one study found the relationship between juice intake and adiposity gain depended on children’s intake of juice at one year of age. Higher juice intake at one year was associated with higher juice intake, as well as with other sugar-sweetened beverage intake and higher BMI z-scores during early and mid-childhood. These findings were strengthened by a recent longitudinal study that determined regular fruit juice intake at two years of age is associated with increased odds of becoming overweight between two and four years.48 Conversely, a meta-analysis of studies in the area concluded that fruit juice intake in children aged one to 18 years resulted in small weight gain in those children between one and six years that was not of clinical significance and not associated with weight gain in children aged seven to 18 years.49 It is clear that the evidence in this area, while not conclusive, poses some interesting questions regarding juice intake in young children.
Genetic and environmental factors Parental obesity predicts an early increase in a young child’s BMI, and it more than doubles the chances that a young child will become an obese adult. Children with healthy weight parents have a less than 10 per cent chance of becoming obese in adulthood, whereas overweight teens with at least one obese parent have a greater than 80 per cent chance of being obese adults. Also, as children grow older, their body weight becomes an important factor in determining their obesity as adults.50 The link between parental and child obesity reflects both genetic and environmental factors (as described in Chapter 9). Diet and physical inactivity must also play a role in explaining why children are heavier today than they were 30 or so years ago. As the prevalence of childhood overweight throughout Australia has more than doubled for children and adolescents (and tripled for obesity), the society our children live in has changed considerably. In many families today, both parents work outside the home and work longer hours; more emphasis is placed on foods that are easy to prepare and foods eaten away from home; school lunchbox items are more diverse and often less nutritious; sedentary activities such as watching television and playing video or computer games occupy much of children’s free time; and opportunities for physical activity and outdoor play both during and after school have declined. All of these factors – and many others – influence children’s eating and activity patterns. Children learn food behaviours from their families, and research confirms the significant roles parents play in teaching their children about healthy food choices, providing nutrientdense foods and serving as role models.51 When parents eat fruits and vegetables frequently, their children do, too.52 The more fruits and vegetables children eat, the more vitamins, minerals and fibre, and the less saturated fat in their diets.
APPLICATIONS OF NUTRITIONAL RESEARCH Fathers and children’s diets Interestingly, recent research on the dietary intakes of fathers and children has found associations between intakes of fruit and some energy dense foods. Children’s intakes of fruit and some energy-dense, nutrient-poor foods, but not vegetables, were related to their father’s intakes.53 Fathers’ intakes of sugar-sweetened drinks when children were younger were also predictive of children’s sugar-sweetened drink intake at age five. This suggests that the influence of fathers on the diets of young children should be considered when contemplating dietary changes for improvements to child and family eating habits.54
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
Research shows that one in four toddlers (19 to 24 months of age) exceeds estimated energy requirements as a result of eating such foods as takeaway foods, lollies, sweet drinks and salty snacks like chips.55 Thus, when researchers ask, ‘Are today’s children eating more kilojoules than those of 30 years ago?’, the answer is, ‘Yes’. A major contributing factor to the obesity epidemic can be explained by a decrease in physical activity. Children have become more sedentary, and sedentary children are more often overweight. Television watching may contribute most to physical inactivity. Associations exist between screen time and weight status.56 Children who have television sets in their bedrooms spend more time watching TV and are more likely to be overweight than children who do not have televisions in their rooms.57 Children who watch hours of television each day are most likely to be overweight and least likely to eat family meals or fruits and vegetables.58 They often snack on the nutrient-poor, energy-dense foods that are advertised. The average child sees an estimated 30 000 TV commercials a year – many advertising foods high in sugar, saturated fat and salt, such as sugar-coated breakfast cereals, chips, fast foods and soft drinks. More than half of all food advertisements are aimed specifically at children and market their products as fun and exciting. Not surprisingly, the more time children spend watching television, the more they request these advertised foods and drinks. The most popular foods and drinks are also marketed to children and adolescents on the Internet as well, using ‘advergaming’ (advertised product as part of a game), cartoon characters or ‘spokes-characters’, and designated children’s areas. The physically inactive time spent watching television is second only to time spent sleeping. Children also spend more time playing video games whether on gaming consoles or handheld devices. These activities use no more energy than resting, displace participation in more vigorous activities and foster snacking on high-fat foods. Simply reducing the amount of time spent watching television (and playing video games) can improve a child’s BMI.
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TV fosters obesity because it: • requires no energy beyond basal metabolism • replaces vigorous activities • encourages snacking • promotes a sedentary lifestyle. Playing computer or video games influences children’s activity patterns similarly.
Growth Overweight children develop a characteristic set of physical traits. They typically begin puberty earlier and so grow taller than their peers at first, but then they stop growing at a shorter height. They develop greater bone and muscle mass in response to the demand of having to carry more weight – both fat and lean weight. Consequently, they appear ‘stocky’ even when they lose their excess fat.
Like overweight adults, overweight children display a blood lipid profile indicating that atherosclerosis is beginning to develop – high levels of total cholesterol, triglycerides and LDL cholesterol. Overweight children also tend to have high blood pressure; in fact, obesity is a leading cause of paediatric hypertension. Their risks for developing type 2 diabetes and respiratory diseases (such as asthma) are also exceptionally high. These relationships between childhood obesity and chronic diseases are discussed fully in Highlight 16.
Psychological development
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Physical health
Television watching influences children’s eating habits and activity patterns.
In addition to the physical consequences, childhood obesity brings a host of emotional and social problems. Because people frequently judge others on appearance more than on character, overweight children are often victims of prejudice. Many suffer discrimination by adults and rejection by their peers. They may have poor self-image, a sense of failure and a passive approach to life. Television shows, which are a major influence in children’s lives, often portray the fat person as the bumbling misfit. Overweight children may come to accept this negative stereotype in themselves and in others, which can lead to additional emotional and social problems. Researchers investigating children’s reactions to various
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body types find that both normal-weight and underweight children respond unfavourably to overweight bodies.
Prevention and treatment of obesity Medical science has worked wonders in preventing or curing many of even the most serious childhood diseases, but obesity remains a challenge. Once excess fat has been stored, it is challenging to lose. In light of all this, parents are encouraged to make major efforts to prevent childhood obesity or to begin treatment early – before adolescence. Treatment must consider the many aspects of the problem and possible solutions. The most successful approach integrates diet, physical activity, psychological support and behavioural changes.
Diet AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Physical activity is important for all children and adolescents. Australia’s Physical Activity Recommendations for 5- to 12-yearolds suggest children need at least 60 minutes of moderate to vigorous physical activity every day and that children should not spend more than two hours a day using electronic media for entertainment (for example, computer games, TV, Internet), particularly during daylight hours.
The initial goal for overweight children is to reduce the rate of weight gain; that is, to maintain weight while the child grows taller. Continued growth will then accomplish the desired change in weight for height. Weight loss is usually not recommended because diet restriction can interfere with growth and development. Intervention for some older, overweight children with accompanying medical conditions may warrant weight loss, but this treatment requires an individualised approach based on the degree of overweight and severity of the medical conditions. Whether the goal is to treat or prevent obesity, the following strategies may be helpful: • Serve family meals that reflect kilojoule control both in the foods offered and in the ways foods are prepared. • Involve children in shopping for food and preparing meals. • Encourage children to eat only when they are hungry, to eat slowly, to pause and enjoy their table companions, and to stop eating when they are full. • Teach them how to select nutrient-dense foods (low-fat and non-fat milk and milk products for children three years of age and older, fruits and vegetables, whole grains, legumes, fish and lean meat) that will meet their nutrient needs within their energy allowances. Also, teach them to serve themselves appropriate portions at meals; the amount of food offered influences the amount of food eaten. • Limit foods high in saturated and trans fats (see Figure H5.1 on page 172) and high-sugar foods, including sugar-sweetened soft drinks. • Never force children to finish everything on their plates. • Plan for snack times and provide a variety of nutritious snacks (see Table 16.6 later in this chapter). • Discourage eating while watching TV.
Physical activity The many benefits of physical activity are well known, but often are not enough to motivate overweight people, especially children. Yet regular vigorous activity can improve a child’s weight, body composition and physical fitness. Ideally, parents will limit sedentary activities and encourage daily physical activity to promote strong skeletal, muscular and cardiovascular development and instil in their children the desire to be physically active throughout life. Most importantly, parents need to set a good example. Physical activity is a natural and lifelong behaviour of healthy living. It can be as simple as riding a bike, playing tag, skipping or doing chores. It need not be an organised sport; it just needs to be some activity on a regular basis.
Psychological support Weight-loss programs that involve parents and other caregivers in treatment report greater success than those without parental involvement. Because obesity in parents and their children tends to be positively correlated, both benefit when parents participate in a weight-loss
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
program. Parental attitudes about food greatly influence children’s eating behaviour, so it is important that the influence is positive. Otherwise, eating problems may become exacerbated.
Behavioural changes
In contrast to traditional weight-loss programs that focus on what to eat, behavioural programs focus on how to eat. These techniques involve changing learnt habits that lead a child to eat excessively. Obesity is prevalent in our society. Because treatment of obesity is frequently unsuccessful, it is most important to prevent its onset. Above all, be sensible in teaching children how to maintain appropriate body weight. Children can easily get the impression that their worth is tied to their body weight. Parents and the media are most influential in shaping selfconcept, weight concerns and dieting practices. Some parents fail to realise that society’s ideal of slimness can be perilously close to starvation and that a child encouraged to ‘diet’ cannot obtain the energy and nutrients required for normal growth and development. Even healthy children without diagnosable eating disorders have been observed to limit their growth through ‘dieting’. Weight gain in truly overweight children can be managed without compromising growth, but it should be overseen by a healthcare professional.
Mealtimes at home Traditionally, parents served as gatekeepers, determining what foods and activities were available in their children’s lives. Then the children made their own selections. Gatekeepers who wanted to promote nutritious choices and healthful habits provided access to nutrientdense, delicious foods and opportunities for active play at home. In today’s consumer-oriented society, children have greater influence over family decisions concerning food – the fast-food restaurant the family chooses when eating out, the type of food the family eats at home and the specific brands the family purchases at the supermarket. Parental guidance in food choices is still necessary, but teaching children consumer skills to help them make informed choices is equally important.
Honouring children’s preferences Researchers attempting to explain children’s food preferences encounter contradictions. Children say they like colourful foods, yet they most often reject green and yellow vegetables in favour of brown peanut butter and white potatoes, apple wedges and bread. They seem to like raw vegetables better than cooked ones, so it is wise to offer vegetables that are raw or slightly undercooked, served separately and easy to eat. Foods should be warm, not hot, because a child’s mouth is much more sensitive than an adult’s and flavours should be milder because a child has more taste buds. Children prefer foods that are familiar, so offer various foods regularly. Make mealtimes fun for children. Young children like to eat at little tables and to be served small portions of food. They like sandwiches cut in different geometric shapes and common foods called silly names. They also like to eat with other children, and they tend to eat well when in the company of their friends. Children are also more likely to give up their prejudices against foods when they see their peers eating them.
Learning through participation Allowing children to help plan and prepare the family’s meals provides enjoyable learning experiences and encourages children to eat the foods they have prepared. Vegetables are pretty, especially when fresh, and provide opportunities for children to learn about colour, seeds, growing vegetables and shapes and textures – all of which are fascinating to young children. Measuring, stirring, washing and arranging foods are skills that even a young child can practise with enjoyment and pride (see Table 16.5).
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TABLE 16.5 Food skills of preschool childrena Age one to two years, when large muscles develop: • Uses short-shanked spoon • Helps feed self • Lifts and drinks from cup • Helps scrub, tear, break or dip foods Age three years, when medium hand muscles develop: • Spears food with fork • Feeds self independently • Helps wrap, pour, mix, shake or spread foods • Helps crack nuts with supervision Age four years, when small finger muscles develop: • Uses all utensils and napkin • Helps roll, juice, mash or peel foods • Cracks egg shells Age five years, when fine coordination of fingers and hands develops: • Helps measure, grind, grate and cut (soft foods with dull knife) • Uses hand-mixer with supervision a
These ages are approximate. Healthy children develop at their own pace.
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Avoiding power struggles
Teaching children how to make healthy meals gives them valuable skills that will last a lifetime.
Problems over food often arise during the second or third year, when children begin asserting their independence. Many of these problems stem from the conflict between children’s developmental stages and capabilities and parents who, in attempting to do what they think is best for their children, try to control every aspect of eating. Such conflicts can disrupt children’s abilities to regulate their own food intakes or to determine their own likes and dislikes. For example, many people share the misconception that children must be persuaded or coerced to try new foods. In fact, the opposite is true. When children are forced to try new foods, even by way of rewards, they are less likely to try those foods again than are children who are left to decide for themselves. Similarly, when children are restricted from eating their favourite foods, they are more likely to want those foods.59 Wise parents provide healthful foods and allow their child to determine how much and even whether to eat. When introducing new foods, offer them one at a time and only in small amounts, such as one bite at first. The more often a food is presented to a young child, the more likely the child will accept that food. Offer the new food at the beginning of the meal, when the child is hungry, and allow the child to make the decision to accept or reject it. Never make an issue of food acceptance.
Choking prevention Parents must always be alert to the dangers of choking. A choking child is silent, so an adult should be present whenever a child is eating. Make sure the child sits when eating; choking is more likely when a child is running or falling. (See page 574 for a list of foods most likely to cause choking.)
Playing first Children may be more relaxed and attentive at mealtime if outdoor play or other fun activities are scheduled before, rather than immediately after, mealtime. Otherwise, children ‘hurry up and eat’ so that they can go and play.
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Snacking Parents may find that when their children snack, they aren’t hungry at mealtimes. Instead of teaching children not to snack, parents are wise to teach them how to snack. Provide snacks that are as nutritious as the foods served at mealtime. Snacks can even be mealtime foods served individually over time, instead of all at once on one plate. When providing snacks to children, think of the five food groups and offer such snacks as pieces of cheese, mandarin slices and egg salad on wholegrain biscuits (see Table 16.6). Snacks that are easy to prepare should be readily available to children, especially if they arrive home from school before their parents.
TABLE 16.6 Healthful snack ideas – think food groups, alone and in combination Selecting two or more foods from different food groups adds variety and nutrient balance to snacks. The combinations are endless, so be creative. Whenever possible, choose whole grains, low- or reduced-fat milk products, and lean meats. GRAINS Grain products are filling snacks, especially when combined with other foods: • Cereal with fruit and milk • Dry biscuits and cheese • Wholegrain toast with peanut butter • Popcorn with grated cheese VEGETABLES Cut-up, fresh, raw vegetables make great snacks alone or in combination with foods from other food groups: • Celery with peanut butter • Broccoli, cauliflower and carrot sticks with a flavoured cottage cheese dip FRUITS Fruits are delicious snacks and can be eaten alone – fresh, dried or juiced – or combined with other foods: • Apples and cheese • Bananas and peanut butter • Peaches with yoghurt • Raisins mixed with sunflower seeds or nuts MEATS AND LEGUMES Meats and legumes add protein to snacks: • Tuna on crackers • Peanut butter on wholegrain bread MILK AND MILK PRODUCTS Milk can be used as a beverage with any snack, and many other milk products, such as yoghurt and cheese, can be eaten alone or with other foods as listed above.
To ensure that children have healthy appetites and plenty of room for nutritious foods when they are hungry, parents and teachers must limit access to lollies, soft drinks and other non-nutritious snack foods. Limiting access includes limiting the amount of pocket money children have to buy such foods themselves. If these foods are permitted in large quantities, the only possible outcomes are nutrient deficiencies, obesity or both. The preference for sweets is innate; most children do not naturally select nutritious foods on the basis of taste. When children are allowed to create meals freely from a variety of foods, they typically select foods that provide a lot of sugar. When their parents are watching, or even when they only think their parents are watching, children improve their selections. Sweets need not be banned altogether. Children who are exceptionally active can enjoy high-kilojoule foods such as ice-cream or pudding from the milk group, or pancakes from the bread group. Sedentary children need to become more active so they can also enjoy some of these foods without unhealthy weight gain.
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Preventing dental caries Children frequently snack on sticky, sugary foods that stay on the teeth and provide an ideal environment for the growth of bacteria that cause dental caries. Teach children to brush and floss after meals, to brush or rinse after eating snacks, to avoid sticky foods and to select crisp or fibrous foods frequently.
Serving as role models In an effort to practise these many tips, parents may overlook perhaps the single most important influence on their children’s food habits – themselves. Parents who don’t eat carrots shouldn’t be surprised when their children refuse to eat carrots. Likewise, parents who comment negatively on the smell of brussels sprouts may not be able to persuade children to try them. Children learn much through imitation. It is not surprising that children prefer the foods other family members enjoy and dislike foods that are never offered to them.60 Parents, older siblings and other caregivers set an irresistible example by sitting with younger children, eating the same foods and having pleasant conversations during mealtimes. While serving and enjoying food, caregivers can promote both physical and emotional growth at every stage of a child’s life. They can help their children develop both a positive self-concept and a positive attitude towards food. With good beginnings, children will grow without the conflicts and confusions about food that can lead to nutrition and health problems.
REVIEW IT
Children’s appetites and nutrient needs reflect their stage of growth. Those who are chronically hungry and malnourished suffer growth retardation; when hunger is temporary and nutrient deficiencies are mild, the problems are usually more subtle – such as poor academic performance. Iron deficiency is widespread and has many physical and behavioural consequences. ‘Hyper’ behaviour is not caused by poor nutrition; misbehaviour may be due to lack of sleep, too little physical activity or too much television, among other things. Childhood obesity has become a major health problem. Adults need to provide children with nutrient-dense foods and teach them how to make healthful diet and activity choices.
Alamy Stock Photo/ Kjetil Kolbjørnsrud
16.3 Nutrition during adolescence
Nutritious snacks contribute valuable nutrients to an active teen’s diet.
Teenagers make many more choices for themselves than they did as children. They are not fed, they eat; they are not sent out to play, they choose to go. At the same time, social pressures thrust choices at them, such as whether to drink alcohol and whether to develop their bodies to meet extreme ideals of slimness or athletic prowess. Their interest in nutrition – both valid information and misinformation – derives from personal, immediate experiences. They are concerned with how diet can improve their lives now – they engage in fad dieting in order to fit into a new bathing suit, avoid greasy foods in an effort to clear acne or eat a pile of spaghetti to prepare for a big sporting event. In presenting information on the nutrition and health of adolescents, this section includes many topics of interest to teens.
Growth and development With the onset of adolescence, the steady growth of childhood speeds up abruptly and dramatically, and the growth patterns of female and male become distinct. Hormones direct the intensity of the adolescent growth spurt, profoundly affecting every organ of the body, including the brain. After two to three years of intense growth and a few more at a slower pace, physically mature adults emerge.
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In general, the adolescent growth spurt begins at age 10 or 11 for females and at 12 or 13 for males. It lasts about two and a half years. Before puberty, male and female body compositions differ only slightly, but during the adolescent spurt, differences between the genders become apparent in the skeletal system, lean body mass and fat stores. In females, fat assumes a larger percentage of the total body weight, and in males, the lean body mass – principally muscle and bone – increases much more than in females (review Figure 8.6 on page 267). On average, males grow 20 centimetres taller, and females 15 centimetres taller. Males gain approximately 20 kilograms, and females about 16 kilograms.
Energy and nutrient needs Absolute energy and nutrient needs are greater during adolescence than at any other time of life, except pregnancy and lactation. In general, nutrient needs rise throughout childhood, peak in adolescence and then level off or even diminish as the teenager becomes an adult.
Energy intake and activity The energy needs of adolescents vary greatly, depending on their current rate of growth, gender, body composition and physical activity. Boys’ energy needs may be especially high; they typically grow faster than girls and, as mentioned, develop a greater proportion of lean body mass. An exceptionally active boy of 15 may need 14 000 kilojoules or more a day just to maintain his weight. Girls start growing earlier than boys and attain shorter heights and lower weights, so their energy needs peak sooner and decline earlier than those of their male peers. A sedentary girl of 15 whose growth is nearly at a standstill may need fewer than 8200 kilojoules a day if she is to avoid excessive weight gain. However, in the current climate of child and adolescent overweight, both adolescent boys and girls need to pay special attention to being physically active and selecting foods of high nutrient density so as to meet their nutrient needs without exceeding their energy needs. The insidious problem of obesity becomes ever more apparent in adolescence and often continues into adulthood. Without intervention, overweight adolescents face numerous physical and socioeconomic consequences for years to come. The consequences of obesity are so dramatic and our society’s attitude towards obese people is so negative that even teens of normal or below-normal weight may perceive a need to lose weight. When taken to extremes, restrictive diets bring dramatic physical consequences of their own, as Highlight 8 explains.
Vitamins The RDI (or AI) for most vitamins increases during the adolescent years (see the table on the inside cover). Several of the vitamin recommendations for adolescents are similar to those for adults, including the recommendation for vitamin D. During puberty, both the activation of vitamin D and the absorption of calcium are enhanced, thus supporting the intense skeletal growth of the adolescent years without additional vitamin D.
Iron The need for iron increases during adolescence for both females and males, but for different reasons. Iron needs increase for females as they start to menstruate and for males as their lean body mass develops. Hence, the RDI increases at age 14 for both males and females. For females, the RDI remains high into late adulthood. For males, the RDI returns to preadolescent values in early adulthood. Iron intakes often fail to keep pace with increasing needs, especially for females, who typically consume less iron-rich food such as meat and fewer total kilojoules than males. Not surprisingly, iron deficiency is prevalent among adolescent girls. Iron-deficient children and teens score lower on standardised tests than those who are not iron-deficient.
Iron RDI for males: • 9−13 years: 8 mg/day • 14−18 years: 11 mg/day Iron RDI for females: • 9−13 years: 8 mg/day • 14−18 years: 15 mg/day
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Monkey Business Images/Shutterstock.com
Calcium
Because their lunches rarely include fruits, vegetables or milk, many teens fail to get all the vitamins and minerals they need each day.
Adolescence is a crucial time for bone development, and the requirement for calcium reaches its peak during these years. Unfortunately, between 82 and 89 per cent of girls aged 12 to 16 have calcium intakes below recommendations.61 Low calcium intakes during times of active growth, especially if paired with physical inactivity, can compromise the development of peak bone mass. In fact, inactivity may have a greater detrimental impact on bone mass than poor calcium intake during the pubertal years. Increasing milk products in the diet to meet calcium recommendations greatly increases bone density. Once again, however, teenage girls are most vulnerable, for their milk – and therefore their calcium – intakes begin to decline at the time when their calcium needs are greatest. Furthermore, women have much greater bone losses than men in later life.
Food choices and healthy habits Teenagers like the freedom to come and go as they choose. They eat what they want if it is convenient and if they have the time. With a multitude of after-school, social and job activities, they almost inevitably fall into irregular eating habits. At any given time on any given day, a teenager may be skipping a meal, eating a snack, preparing a meal or consuming food prepared by a parent or restaurant. Adolescents who frequently eat meals with their families, however, eat more fruits, vegetables, grains and calcium-rich foods, and drink fewer soft drinks, than those who seldom eat with their families.62 Many adolescents also begin to skip breakfast on a regular basis, missing out on important nutrients that are not made up at later meals during the day. Teenagers who eat breakfast are more likely to meet their nutrient intake recommendations. Ideally, in light of adolescents’ busy schedules and desire for freedom, the adult continues to play the role of gatekeeper, controlling the type and availability of food in the teenager’s home environment. Teenagers should find plenty of nutritious, easy-to-grab foods in the refrigerator (meats for sandwiches; low-fat cheeses; fresh, raw vegetables and fruits; fruit juices; and milk) and more in the cupboards (wholegrain breads, nut pastes, nuts, popcorn and cereal).
PUTTING COMMON SENSE TO THE TEST
The calcium requirement for an adolescent is reduced after the age of 14. FALSE
Snacks Snacks typically provide at least a quarter of the average teenager’s daily food energy intake. Most often, favourite snacks are too high in saturated fat and sodium and too low in fibre to support good future health. Table 16.6 on page 587 shows how to combine foods from different food groups to create healthy snacks.
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Eat a wide variety of nutritious foods – milk, yoghurt, cheese and/or their alternatives, mostly reduced-fat.
Beverages
Caffeinecontaining soft drinks typically deliver between 30 and 55 mg of caffeine per can. For perspective, a pharmacologically active dose of caffeine is defined as 200 mg.
Most frequently, adolescents drink soft drinks instead of fruit juice or milk. About the only time they select fruit juices is at breakfast. When teens drink milk, they are more likely to consume it with a meal (especially breakfast) than as a snack. Soft drinks, when chosen as the primary beverage, may affect bone density because they displace milk from the diet. Because of their greater food intakes, boys are more likely than girls to drink enough milk to meet their calcium needs. Over the past three decades, teens (especially girls) have been drinking more soft drinks and less milk.63 Adolescents who drink soft drinks regularly have a higher energy intake and a lower calcium intake than those who do not; they are also more likely to be overweight.64 Soft drinks containing caffeine present a different problem if caffeine intake becomes excessive. Caffeine seems to be relatively harmless when used in moderate doses (the equivalent of fewer than three cans of cola beverages a day). In greater amounts, however, it can cause the symptoms associated with anxiety, such as sweating, tenseness and inability to concentrate.
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
Eating away from home Adolescents eat about one-third of their meals away from home, and their nutritional welfare is enhanced or hindered by the choices they make. A lunch consisting of a hamburger, a chocolate shake and chips supplies substantial quantities of many nutrients at a cost of around 3500 kilojoules, an energy intake some adolescents can’t afford. When they eat this sort of lunch, teens can adjust their breakfast and dinner choices to include fruits and vegetables for vitamin A, vitamin C, folate and fibre, and lean meats and legumes for iron and zinc. Fortunately, many fast-food restaurants are offering more nutritious choices than the standard hamburger meal.
Peer influence Many of the food and health choices adolescents make reflect the opinions and actions of their peers. When others perceive milk as ‘babyish’, a teen may choose soft drinks instead; when others skip lunch and hang out in the park, a teen may join in for the camaraderie, regardless of hunger. Adults need to remember that adolescents have the right to make their own decisions – even if they are contrary to the adults’ views. Gatekeepers can set up the home environment so that nutritious foods are available and can stand by with reliable nutrition information and advice, but the rest is up to the adolescent. Ultimately, they make the choices. (Highlight 8 examines the influence of social pressures on the development of eating disorders.)
REVIEW IT
Nutrient needs rise dramatically as children enter the rapid growth phase of adolescence. Teenagers’ busy lifestyles add to the challenge of meeting their nutrient needs, especially for iron and calcium.
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 An infant’s weight doubles every year of life up to five years of age. FALSE
4 Infants require additional iron at around six months – more than body stores or breastfeeding alone can provide. TRUE
An infant’s growth during the first year of life is substantial – so much so that weight doubles. After this time, however, the rate of growth slows each year until the onset of puberty.
2 All infants require additional water irrespective of whether they are breast-fed or formula-fed. FALSE
Occasionally, in very hot climates, infants may require additional water. However, for the vast majority of infants, whether breast-fed or formula-fed, additional water is not needed.
Initial iron requirements are met through breast or formula feeding, but at around six months of age, iron requirements increase and body stores and breast-feeding or formula-feeding does not provide enough. The introduction of an iron-fortified cereal is generally considered appropriate.
5 Hyperactive children respond well to dietary modification. FALSE
There have been many diets purporting to ‘cure’ the hyperactive child, but none has proven to be effective.
3 Low-fat milks may be introduced to children from around two years of age. TRUE
6 The calcium requirement for an adolescent is reduced after the age of 14 years. FALSE
Prior to the age of two years, the additional energy from full-fat milk products assist with adequate growth. From the age of two years, reduced fat milk drinks can be introduced, as dietary variety allows appropriate energy for growth and activity to be achieved.
The RDI for calcium for adolescents peaks at age 12 and is then maintained at the same level through to 18 years of age (1300 mg for boys and girls).
NUTRITION PORTFOLIO Encouraging children to eat nutritious foods today helps them learn how to make healthy food choices tomorrow. • If there are children in your life, think about the food they eat and consider whether they receive enough food for healthy growth, but not so much as to lead to overweight or obesity.
• •
Describe the advantages of physical activity to children’s health and wellbeing. Plan a day’s menu for a child four to eight years of age, making sure to include foods that provide enough calcium and iron.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1
The approximate energy requirement for infants is: a b c d
2
380–410kJ/kg/day 400–430kJ/kg/day 420–450kJ/kg/day 440–470kJ/kg/day
5
Dehydration can develop quickly in infants because: a b c d
3
4
much of their body water is extracellular they lose a lot of water through urination and tears only a small percentage of their body weight is water they drink lots of breast milk or formula, but little water
Introducing solid foods to an infant should begin at around: a b c d
6 weeks 3 months 6 months 8 months
6
7
Approximately how many feeds each day is normal in the first few weeks of life? a Four feeds per day b Six feeds per day c Eight feeds per day d 10 feeds per day A true food allergy always: a elicits an immune response b causes an immediate reaction c creates an aversion to the offending food d involves symptoms such as headaches or hives Which of the following strategies is effective? a Play later, eat first b Provide large portions c Encourage children to help prepare meals d Use dessert as a reward for eating vegetables A well-nourished child’s eyes will: a adjust slowly to the dark b appear red and with spots c appear bright and adjust well to light d have pale membranes
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
8
To help teenagers consume a balanced diet, parents can:
4
a b c
Which foods are inappropriate for infants? Why are they inappropriate. (Section 16.1)
5
What are some common nutrition problems in children? What strategies can help prevent these problems? (Section 16.2)
6
Describe a true food allergy. What is the difference between a food allergy and a food intolerance? Which foods most often cause allergic reactions? Do these foods differ in different cultures? How do food allergies influence nutrition status? (Section 16.2)
7
Is there a suggested manner in which foods should be introduced when there is a family history of allergy? (Section 16.1)
8
What are the current rates of overweight and obesity in Australian and New Zealand children? What are some strategies for prevention and treatment? (Section 16.2)
9
Describe the changes in nutrient needs from childhood to adolescence. Do these needs increase or decrease when considering body weight? Why is an adolescent girl more likely to develop an iron deficiency than an adolescent boy? (Sections 16.1 and 16.4)
d 9
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monitor the teens’ food intake give up – parents can’t influence teenagers keep the pantry and refrigerator well stocked with healthy options forbid snacking and insist on regular, wellbalanced meals
During adolescence, energy and nutrient needs: a b c d
reach a peak fall dramatically rise, but do not peak until adulthood fluctuate so much that generalisations can’t be made
10 The nutrients most likely to fall short in the adolescent diet are: a b c d
sodium and fat folate and zinc iron and calcium protein and vitamin A
Review questions 1
Describe some of the nutrient and immunological qualities of breast milk. (Section 16.1)
2
When is the use of formula feeding appropriate? What criteria would you use in selecting an infant formula? What precautions should be adopted when preparing infant formula? (Section 16.1)
3
Why are solid foods not recommended for an infant prior to around six months of age? What are the common types of food introduced first? (Section 16.1)
10 What is a typical eating pattern for an adolescent? How do adolescents’ eating habits influence their nutrient intakes? What strategies can be used to assist adolescents to eat a well-balanced diet? (Section 16.4)
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Learn how to care for infants, children and adolescents: http://raisingchildren.net.au/ • Download growth charts and learn about their most recent revision: http://www.who.int/childgrowth/en/ and http://www.cdc.gov/growthcharts • Get information on the Australian Dietary Guidelines: http://www.nhmrc.gov.au
• • •
• •
•
Get tips for feeding children from the Dietitians Association of Australia: http://www.daa.asn.au Get tips for keeping children healthy from the Royal Children’s Hospital: http://www.rch.org.au Visit the Victorian Department of Education and Early Childhood Development: http://www.education.vic. gov.au Learn how UNICEF works to protect children: http://www.unicef.org Learn more about allergies from the Australasian Society of Clinical Immunology and Allergy: http://www.allergy.org.au Learn more about attention deficit hyperactivity disorders: http://www.adhd.com.au
SEARCH ME! NUTRITION Keyword: childhood obesity Read the article Evidence-guided approaches to addressing child obesity: what approaches can dietitians use in their everyday practice? What are the
consequences of childhood obesity? What types of interventions may be effective in preventing and treating this condition?
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HIGHLIGHT
16
16.4 CHILDHOOD OBESITY AND THE EARLY DEVELOPMENT OF CHRONIC DISEASES
Alamy Stock Photo/D. Hurst
When people think about the health problems of children and adolescents, they typically think of ear infections, colds and acne – not heart disease, diabetes or hypertension. Today, however, Australian and New Zealand children are being diagnosed with obesity and other serious ‘adult diseases’, such as type 2 diabetes, that accompany overweight. Currently, prevalence rates for type 2 diabetes in Australian and New Zealand children can’t reliably be reported but the number of diagnoses each year is increasing.1 When type 2 diabetes develops before the age of 20 years, the incidence of diabetic kidney disease and death in middle age increases dramatically, largely because of the long duration of the disease.2 Australian children are not alone – rapidly rising rates of obesity threaten the health of an alarming number of children around the globe. Without immediate intervention, millions of children are destined to develop type 2 diabetes and hypertension in childhood, followed by cardiovascular disease (CVD) in early adulthood. This highlight focuses on efforts to prevent childhood obesity and the development of heart disease and type 2 diabetes, but the benefits extend to other obesity-related diseases as well. The years of childhood (ages two to 18) are emphasised here, because the earlier in life that health-promoting habits become established, the better
Unhealthy eating patterns in early life may be the precursor to later chronic disease.
they will stick. Chapter 18 fills in the rest of the story of nutrition’s role in reducing chronic disease risk. Invariably, questions arise as to what extent genetics is involved in disease development. For heart disease and type 2 diabetes, genetics does not appear to play a determining role; that is, a person is not simply destined at birth to develop these diseases. Instead, genetics appears to play a permissive role – the potential is inherited and will develop if given a push by poor health choices such as excessive weight gain, poor diet, sedentary lifestyle and cigarette smoking. Many experts agree that preventing or treating obesity in childhood will reduce the rate of chronic diseases in adulthood. Without intervention, most overweight children become overweight adolescents who become overweight adults, and being overweight exacerbates every chronic disease that adults face.
Early development of type 2 diabetes In recent years, type 2 diabetes, a chronic disease closely linked with obesity, has been on the rise among children and adolescents as the prevalence of obesity in Australia and New Zealand has increased.3 Obesity is the most important risk factor for type 2 diabetes – most of the children diagnosed with it are obese. Most are diagnosed during puberty, but as children become more obese and less active, the trend is shifting to younger children. Type 2 diabetes is most likely to occur in those who are obese and sedentary and have a family history of diabetes. In type 2 diabetes, the cells become insulin-resistant – that is, the cells become less sensitive to insulin, reducing the amount of glucose entering the cells from the blood. The combination of obesity and insulin resistance produces a cluster of symptoms, including high blood cholesterol and high blood pressure, which, in turn, promotes the development of atherosclerosis and the early development of CVD.4 Other common problems evident by early adulthood include kidney disease, blindness and miscarriages. The complications of diabetes, especially when encountered at a young age, can shorten life expectancy. Prevention and treatment of type 2 diabetes depend on weight management, which can be particularly difficult in
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
a youngster’s world of food advertising, video games and pocket money for snack foods. The activity and dietary suggestions to help defend against heart disease later in this highlight apply to type 2 diabetes as well.
Early development of heart disease Most people consider heart disease to be an adult disease because its incidence rises with advancing age, and symptoms rarely appear before age 30. The disease process actually begins much earlier.
Atherosclerosis Most cardiovascular disease involves atherosclerosis. Atherosclerosis develops when regions of an artery’s walls become progressively thickened with plaque – an accumulation of fatty deposits, smooth muscle cells and fibrous connective tissue. If it progresses, atherosclerosis may eventually block the flow of blood to the heart and cause a heart attack or cut off blood flow to the brain and cause a stroke. Infants are born with healthy, smooth, clear arteries, but within the first decade of life, fatty streaks may begin to appear
(see Figure H16.1). During adolescence, these fatty streaks may begin to accumulate fibrous connective tissue. By early adulthood, the fibrous plaques may begin to calcify and become raised lesions, especially in boys and young men. As the lesions grow more numerous and enlarge, the heart disease rate begins to rise, most dramatically at about age 45 in men and 55 in women. From this point on, arterial damage and blockage progress rapidly, and heart attacks and strokes threaten life. In short, the consequences of atherosclerosis, which become apparent only in adulthood, have their beginnings in the first decades of life.5 Atherosclerosis is not inevitable; people can grow old with relatively clear arteries. Early lesions may either progress or regress, depending on several factors, many of which reflect lifestyle behaviours. Smoking, for example, is strongly associated with the prevalence of fatty streaks and raised lesions, even in young adults.
Blood cholesterol As blood cholesterol rises, atherosclerosis worsens. Cholesterol values at birth are similar in all populations; differences emerge in early childhood. In general, blood
FIGURE H16.1 The formation of plaques in atherosclerosis
Courtesy of Zeneca Pharmaceutical Division, Cheshire, England
1 The coronary arteries deliver oxygen and nutrients to the heart muscle.
Plaque 1 2
2 Plaques can begin to form in a person as young as 15 years.
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A healthy artery provides an open passage for the flow of blood.
Courtesy of Zeneca Pharmaceutical Division, Cheshire, England
3 3 When these arteries become blocked by plaque, the part of the muscle that they feed will die.
Plaques form along the artery’s inner wall, reducing blood flow. Clots can form, aggravating the problem.
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cholesterol tends to rise as dietary saturated fat intakes increase. Blood cholesterol also correlates with childhood obesity, especially abdominal obesity.6 LDL cholesterol rises with obesity, and HDL declines. These relationships are apparent throughout childhood, and their magnitude increases with age. Children who are both overweight and have high blood cholesterol are likely to have parents who develop heart disease early. Early – but not advanced – atherosclerotic lesions are reversible, making education a high priority. Both those with family histories of heart disease and those with multiple risk factors need intervention. Children with the highest risks of developing heart disease are sedentary and obese, with high blood pressure and high blood cholesterol. In contrast, children with the lowest risks of heart disease are physically active and of normal weight, with low blood pressure and favourable lipid profiles. Routine paediatric care should identify these known risk factors and provide intervention when needed.
Blood pressure High blood pressure may signal an underlying disease or the early onset of hypertension. Hypertension accelerates the development of atherosclerosis. Like atherosclerosis and high blood cholesterol, hypertension may develop in the first decades of life, especially among obese children, and worsen with time. Children can control their hypertension by participating in regular aerobic activity and by losing weight or maintaining their weight as they grow taller. New evidence suggests that restricting sodium in children’s and adolescents’ diets does lower blood pressure.7
Physical activity Research has also confirmed an association between blood lipids and physical activity in children, similar to that seen in adults. Physically active children have a better lipid profile and lower blood pressure than physically inactive children, and these positive findings often persist into adulthood. Just as blood cholesterol and obesity track over the years, so does a youngster’s level of physical activity. Those who are inactive now are likely to still be inactive years later. Similarly, those who are physically active now tend to remain so. Compared with inactive teens, those who are physically active weigh less, smoke less, eat a diet lower in saturated fats and have better blood lipid profiles. Both obesity and blood cholesterol correlate with
the inactive pastime of watching television. The message is clear: physical activity offers numerous health benefits, and children who are active today are most likely to be active for years to come.
Dietary recommendations for children Regardless of family history, experts agree that all children over the age of two years should eat a variety of foods and maintain desirable weight. Children (two to 18 years of age) should receive around 30 per cent of total energy from fat, with less than 10 per cent from saturated fat.8 Recommendations limiting fat are not intended for infants or children under two years old. Infants and toddlers need a higher percentage of fat to support their rapid growth.
Moderation, not deprivation Healthy children over the age of two years can begin the transition to eating according to recommendations by eating fewer foods high in saturated fat and selecting more fruits and vegetables. Healthy meals can occasionally include moderate amounts of a child’s favourite foods, even if they are high in saturated fat, such as chips and ice-cream. A steady diet of offerings from some ‘children’s menus’ in restaurants, such as chicken nuggets, hot dogs and chips, easily exceeds a prudent intake of saturated fat, trans fat and kilojoules, however, and invites both nutrient shortages and weight gains. Fortunately, most restaurants chains are changing children’s menus to include healthier options – additions welcomed by busy parents who often dine out or purchase takeaway foods. Other fatty foods, such as nuts, vegetable oils and some varieties of fish like tinned tuna and salmon, are important for their essential fatty acids. Low-fat milk and milk products also deserve special attention in a child’s diet for the needed calcium and other nutrients they supply.9 Parents and caregivers play a key role in helping children establish healthy eating habits. Balanced meals need to provide lean meat, poultry, fish and legumes; fruits and vegetables; whole grains; and low-fat milk products. Such meals can provide enough energy and nutrients to support growth and maintain blood cholesterol within a healthy range. Paediatricians warn parents to avoid extremes. Although intentions may be good, excessive food restriction may create nutrient deficiencies and impair growth. Furthermore, parental control over eating may instigate battles and foster attitudes about foods that can lead to inappropriate eating behaviours.
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HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A How does childhood obesity influence a person’s health and a country’s health care system?
Is severe childhood obesity (for example, a child weighing over twice their adult healthy weight) a lifethreatening form of abuse that justifies removing a child from his or her parents?
B Child abuse is defined as either action or neglect that damages a child or puts the child at risk of injury.
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Download the current growth charts and learn about their most recent revision: http://www.who.int/ childgrowth/en/ and http://www.cdc.gov/growth charts
• • • •
Get information on the Australian Dietary Guidelines: http://www.nhmrc.gov.au Get tips for feeding children from the Dietitians Association of Australia: http://www.daa.asn.au Get tips for keeping children healthy from the Royal Children’s Hospital: http://www.rch.org.au Find information on diabetes and heart disease at Diabetes Australia and Baker IDI: http://www. diabetesaustralia.com.au and http://www.baker. edu.au
REFERENCES CHAPTER 1
2
3
4
5
6
7
Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). Formula feeding of term infants, in Pediatric Nutrition, R. E. Kleinman and F. R. Greer (eds), 7th edn, (Elk Grove Village, IL: American Academy of Pediatrics, 2014): 61–81. Royal Australasian College of Physicians, Paediatrics & Child Health Division, Breastfeeding, Sydney: RACGP (2007), available at http:// www.racp.edu.au/docs/default-source/advocacy-library/pa-polbreastfeeding.pdf National Health and Medical Research Council, Australian Dietary Guidelines, Canberra: Commonwealth of Australia (2013), available at https://www.nhmrc.gov.au/guidelines-publications/n55 American Academy of Pediatrics, Policy statement: Breastfeeding and the use of human milk, Pediatrics 129 (2012): e827–e841, available at http://pediatrics.aappublications.org/content/129/3/e827.full K. Davis-Bruno and M. S. Tassinari, Essential fatty acid supplementation of DHA and ARA and effects on neurodevelopment across animal species: a review of the literature. Birth Defects Research. Part B, Devopmental and Reproductive Toxicology 92 (2011): 240–250; N. Auestad and co-authors, Visual, cognitive, and language assessments at 39 months: A follow-up study of children fed formulas containing long-chain polyunsaturated fatty acids to 1 year of age, Pediatrics 112 (2003): e177–e183. C. Campoy and co-authors, Omega 3 fatty acids on child growth, visual acuity and neurodevelopment, British Journal of Nutrition 107 (2012): S85–S106.
8
9
10
11 12
13
14 15
P. Willatts and co-authors, Effects of long-chain PUFA supplementation in infant formula on cognitive function in later childhood, American Journal of Clinical Nutrition 98 (2013): 536S–542S. E. E. Birch and co-authors, The DIAMOND (DHA Intake and Measurement of Neural Development) Study: A double-masked, randomized controlled clinical trial of the maturation of infant visual acuity as a function the dietary level of docosahexaenoic acid, American Journal of Clinical Nutrition 91 (2010): 848–59. P. Willatts and co-authors, Effects of long-chain PUFA supplementation in infant formula on cognitive function in later childhood, American Journal of Clinical Nutrition 98 (2013): 536S–542S. K. Thomson, D. Tey and M. Marke (eds.), Paediatric handbook, 9th edn, Melbourne: Wiley-Blackwell (2015). E. Theodoratou and co-authors, Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of observational studies and randomised trials, British Medical Journal, (2014); 348:g2035. C.F. Manthey and co-authors, Human milk oligosaccharides protect against enteropathogenic Escherichia coli attachment in vitro and EPEC colonization in suckling mice, Journal of Pediatric Gastroenterology and Nutrition, 58 (2014) 165–8. B. Lonnerdal, Bioactive proteins in breast milk, Journal of Paediatrics and Child Health (Supplement S1) 49 (2013): 1–7. D. S. Newburg, Neonatal protection by an innate immune system of human milk consisting of oligosaccharides and glycans. Journal of Animal Science 87(13 Suppl.) (2009): 26–34.
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16 B. K. Brew and co-authors, Systematic review and meta-analysis investigating breast feeding and childhood wheezing illness. Paediatric and Perinatal Epidemiology 25 (2011): 507–18. 17 J. Lodge and coauthors, Breastfeeding and asthma and allergies: A systematic review and meta-analysis, Acta Paediatrica 104 (2015): 38–53. 18 T. W. Guilbert and A. L. Wright, Does breastfeeding impact lung function and asthma risk? American Journal of Respiratory and Critical Care Medicine 185 (2012): 801–2. 19 S. Pirilä and coauthors, Breast-fed infants and their later cardiovascular health: A prospective study from birth to age 32 years, British Journal of Nutrition 111 (2014): 1069–76. 20 W. Liang and coauthors, Breastfeeding reduces childhood obesity risks, Childhood Obesity (2017) doi:10.1089/chi.2016.0210 21 J. A. Scott, S. Y. Ng and L Cobiac, The relationship between breastfeeding and weight status in a national sample of Australian children and adolescents. BMC Public Health 12 (2012): 107. 22 N. Stettler, Infant feeding practices and subsequent development of adipose tissue. Nestle Nutrition Workshop Series Pediatric Programme 68 (2011): 215–221; discussion 222–5. 23 S. Cai and coauthors, Infant feeding effects on early neurocognitive development in Asian children, American Journal of Clinical Nutrition 101 (2015): 326–36. 24 Formula feeding of term infants, in Pediatric Nutrition, 7th edn, ed. R. E. Kleinman and F. R. Greer, Elk Grove Village, IL: American Academy of Pediatrics (2014): 61–81. 25 National Health and Medical Research Council, Infant feeding guidelines, Canberra: Commonwealth of Australia (2012). 26 National Health and Medical Research Council, Infant feeding guidelines, Canberra: Commonwealth of Australia (2012). 27 E. E. Ziegler and co-authors, Dry cereals fortified with electrolytic iron or ferrous fumarate are equally effective in breast-fed infants, Journal of Nutrition 141 (2011): 243–8. 28 Formula feeding of term infants, in Pediatric Nutrition, 7th edn, ed. R. E. Kleinman and F. R. Greer, Elk Grove Village, IL: American Academy of Pediatrics (2014): 61–81. 29 Formula feeding of term infants, in Pediatric Nutrition, 7th edn, ed. R. E. Kleinman and F. R. Greer, Elk Grove Village, IL: American Academy of Pediatrics (2014): 61–81. 30 Policy Statement From the American Academy of Pediatrics Prevention of choking among children, Pediatrics 125 (2010): 601–7. 31 Nutritional aspects of vegetarian diets, in Pediatric Nutrition, 7th ed., ed. R. E. Kleinman (Elk Grove Village, Ill.: American Academy of Pediatrics, 2014), pp. 241–64. 32 D. M. Hoelscher and co-authors, Position of the Academy of Nutrition and Dietetics: Interventions for the prevention and treatment of pediatric overweight and obesity, Journal of the Academy of Nutrition and Dietetics 113 (2013): 1375–94. 33 Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). 34 M. Van Winckel and co-authors, Clinical practice: vegetarian infant and child nutrition, European Journal of Pediatrics 170 (2011): 1489–94. 35 Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). 36 C. Wong, Iron deficiency anaemia, Paediatrics and Child Health 27 (11) (2017): 527–9.
37 Feeding the child, in Pediatric Nutrition, 7th ed., ed. R. E. Kleinman and F. R. Greer (Elk Grove Village, Ill.: American Academy of Pediatrics, 2014): 143–73. 38 N. Overby and co-authors, Diet and behavioral problems at school in Norwegian adolescents, Food & Nutrition Research 56 (2012). 39 V. Edefonti and coauthors, The effect of breakfast composition and energy contribution on cognitive and academic performance: A systematic review, American Journal of Clinical Nutrition 100 (2014): 626–56. 40 P. M. Gupta and coauthors, Iron, anemia, and iron deficiency anemia among young children in the United States, Nutrients, 2016, oi:10.3390/ nu8060330; 41 P. M. Gupta and coauthors, Iron, anemia, and iron deficiency anemia among young children in the United States, Nutrients, 2016, oi:10.3390/ nu8060330 42 J. G. Millichap and M. M. Yee, The diet factor in attention-deficit/ hyperactivity disorder, Pediatrics 129 (2012): 330–7. 43 P. Pedersen, Nutritional interventions to reduce symptoms in children and adults with attention deficit hyperactivity disorder: a scoping review protocol, JBI Database System Rev Implement Rep 15(9) (2017): 2265–9. 44 Australasian Society of Clinical Immunology and Allergy, Food allergy (2018). 45 Australian Bureau of Statistics (ABS). Australian Health Survey: updated results, 2011–2012. ABS cat. no. 4364.0.55.003, (2013) Canberra: ABS; Department of Health and Ageing, 2007 Australian national children’s nutrition and physical activity survey, Canberra: Commonwealth of Australia (2008). 46 T. Olds and co-authors, Evidence that the prevalence of childhood overweight is plateauing: Data from nine countries. International Journal of Pediatric Obesity, 2011; 6: 342–60; Ministry of Health, A Portrait of Health. Key Results of the 2006/07 New Zealand Health Survey, Wellington: Ministry of Health (2008). 47 K. Sonneville and co-authors, Juice and water intake in infancy and later beverage intake and adiposity: could juice be a gateway drink? Obesity 23(1) (2015): 170–6. 48 A Shefferly and coauthors, Longitudinal evaluation of 100% fruit juice consumption on BMI status in 2–5-year-old children, Pediatric Obesity 11 (2015): 221–7. 49 B Auerback and coauthors, Fruit Juice and Change in BMI: A Metaanalysis, Pediatrics 2017; 139(4):e20162454 50 J. Reilly and co-authors, Long-term impact of overweight and obesity in childhood and adolescence on morbidity and premature mortality in adulthood: systematic review. International Journal of Obesity (2011) 35, 891–8. 51 L. D. Stephens and co-authors, Longitudinal predictors of frequent vegetable and fruit consumption among socio-economically disadvantaged Australian adolescents, Appetite 78 (2014): 165–71. 52 A. C. Lindsay and co-authors, Exploring How the Home Environment Influences Eating and Physical Activity Habits of Low-Income, Latino Children of Predominantly Immigrant Families: A Qualitative Study, International Journal of Environmental and Research and Public Health 15(5) (2018): E978. 53 L. Hall and co-authors, Children’s intake of fruit and selected energydense nutrient-poor foods is associated with fathers’ intake, Journal of the American Dietetic Association 111 (2011): 1039–44. 54 A. Walsh and co-authors, Dietary associations of fathers and their children between the ages of 20 months and 5 years, Public Health Nutrition 19(11) (2016): 2033–9. 55 Centers for Disease Control and Prevention, Overweight and obesity: a growing problem, http://www.cdc.gov/obesity/childhood/problem. html, updated 19 June 2015.
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Chapter 16: Life cycle nutrition: infancy, childhood and adolescence
56 M. H. Proctor and co-authors, Television viewing and change in body fat from preschool to early adolescence: The Framingham Children’s Study, International Journal of Obesity and Related Metabolic Disorders 27 (2003): 827–33. 57 A.J. Cameron and co-authors, Television in the bedroom and increased body weight: potential explanations for their relationship among European schoolchildren, Pediatric Obesity 8(2) (2013): 130–41. 58 A. J. Cameron and co-authors, Socioeconomic variation in diet and activity-related behaviours of Australian children and adolescents aged 2–16 years. Pediatric Obesity 7 (2012): 329–42. 59 K. W. Bauer, J. M. Berge, and D. Neumark-Sztainer, The importance of families to adolescents’ physical activity and dietary intake, Adolescent Medicine: State of the Art Reviews 22 (2011): 601–13. 60 Y. Yang and co-authors, Do children and their parents eat a similar diet? Resemblance in child and parental dietary intake: systematic
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review and meta-analysis, Journal of Epidemiology and Community Health 65 (2011): 177–89. Department of Health and Ageing, 2007 Australian National Children’s Nutrition and Physical Activity Survey, Canberra: Commonwealth of Australia (2008). J. M. Berge and co-authors, Structural and interpersonal characteristics of family meals: Associations with adolescent body mass index and dietary patterns, Journal of the Academy of Nutrition and Dietetics 113 (2013): 816–22. C. E. Rissel and co-authors, Soft drink consumption and obesity in NSW school students. Medical Journal of Australia 196 (2012): 171–2. M. Verloigne and co-authors, Family- and school-based correlates of energy balance-related behaviours in 10–12-year-old children: a systematic review within the ENERGY (EuropeaN Energy balance Research to prevent excessive weight Gain among Youth) project. Public Health Nutrition 24 (2012): 1–16.
HIGHLIGHT 1
2 3
4
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Australian Institute of Health and Welfare, Type 2 diabetes in Australia’s children and young people: a working paper, Diabetes Series no. 21. Cat. no. CVD 64, (2014) Canberra: AIHW. D’Adamo and co-authors, Type 2 Diabetes in youth: epidemiology and pathophysiology, Diabetes Care, (2011) 34, S161–5. Australian Institute of Health and Welfare, Type 2 diabetes in Australia’s children and young people: a working paper, Diabetes Series no. 21. Cat. no. CVD 64, (2014) Canberra: AIHW. S. Li and co-authors, Childhood cardiovascular risk factors and carotid vascular changes in adulthood: The Bogalusa Heart Study, Journal of the American Medical Association 290 (2003): 2271–6. R. Kelishadi and co-authors, Changes in serum lipid profile of obese or overweight children and adolescents following a lifestyle modification course. ARYA Atherosclerosis 8 (2012): 143–8.
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D. Freedman and co-authors, Cardiovascular risk factors and excess adiposity among overweight children and adolescents: the Bogalusa Heart Study. Journal of Pediatrics, (2007): 150:12–17.e2. C. Grimes and co-authors, Dietary intake and sources of sodium and potassium among Australian schoolchildren: results from the cross-sectional Salt and Other Nutrients in Children (SONIC) study, British Medical Journal Open 22 (2017) 7(10): e016639. doi:10.1136/ bmjopen-2017-016639 Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient reference values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). N. Golden, S. Abrams and the Committee on Nutrition, American Academy of Pediatrics, Optimizing bone health in children, and adolescents, Pediatrics 134 (2014): 1229–43.
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17
LIFE CYCLE NUTRITION: ADULTHOOD AND THE LATER YEARS Nutrition in your life
Take a moment to envision yourself 40 or even 60 years from now. Are you physically fit and healthy? Can you see yourself walking on the beach with friends or playing with grandchildren? Are you able to climb stairs and carry your own shopping? Importantly, are you enjoying life? If you’re lucky, you will grow old with good health, but much of that depends on your actions today – and every day from now until then. Making nutritious foods and physical activities a priority in your life can help bring rewards of continued health and enjoyment in later life. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F The majority of people’s life expectancy is determined by individual health-related behaviours. T F Older people are vulnerable to falls and immobility due to declining muscle mass and
muscle strength.
T F Older people with a BMI up to 27 are more vulnerable to obesity-related diseases. T F People over the age of 70 who are institutionalised should receive a vitamin D
supplement because of lack of sunshine.
T F Choline supplements are known to assist with memory and slow the progression of
Alzheimer’s disease.
LEARNING OBJECTIVES 17.1 Describe the role nutrition plays in longevity. 17.2 Summarise how nutrition interacts with the physical, psychological, economic and social changes involved in ageing. 17.3 Explain why the needs for some nutrients increase or decrease during ageing. 17.4 Identify how nutrition might contribute to, or prevent, the development of age-related
problems associated with vision, arthritis, the brain and alcohol use. 17.5 Instruct an adult on how to shop for groceries and prepare healthy meals for one person on a tight budget. 17.6 Explain why certain nutrients and medications interact.
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Chapter 17: Life cycle nutrition: adulthood and the later years
Wise food choices made throughout adulthood can support a person’s ability to meet physical, emotional and mental challenges and to enjoy freedom from disease. Two goals can motivate adults to pay attention to their diets: promoting health and slowing ageing. Much of this text has focused on nutrition to support health, and Chapter 18 features prevention of chronic diseases such as cancer and heart disease. This chapter focuses on ageing and the nutrition needs of older adults. The populations of Australian and New Zealand are growing older and the ratio of older people to young is increasing, as Figure 17.1 shows. In 1900, Australia’s total population was approximately 3.7 million. In 2014, approximately 14.7 per cent of Australians were over 65. Projections for 2050 indicate that one out of four Australians will be over 65.1 The figures are similar in New Zealand, where approximately 14 per cent of the population are aged over 65 years and around 26 per cent of the population will be over this age by 2050.2
FIGURE 17.1 The ageing of the Australian population In general, the percentage of older people in the population has increased over the decades, whereas the percentage of younger people has decreased. 4.0
4.3
4.5
6.1
7.4
8.1
12.0
14.8
17.0
18.0
20.9
29.3
19.3
35.1
1901
28.7
20.1
31.6
1911
30.0
16.9
31.7
1921
29.4
18.1
28.5
1931
30.0
8.5
8.3
9.7
11.2
12.5
13.1
20.4
19.9
20.0
19.2
19.3
23.1
25.0
30.2
27.0
25.6
28.7
31.5
30.1
28.5
17.4
16.0
13.7
14.0
25.0
22.0
20.5
19.4
1981
1991
2001
2007
14.3 17.5
27.1
1941
1951
30.3
1961
$65 years 45–64 years 25–44 years 15–24 years ,15 years
17.4
14.1
24.2
Key:
28.7
1971
Source: Taken from Australian Bureau of Statistics, Australian Demographic Statistics, ABS Catalogue Number 3101.0 (2014) Canberra: ABS. CC BY 4.0 International Licence.
Our society uses the arbitrary age of 65 years to define the transition point between middle age and old age, but growing ‘old’ happens day by day, with changes occurring gradually over time. Since 1950 the population of those over 65 has almost tripled. Remarkably, the fastest-growing age group has been people aged 100 and over; their numbers have increased by 8.5 per cent over the past 25 years with predictions of even greater growth.3 Life expectancy for non-Indigenous Australians and New Zealanders is 84.3 and 83.2 years, respectively, for women, whereas for men it is 80.1 years in Australia and 79.5 years in New Zealand4 – all of which are record highs and much higher than the average life expectancy of 60 to 62 years in 1900.5 Advances in medical science – antibiotics and other treatments – are largely responsible for the increase in life expectancy over the past century. Improved nutrition and an abundant food supply have also contributed to lengthening life expectancy. The life span has not lengthened as dramatically; human longevity appears to have an upper limit. The potential human life span is currently 130 years. With recent advances in medical technology and genetic knowledge, however, researchers may one day be able to extend the life span even further by slowing, or perhaps preventing, ageing and its accompanying diseases.
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17.1 Nutrition and longevity
Research in the field of ageing is active – and difficult. Researchers are challenged by the diversity of older adults. When older adults experience health problems, it is hard to know whether to attribute these problems to genetics, ageing or other environmental factors such as nutrition. The idea that nutrition can influence the ageing process is particularly appealing because people can control and change their eating habits. The questions being asked include the following: • To what extent is ageing inevitable, and can it be slowed through changes in lifestyle and environment? • What role does nutrition play in the ageing process, and what role can it play in slowing ageing? With respect to the first question, it seems that ageing is an inevitable, natural process, programmed into the genes at conception. People can, however, slow the process within genetic limits by adopting healthy lifestyle habits such as eating nutritious food and engaging in physical activity. In fact, an estimated 70 to 80 per cent of the average person’s life expectancy may depend on individual health-related behaviours; genes determine the remaining 20 to 30 per cent.6 With respect to the second question, good nutrition helps to maintain a healthy body and can therefore ease the ageing process in many significant ways. Clearly, nutrition can improve the quality of life in the later years.
Observation of older adults The strategies adults use to meet the two goals mentioned at the start of this chapter – promoting health and slowing ageing – are actually very much the same. What to eat, when to sleep, how physically active to be and other lifestyle choices greatly influence both physical health and the ageing process. PUTTING COMMON SENSE TO THE TEST
The majority of people’s life expectancy is determined by individual healthrelated behaviours. TRUE
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
To achieve and maintain a healthy weight, be physically active and choose amounts of nutritious food and drinks to meet your energy needs.
Healthy habits
A person’s physiological age reflects health status and may or may not reflect the person’s chronological age. Quite simply, some people seem younger, and others older, than their years. Lifestyle behaviours that seem to have the greatest influence on people’s health and therefore on their physiological age include: • sleeping regularly and adequately • eating well-balanced meals, including breakfast, regularly • engaging in physical activity regularly • not smoking • not drinking alcohol, or drinking it in moderation • maintaining a healthy body weight • regular social engagement • using the mind. Over the years, the effects of these lifestyle choices accumulate – that is, people who follow most of these practices live longer and have fewer disabilities as they age. They are in better health, even when older in chronological age, than people who do not adopt these behaviours. Even though people cannot change their birth dates, they may be able to add years to, and enhance the quality of, their lives. Physical activity seems to be most influential in preventing or slowing the many changes that define a stereotypical ‘old’ person. After all, many of the physical limitations that accompany ageing occur because people become inactive, not because they become older.
Physical activity The many remarkable benefits of regular physical activity outlined in Chapter 14 are not limited to the young. Compared with those who are inactive, older adults who are active weigh less; have greater flexibility, more endurance, better balance and better health; and live longer. They reap additional benefits from various activities as well: aerobic activities
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improve cardiorespiratory endurance, blood pressure and blood lipid profiles; moderate endurance activities improve the quality of sleep; and strength training improves posture and mobility. In fact, regular physical activity is the most powerful predictor of a person’s mobility in the later years. Physical activity also increases blood flow to the brain, thereby preserving mental ability, alleviating depression, supporting independence and improving quality of life.7 Muscle mass and muscle strength tend to decline with ageing, making older people vulnerable to falls and immobility. Falls are a major cause of injury, disability and even death among older adults.8 Many lose their independence as a result of falls. Regular physical activity assists in maintaining strong muscles, helping to improve confidence, reduce the risk of falling and lessen the risk of injury should a fall occur. Even without a fall, older adults may become so weak that they can no longer perform life’s daily tasks, such as climbing stairs, carrying packages and opening jars. Improving muscle strength allows a person to continue to perform these tasks. Even in frail, elderly people over 85 years of age, strength training not only improves balance, muscle Regular physical activity promotes a healthy, independent lifestyle. strength and mobility but also increases energy expenditure and energy intake, thereby enhancing nutrient intakes. This finding highlights another reason to be physically active: a person spending energy can afford to eat more food and thus receives more nutrients. People who are committed to an ongoing fitness program can benefit from higher energy and nutrient intakes and still maintain their body weight. Ideally, physical activity should be part of each day’s schedule and should be intense enough to prevent muscle atrophy and to speed up the heartbeat and respiration rate. Although ageing reduces both speed and endurance to some degree, older adults can still train and achieve exceptional performances. Healthy older adults who have not been active can ease into a suitable routine. They can start by walking short distances until they are walking at least 10 minutes continuously and then gradually increase the time walking to 30 to 45 minutes, five days a week. Table 17.1 provides exercise guidelines for older adults. People with medical conditions should check with a doctor before beginning an exercise routine, as should sedentary men over 40 and sedentary women over 50 who want to participate in a vigorous exercise program.
Manipulation of diet In their efforts to understand longevity, researchers have not only observed people, but have also manipulated influencing factors, such as diet, in animal studies. This research has given rise to some interesting and suggestive findings.
Energy restriction in animals Animals live longer and have fewer age-related diseases when their energy intakes are restricted. These life-prolonging benefits become evident when the diet provides enough food to prevent malnutrition and an energy intake of about 70 per cent of normal. Exactly how energy restriction prolongs life remains largely unexplained, although gene activity appears to play a key role. The genetic activity of old mice differs from that of young mice, with some genes becoming more active with age and others less active. With an energy-restricted diet, many of the genetic activities of older mice revert to those of younger mice. These ‘slowageing’ genetic changes are apparent in as little as one month on an energy-restricted, but still nutritionally adequate, diet. The consequences of energy restriction in animals include a delay in the onset, or prevention, of diseases such as atherosclerosis; prolonged growth and development; and improved blood glucose, insulin sensitivity and blood lipids. In addition, energy metabolism
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PUTTING COMMON SENSE TO THE TEST
Older people are vulnerable to falls and immobility due to declining muscle mass and muscle strength. TRUE
Shutterstock.com/Lisa F Young
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TABLE 17.1 Exercise guidelines for older adults
Stock Free
Jupiter Images/IT
BALANCE
Chapple
Thinkstock/Ron
FLEXIBILITY
Stock Free
Jupiter Images/IT
STRENGTH
Manasse
PhotoDisc/Geoff
Shutterstock.com/Paul
Examples
ENDURANCE
B Moore
LIFESTYLE/ INCIDENTAL
Frequency (days/wk)
5−7
5−7
2−3
2−3
1−7
Intensity
Moderate
Somewhat hard; 40−60% estimated HRmax
Resistance to movement that overloads with greater resistance has a greater effect
To point of resistance or mild discomfort
Progress difficulty by decreasing support as competence increases
Volume
At least 30 mins accumulated in bouts of 10 mins or longer
At least 30 mins
2−3 sets, 10−12 repetitions; 4 upper (biceps, shoulder flexion, chest press, back row) and 4 lower body (hamstrings, quadriceps, leg press, calves)
10−30, progressing longer if desired. Repeat 3−4 times for each stretch. Areas to include: chest, neck ROM; hands, triceps, hamstrings, quadriceps and hip flexors; calf soleus, gastrocnemius
Dynamic, focus on mobility; static, focus on 1-leg stance. 4−10 different exercises are available
Special instructions
Incorporated into or added to the endurance volume for long-term adherence
Weight-bearing encouraged. Increase duration ($30 mins) before increasing intensity up to moderate
Sets separated by 1 min, sessions separated by 1 day. Options: free weights, machines, elastic resistance bands and callisthenics
No bouncing. PNF technique. Incorporate into lifestyle – e.g. gardening and putting away dishes on high and low shelves
Incorporate into lifestyle – e.g. balance exercise while standing in line, performing other tasks. Environmental safety important
HR 5 heart rate; ROM 5 range of motion; PNF 5 proprioceptive neuromuscular facilitation; RM 5 repetition maximum. M. E. Cress, and co-authors., Best practices for physical activity programs and behavior counseling in older adult populations, Journal of Aging and Physical Activity 13 (1) (2005): 61–74, cited in National Ageing Research Institute, National Physical Activity Recommendations for Older Australians: Discussion Document, Melbourne: NARI (2006): 66.
Energy restriction research has been conducted on various species, including mice, rats, rhesus monkeys, cynomolgus monkeys, spiders and fish.
slows and body temperature drops – indications of a reduced rate of oxygen consumption. The use of oxygen during energy metabolism produces free radicals, which have been implicated in the ageing process. Restricting energy intake in animals not only produces fewer free radicals, but also increases antioxidant activity and enhances DNA repair. Reducing oxidative stress may at least partially explain how restricting energy intake lengthens life expectancy.9 Interestingly, longevity appears to depend on restricting energy intake and not on the amount of body fat. Genetically obese rats live longer when given a restricted diet even though their body fat is similar to that of other rats allowed to eat freely.
Energy restriction in human beings Research on a variety of animals confirms the relationship between energy restriction and longevity. Applying the results of animal studies to human beings is problematic, however, and conducting studies on human beings raises numerous questions – beginning with how to
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Chapter 17: Life cycle nutrition: adulthood and the later years
define energy restriction.10 Does it mean eating less or just weighing less? Is it less than you want or less than the average? Does eating less have to result in weight loss? Does it matter whether weight loss results from more exercise or from less food? Or whether weight loss is intentional or unintentional? Answers await research. Extreme starvation to extend life, like any extreme, is rarely, if ever, worth the price. Moderation, on the other hand, may be valuable. Many of the physiological responses to energy restriction seen in animals also occur in people whose intakes are moderately restricted. When people cut back on their usual energy intake by 10 to 20 per cent, body weight, body fat and blood pressure drop, and blood lipids and insulin response improve – favourable changes for preventing chronic diseases. Some research suggests that fasting on alternative days may provide similar benefits. The reduction in oxidative damage that occurs with energy restriction in animals also occurs in people whose diets include antioxidant nutrients and phytochemicals. Diets such as the Mediterranean diet that include an abundance of fruits, vegetables, olive oil and red wine – with their array of antioxidants and phytochemicals – support good health and long life.11 Clearly, nutritional adequacy is essential to living a long and healthy life.
For perspective, a person with a usual energy intake of 8700 kilojoules might cut back to 6900 to 7800 kilojoules.
CURRENT RESEARCH IN NUTRITION Delaying ageing through energy restriction Underlying the importance of research on the biology of ageing is the fact that many nations face the reality of rapidly ageing populations. This reality is a result of ageing itself being the most significant risk factor for a range of the most prevalent diseases, including many cancers, cardiovascular disease and diabetes. Accordingly, interventions are required that would be able to delay or prevent diseases and disorders associated with the ageing process and thereby increase the period of time that ageing individuals are in good health. Energy restriction has emerged as a model of major interest as it is widely agreed that it is the most potent environmental intervention that delays the onset of ageing and extends life span in diverse experimental organisms. A better understanding of the mechanisms by which energy restriction delays ageing will reveal insights into the ageing process and the underlying causes of disease vulnerability with age. These insights will allow the development of preventive measures for age-associated diseases and disorders.
REVIEW IT
Life expectancy in Australia and New Zealand increased dramatically in the twentieth century. Factors that enhance longevity include limited or no alcohol consumption, regular balanced meals, weight control, adequate sleep, regular physical activity and abstinence from smoking. Energy restriction in animals seems to lengthen their lives. Whether such dietary intervention in humans is beneficial remains unknown. At the very least, nutrition – especially when combined with regular physical activity – can influence ageing and longevity in humans by supporting good health and preventing disease.
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17.2 The ageing process
As people get older, each person becomes less and less like anyone else. The older people are, the more time has elapsed for such factors as nutrition, genetics, physical activity and everyday stress to influence physical and psychological ageing. Stress promotes the early onset of age-related diseases. Both physical stressors (such as alcohol abuse, other drug abuse, smoking, pain and illness) and psychological stressors (such as exams, divorce and the death of a loved one) elicit the body’s stress response. The body responds to such stressors with an elaborate series of physiological steps, as the nervous and hormonal systems bring about defensive readiness in every body part. These effects favour physical action – the classic fight-or-flight response. Prolonged or severe stress can drain the
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Understanding nutrition
body of its reserves and leave it weakened, aged and vulnerable to illness, especially if physical action is not taken. As people age, they lose their ability to adapt to both external and internal disturbances. When disease strikes, the reduced ability to adapt makes the ageing individual more vulnerable to death than a younger person. Because the stress response is mediated by hormones, it differs between men and women. The fight-or-flight response may be more typical of men than of women. Women’s reactions to stress more typically follow a pattern of ‘tend and befriend’. Women tend by nurturing and protecting themselves and their children. These actions promote safety and reduce stress. Women befriend by creating and maintaining a social group that can help in the process. Oxidative stresses and cellular damage occur when free radicals exceed the body’s ability to defend itself. Increased free-radical activity and decreased antioxidant protection are common features of ageing – and antioxidants seem to help slow the ageing process.12 Such findings seem to suggest that the fountain of youth may actually be a cornucopia of fruits and vegetables rich in antioxidants.
Physiological changes As ageing progresses, inevitable changes in each of the body’s organs contribute to the body’s declining function. These physiological changes influence nutrition status, just as growth and development do in the earlier stages of the life cycle.
Body weight Chapter 8 presented the many health problems that accompany obesity and the BMI guidelines for a healthy body weight (18.5 to 24.9 kg/m2). These guidelines apply to all adults, regardless of age, but they may be too restrictive for older adults. The importance of body weight in defending against chronic diseases is different for older adults. Being moderately overweight may not be harmful. For adults over 65 years, health risks do not become apparent until BMI reaches at least 27 kg/m2 – and the relationship tends to diminish with age until it disappears by age 75. Older adults who are obese, however, face serious medical complications and can significantly improve their quality of life with weight loss.13 For some older adults, a low body weight may be more detrimental than a high one. Low body weight often reflects malnutrition and the trauma associated with a fall. Many older adults experience unintentional weight loss, in large part because of an inadequate food intake. Without adequate nutrient reserves, an underweight person may be unprepared to fight against diseases. For underweight people, even a slight weight loss (5 per cent) increases the likelihood of disease and premature death.
Body composition In general, older people tend to lose bone and muscle and gain body fat. Many of these changes occur because some hormones that regulate appetite and metabolism become less active with age, whereas others become more active.* Loss of muscle, known as sarcopenia, can be significant in the later years, and its consequences can be quite dramatic (see Figure 17.2).14 As muscles diminish and weaken, people lose the ability to move and maintain balance – making falls likely. The limitations that accompany the loss of muscle mass and strength play a key role in the diminishing health that often accompanies ageing. Optimal nutrition and regular physical activity can *Causes of diminished appetite in older adults include increased cholecystokinin, leptin and cytokines, and decreased ghrelin and testosterone. Additional examples of hormones that change with age include growth hormone and androgens, which decline with advancing age, thus contributing to the decrease in lean body mass, and prolactin, which increases with age, helping to maintain body fat. Insulin sensitivity also diminishes as people grow older, most likely because of increases in body fat and decreases in physical activity.
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FIGURE 17.2 Sarcopenia
Courtesy of Dr. William Evans
Courtesy of Dr. William Evans
These cross-sections of two women’s thighs may appear to be about the same size from the outside, but the 20-year-old woman’s thigh (left) is dense with muscle tissue. The 64-year-old woman’s thigh (right) has lost muscle and gained fat, changes that may be largely preventable with strength-building physical activities.
help maintain muscle mass and strength and minimise the changes in body composition associated with ageing. Risk factors for sarcopenia include weight loss, little physical activity and cigarette smoking. Obesity and the inflammation that accompanies it may also contribute to sarcopenia.15
PUTTING COMMON SENSE TO THE TEST
Older people with a BMI up to 27 are more vulnerable to obesity-related diseases. FALSE
Immune system Changes in the immune system also bring declining function with age. In addition, the immune system is compromised by nutrient deficiencies. Thus, the combination of age and malnutrition makes older people vulnerable to infectious diseases. Older adults may also improve their immune system responses by exercising regularly.
The gastrointestinal tract In the gastrointestinal (GI) tract, the intestinal wall loses strength and elasticity with age, and GI hormone secretions change. All of these actions slow motility. Constipation is much more common in the elderly than in the young. Changes in GI hormone secretions also diminish appetite, leading to decreased energy intake and weight loss. Atrophic gastritis, a condition that affects almost one-third of those over 60, is characterised by an inflamed stomach, bacterial overgrowth, and a lack of hydrochloric acid and intrinsic factor. All of these can impair the digestion and absorption of nutrients, most notably vitamin B12, but also biotin, folate, calcium, iron and zinc. Difficulty in swallowing, medically known as dysphagia, can occur in all age groups, but especially in the elderly. Being unable to swallow a mouthful of food can be scary, painful and dangerous. Even swallowing liquids can be a problem for some people. Consequently, the person may eat less food and drink fewer beverages, resulting in weight loss, malnutrition and dehydration. Dietary intervention for dysphagia is highly individualised and based on the person’s abilities and tolerances. A qualified speech pathologist will assess an individual’s abilities and prescribe food modifications, which may include texture modified foods (soft, minced and moist, or smooth puree) and fluids (mildly thick, moderately thick and extremely thick).
Tooth loss Regular dental care over a lifetime protects against tooth loss and gum disease, which are common in old age. These conditions make chewing difficult or painful. Dentures, even when they fit properly, are less effective than natural teeth, and inefficient chewing can cause
Consequences of atrophic gastritis include: • inflamed stomach • increased bacterial growth • reduced hydrochloric acid • reduced intrinsic factor • increased risk of nutrient deficiencies, notably of vitamin B12.
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The medical term for lack of teeth is edentulous. • e 5 without • dens 5 teeth Conditions requiring dental care: • dry mouth • eating difficulty • no dental care within two years • tooth or mouth pain • altered food selections • lesions, sores or lumps in mouth.
choking episodes. People with tooth loss, gum disease and ill-fitting dentures tend to limit their food selections to soft foods. If foods such as corn on the cob, apples and hard rolls are replaced by creamed corn, apple sauce and rice, then nutrition status may not be greatly affected. However, when food groups are eliminated and variety is limited, poor nutrition follows. People without teeth typically eat fewer fruits and vegetables and have less variety in their diets.16 Consequently, they have low intakes of fibre and vitamins, which exacerbates their dental and overall health problems.
Sensory losses and other physical problems Sensory losses and other physical problems can also interfere with an older person’s ability to obtain adequate nourishment. Failing eyesight, for example, can make driving to the supermarket impossible and shopping for food a frustrating experience. It may become so difficult to read food labels and count money that the person doesn’t buy needed foods. Carrying bags of shopping may be an unmanageable task. Similarly, a person with limited mobility may find cooking and cleaning too difficult. Not too surprisingly, the prevalence of undernutrition is high among those who are limited in mobility or access to care facilities. Sensory losses can also interfere with a person’s ability or willingness to eat. Taste and smell sensitivities tend to diminish with age and may make eating less enjoyable. If a person eats less, then weight loss and nutrient deficiencies may follow. Loss of vision and hearing may contribute to social isolation, and eating alone may lead to poor intake.
Other changes In addition to the physiological changes that accompany ageing, adults change in many other ways that influence their nutrition status. Psychological, economic and social factors play big roles in a person’s ability and willingness to eat.
iStockphoto.com/peepo
Psychological changes
Shared meals can brighten the day and enhance the appetite.
Although not an inevitable component of ageing, depression is common among older adults. People with depression, even those without disabilities, lose their ability to perform simple physical tasks. They frequently lose their appetite and the motivation to cook or even to eat. An overwhelming sense of grief and sadness at the death of a spouse, friend or family member may leave a person, especially an elderly person, feeling powerless to overcome depression. When a person is suffering the heartache and loneliness of bereavement, cooking meals may not seem worthwhile. The support and companionship of family and friends, especially at mealtimes, can help overcome depression and enhance appetite.
Economic changes Overall, older adults today have higher incomes than older adults of previous generations. Factors such as living arrangements and income make significant differences in the food choices, eating habits and nutrition status of older adults, especially those over 80. People of low socioeconomic means are much more likely to have inadequate food and nutrient intakes.
Social changes Malnutrition among older adults is most common in hospitals and nursing homes.17 In the community, malnutrition is most likely to occur among those living alone, especially men; those with the least education; those living in government-funded housing (an indicator of low income); and those who have recently experienced a change in lifestyle. Adults who live alone do not necessarily make poor food choices, but they often consume too little food. Loneliness is directly related to nutritional inadequacies, especially of energy intake.
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Chapter 17: Life cycle nutrition: adulthood and the later years
REVIEW IT
Many changes that accompany ageing can impair nutrition status. Among physiological changes, hormone activity alters body composition, immune system changes raise the risk of infections, atrophic gastritis interferes with digestion and absorption, and tooth loss limits food choices. Psychological changes such as depression, economic changes such as loss of income and social changes such as loneliness contribute to poor food intake.
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Knowledge about the nutrient needs and nutrition status of older adults has grown considerably in recent years. The Nutrient Reference Values (NRV) for Australia and New Zealand cluster people over 50 into two age categories – one group of 51 to 70 years and one of 71 years and older. Increasingly, research is showing that the nutrition needs of people 50 to 70 years old are different from those of people over 70. Setting standards for older people is difficult because individual differences become more pronounced as people grow older. People start out with different genetic predispositions and ways of handling nutrients, and the effects of these differences become magnified with years of unique dietary habits. For example, one person may tend to omit fruits and vegetables from his diet, and by the time he is old, he may have a set of nutrition problems associated with a lack of fibre and antioxidants. Another person may have omitted milk and milk products all her life – her nutrition problems may be related to a lack of calcium. Also, as people age they suffer different chronic diseases and take various medicines – both of which will affect nutrient needs. For all of these reasons, researchers have difficulty even defining ‘healthy ageing’, a prerequisite to developing recommendations to meet the needs of practically all healthy persons. The following discussion gives special attention to the nutrients of greatest concern.
Shutterstock.com/Arek Malang
17.3 Energy and nutrient needs of older adults
Growing old can be enjoyable for people who take care of their health and live each day fully.
Water Despite real fluid needs, many older people do not seem to feel thirsty or notice a dry mouth. Many nursing home employees say it is hard to persuade their elderly clients to drink enough fluid. Older adults may find it difficult and bothersome to get a drink or to get to a toilet. Those who have lost bladder control may be afraid to drink too much water. Dehydration is a risk for older adults. Total body water decreases as people age, so even mild stresses such as fever or hot weather can precipitate rapid dehydration in older adults. Dehydrated older adults seem to be more susceptible to urinary tract infections, pneumonia, pressure ulcers, and confusion and disorientation. To prevent dehydration, older adults need to drink at least six glasses of fluid a day in combination with a balanced diet to achieve adequate fluid intake.
Energy and energy nutrients On average, energy needs decline an estimated 5 per cent per decade beyond the age of 50. One reason is that people usually reduce their physical activity as they age, although they need not do so. Another reason is that BMR declines 1 to 2 per cent per decade, in part because lean body mass and thyroid hormones diminish.18 On limited energy allowances, people must select mostly nutrient-dense foods. There is little leeway for added sugars, solid fats or alcohol. The Australian Guide to Healthy Eating offers a dietary framework for adults of all ages.
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Protein Because energy needs decrease, protein must be obtained from low-kilojoule sources of high-quality protein, such as lean meats, poultry, fish and eggs; fat-free and low-fat milk products; and legumes. Protein is especially important for the elderly to support a healthy immune system, prevent muscle wasting and optimise bone mass. Underweight or malnourished older adults need snacks that are protein- and energydense, such as eggs, tuna and crackers, peanut butter on wholegrain toast, and hearty soups. Importantly, the diet should provide enjoyment as well as nutrients.
Carbohydrate and fibre Carbohydrate is needed to protect protein from being used as an energy source. Sources of complex carbohydrates such as legumes, vegetables, whole grains and fruits are also rich in fibre and essential vitamins and minerals. Average fibre intakes among older adults are lower than current recommendations (25 grams/day for women and 30 grams/day for men).19 Eating high-fibre foods and drinking water can alleviate constipation – a condition common among older adults, especially nursing home residents. Physical inactivity and medications also contribute to the high incidence of constipation.
Fat As is true for people of all ages, fat intake needs to be moderate in the diets of most older adults – enough to enhance flavours and provide valuable nutrients, but not so much as to raise the risks of cancer, atherosclerosis and other degenerative diseases. This recommendation should not be taken too far; limiting fat too severely may lead to nutrient deficiencies and weight loss – two problems that carry greater health risks in the elderly than overweight.
Reminder: Atrophic gastritis is a chronic inflammation of the stomach characterised by inadequate hydrochloric acid and intrinsic factor – two important aspects of vitamin B12 absorption.
Vitamins and minerals Most people can achieve adequate vitamin and mineral intakes simply by including foods from all food groups in their diets, but older adults often omit fruits and vegetables. Similarly, few older adults consume the recommended amounts of milk or milk products.
Vitamin B12
An estimated 10 to 30 per cent of adults over 50 have atrophic gastritis. As Chapter 10 explains, people with atrophic gastritis are particularly vulnerable to vitamin B12 deficiency. The bacterial overgrowth that accompanies this condition uses up the vitamin, and without hydrochloric acid and intrinsic factor, digestion and absorption of vitamin B12 are inefficient. Given the poor cognition, anaemia and devastating neurological effects associated with a vitamin B12 deficiency, an adequate intake is imperative.20 The RDI for older adults is the same as for younger adults, so those with poor intakes may require supplementation.
iStockphoto.com/Urilux
Vitamin D
Taking time to nourish your body well is a gift you give yourself.
Vitamin D deficiency is a problem among older adults as they are often less exposed to sunlight, and consumption becomes inadequate. It is possible that regular sunlight exposure is not sufficient to meet the needs of people aged 51 to 70, and unlikely that regular sunlight meets the needs of people over 70. Housebound or institutionalised elderly people are likely to require supplements. Ageing also reduces the skin’s capacity to make vitamin D and the kidneys’ ability to convert it to its active form. Not only are older adults not getting enough vitamin D, they may actually need more to improve both muscle and bone strength.21 To prevent bone
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loss and to maintain vitamin D status, especially in those who engage in minimal outdoor activity, adults 51 to 70 years old need 10 micrograms daily, and those over 70 need 15 micrograms.22
Calcium Both Chapter 12 and Highlight 12 emphasise the importance of adequate dietary calcium throughout life, especially for women after menopause, to protect against osteoporosis. The RDI for calcium is 1300 mg/day for women over 50 years and men over 70 years, but the calcium intakes of older people in Australia and around the world are often below recommendations.23 Some older adults avoid milk and milk products because they dislike these foods or associate them with stomach discomfort. Simple solutions include using calciumfortified juices, adding powdered milk to recipes and taking supplements if intake is still inadequate. Chapter 12 offers many other strategies for including non-milk sources of calcium for those who do not drink milk.
Iron The iron needs of men remain unchanged throughout adulthood. For women, iron needs decrease substantially when blood loss through menstruation ceases. Consequently, iron-deficiency anaemia is less common in older adults than in younger people. In fact, elevated iron stores are more likely than deficiency in older people, especially those who take iron supplements, eat red meat regularly and include vitamin C-rich fruits in their daily diet. Nevertheless, iron deficiency may develop in older adults, especially when their food energy intakes are low. Aside from diet, two other factors may lead to iron deficiency in older people: chronic blood loss from diseases and medicines, and poor iron absorption due to reduced stomach acid secretion and antacid use. Iron deficiency impairs immunity and leaves older adults vulnerable to infectious diseases. Anyone involved in the area of older people’s nutrition should keep these possibilities in mind.
Nutrient supplements People judge for themselves how to manage their nutrition and this may involve the use of dietary supplements. When recommended by a doctor or qualified nutrition professional, vitamin D and calcium supplements for osteoporosis, or vitamin B12 for pernicious anaemia may be beneficial. People with small energy allowances would do well to become more active so they can afford to eat more food. Food is the best source of nutrients for everybody. Supplements are just that – supplements to foods, not substitutes for them. For anyone who is motivated to obtain the best possible health, it is never too late to learn to eat well, drink water, exercise regularly and adopt other lifestyle habits such as quitting smoking and moderating alcohol intake.
PUTTING COMMON SENSE TO THE TEST
People over the age of 70 who are institutionalised should receive a vitamin D supplement due to lack of sunshine. TRUE
NUTRIENT
EFFECT OF AGEING
COMMENTS
Water
Lack of thirst and decreased total body water make dehydration likely.
Mild dehydration is a common cause of confusion. Difficulty obtaining water or getting to the toilet may compound the problem.
Energy
Need decreases as muscle mass decreases (sarcopenia).
Physical activity moderates the decline.
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REVIEW IT
The following table summarises the nutrient concerns of ageing. Although some nutrients need special attention in the diet, supplements are not routinely recommended. The ever-growing number of older people creates an urgent need to learn more about how their nutrient requirements differ from those of others and how such knowledge can enhance their health.
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NUTRIENT
EFFECT OF AGEING
COMMENTS
Fibre
Likelihood of constipation increases with low intakes and changes in the GI tract.
Inadequate water intakes and lack of physical activity, as well as some medications, compound the problem.
Protein
Needs may stay the same or increase slightly.
Low-fat, high-fibre legumes and grains meet both protein and other nutrient needs.
Vitamin B12
Atrophic gastritis is common.
Deficiency causes neurological damage; supplements may be needed.
Vitamin D
There is increased likelihood of inadequate intake; skin synthesis declines.
Daily sunlight exposure in moderation or supplements may be beneficial.
Calcium
Intakes may be low; osteoporosis is common.
Stomach discomfort commonly limits milk intake; calcium substitutes or supplements may be needed.
Iron
In women, status improves after menopause; deficiencies are linked to chronic blood losses and low stomach acid output.
Adequate stomach acid is required for absorption; antacid or other medicine use may aggravate iron deficiency; vitamin C and meat increase absorption.
17.4 Nutrition-related concerns of older adults
Nutrition may play a greater role than has been realised in preventing many changes once thought to be inevitable consequences of growing older. The following discussions of vision, arthritis and the ageing brain show that nutrition may provide at least some protection against some of the conditions associated with ageing.
Inflammaging Human ageing is characterised by a chronic, low-grade inflammation which has been termed inflammaging. Inflammaging is a significant risk factor for both morbidity and mortality in elderly people. This is because most age-related diseases share an inflammatory pathogenesis. The precise cause of inflammaging and its potential role in contributing to adverse health outcomes remain largely unknown. The identification of the causes and pathways related to age-related inflammation is important to understand so that any potential treatments that reduce inflammaging may be utilised in older people. It is thought that leading an ageappropriate healthy lifestyle – physical activity and healthy dietary intake, including pro- and prebiotics – may contribute to the reduction of inflammaging.24
Vision One key aspect of healthy ageing is maintaining good vision. Age-related eye diseases that impair vision, such as cataract and macular degeneration, correlate with poor survival that cannot be explained by other risk factors.25 Following a healthy diet as described by the Australian Dietary Guidelines is one way to protect against these age-related vision problems.
Cataracts
Cataracts are age-related thickenings in the lenses of the eyes that impair vision. If not surgically removed, they ultimately lead to blindness. Cataracts occur even in well-nourished individuals as a result of ultraviolet light exposure, oxidative stress, injury, viral infections,
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toxic substances and genetic disorders. Many cataracts, however, are vaguely called senile cataracts – meaning ‘caused by ageing’. Oxidative stress appears to play a significant role in the development of cataracts, and the antioxidant nutrients may help minimise the damage. Studies have reported an inverse relationship between cataracts and dietary intakes of vitamin C, vitamin E and carotenoids; taking supplements or eating fruits and vegetables rich in these antioxidant nutrients seems to slow the progression or reduce the risk of developing cataracts.26 Obesity may also play a role in the development of cataracts. Obesity appears to be associated with cataracts, but its role has not been identified. Risk factors that typically accompany overweight, such as inactivity, diabetes or hypertension, do not explain the association.
Macular degeneration
The leading cause of visual loss among older people is age-related macular degeneration, a deterioration of the macular region of the retina. As with cataracts, risk factors for agerelated macular degeneration include oxidative stress from sunlight, and preventive factors may include supplements of antioxidant vitamins plus zinc and the carotenoids lutein and zeaxanthin.27 Total dietary fat may also be a risk factor for macular degeneration, but the omega-3 fatty acids found in fish may be protective.
Arthritis Approximately 4.5 million people across Australia and New Zealand have some form of arthritis. As the population ages, it is expected that the prevalence will increase to 7 million by 2050.
Osteoarthritis
The most common type of arthritis that disables older people is osteoarthritis, a painful deterioration of the cartilage in the joints. During movement, the ends of bones are normally protected from wear by cartilage and by small sacs of fluid that act as a lubricant. With age, the cartilage sometimes disintegrates, and the joints become malformed and painful to move. One known connection between osteoarthritis and nutrition is overweight. Weight loss may relieve some of the pain for overweight persons with osteoarthritis, partly because the joints affected are often weight-bearing joints that are stressed and irritated by having to carry excess weight. However, weight loss often relieves much of the pain of arthritis in the hands as well, even though they are not weight-bearing joints. Jogging and other weightbearing exercises do not worsen arthritis. In fact, both aerobic activity and strength training offer improvements in physical performance and pain relief, especially when accompanied by even modest weight loss.28
Risk factors for osteoarthritis include: • age • smoking • high BMI at age 40 • lack of hormone therapy (in women) • joint trauma/injury.
Rheumatoid arthritis
Another type of arthritis known as rheumatoid arthritis has possible links to diet through the immune system.29 In rheumatoid arthritis, the immune system mistakenly attacks the bone coverings as if they were made of foreign tissue. In some individuals, certain foods, notably vegetables and olive oil, may moderate the inflammatory response and provide some relief. The omega-3 fatty acids commonly found in fish oil reduce joint tenderness and improve mobility in some people with rheumatoid arthritis.30 The same diet recommended for heart health – one low in saturated fat from meats and milk products, and high in omega-3 fats from fish – helps prevent or reduce the inflammation in the joints that makes arthritis so painful. Another possible link between nutrition and rheumatoid arthritis involves the oxidative damage to the membranes within joints that causes inflammation and swelling. The antioxidant vitamins C and E and the carotenoids defend against oxidation, and increased intakes of these nutrients may help prevent or relieve the pain of rheumatoid arthritis.
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Gout
Another form of arthritis, which most commonly affects men, is gout, a condition characterised by deposits of uric acid crystals in the joints. Uric acid derives from the breakdown of purines, primarily from those made by the body but also from those found in foods. Foods such as meat and seafood that are rich in purines increase uric acid levels and the risk of gout, whereas milk products seem to lower uric acid levels and the risk of gout.31
Treatment Treatment for arthritis – dietary or otherwise – may help relieve discomfort and improve mobility, but it does not cure the condition. Traditional medical intervention for arthritis includes medication and surgery. Alternative therapies to treat arthritis abound, but none have proved in scientific studies to be safe and effective. Popular supplements – glucosamine, chondroitin or a combination of the two – may relieve pain and improve mobility, as may some over-the-counter pain relievers, but mixed reports from studies emphasise the need for additional research.32 Drugs and supplements used to relieve arthritis can impose nutrition risks; many affect appetite and alter the body’s use of nutrients, as Highlight 17 explains.
APPLICATIONS OF NUTRITIONAL RESEARCH Glucosamine and chondroitin treatments for osteoarthritis Oral glucosamine and chondroitin have been used worldwide for the treatment of osteoarthritis. Clinical studies aim to investigate the potential effects of glucosamine and chondroitin for osteoarthritis care. While the area requires further studies to replicate results, so far the effects of supplementation appear promising, with sufferers reporting better functioning and fewer symptoms, and analyses of cartilage metabolism biomarkers showing improvements in certain types of collagen synthesis.
The ageing brain The brain, like all of the body’s organs, responds to both genetic and environmental factors that can enhance or diminish its amazing capacities. One of the challenges researchers face when studying the human brain is to distinguish between normal age-related physiological changes, changes caused by diseases, and changes that result from cumulative environmental factors such as diet. The brain normally changes in some characteristic ways as it ages. Its blood supply decreases and the number of neurones, the brain cells that specialise in transmitting information, diminishes as people age. When the number of nerve cells in one part of the cerebral cortex diminishes, hearing and speech are affected. Losses of neurone in other parts of the cortex can impair memory and cognitive function. When the number of neurones in the hindbrain diminishes, balance and posture are affected. Losses of neurone in other parts of the brain affect still other functions. Some of the cognitive loss and forgetfulness generally attributed to ageing may be due in part to environmental, and therefore controllable, factors – including nutrient deficiencies.
Nutrient deficiencies and brain function Nutrients influence the development and activities of the brain. The ability of neurones to synthesise specific neurotransmitters depends in part on the availability of precursor nutrients that are obtained from the diet.33 The neurotransmitter serotonin, for example, derives from the amino acid tryptophan. To function properly, the enzymes involved in neurotransmitter synthesis require vitamins and minerals. Thus, nutrient deficiencies may contribute to the loss of memory and cognition that some older adults experience. Such losses may be preventable, or at least diminished or delayed, through diet and exercise. Table 17.2 summarises some of the better-known connections between brain function and nutrients.
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Chapter 17: Life cycle nutrition: adulthood and the later years
TABLE 17.2 Summary of nutrient–brain relationships BRAIN FUNCTION
DEPENDS ON AN ADEQUATE INTAKE OF:
Short-term memory
Vitamin B12, vitamin C, vitamin E
Performance in problem-solving tests
Riboflavin, folate, vitamin B12, vitamin C
Mental health
Thiamin, niacin, zinc, folate
Cognition
Folate, vitamin B6, vitamin B12, iron, vitamin E
Vision
Essential fatty acids, vitamin A
Neurotransmitter synthesis
Tyrosine, tryptophan, choline
In some instances, the degree of cognitive loss is extensive. Such senile dementia may be attributable to a specific disorder such as a brain tumour or Alzheimer’s disease. Table 17.3 lists common signs of dementia.
TABLE 17.3 Common signs of dementia • Agitated behaviour • Becoming lost in familiar surroundings or circumstances • Confusion • Delusions • Loss of interest in daily activities • Loss of memory • Loss of problem-solving skills • Unclear thinking
Alzheimer’s disease
Much attention has focused on the abnormal deterioration of the brain called Alzheimer’s disease. Diagnosis of Alzheimer’s disease depends on its characteristic symptoms: the victim gradually loses memory and reasoning, the ability to communicate, physical capabilities and eventually life.34 Nerve cells in the brain die, and communication between the cells breaks down. These changes should not be confused with typical age-related changes, the differences of which can be seen in Table 17.4.
TABLE 17.4 Signs of Alzheimer’s and typical age-related changes compared SIGNS OF ALZHEIMER’S DISEASE
TYPICAL AGE-RELATED CHANGES
Memory loss that disrupts daily life, such as asking for the same information repeatedly or asking others to handle tasks of daily living
Forgetting a name or missing an appointment
Challenges in planning or solving problems, such as following a recipe or paying monthly bills
Missing a monthly payment or making an error when balancing the chequebook.
Difficulty completing familiar tasks at home, such as using the microwave; at work, such as preparing a report; or at leisure, such as playing a game
Needing help recording a television program
Confusion with time or place, including current season and location
Not knowing today’s date
Trouble understanding visual images and spatial relationships, such as judging distances and recognising self in a mirror
Experiencing visual changes due to cataracts
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SIGNS OF ALZHEIMER’S DISEASE
TYPICAL AGE-RELATED CHANGES
New problems with words in speaking or writing, such as knowing the name of a common object
Being unable to find the right word to use
Misplacing things and losing the ability to retrace steps, such as putting the milk in the closet and having no idea when or where the milk was last seen
Misplacing a pair of glasses or the car keys
Decreased or poor judgement, such as giving large sums of money to strangers
Making a bad decision on occasions
Withdrawal from work projects or social activities
Feeling too tired to participate in work, family or social activities
Changes in mood and personality, such as confusion, suspicion, depression and anxiety, especially when in unfamiliar places or with unfamiliar people
Becoming irritable when routines are disrupted
Adapted from Alzheimer’s Association, http://www.alz.org/alzheimers_disease_10_signs_of_alzheimers.asp
Researchers are closing in on the exact cause of Alzheimer’s disease. Clearly, genetic factors are involved.35 Free radicals and oxidative stress also seem to be involved.36 Nerve cells in the brains of people with Alzheimer’s disease show evidence of free-radical attack – damage to DNA, cell membranes and proteins. They also show evidence of the minerals that trigger free-radical attacks – iron, copper, zinc and aluminium. Some research suggests that the antioxidant nutrients can limit free-radical damage and delay or prevent Alzheimer’s disease.37 In Alzheimer’s disease, the brain develops senile plaques and neurofibrillary tangles. Senile plaques are clumps of a protein fragment called beta-amyloid; neurofibrillary tangles are snarls of the fibres that extend from the nerve cells. Both seem to occur in response to oxidative stress.38 The differences between a healthy brain and one afflicted with Alzheimer’s can be seen in Figure 17.3. Researchers question whether these characteristics are the cause or the result of Alzheimer’s disease. In fact, scientists are unsure whether these plaques and tangles are causing the damage, serving as markers or even protecting by sequestering the proteins that begin the dementia process.39
FIGURE 17.3 Alzheimer’s and healthy brains compared Alzheimer’s brain
Science Source/Jessica Wilson/Medical Body Scans
Healthy brain
© 2012 Alzheimer’s Association; illustration by Stacy Janis
TABLE 17.4
616
Healthy nerve cells
Alzheimer’s nerve cells Plaques – clumps of beta-amyloid protein pieces – block cell-to-cell synapse signals. Tangles – twisted strands of protein – destroy the cell transport system. As plaques and tangles block essential nutrients from reaching the nerve cells, the nerve cells eventually die.
As nerve cells die, the brain shrinks and loses its ability to think, plan, remember and form new memories. The fluid-filled spaces within the brain grow larger.
Alzheimer’s Association, http://www.alz.org/research/science/alzheimers_brain_tour.asp
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Late in the course of the disease, there is a decline in the activity of the enzyme that assists in the production of the neurotransmitter acetylcholine from choline and acetyl CoA. Acetylcholine is essential to memory, but supplements of choline (or of lecithin, which contains choline) have no effect on memory or on the progression of the disease. Drugs that inhibit the breakdown of acetylcholine, on the other hand, have proved beneficial. Research suggests that cardiovascular disease risk factors such as high blood pressure, diabetes and elevated levels of homocysteine may be related to the development of Alzheimer’s disease.40 Diets designed to support a healthy heart, including omega-3 fatty acids and light-to-moderate alcohol intake, may benefit a healthy brain as well. Treatment for Alzheimer’s disease involves providing care to clients and support to their families. Drugs are used to improve or at least to slow the loss of short-term memory and cognition, but they do not cure the disease. Other drugs may be used to control depression, anxiety and behaviour problems. Both foods and mental challenges Maintaining appropriate body weight may be the most important nutrition nourish the brain. concern for the person with Alzheimer’s disease. Depression and forgetfulness can lead to changes in eating behaviours and poor food intake. Furthermore, changes in the body’s weight-regulation system may contribute to weight loss. Perhaps the best that a caregiver can do nutritionally for a person with Alzheimer’s disease is to supervise food planning and mealtimes. Providing well-liked and well-balanced meals and snacks in a PUTTING cheerful atmosphere encourages food consumption. To minimise confusion, offer a few COMMON SENSE TO THE TEST ready-to-eat foods, in bite-size pieces, with seasonings and sauces. To avoid mealtime disruptions, control distractions such as music, television and the telephone. Choline supplements REVIEW IT
Senile dementia and other losses of brain function afflict millions of older adults, and others face loss of vision due to cataracts or macular degeneration, or cope with the pain of arthritis. As the number of people over age 65 continues to grow, the need for solutions to these problems becomes urgent. Some problems may be inevitable, but others are preventable and good nutrition may play a key role.
are known to assist with memory and slow the progression of Alzheimer’s disease. FALSE
17.5 Food choices and eating habits of older adults
Older people are an incredibly diverse group, and for the most part, they are independent, socially sophisticated, mentally lucid, fully participating members of society who report themselves to be happy and healthy. In fact, the quality of life among the elderly has improved, and their chronic disabilities have declined dramatically in recent years.41 By practising stressmanagement skills, maintaining physical fitness, participating in activities of interest and cultivating spiritual health, as well as obtaining adequate nourishment, people can support a high quality of life into old age – see Table 17.5 for some strategies. To determine the risk of malnutrition in older clients, healthcare professionals can keep in mind the characteristics and questions listed in Table 17.6.
TABLE 17.5 Some strategies for growing old healthfully • Choose nutrient-dense foods. • Be physically active. Walk, run, dance, swim, bike or row for aerobic activity. Lift weights, do callisthenics or pursue some other activity to tone, firm and strengthen muscles. Practise balancing on one foot or doing simple movements with your eyes closed. Modify activities to suit changing abilities and tastes. • Maintain appropriate body weight.
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Chapter 17: Life cycle nutrition: adulthood and the later years
TABLE 17.5
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• Reduce stress (cultivate self-esteem, maintain a positive attitude, manage time wisely, know your limits, practise assertiveness, release tension and take action). • For women, there may be the need to consult with a doctor about the risks and benefits of oestrogen replacement therapy. The doctor may want to refer you to a specialist in the area for further expert advice. • For people who smoke, discuss with a doctor strategies and programs to help you quit. • Expect to enjoy sex, and learn new ways of enhancing it. • Use alcohol only moderately, if at all; use only prescribed drugs. • Take care to prevent accidents. • Expect good vision and hearing throughout life; obtain glasses and hearing aids if necessary. • Take care of your teeth; obtain dentures if necessary. • Be alert to confusion as a disease symptom, and seek diagnosis. • Take medications as prescribed; see a doctor before self-prescribing medicines or herbal remedies, and a qualified nutrition professional before self-prescribing supplements. • Control depression through activities and friendships; seek professional help if necessary. • Drink 6 to 8 glasses of water every day. • Practise mental skills. Keep on solving maths problems and crossword puzzles, playing cards or other games, reading, writing, imagining and creating. • Make financial plans early to ensure security. • Accept change. Work at recovering from losses; make new friends. • Cultivate spiritual health. Cherish personal values. Make life meaningful. • Go outside for sunshine and fresh air as often as possible. • Be socially active – play bridge, join an exercise or dance group, take a class, teach a class, eat with friends, volunteer time to help others. • Stay interested in life – pursue a hobby, spend time with grandchildren, take a trip, read, grow a garden or go to the movies. • Enjoy life.
TABLE 17.6 Risk factors for malnutrition in older adults QUESTIONS THAT HELP DETERMINE THE RISK OF MALNUTRITION IN OLDER ADULTS Disease
Do you have an illness or condition that changes the types or amounts of foods you eat?
Eating poorly
Do you eat fewer than two meals a day? Do you eat fruits, vegetables and milk products daily?
Tooth loss or mouth pain
Is it difficult or painful to eat?
Economic hardship
Do you have enough money to buy the food you need?
Reduced social contact
Do you eat alone most of the time?
Multiple medications
Do you take three or more different prescribed or over-the-counter medications daily?
Involuntary weight loss or gain
Have you lost or gained 5 kilograms or more in the last six months?
Needs assistance
Are you physically able to shop, cook and feed yourself?
Elderly person
Are you older than 80?
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Older people spend more money per person on foods to eat at home than other age groups and less money on foods away from home. Food producers would be wise to cater to the preferences of older adults by providing good-tasting, nutritious (nutrient-dense) foods in easy-to-open, single-serving packages with labels that are easy to read. Such services enable older adults to maintain their independence and to feel a sense of control and involvement in their own lives. Another way older adults can take care of themselves is by remaining or becoming physically active. As mentioned earlier, physical activity helps preserve one’s ability to perform daily tasks and so promotes independence. Familiarity, taste and health beliefs are most influential on older people’s food choices. Eating foods that are familiar, especially ethnic foods that recall family meals and pleasant times, can be comforting. People aged 65 and over are less likely to adopt a diet to lose weight than younger people are, but they are more likely to diet in pursuit of medical goals such as controlling blood glucose and cholesterol.
Meals for singles Many older adults live alone, and singles of all ages face challenges in purchasing, storing and preparing food. Large packages of meat and vegetables are often intended for families of four or more, and even a head of lettuce can spoil before one person can use it all. Many singles live in small dwellings and have little storage space for foods. A limited income presents additional obstacles. This section offers suggestions that can help to solve some of the problems singles face, beginning with a special note about the dangers of food-borne illness.
Food-borne illness The risk of older adults getting a food-borne illness is greater than for other adults. The consequences of an upset stomach, diarrhoea, fever, vomiting, abdominal cramps and dehydration are often more severe, sometimes leading to paralysis, meningitis or even death. For these reasons, older adults need to carefully follow the food safety suggestions presented in Chapter 19.
People who have the means to shop and cook for themselves can cut their food bills simply by being wise shoppers. Large supermarkets are usually less expensive than convenience stores. A shopping list helps reduce impulse buying, and weekly specials can save money when the items featured are those that the shopper uses regularly. Buying the right amount so as not to waste any food is a challenge for people eating alone. They can buy fresh milk in the size best suited for personal needs. Many foods that offer a variety of nutrients for very little money have a long shelf life; staples such as rice, pastas, dry powdered milk and dried legumes can be purchased in bulk and stored for months at room Buy only what you will use. temperature. Other foods that are usually a good buy include whole pieces of cheese rather than sliced or shredded cheese, fresh produce in season and cereals that require cooking instead of ready-to-serve cereals. A person who has ample freezer space can buy large packages of meat, such as pork chops, minced meat or chicken, when they are on sale. Then the meat can be immediately wrapped into individual servings for the freezer. All the individual servings can be put in a bag marked appropriately with the contents and the date. Frozen vegetables can be more economical than fresh vegetables and just as nutritious. After the amount needed is taken, the bag can be closed tightly with a bag clip. If the package is returned immediately to the freezer each time, the vegetables will stay fresh until used.
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Spend wisely
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Finally, breads and cereals usually must be purchased in larger quantities. Again, the amount needed for a few days can be taken out and the rest stored in the freezer. Eggs can be purchased by the half-dozen. Eggs do keep for long periods, though, if stored properly in the refrigerator. Fresh fruits and vegetables can be purchased individually. A person can buy fresh fruit at various stages of ripeness: a ripe one to eat right away, a semi-ripe one to eat soon after, and a green one to ripen in the fruit bowl. If purchasing canned fruits, consider larger cans and place the remaining fruit in a plastic container in the fridge for the next day. This is more cost effective than buying small cans.
APPLICATIONS OF NUTRITIONAL RESEARCH Undernutrition in the elderly Undernutrition in housebound elderly people is a problem that has existed for some years. Research continues to highlight this problem, and provides some strategies in an attempt to reduce its impact. As a first step, nutrition screening has been promoted to indicate whether a more in-depth assessment of those at risk may be necessary. Nutritional supplementation has been shown to reduce mortality risk and improve weight status and a daily multivitamin may offer some benefit to better nutritional health outcomes. It is well understood that the prevalence of undernutrition in older people increases with increasing frailty and, if not treated, undernutrition becomes costly to the individual and society as a whole.
Be creative
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Creative cooks think of various ways to use foods when only large amounts are available. For example, a head of cauliflower can be divided into thirds. Then one-third is cooked and eaten hot. Another third is put into a vinegar and oil marinade for use in a salad. And the last third can be used in a casserole or stew. A variety of vegetables and meats can be enjoyed stir-fried; inexpensive vegetables such as cabbage, celery and onion are delicious when crisp cooked in a little oil with herbs or lemon added. Interesting frozen vegetable mixtures are available in larger supermarkets. Cooked, leftover vegetables can be dropped in at the last minute. A bonus of a stirfried meal is that there is only one pan to wash. Similarly, a microwave oven allows a cook to use fewer pots and pans. Meals and leftovers can also be frozen or refrigerated in microwavable containers to reheat as needed. Many frozen dinners offer nutritious options. Adding a fresh salad, a wholegrain roll and a glass of milk can make a nutritionally balanced meal. Also, single people shouldn’t hesitate to invite someone to share meals with them whenever there is enough food. It’s likely that the person will return the invitation, and both parties will get to enjoy companionship and a meal prepared by others.
Invite guests to share a meal.
REVIEW IT
Older people can benefit from both the nutrients provided and the social interaction available at shared meals. With creativity and careful shopping, those living alone can prepare nutritious, inexpensive meals. Physical activity, mental challenges, stress management and social activities can also help people grow old comfortably.
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 The majority of people’s life expectancy is determined by individual health-related behaviours. TRUE
While approximately 20 to 30 per cent of a person’s life expectancy is determined by genetics, it is thought that approximately 70 to 80 per cent is determined by individual health-related behaviours.
2 Older people are vulnerable to falls and immobility due to declining muscle mass and muscle strength. TRUE
There are many reasons an older person may have a fall but the greatest risk factor for this occurrence is the decline in muscle mass and strength.
3 Older people with a BMI up to 27 are more vulnerable to obesity-related diseases. FALSE
and mortality. However, obese older people still carry with them the risks associated with being obese.
4 People over the age of 70 who are institutionalised should receive a vitamin D supplement because of lack of sunshine. TRUE
Sunshine is the primary source of vitamin D and regular exposure is required to maintain appropriate levels and bone health. Older people who have little exposure to sunlight should have vitamin supplements.
5 Choline supplements are known to assist with memory and slow the progression of Alzheimer’s disease. FALSE
In fact the opposite appears to be true. Slightly overweight older people with a BMI up to 27 appear to be less vulnerable to morbidity
Although there is a decline in the activity of the enzyme that assists in the production of the neurotransmitter acetylcholine from choline and acetyl CoA (acetylcholine is essential to memory), supplements of choline have no effect on memory or on the progression of Alzheimer’s disease.
NUTRITION PORTFOLIO By eating a balanced diet, maintaining a healthy body weight and engaging in a variety of physical, social and mental activities, you can enjoy good health in later life. • Visit older adults in your community and consider whether they have the financial means, physical ability and social support they need to eat adequately.
• •
Note whether they have experienced an unintentional loss of weight recently. Discuss how they occupy their time physically, socially and mentally.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1
5
sarcopenia sacromyalgia sarcoidodis sarcophagus
6
a b c d
chronological age of 62 physiological age of 72 physiological age of 62 absolute age of minus 10
7
Inflamed stomach Vitamin B12 toxicity Constipation High-salt diet
On average, adult energy needs: a b c d
A 72-year-old person whose physical health is similar to that of people 10 years younger has a(n):
lose bone and fat and gain muscle lose bone and gain fat and muscle lose bone and muscle and gain fat lose bone, muscle and fat
Which characteristic is commonly associated with atrophic gastritis? a b c d
The process of losing muscle and gaining fat in ageing is known as: a b c d
3
48 to 60 years 58 to 70 years 79 to 85 years 78 to 90 years
In general, older people tend to: a b c d
Life expectancy in Australia is approximately: a b c d
2
4
decline 5 per cent per year after 50 decline 5 per cent per decade after 50 remain stable throughout life rise gradually throughout life
In older adults, poor dentition can lead to: a b c d
lower intakes of fibre and vitamins increased intakes of fruits and vegetables lower intakes of dairy foods increased intakes of meats
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Understanding nutrition
2
What are some of the physiological changes that occur in the body’s systems with ageing? To what extent can ageing be prevented? What are some strategies to delay or prevent ageing? (Section 17.1)
3
The swallowing changes that may occur in older adults are known as:
Why does the risk of dehydration increase as people age? What strategies would you suggest to reduce the risk of dehydration? (Section 17.3)
4
a b c d
What occurs with energy needs with advancing age? What about nutrient needs? What strategies would you suggest to ensure nutrient-dense foods are eaten while ensuring energy needs are met? (Section 17.3)
5
Which vitamins and minerals need special consideration for the elderly? Explain why. Identify some factors that complicate the task of setting nutrient standards for older adults. When would you recommend a nutrient supplement? (Section 17.3)
6
Investigate the relationships between nutrition and arthritis. Are there any nutrients that can assist in treatment of arthritis? (Section 17.4)
7
What characteristics contribute to malnutrition in older people? (Section 17.5)
8
Discuss the potential dietary relationship between Alzheimer’s and cardiovascular disease risk. Are there any nutrients that have been implicated in these disease states? (Section 17.4)
•
Get nutrition tips for growing older in good health from the Dietitians Association of Australia: http://www.daa.asn.au Learn more about cataracts and macular degeneration from Vision Australia and the Macular Degeneration Foundation: http://www.visionaustralia. org.au and http://www.mdfoundation.com.au Learn more about arthritis from Arthritis Australia: http://www.arthritisaustralia.com.au Find out about Australian Government programs designed to help senior citizens maintain good health: http://www.seniors.gov.au Explore issues regarding research and policy at the International Federation on Ageing website: http://www.ifa-fiv.org
The best dietary advice for a person with gout might be to: a b c d
9
avoid milk products take fish oil supplements take vitamin E supplements avoid foods containing purines
atrophy dysphagia sarcopenia edentulia
10 Three risk factors for malnutrition in the elderly are: a b c d
wealth, social activity and being over 65 disease, tooth loss and multiple medications education, work and travel being over 80, grandchildren and takeaway foods
Review questions 1
What roles does nutrition play in ageing? What roles can it play in maintaining health during ageing? Can nutrition prevent or delay age-related declines in cognition? (Section 17.1)
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Visit the Alzheimer’s Australia website: https://fightdementia.org.au/ • Visit the National Ageing Research Institute: https://www.nari.net.au/ • Visit the Department of Health and Ageing: http://www.health.gov.au • Visit the National Seniors Australia site: http://www.nationalseniors.com.au
•
• •
•
SEARCH ME! NUTRITION Keyword: ageing nutrition The article Barriers to effective nutritional care for older
adults explores nutritional issues as we age. What makes older people more at risk of nutritional deficiencies?
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Chapter 17: Life cycle nutrition: adulthood and the later years
17.6 NUTRIENT–DRUG INTERACTIONS People over the age of 65 are among the highest users of over-the-counter and prescription medications in Australia and New Zealand. The older a person is, the more likely they are to take more than one medication at a time. There is also higher use of non-vitamin–mineral supplements, such as glucosamine.1 Most often, these drugs and supplements are for heart disease, but they are also used to treat arthritis, respiratory problems and GI disorders. It is not uncommon for different doctors to have been seen for each condition, with different prescriptions received from each. To avoid harmful drug interactions, it’s important that all doctors and pharmacists are informed of the medicines being taken.2 These medicines enable people of all ages to enjoy better health, but they also bring side effects and risks. This Highlight focuses on some of the nutritionrelated consequences of medical drugs, both prescription drugs and non-prescription (over-the-counter) drugs. Highlight 7 describes the relationships between nutrition and the drug alcohol, and Highlight 18 presents information on herbal supplements and other alternative therapies.
The actions of drugs Most people think of drugs either as medicines that help them recover from illnesses or as illegal substances that lead to bodily harm and addiction. Actually, both uses of the term drug are correct because any substance that modifies one or more of the body’s functions is, technically, a drug. Even medical drugs have both desirable and undesirable consequences within the body. Consider aspirin. One action of aspirin is to limit the production of certain prostaglandins. Some prostaglandins help to produce fevers, some sensitise pain receptors, some cause contractions of the uterus, some stimulate digestive tract motility, some control nerve impulses, some regulate blood pressure, some promote blood clotting and some cause inflammation. By interfering with prostaglandin actions, aspirin reduces fever and inflammation, relieves pain and slows blood clotting, among other things. A person cannot use aspirin to produce one of its effects without producing all its other effects. Someone who is prone to strokes and heart attacks might take
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17
aspirin to prevent blood clotting, but it will also dull that person’s sense of pain. Another person who takes aspirin only for pain will also experience slow blood clotting. The anticlotting effect might be dangerous if it causes abnormal bleeding. A single two-tablet dose of aspirin doubles the bleeding time of wounds, an effect that lasts from four to seven hours. For this reason, doctors instruct clients to refrain from taking aspirin before surgery.
The interactions between drugs and nutrients Hundreds of drugs and nutrients interact, and these interactions can lead to nutrient imbalances or interfere with drug effectiveness.3 As more research is undertaken on drug therapies, more becomes known about drug– nutrient interactions. What was once considered safe may change with greater understanding. Adverse nutrient–drug interactions are most likely if drugs are taken over long periods, if several drugs are taken or if nutrition status is poor or deteriorating. Understandably, then, elderly people with chronic diseases are most vulnerable. Nutrients and medications may interact in many ways: • Drugs can alter food intake and the absorption, metabolism and excretion of nutrients. • Foods and nutrients can alter the absorption, metabolism and excretion of drugs. The following paragraphs describe these interactions, and Table H17.1 summarises this information and provides specific examples.
Drugs alter food intake Some medications can make eating difficult or unpleasant. Some induce nausea or vomiting, which diminishes the desire to eat. Some cause inflammation or lesions in the mouth, stomach or intestinal lining, resulting in pain or discomfort when food is eaten. Taste perceptions may change, leading to food aversions that may persist even after treatment has been discontinued. All of these complications limit food intake and can lead to weight loss and malnutrition if not resolved. Some medications, such as megestrol acetate, stimulate food intake and encourage weight gain. These medications may be prescribed in patients with debilitating diseases
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TABLE H 17.1 Examples of nutrient – drug interactions DRUGS MAY ALTER FOOD INTAKE BY: • altering the appetite (amphetamines suppress appetite; corticosteroids increase appetite) • interfering with taste or smell (amphetamines change taste perceptions) • inducing nausea or vomiting (digitalis may do both) • interfering with oral function (some antidepressants may cause dry mouth) • causing sores or inflammation in the mouth (methotrexate may cause painful mouth ulcers). DRUGS MAY ALTER NUTRIENT ABSORPTION BY: • changing the acidity of the digestive tract (e.g. antacids may interfere with iron and folate absorption) • damaging mucosal cells (e.g. cancer chemotherapy may damage mucosal cells) • binding to nutrients (e.g. bile acid binders bind to fat-soluble vitamins). FOODS AND NUTRIENTS MAY ALTER DRUG ABSORPTION BY: • stimulating secretion of gastric acid (e.g. the antifungal agent ketoconazole is absorbed better with meals due to increased acid secretion) • altering rate of gastric emptying (e.g. intestinal absorption of drugs may be delayed when they are taken with food) • binding to drugs (e.g. calcium binds to tetracycline, reducing drug and calcium absorption) • competing for absorption sites in the intestines (e.g. dietary amino acids interfere with levodopa absorption). DRUGS AND NUTRIENTS MAY INTERACT AND ALTER METABOLISM BY: • acting as structural analogues (as do warfarin and vitamin K) • using similar enzyme systems (e.g. phenobarbital induces liver enzymes that increase metabolism of folate, vitamin D and vitamin K) • competing for transport on plasma proteins (e.g. fatty acids and drugs may compete for the same sites on the plasma protein albumin) • increasing side effects of the drug (e.g. caffeine in beverages can increase adverse effects of stimulants) • increasing drug action to excessive levels (e.g. grapefruit components may block metabolism of some drugs and enhance those drugs’ actions and side effects). DRUGS MAY ALTER NUTRIENT EXCRETION BY: • altering reabsorption in the kidneys (e.g. some diuretics increase the excretion of sodium and potassium) • causing diarrhoea or vomiting (and diarrhoea and vomiting may cause electrolyte losses). FOODS MAY ALTER MEDICATION EXCRETION BY: • inducing activities of liver enzymes that metabolise drugs to allow their excretion (e.g. components of grilled meats increase metabolism of warfarin, theophylline and paracetamol).
such as cancer or AIDS. Unintentional weight gain may result from the use of some antipsychotics, antidepressants and corticosteroids (for example, prednisolone). People using these drugs do not feel satiated and sometimes gain 20 to 30 kilograms in just a few months. Medications prescribed for obesity intentionally suppress the appetite and promote weight loss. Examples include amphetamines and amphetamine-like compounds such as phentermine. When amphetamines are prescribed for other purposes, such as narcolepsy or attention deficit hyperactivity disorder, appetite suppression and weight loss may be unwanted side effects.
Drugs alter nutrient absorption Nutrient malabsorption is most likely to occur with medications that damage the intestinal mucosa.
Antineoplastic and antiretroviral drugs are especially detrimental; non-steroidal anti-inflammatory drugs (NSAIDs) and some antibiotics can have similar, though milder, effects. Some medications bind nutrients in the GI tract, preventing their absorption. For example, bile acid binders, used to reduce cholesterol levels, also bind to the fat-soluble vitamins A, D, E and K. Some antibiotics, notably tetracycline and ciprofloxacin, bind to the calcium in foods and supplements, which reduces the absorption of both the drug and the calcium. Other minerals, such as iron, magnesium and zinc, may also bind to antibiotics. For this reason, pharmacists advise consumers to use dairy products and all mineral supplements at least two hours apart from these medications.
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Chapter 17: Life cycle nutrition: adulthood and the later years
Medications, such as antacids, that reduce stomach acidity may interfere with the absorption of vitamin B12, folate and iron. Other drugs impede absorption by interfering with the intestinal metabolism or transport of nutrients into mucosal cells. For example, the antibiotics trimethoprim and pyrimethamine compete with folate for absorption into intestinal cells.
Diet alters drug absorption Most drugs are absorbed in the upper small intestine. Major influences on drug absorption include the stomach emptying rate, level of acidity and direct interactions with dietary components. The drug’s formulation also influences its absorption, and pharmacists often provide instructions advising whether food should be eaten or avoided when using a medication. Drugs reach the small intestine more quickly when the stomach is empty. Therefore, taking a medication with meals may delay its absorption, although the total amount absorbed may not be affected. For example, aspirin works faster when taken on an empty stomach, but taking it with food is often encouraged to minimise stomach irritation. Both nutrients and non-nutrients may bind to drugs and inhibit their absorption. For example, high-fibre diets may decrease the absorption of some tricyclic antidepressants. Phytates in foods can bind to digoxin, a drug prescribed for heart disease. As mentioned earlier, calcium and other minerals may bind to some antibiotics, reducing absorption of both the minerals and the drug.
Drugs alter nutrient metabolism Drugs and nutrients interact metabolically because they use many of the same enzyme systems in the small intestine and the liver. Drugs may enhance or inhibit the activities of enzymes that are needed for nutrient metabolism, and, conversely, dietary components may
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enhance or inhibit the activities of enzymes that break down drugs prior to excretion. These alterations may affect the availability of nutrients, the actions of medications in the body or various other physiological processes. To appreciate how nutrient–drug interactions can affect metabolism, consider medicines that resemble vitamins in structure. The drug methotrexate, used to treat cancer and inflammatory conditions, resembles folate in structure (see Figure H17.1) and competes with the enzyme that converts folate to its active form.* The adverse effects of using methotrexate therefore include symptoms of folate deficiency. These adverse effects can be reduced by prescribing a pre-activated form of folate (called leucovorin) along with methotrexate. Some foods affect the activities of enzymes that metabolise drugs or counteract the drugs’ effects in other ways. For example, compounds in grapefruit juice interfere with enzymes that metabolise a number of drugs, resulting in increased blood concentrations of the drugs, and consequently, stronger physiological effects.4 Table H17.2 gives examples of drugs that interact with grapefruit juice as well as some that are not affected. A number of dietary factors affect the activity of the anticoagulant drug warfarin. The most important interaction is with vitamin K, which is structurally similar to warfarin. Warfarin acts by blocking the enzyme that activates vitamin K, thereby preventing the synthesis of blood-clotting factors. The amount of warfarin prescribed is dependent, in part, on how much vitamin K is in the diet. If vitamin K consumption from foods or supplements were to increase dramatically, it could weaken the effect of the drug. Individuals using warfarin are advised to consume similar amounts of vitamin K daily to keep *Other folate antagonists include aminopterin, sulfasalazine, pyrimethamine, trimethoprim, triamterene, carbamazepine, phenytoin, phenobarbital and primidone.
FIGURE H17.1 Folate and methotrexate Methotrexate (a drug used in the treatment of cancer and rheumatoid arthritis) is structurally similar to the B vitamin folate. When this medication is used, it competes for the enzyme that normally activates folate, creating a secondary deficiency of folate. Notice the similarities in their chemical structures. N
H2N
N H
N
N
CH2 — N
O
COOH
C — NH — CH — CH2 — CH2 — COOH Folate
OH N
H2N
N CH3
N
N NH2
CH2 — N
O
COOH
C — NH — CH — CH2 — CH2 — COOH Methotrexate
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TABLE H17.2 Examples of grapefruit juice–drug interactions DRUG CATEGORY
DRUGS AFFECTED BY GRAPEFRUIT JUICE
DRUGS UNAFFECTED BY GRAPEFRUIT JUICE
Cardiovascular drugs
Felodipine Nicardipine Nifedipine Verapamil
Amlodipine Diltiazem Propafenone Quinidine
Cholesterol-lowering drugs
Atorvastatin Lovastatin Simvastatinx
Pravastatin
Central nervous system drugs
Buspirone Carbamazepine Diazepam Triazolam
Clomipramine Haloperidol
Anti-infective drugs
Saquinavir
Clarithromycin Itraconazole
Oestrogens
Ethinyl estradiol
17-ß-estradiol Acenocoumarol Warfarin
Anticoagulants Immunosuppressants
Cyclosporine Tacrolimus
Anti-asthmatic drugs
Prednisolone Theophylline
D. G. Bailey, M. O. Arnold and J. D. Spence, Inhibitors in the Diet: Grapefruit Juice-Drug Interactions, in R. H. Levy and coeditors, Metabolic Drug Interactions, Philadelphia: Lippincott Williams & Wilkins (2000): 661– 9.
warfarin activity stable. The dietary sources highest in vitamin K are green leafy vegetables.
Drugs alter nutrient excretion Some medications may interfere with the reabsorption of minerals by the kidneys, increasing urinary losses. For example, some diuretics accelerate the excretion of calcium, potassium and magnesium. Others may cause mineral retention instead. Risk of mineral depletion is highest if multiple drugs with the same effect are used, if kidney function is impaired or if medications are used for a long time. A number of drugs can increase excretion of vitamin B6. An example is isoniazid, an anti-tuberculosis drug that is similar in structure to vitamin B6. This drug induces excretion of vitamin B6 and therefore has the potential to create a vitamin B6 deficiency. Because the drug must be taken for at least six months to treat infection, vitamin B6 supplements are routinely given to prevent deficiency.
Diets alter drug excretion Nutrients may influence the reabsorption of drugs by the kidneys. For example, the amount of the medication lithium that is reabsorbed by the kidneys correlates with the amount of sodium reabsorbed. Consequently, dehydration or sodium depletion, which increase sodium reabsorption, may result in lithium retention. Similarly, a person with a high sodium intake will excrete more sodium in the urine and therefore more lithium. Individuals using lithium are advised to maintain a consistent sodium intake from day to day in order to maintain a stable blood level of lithium. Urine acidity can also affect medication excretion. The medication quinidine, used to treat arrhythmias, is excreted more readily in acidic urine. Foods or drugs that cause urine to become more alkaline (for example, sodium bicarbonate) may reduce quinidine excretion and raise blood levels.
Diet – drug toxicities Some interactions between foods and drugs can cause toxicity or exacerbate a drug’s side effects. The combination of tyramine, a compound in some foods, and monoamine oxidase (MAO) inhibitors, which treat depression and Parkinson’s disease, can be fatal. MAO inhibitors block an enzyme that normally inactivates tyramine, as well as the hormones adrenaline and noradrenaline. When people who take MAO inhibitors consume excessive tyramine, the increased tyramine in the blood can cause a sudden release of accumulated noradrenaline. This surge in noradrenaline results in severe headaches, rapid heartbeat and a dangerous increase in blood pressure. For this reason, people taking MAO inhibitors are advised to restrict their intakes of foods rich in tyramine. Tyramine occurs naturally in foods and is also formed when bacteria degrade the protein in foods. Thus, the tyramine content of a food usually increases when a food ages or spoils. Individuals at risk of tyramine toxicity are advised to buy mainly fresh foods and consume them promptly (see Table H17.3).
The inactive ingredients in drugs Besides the active ingredients, medicines may contain other substances such as sugar, sorbitol, lactose and sodium. For most people who use medicines on occasion and in small amounts, such ingredients pose no problem. When medicines are taken regularly or in large doses, however, people on special diets may need to be aware of these additional ingredients and their effects.
Sugar, sorbitol and lactose Many liquid preparations contain sugar or sorbitol to make them taste better. For people who must regulate their intakes
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Chapter 17: Life cycle nutrition: adulthood and the later years
TABLE H17.3 Foods restricted in a tyramine-controlled diet Beverages
Red wines including chianti; sherrya
Cheeses
Aged cheeses, Camembert, cheddar, Gouda, Gruyère, mozzarella, Parmesan, provolone, Romano, Roquefort, Stiltonb
Meats
Liver; dried, salted, smoked or pickled fish; sausage, salami; dried meats
Vegetables
Fava beans; Italian broad beans; sauerkraut; fermented pickles and olives
Other
Brewer’s yeast;c all aged and fermented products; soy sauce in large amounts; cheese-filled breads, salad dressings containing cheese
Note: The tyramine contents of foods vary from product to product depending on the methods used to prepare, process and store the food. In some cases, as little as 30 grams of cheese can cause a severe hypertensive reaction in people taking monoamine oxidase (MAO) inhibitors. In general, the following foods contain small enough amounts of tyramine that they can be consumed in small quantities: ripe avocado, banana, yoghurt, sour cream, acidophilus milk, buttermilk, raspberries and peanuts. a Most wine and beer can be consumed in small quantities. Unfermented cheeses, such as ricotta, cottage cheese and cream cheese, are allowed.
b
c
Products made with baker’s yeast are allowed.
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of carbohydrates, such as people with diabetes, the amount of sugar in these medicines may need to be considered. Large doses of liquids containing sorbitol may cause diarrhoea. The lactose added as filler to some medications may cause problems for people who are lactose intolerant.
Sodium Antibiotics and antacids often contain sodium. People who take Alka Seltzer, for example, may not realise that a single two-tablet dose may exceed their recommended sodium intake for a whole day. In addition, antacids neutralise stomach acid, and many nutrients depend on acid for their digestion. Taking any antacid regularly will reduce the absorption of many nutrients. Nutrient interactions and risks are not unique to prescription drugs. People who buy over-the-counter medications also need to protect themselves. The increasing availability of over-the-counter medications allows people to treat themselves for many ailments from arthritis to yeast infections. Consumers need to ask their doctors about potential interactions and check with their pharmacists for instructions about taking drugs with foods. If problems arise, they should seek professional care without delay.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A What could be done to minimise the risks associated with nutrient–drug interactions?
including possible nutrient–drug interactions. Unfortunately, few people take the time to carefully read and follow these instructions. How might you improve patient education and compliance with these instructions?
B Drug packaging commonly includes an oversized sheet of paper with small writing that includes a description of the many possible side effects,
REFERENCES CHAPTER 1 2
3 4
5
Australian Bureau of Statistics, Australian Demographic Statistics, ABS Catalogue Number 3101.0, Canberra: ABS (2014). New Zealand Government, Statistics New Zealand at http://www. stats.govt.nz/ (licensed by Statistics NZ for re-use under the Creative Commons Attribution 4.0 International licence). Australian Bureau of Statistics, Australian Demographic Statistics, June 2017 (2017), cat. No. 3101.0 Statistics New Zealand & The Ministry of Foreign Affairs and Trade, New Zealand in profile 2012: An overview of New Zealand’s people, economy and environment (2012). Australian Institute of Health and Welfare. Mortality over the twentieth century in Australia: trends and patterns in major causes of death.
6
7
8
Mortality Surveillance Series no. 4. AIHW cat. no. PHE73. Canberra: AIHW (2005). R. D. Pollock and coauthors, An investigation into the relationship between age and physiological function in highly active older adults, Journal of Physiology 593 (2015): 657–80. A. Yuki and co-authors, Relationship between physical activity and brain atrophy progression, Medicine and Science in Sports and Exercise 44 (2012): 2362–8. L. Krist, F. Dimeo and T. Keil, Can progressive resistance training twice a week improve mobility, muscle strength, and quality of life in very elderly nursing-home residents with impaired mobility? A pilot study, Clinical Interventions in Aging 8 (2013): 443–8.
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11
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18 19
20
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L. Fontana and L. Partridge, Promoting health and longevity through diet: From model organisms to humans, Cell 161 (2015): 106–18. S. Brandhorst and coauthors, A periodic diet that mimics fasting promotes multi-system regeneration, enhanced cognitive performance, and health-span, Cell Metabolism 22 (2015): 86–99. S. Bo and co-authors, Predictive role of the Mediterranean diet on mortality in individuals at low cardiovascular risk: a 12-year follow-up population-based cohort study, Journal of Translational Medicine 14:91 (2016). R. Aversa and co-authors, One can slow down the aging through antioxidants, American Journal of Engineering and Applied Sciences 9 (4) (2016). E. M. Mathus-Vliegen and co-authors, Prevalence, pathophysiology, health consequences and treatment options of obesity in the elderly: a guideline, Obesity Facts 5 (2012): 460–83. D. G. Candow and co-authors, Effect of nutritional interventions and resistance exercise on aging muscle mass and strength, Biogerontology 13 (2012): 345–58. H. J. Denison and co-authors, Prevention and optimal management of sarcopenia: a review of combined exercise and nutrition interventions to improve muscle outcomes in older people, Clinical Interventions in Aging 11 (2015): doi: 10.2147/CIA.S55842. eCollection 2015. Position of the Academy of Nutrition and Dietetics: Food and Nutrition for older adults—Promoting health and wellness, Journal of the Academy of Nutrition and Dietetics 112 (2012): 1255–77. K. Riches and co-authors, The prevalence of malnutrition in elderly residents in a warden-assisted setting compared with a home-living environment, British Journal of Community Nursing 19(7) (2014): doi: 10.12968/bjcn.2014.19.7.324. R. Mullur and co-authors, Thyroid hormone regulation of metabolism, Physiological Reviews 94(2) (2015): 355–82. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). M. De la Calle, M. L. Palomo and C. Fernández-Miranda, Hyperhomocysteinemia due to vitamin B(12) deficiency after bariatric surgery, Medicina Clinica (Barc) 140 (2012): 188–9. I. H de Boer and co-authors, Serum 25-hydroxyvitamin D concentration and risk for major clinical disease events in a community-based population of older adults: a cohort study, Annals of Internal Medicne 156 (2012): 627–34. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient Reference Values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). B. Tang and co-authors, Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis, Lancet 370 (2007): 657–66. C. Franceschi and J. Campisi, Chronic inflammation (inflammaging) and its potential contribution to age-associated diseases, Journal of Gerontology Series A: Biological Sciences and Medical Sciences 69(S1) (2014) S4–S9 doi:10.1093/gerona/glu057
25 K. A. Weikel and co-authors, Nutritional modulation of cataract, Nutrition Reviews 72 (2014): 30–47. 26 R. Hayashi and co-authors, Effects of antioxidant supplementation on mRNA expression of glucose-6-phosphate dehydrogenase, ß-actin and 18S rRNA in the anterior capsule of the lens in cataract patients, Experimental Eye Research 96 (2012): 48–54. 27 J. R. Evans and J. G. Lawrenson, Antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration, Cochrane Database of Systematic Reviews 11 (2012): CD000254. 28 K. R. Vincent and H. K. Vincent, Resistance exercise for knee osteoarthritis, Journal of Injury, Function, and Rehabilitation 4 (2012): S45–S52. 29 I. B. McInnes and G. Schett, Pathogenetic insights from the treatment of rheumatoid arthritis, The Lancet 389 (2017): 2328–37. 30 R. L. Ragle and A. D. Sawitzke, Nutraceuticals in the management of osteoarthritis: a critical review, Nutrition Reviews 29 (2012): 717–31. 31 D. Khanna and co-authors, 2012 American College of Rheumatology guidelines for management of gout, Arthritis Care Research 64 (2012):1431–46. 32 N. Kanzaki and co-authors, Effect of a dietary supplement containing glucosamine hydrochloride, chondroitin sulfate and quercetin glycosides on symptomatic knee osteoarthritis: A randomized, doubleblind, placebo-controlled study, Journal of the Science of Food and Agriculture 92 (2012): 862–69. doi: 10.1002/jsfa.4660 33 J. G. Walker and co-authors, Oral folic acid and vitamin B–12 supplementation to prevent cognitive decline in community-dwelling older adults with depressive symptoms—The Beyond Ageing Project: a randomized controlled trial, American Journal of Clinical Nutrition 95 (2012): 194–203. 34 National Institute on Aging, Alzheimer’s disease fact sheet, www.nia. nih.gov/alzheimers, August 18, 2016. 35 M. T. Heneka and coauthors, Neuroinflammation in Alzheimer’s disease, Lancet: Neurology 14 (2015): 388–405. 36 M. J. McGuire and M. Ishii, Leptin dysfunction and Alzheimer’s disease: Evidence from cellular, animal, and human studies, Cellular and Molecular Neurobiology 36 (2016): 203–17 37 H. N. Yassine and coauthors, Association of serum docosahexaenoic acid with cerebral amyloidosis, JAMA Neurology 73 (2016): 1208–16. 38 A. J. Hanson and coauthors, Effect of apolipoprotein E genotype and diet on apolipoprotein E lipidation and amyloid peptides, JAMA Neurology 70 (2013): 972–80. 39 N. E. Edwards and A. M. Beck, The influence of aquariums on weight in individuals with dementia, Alzheimer Disease and Associated Disorders 27 (2013): 379–83. 40 M. W. Dysken and co-authors, Effect of vitamin E and memantine on functional decline in Alzheimer disease, Journal of the American Medical Association 311 (2014): 33–44. 41 K. B. Randström, K. Asplund and M. Svedlund, Impact of environmental factors in home rehabilitation – a qualitative study from the perspective of older persons using the International Classification of Functioning, Disability and Health to describe facilitators and barriers, Disability and Rehabilitation 34 (2012): 779–87.
HIGHLIGHT 1 2
American Society of Consultant Pharmacists, ASCP Fact sheet, https://www.ascp.com/articles/about-ascp/ascp-fact-sheet L. E. Hines and J. E. Murphy, Potentially harmful drug-drug interactions in the elderly: a review, American Journal of Geriatric Pharmacotherapy 9 (2011): 364–77.
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J. K. Anderson and J. R. Fox, Potential food-drug interactions in longterm care, Journal of Gerontological Nursing 38 (2012): 38–46. doi: 10.3928/00989134-20120307-04. Epub 2012 Mar 14. A. Messer and co-authors, Major furocoumarins in grapefruit juice I: Levels and urinary metabolite(s), Food and Chemical Toxicology 49 (2011): 3224–31.
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CHAPTER
18
DIET-RELATED DISEASE Nutrition in your life
No doubt you are familiar with the following recommendations: Eat more vegies. Eat more fibre. Eat more fish. Don’t add salt. Limit the fat. Be active. Don’t smoke. Don’t drink too much alcohol. What’s the deal? If you follow this advice, will it really make a difference in how well or how long you live? In a word, yes. You can bet your life on it. If you could grow old in good health without having a heart attack or stroke, or getting diabetes, hypertension or cancer, wouldn’t you be willing to do just about anything – including improving your diet and activity habits? Of course, you would. And you can start today. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F Two of the top three causes of death in Australia and New Zealand have a relationship
with diet.
T F Eicosanoids are often the cause of heart attack and stroke. T F Limiting the intake of foods that contain salt is one of the best ways to prevent and treat
hypertension
T F People with diabetes may have insufficient insulin or ineffective insulin. T F Diets high in red meat cause cancer.
LEARNING OBJECTIVES 18.1 Identify factors that protect people from the spread of infectious diseases and describe the role of nutrition in immunity. 18.2 List the leading nutrition-related causes of death in Australia and New Zealand. 18.3 Describe how atherosclerosis develops and strategies to lower blood cholesterol levels. 18.4 Present strategies to lower blood pressure. 18.5 Compare the dietary strategies to manage type 1 diabetes with those to prevent and treat type 2 diabetes.
18.6 Differentiate among cancer initiators, promoters and anti-promoters and describe how nutrients or foods might play a role in each category. 18.7 Summarise dietary recommendations to prevent chronic diseases. 18.8 Present arguments for and against the use of complementary and alternative medicine.
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Other lifestyle factors that contribute to the development of chronic diseases are: • physical inactivity • overweight • tobacco use • alcohol and drug use.
Much of this text has described how good nutrition supports good health. This chapter examines some of the relationships between nutrition and disease – exploring how poor nutrition may promote the progression of diseases and how good nutrition may guard against the development of diseases. The bulk of this chapter focuses on the chronic diseases that pose the greatest threat to the lives of most people in industrialised countries, but it begins with a description of the immune system and its inflammatory response. As you will see, inflammation underlies the development of many chronic diseases. Chronic diseases develop over a lifetime as a result of metabolic abnormalities induced by such factors as genetics, age, gender, and lifestyle. As you have learned, diet is among the many lifestyle factors that influence the development of chronic diseases.1 In their efforts to prevent and treat chronic diseases, many people in Australia and New Zealand turn to complementary and alternative medicines – which includes products such as herbs and practices such as acupuncture. Because complementary and alternative approaches range from useful folk medicine to dangerous frauds, consumers need to become informed about the products and practices they are considering and discuss their decisions with their healthcare providers. Highlight 18 explores the usefulness and safety of complementary and alternative medicine and its role in improving health care.
18.1 Nutrition and infectious diseases
Infectious diseases such as smallpox once claimed the lives of many children and limited the average life expectancy of adults. Thanks to medical science’s ability to identify diseasecausing microorganisms and develop preventive strategies, most people now live well into their later years, with the average life expectancy far exceeding that of our ancestors. In industrialised nations, purification of water and safe handling of foods help prevent the spread of infection. Antibiotics and immunisations provide additional protection for individuals. Despite these advances, some infectious diseases still endanger many lives today: different strains of the influenza virus and disease strains such as tuberculosis and some food-borne infections that have become resistant to antibiotics.2 Although government security and public health measures such as emergency preparedness, safe food and water supplies, and medical care do much to contain infectious diseases, people are exposed to millions of microbes each day. Nutrition cannot directly prevent or cure infectious diseases, but good nutrition can strengthen the body’s defences against them. This chapter begins with a description of the immune system and the relationships between nutrition and infectious diseases, but most of the chapter focuses on the chronic diseases that pose the greatest threat to the lives of most people in industrialised countries. It is difficult to know exactly where infectious diseases fall among the leading causes of death. Compared with chronic diseases, infectious diseases pose a much greater challenge for public health officials who track disease prevalence. One doctor might classify an ear infection as an infectious disease, whereas another calls it a disease of the ear. Trends change quickly as well. A disease, such as AIDS, which did not even exist until the early 1980s, may suddenly appear and become one of the leading causes of death. A preventive strategy, such as food irradiation, may just as quickly eliminate hundreds of thousands of cases of foodborne infections each year. Public health strategies help the entire country defend against the spread of infection, and each individual’s immune system provides a personal line of defence. A strong immune system depends on adequate nutrition. Poor nutrition weakens the immune system, which increases susceptibility to infections.
The immune system The immune system defends the body so diligently and silently that people do not even notice the thousands of enemy attacks mounted against them every day. If the immune system fails, though, the body suddenly becomes vulnerable to every disease-causing agent that comes its way. Infectious disease invariably follows.
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Chapter 18: Diet-related disease
The body’s first lines of defence against foreign substances – the skin, mucous membranes and gastrointestinal (GI) tract – normally deter invaders. If an invader penetrates these barriers and gains entry into the body, then the organs and cells of the immune system race into action. Foreign substances that elicit such a response are called antigens. Examples are bacteria, viruses, toxins and food proteins that cause allergies. Of the 100 trillion cells that make up the human body, one in every 100 is a white blood cell. Two types of white blood cells, the phagocytes and lymphocytes, defend the body against infectious diseases. There are two distinct types of lymphocytes: B-cells and T-cells.
Phagocytes
Phagocytes, the scavengers of the immune system, are the first to arrive at the scene if an invader, such as a microorganism, gains entry. Upon recognising the foreign invader, the phagocyte engulfs and digests it, if possible, in a process called phagocytosis. Phagocytes also secrete special proteins called cytokines that activate the metabolic and immune responses to infection.
Lymphocytes: B-cells
B-cells respond to infection by rapidly dividing and producing large proteins known as antibodies. Antibodies travel in the bloodstream to the site of the infection. There they stick to the surfaces of the foreign particles and kill or otherwise inactivate them, making the foreign particles easy for the phagocytes to ingest. The antibodies are members of a class of proteins known as immunoglobulins – literally, large globular proteins that produce immunity. Antibodies react selectively to a specific foreign organism, and the B-cells retain a memory of how to make them. Consequently, the immune system can respond with greater speed the next time it encounters the same foreign organism. B-cells play a major role in resistance to infection.
Lymphocytes: T-cells
The T-cells travel directly to the invasion site to battle the invaders. T-cells recognise the antigens displayed on the surfaces of phagocyte cells and multiply in response. Then they release powerful chemicals to destroy all the foreign particles that have this antigen on their surfaces. As the T-cells begin to win the battle against infection, they release signals to slow down the immune response. Unlike the phagocytes, which are capable of inactivating many different types of invaders, T-cells are highly specific. Each T-cell can attack only one type of antigen. This specificity is remarkable, for nature creates millions of antigens. After destroying a particular antigen, some T-cells retain the necessary information to serve as memory cells so that the immune system can rapidly produce the same type of T-cells again if the identical infection recurs. T-cells actively defend the body against fungi, viruses, parasites and a few types of bacteria; they can also destroy cancer cells. In organ transplant patients, T-cells participate in the rejection of newly transplanted tissues, which is why doctors prescribe immunosuppressive drugs following such surgery.
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Reminder: Antigens are substances that elicit the formation of antibodies or an inflammation reaction from the immune system. Organs of the immune system are: • spleen • lymph nodes • thymus. Cells of the immune system are: • phagocytes: • neutrophils • macrophages • lymphocytes: – B-cells – T-cells. Two types of immune system cells ingest and destroy foreign antigens by phagocytosis: neutrophils and macrophages. Reminder: Antibodies are large proteins of the blood and body fluids, produced by the immune system in response to the invasion of the body by foreign molecules (usually proteins called antigens). Antibodies combine with and inactivate the foreign invaders, thus protecting the body.
Nutrition and immunity Of all the body’s systems, the immune system responds most sensitively to subtle changes in nutrition status. Malnutrition compromises immunity. Impaired immunity opens the way for infectious diseases, which typically raise nutrient needs and lower food intake. Consequently, nutrition status suffers further. Thus, disease and malnutrition create a synergistic downward spiral that must be broken for recovery to occur (see Figure 18.1).
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FIGURE 18.1 Nutrition and immunity Regardless of where a person enters the spiral, malnutrition, illness and weakened immunity interact to compromise recovery and worsen malnutrition.
u Maln
on triti
Impaired immunity is a hallmark of protein–energy malnutrition (PEM). Table 18.1 presents the effects of PEM on the body’s defences. As Chapter 6 explained, without sufficient protein to make antibodies, the immune system loses its ability to fight infections. Deficiencies of vitamins and minerals also diminish the immune response, as may excesses. Likewise, interactions between nutrients may enhance or impair immunity. Quite simply, optimal immunity depends on optimal nutrition – enough, but not too much, of each of the nutrients. People with weakened immune systems, such as the elderly, may benefit from a nutritious diet and supplements of selected nutrients.
TABLE 18.1 Effects of protein–energy malnutrition (PEM) on the body’s defence systems
s es lln i d an
BODY’S DEFENCE SYSTEM Skin
ism bol eta petite m ed p Alter s of a los
Thinned, with less connective tissue to serve as a barrier to protect underlying tissues; delayed skin sensitivity reaction to antigens
d an
Digestive tract and other body linings Antibody secretions and immune cell number reduced Lymph tissuesa
Immune system organs reduced in size; cells of immune defence depleted
General response
Invader kill-time prolonged; circulating immune cells reduced; antibody response impaired
s
tu sta
ne
Lymph tissues include the thymus gland, lymph nodes and spleen.
a
ty ni mu m di
s es lln
tio ra s o i r u te at de n st r o the iti u r n u tr f
Public health measures such as the purification of water and safe handling of food help prevent the spread of infection in industrialised nations, and immunisations and antibiotics protect individuals. Nevertheless, some infectious diseases still endanger people today. Nutrition cannot prevent or cure infectious diseases, but adequate intakes of all the nutrients can help support the immune system as the body defends against disease-causing agents. If the immune system is impaired because of malnutrition, a person becomes vulnerable to infectious disease.
o
F
i ed se n Wor
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ke Wea
n itio u tr
n
Im
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EFFECTS OF PEM
18.2 Nutrition and chronic diseases
Nutrients known to affect immunity are: • protein • fatty acids • vitamin A • vitamin E • vitamin B6 • folate • vitamin C • iron • zinc • selenium.
Figure 18.2 shows the seven leading causes of death in Australia.3 Four of these causes, including two of the top three, have some relationship with diet. Worldwide, statistics are similar, with developing nations sharing many of the same chronic diseases as industrialised nations.4 This chapter explains how the major chronic diseases develop and summarises their major links with nutrition. Earlier chapters that described the connections between individual nutrients and diseases may have left the mistaken impression of ‘one disease – one nutrient’ relationships. Indeed, valid links do exist between saturated fat and heart disease, calcium and osteoporosis, and antioxidant nutrients and cancer, but focusing only on these links oversimplifies the story. In reality, each nutrient may have connections with several diseases because its role in the body is not specific to a disease, but to a body function. Furthermore, each of the chronic diseases develops in response to multiple risk factors, including many non-dietary factors such as genetics, physical inactivity and smoking. This chapter presents an integrated and balanced approach to disease prevention, paying careful attention to all of the factors involved. Figure 18.3 illustrates some of the relationships between risk factors and chronic diseases.
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FIGURE 18.2 The seven leading causes of death in Australia Many deaths have multiple causes, but diet influences the development of several chronic diseases – notably, ischaemic heart disease, cerebrovascular disease, diabetes and some types of cancer. Key:
Ischaemic heart disease
Diet-related
Dementia and Alzheimer’s disease
Other causes
Cerebrovascular disease Trachea, bronchus and lung cancer Chronic lower respiratory diseases Diabetes Colon, sigmoid and anus cancer 0
10
20 30 Deaths in 2016 (000s)
40
50
Notice how many of the diseases listed in Figure 18.3 have a genetic component. A family history of a certain disease is a powerful indicator of a person’s tendency to contract that disease. Still, lifestyle factors are often pivotal in determining whether that tendency will be expressed. Genetics and lifestyle often work synergistically; for instance, cigarette smoking is
PUTTING COMMON SENSE TO THE TEST
Two of the top three causes of death in Australia and New Zealand have a relationship with diet.
FIGURE 18.3 Risk factors and chronic diseases OTHER RISK FACTORS
TRUE
Chronic diseases
Die
t hi
Exc gh in fat, ess Low ive a satur at com lcoh ol i ed fat ple Low nta and x c v k arb /or Hig itami ohy e tra na ns dra hs n fat u t d e gar /fib /or Hig re i inta min h in nta ke tak era eo l in ke f sa tak lty e or Ge pic net kle ics d fo Age ods Sed ent Sm ary l ifes oki Str ng an tyle ess d to bac En co viro use nm ent al c ont am ina nts
DIET RISK FACTORS
Cancers Hypertension Diabetes (type 2) Osteoporosis Atherosclerosis Obesity Stroke Diverticulosis Dental and oral disease
This chart shows that the same risk factor can affect many chronic diseases. Notice, for example, how many diseases have been linked to a sedentary lifestyle. The chart also shows that a particular disease, such as atherosclerosis, may have several risk factors.
Some cancers
Atherosclerosis
Hypertension
Obesity
Gall bladder disease
Stroke and heart attack
Diabetes
This flow chart shows that many of these conditions are themselves risk factors for other chronic diseases. For example, a person with diabetes is likely to develop atherosclerosis and hypertension. These two conditions, in turn, worsen each other and may cause a stroke or heart attack. Notice how all of these chronic diseases are linked to obesity.
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© 2001 PhotoDisc, Inc.
especially likely to bring on heart disease in people who are genetically predisposed to develop it. Not smoking would benefit everyone’s health, of course, regardless of genetic predisposition, but some recommendations to prevent chronic diseases best meet an individual’s needs when family history is considered. For example, women with a family history of breast cancer might reduce their risks if they abstain from alcohol, whereas those with a family history of heart disease might benefit from one or two glasses of wine a week.
Cardiovascular disease (CVD) is a general term for all diseases of the heart and blood vessels. Reminder: Atherosclerosis is a type of artery disease characterised by plaques along the inner walls of the arteries. Plaque associated with atherosclerosis is known as atheromatous plaque. Plaques are mounds of lipid material mixed with smooth muscle cells and calcium that develop in the artery walls in atherosclerosis. Reminder: Inflammation is an immunological response to cellular injury characterised by an increase in white blood cells, redness, heat, pain, swelling and often loss of function of the affected body part. Macrophages are large, phagocytic cells of the immune system. • macro 5 large • phagein 5 to eat
REVIEW IT
Vegetables rich in fibre, phytochemicals and the antioxidant nutrients (betacarotene, vitamin C and vitamin E) help to protect against chronic diseases.
Heart disease and cerebrovascular disease are two of the three leading causes of death in Australia and New Zealand, with diabetes also ranking in the top six. All three of these chronic diseases have significant links to nutrition, although other lifestyle risk factors and genetics are also important.
The major causes of death around the world today are diseases of the heart and blood vessels, collectively known as cardiovascular disease (CVD). Across Australia and New Zealand, CVD claims the lives of around 40 000 people each year.5 Coronary heart disease (CHD) is the most common form of cardiovascular disease and is usually caused by atherosclerosis in the coronary arteries that supply blood to the heart muscle. Atherosclerosis is the accumulation of lipids and other materials in the arteries.
How atherosclerosis develops As Highlight 16 points out, no one is free of the fatty streaks that may one day become the plaques of atherosclerosis. For most adults, the question is not whether you have plaques, but how advanced they are and what you can do to slow or reverse their progression. Atherosclerosis, or ‘hardening of the arteries’, usually begins with the accumulation of soft fatty streaks along the inner arterial walls, especially at branch points (see Figure H16.1 on page 595). These fatty streaks gradually enlarge and harden as they fill with cholesterol, other lipids and calcium, and they become encased in fibrous connective tissue, forming plaques. Plaques stiffen the arteries and narrow the passages through them. Most people have well-developed plaques by the age of 30. A diet high in saturated fat is a major contributor to the development of plaques and the progression of atherosclerosis (see Chapter 5). But atherosclerosis is much more than the simple accumulation of lipids within the artery wall – it is a complex inflammatory response to tissue damage. Indeed, extensive evidence confirms that inflammation is centrally involved in all stages of atherosclerosis.6
Inflammation The cells lining the blood vessels may incur damage from high LDL cholesterol, hypertension, toxins from cigarette smoking, elevated homocysteine, or some viral and bacterial infections. Such damage increases the permeability of the blood vessel walls and elicits an inflammatory response. The immune system sends in macrophages, and the smooth muscle cells of the artery wall try to repair the damage. Particles of LDL cholesterol become trapped in the blood vessel walls. Free radicals produced during inflammatory responses oxidise the LDL cholesterol, and the macrophages engulf it. Once engulfed, the macrophages are known as foam cells. These swell with large quantities of oxidised LDL cholesterol and eventually become the cells of plaque. Arterial damage and the inflammatory response also favour the formation of blood clots and allow minerals to harden plaque and form the fibrous connective tissue that encapsulates it.
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18.3 Cardiovascular disease
The inflammatory response of atherosclerosis weakens the walls of the arteries and may cause an aneurysm – the abnormal bulging of a blood vessel wall. Aneurysms can rupture and lead to massive bleeding and death, particularly when a large blood vessel such as the aorta is affected. The central role of the inflammatory response in atherosclerosis has led researchers to look for signs or markers of inflammation in the blood vessel walls and while there isn’t a good plasma marker for ischaemia, one of the most promising of these markers is a protein known as C-reactive protein (CRP). High levels of CRP have proved to more accurately predict future heart attack than high LDL cholesterol, which has a strong relationship with atherosclerosis, as a later section explains.
Plaques Once plaques have formed, a sudden spasm or surge in blood pressure in an artery can tear away part of the fibrous coat covering a plaque, causing it to rupture. Some types of plaque are more unstable than others and are therefore more vulnerable to rupture.7 Such plaques have a thin fibrous cap, a large lipid core and an abundance of macrophages – characteristics that undermine plaque stability.8 Researchers now know that the composition of a plaque rather than the size of a plaque (and how much arterial blockage it causes) is a key predictor of plaque rupture and subsequent clot formation.9 When plaque ruptures, the body responds to the damage as it would to other tissue injuries.
Blood clots
Platelets are tiny disc-shaped bodies that cover an injured or damaged area and, along with other factors, form a clot. Abnormal blood clotting can trigger life-threatening events. For example, a blood clot may gradually grow large enough to restrict or close off a blood vessel (thrombosis). A clot may also break free from an artery wall and travel through the circulatory system until it lodges in a small artery and suddenly shuts off flow to the tissues (embolism). The action of platelets is under the control of certain eicosanoids, known as prostaglandins and thromboxanes, which are made from the 20-carbon omega-6 and omega-3 fatty acids (introduced in Chapter 5). Each eicosanoid plays a specific role in helping to regulate many of the body’s activities. Sometimes their actions oppose each other. For example, one eicosanoid prevents clot formation and another promotes it. Similarly, one dilates the blood vessels and another constricts them. When omega-3 fatty acids are abundant in the diet, they make more of the kinds of eicosanoids that favour heart health.10
Blood pressure and atherosclerosis The heart must create enough pressure to push blood through the circulatory system. When arteries are narrowed by plaques, clots or both, blood flow is restricted, and the heart must then generate more pressure to deliver blood to the tissues. This higher blood pressure further damages the artery walls, and plaques and clots are especially likely to form at damage points. Thus, the development of atherosclerosis is a self-accelerating process. (A later section describes additional consequences of high blood pressure.)
A coronary thrombosis blocks blood flow through an artery that feeds the heart muscle. A cerebral thrombosis blocks blood flow through an artery that feeds the brain. Eicosanoids help to regulate: • blood pressure • blood clot formation • blood vessel contractions • immune response • nerve impulse transmissions. Major sources of omega-3 fatty acids are: • vegetable oils (canola, olive, soybean, flaxseed) • walnuts, flaxseeds • fatty fish (mackerel, salmon, sardines).
The result: heart attacks and strokes When atherosclerosis in the coronary arteries becomes severe enough to restrict blood flow and deprive the heart muscle of oxygen, CHD develops. The person with CHD often experiences pain and pressure in the area around the heart (angina). If blood flow to the heart is cut off and that area of the heart muscle dies, a heart attack results. Restricted blood flow to the brain causes a transient ischaemic attack (TIA) or stroke. CHD and strokes are the first and third leading causes of death, respectively, for adults in Australia and New Zealand.
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PUTTING COMMON SENSE TO THE TEST
Eicosanoids are often the cause of heart attack and stroke. FALSE
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Risk factors for coronary heart disease Some risk factors, such as diet and physical activity, are modifiable, meaning that they can be changed; others, such as genetics, age and gender, cannot be changed.
Although atherosclerosis can develop in any blood vessel, the coronary arteries are most often affected, leading to CHD. Table 18.2 lists the major risk factors for CHD. The criteria for defining blood lipids, blood pressure and obesity in relation to CHD risk are shown in Table 18.3. By middle age, most adults have at least one risk factor for CHD, and many have more than one.
TABLE 18.2 Major risk factors for CHD MAJOR RISK FACTORS FOR CHD (NOT MODIFIABLE) • Increasing age • Male gender • Family history of premature heart disease MAJOR RISK FACTORS FOR CHD (MODIFIABLE) • High blood LDL cholesterol • Low blood HDL cholesterol • High blood pressure (hypertension) • Diabetes • Obesity (especially abdominal obesity) • Physical inactivity • Cigarette smoking • An ‘atherogenic’ diet (high in saturated fats and low in vegetables, fruits, nuts and whole grains) NOTE: Risk factors highlighted in colour have relationships with diet. D. Mozaffarian and coauthors, Heart disease and stroke statistics – 2016 update: A report from the American Heart Association, Circulation 133 (2016): e38–e360.
TABLE 18.3 Lipid, weight and blood pressure criteria to reduce CHD risk RISK FACTORS Total blood cholesterol (mmol/L) LDL cholesterol (mmol/L) HDL cholesterol (mmol/L)
DESIRABLE ,4.0 ,1.8 (,2 in New Zeland) $1
Triglycerides, fasting (mmol/L)
,2 (,1.7 in New Zealand)
Body mass index (BMI; kg/m2)
18.5 – 24.9
Blood pressure (systolic and/or diastolic pressure; mmHg)
,120/,80
Adapted from Reducing Risk in Heart Disease. An Expert Guide to Clinical Practice for Secondary Prevention of Coronary Heart Disease, Heart Foundation Australia (2012); Heart Foundation New Zealand, http://www.heartfoundation.org.nz
Age, gender and family history
Table 18.2 shows that three of the major risk factors for CHD cannot be modified by diet or any other means: age, gender and family history. As men and women grow older, the risk of CHD rises. The increasing risk of CHD with advancing age reflects the steady progression of atherosclerosis.11 On average, older people have more atherosclerosis than younger people do. In men, ageing becomes a significant risk factor at age 45 years or older. CHD occurs about 10 to 15 years later in women than in men. Women younger than 45 years tend to have lower LDL cholesterol than men of the same age, but women’s blood cholesterol typically begins to rise between ages 45 and 55 years. Thus, ageing becomes a significant risk factor for women
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who are 55 years or older. The gender difference has been attributed to a protective effect of oestrogen in women, but CHD rates do not suddenly accelerate at menopause as naturally occurring oestrogen levels taper off. Rather, as in men, heart disease rates increase linearly with age. And, as in men, all of the major risk factors raise the risk of CHD in women. Nonetheless, at every age, men have a greater risk of CHD than women do. The reasons for this gender difference are not completely understood, but they can be partly explained by the earlier onset of risk factors such as elevated LDL cholesterol and blood pressure in men. Levels of the amino acid homocysteine, which may damage artery walls and increase oxidative stress, rise with age and are generally higher in men.12 A history of early CHD in immediate family members is an independent risk factor even when other risk factors are considered. The more family members affected and the earlier the age of onset, the greater the risk.
High LDL and low HDL cholesterol In population studies, the relationship between total blood cholesterol and atherosclerosis is strong – and most of the total cholesterol is made up of LDL cholesterol. The higher the LDL cholesterol, the greater the risk of CHD. The LDL are clearly the most atherogenic lipoproteins. HDL also carry cholesterol, but raised HDL represents cholesterol returning from the cells to the liver and thus indicates a reduced risk of atherosclerosis and heart attack. High LDL and low HDL correlate directly with heart disease, whereas low LDL and high HDL correlate inversely with risk. Any LDL cholesterol that remains in the blood after the body’s cells take up the amount they need becomes vulnerable to oxidation. High blood levels of LDL cholesterol, especially oxidised LDL, promote the development of fibrous plaques. When the plaques weaken and become unstable, they can rupture, causing a heart attack. Evidence shows that elevated LDL contributes to plaque instability.13 In the early stages of atherosclerosis, the goal of treatment is to slow the development of plaques. In the later stages, the goal of treatment is to stabilise plaques.
High blood pressure (hypertension)
Chronic high blood pressure (hypertension) frequently accompanies atherosclerosis, diabetes and obesity. The higher blood pressure is above normal, the greater the risk of heart disease. The relationship between hypertension and heart disease risk holds true for men and women, young and old. High blood pressure injures the artery walls and accelerates plaque formation, thus initiating or worsening the progression of atherosclerosis. Then the plaques and reduced blood flow raise blood pressure further, and hypertension and atherosclerosis become mutually aggravating conditions.
Cholesterol is carried in several lipoproteins, particularly LDL and HDL (see Chapter 5 for details). Remember them this way: • LDL 5 Low-density lipoproteins 5 Less healthy • HDL 5 High-density lipoproteins 5 Healthy.
Diabetes
Digoarpi/Shutterstock.com
Diabetes – a major independent risk factor for all forms of cardiovascular disease – substantially increases the risk of death from CHD.14 In diabetes, blood vessels often become blocked and circulation diminishes. Atherosclerosis progresses rapidly. For many people with diabetes, the risk of CHD is similar to that of people with established CHD.15 In fact, doctors can describe diabetes and other disorders that have risks similar to CHD as CHD risk equivalents. Treatment to lower LDL cholesterol in diabetes follows the same recommendations as in CHD.
Obesity and physical inactivity Obesity, especially abdominal obesity, and physical inactivity significantly modify several of the risk factors for CHD, contributing to high LDL cholesterol, low HDL cholesterol, hypertension and diabetes.16 Conversely, weight loss and physical activity protect against CHD by lowering LDL, raising HDL, improving insulin sensitivity and lowering blood pressure. Regular physical activity also increases energy expenditure and builds lean body mass, thereby improving body composition and physical fitness.
Regular aerobic exercise can help to defend against heart disease by strengthening the heart muscle, promoting weight loss and improving blood lipid and blood glucose levels.
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Cigarette smoking Cigarette smoking is a powerful risk factor for CHD and other forms of cardiovascular disease. The risk increases the more a person smokes and is the same for men and women. Smoking damages the heart directly by increasing blood pressure and the heart’s workload. It deprives the heart of oxygen and damages platelets, making blood clot formation likely. Toxins in cigarette smoke damage blood vessels, setting the stage for atherosclerosis. When people quit smoking, their risk of CHD declines within a few months.
Atherogenic diet Reminder: Insulin resistance is the condition in which a normal amount of insulin produces an insufficient effect, resulting in an elevated fasting glucose; it is a metabolic consequence of obesity that precedes type 2 diabetes. Metabolic syndrome includes any three of the following: • abdominal obesity: waist circumference .94 cm (for men) or .80 cm (for women) • triglycerides: $1.7 mmol/L • HDL:,1.03 mmol/L (in men) or , 1.29 mmol/L (in women) • blood pressure: $130/85 mmHg • fasting glucose: $5.6 mmol/L
Diet influences the risk of CHD. An ‘atherogenic diet’ – high in saturated fats, trans fat and cholesterol, and low in fruits and vegetables – elevates LDL cholesterol. Conversely, diets rich in fruits, vegetables and whole grains seem to lower the risk of CHD even more than might be expected based on risk factors such as LDL cholesterol alone. The specific nutrients responsible for this benefit remain to be defined, but some of the likely contenders include the antioxidant nutrients and omega-3 fatty acids. Dietary strategies to reduce the risk of CHD are discussed in a later section.
Other risk factors
The major risk factors for CHD listed in Table 18.2 and discussed in the previous sections have solid associations with the development of CHD. Nevertheless, other factors also seem to influence a person’s risk of CHD. These factors, known as emerging risk factors, may be helpful in assessing an individual’s risk of CHD. For example, some people with CHD, especially those with diabetes and those who are overweight, have elevated triglycerides. Whether elevated blood triglycerides represent an independent risk factor for CHD remains debatable. In the latest report by the National Cholesterol Education Program Expert Panel,17 elevated blood triglycerides are considered a marker for other risk factors (high LDL, low HDL, overweight and diabetes, for example), but not designated as a major risk factor, whereas more recent research has indicated that triglycerides may actually be an independent risk factor.18
Metabolic syndrome
As Table 18.2 shows, most of the modifiable risk factors for CHD are directly related to diet. Several of these diet-related risk factors – low HDL, high blood pressure, insulin resistance and abdominal obesity – along with high blood triglycerides, comprise a cluster of health risks known as metabolic syndrome. Metabolic syndrome predicts an increased risk of coronary heart disease, but no more so than when each risk factor is considered individually. Overeating and physical inactivity play a major role in the development of the metabolic syndrome. Based on the criteria for metabolic syndrome, about 29 per cent of Australian and New Zealand adults over 25 years of age have metabolic syndrome; this figure increases significantly when considering Indigenous populations.19 Treatment to reduce these risk factors for heart disease and diabetes should begin early and focus on changes in lifestyle.
Recommendations for reducing coronary heart disease risk Recommendations to reduce cardiovascular disease risk include both screening and intervention. The accompanying ‘How to’ box provides a tool to assess a person’s 10-year heart disease risk. Notice that total cholesterol and HDL cholesterol are included in the assessment, but LDL cholesterol is not. LDL cholesterol is routinely estimated from measures of total cholesterol and HDL cholesterol and thus would not add information to this assessment.20 Once a person’s risks have been identified, treatment focuses on lowering LDL cholesterol. Lowering LDL significantly reduces the incidence of CHD. Treatment plans may include major lifestyle changes in diet, physical activity and smoking cessation; medications; or both. The LDL cholesterol goals and treatment plans are specific to individuals, so they are best prescribed by a qualified healthcare provider.
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Chapter 18: Diet-related disease
ASSESS YOUR RISK OF HEART DISEASE
HOW TO:
Do you know your heart disease risk score? This assessment estimates your 10-year risk for CHD using charts from the Framingham Heart Study.* Be aware that a high score does not mean that you will develop heart disease, but it should warn you of the possibility and prompt you to consult a doctor about your health. You will need to know your blood cholesterol (ideally, the average of at least two recent measurements) and blood pressure (ideally, the average of several recent measurements). With this information in hand, find yourself in the five tables below and add the points for each risk factor. AGE (YEARS):
HDL (mmol/L):
MEN WOMEN
SYSTOLIC BLOOD PRESSURE (mmHg):
MEN WOMEN
20–34
–9
–7
$1.55
–1
–1
35–39
–4
–3
1.3 –1.53
0
0
40–44
0
0
1.04 –1.27
1
45–49
3
3
,1.04
2
50–54
6
UNTREATED
TREATED
Men
Women
Men
Women
,120
0
0
0
0
1
120–129
0
1
1
3
2
130–139
1
2
2
4
6
140–159
1
3
2
5
$160
2
4
3
6
55–59
8
8
60–64
10
10
65–69
11
12
70–74
12
14
75–79
13
16
TOTAL CHOLESTEROL (mmol/L) AND SMOKING (ANY CIGARETTE SMOKING IN THE PAST MONTH): AGE 20–39 ,4.14
AGE 40–49
AGE 50–59
AGE 60–69
AGE 70–79
Men
Women
Men
Women
Men
Women
Men
Women
Men
Women
0
0
0
0
0
0
0
0
0
0
4.14–5.15
4
4
3
3
2
2
1
1
0
1
5.18–6.19
7
8
5
6
3
4
1
2
0
1
6.22–7.23
9
11
6
8
4
5
2
3
1
2
$7.25
11
13
8
10
5
7
3
4
1
2
Smoker
8
9
5
7
3
4
1
2
1
1
Non-smoker
0
0
0
0
0
0
0
0
0
0
SCORING YOUR HEART DISEASE RISK MEN Total
WOMEN Risk
Total
Risk
,0
,1%
,9
,1%
0–4
1%
9–12
1%
5–6
2%
13–14
2%
7
3%
15
3%
8
4%
16
4%
*An electronic version of this assessment is available on the ATP III page of the National Heart, Lung, and Blood Institute’s website (https://www.nhlbi.nih.gov/files/docs/guidelines/atglance.pdf).
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SCORING YOUR HEART DISEASE RISK MEN
WOMEN
9
5%
17
5%
10
6%
18
6%
11
8%
19
8%
12
10%
20
11%
13
12%
21
14%
14
16%
22
17%
15
20%
23
22%
16
25%
24
27%
$17
$30%
$25
$30%
Add up your total points: . Now find your total in the first column for your gender in the table and then look to the next column for your approximate risk of developing heart disease within the next 10 years. Depending on your risk category, the following strategies can help reduce your risk: ›› $ 20% 5 high risk (CHD risk equivalent) Try to lower LDL using all lifestyle changes and, most likely, lipid-lowering medications as well. ›› 10 –20% 5 moderate risk. Try to lower LDL using all lifestyle changes and, possibly, lipid-lowering medications. ›› ,10% 5 low risk. Maintain or initiate lifestyle choices that help prevent elevation of LDL to prevent future heart disease. Adapted from Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), Third Report of the National Cholesterol Education Program (NCEP), NIH publication no. 02-5216, Bethesda, MD.: National Heart, Lung, and Blood Institute (2002): section III.
Cholesterol screening To determine an individual’s risk of CHD, healthcare professionals review the person’s health history and measure several blood lipids, including total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides. Ideally, at least two measurements are taken at least one week apart and then compared to standards (shown earlier in Table 18.3 on page 636). Single measurements may fail to identify those at risk or may misclassify them because blood cholesterol and other lipid concentrations vary significantly from day to day.
Lifestyle changes Recommendations to reduce the risk of CHD focus on lifestyle changes. To that end, people are encouraged to increase physical activity, lose weight (if necessary), implement dietary changes and reduce exposure to tobacco smoke either by quitting smoking or by avoiding second-hand smoke. Treatment plans for people with existing CHD or conditions that place them at high risk for heart attacks and strokes (CHD risk equivalents) also focus on lifestyle changes first, but their target LDL is lower. Altering one’s lifestyle is challenging, and instruction and counselling are critical for success. Health professionals can explain the reasons for change, set obtainable goals and offer practical suggestions. If lifestyle changes fail to lower LDL or blood pressure to acceptable levels, then medications are prescribed. Table 18.4 summarises strategies to reduce the risk of heart disease.21 The following ‘How to’ box offers suggestions for implementing a heart-healthy diet.
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TABLE 18.4 Strategies to reduce risk of CHD DIETARY STRATEGIES • Energy: Balance energy intake and physical activity to prevent weight gain and to achieve or maintain a healthy body weight. • Saturated fat, trans fat and cholesterol: Choose lean meats, vegetables and low-fat milk products; minimise intake of hydrogenated fats. Limit saturated fats to less than 7 per cent of total kilojoules and trans fat to less than 1 per cent of total kilojoules (see Table H5.1 on page 172). • Soluble fibres: Choose a diet rich in vegetables, fruits, whole grains and other foods high in soluble fibres. • Potassium and sodium: Choose a diet high in potassium-rich fruits and vegetables, low-fat milk products, nuts and whole grains (see Table 18.6 on page 645). Choose and prepare foods with little or no salt (limit sodium intake to 2300 milligrams per day). • Added sugars: Minimise intake of beverages and foods with added sugars. • Fish and omega-3 fatty acids: Consume fatty fish rich in omega-3 fatty acids (salmon, tuna, sardines) at least twice a week. • Alcohol: If alcohol is consumed, limit it to two standard drinks daily. LIFESTYLE CHOICES • Physical activity: Participate in at least 30 minutes of moderate-intensity endurance activity on most days of the week. The eventual goal should be an expenditure of at least 2000 kilojoules weekly. • Smoking cessation: Minimise exposure to any form of tobacco or tobacco smoke. Adapted from National Heart Foundation of Australia and Cardiac Society of Australia and New Zealand, Reducing risk in heart disease: an expert guide to clinical practice for secondary prevention of coronary heart disease, Melbourne: National Heart Foundation of Australia (2012).
HOW TO:
IMPLEMENT A HEART-HEALTHY DIET
Following a heart-healthy diet can require major changes in dietary choices. People may find it easier to adopt a new diet if only a few changes are made at a time. It also helps to focus on positive choices (what to eat) first, rather than negative ones (what not to eat). Breads, cereals and pasta ›› Choose wholegrain breads and cereals. ›› Bakery products often contain trans-fatty acids. Choose foods whose labels list minimal trans fat in the Nutrition Information Panel or ‘hydrogenated oil’ in the ingredients list. Crackers, chips, biscuits and other bakery items often include trans fats. ›› Avoid products that contain coconut, palm and palm kernel oils, which are high in saturated fat. Fruits and vegetables ›› Consume fruits and vegetables frequently. Keeping the refrigerator stocked with a variety of colourful fruits and vegetables (carrots, grapes, strawberries, watermelon) makes it easier to choose healthy foods when the urge to nibble arises. ›› Incorporate at least one or two servings of fruits and vegetables into each meal. People who rarely eat fruits or vegetables may start by adding at least one of their favourites to each meal. ›› Choose canned products carefully. Canned vegetables (especially tomato-based products) may be high in sodium. Fruits that are canned in juice are higher in nutrient density than those canned in syrup. ›› Restrict high-sodium foods such as pickles and olives. ›› Avoid French fries from fast-food restaurants, which are often loaded with trans fats. Lunch and dinner ›› Select lean cuts of beef, such as sirloin and eye fillet, and lean cuts of pork, such as loin chops. Trim visible fat before cooking. ›› Select extra-lean minced meat and drain well after cooking. Use lean minced chicken without skin to occasionally replace minced beef. ›› Include more vegetarian or legume dishes to boost soluble fibre. Pasta and stir-fry recipes can help to reduce meat intake and increase vegetables in the diet.
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›› Restrict the high-sodium foods of: ›› cured or smoked meats such as salami, corned beef, frankfurts, ham and other luncheon meats ›› salty or smoked fish, such as anchovies, caviar, salted or dried cod, herring, sardines and smoked salmon ›› packaged, canned or frozen soups and sauces. Milk products ›› Milk products can be good sources of protein, calcium, vitamin D and potassium. To obtain two to three servings daily, include a portion of low-fat milk, yoghurt or cottage cheese in each meal. ›› Use yoghurt or fat-free sour cream to make dips or salad dressings. Substitute evaporated fat-free milk for heavy cream. ›› Restrict foods high in saturated fat or sodium, such as cheese, processed cheeses, icecream and many other milk-based desserts. Fats and oils ›› Add nuts (not salted) and avocados to meals to increase mono-unsaturated fat intakes and make meals more appetising. ›› Include vegetable oils in salad dressings and recipes, such as canola, corn, olive, peanut, safflower, sesame, soybean and sunflower oils. ›› Use polyunsaturated margarines or those with added plant sterols or stanols to lower LDL cholesterol levels. Spices and seasonings ›› Use salt only at the end of cooking – you will add much less. ›› Spices and herbs improve the flavour of foods without adding sodium. Try using more garlic, ginger, basil, curry or chilli powder, cumin, pepper, lemon, mint, oregano, rosemary and thyme. ›› Check the sodium content on labels. Flavourings and sauces that are usually high in sodium include stock cubes, soy sauce, steak and barbecue sauces, tomato sauce, relishes and mustard. Snacks and desserts ›› Select low-sodium and low-saturated fat choices such as unsalted pretzels and nuts, plain popcorn and unsalted chips and crackers. ›› Choose canned or dried fruits and some raw vegetables to boost fruit and vegetable intake. ›› Select low-fat frozen desserts such as frozen yoghurt, sorbet and low-fat ice-cream.
REVIEW IT
Atherosclerosis is characterised by a build-up of plaque in an artery wall. Rupture of plaque or abnormal blood clotting can cause heart attacks and strokes. Dietary recommendations to lower the risks of cardiovascular disease are summarised in Table 18.4. Quitting smoking and engaging in regular physical activity also improve heart health.
18.4 Hypertension
Anyone concerned about atherosclerosis and the risk it presents must also be concerned about hypertension. Together, the two are a life-threatening combination. The higher the blood pressure is above normal, the greater the risk. (Low blood pressure, on the other hand, is generally a sign of long life expectancy and low heart-disease risk.) Hypertension is the most consistent and powerful predictor of stroke. People cannot feel the physical effects of high blood pressure, but it can impair life’s quality and end life prematurely.
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The underlying causes of most cases of hypertension are not fully understood, but much is known about the physiological factors that affect blood pressure. As shown in Figure 18.4, blood pressure arises from the contractions in heart muscle that pump blood away from the heart (cardiac output) and the resistance blood encounters in the arterioles (peripheral resistance). When either cardiac output or peripheral resistance increases, blood pressure rises. Cardiac output is raised when heart rate or blood volume increases; peripheral resistance is affected mostly by the diameters of the arterioles. Blood pressure is therefore influenced by the nervous system, which regulates heart muscle contractions and the arteriole’s diameters, and hormonal signals, which may cause fluid retention or blood vessel constriction. The kidneys also play a role in regulating blood pressure by controlling the secretion of the hormones involved in vasoconstriction and retention of sodium and water.
FIGURE 18.4 Determinants of blood pressure
ESB Professional/Shutterstock.com
How hypertension develops
To guard against hypertension, have your blood pressure checked regularly.
Reminder: Cardiac output is the volume of blood discharged by the heart each minute. The equation describing this relationship is blood pressure 5 cardiac output 3 peripheral resistance.
Cardiac output is the volume of blood pumped by the heart within a specified period of time.
Peripheral resistance refers to the resistance to pumped blood by the small arterial branches (arterioles) that carry blood to tissues.
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Risk factors for hypertension
Blood pressure is measured in millimetres of mercury (mmHg). Blood pressure is measured both when the heart muscle contracts (systolic blood pressure) and when it relaxes (diastolic blood pressure). The optimal resting blood pressure for adults is ,120 mmHg for systolic and ,80 mmHg for diastolic (written ,120/,80). For adults 40–70 years of age, each increase of 20 mmHg in systolic or 10 mmHg in diastolic blood pressure doubles the risk of cardiovascular disease.
Several major risk factors predicting the development of hypertension have been identified, including the following: • Ageing: Hypertension risk increases with age. Individuals who have normal blood pressure at age 55 still have a 90 per cent risk of developing high blood pressure during their lifetime.22 • Genetics: Hypertension risk is similar among family members. It is also more prevalent and severe in certain ethnic groups. • Obesity: Most people with hypertension are obese.23 Obesity raises blood pressure in part by altering kidney function, promoting insulin resistance which damages blood vessels, and increasing blood volume and cardiac output without an appropriate reduction in peripheral resistance. • Salt sensitivity: Among those with hypertension, approximately 30 to 50 per cent have blood pressure that is sensitive to salt and can benefit by reducing salt in their diets.24 • Alcohol: Alcohol consumption, especially if consumed regularly in amounts greater than two drinks per day, is strongly associated with hypertension. Alcohol may interfere with drug therapy and is associated with strokes independently of hypertension.
Treatment of hypertension The single most effective step people can take against hypertension is to find out whether they have it. At check-up time, a healthcare professional can provide an accurate resting blood pressure reading. Under normal conditions, blood pressure fluctuates continuously in response to a variety of factors including stress and such actions as talking or shifting position. Some people react emotionally to the procedure, which raises the blood pressure reading. For these reasons, if the resting blood pressure is above normal, the reading should be repeated before confirming the diagnosis of hypertension. Thereafter, the blood pressure should be checked regularly. Both lifestyle modifications and drug therapies are used to treat hypertension. Table 18.5 describes the lifestyle changes that reduce blood pressure and the expected reduction in systolic blood pressure for each change.
Weight control Efforts to reduce high blood pressure focus on weight control. Weight loss alone is one of the most effective non-drug treatments for hypertension. Those who are using medications to control their blood pressure can often reduce or discontinue them if they lose weight. Even a modest weight loss of 5 kilograms can lower blood pressure significantly.
TABLE 18.5 Lifestyle modifications to reduce blood pressure MODIFICATION
RECOMMENDATION
EXPECTED REDUCTION IN SYSTOLIC BLOOD PRESSURE
Weight reduction
Maintain healthy body weight (BMI between 18.5 and 25 kg/m2).
5−20 mmHg/10 kg lost
OZDASH eating plan
Adopt a diet rich in fruits, vegetables and low-fat milk products with reduced saturated fat intake.
8−14 mmHg
Sodium restriction
Reduce dietary sodium intake to less than 2300 milligrams sodium (less than 6 grams salt) per day.
2−8 mmHg
Physical activity
Perform aerobic physical activity for at least 30 minutes per day, most days of the week.
4−9 mmHg
Moderate alcohol consumption
Limit alcohol to 2 drinks per day.
2−4 mmHg
Adapted from National Health and Medical Research Council, Australian Dietary Guidelines, Canberra: Commonwealth of Australia (2011), available at http://www.nhmrc.gov.au/publications/synopses/dietsyn.htm; National Heart Foundation, Guide to Management of Hypertension: Assessing and Managing Raised Blood Pressure in Adults, Canberra: Heart Foundation (2008); National Health and Medical Research Council, Australian Guidelines to Reduce Health Risks from Drinking Alcohol, Canberra: Commonwealth of Australia (2009).
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CURRENT RESEARCH IN NUTRITION Fructose and blood pressure Recently, concerns have been raised about the adverse effect of fructose on blood pressure. Internationally, however, dietary guidelines have not addressed fructose intake directly. Current research in humans has examined the effect of fructose in isocaloric exchange for other carbohydrates on systolic, diastolic and mean arterial blood pressures. It has been found that fructose intake in isocaloric exchange for other carbohydrates significantly decreases diastolic blood pressure, but there doesn’t appear to be any effect of fructose on systolic blood pressure.
Physical activity The higher the blood pressure and the less active a person is to begin with, the greater the effect physical activity has in reducing blood pressure. Physical activity helps with weight control, of course, but moderate aerobic activity, such as 30 to 60 minutes of brisk walking most days, also helps to lower blood pressure directly. Those who engage in regular aerobic activity may not need medication for mild hypertension.
The OZDASH diet The results of the Australian Dietary Approaches to Stop Hypertension (OZDASH) study show that a diet rich in fruits, vegetables, nuts and low-fat milk products, and low in total fat and saturated fat, can significantly lower blood pressure. The OZDASH eating plan provides more fibre, potassium, magnesium and calcium than the typical Australian diet, which helps to reduce blood pressure. The diet also limits red meat, sweets and sugar-containing beverages. Table 18.6 compares the OZDASH diet with the Australian Guide to Healthy Eating (introduced in Chapter 2).
TABLE 18.6 The OZDASH eating plan and the Australian Guide to Healthy Eating compared FOOD GROUP
OZDASH
THE AUSTRALIAN GUIDE TO HEALTHY EATING
Cereals
7−8 serves
6−12 serves
Vegetables, legumes
$4−5 serves
5 serves
Fruits
$3−4 serves
2 serves
Milk, yoghurt, cheese
$3 serves (low fat)
2 serves
Lean meats, poultry, fish, nuts, legumes
• #3 serves/wk (meat) • $3 serves/wk (fish) • $4 serves/wk (nuts and seeds) • $1 serve/wk (legumes)
1 servea
Note: These diet plans are based on the average requirements for a healthy male between the ages of 19 and 60 years. Both OZDASH and the Australian Guide to Healthy Eating recommend that fats and sugars be used sparingly and with discretion. a The Australian Guide to Healthy Eating combines nuts, seeds and legumes with meat, poultry and fish but also includes legumes with the vegetable food group.
When the OZDASH diet is combined with a limited intake of sodium, the effects on blood pressure are greater still.25 In addition to lowering blood pressure, an OZDASH-type diet lowers total cholesterol and LDL cholesterol.26 Thus, the heart-healthy dietary guidelines embrace these strategies in an overall diet to prevent and treat CHD. For many years, controversy surrounded recommendations to restrict sodium or salt, but strong evidence supports the important role this strategy plays in preventing and reducing hypertension. Lowering sodium intake reduces blood pressure regardless of gender or race, the
Like other low-fat diets, the OZDASH diet also lowers HDL – a seemingly undesirable outcome. Whether a lowered HDL raises the risk of CHD is unknown, although some studies suggest that people with both low LDL and low HDL do not have an increased risk of CHD.
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presence or absence of pre-existing hypertension, and whether people follow the OZDASH diet or a typical Australian diet. Furthermore, the lower the sodium intake, the greater the drop in blood pressure. (See the ‘How to’ box in Chapter 12 on page 422 for suggestions about limiting sodium intake.)
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Drug therapy When diet and physical activity fail to reduce blood pressure, diuretics and antihypertensive agents may be prescribed. Diuretics lower blood pressure by increasing fluid loss. Some diuretics can lead to a potassium deficiency. People taking these diuretics need to include rich sources of potassium or supplements daily and to watch for signs of potassium imbalances such as weakness (particularly of the legs), unexplained numbness or tingling sensation, cramps, irregular heartbeats, and excessive thirst and urination. Blood potassium should be monitored regularly. Although some diuretics can lead to a potassium deficiency, others spare potassium. A combination of these two types of diuretics may be prescribed to prevent potassium deficiency.
Limit intake of foods containing added salt.
PUTTING COMMON SENSE TO THE TEST
TRUE
REVIEW IT
Limiting the intake of foods that contain salt is one of the best ways to prevent and treat hypertension.
The most effective dietary strategy for preventing hypertension is weight control. Also beneficial are diets rich in fruits, vegetables, nuts and low-fat milk products, and low in fat, saturated fat and sodium.
Jupiter Images/Index Stock Imagery/Stefan Hallberg
18.5 Diabetes mellitus
The incidence of diabetes among children and adults has risen dramatically in the last decade (see Figure 18.5) – 0.8 per cent of Australians will develop diabetes.27 Diabetes mellitus ranks sixth among the leading causes of death (review Figure 18.2 on page 633). In addition, diabetes underlies, or contributes to, several other major diseases, including heart disease, stroke, blindness and kidney failure. Heart disease is the leading cause of diabetes-related deaths. In fact, people with diabetes are twice as likely to develop these cardiovascular problems as those without diabetes.
How diabetes develops Diabetes mellitus describes a group of metabolic disorders characterised by high blood glucose concentrations and disordered insulin metabolism. People with diabetes may have insufficient insulin, ineffective insulin or a combination of the two. The result is hyperglycaemia, a marked elevation in blood glucose that can ultimately cause damage to blood vessels, nerves and tissues. The incidence of prediabetes in Australia and New Zealand is approximately 2 per cent (blood glucose is elevated but not to such an extent as to be classified as diabetes). People with prediabetes are 10–20 times more likely to develop diabetes. Table 18.7 shows the distinguishing features of its two main forms of diabetes: type 1 and type 2. As is described in the next section, the development of type 1 and type 2 diabetes is different, but some of the complications are similar. To appreciate the problems presented by an absolute or relative lack of insulin, consider insulin’s normal action. After a meal, insulin signals the body’s cells to receive the energy nutrients from the blood – amino acids, glucose and fatty acids. Insulin helps to maintain
The richest sources of potassium are fresh foods of all kinds.
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FIGURE 18.5 Incidence of diabetes among adults in Australia
Incidence (% per year)
2.0 1.6 1.2 Key: Males
0.8 0.4 0.0
Females All 25–34
35–44
55–64 45–54 Baseline age (yrs)
65–74
$75
Adapted from S.K. Tanamas and co-authors, AusDiab 2012: The Australian diabetes, obesity and lifestyle study. Melbourne: International Diabetes Institute (2013).
TABLE 18.7 Features of type 1 and type 2 diabetes TYPE 1
TYPE 2
Prevalence in diabetic population
5 –10% of cases
90 –95% of cases
Age of onset
,30 years
,40 yearsa
Associated conditions
Autoimmune diseases, viral infections, inherited factors
Obesity, ageing, inherited factors
Major defect
Destruction of pancreatic beta cells; insulin deficiency
Insulin resistance; insulin deficiency (relative to needs)
Insulin secretion
Little or none
Varies; may be normal, increased or decreased
Requirement for insulin therapy
Always
Sometimes
Older names
• Juvenile-onset diabetes • Insulin-dependent diabetes mellitus (IDDM)
• Adult-onset diabetes • Non-insulin-dependent diabetes mellitus (NIDDM)
Incidence of type 2 diabetes is increasing in children and adolescence; in more than 90 per cent of these cases, it is associated with overweight or obesity and a family history of type 2 diabetes.
a
blood glucose within normal limits and stimulates protein synthesis, glycogen synthesis in liver and muscle, and fat synthesis. Without insulin, glucose regulation falters, and metabolism of the energy-yielding nutrients changes.
Type 1 diabetes
Fasting blood glucose • normal: ,6.1 mmol/L (and ,7.8 mmol/L two hours after food) • impaired glucose tolerance (IGT): ,7 mmol/L (and 7.8 – 11 mmol/L two hours after food) • impaired fasting glucose (IFT): 6.1–6.9 mmol/L (and ,7.8 mmol/L two hours after food) • diabetes: $7 mmol/L (or .11.1 mmol/L two hours after food). Note: The term prediabetes is used to include both IGT and IFT.
In type 1 diabetes, the less common type of diabetes (about five to 10 per cent of all diagnosed cases), the pancreas loses its ability to synthesise the hormone insulin. Type 1 diabetes is an autoimmune disorder.28 In most cases, the individual inherits a defect in which immune cells mistakenly attack and destroy the insulin-producing beta cells of the pancreas. The rate of beta cell destruction in type 1 diabetes varies. In some people (mainly infants and children), destruction is rapid; in others (mainly adults), it is slow. Type 1 diabetes commonly occurs in childhood and adolescence, but it can occur at any age, even late in life. Without insulin, the body’s energy metabolism changes, with such severe consequences as to threaten survival. The cells must have insulin to take up the needed fuels from the blood. People with type 1 diabetes must inject insulin or use external pumps; insulin cannot be taken orally because it is a protein, and the enzymes of the GI tract would digest it.
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Type 2 diabetes Type 2 diabetes is the most prevalent form of diabetes, accounting for 90 to 95 per cent of cases, and is often asymptomatic.29 The primary defect in type 2 diabetes is insulin resistance, a reduced sensitivity to insulin in muscle, adipose and liver cells. To compensate, the pancreas secretes larger amounts of insulin, and plasma insulin concentrations can rise to abnormally high levels (hyperinsulinaemia). Over time, the pancreas becomes less able to compensate for the cells’ reduced sensitivity to insulin, and hyperglycaemia worsens. The high demand for insulin can eventually exhaust the beta cells of the pancreas and lead to impaired insulin secretion and reduced plasma insulin concentrations. Type 2 diabetes is therefore associated both with insulin resistance and with relative insulin deficiency; that is, the amount of insulin is insufficient to compensate for its diminished effect in cells. Although the actual causes of type 2 diabetes are unknown, the risk is substantially increased by obesity (especially abdominal obesity), ageing and physical inactivity. Most people with type 2 diabetes are obese, and obesity itself can directly cause some degree of insulin resistance. As discussed in Highlight 16, obesity has led to a dramatic rise in the incidence of type 2 diabetes among children and adolescents during the past decade. Inherited factors also strongly influence risk, and type 2 diabetes is more common in certain ethnic populations, and among Indigenous Australians and Pacific Islanders.
Complications of diabetes In both types of diabetes, glucose fails to gain entry into the cells and consequently accumulates in the blood. These two problems lead to both acute and chronic complications. Figure 18.6 summarises the metabolic changes and acute complications that can arise in uncontrolled diabetes. Notice that when some glucose enters the cells, as in type 2 diabetes, many of the symptoms of type 1 do not occur. Over the long term, the person with diabetes suffers not only from the acute complications shown in Figure 18.6, but also from its chronic effects. Chronically elevated blood glucose alters glucose metabolism in virtually every cell of the body. Some cells begin to convert excess glucose to sugar alcohols, for example, causing toxicity and cell distension (and distended cells in the lenses of the eyes, for example, cause blurry vision). Some cells produce glycoproteins by attaching excess glucose to an amino acid in a protein; the altered proteins cannot function normally, which leads to a host of other problems. The structures of the blood vessels and nerves become damaged, leading to loss of circulation and nerve function. Infections occur due to poor circulation coupled with glucose-rich blood and urine. People with diabetes must pay special attention to hygiene and keep alert for early signs of infection. Early aggressive treatment to control blood glucose significantly reduces the risk of long-term diabetes-related complications.
Diseases of the large blood vessels
Disorders of the small blood vessels are called microangiopathies. • micro 5 small • angeion 5 vessel • pathos 5 disease
Atherosclerosis tends to develop early, progress rapidly, and be more severe in people with diabetes. The interrelationships among insulin resistance, obesity, hypertension and atherosclerosis help explain why about 75 per cent of people with diabetes die as a consequence of cardiovascular diseases, especially heart attacks. Research shows that intensive diabetes treatment, which keeps blood glucose levels tightly controlled, can reduce the risk of cardiovascular disease among those with type 1 diabetes.30
Diseases of the small blood vessels For people with diabetes, disorders of the small blood vessels (capillaries) may also develop and lead to loss of kidney function and retinal degeneration, with accompanying loss of vision. About 85 per cent of people with diabetes have impaired kidney function, loss of vision or both. Consequently, diabetes is a leading cause of both kidney failure and blindness.
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FIGURE 18.6 Metabolic consequences of untreated diabetes The metabolic consequences of type 1 diabetes differ from those of type 2. In type 1, no insulin is available to allow any glucose to enter the cells. When glucose cannot enter the cells, a cascade of metabolic changes quickly follows. In type 2 diabetes, some glucose enters the cells. Because the cells are not ‘starved’ for glucose, the body does not shift into the metabolism of fasting (losing weight and producing ketones). Type 1
Type 2
No glucose enters the cells
Cells break down protein and fat
Ketones produced for energy (ketosis)
Blood glucose rises (hyperglycaemia)
Hunger
Glucose moves into the urine (glycosuria)
Weight loss
Diabetic ketoacidosis manifested by: ketones in the breath (acetone breath) ketones in the blood (ketonemia) ketones in the urine (ketonuria)
Excessive eating (polyphagia)
Diabetic coma (can be fatal) aHyperosmolar hyperglycaemic state usually develops in the absence of ketosis and is most often associated with type 2 diabetes.
Some glucose enters the cells, but slowly
Water moves into the blood (osmotic effect)
Hunger
Frequent urination (polyuria) and fluid losses
Excessive eating (polyphagia)
Dehydration (blood volume depletion and electrolyte imbalances) and excessive thirst (polydipsia)
Weight gain
Hyperosmolar hyperglycaemic state or comaa (can be fatal)
Diseases of the nerves Nerve tissues may also deteriorate with diabetes, expressed at first as a painful prickling sensation, often in the arms and legs. Later, the person loses sensation in the hands and feet. Injuries to these areas may go unnoticed, and infections can progress rapidly. With loss of both circulation and nerve function, undetected injury and infection may lead to death of tissue (gangrene), necessitating amputation of the limbs (most often the legs or feet). People with diabetes are advised to take conscientious care of their feet and visit a podiatrist regularly.
The death of tissue, usually due to deficient blood supply, is gangrene.
Recommendations for diabetes Diet is an important component of diabetes treatment. To maintain near-normal blood glucose levels, the diet is designed to deliver a similar amount of carbohydrate each day, spaced reasonably evenly throughout the day. Several approaches can be used to plan such diets, but many people with diabetes learn to count carbohydrates using an exchange system.
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Total carbohydrate intake Providing a consistent carbohydrate intake spaced throughout the day helps people with diabetes maintain appropriate blood glucose levels and maximises the effectiveness of any drug therapy being used. Eating too much carbohydrate at one time can raise blood glucose too high, stressing the already-compromised insulin-producing cells. Eating too little carbohydrate can lead to abnormally low blood sugar (hypoglycaemia). Both the amount and type of carbohydrate affects blood glucose levels.31 Low-carbohydrate diets (less than 130 grams of carbohydrate per day) are not recommended.32
Carbohydrate sources
Blood sugar levels
Different carbohydrate-containing foods have varying effects on blood glucose levels; for example, consuming a portion of white rice may cause blood glucose to rise higher and quicker than would a similar portion of barley. As Chapter 4 describes, this glycaemic effect (or glycaemic index – GI) of foods is influenced by a number of factors, including the food’s fibre, fat and protein content, the preparation method and other foods included in a meal. There are low, moderate and FIGURE 18.7 Glycaemic index (GI) of carbohydratehigh GI foods, all of which have different effects on blood containing foods sugar levels, as can be seen in Figure 18.7. It is incorrect to The GI of carbohydrate-containing foods can be high, assume that the same amount of carbohydrate, no matter moderate or low. the source of the carbohydrate, has the same effect on blood sugar levels. Fifty grams of carbohydrate supplied from an apple, for example, will not provide the same effect on blood sugar levels as 50 grams of carbohydrate from a can of soft drink. While the GI of individual foods is a useful tool when treating diabetes, it must not be considered in isolation, as some low GI foods can be high in fat, low in fibre or high in salt. As for the general population, people with diabetes should try to adhere to the Australian Dietary Guidelines for optimum health and control of their diabetes. A common misconception is that people with diabetes 2 hours 0 1 hour need to avoid sugar and sugar-containing foods. Moderate Key: consumption of sugar has not been shown to adversely High GI affect glycaemic control – as such, sugar recommendations Low GI for people with diabetes are similar to those for the general Moderate GI population.
Dietary fat People with diabetes have a high risk of developing cardiovascular diseases; as such, their guidelines for dietary fat are similar to those for others with high risks. Saturated fat intake should be limited to less than 7 per cent of total kilojoule intake. Dietary strategies for cardiovascular disease were discussed earlier in this chapter.
Protein Protein intakes in Australia and New Zealand generally range from 15 to 25 per cent of total kilojoules. Protein intakes in this range need not be modified for individuals with diabetes and normal kidney function.33 Higher protein intakes are discouraged because they may be detrimental to kidney function.
Alcohol consumption in diabetes Adults with diabetes can drink alcohol in moderation. Guidelines are similar to those for the general population, which advise a daily limit of two standard drinks for women and men.
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Recommendations for type 1 diabetes
Alamy Stock Photo Science Photo Library
Normally, the body secretes a constant baseline amount of insulin at all times and then secretes more as blood glucose rises following meals. People with type 1 diabetes, however, produce little or no insulin. They must learn to adjust the amount and schedule of their insulin doses to accommodate meals, physical activity and health status. To maintain blood glucose within a fairly normal range requires a lifelong commitment to a carefully coordinated program of diet, physical activity and insulin. Nutrition therapy for type 1 diabetes focuses on maintaining optimal nutrition status, controlling blood glucose, achieving a desirable blood lipid profile, controlling blood pressure, and preventing and treating the complications of diabetes. In addition to meeting basic nutrient requirements, the diet must provide a fairly consistent carbohydrate intake from day to day and at each meal and snack to help minimise large fluctuations in blood glucose. Further alterations in diet may be necessary for the person with chronic complications such as cardiovascular or kidney disease. Participation in all levels of physical activity is possible for people with type 1 diabetes who have good blood glucose control and no complications, but they should check with their doctor or their accredited practising or registered dietitian first. One potential problem is hypoglycaemia, which can occur during, immediately after or many hours after physical activity.34 To avoid hypoglycaemia, the person must monitor blood glucose before and after activity to identify when changes in insulin or food intake are needed. Carbohydrate-rich foods should be readily available during and after activity to prevent hypoglycaemia.
Recommendations for type 2 diabetes In overweight people with type 2 diabetes, even moderate weight loss (five to 10 kilograms) can help improve insulin sensitivity, blood lipids and blood pressure. Together with diet, a regular routine of moderate physical activity not only supports weight loss, but also improves blood glucose control, blood lipid profiles and blood pressure. Thus, the benefits of regular, long-term physical activity for the treatment and prevention of type 2 diabetes are substantial.35
For a person with type 1 diabetes, good health depends on coordinating the timing of meals, activities and insulin.
APPLICATIONS OF NUTRITIONAL RESEARCH Fibre intake and diabetes control Evidence exists of the relationship between fibre intake and control of diabetes, with an increase in dietary fibre intake in patients with type 2 diabetes shown to be beneficial by reducing fasting blood glucose and HbA1c (glycosylated haemoglobin – an indication of diabetes control over the preceding three months). Meeting the Recommended Dietary Intake (RDI) for fibre intake each day should be encouraged, along with other healthy eating principles, as a disease management strategy for people with type 2 diabetes, to promote better long-term control and minimise long-term complications.
REVIEW IT
Diabetes is characterised by high blood glucose and either insufficient insulin, ineffective insulin or a combination of the two. People with type 1 diabetes coordinate diet, insulin injections and physical activity to help control their blood glucose. Those with type 2 benefit most from a diet and physical activity program that controls glucose fluctuations and promotes weight loss.
PUTTING COMMON SENSE TO THE TEST
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People with diabetes may have insufficient insulin or ineffective insulin. TRUE
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18.6 Cancer
Cancers of all types rank just below cardiovascular disease as a cause of death in Australia and New Zealand. As with cardiovascular disease, the prognosis for cancer today is far brighter than in the past. Identification of risk factors, new detection techniques and innovative therapies offer hope and encouragement. Cancer is not a single disorder. There are many cancers; that is, many different kinds of malignant growths. They have different characteristics, occur in different locations in the body, take different courses and require different treatments. Table 18.8 shows how cancers are classified. TABLE 18.8 Classification of cancers Cancers are classified by the tissues or cells from which they develop: • adenomas: cancers that arise from glandular tissues • carcinomas: cancers that arise from epithelial tissues • gliomas: cancers that arise from glial cells of the central nervous system • leukaemias: cancers that arise from white blood cell precursors • lymphomas: cancers that arise from lymph tissue • melanomas: cancers that arise from pigmented skin cells • sarcomas: cancers that arise from connective tissues, such as muscle or bone.
How cancer develops
An abnormal mass of cells that is noncancerous is called a benign tumour.
The development of cancer, called carcinogenesis, often proceeds slowly and continues for several decades. A cancer arises from mutations in the genes that control cell division in a single cell. These mutations may promote cellular growth, interfere with growth restraint or prevent cellular death.36 The affected cell thereby loses its built-in capacity for halting cell division, and it produces daughter cells with the same genetic defects. As the abnormal mass of cells, called a tumour, grows, a network of blood vessels develop to supply the tumour with the nutrients it needs to support its growth. The tumour can disrupt the functioning of the normal tissue around it, and some tumour cells may metastasise, or spread to another region in the body. Figure 18.8 illustrates cancer development. In leukaemia (cancer affecting the white blood cells) the cells do not form a tumour, but rather accumulate in blood and other tissues.
FIGURE 18.8 Cancer development Normal cells Malignant cells
Initiation
Normal cells
Promotion
Mutagens alter the DNA in a cell and induce abnormal cell division.
Further tumour development
Promoters enhance the development of abnormal cells, resulting in formation of a tumour.
The cancerous tumour releases cells into the bloodstream or lymphatic system (metastasis).
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The reasons cancers develop are numerous and varied. Vulnerability to cancer is sometimes inherited, as when a person is born with a genetic defect that alters DNA structure, function or repair. Certain metabolic processes may initiate carcinogenesis, as when phagocytes (immune cells) produce oxidants that cause DNA damage or when chronic inflammation enhances the rate of cell division, which increases the risk of a damaging mutation. More often, cancers are caused by interactions between a person’s genes and the environment. Exposure to cancer-causing substances, or carcinogens, may either induce genetic mutations that lead to cancer or promote proliferation of cancerous cells.
Environmental factors Among environmental factors, exposure to radiation and sun, water and air pollution, and smoking are known to cause cancer. Lack of physical activity may also play a role in the development of some types of cancer. Men and women whose lifestyles include regular vigorous physical activity have the lowest risk of colon cancer.37 Physical activity may also protect against breast cancer by reducing body weight and by other mechanisms not related to body weight.38 Different cancers have various causes. The way obesity influences cancer development depends on the site as well as other factors, such as hormonal interactions. In the case of breast cancer in postmenopausal women, for example, the hormone oestrogen is implicated. Obese postmenopausal women have much higher levels of oestrogen than lean women do because fat tissue produces oestrogen. Researchers believe that the extended exposure to oestrogen in obese women is linked to an increased risk of breast cancer after menopause.39 The relationships between excessive body weight and certain cancers provide yet another reason to adopt a lifestyle that embraces physical activity and sound nutrition. As Table 18.9 shows, dietary constituents are also associated with an increased risk of certain cancers. Some dietary factors may initiate cancer development (initiators), others may promote cancer development once it has started (promoters), and still others may protect against the development of cancer (protective effect).
We do not know to what extent diet contributes to cancer development, although some experts estimate that diet may be linked to as many as a third of all cases. Consequently, many people think that certain foods are carcinogenic, especially those that contain additives or pesticides. As Chapter 19 explains, our food supply is one of the safest in the world. Additives that have been approved for use in foods are not carcinogens. Some pesticides are carcinogenic at high doses, but not at the concentrations allowed on fruits and vegetables. The benefits of eating fruits and vegetables are far greater than any potential risk. Cancers of the head and neck correlate strongly with the combination of People with cancer take comfort from the alcohol and tobacco use and with low intakes of green and yellow fruits and support of others and from the knowledge that medical science is waging an vegetables. Alcohol intake alone is associated with cancers of the mouth, throat unrelenting battle in their defence. and breast, and alcoholism often damages the liver and precedes the development of liver cancer. Any potential benefit of moderate alcohol consumption on cardiovascular disease must be weighed against the potential dangers. To minimise carcinogen formation Grilling meat, fish or other foods over a direct flame causes fat and added oils to splash during cooking: on the fire and then vaporise, creating carcinogens that rise and stick to the food.* Eating • when grilling, line grilled food introduces these carcinogens to the digestive system, where they may damage the the grill with foil, or stomach and intestinal lining. Once these compounds are absorbed into the blood, however, wrap the food in foil they are detoxified by the liver. • take care not to burn foods • marinate meats beforehand. *The carcinogens of greatest concern are heterocyclic amines and benzopyrene.
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TABLE 18.9 Factors associated with cancer at specific sites CANCER SITES
RISK FACTORS
PROTECTIVE FACTORS:
Breast (postmenopause)
Alcoholic drinks, body fatness, adult attained height, abdominal fatness, adult weight gain
Lactation, physical activity
Breast (premenopause)
Alcoholic drinks, adult attained height,a greater birth weight
Lactation, body fatness
Colon and rectum
Red meat, processed meat, alcoholic drinks, body fatness, abdominal fatness, adult attained heighta
Physical activity, foods containing dietary fiber, garlic, milk, calcium
Endometrium
Body fatness, abdominal fatness
Physical activity
Esophagus
Alcoholic drinks, body fatness, maté
Gallbladder
Body fatness
Kidney
Body fatness
Liver
Aflatoxins,c alcoholic drinks
Lung
Arsenic in drinking water, beta-carotene supplementsd
Fruits, foods containing carotenoids
Mouth, pharynx, and larynx
Alcoholic drinks
Nonstarchy vegetables, fruits, foods containing carotenoids
Nasopharynx
Cantonese-style salted fish
Ovary
Adult attained heighta
Pancreas
Body fatness, abdominal fatness, adult attained heighta Foods containing folate
Prostate
Diets high in calcium
Skin
Arsenic in drinking water
Stomach
Salt, salty and salted foods
a
b
Nonstarchy vegetables, fruits, foods containing beta-carotene, foods containing vitamin C
Foods containing lycopene, foods containing selenium, seleniume Nonstarchy vegetables, allium vegetables,f fruits
a Adult attained height is unlikely to directly modify the risk of cancer. It is a marker for genetic, environmental, hormonal and also nutritional factors affecting growth during the period from preconception to completion of linear growth. b As drank traditionally in parts of South America, scalding hot through a metal straw. Any increased risk of cancer is judged to be caused by epithelial damage resulting from the heat, and not by the herb itself. c Aflatoxins are toxins produced by molds or fungi. The main foods that may be contaminated are all types of grains (wheat, rye, rice, corn, barley, oats) and legumes, notably peanuts. d The evidence is derived from studies using high-dose supplements (20 mg/day for beta-carotene; 25,000 IU/day for retinol) in smokers. e The evidence is derived from studies using supplements at a dose of 200 μg/day. Selenium is toxic at higher doses. f This includes vegetables such as garlic, onions, leeks, and shallots. NOTE: Strength of evidence for all these factors is either “convincing” or “probable.” SOURCES: W. C. Willett, T. Key, and I. Romieu, Diet, obesity, and physical activity, in B. W. Stewart and C. P. Wild (eds.), World Cancer Report 2014 (Lyon, France: International Agency for Research on Cancer, 2014), pp. 124–133; World Cancer Research Fund/American Institute for Cancer Research, Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective (Washington,DC: AICR, 2007).
Evidence from population studies spanning the globe for over 20 years supports the theory that diets high in meat, especially red meat, are related to a moderately elevated risk of developing colon cancer.40 Remember, however, that even strong correlation is not causation – certain foods may be implicated, but they have not been proven to actually cause cancer. Another reason to moderate consumption of fried foods such as French fries and potato chips is the presence of a substance called acrylamide, which is a potential carcinogen. Acrylamide is produced when certain starches such as potatoes are fried or baked at high temperatures. Chapter 19 offers a discussion of acrylamide in foods.
Dietary factors – cancer promoters Unlike carcinogens, which initiate cancers, some dietary components promote cancers; that is, once the initiating step has taken place, these components may accelerate tumour development.
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Studies of animals suggest that high-fat diets may promote cancer, but in studies of humans, evidence is mixed. One attribute of dietary fat is energy density – gram for gram, fat provides more kilojoules than either carbohydrate or protein. Diets high in kilojoules do seem to promote cancer, especially in laboratory settings.
PUTTING COMMON SENSE TO THE TEST
Dietary factors – protective effect
FALSE
Diets high in red meat cause cancer.
Some foods offer protective effects – dietary compounds that may defend against cancer. Research on dietary patterns of populations has identified such foods and has led to recommendations aimed at reducing cancer risks.
Almost without exception, epidemiological studies find a link between eating plenty of fruits and vegetables and a low incidence of cancers. Fruits and vegetables contain both nutrients and phytochemicals with antioxidant activity, and these substances may prevent or reduce the oxidative reactions in cells that cause DNA damage. Phytochemicals may also help to inhibit carcinogen production in the body, enhance immune functions that protect against cancer development and promote enzyme reactions that inactivate carcinogens.41 For example, the cruciferous vegetables – cabbage, cauliflower, broccoli and brussels sprouts – contain a variety of phytochemicals that have proven beneficial in defending against colon cancer. In addition, fruits and vegetables, as well as legumes and whole grains, are rich in fibre. As Chapter 4 explains, fibre may protect against cancer by binding, diluting and rapidly removing potential carcinogens from the GI tract. High-fibre and wholegrain foods also help a person to maintain a healthy body weight – another Cruciferous vegetables, such as preventive measure against cancer. Physical activity also helps to maintain a healthy cauliflower, broccoli and brussels sprouts, contain nutrients and phytochemicals that body weight and reduce the risks of some cancers. Table 18.10 summarises dietary may inhibit cancer development. and lifestyle recommendations for reducing cancer risk.
TABLE 18.10 Recommendations for reducing cancer risk Healthy body weight: Choose foods that help maintain a healthy weight throughout life. • Choose foods low in energy, fat and sugar. • Eat small portions of high-kilojoule, high-fat or high-sugar foods. • Balance energy intake with physical activity. • Lose weight if currently overweight or obese. Variety: Eat a variety of healthful foods, with an emphasis on plant sources. Vegetables and fruits: Eat seven or more servings of a variety of vegetables and fruits each day. • Include vegetables and fruits at every meal and for snacks. • Limit fried vegetables. • If you drink juices, choose 100-per-cent fruit or vegetable juices. Whole grains: Choose whole grains (such as oats and multigrain bread) instead of refined grains (such as sweetened breakfast cereals and pastries) and sugars (such as soft drinks and lollies). Meats: Limit consumption of red meats, especially those high in fat and processed. • Choose fish, poultry and legumes as alternatives to beef, pork and lamb. • Select lean cuts and small portions. • Grill instead of frying. Alcohol: If you drink alcoholic beverages, limit consumption to no more than two standard drinks a day. Physical activity: Adopt a healthy, active lifestyle. • Engage in at least moderate activity for 30 minutes for most, if not every, day of the week (60 minutes or more of moderate to vigorous activity each day may further reduce the risk of some cancers). Adapted from L. H. Kushi and co-authors, American Cancer Society guidelines on nutrition and physical activity for cancer prevention: reducing the risk of cancer with healthy food choices and physical activity, CA: A Cancer Journal for Clinicians 56 (2006): 254–81, available at http://caonline.amcancersoc.org/cgi/ content/full/56/5/254; Cancer Council Australia, Position Statement: Physical Activity and Reducing Cancer Risk, Sydney: Cancer Council (2009).
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REVIEW IT
Some dietary factors, such as alcohol and heavily smoked foods, may initiate cancer development; others, such as saturated fat or trans-fatty acids, may promote cancer once it has started; and still others, such as fibre, antioxidant nutrients and phytochemicals, may have protective effects against the development of cancer. By eating many fruits, vegetables, legumes and whole grains, and reducing saturated and trans fat intake, people obtain the best possible nutrition at the lowest possible risk. Minimising weight gain through regular physical activity and a healthy diet is also beneficial.
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18.7 Recommendations for chronic disease prevention
This chapter’s discussion of chronic diseases began with the major cardiovascular diseases, described diabetes and then went on to cancer – three different conditions with distinct sets of causes. Yet dietary excesses, particularly excess food energy and fat intakes, increase the likelihood of all three diseases. Similarly, all are responsive to diet, and in most cases, the beneficial foods are similar. Not all diet recommendations apply equally to all of the diseases or to all people with a particular disease, but fortunately for the consumer, dietary recommendations do not contradict one another. In fact, they support each other. Most people can gain some disease-prevention benefits by making dietary changes. Several recommendations are aimed at weight control. Obesity is common in Australia and New Zealand, and it is linked with most of the chronic diseases that Physical activity and a moderate weight loss of even five to 10 kilograms can help threaten life (review Figure 18.3 on page 633). The problems of overweight people improve blood glucose, blood lipids and multiply when medical conditions develop. For example, overweight people readily blood pressure. develop diabetes, which is often accompanied by high blood pressure and high blood cholesterol. Such a combination of problems may require only one treatment: adopting a healthful diet and regular exercise program.
Recommendations that urge all people to make dietary changes believed to forestall or prevent diseases are taking a preventive or population approach. Alternatively, recommendations that urge dietary changes only for people who are known to need them are taking a medical or individual approach.
Recommendations for the population The recommendations to prevent chronic diseases address the general population in the hope that all people at all levels of risk may benefit. Such a strategy is similar to national efforts to vaccinate to prevent measles, fluoridate water to prevent dental caries, and fortify grains with folate to prevent neural tube defects.
Recommendations for individuals People’s hereditary susceptibility to diseases and their responsiveness to dietary measures vary. Unlike nutrient-deficiency diseases, which develop when nutrients are lacking and disappear when the nutrients are provided, chronic diseases are neither caused nor prevented by diet alone. Many people have followed dietary advice and developed heart disease or cancer anyway; others have ignored all advice and lived long and healthy lives. For many people, though, diet does influence the time of onset and course of some chronic diseases, and many healthcare professionals urge dietary measures as part of a disease-prevention strategy. To determine whether dietary recommendations are important to you personally, look at your family history to see which diseases are common to your relatives. In addition, examine your personal history, taking note of your blood pressure, blood lipid profile and lifestyle habits such as smoking and physical activity.
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Recommendations for each individual Even when recommendations are made ‘for individuals’, they apply to large groups of people; for example, those with hypertension or those with diabetes. But that is expected to change in the next decade or so as research on the human genome provides the knowledge needed to create specific recommendations for each individual (as Highlight 6 explains).
REVIEW IT
Clearly, optimal nutrition plays a key role in keeping people healthy and reducing the risk of chronic diseases. To have the greatest impact possible, dietary recommendations are aimed at the entire population, not just at the individuals who might benefit most. Recommendations focus on weight control and urge people to limit saturated and trans fat, increase fibre-rich carbohydrates and balance food intake with physical activity. A person can do no better than to incorporate those suggestions into their daily life.
Reminder: The full complement of genetic material (DNA) in the chromosomes of a cell is called the genome. In human beings, the genome consists of 46 chromosomes. The study of genomes is called genomics.
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 Two of the top three causes of death in Australia and New Zealand have a relationship with diet. TRUE
Two of the top three causes of death have a dietary relationship. These causes of death are ischaemic heart disease and CVD/CVS.
2 Eicosanoids are often the cause of heart attack and stroke. FALSE
Eicosanoids play a specific role in helping to regulate many of the body’s activities. Although some favour heart health more, those that do not are not the cause of heart attack or stroke.
Up to 50 per cent of people with hypertension have blood pressure that is sensitive to salt and can benefit by reducing salt in their diet.
4 People with diabetes may have insufficient insulin or ineffective insulin. TRUE
People with diabetes may have insufficient insulin or ineffective insulin or possibly even both.
5 Diets high in red meat cause cancer. FALSE
3 Limiting the intake of foods that contain salt is one of the best ways to prevent and treat hypertension. TRUE
Even though there is a strong correlation between high red meat intakes and cancer, correlation does not mean causation – certain foods may be implicated, but they have not been proven to actually cause cancer.
NUTRITION PORTFOLIO Identifying your risk factors is the first step in taking action to defend yourself against heart attack, stroke, hypertension, diabetes and cancer. • Review your personal and family history of heart disease, hypertension, diabetes and cancer.
•
•
Consider whether you are sedentary or overweight and how you might become more physically active and achieve a healthy body weight. If you smoke cigarettes, develop a reasonable plan for quitting. Learn whether you have high blood cholesterol or high blood pressure.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1
Two immune system cells that destroy foreign antigens through phagocytosis are: a b c d
2
Which of the following produce antibodies? a b
3
c d
IDS cancer
c d
diabetes heart disease
Raising LDL and insulin levels Lowering LDL and increasing clot formation Raising HDL and lowering blood pressure Improving insulin sensitivity and raising blood pressure
Which blood lipid correlates directly with alcohol intake? a b
HDL LDL
c d
VLDL Triglycerides
The optimal resting blood pressure (BP) for adults is: a b
7
8
c d
130/85 mmHg 140/90 mmHg
Lose weight Restrict salt
c d
Monitor glucose Exercise regularly
All of the following factors increase the risk of type 2 diabetes, except: a b
9
100/70 mmHg 120/80 mmHg
What is the least effective strategy for most people to lower their blood pressure? a b
Antigens B-cells
Which of the following is protective against heart disease? a b c d
5
Phagocytes T-cells
The leading cause of death in Australia is: a b
4
neutrophils and macrophages B-cells and T-cells cytokines and immunoglobulins lymphocytes and antigens
6
ageing inactivity
c d
obesity smoking
The most important dietary strategy in diabetes is to: a b c d
provide for a consistent carbohydrate intake restrict fat to 30 per cent of daily kilojoules limit cholesterol intake by eating fewer eggs take multiple vitamin and mineral supplements daily
10 Which foods are considered likely to be protective against cancer? a b c d
Alcohol Meats Fruits and vegetables Saturated fats
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Chapter 18: Diet-related disease
Review questions
5
What types of foods are the major contributors of salt in the diet? What are some steps that people with hypertension can take to lower their blood pressure? Do these differ from the steps needed to prevent hypertension? (Section 18.3)
6
What are the two main types of diabetes? In what types of populations do we generally see type 1 and type 2 diabetes? How do dietary recommendations for diabetes compare with the healthy diet recommended for all people? Are the dietary recommendations the same for each type of diabetes? (Section 18.5)
7
What are the metabolic consequences of untreated diabetes? (Section 18.5)
8
What are the differences between cancer initiators, promoters and protective effects? Describe the nutrients or foods that belong in each of these categories? (Section 18.6)
9
Describe the characteristics of a diet that might offer the best protection against the onset of cancer. Do these characteristics differ depending on the type of cancer? (Section 18.6)
•
Find information about health statistics at the Australian Bureau of Statistics site: http://www.abs.gov.au Learn about women’s health from the healthdirect site: https://www.healthdirect.gov.au/ Review the Physical Activity Recommendations: http://www.health.gov.au Assess your heart disease risk at the American Heart Association site: http://www.americanheart.org Visit the National Stroke Foundation: http://www. strokefoundation.com.au Find information on the OZDASH diet by visiting its parent, the DASH diet: http://www.dashdiet.org
These questions will help you review the chapter. You will find the answers in the discussions in the sections provided.
1
How do the major diseases of today as a group differ from those of several decades ago as a group? Why is nutrition considered so important in connection with today’s major diseases? (Sections 18.1, 18.2)
2
What are the major diet-related risk factors for atherosclerosis, hypertension, type 2 diabetes and cancer? (Section 18.2)
3
What are the potential concerns with high cholesterol levels? How can people alter their diets to lower their blood cholesterol levels? Do any particular dietary patterns lead to better cholesterol profiles? (Section 18.3)
4
How does hypertension develop? What impact does diet have on the development of hypertension? (Section 18.4)
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NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Review strategies regarding chronic disease prevention and health promotion: http://www.health.gov.au • Find information on health at the Australian Institute of Health and Welfare site: http://www.aihw.gov.au • Visit the Department of Health and Ageing site: http://www.health.gov.au
• • • • •
SEARCH ME! NUTRITION Keyword: nutrition diabetes What are some of the cornerstones in dietary advice for someone with diabetes? The article Dietary guidelines
for the management of diabetes will help answer this question. Can low GI diets help with the management of this condition?
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HIGHLIGHT
18
18.8 COMPLEMENTARY AND ALTERNATIVE MEDICINE
If you suffered from migraine headaches or severe joint pain, where would you turn for relief? Would you visit a doctor? Or are you more likely to go to a herbalist or an acupuncturist? Most doctors diagnose and treat medical conditions in ways that are accepted by the established medical community; herbalists and acupuncturists, among others, offer alternatives to standard medical practice. Instead of taking two aspirin, for example, you might be prescribed fresh leaves of the herb feverfew, or directed to swallow a small amount of white willow bark. Or you might receive a therapeutic massage and several acupuncture needles.
Complementary and alternative medicine (CAM)
has become increasingly popular in recent decades.1 People use these therapies for a variety of reasons. Some want to take more responsibility for both maintaining their own health and finding cures for their own diseases, especially when traditional medical therapies prove ineffective. Others have become distrustful of, and feel overwhelmed by, the high-tech diagnostic tests and costly treatments that conventional medicine offers. This highlight explores alternative therapies in search of their possible benefits and with an awareness of their potential harms.
Defining complementary and alternative medicine
Pat_Hastings/Shutterstock.com
By definition, complementary and alternative medicine is not conventional medicine. It includes a variety of
approaches, philosophies and treatments, some of which are defined in Table H18.1 below. When these therapies are used instead of conventional medicine, they are called alternative; when used together with conventional medicine, they are called complementary. For some alternative therapies, preliminary and limited scientific evidence suggests some effectiveness; but for most, well-designed scientific studies have yet to determine safety and effectiveness. If proved safe and effective, an alternative therapy may be adopted by conventional medicine. Cancer radiation therapy, for example, was once considered an unconventional therapy, but it proved its clinical value and became part of accepted medical practice. In some cases, a therapy that is accepted by conventional medicine for a specific ailment is used for a different purpose in an alternative therapy. For example, chelation therapy, the preferred medical treatment for lead poisoning, is a common alternative therapy for cardiovascular disease.
Sound research, loud controversy Much information on alternative therapies comes from folklore, tradition and testimonial accounts. Relatively few clinical trials have been conducted. Consequently, scientific evidence proving the safety and effectiveness of many alternative therapies is lacking. Some say that alternative therapies simply do not work; others suggest that these therapies have not been given a fair trial. In an effort to explore complementary and alternative healing practices through vigorous science, clinical trials of these therapies are being conducted. Articles reporting the results of these clinical trials are available online in a subset of PubMed created specifically for scientifically based, peerreviewed journals on complementary and alternative therapies. Sound research would answer two important questions. First, does the treatment offer better results than either doing nothing or giving a placebo? Second, do the benefits clearly outweigh the risks? Each of these points is worthy of elaboration.
Placebo effect Alternative medicine often includes the use of plant-based products.
Stories abound that credit alternative therapies with miraculous cures. Without scientific research to determine effectiveness, however, one is left to wonder whether it is the
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TABLE H18.1 Examples of alternative therapies acupuncture: a technique that involves piercing the skin with long thin needles at specific anatomical points to relieve pain or illness. Acupuncture sometimes uses heat, pressure, friction, suction or electromagnetic energy to stimulate the points
aroma therapy: a technique that uses oil extracts from plants and flowers (usually applied by massage or baths) to enhance physical, psychological and spiritual health
Ayurveda: a traditional Hindu system of improving health by using herbs, diet, meditation, massage and yoga to stimulate the body, mind and spirit to prevent and treat disease bioelectromagnetic medical applications: the use of electrical energy, magnetic energy or both to stimulate bone repair, wound healing and tissue regeneration
biofeedback: the use of special devices to convey information about heart rate, blood pressure, skin temperature, muscle relaxation and the like to enable a person to learn how to consciously control these medically important functions
cartilage therapy: the use of cleaned and powdered connective tissue, such as collagen, to improve health chelation therapy: the use of ethylene diamine tetraacetic acid (EDTA) to bind with metallic ions, thus healing the body by removing toxic metals
chiropractic: a manual healing method of manipulating the spine to restore health faith healing: healing by invoking divine intervention without the use of medical, surgical or other traditional therapy herbal medicine: the use of plants to treat disease or improve health; also known as botanical medicine or phytotherapy homoeopathy: a practice based on the theory that ‘like cures like’; that is, that substances that cause symptoms in healthy people can cure those symptoms when given in very diluted amounts • homoeo 5 like • pathos 5 suffering
hydrotherapy: the use of water (in whirlpools, as douches or packed as ice, for example) to promote relaxation and healing hypnotherapy: a technique that uses hypnosis and the power of suggestion to improve health behaviours, relieve pain and heal imagery: a technique that guides clients to achieve a desired physical, emotional or spiritual state by visualising themselves in that state
iridology: the study of changes in the iris of the eye and their relationships to disease macrobiotic diets: extremely restrictive diets limited to a few grains and vegetables; based on metaphysical beliefs and not nutrition. A macrobiotic diet might consist of brown rice, miso soup and sea vegetables, for example
massage therapy: a healing method in which the therapist manually kneads muscles to reduce tension, increase blood circulation, improve joint mobility and promote the healing of injuries
meditation: a self-directed technique of relaxing the body and calming the mind naturopathic medicine: a system that taps the natural healing forces within the body by integrating several practices, including traditional medicine, herbal medicine, clinical nutrition, homoeopathy, acupuncture, East Asian medicine, hydrotherapy and manipulative therapy
orthomolecular medicine: the use of large doses of vitamins to treat chronic disease ozone therapy: the use of ozone gas to enhance the body’s immune system qi gong: a Chinese system that combines movement, meditation and breathing techniques to enhance the flow of qi (vital energy) in the body
therapies or the placebo effect that produces the cure. Recall from Chapter 1 that giving a placebo often brings about a healing effect in people who believe they are receiving the treatment. Traditional medicine tends to neglect this powerful remedy, whereas many alternative therapies embrace it.
Risks versus benefits Ideally, a therapy provides benefits with little or no risk. Figure H18.1 presents several examples of herbal remedies
that appear to be generally safe and possibly effective in treating various conditions.2 Such findings, if replicated, hold promise that these alternative therapies may one day be integrated into conventional medicine. Some alternative therapies are innocuous, providing little or no benefit for little or no risk. Sipping a cup of warm tea with a pleasant aroma, for example, won’t cure heart disease, but it may improve one’s mood and help relieve tension. Given no physical hazard and little financial risk, such therapies are acceptable.
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James Worrell/Getty Images
James Worrell/Getty Images
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FIGURE H18.1 Examples of herbal remedies
Saw palmetto may improve the symptoms associated with an enlarged prostate.
In contrast, other products and procedures are absolutely dangerous, posing great risks while providing no benefits. One example is the folk practice of geophagia (eating earth or clay), which can cause GI impaction and impair iron absorption. Another is the taking of laetrile to treat cancer, which can cause cyanide poisoning. Clearly, such therapies are too harmful to be used. Perhaps most controversial are alternative therapies that may provide benefits, but also carry significant, unknown or debatable risks. Smoking marijuana is an example of such an alternative therapy.3 The compounds in marijuana seem to provide relief from symptoms such as nausea, vomiting and pain that commonly accompany cancer, AIDS and other diseases, but marijuana use also poses risks that some people consider acceptable but which others deem intolerable. Doctors have focused on individuals and recognise that marijuana stimulates the appetite in their nauseated clients; politicians and others have focused on society and realise that marijuana is one of many drugs that can be abused. Figure H18.2 summarises the relationships between risks and benefits.
Nutrition-related alternative therapies Most alternative therapies fall outside the field of nutrition, but nutrition itself can be an alternative
The gel of an aloe vera plant soothes a minor burn.
therapy. Furthermore, many alternative therapies prescribe specific dietary regimens even though most practitioners are not accredited practising or registered dietitians (see Highlight 1). Nutrition-related alternative therapies include the use of foods, vitamin and mineral supplements, and herbs to prevent and treat illnesses.
Foods The many dietary recommendations presented throughout this text are based on scientific evidence and do not fall into the alternative therapies category; strategies that are still experimental, however, do. For example,
FIGURE H18.2 Risk–benefit relationship No (or little)
No (or little) BENEFIT Much
American ginseng may improve glucose control in people with type 2 diabetes.
St. John’s wort may be effective in treating mild depression.
Siriwat Wongchana/Shutterstock.com
Ginkgo may slow the loss of cognitive function associated with aging.
James Worrell/Getty Images
joannawnuk/Shutterstock.com
Ginger may relieve nausea and vomiting due to motion sickness or pregnancy.
RISK
Much
Ideal situation Benefits with little or no risk (Accept)
Cautionary situation Possible benefits with great or unknown risks (Consider car efully)
Neutral situation Little or no benefit with little or no risk (Accept or reject as preferred)
Dangerous situation No benefits with great risks (Reject)
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Chapter 18: Diet-related disease
alternative therapists may recommend macrobiotic diets to help prevent chronic diseases, whereas most accredited practising or registered dietitians would advise people to eat a balanced diet that includes five serves of fresh vegetables daily. Similarly, enough scientific evidence is available to recommend including soy foods in the diet to protect against heart disease – but not to determine whether the phyto-oestrogens of soy are safe or beneficial in managing the symptoms of menopause. Highlight 13 explores the potential health benefits of soy and many other functional foods and concludes that no one food is magical. As part of a balanced diet, these foods can support good health and protect against disease. Importantly, the benefits derive from a variety of foods. More research is needed to determine the safety and effectiveness of taking supplements of the phytochemicals found in these foods.
Vitamin and mineral supplements Like foods, vitamin and mineral supplements may fall into either the conventional or the alternative realm of
663
medicine. For example, conventional advice recommends consuming an additional 400 micrograms of folate to prevent neural tube defects, but not the taking of 1000 milligrams of vitamin C to prevent the common cold. Highlight 10 examines the appropriate use of supplements and potential dangers of excessive intakes. As research on nutrition and chronic diseases has revealed the many roles played by the vitamins and minerals in supporting health, conventional medicine has warmed up to the possibility that vitamin and mineral supplements might be an appropriate preventive therapy.4 Some vitamin and mineral supplements appear to be in transition from alternative medicine to conventional medicine; that is, they have begun to prove their safety and effectiveness. Table H18.2 includes several nutrition-related therapies among those recognised to slow the progression of cancer and treat related symptoms. Herbal remedies, however, still remain clearly in the realm of complementary and alternative medicine.
TABLE H18.2 Advice and precautions on alternative therapies for cancer and related conditions THERAPY
PRECAUTIONS
Accept or consider recommending – evidence supports effectiveness and safety Vitamin E (for prostate cancer)
Not appropriate for people with a low platelet count; those taking anticoagulant medications; or those undergoing radiation, chemotherapy or surgery
Acupuncture (for nausea and vomiting)
Not appropriate for people with a low platelet count or those taking anticoagulant medications
Massage (for anxiety, nausea and lymph drainage)
Not appropriate directly over tumours, stents or prosthetic devices and in areas damaged by surgery or radiation; or in people with bleeding abnormalities
Accept – evidence supports safety, but inconclusive on effectiveness Low-fat diet (for breast and prostate cancer) Not appropriate for people with poor nutrition status Macrobiotic diet
Not appropriate for people with poor nutrition status or those who have breast or endometrial cancer
Vitamin E (for some cancers)
Not appropriate for people with a low platelet count; those taking anticoagulant medications; or those undergoing radiation, chemotherapy or surgery
Soy (for prostate cancer)
Not appropriate for people with a low platelet count or those taking anticoagulant medications or undergoing surgery
Mind−body therapies
Not appropriate for people who do not have reasonable expectations
Acupuncture (for chronic pain)
Not appropriate for people with a low platelet count or those taking anticoagulant medications
Massage (for pain)
Not appropriate directly over tumours, stents or prosthetic devices and in areas damaged by surgery or radiation; or in people with bleeding abnormalities
Discourage – evidence indicates either ineffectiveness or serious risk Vitamin A supplements
May increase the incidence of cancer in high-risk populations (both retinols and carotenoid precursors)
Vitamin C supplements
May have anticoagulant effects
Soy (for breast or endometrial cancer)
May stimulate tumour growth and inhibit platelet aggregation
Adapted from W. A. Weiger and co-authors, Advising patients who seek complementary and alternative medical therapies for cancer, Annals of Internal Medicine 137 (2002): 889–903.
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Herbal remedies From earliest times, people have used a myriad of herbs and other plants to cure aches and ills with varying degrees of success (review Figure H18.1). Upon scientific study, dozens of these folk remedies reveal their secrets. Examples are the following: • Myrrh, a plant resin used as a painkiller in ancient times, does indeed have an analgesic effect. • Valerian, which has long been used as a tranquilliser, contains oils that have a sedative effect. • Senna leaves, brewed as a laxative tea, produce compounds that act as a potent cathartic drug. • Green tea, brewed from the dried leaves of Camellia sinensis, contains phytochemicals that induce cancer cells to self-destruct. • Naturally occurring salicylates provide the same protective effects as low doses of aspirin. Salicylates are found in spices such as curry, paprika and thyme; fruits; vegetables and teas. Beneficial compounds from wild species contribute to about half of our modern medicines. By analysing these compounds, pharmaceutical laboratories can synthesise pure forms of the drugs. Unlike herbs and wild species, which vary from batch to batch, synthesised medicines deliver exact dosages. By synthesising drugs, we are also able to conserve endangered species. Consider that it took all of the bark from one 12-metre-tall, 100-year-old Pacific yew tree to produce one 300-milligram dose of the anticancer drug paclitaxel (Taxol) until scientists learned how to synthesise it. Many as yet undiscovered cures may be forever lost as wild species are destroyed, long before their secrets are revealed to medicine.
•
•
•
•
•
Herbal precautions Plants are ‘natural’, but that does not mean all plants are beneficial or even safe. Nothing could be more natural – and deadly – than the poisonous herb hemlock. Several herbal remedies have toxic effects. The popular Chinese herbal potion jin bu huan, which is used as a pain and insomnia remedy, has been linked with several cases of acute hepatitis. Germanium, a non-essential mineral commonly found in many herbal products, has been associated with chronic kidney failure. Paraguay tea produces symptoms of agitation, confusion, flushed skin and fever. Kombucha tea, commonly used in the hopes of preventing cancer, relieving arthritis, curing insomnia and stimulating hair regrowth, can cause severe metabolic acidosis. Table H18.3 (on page 665) lists selected herbs, their common uses and risks.5 Problems with herbal remedies include the following: • True identification and purity of herbs: Most mint teas are safe, for instance, but some varieties contain the highly toxic pennyroyal oil, and cases of lead poisoning
•
among adults using Ayurvedic remedies are known to have occurred. Appropriate uses and contra-indications of herbs: Herbal remedies alone may be appropriate for minor ailments – a cup of chamomile tea to ease gastric discomfort or the gel of an aloe vera plant to soothe a sunburn, for example – but not for major health problems such as cancer or AIDS. Effectiveness of herbs: Herbal remedies may claim to work wonders without having to prove effectiveness. Research studies often report conflicting findings, with some suggesting a benefit and others indicating no effectiveness.6 Variability of herbs: Not all species are created equal! The various species of coneflower provide an example. Echinacea purpurea, for example, may help in the early treatment of colds, but Echinacea angustifolia may not. Similarly, not all parts of a plant provide the same compounds. Leaves, roots and oils contain different compounds and extracts, and the temperatures used during manufacturing may affect their potency. Consumers are not always aware of such differences, and manufacturers do not always make such distinctions when preparing and labelling supplements. Accuracy of labels: Supplements may contain none of a herb, or mixed species, and labels are often inaccurate. Supplements often do not contain the species or the quantities of active ingredients stated on their labels.7 Safe dosages of herbs: Herbs may contain active ingredients – compounds that affect the body. Each of these active ingredients has a different potency, time of onset, duration of activity and consequent effects, making the plant itself too unpredictable to be useful. Foxglove leaves, for example, contain dozens of compounds that have an effect on the heart; digoxin, a drug derived from foxglove, offers a standard dosage that allows for a more predictable cardiac response. Even when herbs are manufactured into capsules or liquids, their concentrations of active ingredients differ dramatically from batch to batch and from the quantities stated on the labels. Interactions of herbs with medicines and other herbs: Like drugs, herbs may interfere with, or potentiate, the effects of other herbs and drugs (see Table H18.4). A person taking both cardiac medication and the herb foxglove may be headed for disaster from the combined effect on the heart. Similarly, taking St John’s wort with medicines used to treat heart disease, depression, seizures and certain cancers might diminish or exaggerate the intended effects.8 Because Ginkgo biloba impairs blood clotting, it can cause bleeding problems for people taking aspirin or other blood-thinning medicines regularly.
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TABLE H18.3 Selected herbs, their common use and risks COMMON NAME
a
SCIENTIFIC SOURCE NAME
CLAIMS AND USES
RISKSa
Aloe (gel)
Aloe vera
Promote wound healing
Generally considered safe
Black cohosh
Actaea racemosa (formerly Cimicifuga racemosa)
Ease menopause symptoms
May cause clotting in blood vessels of the eye, and change the curvature of the cornea
Chamomile (flowers)
Matricaria chamomilla
Relieve indigestion
Generally considered safe
Chaparral (leaves and twigs)
Larrea tridentata
Slow ageing, ‘cleanse’ blood, heal wounds, cure cancer, treat acne
Acute, toxic hepatitis; liver damage
Comfrey (leafy plant)
Symphytum officinale, S. asperum, S. x uplandicum
Soothe nerves
Liver damage
Echinacea (roots)
Echinacea angustifolia, E. pallida, E. purpurea
Alleviate symptoms of colds, flus and infections; promote wound healing; boost immunity
Generally considered safe; may cause headache, dizziness, nausea
Ephedra (stems)
Ephedra sinica
Promote weight loss
Rapid heart rate, tremors, seizures, insomnia, headaches, hypertension
Feverfew (leaves)
Tanacetum parthenium
Prevent migraine headaches
Generally considered safe; may cause mouth irritation, swelling, ulcers and GI distress
Garlic (bulbs)
Allium sativum
Lower blood lipids and blood pressure
Generally considered safe; may cause garlic breath, body odour, gas and GI distress; inhibits blood clotting
Ginger
Zingiber officinale
Prevent motion sickness, nausea
Generally considered safe
Ginkgo (tree leaves)
Ginkgo biloba
Improve memory, relieve vertigo
Generally considered safe; may cause headache, GI distress, dizziness; may inhibit blood clotting
Ginseng (roots)
Panax ginseng (Asian), P. quinquefolius (American)
Boost immunity, increase endurance
Generally considered safe; may cause insomnia and high blood pressure
Goldenseal (roots)
Hydrastis canadensis
Relieve indigestion, treat urinary infections
Generally considered safe; not safe for people with hypertension or heart disease
Kava
Piper methysticum
Relieves anxiety, promotes relaxation
Liver failure
Saw palmetto (ripe fruits)
Serenoa repens
Relieve symptoms of enlarged prostate; diuretic, enhance sexual vigour
Generally considered safe; may cause nausea, vomiting, diarrhoea
St John’s wort (leaves and tops)
Hypericum perforatum
Relieve depression and anxiety
Generally considered safe; may cause fatigue and GI distress
Valerian (roots)
Valeriana officinalis
Calm nerves, improve sleep
Long-term use associated with liver damage
Yohimbe (tree bark)
Pausinystalia yohimbe
Enhance ‘male performance’
Kidney failure, seizures
Allergies are always a possible risk; see Table H18.4 for drug interactions. Pregnant women should not use herbal supplements.
• Adverse reactions and toxicity levels of herbs: Herbs may produce undesirable reactions. The herb ephedra, commonly known as ma huang and used to promote weight loss, acts as a strong central nervous system stimulant, causing rapid heart rate, headaches, insomnia, tremors, seizures and sometimes death. The herbal root kava, commonly used to treat anxiety and insomnia, can cause liver abnormalities and may have
such a sedating effect as to impair driving. Chinese herbal treatments containing Aristolochia fangchi are notorious for causing kidney damage and cancers.
The consumer’s perspective Some healthcare professionals may dismiss alternative therapies as ineffective and perhaps even dangerous, but
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TABLE H18.4 Herb and drug interactions HERB
DRUG
INTERACTION
Oestrogens, corticosteroids
Enhances hormonal response
American ginseng
Breast cancer therapeutic agent
Synergistically inhibits cancer cell growth
American ginseng, karela
Blood glucose regulators
Affect blood glucose levels
Echinacea (possible immunostimulant)
Cyclosporine and corticosteroids (immunosuppressants)
May reduce drug effectiveness
Evening primrose oil, borage
Anticonvulsants
Lower seizure threshold
Feverfew
Aspirin, ibuprofen and other nonsteroidal anti-inflammatory drugs
Negates the effect of the herb in treating migraine headaches
Feverfew, garlic, ginkgo, ginger and Asian ginseng
Warfarin, coumarin (anticlotting drugs, ‘blood thinners’)
Prolong bleeding time; increase likelihood of haemorrhage
Garlic
Protease inhibitor (HIV drug)
May reduce drug effectiveness
Kava, valerian
Anaesthetics
May enhance drug action
Kelp (iodine source)
Synthroid (levothyroxine) or other thyroid hormone replacers
Interferes with drug action
Kyushin, licorice, plantain, uzara root, hawthorn, Asian ginseng
Digoxin (cardiac antiarrhythmic drug derived from the herb foxglove)
Interfere with drug action and monitoring
St John’s wort, saw palmetto, black tea
Iron
Tannins in herbs inhibit iron absorption
St John’s wort
Protease inhibitors (HIV drugs), warfarin (anti-clotting drug), digoxin (cardiac antiarrhythmic drug), oral contraceptives, tamoxifen (breast cancer drug)
May enhance or reduce drug effectiveness
Valerian
Barbiturates
Causes excessive sedation
many consumers may think otherwise. Interestingly, those who seek alternative therapies seem to do so not so much because they are dissatisfied with conventional medicine as because they find these alternatives more in line with their beliefs about health and life. Most often, people use alternative therapies in addition to, rather than in place of, conventional therapies. Few consult an alternative therapist without also seeing a doctor. In fact, most people seek alternative therapies for nonserious medical conditions or for health promotion. They simply want to feel better and access is easy. Sometimes their symptoms are chronic and subjective, such as pain and fatigue, and difficult to treat. In these cases, the chances of finding relief are often as good with a placebo, standard medical intervention or even non-intervention. In addition, consumers should inform their doctors about the use of any alternative therapies so that a comprehensive treatment plan can be developed and potential problems can be averted. When considering herbal products, remember to include supplements, teas and garden plants. Sometimes herbal products may need to be discontinued, especially before surgery when interactions with anaesthesia or normal blood clotting can be life-threatening.9
Organica/Alamy Stock Photo
American ginseng
Digoxin, the most commonly prescribed heart medication, derives from the leaves of the foxglove plant (Digitalis purpurea).
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Chapter 18: Diet-related disease
Alternative therapies come in a variety of shapes and sizes. Both their benefits and their risks may be small, none or great. Wise consumers and healthcare professionals accept the beneficial, or even neutral,
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practices with an open mind and reject those practices known to cause harm. Making healthful choices requires understanding all the choices.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A How would you judge the accuracy or validity of complementary and alternative medicine practices?
acupuncture sessions and yoga classes. His roommate disagreed, suggesting that instead of following the physician’s recommendations, your friend should start taking high doses of dietary supplements and doing colonic enemas daily. At this point, your friend is confused. What advice might you offer to help him make an informed decision?
B A friend of yours was recently diagnosed with cancer. His physician discussed surgery, radiation, and possibly chemotherapy as recommended treatment options. His sister suggested that, in addition to the physician’s treatment, your friend might also benefit from a few
NUTRITION ON THE NET Analyse the nutrient composition of foods online. To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Search ‘alternative medicine’ at the Department of Health and Ageing site: http://www.health.gov.au • Learn about complementary and alternative medicine from the National Institute of Complementary Medicine: http://www.nicm.edu.au
•
•
•
Search the National Centre for Complementary and Alternative Medicine website: http://nccam. nih.gov/ Obtain information on herbal medications from HerbMed or from the Integrative Medicine Service at Memorial Sloan-Kettering Cancer Center: http://www. herbmed.org or http://www.mskcc.org/aboutherbs Review the backgrounds and practices of many popular practitioners of alternative treatments: http://www.quackwatch.com
REFERENCES CHAPTER 1
2 3
4
5
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Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand), Nutrient reference values for Australia and New Zealand, Canberra: Commonwealth of Australia and New Zealand Government (2006). C. Ventola, The Antibiotic Resistance Crisis, Pharmacy and Therapeutics 40(4) (2015): 277–83. Australian Institute of Health and Welfare, Causes of death 2013, AIHW Catalogue Number 3303.0, Canberra: AIHW (2015) http:// www.abs.gov.au/ausstats/[email protected]/mf/3303.0 S. L. Marrero, D. E. Bloom and E. Y. Adashi, Non-communicable diseases: a global health crisis in a new world order, Journal of the American Medical Association 307 (2012): 2037–8. Australian Institute of Health and Welfare, Causes of death 2013, AIHW Catalogue Number 3303.0, Canberra: AIHW (2015) http://www. abs.gov.au/ausstats/[email protected]/mf/3303.0; Ministry of Health. 2014. Mortality and Demographic Data 2011. Wellington: Ministry of Health. H. N. Siti and co-authors, The role of oxidative stress, antioxidants and vascular inflammation in cardiovascular disease (a review), Vascular Pharmacology 71 (2015): 40–56.
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J. Malpeso and M. J. Budoff, Predicting peri-procedural myocardial infarction: target-lesion plaque characterization with coronary computed tomography angiography. Journal of the American College of Cardiology 59 (2012): 1889–90. 8 K. K. Wong and co-authors, Effect of calcification on the mechanical stability of plaque based on a three-dimensional carotid bifurcation model, BMC Cardiovascular Disorders 12 (2012): 7. 9 A. Papapanagiotou and co-authors, The role of platelets in cardiovascular disease: Molecular mechanisms, Current Pharmaceutical Design 22 (29) (2016): 4493–505. 10 S. M. Afonso and co-authors, The impact of dietary fatty acids on macrophage cholesterol homeostasis, Journal of Nutritional Biochemistry 25 (2014): 95–103. 11 G. Niccoli and co-authors, Advances in mechanisms, imaging and management of the unstable plaque, Atherosclerosis 233 (2014): 467–77. 12 J. Ando and K. Yamamoto, Protective effect of quercetin on homocysteine-induced oxidative stress, Nutrition 33 (2017): 291–6. 13 M. van Rooy and E. Pretorius, Obesity, hypertension, and hypercholesterolemia as risk factors for atherosclerosis leading to ischemic events, Current Medicinal Chemistry 21 (2014): 2121–9.
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14 J. E. Kanter and co-authors, Diabetes promotes an inflammatory macrophage phenotype and atherosclerosis through acyl-CoA synthetase 1, Proceedings of the National Academy of Sciences of the United States of America 109 (2012): E715–E724. 15 K. Mahdy Ali and co-authors, Cardiovascular disease risk reduction by raising HDL cholesterol—current therapies and future opportunities, British Journal of Pharmacology 167 (2012): 1177–94. 16 D. J. Hunter and K. S. Reddy, Noncommunicable diseases, New England Journal of Medicine 369 (2013): 1136–43. 17 NCEP Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), Third report of the national cholesterol education program (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III) final report, Circulation 106 (2002): 3143–421. 18 B. G. Nordestgaard and co-authors, Triglycerides and cardiovascular disease, The Lancet 384(9943) (2014): 626–35. 19 P. Z. Zimmet and co-authors, Mainstreaming the metabolic syndrome: a definitive definition, Medical Journal of Australia 183 (2005): 175–6. 20 National Heart Foundation of Australia and Cardiac Society of Australia and New Zealand, Reducing risk in heart disease: an expert guide to clinical practice for secondary prevention of coronary heart disease, Melbourne: National Heart Foundation of Australia (2012). 21 National Heart Foundation of Australia and Cardiac Society of Australia and New Zealand, Reducing risk in heart disease: an expert guide to clinical practice for secondary prevention of coronary heart disease, Melbourne: National Heart Foundation of Australia (2012). 22 R. S. Vasan and co-authors, Residual lifetime risk for developing hypertension in middle-aged women and men: The Framingham Heart Study, Journal of the American Medical Association (287): 1003–10. 23 P. A. James and co-authors, Evidence based guidelines for the management of high blood pressure in adults: report from the panel members appointed to the Eighth Joint National Committee (JNC8), Journal of the American Medical Association 311 (2014): 507–20. 24 P. A. James and co-authors, Evidence based guidelines for the management of high blood pressure in adults: report from the panel members appointed to the Eighth Joint National Committee (JNC8), Journal of the American Medical Association 311 (2014): 507–20. 25 C. Margerison and co-authors, Food sources of sodium prior to and during the OZDASH study, Asia Pacific Journal of Clinical Nutrition 13 (2004): S58. 26 K. C. Fitzgerald and co-authors, Comparison of associations of adherence to a Dietary Approaches to Stop Hypertension (DASH)-style diet with risks of cardiovascular disease and venous thromboembolism. Journal of Thrombosis and Haemostasis 10 (2012): 189–98. 27 E. Barr and co-authors, AusDiab 2005, The Australian Diabetes, Obesity and Lifestyle Study, tracking the accelerating epidemic:
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its causes and outcomes (Melbourne: International Diabetes Institute, 2006). American Diabetes Association, Position statement: Standards of medical care in diabetes—2014, Diabetes Care 37 (2014): S14–S80. E. Barr and co-authors, AusDiab 2005, The Australian Diabetes, Obesity and Lifestyle Study, tracking the accelerating epidemic: its causes and outcomes (Melbourne: International Diabetes Institute, 2006). The Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) Study Research Group, Intensive diabetes treatment and cardiovascular disease in patients with type 1 diabetes, New England Journal of Medicine 353 (2005): 2643–53. Dietitians Association of Australia, Evidence based practice guidelines for the nutritional management of type 2 diabetes mellitus for adults, Canberra: DAA (2006). Dietitians Association of Australia, Evidence based practice guidelines for the nutritional management of type 2 diabetes mellitus for adults, Canberra: DAA (2006). Dietitians Association of Australia, Evidence based practice guidelines for the nutritional management of type 2 diabetes mellitus for adults, Canberra: DAA (2006). Dietitians Association of Australia, Evidence based practice guidelines for the nutritional management of type 2 diabetes mellitus for adults, Canberra: DAA (2006). Dietitians Association of Australia, Evidence based practice guidelines for the nutritional management of type 2 diabetes mellitus for adults, Canberra: DAA (2006). R. A. Stein, Epigenetics—the link between infectious diseases and cancer, Journal of the American Medical Association 305 (2011): 1484–5. K. Aleksandrova and co-authors, Physical activity, mediating factors and risk of colon cancer: insights into adiposity and circulating biomarkers from the EPIC cohort, International Journal Epidemiology 46 (6) (2017): 1823–35. S. Ghosh and co-authors, Association of obesity and circulating adipose stromal cells among breast cancer survivors, Molecular Biology Reports 41 (2014): 2907–16. S. Ghosh and co-authors, Association of obesity and circulating adipose stromal cells among breast cancer survivors, Molecular Biology Reports 41 (2014): 2907–16. D. Aune and co-authors, Red and processed meat intake and risk of colorectal adenomas: a systematic review and meta-analysis of epidemiological studies, Cancer Causes and Control: CCC 24 (2013): 611–27. J. M. Estrela and co-authors, Polyphenolic phytochemicals in cancer prevention and therapy: bioavailability versus bioefficacy Journal of Medicinal Chemistry 60 (23) (2017): 9413–36.
HIGHLIGHT 1
2
3
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T. C. Clarke and co-authors, Trends in the use of complementary health approaches among adults: United States, 2002–2012, National Health Statistics Reports 79, 10 February 2015. W. Marx and co-authors, Ginger—mechanism of action in chemotherapy induced nausea and vomiting: A review, Critical Reviews in Food Science and Nutrition 57 (2017): 141–6. K. P. Hill, Medical marijuana for treatment of chronic pain and other medical and psychiatric problems: A clinical review, Journal of the American Medical Association 313 (2015): 2474–83. G. Angelo, V. J. Drake, and B. Frei, Efficacy of multivitamin/mineral supplementation to reduce chronic disease risk: A critical review of the evidence from observational studies and randomized trials, Critical Review in Food Science and Nutrition 55 (2015): 1968–91. National Institutes of Health, National Center for Complementary and Alternative Medicine, Herbs at a glance, http://nccam.nih.gov/ health, updated 19 September 2016.
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M. Payab and co-authors, Efficacy, safety and mechanisms of herbal medicines used in the treatment of obesity, Medicine 97(1) (2017): doi:10.1097/MD.0000000000008825 S. G. Newmaster and co-authors, DNA barcoding detects contamination and substitution in North American herbal products, BMC medicine 11 (2013): 222. National Institutes of Health, National Center for Complementary and Alternative Medicine, Herbs at a glance, St. John’s wort, https:// nccih.nih.gov/health/stjohnswort/ataglance.htm#hed4, updated 1 December 2016. I. Levy and co-authors, Use and safety of dietary and herbal supplements among hospitalized patients: What have we learned and what can be learned? – A narrative review, European Journal of Integrative Medicine 16 (2017): 39–45.
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CHAPTER
19
CONSUMER CONCERNS ABOUT FOODS AND WATER Nutrition in your life
Do you know what causes food poisoning and how to protect yourself against it? Do you know that fish contain mercury? Are you concerned about the pesticides that might linger on fruits and vegetables? Do you wonder whether foods contain enough nutrients – or too many additives? Making informed choices and practising a few food safety tips will allow you to enjoy a variety of foods while limiting the risk of experiencing food-related illnesses. PUTTING COMMON SENSE TO THE TEST Circle your answer
T F One way to prevent potential food-borne illness is to avoid buying damaged food
products.
T F There is no need to wash chopping boards and utensils in hot, soapy water before and
after each step of food preparation.
T F Organic foods are known to be of better quality than foods produced using pesticides. T F The majority of food additives in the food supply are unsafe at levels of normal
consumption.
LEARNING OBJECTIVES 19.1 Describe how foodborne illnesses can be prevented. 19.2 Explain how environmental contaminants get into foods and how people can protect themselves against contamination. 19.3 Identify natural toxicants and determine whether they are hazardous.
19.4 Debate the risks and benefits of using pesticides. 19.5 List common food additives, their purposes, and examples. 19.6 Discuss consumer concerns about water. 19.7 Debate the pros and cons surrounding genetically engineered foods. Raspberries are an excellent source of vitamin C and manganese
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Take a moment to consider the task of supplying food to nearly 29 million Australians and New Zealanders (and millions more in all corners of the world). To feed these two nations, farmers grow and harvest crops and raise livestock; dairy producers supply milk products; shippers deliver foods to manufacturers by land, sea and air; manufacturers prepare, process, preserve and package products; and supermarkets store the food and supply it to consumers. After much time, much labour and extensive transport, an abundant supply of a large variety of safe foods finally reaches consumers. Food Standards Australia New Zealand (FSANZ) and other government and international agencies monitor this huge system using a network of people and sophisticated equipment. Table 19.1 identifies various food regulatory agencies. These agencies focus on the potential hazard of foods, which differs from the toxicity of a substance – a distinction worth understanding. Anything can be toxic. Toxicity simply means that a substance can cause harm if enough is consumed. We consume many substances that are toxic, without risk, because the amounts are so small. The term hazard, on the other hand, is more relevant to our daily lives because it refers to the harm that is likely under real-life conditions. Consumers rely on these monitoring agencies to set safety standards and can learn to protect themselves from food hazards by taking a few preventive measures.
TABLE 19.1 Agencies that monitor the food supply FSANZ (Food Standards Australia New Zealand): an independent statutory agency that is part of the Australian Government’s ‘Health and Ageing’ portfolio (http://www.foodstandards.gov.au)
State and territory health services: each Australian state and territory has its own health department under which the responsibility for many food safety aspects falls: • Australian Capital Territory (ACT) Department of Health (http://www.health.act.gov.au) • New South Wales (NSW) Department of Health (http://www.health.nsw.gov.au) • Northern Territory (NT) Department of Health and Families (http://www.health.nt.gov.au) • Queensland (QLD) Department of Health (http://www.health.qld.gov.au) • South Australia (SA) Department of Health (http://www.health.sa.gov.au) • Tasmania (TAS) Department of Health and Human Services (http://www.dhhs.tas.gov.au) • Victoria (VIC) Department of Human Services (http://www.dhhs.vic.gov.au) • Western Australia (WA) Department of Health (http://www.health.wa.gov.au) NZFSA (New Zealand Food Safety Authority): the agency responsible for the administration of the Australia New Zealand Food Standards Code in New Zealand (http://www.nzfsa.govt.nz)
EPA (Environmental Protection Agency): each Australian state has its own EPA that is responsible for, among other things, water quality
FAO (Food and Agriculture Organization): an international agency (part of the United Nations) that has adopted standards to regulate pesticide use, among other responsibilities (http://www.fao.org)
WHO (World Health Organization): an international agency concerned with promoting health and eradicating disease (http://www.who.int)
This chapter focuses on the actions of individuals to promote food safety. It addresses the following food safety concerns: • food-borne illnesses • environmental contaminants • naturally occurring toxins • pesticides • food additives • water safety.
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Chapter 19: Consumer concerns about foods and water
The chapter begins with the serious and prevalent threat of food-borne illnesses. The Highlight that follows looks at genetically modified foods.
19.1 Food safety and food-borne illnesses
Food-borne illness is the leading food safety concern because episodes of food poisoning far outnumber episodes of any other kind of food contamination. FSANZ estimates that there are 5.4 million cases of food-borne illness each year in Australia and New Zealand, costing approximately $1.2 billion.1 Most vulnerable are pregnant women; very young, very old, sick or malnourished people; and those with a weakened immune system (such as people with AIDS). By taking the proper precautions, people can minimise their chances of contracting food-borne illnesses.
Food-borne infections and food toxins Food-borne illness can be caused by either an infection or a toxin. Table 19.2 summarises the most common or severe food-borne illnesses, along with their food sources, general symptoms and prevention methods.
Food-borne infections Food-borne infections are caused by eating foods contaminated by infectious microbes. The most common food-borne pathogen is Salmonella, which enters the GI tract in contaminated foods such as undercooked poultry and milk that has not been pasteurised. Symptoms generally include abdominal cramps, fever, vomiting and diarrhoea.
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Get medical help for these symptoms: • bloody diarrhoea • diarrhoea lasting more than three days • difficulty breathing • difficulty swallowing • double vision • fever lasting more than 24 hours • headache, muscle stiffness and fever • numbness, muscle weakness and tingling sensations in the skin • rapid heart rate, fainting and dizziness. Among food-borne infections, Salmonella is a major cause of illness.
Food poisoning can be caused by eating foods containing natural toxins or, more likely, microbes that produce toxins. The most common food toxin is produced by Staphylococcus aureus; it affects more than one million people each year. Less common, but more infamous, is Clostridium botulinum, an organism that produces a deadly toxin in anaerobic conditions such as improperly canned (especially home-canned) foods and homemade garlic or herb-flavoured oils stored at room temperature. Because the toxin paralyses muscles, a person with botulism has difficulty seeing, speaking, swallowing and breathing.2 Because death can occur within 24 hours of onset, botulism demands immediate medical attention. Even then, survivors may suffer the effects for months or years.
Shutterstock.com/Altafulla
Food toxins
With the benefits of a safe and abundant food supply come the responsibility to select, prepare and store foods safely.
Food safety in the marketplace
Polara Studios, Inc.
Transmission of food-borne illness has changed as our food supply and lifestyles have changed. In the past, food-borne illness was caused by one person’s error in a small setting, such as improperly refrigerated egg salad at a family picnic, and it affected only a few victims. Today, we eat more foods that have been prepared and packaged by others. Consequently, when a food manufacturer or restaurant chef makes an error, food-borne illness can become epidemic. To prevent food poisoning from homemade flavoured oils, wash and dry the herbs before adding them to the oil and keep the oil refrigerated.
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TABLE 19.2 Food-borne illnesses DISEASE AND ORGANISM THAT CAUSES IT
MOST FREQUENT FOOD SOURCES
ONSET AND GENERAL SYMPTOMS
PREVENTION METHODSa
Food-borne infections Campylobacteriosis Campylobacter bacterium
Raw and undercooked poultry, unpasteurised milk, contaminated water
Onset: 2 to 5 days Diarrhoea, vomiting, abdominal cramps, fever; sometimes bloody stools
Cook foods thoroughly; use pasteurised milk; use sanitary food-handling methods.
Lasts 2 to 10 days Cryptosporidiosis Crytosporidium parvum parasite
Cyclosporiasis Cyclospora cayetanensis parasite
Commonly contaminated swimming or drinking water, even from treated sources. Highly chlorine-resistant. Contaminated raw produce and unpasteurised juices and ciders Contaminated water; contaminated fresh produce
Onset: 2 to 10 days Diarrhoea, stomach cramps, upset stomach, slight fever Symptoms may come and go for weeks or months
Onset: 1 to 14 days Watery diarrhoea, loss of appetite, weight loss, stomach cramps, nausea, vomiting, fatigue
Wash all raw vegetables and fruits before peeling. Use pasteurised milk and juice. Do not swallow drops of water while using pools, hot tubs, ponds, lakes, rivers or streams for recreation. Use treated, boiled or bottled water; cook foods thoroughly; peel fruits.
Symptoms may come and go for weeks or months Undercooked minced beef, unpasteurised milk and juices, raw fruits and vegetables, contaminated water, and person-to-person contact
E. coli infection Escherichia coli b bacterium
Gastroenteritisc Norwalk virus
Person-to-person contact; raw foods, salads, sandwiches
Giardiasis Giardia intestinalis parasite
Contaminated water; uncooked foods
Hepatitis Hepatitis A virus
Undercooked or raw shellfish
Onset: 1 to 8 days Severe bloody diarrhoea, abdominal cramps, vomiting Lasts 5 to 10 days
Onset: 1 to 2 days Vomiting; lasts 1 to 2 days
Onset: 7 to 14 days Diarrhoea (but occasionally constipation), abdominal pain, gas
Onset: 15 to 50 days (28 days average)
Cook minced beef thoroughly; use pasteurised milk; use sanitary foodhandling methods; use treated, boiled or bottled water. Use sanitary food-handling methods. Use sanitary food-handling methods; avoid raw fruits and vegetables where parasites are endemic; dispose of sewage properly. Cook foods thoroughly.
Diarrhoea, dark urine, fever, headache, nausea, abdominal pain, jaundice (yellowed skin and eyes from build-up of wastes) Lasts 2 to 12 weeks Listeriosis Listeria monocytogenes bacterium
Unpasteurised milk; fresh soft cheeses; deli meats, hot dogs
Onset: 1 to 21 days Fever, muscle aches; nausea, vomiting, blood poisoning, complications in pregnancy, and meningitis (stiff neck, severe headache and fever)
Use sanitary food-handling methods; cook foods thoroughly; use pasteurised milk.
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TABLE 17.4
Chapter 19: Consumer concerns about foods and water
DISEASE AND ORGANISM THAT CAUSES IT
MOST FREQUENT FOOD SOURCES
Perfringens food poisoning Clostridium perfringens bacterium
Meats and meat products stored at between 50 °C and 55 °C
Salmonellosis Salmonella bacteria (.2300 types)
Raw or undercooked eggs, meats, poultry, raw milk and other dairy products, prawns, frog legs, yeast, coconut, pasta and chocolate
ONSET AND GENERAL SYMPTOMS
Onset: 8 to 16 hours Abdominal pain, diarrhoea, nausea Lasts 1 to 2 days
Shigellosis Shigella bacteria (.30 types)
Person-to-person contact, raw foods, salads, sandwiches and contaminated water
Vibrio bacteria Vibrio vulnificusd bacterium
Raw or undercooked seafood and contaminated water
Onset: 1 to 3 days Fever, vomiting abdominal cramps, diarrhoea Lasts 4 to 7 days; can be fatal
Onset: 1 to 2 days Bloody diarrhoea, cramps, fever Lasts 4 to 7 days
Onset: 1 to 7 days Diarrhoea, abdominal cramps, nausea, vomiting
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PREVENTION METHODSa Use sanitary food-handling methods; cook foods thoroughly; refrigerate foods promptly and properly. Use sanitary food-handling methods; use pasteurised milk; cook foods thoroughly; refrigerate foods promptly and properly. Use sanitary foodhandling methods; cook foods thoroughly; proper refrigeration. Use sanitary food-handling methods; cook foods thoroughly.
Lasts 2 to 5 days; can be fatal Yersiniosis Yersinia enterocolitica bacterium
Raw and undercooked pork, unpasteurised milk
Onset: 1 to 2 days Diarrhoea, vomiting, fever, abdominal pain
Cook foods thoroughly; use pasteurised milk; use treated, boiled or bottled water.
Lasts 1 to 3 weeks Food toxins Botulism Botulinum toxin (produced by Clostridium botulinum bacterium, which grows without oxygen, in low-acid foods and at temperatures between 4 °C and 50 °C; the botulinum toxin responsible for botulism is called botulin)
Anaerobic environment of low acidity (canned corn, peppers, green beans, soups, beets, asparagus, mushrooms, ripe olives, spinach, tuna, chicken, chicken liver, pâte, deli meats, ham, sausage, stuffed eggplant, lobster and smoked and salted fish)
Staphylococcal food poisoning Staphylococcal toxin (produced by Staphylococcus aureus bacterium)
Toxin produced in improperly refrigerated meats; egg, tuna, potato and pasta salads; cream-filled pastries
Onset: 4 to 36 hours Nervous system symptoms, including double vision, inability to swallow, speech difficulty, and progressive paralysis of the respiratory system Often fatal
Use proper canning methods for low-acid foods; refrigerate homemade garlic and herb oils; avoid commercially prepared foods with leaky seals or with bent, bulging or broken cans.
Leaves prolonged symptoms in survivors
Onset: 1 to 6 hours Diarrhoea, nausea, vomiting, abdominal cramps, fever Lasts 1 to 2 days
Use sanitary food-handling methods; cook food thoroughly; refrigerate foods promptly and properly; use proper home-canning methods.
NOTE: Travellers’ diarrhoea is most commonly caused by E. coli, Campylobacter jejuni, Shigella and Salmonella. a The ‘How to’ box on page 676 provides more details on the proper handling, cooking and refrigeration of foods. b The most serious strain is E. coli (STEC) O157. c Gastroenteritis refers to an inflammation of the stomach and intestines; however, it is the most common name used for illnesses caused by Norwalk viruses. d Most cases of Vibrio vulnificus occur in people with underlying illness, particularly those with liver disorders, diabetes, cancer and AIDS, and those who require long-term steroid use. The fatality rate is 50 per cent for this population.
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Understanding nutrition
Industry controls
PUTTING COMMON SENSE TO THE TEST
To make the food supply safe for consumers, the food-processing industry implemented a program to control food-borne illness.* The Hazard Analysis Critical Control Points (HACCP) system requires food manufacturers to identify points of contamination and implement controls to prevent food-borne disease (for example, the use of chlorinated water to wash melons and to make ice for packing and shipping). Safety procedures such as this prevent thousands of food-borne illnesses each year.3
One way to prevent potential food-borne illness is to avoid buying damaged food products. TRUE
Consumer awareness Canned and packaged foods sold in supermarkets are easily controlled, but rare accidents do happen. Batch numbering makes it possible to recall contaminated foods through public announcements via newspapers, television, radio and the Internet. In the supermarket, consumers can buy items before the ‘use by’ or ‘best before’ date and inspect the safety seals and wrappers of packages. A broken seal, bulging can lid or mangled package fails to protect the consumer against microbes, insects, spoilage or even vandalism. State and local health regulations provide guidelines on the cleanliness of facilities and the safe preparation of foods for restaurants, cafes and fast-food establishments. Even so, consumers can also take the following actions to help prevent food-borne illnesses when dining out: • Wash hands with hot, soapy water before meals. • Expect clean tabletops, dinnerware, utensils and food preparation areas. • Expect cooked foods to be served piping hot and salads to be fresh and cold. • Refrigerate ‘doggy’ bags within two hours. Improper handling of foods can occur anywhere along the line from commercial manufacturers to large supermarkets to small restaurants to private homes. Maintaining a safe food supply requires everyone’s efforts (see Figure 19.1).
FIGURE 19.1 Food safety from farms to consumers
FARMS Workers must use safe methods of growing, harvesting, sorting, packing and storing food to minimise contamination hazards.
PROCESSING Processors must follow FSANZ guidelines concerning contamination, cleanliness and education and training of workers, and must monitor for safety at critical control points (use HACCP; see text).
TRANSPORTATION Containers and vehicles transporting food must be clean. Cold food must be kept cold at all times.
RETAIL SHOPS AND RESTAURANTS Employees must follow local food codes on how to prevent food-borne illnesses. Establishments must pass local health inspections and train staff in sanitation.
CONSUMERS Consumers must learn and use sound principles of food safety as taught in this chapter. Be mindful that food-borne illness is a real possibility and take steps to prevent it.
Food safety in the kitchen Whether microbes multiply and cause illness depends, in part, on a few key food-handling behaviours in the kitchen – whether the kitchen is in your home or a gourmet restaurant.4
* In addition to HACCP, these programs include the Australian Government initiative OzFoodNet and the New Zealand Government Foodsmart initiative.
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Figure 19.2 summarises the four simple things that can help most to prevent FIGURE 19.2 Fight Bac! food-borne illness: The Fight Bac! website (http:// www. fightbac.org) describes four ways to keep • Keep a clean, safe kitchen: Wash bench tops, cutting boards, hands, sponges food safe. and utensils in hot, soapy water before and after each step of food preparation. • Avoid cross-contamination: Keep raw eggs, meat, poultry and seafood separate from other foods. Wash all utensils and surfaces (such as cutting boards or platters) that have been in contact with these foods with hot, soapy water before using them again. Bacteria inevitably left on the surfaces from the raw meat can re-contaminate the cooked meat or other foods – a problem known as cross-contamination. Washing raw eggs, meat and poultry is not recommended because the extra handling increases the risk of cross-contamination. • Keep hot foods hot: Cook foods long enough to reach internal temperatures that will kill microbes, and maintain adequate temperatures to prevent bacterial growth until the foods are served. • Keep cold foods cold: Go directly home upon leaving the supermarket and immediately place foods in the refrigerator or freezer. After a meal, refrigerate any leftovers immediately. Unfortunately, many consumers commonly fail to follow these simple food-handling recommendations. See the ‘How to’ box on p. 676 for additional food safety tips.
Safe handling of meats and poultry Meats and poultry contain bacteria and provide a moist, nutrient-rich environment that favours microbial growth. Minced meat is especially susceptible because it receives more handling than other kinds of meat and has more surface exposed to bacterial contamination. Consumers cannot detect the harmful bacteria in or on meat. For safety’s sake, cook meat thoroughly, using a thermometer to test the internal temperature (see Figure 19.3).
FIGURE 19.3 Recommended safe temperatures (celsius) Bacteria multiply rapidly at temperatures between 4 °C and 60 °C. Cook foods to the temperatures shown on this thermometer and hold them at 60 °C or higher.
AUSTRALIAN DIETARY GUIDELINES 2013 ---------------
Care for your food; prepare and store it safely.
PUTTING COMMON SENSE TO THE TEST
808C
Well-done meats
758C
Stuffing, poultry, reheat leftovers
There is no need to wash chopping boards and utensils in hot, soapy water before and after each step of food preparation.
708C
Medium-done meats, raw eggs, egg dishes, pork, minced meats
FALSE
658C
Medium-rare beef steaks, roasts, veal, lamb
608C
Hold hot foods DANGER ZONE: Do not keep foods between 4 8C and 60 8C for more than two hours or for more than one hour when the air temperature is greater than 30 8C.
48C 2158C
Refrigerator temperatures Freezer temperatures
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Safe handling of seafood Most seafood available in Australia is safe, but eating it undercooked or raw can cause severe illnesses – hepatitis, worms, parasites, viral intestinal disorders and other diseases. Commercial freezing kills mature parasitic worms, but only cooking can kill all worm eggs and other microorganisms that can cause illness. For safety’s sake, all seafood should be cooked until it is opaque. Even sushi can be safe to eat if chefs combine cooked seafood and other ingredients into these delicacies. Eating raw oysters can be dangerous for anyone, but people with liver disease and weakened immune systems are most vulnerable. At least 10 species of bacteria Eating raw seafood can be a risky proposition. found in raw oysters can cause serious illness and even death.* Raw oysters may also carry the hepatitis A virus, which can cause liver disease. Some hot sauces can kill many of these bacteria, but not the virus; alcohol may also protect some people against some oysterborne illnesses, but not enough to guarantee protection (or to recommend drinking alcohol). Pasteurisation of raw oysters – holding them at a specified temperature for a specified time – holds promise for killing bacteria without cooking the oyster or altering its texture or flavour.
HOW TO:
PREVENT FOOD-BORNE ILLNESS
Most food-borne illnesses can be prevented by following four simple rules: keep a clean kitchen, avoid cross-contamination, keep hot foods hot and keep cold foods cold. Keep a clean kitchen ›› Wash fruits and vegetables in a clean sink with a scrubbing brush and warm water; store washed and unwashed produce separately. ›› Use hot, soapy water to wash hands, utensils, dishes, non-porous cutting boards and bench tops before handling food and between tasks when working with different foods. Use a bleach solution on cutting boards (approximately one capful per 3 litres of water). ›› Cover cuts with clean bandages before food preparation; dirty bandages carry harmful microorganisms. ›› Mix foods with utensils, not hands; keep hands and utensils away from mouth, nose and hair. ›› Anyone may be a carrier of bacteria and should avoid coughing or sneezing over food. A person with a skin infection or infectious disease should not prepare food. ›› Wash or replace sponges and tea towels regularly. ›› Clean up food spills and crumb-filled crevices. Avoid cross-contamination ›› Wash all surfaces that have been in contact with raw meats, poultry, eggs, fish and shellfish before reusing. ›› Serve cooked foods on a clean plate. Separate raw foods from those that have been cooked. ›› Don’t use marinade that was in contact with raw meat for basting or sauces. Keep hot foods hot ›› When cooking meats or poultry, use a thermometer to test the internal temperature. Insert the thermometer between the thigh and the body of a chicken or into the thickest part of other meats, making sure the tip of the thermometer is not in contact with bone or the pan. Cook to the temperature indicated for that particular meat (see Figure 19.3 on page 675); cook hamburgers to at least medium-well-done. ›› Cook stuffing separately, or stuff poultry just prior to cooking. ›› Do not cook large cuts of meat in a microwave oven; it leaves some parts undercooked while overcooking others. ›› Cook eggs before eating them (soft-boiled for at least 3½ minutes; scrambled until set, not runny; fried until there is no uncooked component).
* Raw oysters can carry the bacterium Vibrio vulnificus; see Table 19.2 on page 672 for details. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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›› Cook seafood thoroughly. ›› When serving foods, maintain temperatures at 70 °C or higher. ›› Heat leftovers thoroughly to at least 75 °C or higher. Keep cold foods cold ›› When running errands, stop at the supermarket last. When you get home, refrigerate the perishable groceries (such as meats and dairy products) immediately. Do not leave perishables in the car any longer than it takes for ice-cream to melt. ›› Put packages of raw meat, fish or poultry on a plate before refrigerating to prevent juices from dripping on food stored below. ›› Buy only foods that are solidly frozen in store freezers. ›› Keep cold foods at 4 °C or less. ›› Marinate meats in the refrigerator, not on the counter. ›› Refrigerate leftovers promptly; use shallow containers to cool foods faster; use leftovers within three to four days. ›› Thaw meats or poultry in the refrigerator, not at room temperature. If you must hasten thawing, use cool water (changed every 30 minutes) or a microwave oven. ›› Freeze meat, fish or poultry immediately if not planning to use within a few days. In general ›› Do not reuse disposable containers; use non-disposable containers or recycle instead. ›› Do not taste food that is suspect. ‘If in doubt, throw it out.’ ›› Throw out foods with danger-signalling odours. Be aware, though, that most foodpoisoning bacteria are odourless, colourless and tasteless. ›› Do not buy or use items that have broken seals or mangled packaging; such containers cannot protect against microbes, insects, spoilage or even vandalism. Check safety seals, buttons and expiration dates. ›› Follow label instructions for storing and preparing packaged and frozen foods; throw out foods that have been thawed or refrozen. ›› Discard foods that are discoloured, mouldy or decayed, or that have been contaminated by insects or rodents. For specific food items ›› Canned goods: Carefully discard food from cans that leak or bulge so that other people and animals will not accidentally ingest it. ›› Milk and cheeses: Use only pasteurised milk and milk products. Aged cheeses, such as cheddar and Swiss, do well for an hour or two without refrigeration, but they should be refrigerated or stored in an Esky for longer periods. ›› Eggs: Use clean eggs with intact shells. Ideally, cook eggs until whites are firmly set and yolks begin to thicken. ›› Honey: Honey may contain dormant bacterial spores, which can awaken in the human body to produce botulism. In adults, this poses little hazard, but infants under one year of age should never be fed honey. Honey can accumulate enough toxin to kill an infant; it has been implicated in several cases of sudden infant death. (Honey can also be contaminated with environmental pollutants picked up by the bees.) ›› Mayonnaise: Commercial mayonnaise may actually help a food to resist spoilage because of the acid content. Still, keep it cold after opening. ›› Mixed salads: Mixed salads of chopped ingredients spoil easily because they have extensive surface area for bacteria to invade, and they have been in contact with cutting boards, hands and kitchen utensils that easily transmit bacteria to food (regardless of their mayonnaise content). Chill them well before, during and after serving. ›› Picnic foods: Choose foods that last without refrigeration such as fresh fruits and vegetables, breads and crackers, and canned spreads and cheeses that can be opened and used immediately. Pack foods cold, layer ice between foods, and keep foods out of water. ›› Seafood: Buy only fresh seafood that has been properly refrigerated or iced. Cooked seafood should be stored separately from raw seafood to avoid cross-contamination. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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Wash your hands with warm water and soap for at least 20 seconds before preparing or eating food to reduce the chance of microbial contamination.
As population density increases along the shores of seafood-harvesting waters, pollution inevitably invades the sea life there. Preventing seafood poisoning is in large part a task of controlling water pollution. To help ensure a safe seafood market, processors must adopt food safety practices based on the HACCP system mentioned earlier. Chemical pollution and microbial contamination lurk not only in the water, but also in the boats and warehouses where seafood is cleaned, prepared and refrigerated. Because seafood is one of the most perishable foods, time and temperature are critical to its freshness, flavour and safety. To keep seafood as fresh as possible, people in the industry must ‘keep it cold, keep it clean and keep it moving’. Wise consumers eat it cooked.
Other precautions and procedures Fresh food generally smells fresh. Not all types of food poisoning are detectable by odour, but some bacterial wastes produce ‘off’ odours. If an abnormal odour exists, the food is spoiled. Throw it out or, if it was recently purchased, return it to the supermarket. Do not taste it. Table 19.3 lists safe refrigerator storage times for selected foods.
TABLE 19.3 Safe refrigerator storage times (,4 °C) 1–2 DAYS Raw minced meats, breakfast or other raw sausages, raw fish or poultry 3–5 DAYS Raw steaks, roasts or chops; cooked meats, poultry, vegetables and mixed dishes; deli meats (packages opened); mayonnaise salads (chicken, egg, pasta, tuna). 1 WEEK Hard-cooked eggs, bacon or hot dogs (opened packages); smoked sausages or seafood 2–4 WEEKS Raw eggs (in shells); deli meats, bacon or hot dogs (packages unopened); dry sausages (hard salami); most aged and processed cheeses (for example, Swiss) 2 MONTHS Mayonnaise (opened jar); most dry cheese (for example, Parmesan, Romano)
Local health departments can provide additional information about food safety. If precautions fail and a mild food-borne illness develops, drink clear liquids to replace fluids lost through vomiting and diarrhoea. If serious food-borne illness is suspected, first call a doctor. Then wrap the remainder of the suspected food and label the container so that the food cannot be mistakenly eaten, place it in the refrigerator and hold it for possible inspection by health authorities.
Food safety while travelling People who travel to other countries have a 50–50 chance of contracting a food-borne illness, commonly described as travellers’ diarrhoea.5 Like many other food-borne illnesses, travellers’ diarrhoea is a sometimes serious, always annoying, bacterial infection of the Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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digestive tract. The risk is high because some countries’ cleanliness standards for food and water are lower than those in Australia and New Zealand. Also, every region’s microbes are different, and although people are immune to the microbes in their own neighbourhoods, they have had no chance to develop immunity to the pathogens in places they are visiting for the first time.
Advances in food safety Advances in technology have dramatically improved the quality and safety of foods available on the market. From pasteurisation in the early 1900s to irradiation in the early 2000s, these advances offer numerous benefits, but they also raise consumer concerns.6
Cook hamburgers to 70 °C; colour alone cannot determine how well cooked a hamburger is. Some burgers will turn brown before reaching 70 °C, whereas others may retain some pink colour, even when cooked to 80 °C.
Irradiation
The use of low-dose irradiation has the potential to protect consumers from food-borne illnesses by: • controlling mould in grains • sterilising spices and teas for storage at room temperature • controlling insects and extending shelf-life in fresh fruits and vegetables (inhibits the growth of sprouts on potatoes and onions and delays ripening in some fruits such as strawberries and mangoes) • destroying harmful bacteria in fresh and frozen beef, poultry, lamb and pork. Some foods are not candidates for the treatment. For example, when irradiated, high-fat meats develop off-odours, egg whites turn milky, grapefruits become mushy and milk products change flavour. (Incidentally, the milk in those boxes kept at room temperature on shop shelves is not irradiated; it is sterilised with an ultrahigh temperature [UHT] treatment.) The use of food irradiation has been extensively evaluated over the past 50 years, approved for use in more than 40 countries and supported by numerous health agencies, including the FAO and WHO. Irradiation does not make foods radioactive, nor does it noticeably change the taste, texture or appearance of approved foods. Vitamin loss is minimal and comparable to amounts lost in other food-processing methods such as canning. Because irradiation kills bacteria without the use of heat, it is sometimes called ‘cold pasteurisation’. All food that is irradiated in Australia and New Zealand must be labelled accordingly.
During the last century, pasteurisation of milk helped to control typhoid fever, tuberculosis, scarlet fever, diphtheria and other infectious diseases. Foods approved for irradiation in Australia and New Zealand are: • herbs and spices • herbal teas • some tropical fruits (breadfruit, carambola, custard apple, lychee, longan, mango, mangosteen, papaya and rambutan).
CURRENT RESEARCH IN NUTRITION Antimicrobial plastic wrap Recent research studying the improvement of plastic wrap found on much of the fresh produce in supermarkets has investigated the application of a combination of techniques to enable the plastic wrap to fight off unwanted germs. Investigations into the application of natural enzymes and natural extracts (such as cinnamon, garlic, clove, thyme and rosemary) into plastic wrap used for food packaging have shown these to be powerful antimicrobial substances. The challenge now is for researchers is to ensure the natural enzymes and extracts do not alter the taste or smell of the wrapped food.
REVIEW IT
Millions of people suffer mild to life-threatening symptoms caused by food-borne illnesses (review Table 19.2 on page 672). As the ‘How to’ box on pages 676–7 describes, most of these illnesses can be prevented by storing and cooking foods at their proper temperatures and by preparing them in sanitary conditions. Irradiation of certain foods can protect consumers from food-borne illnesses.
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19.2 Environmental contaminants
Concern about environmental contamination of foods is growing as the world becomes more populated and more industrialised. Industrial processes pollute the air, water and soil. Plants absorb the contaminants, and people consume the plants (grains, vegetables, legumes and fruits) or the meat and milk products from livestock that have eaten the plants. Similarly, polluted water contaminates the fish and other seafood that people eat. Environmental contaminants present in air, water and foods find their way into our bodies and have the potential to cause numerous health problems.7
Harmfulness of environmental contaminants The potential harmfulness of a contaminant depends in part on its persistence – the extent to which it lingers in the environment or in the body. Some contaminants in the environment are short-lived because microorganisms or agents such as sunlight or oxygen can break them down. Some contaminants in the body may linger for only a short time because the body rapidly excretes them or metabolises them to harmless compounds. These contaminants present little cause for concern. Some contaminants, however, resist breakdown and can accumulate. Each level of the food chain, then, has a greater concentration than the one below (bioaccumulation). Figure 19.4 shows how bioaccumulation leads to high concentrations of toxins in people at the top of the food chain.
FIGURE 19.4 Bioaccumulation of toxins in the food chain This example features fish as the food for human consumption, but bioaccumulation of toxins occurs on land as well when cows, pigs and chickens eat or drink contaminated foods or water.
Key: Toxic chemicals
4 If none of the chemicals are lost along the way, people ultimately receive all of the toxic chemicals that were present in the original plants and plankton.
Level 4 A 68-kilogram person
3 Contaminants become further concentrated in larger fish that eat the small fish from the lower part of the food chain.
Level 3 45 kilograms of fish-eating fish such as lake trout and bass
2 Contaminants become more concentrated in small fish that eat the plants and plankton.
1 Plants and plankton at the bottom of the food chain become contaminated with toxic chemicals, such as methylmercury (shown as red dots).
Level 2 A few tonnes of plankton-eating fish such as bluegill, perch, stream trout and smelt
Level 1 Several tonnes of producer organisms (plant and animal plankton)
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Contaminants enter the environment in various ways. Accidental spills are rare but can have devastating effects. More commonly, small amounts are released over long periods. The following paragraphs describe how three contaminants found their way into the food supply in the past. The first example involves a heavy metal; the others involve organic halogens.
Methylmercury A classic example of acute contamination occurred in 1953 when a number of people in Minamata, Japan became ill with a disease no-one had seen before. By 1960, 121 cases had been reported, including 23 in infants. Mortality was high; 46 died, and the survivors suffered blindness, deafness, lack of coordination and intellectual deterioration. The cause was ultimately revealed to be methylmercury contamination of fish from the bay where these people lived. The infants who contracted the disease had not eaten any fish, but their mothers had, and even though the mothers exhibited no symptoms during their pregnancies, the poison affected their unborn babies. Manufacturing plants in the region were discharging mercury-containing waste into the waters of the bay, the mercury was turning into methylmercury, and the fish in the bay were accumulating this poison in their bodies. Some of the affected families had been eating fish from the bay every day.
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Reminder: A heavy metal is any of a number of mineral ions such as mercury and lead, so called because they are of relatively high atomic weight. Many heavy metals are poisonous.
PBB and PCB
In 1973, half a tonne of PBB (polybrominated biphenyl), a toxic organic compound, was accidentally mixed into some livestock feed that was distributed throughout the state of Michigan in the United States. The chemical found its way into millions of animals and then into the people who ate the meat. The seriousness of the accident came to light when dairy farmers reported that their cows were going dry, aborting their calves and developing abnormal growths on their hooves. Although more than 30 000 cattle, sheep and swine and more than a million chickens were destroyed, an estimated 97 per cent of Michigan’s residents had been exposed to PBB. Some of the exposed farm residents suffered nervous system aberrations and liver disorders. A similar accident occurred in 1979 when PCB (polychlorinated biphenyls) contaminated rice oil in Taiwan. Women who had eaten the tainted rice oil gave birth to children with developmental problems. Decades later, young men who were exposed to PCB during gestation have reduced fertility. The interactive effects of PCB and mercury are especially damaging to brain functions such as balance and coordination.8
Guidelines for consumers How much of a threat do environmental contaminants pose to the food supply? For the most part, the hazards appear to be small. Health agencies may issue advisories informing consumers about the potential dangers of eating contaminated foods. Most recently, mercury poisoning has aroused concerns – even at levels one-tenth of those in the Minamata catastrophe. Virtually all fish have at least trace amounts of mercury (on average, 0.12 parts per million). Fish and other seafood are the main source of dietary mercury.9 Mercury, PCB, chlordane, dioxins and DDT are the toxins most responsible for fish contamination, but mercury leads the list threefold.10 Review Figure 19.4 (on page 680) and notice how toxins such as mercury become more concentrated in animals and in people high in the food chain. Because of bioaccumulation, large game-fish at the top of the aquatic food chain generally have the highest concentrations of mercury (10 times the average). Consumers who enjoy eating these fish should select the smaller, younger ones (within legal limits). Also because of bioaccumulation, the concentrations in fish may be a million times higher than the concentrations in the water itself. Pregnant and lactating women and young children are most vulnerable because mercury toxicity damages the developing brain.11 However, they are also likely to benefit from consuming seafood rich in omega-3 fatty acids. Review Chapter 2 for guidelines regarding fish consumption and mercury in Australia and New Zealand.
For perspective, 1 ppm (part per million) is equivalent to about one minute in two years or 1 cent in $10 000.
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What about the non-commercial fish a person catches from a local lake, river or ocean? After all, it’s almost impossible to tell whether water is contaminated without sophisticated equipment. Each State monitors its waters and issues advisories to inform the public if chemical contaminants have been found in the local fish. To find out whether a fish advisory has been posted in your region, call the local or state/territory environmental health department. All things considered, fish continue to support a healthy diet, providing valuable protein, omega-3 fatty acids and minerals. For most adults, the benefits of protecting against heart disease outweigh the risks of consuming seafood regularly. Ideally, consumers would select fish with high omega-3 fatty acids and low mercury.12 In addition, they should select a variety of seafood to reduce the risk of exposure to contaminants from a single source.
Fish relatively high in omega-3 fatty acids and low in mercury are: • salmon • herring • sardines • lake trout • mackerel • whitefish • flounder • sole. REVIEW IT
Environmental contamination of foods is a concern, but so far, the hazards appear relatively small. In all cases, two principles apply. First, remain alert to the possibility of contamination of foods, and keep an ear open for public health announcements and advice. Second, eat a variety of foods. Varying food choices is an effective defensive strategy against the accumulation of toxins in the body. Each food eaten dilutes contaminants that may be present in other components of the diet.
19.3 Natural toxins in foods
Consumers concerned about food contamination may think that they can eliminate all poisons from their diets by eating only ‘natural’ foods. On the contrary, nature has provided plants with an abundant array of toxins. A few examples will show how even ‘natural’ foods may contain potentially harmful substances. They also show that although the potential for harm exists, actual harm rarely occurs. Poisonous mushrooms are a familiar example of plants that can be harmful when eaten. Few people know, though, that other commonly eaten foods contain substances that can cause illnesses. Cabbage, turnips, kale, brussels sprouts, cauliflower, broccoli and radishes contain small quantities of goitrogens – compounds that can enlarge the thyroid gland. Eating exceptionally large amounts of goitrogen-containing vegetables can aggravate a pre-existing thyroid problem, but it usually does not initiate one. Lima beans and fruit seeds such as apricot pips contain cyanogens – inactive compounds that produce the deadly poison cyanide upon activation by a specific plant enzyme. For this reason, many countries restrict commercially grown lima beans to those varieties with the lowest cyanogen contents. As for fruit seeds, they are seldom deliberately eaten. An occasional swallowed seed or two presents no danger, but a couple of dozen seeds can be fatal to a small child. Perhaps the most infamous cyanogen in seeds is laetrile – a compound erroneously represented as a cancer cure. True, laetrile kills cancer, but only at doses that kill the person, too. The combination of cyanide poisoning and lack of medical attention is life-threatening. The humble potato contains many natural poisons including solanine , a powerful narcotic-like substance. The small amounts of solanine normally found in potatoes are harmless, but solanine is toxic and presents a hazard when consumed in large quantities. Physical symptoms of solanine poisoning include headache, vomiting, abdominal pain, diarrhoea and fever; neurological symptoms include apathy, restlessness, drowsiness, confusion, stupor, hallucinations and visual disturbances. Solanine production increases when potatoes are improperly stored in the light and in either very cold or fairly warm places. Cooking does not destroy solanine, but because most of a potato’s solanine is in the green layer that develops just beneath the skin, it can be peeled off, making the potato safe to eat.
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REVIEW IT
Natural toxins include the goitrogens in cabbage, cyanogens in lima beans, and solanine in potatoes. These examples of naturally occurring toxins illustrate two familiar principles. First, any substance can be toxic when consumed in excess. Second, poisons are poisons, whether made by people or by nature. Remember: it is not the source of a chemical that makes it hazardous, but its chemical structure and the quantity consumed.
19.4 Pesticides
The use of pesticides in agriculture is controversial. They help to ensure the survival of crops, but they leave residues in the environment and on some of the foods that are eaten.
Hazards and regulation of pesticides Ideally, pesticides destroy the pest and quickly degenerate to non-toxic products without accumulating in the food chain. Then, by the time consumers eat the food, no harmful residues remain. Unfortunately, no such perfect pesticide exists. As new pesticides are developed, government agencies assess their risks and benefits and vigilantly monitor their use.
Hazards of pesticides Pesticides applied in the field may linger on the crops. Health risks from pesticide exposure are likely small for healthy adults, but children, the elderly and people with weakened immune systems may be vulnerable to some types of pesticide poisoning. To protect consumers, FSANZ sets the maximum permissible limits for agricultural chemical residues present in foods in Australia and New Zealand within the FSANZ Food Standards Code. The levels of agricultural residues that are allowed in foods are considered safe and must represent the lowest level possible, complying with best industry practices.
Regulation of pesticides Consumers rely on government authorities to keep pesticide use within safe limits. The risks and benefits of a pesticide’s use are evaluated by asking such questions as: How dangerous is it? How much residue is left on the crop? How much harm does the pesticide do to the environment? How necessary is it? What are the alternatives to its use? If the pesticide is approved, FSANZ establishes a tolerance level for its presence in foods, well below the level at which it could cause any conceivable harm. Once tolerances are set, local health departments enforce them by monitoring foods and livestock feeds for the presence of pesticides.
Monitoring pesticides The Department of Agriculture and Water Resources collects and analyses samples of both plant and animal products in a process of random residue monitoring for its National Residue Survey. If samples are found in violation of regulations, the department notifies state and territory authorities immediately so that investigation and preventive action can be taken and consumers can be protected from possible exposure.
Food in the fields In addition to its random residue monitoring, the Department of Agriculture and Water Resources a number of other monitoring projects relating to residue limits. These include: • targeted monitoring – to obtain more focused information about a known or potential residue problem through a non-random sampling process • compliance testing – to prevent the normal marketing of products with a known contamination risk • residue prevention – to prevent or minimise the risks of unacceptable residues to public health and trade Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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c onsignment testing – to meet specific requirements of client industries for market access support (for example, products where each consignment must be sampled prior to export).
Food on the plate
Michael Blann/Getty Images
The Australian Total Diet Survey is conducted by FSANZ to estimate the dietary exposure of pesticide residues, contaminants and other substances. The Total Diet Survey provides a direct estimate of the amounts of pesticide residues that remain in foods as they are usually eaten – after they have been washed, peeled and cooked. FSANZ has reported results that demonstrate that the levels of pesticide residues, contaminants and other substances in our food are very low, and in all cases they are within acceptable safety limits.13
Consumer concerns Many varieties of fruits and vegetables are imported from other countries.
Despite these reassuring reports, consumers still worry that food monitoring may not be adequate. FSANZ, the Department of Agriculture and Water Resources and other government departments do not sample all foods or test for all pesticides in each sample. The sheer volume of foods, both domestic and imported, makes this an impossible task. These government agencies cannot be expected to guarantee 100 per cent safety in the food supply. Instead, they set standards so that substances do not become a hazard, check enough samples to adequately assess average food safety and act promptly when problems or suspicions arise.
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Minimising risks
Washing fresh fruits and vegetables removes most, if not all, of the pesticide residues that might have been present.
HOW TO:
Whether consumers ingest pesticide residues depends on a number of factors. How much of a given food does the consumer eat? What pesticide was used on it? How much was used? How long ago was the food last sprayed? Did environmental conditions promote pest growth or pesticide breakdown? How well was the produce washed? Was it peeled or cooked? With so many factors, consumers cannot know for sure whether pesticide residues remain on foods, but they can minimise their risks by following the guidelines offered in the ‘How to’ box below. The food supply is protected well enough that consumers who take these precautions can feel secure that the foods they eat are safe.
PREPARE FOODS TO MINIMISE PESTICIDE RESIDUES
To remove or reduce any pesticide residues from foods, follow these instructions: ›› Trim the fat from meat, and remove the skin from poultry and fish; discard fats and oils in broths and pan drippings. (Pesticide residues concentrate in the animal’s fat.) ›› Select fruits and vegetables that do not have holes. ›› Wash fresh produce in warm running water. Use a scrub brush, and rinse thoroughly. ›› Use a knife to peel an orange or grapefruit; do not bite into the peel. ›› Discard the outer leaves of leafy vegetables such as cabbage and lettuce. ›› Peel waxed fruits and vegetables; waxes don’t wash off and can seal in pesticide residues. ›› Peel vegetables such as carrots and fruits such as apples when appropriate. (Peeling removes pesticides that remain in or on the peel, but also removes fibres, vitamins and minerals.) ›› Eat a variety of foods to minimise exposure to any one pesticide. ›› Consider buying certified organic foods. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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The use of pesticides has helped to generate higher crop yields that feed the majority of the world and protect against diseases transmitted by insects. Still, many consumers are doubtful. To feed a nation while using fewer pesticides requires creative farming methods. Highlight 19 describes how scientists can genetically alter plants to enhance their production of natural pesticides, but there exist other alternative agriculture methods. These methods include such practices as rotating crops, releasing organisms into fields to destroy pests and planting non-food crops nearby to kill pests or attract them away from the food crops. For example, releasing sterile male fruit flies into orchards helps to curb the population growth of these pests; some flowers, such as marigolds, release natural insecticides and are often planted near crops such as tomatoes. Such alternative farming methods are more labour-intensive and may produce smaller yields than conventional methods, at least initially. Over time, though, by eliminating expensive pesticides, fertilisers and fuels, these alternatives may actually cut costs more than they cut yields.
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Alternatives to pesticides
People can grow organic crops when their gardens or farms are relatively small.
NASAA
Alternative methods are especially useful for farmers who want to produce and market organic crops that are grown and processed according to strict certification rules and are accredited by an authorised organisation as classified by organisations such as the Australian Quarantine and Inspection Service (AQIS) or the International Organic Accreditation Service. Organic farming occurs without the use of synthetic chemicals or genetically modified components. It must be noted, however, that the use of the word ‘organic’ is not regulated in Australia, and as such it’s important to make sure that the produce you buy comes from certified growers and producers. Implied in the marketing of organic foods is that organic products are safer or healthier for consumers than those grown using other methods, which may not be the case. Using unprocessed animal manure as an organic fertiliser, for example, may transmit bacteria, such as E. coli, to human beings. Both Many consumers are willing to pay a little more organic and conventional methods may have advantages and disadvantages, for organic produce. and consumers must remain informed. Pesticide residues in organic foods are substantially lower than in conventionally grown foods but residues are not eliminated completely.14 Are organic foods nutritionally superior to conventional foods? Any nutrient differences reported have been within the range that normally occurs in crops. Some research suggests that organic crops may have a longer shelf life and better flavour, perhaps due to differences in soil type, soil nutrients, or environmental conditions.15 Limited research suggests foods produced organically have increased amounts of some phytochemicals.16 Interestingly, ‘organic’ has intense meanings for many consumers. In one study, participants tasting foods, such as two Organic foods yoghurts, rated the one labelled ‘organic’ as more nutritious, lower in fat, and worth more that have met organic money and the one labelled ‘regular’ as more flavourful – even though both yoghurts were standards may use organic and identical (only their labels differed).17 certification labels on their products from AQIS-accredited Pesticides can safely improve crop yields when used according to regulations, but they can also be organisations, such hazardous when used inappropriately. Testing of foods for pesticide residues in the field and in diet as this seal from the surveys of foods prepared table-ready occur through FSANZ and the Department of Agriculture and National Association Water Resources. Consumers can minimise their ingestion of pesticide residues on foods by following for Sustainable the suggestions in the ‘How to’ box on page 684. Alternative farming methods may allow farmers to Agriculture, Australia. grow crops with few or no pesticides. REVIEW IT
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19.5 Food additives
PUTTING COMMON SENSE TO THE TEST
Additives confer many benefits on foods. Some reduce the risk of food-borne illness (for example, nitrites used in curing meat prevent poisoning from the botulinum toxin). Others can enhance nutrient quality (as in calcium in fortified juices). Most additives are preservatives that help prevent spoilage during the time it takes to deliver foods long distances to supermarkets and then to kitchens. Some additives simply make foods look good and taste better. Intentional additives are put into foods on purpose, whereas indirect additives may get in unintentionally before or during processing.
Organic foods are known to be of better quality than foods produced using pesticides.
AAP Photo/Universal Images Group/Dorling Kindersley
FALSE
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Without additives, bread would quickly get mouldy and salad dressing would become rancid.
Regulations governing additives FSANZ’s concern with additives hinges primarily on safety. FSANZ carries out safety assessments of food additives before they are allowed to be used. The following things are checked: • Is the food additive safe (at the requested level in that particular food)? • Are there good technological reasons for the use of the food additive? • Will consumers be clearly informed about its presence? A food additive is approved for use by FSANZ only if it can be demonstrated that no harmful effects are expected to result from the requested use. Extensive testing of the food additive is required, and FSANZ evaluates any data to determine if the food additive is safe. In addition, an ‘exposure assessment’ is undertaken, which estimates the likely amount that would be consumed if the food additive were approved. This estimated amount of consumption is then compared to the ‘acceptable daily intake’ (ADI), which is the amount of a food additive that can be eaten every day for an entire lifetime without adverse effect. If satisfied on these points, FSANZ recommends a maximum level of the food additive for use in particular foods, based on technological need and providing it is well within safe limits.
Margin of safety Whatever risk level is permitted, actual risks must be determined by experiments. To determine risks posed by an additive, researchers feed test animals the additive at several concentrations throughout their lives. The additive is then permitted in foods in amounts 100 times below the lowest level that is found to cause any harmful effect; that is, at a one-hundredth margin of safety. In many foods, there are naturally occurring substances with narrower margins of safety. Even nutrients pose risks at dose levels above those recommended and normally consumed: for young adults, the recommendation for vitamin D is only one-tenth of the Upper Level of Intake. People consume common table salt daily in amounts only three to five times less than those that pose a hazard.
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Risks versus benefits
Polara Studios, Inc.
Of course, additives would not be added to foods if they only presented risks. Additives are in foods because they offer benefits that outweigh the risks they present, or make the risks worth taking. In the case of colour additives that only enhance the appearance of foods but do not improve their health value or safety, no amount of risk may be deemed worth taking. In contrast, it may be worth taking the small risks associated with the use of nitrites on meat products, for example, because nitrites inhibit the formation of the deadly botulinum toxin. The choice involves a compromise between the risks of using additives and the risks of doing without them.
Intentional food additives Intentional food additives are added to foods to give them some desirable characteristic: resistance to spoilage, colour, flavour, texture, stability or nutritional value. Table 19.4 presents an overview of additives, and the next sections describe additives people most often ask about.
Both salt and sugar act as preservatives by withdrawing water from food; microbes cannot grow without water.
TABLE 19.4 Intentional food additives FOOD ADDITIVE
PURPOSE
COMMON EXAMPLES
Antimicrobial agents
Prevent microorganisms from growing
Salt, sugar, nitrites and nitrates (such as sodium nitrate)
Antioxidants
Delay or prevent rancidity of fats and other damage to foods caused by oxygen
Vitamin C (erythorbic acid, sodium ascorbate), vitamin E (tocopherol), sulphites, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT)
Colours
Enhance appearance
Artificial: indigotine, erythrosine, tartrazine. Natural: annatto (yellow), caramel (yellowish brown), carotenoids (yellowish orange), dehydrated beets (reddish brown), grape skins (red, green)
Flavours
Enhance taste
Salt, sugar, spices, artificial sweeteners, monosodium glutamate (MSG)
Emulsifiers and gums
Thicken, stabilise or otherwise improve the consistency
Emulsifiers: lecithin, alginates, mono- and diglycerides. Gums: agar, alginates, carrageenan, guar, locust bean, psyllium, pectin, xanthan gum, gum arabic, cellulose derivatives
Antimicrobial agents Foods can spoil in two ways. One way is relatively harmless: by losing their flavour and attractiveness. (Additives to prevent this kind of spoilage include antioxidants, discussed later.) The other way is by becoming contaminated with microbes that cause food-borne illnesses, a hazard that justifies the use of antimicrobial agents. The most widely used antimicrobial agents are ordinary salt and sugar. Salt has been used throughout history to preserve meat and fish; sugar serves the same purpose in canned and frozen fruits and in jams and jellies. Both exert their protective effect primarily by capturing water and making it unavailable to microbes. Other antimicrobial agents, the nitrites, are added to foods for three main purposes: to preserve colour, especially the pink colour of hot dogs and other cured meats; to enhance flavour by inhibiting rancidity, especially in cured meats and poultry; and to protect against
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Colour additives not only make foods attractive, but they identify flavours as well. Everyone agrees that yellow jellybeans should taste lemony and black ones should taste like licorice.
bacterial growth. In amounts smaller than those needed to confer colour, nitrites prevent the growth of the bacteria that produce the deadly botulinum toxin. Nitrites clearly serve a useful purpose, but their use has been controversial. In the human body, nitrites can be converted to nitrosamines. At nitrite levels higher than those used in food products, nitrosamine formation causes cancer in animals. The food industry uses the minimal amount of nitrites necessary to achieve results, and nitrosamine formation has not been shown to cause cancer in human beings. Detectable amounts of nitrosamine-related compounds are found in malt beverages (beer) and cured meats (primarily bacon). Yet even the quantities found in beer and bacon hardly make a difference in a person’s overall exposure to nitrosamine-related compounds. An average cigarette smoker inhales 100 times the nitrosamines that the average bacon eater or beer drinker ingests.
APPLICATIONS OF NUTRITIONAL RESEARCH Antimicrobial properties of plants Recent research has provided promising evidence about the natural antimicrobial properties of native Australian plants. The Kakadu and Davidson plum, both native to Australia, have promising protective properties as food preservatives. Researchers at the University of Queensland are investigating the properties of these two plums and their potential for use in the preservation of meat products such as minced meat. Traditionally, sulphites have been used to preserve minced meat products (such as sausages), but the extracts of these two plants may replace such practices. The antioxidant properties of these plants may also have an additional benefit beyond that of food preservation.
Antioxidants
Sulphites appear on food labels as: • sulphur dioxide • sodium sulphite • sodium bisulphite • potassium bisulphite • sodium metabisulphite • potassium metabisulphite.
Another way food can spoil is by exposure to oxygen (oxidation). Often, these changes involve no hazard to health, but they damage the food’s appearance, flavour and nutritional quality. Oxidation is easy to detect when sliced apples or potatoes turn brown or when oil goes rancid. Antioxidants prevent these reactions. Among the antioxidants approved for use in foods are vitamin C (ascorbate) and vitamin E (tocopherol). Another group of antioxidants include the sulphites. Sulphites prevent oxidation in many processed foods, alcoholic beverages (especially wine) and drugs. For most people, sulphites pose no hazard in the amounts used in products.
Artificial flavours and flavour enhancers Natural flavours, artificial flavours and flavour enhancers are the largest single group of food additives. Many foods taste wonderful because manufacturers have added the natural flavours of spices, herbs, essential oils, fruits and fruit juices. Some spices, notably those used in Mediterranean cooking, provide antioxidant protection as well as flavours. Often, natural flavours are used in combination with artificial flavours. The sugar alternatives discussed in Chapter 4 are among the most widely used artificial flavour additives.
Monosodium glutamate (MSG)
One of the best-known flavour enhancers is monosodium glutamate (MSG) – a sodium salt of the amino acid glutamic acid. MSG is used widely in a number of foods, especially Asian foods. Besides enhancing the well-known sweet, salty, bitter and sour tastes, MSG itself may possess a pleasant flavour. Adverse reactions to MSG may occur in people with asthma and in
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sensitive individuals who consume large amounts of MSG, especially on an empty stomach, but it is otherwise considered safe.
Sugar alternatives Sugar alternatives are among the most widely used artificial flavour additives. This section presents safety issues surrounding a few of the most controversial ones. Questions about the safety of the artificial sweetener saccharin surfaced in 1977, when experiments suggested that large doses of saccharin (equivalent to hundreds of cans of diet soft drink daily for a lifetime) increased the risk of bladder cancer in rats. As a result, there was a proposed ban suggested for saccharin. Public outcry in favour of saccharin was so loud, however, that additional safety studies were conducted. These studies concluded that saccharin did not cause cancer in humans. Common sense dictates that consuming large amounts of any substance is probably not wise, but at current, moderate intake levels, saccharin appears to be safe for most people. Aspartame – a simple chemical compound made of two amino acids (phenylalanine and aspartic acid) and a methyl group (CH3) – must bear a warning label for people with the inherited disease phenylketonuria (PKU). People with PKU are unable to dispose of any excess phenylalanine. The accumulation of phenylalanine and its by-products is toxic to the developing nervous system, causing irreversible brain damage. The little extra phenylalanine from aspartame poses only a small risk, even in heavy aspartame users, but people with PKU need to get all their required phenylalanine from protein- and nutrient-rich foods instead of from an artificial sweetener. During metabolism in the body, the methyl group of aspartame temporarily becomes methyl alcohol (methanol) – a potentially toxic compound. This breakdown also occurs in aspartame-sweetened beverages when they are stored at warm temperatures over time. The amount of methanol produced may be safe to consume, but a person may not want to, considering that the beverage has lost its sweetness. In the body, enzymes convert methanol to formaldehyde, another toxic compound. Finally, formaldehyde is broken down to carbon dioxide. Before aspartame could be approved, the quantities of these products generated during metabolism had to be determined, and they were found to fall below the threshold at which they would cause harm. In fact, tomato juice yields six times as much methanol as diet soft drink. The amount of artificial sweetener considered safe represents the amount of consumption that, if maintained every day throughout a person’s life, would still be considered safe by a wide margin. It usually reflects an amount 100 times less than the level at which no observed effects occur in animal research studies. This amount for aspartame, for example, is 50 milligrams per kilogram of body weight. For a 75-kilogram adult, this is equivalent to 97 packets of Equal or 20 cans of soft drinks sweetened only with aspartame every day for a lifetime. Most people who use aspartame consume less than 5 milligrams per kilogram of body weight per day.
Texture and stability Some additives help to maintain a desirable consistency in foods. Emulsifiers keep mayonnaise stable, control crystallisation in syrups and keep spices dispersed in salad dressings. Gums are added to thicken foods and help form gels. Yeast may be added to provide leavening, and bicarbonates and acids may be used to control acidity.
Indirect food additives Indirect or incidental additives find their way into foods during harvesting, production, processing, storage or packaging. Incidental additives may include tiny bits of plastic, glass, paper, tin and other substances from packages as well as chemicals from processing. This section will discuss the two areas of indirect additives that sometimes make headline news.
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PUTTING COMMON SENSE TO THE TEST
The majority of food additives in the food supply are unsafe at levels of normal consumption. FALSE
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Hormones Hormones are a unique type of incidental additive in that their use is intentional, but their presence in the final food product is not. The Department of Agriculture and Water Resources’ National Residue Survey (NRS) audits the use of currently registered agricultural and veterinary chemicals in Australia that include hormonal growth promotants used to improve growth in livestock. The most recent NRS produced results where no growth promotants above Australian allowable limits were found in any edible testing samples.18
Antibiotics Like hormones, antibiotics are also intentionally given to livestock, and residues may remain in the meats and milks. Antibiotic chemicals are used in livestock to treat infections by microorganisms (for example, bacteria, protozoa, fungi) that cause a range of diseases. Monitoring of antibiotic residues involves a number of sampling regimens, including a general antibiotic screen, and, where the screen test identifies a class of compounds, confirmation and quantification are carried out by further testing that is appropriate for the class of antibiotic. In the most recent NRS, no testing samples were found to be above Australian standards.
REVIEW IT
On the whole, the benefits of food additives seem to justify the risks associated with their use. Regulation exists to control the use of intentional additives: antimicrobial agents (such as nitrites) to prevent microbial spoilage; antioxidants (such as vitamins C and E and sulphites) to prevent oxidative changes; colours (such as tartrazine) and flavour enhancers (such as MSG) to appeal to senses. Incidental additives sometimes get into foods during processing, but rarely present a hazard, although some processes, such as treating livestock with hormones and antibiotics, raise consumer concerns.
19.6 Consumer concerns about water
Water that is suitable for drinking is called potable. Only 1 per cent of all the earth’s water is potable.
Foods are not alone in transmitting diseases; water can do the same. In fact, Cryptosporidium and Cyclospora, commonly found in fresh fruits and vegetables, and Vibrio vulnificus, found in raw oysters, are commonly transmitted through contaminated water. In addition to microorganisms, water may contain many of the same impurities that foods do: environmental contaminants, pesticides, and additives such as chlorine used to kill pathogenic microorganisms and fluoride used to protect against dental caries. A glass of ‘water’ is more than just H2O. This discussion examines the sources of drinking water, harmful contaminants and ways to ensure water safety.
Sources of drinking water Drinking water comes from two sources – surface water and groundwater. Each source supplies water for about half of the population. Most major cities obtain their drinking water from surface water – the water in lakes, rivers and reservoirs. Surface water is readily contaminated because it is directly exposed to acid rain, run-off from highways and urban areas, pesticide run-off from agricultural areas, and industrial wastes that are dumped directly into it. Surface water contamination is reversible, however, because fresh rain constantly replaces the water. It is also cleansed to some degree by aeration, sunlight and the plants and microorganisms that live in it. Groundwater is the water in underground aquifers – rock formations that are saturated with, and yield, usable water. Groundwater is contaminated more slowly than surface water, but also more permanently. Contaminants deposited on the Earth’s surface migrate slowly through the soil before reaching groundwater. Once there, the contaminants break down less rapidly than in surface water due to the lack of aeration, sunlight and aerobic microorganisms. The slow replacement of groundwater also helps contaminants remain for a long time.
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Chapter 19: Consumer concerns about foods and water
Groundwater is especially susceptible to contamination from hazardous waste sites, dumps and landfills, underground tanks storing gasoline and other chemicals, and improperly discarded household chemicals and solvents.
Water systems and regulations Public water systems treat water to remove contaminants that have been detected above acceptable levels. During treatment, a disinfectant (usually, chlorine) is added to kill bacteria. The addition of chlorine to public water is an important public health measure that appears to offer great benefits and small risks. Chlorinated water has eliminated such water-borne diseases as typhoid fever, which once ravaged communities, killing thousands of people, but it has been associated with a slight increase in bladder and rectal cancers and with contamination of the environment with the toxic by-product dioxin. State and territory government authorities are responsible for ensuring that public water systems meet minimum standards for protecting public and environmental health. Even safe water may have characteristics that some consumers find unpleasant. Most of these problems reflect the mineral content of the water. For example, manganese and copper give water a metallic taste, and sulphur produces a ‘rotten egg’ odour. Iron leaves a rusty brown stain on plumbing fixtures and laundry. Calcium and magnesium (commonly found in ‘hard water’) build up in hot-water heaters. Similarly, soap is not easily rinsed away in hard water, leaving bathtubs and laundry looking grimy. For these and other reasons, some consumers have adopted alternatives to the public water system.
Home water filters To ease concerns about the quality of drinking water, some people purchase water filter systems (either in tap, fridge or as part of a water jug). Manufacturers offer a variety of units for removing contaminants from drinking water. None of them removes all contaminants, and each has its own advantages and disadvantages. Choosing the right treatment unit depends on the kinds of contaminants in the water. For example, activated carbon filters are particularly effective in removing chlorine, heavy metals such as mercury, and organic contaminants from sediment; reverse osmosis, which forces pressurised water across a membrane, flushes out sodium, arsenic and some microorganisms such as Giardia; and distillation systems, which boil water and condense the steam to water, remove contaminants such as lead and kill microorganisms in the process.
Bottled water Despite the higher cost, many people turn to bottled water as an alternative to tap water. Labels on bottled water must identify the water’s source. Approximately 75 per cent of bottled waters derive from protected groundwater (from springs or wells) that has been disinfected with ozone rather than chlorine. Ozone kills microorganisms, then disintegrates spontaneously into water and oxygen, leaving behind no toxic by-products. Bottled waters may also be treated by reverse osmosis or ion exchange to remove inorganic compounds. Alternatively, the water may be distilled or de-ionised to remove dissolved solids. Most bottled waters do not contain fluoride; consequently, they do not provide the tooth protection of fluoridated water from community public water systems. Consumers must also note the high environmental cost of bottled water.
Water supply issues and options The environmental changes that have occurred in the last decade have resulted in severe drought conditions in many areas in Australia. Despite recent rainfalls, water supply is still a topic of concern. In recent years, water storage levels in some capital cities were as low as
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26 per cent (Melbourne), 28 per cent (Perth), 40 per cent (Brisbane) and 43 per cent (Canberra). However, regional areas within some States and Territories have continued to experience severe water shortages due to ongoing drought. For example, NSW is experiencing its worst drought in over 20 years. Due to their tropical climates and wet seasons, places such as Darwin and Cairns in Australia’s far north managed to maintain their water storage capacities at near 100 per cent during a recent drought, but permanent water restrictions of some variety are commonplace in almost all areas. See http:// water.bom.gov.au/waterstorage/awris/ for storage levels throughout Clean rivers represent irreplaceable water resources. Australia. The Australian Government’s National Water Commission is responsible for ensuring progress towards sustainable management and use of Australia’s water resources via a water reform known as the National Water Initiative. This is an intergovernmental agreement that was signed by attendees at the June 2004 Council of Australian Governments (COAG) meeting, except for Tasmania and Western Australia, which signed the agreement on 3 June 2005 and 6 April 2006, respectively. The commission was established under the National Water Commission Act 2004. The National Water Initiative commitments undertaken by all governments include: • preparation of water plans with provision for the environment • dealing with over-allocated or stressed water systems • introducing registers of water rights and standards for water accounting • expanding the trade in water • improving pricing for water storage and delivery • meeting and managing urban water demands. Options for alternative water supplies involve finding the most effective combination(s) to secure water for cities and towns across Australia. Traditionally, many towns and cities have been supplied with water by rainfall, which is collected from catchment areas and stored in dams and reservoirs. In other areas, supplies have come from groundwater reserves. With severe drought conditions, there is less run-off filling the dams that supply cities, and increasing pressure on groundwater resources. As such, a range of weather-resilient options to boost urban water supplies is needed. These options include reusing, recycling, desalination and capture of rain and stormwater, and managed aquifer recharge.
Re-use and recycling Recycling for non-drinking consumption has been widely accepted across Australia, with considerable investment to meet increasing recycling targets. Household recycling of grey water is also increasingly being adopted to provide a constant source of water (predominantly for gardens) during times of drought and water restrictions. Introducing recycled water into the drinking water supply is also a viable option to reduce water shortages and make water supplies less vulnerable to climate.
Desalination Desalination is the process of removing salt from water to make it useable for a range of purposes, including drinking. While energy and process costs make this a relatively expensive option, advancing technologies are steadily reducing operational costs. There are a number of large functioning desalination plants in Australia, with smaller plants also in use in Western Australia, South Australia and Queensland.
Stormwater Stormwater is a resource that can provide additional environmental, economic and social benefits to our urban areas beyond water supply. Through more effective water cycle management, stormwater harvesting can help prevent pollution, alleviate floods, relieve
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Chapter 19: Consumer concerns about foods and water
pressure on drinking water supplies and contribute to waterway health. More work is required to overcome some of the challenges associated with the collection, storage, treatment and transport of stormwater in built-up urban areas.
Managed aquifer recharge Managed aquifer recharge is the deliberate recharge of water to aquifers for subsequent recovery or environmental benefit. In urban areas, managed aquifer recharge can provide effective storage for desalinated seawater, recycled water, stormwater and even mains water, reducing transportation costs and water loss through evaporation.
REVIEW IT
Like foods, water may contain infectious microorganisms, environmental contaminants, pesticide residues and additives. State and territory government authorities monitor the safety of the public water system, but many consumers choose home water-treatment systems or bottled water instead of tap water. Water supply issues are an ongoing problem that may be partially resolved by a number of alternative water supply technologies.
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CHAPTER ACTIVITIES PUTTING COMMON SENSE TO THE TEST: ANSWERS 1 One way to prevent potential food-borne illness is to avoid buying damaged food products. TRUE
3 Organic foods are known to be of better quality than foods produced using pesticides. FALSE
Damaged food products may provide an environment that allows the growth of bacteria. Although the bacteria may not be able to be detected to the naked eye, the results of ingestion can be as mild as an upset stomach or as dire as death.
2 There is no need to wash chopping boards and utensils in hot, soapy water before and after each step of food preparation. FALSE
Although this may be thought to be true, currently there is no clear evidence that suggests that foods labelled as organic are of better quality or have a better nutritional profile than those produced using pesticides.
4 The majority of food additives in the food supply are unsafe at levels of normal consumption. FALSE
Not only should chopping boards and utensils be washed in between each stage of preparation, but also hands and any other items used for food preparation.
Food additives consumed at usual levels have been rigorously tested. A safety margin for the use of any food additives is used to ensure safety for human consumption.
NUTRITION PORTFOLIO Practising food safety allows you to eat a variety of foods, with little risk of food-related illnesses. • Review your food-handling practices and describe how effectively you wash your hands, utensils and kitchen surfaces when preparing foods.
• •
Describe the steps you take to separate raw and cooked foods while storing and preparing them. Describe how you can ensure that you cook foods to a safe temperature and refrigerate perishable foods promptly.
STUDY QUESTIONS Multiple choice questions Answers can be found at the back of the book. 1
Eating contaminated food such as undercooked poultry or unpasteurised milk might cause a: a b c d
2
5 to 7 days 1 to 2 days
c d
chlorine ozone
fluoride sulphur
Goitrogens are an example of a(n): a b
6
c d
heavy metal artificial colour
c d
natural toxicant animal hormone
Bio-accumulation is the accumulation of contaminants in:
9
salt and nitrites carrageenan and MSG dioxins and sulphites vitamin C and vitamin E
The average person is likely to consume no more than how many mg/kg of aspartame each day? a b
Bottled water is generally disinfected by: a b
5
10 to 14 days 7 to 10 days
plant matter water used for cleaning fish microorganisms the flesh of animals high on the food chain
Common antimicrobial additives include: a b c d
8
below 25 °C and above 50 °C below 40 °C and above 60 °C below 25 °C and above 40 °C below 10 °C and above 60 °C
The safe refrigeration time for minced raw meats is: a b
4
7
food allergy food infection food toxin botulinum reaction
The safe temperature zone for foods ranges from: a b c d
3
a b c d
0.5 mg/kg 5 mg/kg
c d
50 mg/kg 500 mg/kg
An example of antioxidants added to foods is: a b c d
dioxins folate beta-carotene sulphites
10 Intentional food additives can be used to: a b c d
protect against dental caries destroy harmful minerals such as mercury enhance taste remove the sulphur that produces a ‘rotten egg’ odour
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Chapter 19: Consumer concerns about foods and water
Review questions 1
To what extent does food poisoning present a real hazard to consumers eating Australian foods? How many people are affected each year? (Section 19.1)
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4
What is meant by a ‘persistent’ contaminant of foods? Describe how contaminants get into foods and build up in the food chain. (Section 19.2)
5
Do natural toxins present any dangers to the food supply? (Section 19.3)
2
What are the two types of food-borne illnesses? Provide an example of each. What are some measures that help prevent food-borne illnesses? (Section 19.1)
6
How do pesticides become a hazard to the food supply, and how are they monitored? In what ways can people reduce the concentrations of pesticides in and on foods that they prepare? (Section 19.3)
3
What precautions should be adopted when preparing all foods? (Section 19.1)
7
What are some alternatives to using potable water for all household uses? (Section 19.6)
•
Learn more about food irradiation from the International Food Information Council Foundation: https://www. foodinsight.org/ Learn more about organic foods and national organic food standards from AQIS: http://www.agriculture. gov.au/ag-farm-food/food/organic-biodynamic Find information on food-borne illnesses and safe food handling from the Dietitians Association of Australia: http://www.daa.asn.au Learn more about water supply from the Australian Bureau of Agricultural and Resources Economics and Sciences: http://www.agriculture.gov.au/abares
NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/ monitoringnutrients/pages/default.aspx • Get food safety tips from the Food Safety Information Council site or from the Fight BAC! campaign of the Partnership for Food Safety Education: http://www. foodsafety.asn.au or http://www.fightbac.org • Learn about the Food Safety Standard for thermometers at http://www.foodstandards.gov.au • Find commonsense health tips for travellers at the Australian Government Smart Traveller site: http://www.smartraveller.gov.au
•
•
•
SEARCH ME! NUTRITION Keyword: food illness Read the article Listeriosis: a primer. What are the consequences of listeriosis infection? Who are the groups of people most at risk from this infection?
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HIGHLIGHT
19
19.7 FOOD BIOTECHNOLOGY
Science Source/Tony Freeman
Advances in food biotechnology promise just about everything from the frivolous (a tear-free onion) to the profound (a hunger-free world). Already, biotechnology has produced leaner meats, longer shelf-life, better nutrient composition and greater crop yields grown with fewer pesticides. Overall, biotechnology offers numerous opportunities to overcome food shortages, improve the environment and eliminate disease.1 But it also raises concerns about possible risks to the environment and human health. Critics assert that biotechnology will exacerbate world hunger, destroy the environment and endanger health. This highlight presents some of the many issues surrounding genetically engineered foods. Many of the examples used within this highlight are not approved for production in Australia or New Zealand, but illustrate how biotechnology can be used.
These tomatoes are grown from genetically modified seed stock.
The promises of genetic engineering For centuries, farmers have been selectively breeding plants and animals to shape the characteristics of their crops and livestock. They have created prettier flowers, hardier vegetables and leaner animals. Consider the success of selectively breeding corn. Early farmers in Mexico began with a wild, native plant called teosinte that bears only five or six kernels on each small spike. Many years of patient selective breeding have produced large ears filled with hundreds of plump kernels aligned in perfect formation, row after row. Such genetic improvements, together with the use of irrigation, fertilisers and pesticides, were responsible for these
© Smithsonian Tropical Research Institute/Antonio Montaner, photographer
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This wild predecessor of corn, with its sparse five or six kernels, bears little resemblance to today’s large, full, sweet ears.
increases in crop yields in the twentieth century. Farmers still use selective breeding, but now, in the twenty-first century, advances in genetic engineering have brought rapid and dramatic changes to agriculture and food production. Although selective breeding works, it is slow and imprecise because it involves mixing thousands of genes from two plants and hoping for the best. With genetic engineering, scientists can improve crops (or livestock) by introducing a copy of the specific gene needed to produce the desired trait. Figure H19.1 illustrates the difference. Once introduced, the selected gene acts like any other gene – it provides instructions for making a protein. The protein then determines a characteristic in the genetically modified plant or animal. In short, the process is now faster and more refined. Farmers no longer need to wait patiently for breeding to yield improved crops and animals, nor must they even respect natural lines of reproduction among species. Laboratory scientists can now copy genes from any organism and insert them into almost any other organism – plant, animal or microbe. Their work is changing not only the way farmers plant, fertilise and harvest their crops, but also the ways the food industry processes food and consumers receive nutrients, phytochemicals and drugs.
Extended shelf-life Among the first genetically engineered products were tomatoes that stay firm and ripe longer than regular tomatoes. These genetically modified tomatoes promise less
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FIGURE H19.1 Selective breeding and genetic engineering compared Traditional selective breeding Traditional selective breeding combines many genes from two varieties of the same species to produce one with the desired characteristics.
Donor
In the new variety, many genes have been transferred.
Commercial variety
+
5
Desired gene
Desired gene Genetic engineering
Through genetic engineering, a single gene (or several) are transferred from the same or different species to produce one with the desired characteristics.
Donor
In the new variety, only the desired gene is transferred.
Commercial variety
+
5
Desired gene
Desired gene isolated
waste due to a slower softening process. Tomatoes produce a protein that softens them after they have been picked. Scientists can now introduce into a tomato plant a gene that is a mirror image of the one that codes for the ‘softening’ enzyme. This gene fastens itself to the RNA of the native gene and blocks synthesis of the softening protein. Without this protein, the genetically altered tomato softens more slowly than a regular tomato, allowing growers to harvest it at its most flavourful and nutritious vine-ripe stage.
Improved nutrient composition Genetic engineering can also improve the nutrient composition of foods. Instead of manufacturers adding nutrients to foods during processing, plants can be genetically altered to do their own fortification work – a strategy called biofortification. Biofortification of staple crops with key vitamins and minerals can effectively combat the nutrientdeficiency diseases that claim so many lives worldwide. Examples of biofortification include the following: • Soybeans may be implanted with a gene that upgrades soy protein to a quality approaching that of milk. • Corn may be modified to contain lysine and tryptophan, its two limiting amino acids. • Soybean and canola plants can be genetically modified to alter the composition of their oils, making them richer in the heart-healthy mono-unsaturated fatty acids.
• ‘Golden rice’, which has received genes from a daffodil and a bacterium that enable it to make beta-carotene, offers some promise in helping to correct vitamin A deficiency worldwide. (Chapter 11 described how vitamin A deficiency contributes to the deaths of 2 million children and the blindness of a half-million each year.) Of course, increasing nutrients in crops may have unintended consequences as well. For example, when broccoli is manipulated to increase its selenium content, production of the cancer-fighting phytochemical sulforaphane declines. As you might predict, enhancing the chemical composition of plants is not limited to the essential nutrients. Genetically modified crops can also produce more of the phytochemicals that help maintain health and reduce the risks of chronic diseases (see Highlight 13). Crops can be modified to produce more or less of almost any substance – the possibilities seem endless.
Efficient food processing Genetic engineering also helps to process foods more efficiently, which saves money. For example, the protein rennin, which is used to coagulate milk in the production of cheese, has traditionally been harvested from the stomachs of calves, a costly process. Now scientists can
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insert a copy of the rennin gene into bacteria and then use bacterial cultures to mass-produce rennin – saving time, money, space and animals. Genetic engineering can also help to bypass costly food-processing steps. At present, people who are lactose intolerant can buy milk that has been treated with the lactase enzyme. Wouldn’t it be more convenient, and less expensive, if scientists could induce cows to make lactose-free milk directly? They’re working on it. They have already successfully inserted into mice the genetic material needed to make lactase in their mammary glands, thereby producing low-lactose milk. Decaffeinated coffee beans are another real possibility.
that resist herbicides. As a result, farmers can spray whole soybean fields with the relevant herbicide and kill the weeds without harming the soybeans. Similarly, farmers can grow crops that produce their own pesticides – substances known as plant-pesticides. Corn and potatoes have received a gene from a bacterium that produces a protein that is toxic to insects but not to humans. Growing crops that make their own pesticides allows farmers to save time, increase yields and use fewer, or less harmful, pesticides.
Other possibilities
Efficient drug delivery Genetic research today has progressed well beyond tweaking a gene here and there to produce a desired trait. Scientists can now clone animals. By cloning animals, scientists have the ability to produce both needed food and pharmaceutical products together. Using animals and other organisms in the development of pharmaceuticals is whimsically called ‘biopharming’. For example, a cow cloned with the genetic equipment to make a vaccine in its milk could provide both nourishment and immunisation to a whole village of people left unprotected because they lack food and medical help. Similarly, researchers have figured out how to induce bananas and potatoes to make hepatitis vaccines and tobacco leaves to make AIDS drugs. They can also harvest vaccines by genetically altering hydroponically grown tomato plants to secrete a protein through their root systems into the water. Using foods to deliver drugs is only a small part of the promise and potential biotechnology offers the field of medicine.
Genetically assisted agriculture
Photo courtesy of David Garvin, USDA-ARS
Genetic engineering has the potential to help farmers increase yields, extend growing seasons and grow crops
Genetically modified cauliflower in the United States is orange, reflecting a change in a single gene that increases its production of beta-carotene a hundred-fold. (This crop is not approved in Australia.)
Many other biotechnology possibilities are envisioned for the near future. Prawns may be empowered to fight diseases with genetic ammunition borrowed from sea urchins; plants may be given special molecules to help them grow in polluted soil. With these and other advances, farmers may reliably produce bumper crops of food every year on far fewer acres of land, with less need for water and topsoil, and far less use of toxic pesticides and herbicides. Supporters of biotechnology predict that these efforts will enhance food production and help meet the challenge of feeding an everincreasing world population. They contend that genetically modified crops have the potential to eliminate hunger and starvation. Others suggest that the problems of world hunger are more complex than biotechnology alone can resolve and that the potential risks of genetic engineering may outweigh the potential benefits. The examples mentioned in this highlight are already in progress in many countries around the world. Close on their heels are many more ingenious ideas. What if salt tolerance could be transplanted from a coastal marsh plant into crop plants? Could crops then be irrigated with seawater, thus conserving dwindling freshwater supplies? Would the world food supply increase if rice farmers could grow plants that were immune to disease? What if consumers could dictate which traits scientists insert into food plants? Would they choose to add phytochemicals to fight cancer or reduce the risk of heart disease? These and other possibilities seem unlimited, and though they may sound incredible, many such products have already been developed and are awaiting approval from various food and environmental agencies around the world.
The potential problems and concerns Although many scientists hail biotechnology with confidence, others have reservations. Some consumers also have concerns about what they call ‘Frankenfoods’. Those who oppose biotechnology fear for the safety of a world where genetic tampering produces effects that are not yet fully understood. They suspect that the food
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industry may be driven by potential profits, without ethical considerations or laws to harness its effects. They point out that even the scientists who developed the techniques cannot predict the ultimate outcomes of their discoveries. These consumers don’t want to eat a scientific experiment or interfere with natural systems. Genetic decisions, they say, are best left to the powers of nature. If science and the marketplace are allowed to drive biotechnology without restraint, critics fear that these problems may result: • Disruption of natural ecosystems: New, genetically unusual organisms that have no natural place in the food chain or evolutionary biological systems could escape into the environment and reproduce. • Introduction of diseases: Newly created viruses may mutate to cause deadly diseases that may attack plants, animals or human beings. Genetically modified bacteria may develop resistance to antibiotics, making the drugs useless in fighting infections. • Introduction of allergens and toxins: Genetically modified crops may contain new substances that have consequences, such as causing allergies. • Creation of biological weapons: Fatal bacterial and viral diseases may be developed for use as weapons. • Ethical dilemmas: Critics pose the question, ‘How many human genes does an organism have to contain before it is considered human? For instance, how many human genes would a capsicum have to contain before one would have qualms about eating it?’ Proponents of biotechnology respond that evidence to date does not justify these concerns. Opponents counter that the lack of evidence showing harm does not provide evidence showing safety. These opposing views illustrate the tension between the forward thrust of science and the hesitation of consumers. Both positions highlight the need for more research on the safety and effectiveness of genetically modified food. Table H19.1 summarises the issues.
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Chapter 19: Consumer concerns about foods and water
Some consumers believe that food biotechnology will cause more harm than good.
From another perspective, some argue that the concerns expressed by those protesting against genetically engineered foods reflect prejudices acquired in an elitist world of fertile land and abundant food. Those living in poverty-stricken areas of the world do not have the luxury of determining how to grow crops and process foods. They cannot afford the delays created when protesters destroy test crops and disrupt scientific meetings. They need
TABLE H19.1 Food biotechnology: point, counterpoint ARGUMENTS IN OPPOSITION TO GENETIC ENGINEERING
ARGUMENTS IN SUPPORT OF GENETIC ENGINEERING
1 Ethical and moral issues: It’s immoral to ‘play God’ by mixing genes from organisms unable to do so naturally. Religious and vegetarian groups object to genes from prohibited species occurring in their allowable foods.
1 Ethical and moral issues: Scientists throughout history have been persecuted and even put to death by fearful people who accuse them of playing God. Yet today, many of the world’s citizens enjoy a long and healthy life of comfort and convenience due to once-feared scientific advances put to practical use.
2 Imperfect technology: The technology is young and imperfect – genes rarely function in just one way, their placement is imprecise (‘shotgun’) and all of their potential effects are impossible to predict. Toxins are as likely to be produced as the desired trait. Over 95 per cent of DNA is called ‘junk’ because scientists have not yet determined its function.
2 Advanced technology: Recombinant DNA technology is precise and reliable. Many of the most exciting recent advances in medicine, agriculture and technology were made possible by the application of this technology.
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ARGUMENTS IN OPPOSITION TO GENETIC ENGINEERING
ARGUMENTS IN SUPPORT OF GENETIC ENGINEERING
3 Environmental concerns: Environmental side effects are unknown. The power of a genetically modified organism to change the world’s environments is unknown until such changes actually occur – then the ‘genie is out of the bottle’. Once out, insects, birds and the wind distribute genetically altered seed and pollen to points unknown.
3 Environmental protection: Genetic engineering may be the only hope of saving rainforest and other habitats from destruction. Through genetic engineering, farmers can make use of previously unproductive lands such as salt-rich soils and arid areas.
4 ‘Genetic pollution’: Other kinds of pollution can often be cleaned up with money, time and effort. Once genes are spliced into living things, those genes forever bear the imprint of human tampering.
4 Genetic improvements: Genetic side effects are more likely to benefit the environment than to harm it.
5 Crop vulnerability: Pests and disease can quickly adapt to overtake genetically identical plants or animals around the world. Diversity is key to defence.
5 Improved crop resistance: Pests and diseases can be specifically fought on a case-by-case basis. Biotechnology is the key to defence.
6 Loss of gene pool: Loss of genetic diversity threatens to deplete valuable gene banks from which scientists can develop new agricultural crops.
6 Gene pool preserved: Thanks to advances in genetics, laboratories around the world are able to stockpile the genetic material of millions of species that, without such advances, would have been lost forever.
7 Profit motive: Genetic engineering will profit industry more than the world’s poor and hungry.
7 Everyone profits: Industries benefit from genetic engineering, and a thriving food industry benefits the nation and its people, as witnessed by countries lacking such industries. Genetic engineering promises to provide adequate nutritious food for millions who lack such food today. Developed nations gain cheaper, more attractive, more delicious foods with greater variety and availability year round.
8 Unproven safety for people: Human safety testing of genetically altered products is generally lacking. The population is an unwitting experimental group in a nationwide laboratory study for the benefit of industry.
8 Safe for people: Human safety testing of genetically altered products is unneeded because the products are essentially the same as the original foodstuffs.
9 Increased allergens: Allergens can unwittingly be transferred into foods.
9 Control of allergens: A few allergens can be transferred into foods, but these are known. Also, foods likely to contain them are clearly labelled to warn consumers.
10 Decreased nutrients: A fresh-looking tomato or other produce held for several weeks may have lost substantial nutrients.
10 Increased nutrients: Genetic modifications can easily enhance the nutrients in foods.
11 No product tracking: Without labelling, the food industry cannot track problems to the source.
11 Excellent product tracking: The identity and location of genetically altered foodstuffs are known, and they can be tracked should problems arise.
12 Overuse of herbicides: Farmers, knowing that their crops resist herbicide effects, will use them liberally.
12 Conservative use of herbicides: Farmers will not waste expensive herbicides in second or third applications when the prescribed amount gets the job done the first time.
13 Increased consumption of pesticides: When a pesticide is produced by the flesh of produce, consumers cannot wash it off the skin of the produce with running water as they can with ordinary sprays.
13 Reduced pesticides on foods: Pesticides produced by produce in tiny amounts known to be safe for consumption are more predictable than applications by agricultural workers who make mistakes. Because other genetic manipulations will eliminate the need for post-harvest spraying, fewer pesticides will reach the dinner table.
14 Lack of oversight: Government oversight is run by industry people for the benefit of industry – no one is watching out for the consumer.
14 Sufficient regulation and rapid response: Government agencies are efficient in identifying and correcting problems as they occur in the industry.
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Chapter 19: Consumer concerns about foods and water
solutions now. People are starving, and genetic engineering holds great promise for providing them with food. At a minimum, critics of biotechnology have made a strong case for rigorous safety testing and labelling of new products. They contend, for example, that when a new gene has been introduced into a food, tests should ensure that other, unwanted genes have not accompanied it. If a disease-producing microorganism has donated genetic material, scientists must prove that no dangerous characteristic from the microorganism has also entered the food. If the inserted genetic material comes from a source to which some people develop allergies, such as nuts, then the new product should be labelled to alert them. Furthermore, if the newly altered genetic material creates proteins that have never before been encountered by the human body, their effects should be studied to ensure that people can eat them safely.
Gene technology regulations In Australia, the Office of the Gene Technology Regulator oversees the development and environmental release of genetically modified (GM) organisms under the Gene Technology Act 2000. Most dealings with GM organisms must be licensed, with licences not being issued unless there is satisfaction that any risks posed can be managed to protect the health and safety of people, and to protect the environment. In New Zealand, similar functions are undertaken by the Environmental Protection Authority, under the Hazardous Substances and New Organisms (HSNO) Act 1996. If the GM organism will be used to produce food, FSANZ will also determine if that food is safe for people to eat. GM foods are regulated under the Australia New Zealand Food Standards Code. The standard has two provisions – mandatory pre-market approval, which also includes a food safety assessment and mandatory labelling requirements. The standard ensures that only assessed and approved GM foods enter the food supply.
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FSANZ carries out safety assessments on a case-by-case basis, which means each new genetic modification is assessed individually for its potential impact on the safety of the food. Comparison of the GM food with a similar, commonly eaten, conventional food from a molecular, toxicological, nutritional and compositional point of view occurs. The aim is to find out if there are any differences between the GM food and its conventional counterpart. For example, a new GM corn variety will be compared to existing non-GM corn varieties. Any differences that are detected are then examined to see if they will raise any safety concerns. If the genetic modification causes an unexpected effect in the food, such as increasing its allergenicity or toxicity, it will not be approved. To date there have been no safety concerns identified with any of the GM foods that have been assessed. Labelling requirements are such that it is mandatory for GM foods to be identified on food labels in Australia and New Zealand. GM foods and ingredients (including food additives and processing aids from GM sources) must be identified on labels with the words ‘genetically modified’ if novel DNA and/or novel protein from an approved GM variety is present in the final food product. GM foods must also be labelled if they have altered characteristics. For example, if a GM food has an increased level of a particular nutrient, such as a vitamin, or has to be cooked or prepared in a different way compared to the conventional food, then this also needs to be stated on the label. Some exemptions are allowed under the labelling requirements. For example, foods that do not contain novel DNA or protein do not have to be labelled. Examples of these include highly refined or processed foods such as vegetable oils or sugars. However, if these foods also have altered characteristics (for example, refined oil with an altered fatty acid profile), then the food must be labelled. Will our impressive new technologies provide foods to meet the needs of the future? Some would say yes. Biotechnology holds a world of promise, and with proper safeguards and controls, it may yield products that meet the needs of consumers almost perfectly.
HIGHLIGHT ACTIVITIES CRITICAL THINKING QUESTIONS A How might people from different countries view the risks and benefits of biotechnology? B Controversy surrounds the safety and use of food biotechnology. Genetically modified foods raise concerns about long-term health and environmental consequences. Even though most scientists agree that
these foods are safe and perhaps even beneficial to consumers, many consumers still express uncertainty. What is your position on food bio technology and genetically modified foods? What could be done to minimise any associated risks and alleviate fears?
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NUTRITION ON THE NET Analyse the nutrient composition of foods online: To learn more about the nutrient content of the foods you eat, you can access the full NUTTAB Food Composition Database provided by Food Standards Australia New Zealand from http://www.foodstandards.gov.au/ science/monitoringnutrients/pages/default.aspx • Search ‘GM foods’ on the FSANZ site: http://www.foodstandards.gov.au • Get a ‘pro’ biotechnology perspective from the Council for Biotechnology Information: http://www.whybiotech.com/category/gmo/
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For another ‘pro’ view, search ‘biotechnology’ at the International Food Information Council Foundation: http://www.ific.org Get a ‘con’ biotechnology perspective from searching for genetic modification on the Genetic Engineering section of Greenpeace, Australia: http://www. greenpeace.org/australia/en/what-we-do/Food/ Another ‘against’ view is available from the Gene Ethics website: http://www.geneethics.org
REFERENCES CHAPTER 1
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3
4 5
6
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8
9
Oz Food Net, Monitoring the incidence and causes of diseases potentially transmitted by food in Australia: Annual Report of the Ozfoodnet Network (2010). P. Zhang and co-authors, Clinical analysis of patients with Clostridium Botulinum food poisoning, Eurpoe PMC 29(5) (2017): 459–64. OzFoodNet, Monitoring the incidence and causes of diseases potentially transmitted by food in Australia: Annual Report of the Ozfoodnet Network (2011). C. B. Dalton and co-authors; The OzFoodNet Working Group, Epidemiology and Infection (2015): 1–9. K. M. Angelo and co-authors, What proportion of international travellers acquire a travel-related illness? A review of the literature, Journal of the Travel Medicine 24(5) (2017): doi.org/10.1093/jtm/ tax046. A. Bearth and co-authors, ‘As long as it is not irradiated’ – Influencing factors of US consumers’ acceptance of food irradiation, Food Quality and Preference 71 (2019): 141–8. E. C. Somers and coauthors, Mercury exposure and antinuclear antibodies among females of reproductive age in the United States: NHANES, Environmental Health Perspectives 123 (2015): 792–8. Y. Oulhote and co-authors, Children’s white blood cell counts in relation to developmental exposures to methylmercury and persistent organic pollutants, Reproductive Toxicology 68 (2017): 207–14. P. E. Drevnick, C. H. Lamborg, and M. J. Horgan, Increase in mercury in Pacific yellowfin tuna, Environmental Toxicology and Chemistry 34 (2015): 931–4.
10 FSANZ Fact Sheet: Advice on fish consumption, available at http:// www.foodstandards.gov.au/search/; keywords = fish+consumption 11 E. C. Somers and coauthors, Mercury exposure and antinuclear antibodies among females of reproductive age in the United States: NHANES, Environmental Health Perspectives 123 (2015): 792–8. 12 J. Golding and co-authors, Dietary predictors of maternal prenatal blood mercury levels in the ALSPAC Birth Cohort Study, Environmental Health Perspectives 121 (2013): 1214–18. 13 Food Standards Australia New Zealand, The 23rd Australian total diet survey, Canberra/Wellington: FSANZ (2011). 14 Department of Agriculture, Fisheries and Forestry National Residue Survey Annual Report 2015–2016, Canberra: Department of Agriculture, Fisheries and Forestry (2016). 15 A. Zalecka and coauthors, The influence of organic production on food quality: Research findings, gaps and future challenges, Journal of Science and Food Agriculture 94 (2014): 2600–4. 16 Vallverdú-Queralt and co-authors, Is there any difference between the phenolic content of organic and conventional tomato juices? Food Chemistry 130 (2012): 222–7. 17 J. L. Wan-chen and co-authors, You taste what you see: do organic labels bias taste perceptions? Food Quality and Preference 29 (2013): 33–9. 18 Department of Agriculture, Fisheries and Forestry National Residue Survey Annual Report 2015–2016, Canberra: Department of Agriculture, Fisheries and Forestry (2016).
HIGHLIGHT 1
Food Standards Australia New Zealand, GM foods: Safety assessment of genetically modified foods, Canberra/Wellington: FSANZ (2005).
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Appendix A CONTENTS The cell
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The hormones
704
The nervous system
704
Putting it together
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Cells, hormones and nerves
This appendix is offered as an optional chapter for readers who want to enhance their understanding of how the body coordinates its activities. It presents a brief summary of the structure and function of the body’s basic working unit (the cell) and of the body’s two major regulatory systems (the hormonal system and the nervous system).
The cell The body’s organs are made up of millions of cells and of materials produced by them. Each cell is specialised to perform its organ’s functions, but all cells have common structures (see Figure A.1). Every cell is contained within a cell membrane. The cell membrane assists in moving materials into and out of the cell, and some of its special proteins act as ‘pumps’ (as is described in Chapter 6). Some features of cell membranes, such as microvilli (Chapter 3), permit cells to interact with other cells and with their environments in highly specific ways. Inside the membrane lies the cytoplasm, which is filled with cytosol, or cell ‘fluid’. However, the cytoplasm contains much more than just fluid. It is a highly
organised system of fibres, tubes, membranes, particles and subcellular organelles as complex as a city. These parts intercommunicate, manufacture and exchange materials, package and prepare materials for export, and maintain and repair themselves. Within each cell is another membrane-enclosed body – the nucleus. Inside the nucleus are the chromosomes, which contain the genetic material, the DNA. The DNA encodes all the instructions for carrying out the cell’s activities. The role of DNA in coding for cell proteins is summarised in Figure 6.7 on page 185. Chapter 6 also describes the variety of proteins produced by cells and the ways they perform the body’s work. Among the organelles within a cell are ribosomes, mitochondria and lysosomes. Figure 6.7 briefly refers to the ribosomes; they assemble amino acids into proteins, following directions conveyed to them by RNA. The mitochondria are made of intricately folded membranes that bear thousands of highly organised sets of enzymes on their inner and outer surfaces. Mitochondria are crucial to energy metabolism (as described in Chapter 7), and muscles conditioned to work aerobically are packed with them. Their presence is
FIGURE A.1 The structure of a typical cell The cell shown might be one in a gland (such as the pancreas) that produces secretory products (enzymes) for export (to the intestine). The rough endoplasmic reticulum with its ribosomes produces the enzymes; the smooth reticulum conducts them to the Golgi region; the Golgi membranes merge with the cell membrane, where the enzymes can be released into the extracellular fluid. Nucleus Chromosomes Cytoplasm Golgi apparatus Smooth endoplasmic reticulum Lysosome
Rough endoplasmic reticulum Ribosomes Mitochondrion
Cell membrane
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implied whenever the TCA cycle and electron transport chain are mentioned because the mitochondria house the needed enzymes.* The lysosomes are membranes that enclose degradative enzymes. When a cell needs to self-destruct or to digest materials in its surroundings, its lysosomes free their enzymes. Lysosomes are active when tissue repair or remodelling is taking place – for example, in cleaning up infections, healing wounds, shaping embryonic organs and remodelling bones. Besides these and other cellular organelles, the cell’s cytoplasm contains a highly organised system of membranes, the endoplasmic reticulum. The ribosomes may either float free in the cytoplasm or be mounted on these membranes. A membranous surface dotted with ribosomes looks speckled under the microscope and is called ‘rough’ endoplasmic reticulum; such a surface without ribosomes is called ‘smooth’. Some intracellular membranes are organised into tubules that collect cellular materials, merge with the cell membrane and discharge their contents to the outside of the cell; these membrane systems are named the Golgi apparatus, after the scientist who first described them. The rough and smooth endoplasmic reticula and the Golgi apparatus are continuous with one another, so secretions produced deep in the interior of the cell can be efficiently transported to the outside and released. These and other cell structures enable cells to perform the multitude of functions for which they are specialised. The actions of cells are coordinated by both hormones and nerves, as the next sections show. Among the types of cellular organelles are receptors for the hormones delivering instructions that originate elsewhere in the body. Some hormones penetrate the cell and its nucleus and attach to receptors on chromosomes, where they activate certain genes to initiate, stop, speed up or slow down synthesis of certain proteins as needed. Other hormones attach to receptors on the cell surface and The study of transmit their messages from there. hormones and their The hormones are described in effects is called the next section; the nerves, in the endocrinology. one following.
The hormones A hormone is a chemical compound that originates in a gland and travels in the bloodstream. The hormone flows everywhere in the body, but only its target organs respond to it, because only its target organs possess the receptors to receive it. The hormones, the glands they originate in, and their target organs and effects are described in Table A.1. Figure A.2 identifies the glands that produce the hormones.
A hormone typically has one or more signals that turn it on and another (or others) that turns it off. Hormones are often turned off by their own effects; they are said to be regulated by negative feedback (see Figure 3.12, p. 82). Consider, for example, the hormone prolactin, which promotes milk production. High prolactin levels ensure that milk is made; they also trigger the release of prolactin-inhibiting hormone (PIH), which ensures that prolactin levels don’t get too high. But when the infant is suckling – and creating a demand for milk – PIH is not allowed to work (suckling turns off PIH). The consequence is that prolactin remains high, and milk production continues. Demand from the infant thus directly adjusts the supply of milk. The need is met through the interaction of the nerves and hormones. Every body part is affected by hormones. Each different hormone has unique effects, and hormones that oppose each other are produced in carefully regulated amounts, so each can respond to the exact degree that is appropriate to the condition. As Table A.1 summarises, hormones have an enormous impact on body processes. The body’s other overall regulating agency is the nervous system. Figure A.2 identifies the glands that produce hormones; the hormones discussed in this section are defined in the Glossary.
The nervous system The nervous system has a central control system that can evaluate information about conditions within and outside the body, and a vast system of wiring that receives information and sends instructions. The control unit is the brain and spinal cord, called the central nervous system; the vast complex of wiring between the centre and the parts is the peripheral nervous system. The smooth functioning that results from the system’s adjustments to changing conditions is homeostasis. The nervous system has two general functions: it controls voluntary muscles in response to sensory stimuli from them, and it controls involuntary, internal muscles and glands in response to nerve-borne and chemical signals about their status. In fact, the nervous system is best understood as two systems that use the same or similar pathways to receive and transmit their messages. The somatic nervous system controls the voluntary muscles; the autonomic nervous system controls the internal organs. When scientists were first studying the autonomic nervous system, they noticed that when something hurt one organ of the body, some of the other organs reacted
*For the reactions of glycolysis, the TCA cycle and the electron transport chain, see Chapter 7 and Appendix C. The reactions of glycolysis take place in the cytoplasm; the conversion of pyruvate to acetyl CoA takes place in the mitochondria, as do the TCA cycle and electron transport chain reactions. The mitochondria then release carbon dioxide, water and ATP as their end products. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Appendix A
FIGURE A.2 The endocrine system These organs and glands release hormones that regulate body processes. An endocrine gland secretes its product directly into (endo) the blood; for example, the pancreas cells that secrete insulin into the blood. An exocrine gland secretes its product(s) out (exo) to an epithelial surface either directly or through a duct; the sweat glands of the skin and the pancreas cells that secrete digestive enzymes into the gastrointestinal tract are both examples. The pancreas is therefore both an endocrine and an exocrine gland. Hypothalamus
Pituitary gland (anterior, posterior) Parathyroid glands Thyroid gland
Thymus gland Heart Adrenal glands (cortex, medulla)
Stomach Pancreas
Kidney Female Ovary Male
Placenta (develops in the uterus during pregnancy)
Testicle
TABLE A.1 Summary of major hormones GLAND
HORMONE
TARGET CELLS
ACTION
Anterior pituitary
Adrenocorticotropin (ACTH)
Adrenal cortex
Stimulates secretion of glucocorticoids and androgens
Adrenal cortex
Aldosterone
Kidneys
Stimulates sodium reabsorption, thereby regulating acid-base balance, blood volume, and blood pressure
Posterior pituitary
Antidiuretic hormone (ADH); also called vasopressin
Arteries
Causes vasoconstriction
Kidneys
Promotes water retention
Thyroid gland
Calcitonin
Bones
Lowers blood calcium by moving calcium from the bloodstream into the bones whenever blood calcium rises above normal
Kidneys
Increases excretion of calcium and phosphorus
Duodenum
Cholecystokinin
Gallbladder
Releases bile into the intestine
Pancreas
Releases pancreatic juices into the intestine
Hypothalamus
Corticotropin-releasing hormone (CRH)
Anterior pituitary
Controls release of adrenocorticotropin (ACTH)
Kidneys
Erythropoietin
Bone marrow
Stimulates red blood cell production
Ovaries
Oestrogens
Female sexual tissues
Promotes growth, development, and health of all tissues involved in female sexuality
Anterior pituitary
Follicle-stimulating hormone (FSH)
Ovaries (female)
Stimulates follicular development and ovulation
Testicles (male)
Stimulates sperm production
Gastrin
Stomach
Stimulates gastric acid secretion; slows motility
Stomach, duodenum
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TABLE A.1
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GLAND
HORMONE
TARGET CELLS
ACTION
Hypothalamus
Growth hormone releasing hormone (GHRH) and growth hormone inhibiting hormone (GHIH or somatostatin)
Anterior pituitary
Controls release of growth hormone (GH)
Pancreas (alpha cells)
Glucagon
Liver
Promotes the breakdown of glycogen to glucose
Most cells
Increases use of fat and amino acids for energy
Adrenal cortex
Glucocorticoids
Most cells
Protects against stress; raises blood glucose
Hypothalamus
Gonadotropin-releasing hormone (GnRH)
Anterior pituitary
Controls release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Anterior pituitary
Growth hormone (GH); also called somatotropin
All tissues
Stimulates growth; regulates metabolism
Pancreas (beta cells)
Insulin
Most cells
Stimulates nutrient uptake into cells
Anterior pituitary
Luteinizing hormone (LH)
Ovaries (female)
Stimulates follicular development and ovulation
Testicles (male)
Stimulates testosterone production
Adrenal medulla
Norepinephrine and epinephrine; formerly called noradrenaline and adrenaline, respectively
Many cells
Facilitates the body’s readiness for fight or flight: maintains blood pressure, increases cardiac output, constricts blood vessels, keeps airways open, raises blood glucose levels
Posterior pituitary
Oxytocin
Uterus (female in late pregnancy)
Induces muscle contractions during childbirth
Mammary glands (female in lactation)
Causes milk ejection during lactation
Parathyroid hormone (PTH); also called parathormone
Bones
Releases stored calcium into the blood
Kidneys
Slows calcium excretion
Intestines
Increases calcium absorption
Corpus luteum, placenta
Progesterone
Uterus
Facilitates implantation at the start of pregnancy
Mammary glands
Stimulates mammary gland development for lactation
Anterior pituitary
Prolactin
Mammary glands (female in lactation)
Stimulates milk production
Hypothalamus
Prolactin-inhibiting hormone (PIH)
Anterior pituitary
Controls release of prolactin
Duodenum
Secretin
Pancreas
Stimulates bicarbonate secretion into the intestine; slows stomach motility
Testicles
Testosterone
Male sexual tissues
Promotes growth, development, and health of all tissues involved in male sexuality
Anterior pituitary
Thyroid-stimulating hormone (TSH)
Thyroid gland
Stimulates synthesis and release of thyroid hormones (thyroxine and triiodothyronine)
Thyroid gland
Thyroxine
Many cells
Regulates metabolic rate, growth, and heat production
Hypothalamus
TSH-releasing hormone (TRH)
Anterior pituitary
Controls release of thyroid-stimulating hormone (TSH)
Skin
Vitamin D
Intestines
Increases calcium absorption
Parathyroid gland
as if in sympathy for the afflicted one. They therefore named the nerve network they were studying the sympathetic nervous system. The term is still used today to refer to that branch of the autonomic nervous system that responds to pain and stress. The other branch is called the parasympathetic nervous system. (Think of the sympathetic branch as the responder when homeostasis needs restoring and the parasympathetic branch as the
commander of function during normal times.) Both systems transmit their messages through the brain and spinal cord. Nerves of the two branches travel side by side along the same pathways to transmit their messages, but they oppose each other’s actions (see Figure A.3). An example shows how the sympathetic and parasympathetic nervous systems work to maintain
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Appendix A
FIGURE A.3 The organisation of the nervous system The brain and spinal cord evaluate information about conditions within and outside the body, and the peripheral nerves receive information and send instructions. Brain
Spinal cord Physical structures, such as the brain and nerves, make up all the nervous system divisions. They can be separated by function.
Peripheral nerves
Somatic nervous system (conscious control of voluntary muscles)
Autonomic nervous system (automatic control of involuntary muscles and organs)
Sympathetic nervous system (responds to stressors)
homeostasis. When you go outside in cold weather, your skin’s temperature receptors send ‘cold’ messages to the spinal cord and brain. Your conscious mind may intervene at this point to tell you to zip up your jacket – but let’s say you have no jacket. Your sympathetic nervous system reacts to the external stressor, the cold. It signals your skin-surface capillaries to shut down so that your blood will circulate deeper in your tissues, where it will conserve heat. Your sympathetic nervous system also signals involuntary contractions of the small muscles just under the skin surface. The product of these muscle contractions is heat, and the visible result is goose bumps. If these measures do not raise your body temperature enough, then the sympathetic nerves signal your large muscle groups to shiver; the contractions of these large muscles produce still more heat. All of this activity helps to maintain your homeostasis (with respect to temperature) under conditions of external extremes (cold) that would throw it off balance. The cold was a stressor; the body’s response was resistance. Now let’s say you come in and sit by a fire and drink hot chocolate. You are warm and no longer need all that sympathetic activity. At this point, your parasympathetic nerves take over; they signal your skin-surface capillaries to dilate again, your goose bumps
Parasympathetic nervous system (regulates normal activities)
to subside and your muscles to relax. Your body is back to normal. This is recovery.
Putting it together The hormonal and nervous systems coordinate body functions by transmitting and receiving messages. The point-to-point messages of the nervous system travel through a central switchboard (the spinal cord and brain), whereas the messages of the hormonal system are broadcast over the airways (the bloodstream), and any organ with the appropriate receptors can pick them up. Nerve impulses travel faster than hormonal messages do – although both are remarkably swift. Whereas your brain’s command to wiggle your toes reaches the toes within a fraction of a second and stops as quickly, a gland’s message to alter a body condition may take several seconds or minutes to get started and may fade away equally slowly. Together, the two systems possess every characteristic a superb communication network needs: varied speeds of transmission, along with private communication lines or public broadcasting systems, depending on the needs of the moment. The hormonal system, together with the nervous system, integrates the whole body’s functioning so that all parts act smoothly together.
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707
708
Appendix B CONTENTS Matter: the properties of atoms
708
Chemical bonding
711
Formation of ions
712
Water, acids and bases
713
Chemical reactions
714
Formation of free radicals
715
Basic chemistry concepts
This appendix is intended to provide the background in basic chemistry you need to understand the nutrition concepts presented in this book. Chemistry is the branch of natural science that is concerned with the description and classification of matter, the changes that matter undergoes and the energy associated with these changes.
Matter: the properties of atoms Every substance has physical and chemical properties that distinguish it from all other substances and thus give it a unique identity. The physical properties include such characteristics as colour, taste, texture and odour, as well as the temperatures at which a substance changes its state (from a solid to a liquid, or from a liquid to a gas) and the weight of a unit volume (its density). The chemical properties of a substance have to do with how it reacts with other substances or responds to a change in its environment. A physical change does not change a substance’s chemical composition. The three physical states – ice, water and steam – all consist of two hydrogen atoms and one oxygen atom bound together. In contrast, a chemical change occurs when an electric current passes through water. The water disappears and two different substances are formed: hydrogen gas, which is flammable, and oxygen gas, which supports life.
Substances: elements and compounds The smallest part of a substance that can exist separately without losing its physical and chemical properties is a molecule. If a molecule is composed of atoms that are alike, the substance is an element (for example, O2). If a molecule is composed of two or more different kinds of atoms, the substance is a compound (for example, H2O). More than 100 elements are known; these are listed in Table B.1. A familiar example is hydrogen, whose molecules are composed only of hydrogen atoms linked together in pairs (H2). Whereas only just over 100
elements are known, over a million compounds are known. An example is the sugar glucose. Each of its molecules is composed of 6 carbon, 6 oxygen and 12 hydrogen atoms linked together in a specific arrangement (as described in Chapter 4).
The nature of atoms Atoms themselves are made of smaller particles. Within the atomic nucleus are protons (positively charged particles), and surrounding the nucleus are electrons (negatively charged particles). The number of protons (1) in the nucleus of an atom determines the number of electrons (2) around it. The positive charge on a proton is equal to the negative charge on an electron, so the charges cancel each other out and leave the atom neutral to its surroundings. The nucleus may also include neutrons, subatomic particles that have no charge. Protons and neutrons are of equal mass, and together they give an atom its weight. Electrons bond atoms together to make molecules, and they are involved in chemical reactions. Each type of atom has a characteristic number of protons in its nucleus. The hydrogen atom is the simplest of all. It possesses a single proton, with a single electron associated with it: –
Electron
+
Proton
Hydrogen atom (H), atomic number 1
Just as hydrogen always has one proton, helium always has two, lithium three and so on. The atomic number of each element is the number of protons in the nucleus of that atom, and this never changes in a chemical reaction; it gives the atom its identity. The atomic numbers for the known elements are listed in Table B.1.
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Appendix B
TABLE B.1 Chemical symbols for the elements NUMBER OF PROTONS (ATOMIC NUMBER)
ELEMENT
NUMBER OF ELECTRONS IN OUTER SHELL
NUMBER OF PROTONS (ATOMIC NUMBER)
ELEMENT
NUMBER OF ELECTRONS IN OUTER SHELL
1
Hydrogen (H)
1
36
Krypton (Kr)
8
2
Helium (He)
2
37
Rubidium (Rb)
1
3
Lithium (Li)
1
38
Strontium (Sr)
2
4
Beryllium (Be)
2
39
Yttrium (Y)
2
5
Boron (B)
3
40
Zirconium (Zr)
2
6
Carbon (C)
4
41
Niobium (Nb)
1
7
Nitrogen (N)
5
42
Molybdenum (Mo)
1
8
Oxygen (O)
6
43
Technetium (Tc)
1
9
Fluorine (F)
7
44
Ruthenium (Ru)
1
10
Neon (Ne)
8
45
Rhodium (Rh)
1
11
Sodium (Na)
1
46
Palladium (Pd)
2
12
Magnesium (Mg)
2
47
Silver (Ag)
1
13
Aluminium (Al)
3
48
Cadmium (Cd)
2
14
Silicon (Si)
4
49
Indium (In)
3
15
Phosphorus (P)
5
50
Tin (Sn)
4
16
Sulphur (S)
6
51
Antimony (Sb)
5
17
Chlorine (Cl)
7
52
Tellurium (Te)
6
18
Argon (Ar)
8
53
Iodine (I)
7
19
Potassium (K)
1
54
Xenon (Xe)
8
20
Calcium (Ca)
2
55
Caesium (Cs)
1
21
Scandium (Sc)
2
56
Barium (Ba)
2
22
Titanium (Ti)
2
57
Lanthanum (La)
2
23
Vanadium (V)
2
58
Cerium (Ce)
2
24
Chromium (Cr)
1
59
Praseodymium (Pr)
2
25
Manganese (Mn)
2
60
Neodymium (Nd)
2
26
Iron (Fe)
2
61
Promethium (Pm)
2
27
Cobalt (Co)
2
62
Samarium (Sm)
2
28
Nickel (Ni)
2
63
Europium (Eu)
2
29
Copper (Cu)
1
64
Gadolinium (Gd)
2
30
Zinc (Zn)
2
65
Terbium (Tb)
2
31
Gallium (Ga)
3
66
Dysprosium (Dy)
2
32
Germanium (Ge)
4
67
Holmium (Ho)
2
33
Arsenic (As)
5
68
Erbium (Er)
2
34
Selenium (Se)
6
69
Thulium (Tm)
2
35
Bromine (Br)
7
70
Ytterbium (Yb)
2
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709
TABLE B-1
710
Appendix B
ELEMENT
NUMBER OF PROTONS (ATOMIC NUMBER)
NUMBER OF ELECTRONS IN OUTER SHELL
NUMBER OF PROTONS (ATOMIC NUMBER)
NUMBER OF ELECTRONS IN OUTER SHELL
71
Lutetium (Lu)
2
95
Americium (Am)
2
72
Hafnium (Hf)
2
96
Curium (Cm)
2
73
Tantalum (Ta)
2
97
Berkelium (Bk)
2
74
Tungsten (W)
2
98
Californium (Cf)
2
75
Rhenium (Re)
2
99
Einsteinium (Es)
2
76
Osmium (Os)
2
100
Fermium (Fm)
2
77
Iridium (Ir)
2
101
Mendelevium (Md)
2
78
Platinum (Pt)
1
102
Nobelium (No)
2
79
Gold (Au)
1
103
Lawrencium (Lr)
2
80
Mercury (Hg)
2
104
Rutherfordium (Rf)
2
81
Thallium (Tl)
3
105
Dubnium (Db)
2
82
Lead (Pb)
4
106
Seaborgium (Sg)
2
83
Bismuth (Bi)
5
107
Bohrium (Bh)
2
84
Polonium (Po)
6
108
Hassium (Hs)
2
85
Astatine (At)
7
109
Meitnerium (Mt)
2
86
Radon (Rn)
8
110
Darmstadtium (Ds)
2
87
Francium (Fr)
1
111
Roentgenium (Rg)
1
88
Radium (Ra)
2
112
Copernicium (Cn)
2
89
Actinium (Ac)
2
113
Ununtrium (Uut)
3
90
Thorium (Th)
2
114
Flerovium (Fl)
4
91
Protactinium (Pa)
2
115
Ununpentium (Uup)
5
92
Uranium (U)
2
116
Livermorium (Lv)
6
93
Neptunium (Np)
2
117
Ununseptium (Uus)
7
94
Plutonium (Pu)
2
118
Ununoctium (Uuo)
8
Besides hydrogen, the atoms most common in living things are carbon (C), nitrogen (N) and oxygen (O), whose atomic numbers are 6, 7 and 8, respectively. Their structures are more complicated than that of hydrogen, but each of them possesses the same number of electrons as there are protons in the nucleus. These electrons are found in orbits, or shells (shown below).
–
ELEMENT
–
–
–
–
–
–
+ + 6 + + + + +
–
– –
+
+ + 7 + + + + +
–
– –
– –
Carbon atom (C), atomic number 6
Nitrogen atom (N), atomic number 7
– –
+ + + 8 + + + + ++
–
– – – Oxygen atom (O), atomic number 8
In these and all diagrams of atoms that follow, only the protons and electrons are shown. The neutrons, which contribute only to atomic weight, not to charge, are omitted.
The most important structural feature of an atom for determining its chemical behaviour is the number of
electrons in its outermost shell. The first, or innermost, shell is full when it is occupied by two electrons; so an atom with two or more electrons has a filled first shell. When the first shell is full, electrons begin to fill the second shell. The second shell is completely full when it has eight electrons. A substance that has a full outer shell tends not to enter into chemical reactions. Neon, atomic number 10, is a chemically inert substance because its outer shell is complete. Fluorine, atomic number 9, has a great tendency to draw an electron from other substances to complete its outer shell, and thus it is highly reactive. Carbon has a half-full outer shell, which helps explain its great versatility; it can combine with other elements in a variety of ways to form a large number of compounds. Atoms seek to reach a state of maximum stability or of lowest energy in the same way that a ball will roll down a hill until it reaches the lowest place. An atom achieves a state of maximum stability by: • gaining or losing electrons to either fill or empty its outer shell • sharing its electrons with other atoms and thereby completing its outer shell.
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Appendix B
The number of electrons determines how the atom will chemically react with other atoms. The atomic number, not the weight, is what gives an atom its chemical nature.
Chemical bonding Atoms often complete their outer shells by sharing electrons with other atoms. In order to complete its outer shell, a carbon atom requires four electrons. A hydrogen atom requires one. Thus, when a carbon atom shares electrons with four hydrogen atoms, each completes its outer shell. Electron sharing binds the atoms together and satisfies the conditions of maximum stability for the molecule. The outer shell of each atom is complete, since hydrogen effectively has the required two electrons in its first (outer) shell, and carbon has eight electrons in its second (outer) shell; and the molecule is electrically neutral, with a total of 10 protons and 10 electrons.
Bonds that involve the sharing of electrons, like the bonds between carbon and the four hydrogens, are the most stable kind of association that atoms can form with one another. These bonds are called covalent bonds, and the resulting combination of atoms are called molecules. A single pair of shared electrons forms a single bond. A simplified way to represent a single bond is with a single line. Thus the structure of methane (CH4) could be represented like this: H H
C
H
H Methane (CH4)
Similarly, one nitrogen atom and three hydrogen atoms can share electrons to form one molecule of ammonia (NH3): H
H +
+
–
– –
– –
H
+
–
–
–
+ + + + + +
+
–
– –
+
+ + 7 + + + + +
– –
6+ – H
+
+
–
When a carbon atom shares electrons with four hydrogen atoms, a methane molecule is made.
+
+
– –
– –
+
– –
–H
When a nitrogen atom shares electrons with three hydrogen atoms, an ammonia molecule is made.
H
–
–H
– –
N
C
+
–
6+
+ + + + + +
– – –
+
– –
+
7 + + + + + + +
– – –
– – –
+
+
– –
+
H N
H
H Ammonia (NH3)
The chemical formula for methane is CH4. Note that by sharing electrons, every atom achieves a filled outer shell.
The chemical formula for ammonia is NH3. Count the electrons in each atom’s outer shell to confirm that it is filled.
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711
712
Appendix B
One oxygen atom may be bonded to two hydrogen atoms to form one molecule of water (H2O):
+ – – – + + +8 + + + + ++
– –
+
– –
H
– – –
H O
Water molecule (H2O)
When two oxygen atoms form a molecule of oxygen, they must share two pairs of electrons. This double bond may be represented as two single lines:
–
–
–
–
– + + + 8 + + + + ++ –
–
– – + + + 8 + + + + ++
– – – –
–
O O
–
–
Small atoms form the tightest, most stable bonds. H, O, N and C are the smallest atoms capable of forming one, two, three and four electron-pair bonds, respectively. This is the basis for the statement in Chapter 4 that in drawings of compounds containing these atoms, hydrogen must always have one, oxygen two, nitrogen three and carbon four bonds radiating to other atoms:
O
N
ELEMENT
CHEMICAL SYMBOL
BY WEIGHT (%)
Oxygen
O
65
Carbon
C
18
Hydrogen
H
10
Nitrogen
N
3
Calcium
Ca
1.5
Phosphorus
P
1.0
Potassium
K
0.4
Sulphur
S
0.3
Sodium
Na
0.2
Chloride
Cl
0.1
Magnesium
Mg
0.1
Total
99.6a
a The remaining 0.40 per cent by weight is contributed by the trace elements: chromium (Cr), copper (Cu), zinc (Zn), selenium (Se), molybdenum (Mo), fluorine (F), iodine (I), manganese (Mn) and iron (Fe). Cells may also contain variable traces of some of the following: boron (B), cobalt (Co), lithium (Li), strontium (Sr), aluminium (Al), silicon (Si), lead (Pb), vanadium (V), arsenic (As), bromine (Br) and others.
Formation of ions
Oxygen molecule (O2)
H
TABLE B.2 Elemental composition of the human body
An atom such as sodium (Na, atomic number 11) cannot easily fill its outer shell by sharing. Sodium possesses a filled first shell of two electrons and a filled second shell of eight; there is only one electron in its outermost shell:
– –
C
The stability of the associations between these small atoms and the versatility with which they can combine make them very common in living things. Interestingly, all cells, whether they come from animals, plants or bacteria, contain the same elements in very nearly the same proportions. The elements commonly found in the human body are shown in Table B.2.
– – – + + ++ + + ++ + + ++ 11 –
Sodium atom (Na) 11 + charges 11 – charges – – –
0 net charge with one reactive electron in the outer shell
– –
Loss of 1 electron
– –
– – – + + ++ + + ++ + + ++ 11 – – –
– –
Sodium ion (Na+) 11 + charges 10 – charges 1 + net charge and a filled outer shell
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Appendix B
If sodium loses this electron, it satisfies one condition for stability: a filled outer shell (now its second shell counts as the outer shell). However, it is not electrically neutral. It has 11 protons (positive) and only 10 electrons (negative). It therefore has a net positive charge. An atom or molecule that has lost or gained one or more electrons and so is electrically charged is called an ion. An atom such as chlorine (Cl, atomic number 17), with seven electrons in its outermost shell, can share electrons to fill its outer shell, or it can gain one electron to complete its outer shell and thus give it a negative charge:
– –
– –
– – – – – 17++ + + ++ + + ++ + + ++ + +++ – – –
Chlorine atom (Cl)
– – –
– –
0 net charge but lacks one electron to fill outer shell Gain of 1 electron
– –
– –
17 + charges 17 – charges
– – – – – 17+ + + ++ + + +++ + + ++ + +++ –
Chloride ion (Cl –) – – – –
– –
17 + charges 18 – charges 1 – net charge and a filled outer shell
– –
A positively charged ion such as sodium ion (Na1) is called a cation; a negatively charged ion such as a chloride ion (Cl2) is called an anion. Cations and anions attract one another to form salts:
– –
– –
– –
– – – + ++ + – + + ++ – + + ++ 11 – – – Na+ – – – – – 17++ + + ++ + + ++ + + ++ + +++ – – – ––
– – – –
With all its electrons, sodium is a shiny, highly reactive metal; chlorine is the poisonous greenish yellow gas that was used in the First World War. But after sodium and chlorine have transferred electrons, they form the stable white salt familiar to you as table salt, or sodium chloride (Na1Cl2). The dramatic difference illustrates how profoundly the electron arrangement can influence the nature of a substance. The wide distribution of salt in nature attests to the stability of the union between the ions. Each meets the other’s needs (a good marriage). When dry, salt exists as crystals; its ions are stacked very regularly into a lattice, with positive and negative ions alternating in a three-dimensional chequerboard structure. In water, however, the salt quickly dissolves, and its ions separate from one another, forming an electrolyte solution in which they move about freely. Covalently bonded molecules rarely dissociate like this in a water solution. The most common exception is when they behave like acids and release H1 ions, as discussed in the next section. An ion can also be a group of atoms bound together in such a way that the group has a net charge and enters into reactions as a single unit. Many such groups are active in the fluids of the body. The bicarbonate ion is composed of five atoms – one H, one C and three O – and has a net charge of –1 (HCO32). Another important ion of this type is a phosphate ion with one H, one P and four O, and a net charge of –2 (HPO422). Whereas many elements have only one configuration in the outer shell and thus only one way to bond with other elements, some elements have the possibility of varied configurations. Iron is such an element. Under some conditions iron loses two electrons, and under other circumstances it loses three. If iron loses two electrons, it then has a net charge of 12, and we call it ferrous iron (Fe11). If it donates three electrons to another atom, it becomes the 13 ion, or ferric iron (Fe111). Ferrous iron (Fe11)
Ferric iron (Fe111)
(had 2 outer-shell electrons but has lost them)
(had 3 outer-shell electrons but has lost them)
26 1 charges
26 1 charges
24 2 charges
23 2 charges
28 + charges 28 – charges
2 1 net charge
3 1 net charge
0 net charge and filled outer shells
Remember that a positive charge on an ion means that negative charges – electrons – have been lost and not that positive charges have been added to the nucleus.
Sodium chloride
(Na+Cl –)
Water, acids and bases Cl–
Water The water molecule is electrically neutral, having equal numbers of protons and electrons. When a hydrogen
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713
Appendix B
atom shares its electron with oxygen, however, that electron will spend most of its time closer to the positively charged oxygen nucleus. This leaves the positive proton (nucleus of the hydrogen atom) exposed on the outer part of the water molecule. We know, too, that the two hydrogens both bond towards the same side of the oxygen. These two facts explain why water molecules are polar: they have regions of more positive and more negative charge. Polar molecules like water are drawn to one another by the attractive forces between the positive polar areas of one and the negative poles of another. These attractive forces, sometimes known as polar bonds or hydrogen bonds, occur among many molecules and also within the different parts of single large molecules. Although very weak in comparison with covalent bonds, polar bonds may occur in such abundance that they become exceedingly important in determining the structure of such large molecules as proteins and DNA. + H
–
O
H
+
example, has 10 times as many H1 ions as a solution with pH 4. At pH 7, the concentrations of free H1 and OH2 are exactly the same 21/10 000 000 moles* per litre (1027 moles per litre). At pH 4, the concentration of free H1 ions is 1/10 000 (1024) moles per litre. This is a higher concentration of H1 ions, and the solution is therefore acidic. Figure 3.6 on page 73 presents the pH scale.
Bases A base is a substance that can combine with H1 ions, thus reducing the acidity of a solution. The compound ammonia is such a substance. The ammonia molecule has two electrons that are not shared with any other atom; a hydrogen ion (H1) is just a naked proton with no shell of electrons at all. The proton readily combines with the ammonia molecule to form an ammonium ion; thus a free proton is withdrawn from the solution and no longer contributes to its acidity. Many compounds containing nitrogen are important bases in living systems. Acids and bases neutralise each other to produce substances that are neither acid nor base.
–
This diagram of the polar water molecule shows displacement of electrons towards the O nucleus; thus, the negative region is near the O and the positive regions are near the H atoms.
H N
..
714
H +
H+H
H
H N+ H H
Water molecules have a slight tendency to ionise, separating into positive (H1) and negative (OH2) ions. In pure water, a small but constant number of these ions is present, and the number of positive ions exactly equals the number of negative ions.
Ammonia captures a hydrogen ion from water. The two dots here represent the two electrons not shared with another atom. These dots are ordinarily not shown in chemical structure drawings. Compare this drawing with the earlier diagram of an ammonia molecule (page 711).
Acids
Chemical reactions
An acid is a substance that releases H1 ions (protons) in a water solution. Hydrochloric acid (HCl) is such a substance because it dissociates in a water solution into H1 and Cl2 ions. Acetic acid is also an acid because it dissociates in water to acetate ions and free H1:
A chemical reaction, or chemical change, results in the breakdown of substances and the formation of new ones. Almost all such reactions involve a change in the bonding of atoms. Old bonds are broken and new ones are formed. The nuclei of atoms are never involved in chemical reactions – only their outer-shell electrons take part. At the end of a chemical reaction, the number of atoms of each type is always the same as at the beginning. For example, two hydrogen molecules (2H2) can react with one oxygen molecule (O2) to form two water molecules (2H2O). In this reaction, two substances (hydrogen and oxygen) disappear and a new one (water) is formed, but at the end of the reaction there are still four H atoms and two O atoms, just as there were at the beginning. Because the atoms are now linked in a different way, their characteristics or properties have changed.
H
O
H C
C
H
O H
H
O
H C
C
O– + H+
H
Acetic acid dissociates into an acetate ion and a hydrogen ion.
The more H1 ions released, the stronger the acid.
pH Chemists define degrees of acidity by means of the pH scale, which runs from 0 to 14. The pH expresses the concentration of H1 ions: a pH of 1 is extremely acidic, 7 is neutral and 13 is very basic or alkaline. There is a tenfold difference in the concentration of H1 ions between points on this scale. A solution with pH 3, for
* A mole is a certain number (about 6 3 1023) of molecules. The pH of a solution is defined as the negative logarithm of the hydrogen ion concentration of the solution. For example, if the concentration is 1022 (moles per litre), the pH is 2; if 1028, the pH is 8.
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Appendix B
– –
+
+
– –
+
–
– –
–
+
–
2 Hydrogen molecules
–
– – – –
+ + +8 + + + + ++
–
–
+ + +8 + + + + ++
–
–
– –
1 Oxygen molecule
+
+ –
–
–
–
+ + +8 – + + + – + ++
–
–
–
–
–
+ + +8 – + + + – + ++
–
+
–
–
–
–
–
–
+
2 Water molecules Structures:
H H
+
H O H
+
H H
+
715
(energy [erg] is added into [endo] the compound). An example is the chief result of photosynthesis, the making of sugar in a plant from carbon dioxide and water using the energy of sunlight. Conversely, the oxidation of sugar to carbon dioxide and water is an exergonic, or ‘downhill’, reaction because the end products have less energy than the starting products. Often, but not always, reduction reactions are endergonic, resulting in an increase in the energy of the products. Oxidation reactions often, but not always, are exergonic. Chemical reactions tend to occur spontaneously if the end products are in a lower energy state, and therefore are more stable than the reacting compounds. These reactions often give off energy in the form of heat as they occur. The generation of heat by wood burning in a fireplace and the maintenance of human body warmth both depend on energy-yielding chemical reactions. These downhill reactions occur easily, although they may require some activation energy to get them started, just as a ball requires a push to start rolling. Neither downhill nor uphill reactions occur until something sets them off (activation) or until a path is provided for them to follow. The body uses enzymes as a means of providing paths and controlling chemical reactions (see Chapter 6). By controlling the availability and the action of its enzymes, the cells can ‘decide’ which chemical reactions to prevent and which to promote. Energy change as reaction occurs
H O H
2H2 + O2
O O
Activation energy
Formulas: 2H2 + O2
2H2O
Hydrogen and oxygen react to form water. Energy release
In many instances, chemical reactions involve not the relinking of molecules but the exchanging of electrons or protons among them. In such reactions, the molecule that gains one or more electrons (or loses one or more hydrogen ions) is said to be reduced; the molecule that loses electrons (or gains protons) is oxidised. A hydrogen ion is equivalent to a proton. Oxidation and reduction reactions take place simultaneously because an electron or proton that is lost by one molecule is accepted by another. The addition of an atom of oxygen is also oxidation because oxygen (with six electrons in the outer shell) accepts two electrons in becoming bonded. Oxidation, then, is loss of electrons, gain of protons or addition of oxygen (with six electrons); reduction is the opposite – gain of electrons, loss of protons or loss of oxygen. The addition of hydrogen atoms to oxygen to form water can thus be described as the reduction of oxygen or the oxidation of hydrogen. If a reaction results in a net increase in the energy of a compound, it is called an endergonic, or ‘uphill’, reaction
2H2O
Start of reaction Reactants 2H2 + O2
End of reaction Products 2H2O
Formation of free radicals Normally, when a chemical reaction takes place, bonds break and re-form with some redistribution of atoms and rearrangement of bonds to form new, stable compounds. Bonds don’t usually split in such a way as to leave a molecule with an odd, unpaired electron. When they do, free radicals are formed. Free radicals are highly unstable and quickly react with other compounds, forming more free radicals in a chain reaction. A cascade may ensue in which many highly reactive radicals are generated, resulting finally in the disruption of a living structure such as a cell membrane.
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
716
Appendix B
H O
O H
Heat or light
or R
O
O H
H O + O H R
Hydrogen peroxide or any hydroperoxide (R is any carbon chain with appropriate numbers of H)
Peroxides:
or O + O H Free radical
Free radicals are formed. The dots represent single electrons that are available for sharing (the atom needs another electron to fill its outer shell).
Oxidation of some compounds can be induced by air at room temperature in the presence of light. Such reactions are thought to take place through the formation of compounds called peroxides. Some peroxides readily disintegrate into free radicals, initiating chain reactions like those just described.
H O
O
H
Hydrogen peroxide
R O
O
H
Hydroperoxides (R is any carbon chain with appropriate numbers of H)
R O
O
R
Peroxide
Free radicals are of special interest in nutrition because the antioxidant properties of vitamins C and E as well as beta-carotene and the mineral selenium are thought to protect against the destructive effects of these free radicals. For example, vitamin E on the surface of the lungs reacts with, and is destroyed by, free radicals, thus preventing the radicals from reaching underlying cells and oxidising the lipids in their membranes.
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
717
Appendix C CONTENTS Carbohydrates 717
Amino acid degradation
727
Lipids 719
The TCA cycle
728
Protein: amino acids
The electron transport chain
729
720
Vitamins and coenzymes
721
Glycolysis 725
Alcohol’s interference with energy metabolism 732
Fatty acid oxidation
The urea cycle
732
Formation of ketone bodies
733
727
Biochemical structures and pathways
Chapter 7 – glycolysis, fatty acid oxidation, amino acid degradation, the TCA cycle and the electron transport chain – and a description of how alcohol interferes with these pathways. Discussions of the urea cycle and the formation of ketone bodies complete the appendix.
This appendix describes the biochemical structures and pathways most important to the study of nutrition. It begins by presenting diagrams of nutrients commonly found in the human diet. Following the diagrams of nutrients are sections on the major metabolic pathways mentioned in
Carbohydrates Monosaccharides H H C 6 C H C 4 H O
H O 5
H C
H O
H O H H 2 3 C C H
O
H
H C
O H
H O
O H
Glucose (alpha form). The ring would be at right angles to the plane of the paper. The bonds directed upwards are above the plane; those directed downwards are below the plane. This molecule is considered an alpha form because the OH on carbon 1 points downward.
O
O
C 1 C
CH2OH
H O H
H
C
O H
H
C
C
H
O H
OH
HO
H
OH OH
Glucose (beta form). The OH on carbon 1 points upwards. Fructose, galactose: see Chapter 4.
Glucose (alpha form) shorthand notation. This notation, in which the carbons in the ring and single hydrogens have been eliminated, will be used throughout this appendix.
Disaccharides CH2OH O HO
H H
OH
OH OH
Glucose Maltose
CH2OH O
O
H OH
OH
CH2OH O HO OH
Glucose
OH
O
H
CH2OH O
CH2OH O
OH
OH
OH
HO
OH
OH Glucose
H
CH2OH O
O
Glucose Sucrose
Galactose Lactose (alpha form) Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
HO OH Fructose
CH2OH
718
Appendix C
Polysaccharides As is described in Chapter 4, starch, glycogen and cellulose are all long chains of glucose molecules covalently linked together. • Starch: Two kinds of covalent linkages occur between glucose molecules in starch, giving rise to two kinds of chains. Amylose is OH OH OH OH 1 4 1 4 1 4 (etc.) 4 (etc.) composed of straight chains, with carbon 1 O O O O O of one glucose linked to carbon 4 of the OH OH OH OH next (a-1,4 linkage). Amylopectin is made up of straight chains like amylose but has Amylose (unbranched starch) occasional branches arising where the carbon 6 of a glucose is also linked to the CH2OH CH2OH carbon 1 of another glucose (a-1,6 linkage). O O • Glycogen: The structure of glycogen is like OH OH 1 (etc.) amylopectin, but with many more branches. O O OH OH • Cellulose: Like starch and glycogen, O cellulose is also made of chains of glucose units, but there is an important difference: CH2OH CH2OH CH2OH 6 CH2 in cellulose, the OH on carbon 1 is in the O O O O beta position. When carbon 1 of one glucose OH OH OH OH 1 (etc.) is linked to carbon 4 of the next, it forms a O O O O OH OH OH OH b-1,4 linkage, which cannot be broken by O digestive enzymes in the human GI tract. CH2OH O
(etc.)
CH2OH O
CH2OH O
CH2OH O
CH2OH O
CH2OH O
CH2OH O
OH
OH
OH
O
O
OH
OH
O
6 CH2
CH2OH O
O
OH
OH O
OH
OH
O
(etc.) O
OH
Amylopectin (branched starch)
Fibres, such as hemicelluloses, consist of long chains of various monosaccharides. The most common hemicelluloses are composed of a backbone chain of xylose, mannose and galactose, with branching side chains of arabinose, glucuronic acid and galactose. Monosaccharides common in the backbone chain of hemicelluloses: H H HO
CH2OH
CH2OH O
O H OH
H
OH H Xylose
H*
H
OH
HO
H OH
OH
OH
HO H
H
H
H OH
H
Mannose
Monosaccharides common in the side chains of hemicelluloses: H CO2H O HO H* H H H OH OH H OH H CH3O OH H Arabinose
O H*
H
H
H*
OH
OH
Galactose
CH2OH O
O H*
H OH
Glucuronic acid
OH
HO
H OH
H H
H* H
OH
OH
Galactose
*These structures are shown in the alpha form with the H on the carbon pointing upward and the OH pointing downward, but they may also appear in the beta form with the H pointing downwards and the OH upwards. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Appendix C
Lipids Tables C.1 and C.2 list the common dietary saturated and unsaturated fatty acids, together with their chemical compositions, naming structures and main food sources.
TABLE C.1 Saturated fatty acids found in natural fats SATURATED FATTY ACIDS
CHEMICAL FORMULAS
NUMBER OF CARBONS
Butyric
C3H7COOH
4
Butterfat
Caproic
C5H11COOH
6
Butterfat
Caprylic
C7H15COOH
8
Coconut oil
Capric
C9H19COOH
10
Palm oil
C11H23COOH
12
Coconut oil, palm oil
C13H27COOH
14
Coconut oil, palm oil
Palmitic
C15H31COOH
16
Palm oil
Stearica
C17H35COOH
18
Most animal fats
Arachidic
C19H39COOH
20
Peanut oil
Behenic
C21H43COOH
22
Seeds
Lignoceric
C23H47COOH
24
Peanut oil
Lauric Myristic
a a
MAJOR FOOD SOURCES
Most common saturated fatty acids
a
TABLE C.2 Unsaturated fatty acids found in natural fats CHEMICAL FORMULAS
NUMBER OF CARBONS
NUMBER OF DOUBLE BONDS
STANDARD NOTATIONa
OMEGA NOTATIONb
Palmitoleic
C15H29COOH
16
1
16:1;9
16:1v7
Seafood, beef
Oleic
C17H33COOH
18
1
18:1;9
18:1v9
Olive oil, canola oil
Linoleic
C17H31COOH
18
2
18:2;9,12
18:2v6
Sunflower oil, safflower oil
Linolenic
C17H29COOH
18
3
18:3;9,12,15
18:3v3
Soybean oil, canola oil
Arachidonic
C19H31COOH
20
4
20:4;5,8,11,14
20:4v6
Eggs, most animal fats
Eicosapentaenoic
C19H29COOH
20
5
20:5;5,8,11,14,17
20:5v3
Seafood
Docosahexaenoic
C21H31COOH
22
6
22:6;4,7,10,13,16,19
22:6v3
Seafood
UNSATURATED FATTY ACIDS
MAJOR FOOD SOURCES
NOTE: A fatty acid has two ends; designated the methyl (CH3) end and the carboxyl, or acid (COOH), end. a Standard chemistry notation begins counting carbons at the acid end. The number of carbons the fatty acid contains comes first, followed by a colon and another number that indicates the number of double bonds; next comes a semicolon followed by a number or numbers indicating the positions of the double bonds. Thus the notation for linoleic acid, an 18-carbon fatty acid with two double bonds between carbons 9 and 10 and between carbons 12 and 13, is 18:2;9,12. b Because fatty acid chains are lengthened by adding carbons at the acid end of the chain, chemists use the omega system of notation to ease the task of identifying them. The omega system begins counting carbons at the methyl end. The number of carbons the fatty acid contains comes first, followed by a colon and the number of double bonds; next come the omega symbol (v) and a number indicating the position of the double bond nearest the methyl end. Thus, linoleic acid, with its first double bond at the sixth carbon from the methyl end, would be noted 18:2v6 in the omega system.
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719
720
Appendix C
Protein: amino acids The common amino acids may be classified into the seven groups listed below. Amino acids marked with an asterisk (*) are essential. 1. Amino acids with aliphatic side chains, which consist of hydrogen and carbon atoms (hydrocarbons): H
O
C
C
H
Glycine (Gly)
OH
4. Amino acids with basic side chains:
NH2 CH2
CH2
CH2
CH2
H3C
O
C
C
Alanine (Ala)
OH
NH2 H3C H3C
H3C H3C
H3C
H
O C
NH2 C
NH CH2
NH2
H C
C
CH2
N N
H O CH2 C
C
C
Leucine* (Leu)
OH
H
O
CH2 CH C
C
CH2
H
O
C
C
Isoleucine* (Ile)
OH
OH
H
Serine (Ser)
C
HO OH
C
CH2
C
C
O C
CH2
CH2
O
NH2 C O
CH2
C C
C
CH2
H
O
C
C
CH2
H
C
C
Tyrosine (Tyr)
OH
NH2
H
C
C
C
C
C
C N
CH2 H
H
O
C
C
OH
Tryptophan* (Trp)
NH2
H
6. Amino acids with side chains containing sulphur atoms: H
O
C
C
OH
Glutamic acid (Glu)
HS
CH2
Asparagine (Asn)
C
C
NH2
C
C
OH
CH3
S
CH2
CH2
H C OH
Glutamine (Gln)
H
O
C
C
OH
NH2 Methionine* (Met)
7. Imino acid: H
O
O
Cysteine (Cys)
OH
H
H
NH2
NH2
CH2
H O C
H
C
Phenylalanine* (Phe)
OH
Aspartic acid (Asp)
OH
NH2
NH2 C
O C
H
H
NH2
HO
H C
NH2
H
C
Threonine* (Thr)
3. Amino acids with side chains containing acidic groups or their amides, which contain the group NH2: O
Arginine (Arg)
Histidine* (His)
H
H
OH
OH
C C
H
HO
CH2
H
OH NH2
O
C C C
H O C
C
H
H C
NH2
CH
C
5. Amino acids with aromatic side chains, which are characterised by the presence of at least one ring structure:
H O C
O
H
H
2. Amino acids with hydroxyl (OH) side chains:
H3C
CH2
H
NH2
C C
C
Lysine* (Lys)
H
NH2
CH2
OH
NH2
Valine* (Val)
OH
CH3 NH2
HO
C
NH
CH C
CH
O
NH2
NH2 H
H C
H C H
H H C C N H H
Proline (Pro)
O C
OH
Proline has the same chemical structure as the other amino acids, but its amino group has given up a hydrogen to form a ring.
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Appendix C
721
Vitamins and coenzymes H3C CH3 H C CH H C C H C C C H H H
CH3 C
CH
CH
CH
CH
CH3
H
C
C
CH
N
H
CH3
H3C
Vitamin A: retinol. Retinol is the alcohol form of vitamin A. H3C CH3 H C CH H C C H C C C H H H
CH3 C
CH
CH
CH
CH
CH3
O
C
C
CH
H N H3C
Vitamin A: retinal. Retinal is the aldehyde form of vitamin A.
H C C C H H H
CH3 C
CH
CH
CH
CH
CH3
O
C
C
CH
CH3 C
CH
H3C H3C
CH3
CH
CH
CH
C
CH
CH3 C
CH
C C
CH
CH
C
CH
H
C
C
C
S
CH2
CH2
OH
H
O
NH2
CH3
C
C
C
C
S
N
C C
+
CH2 N H
CH2
CH2
O
P
O O
P
OH
CH
H
OH
OH
OH CH
H
CH2
CH
CH
C
N
N
O
C C
C
H
CH
H3C
CH3 H3C
C C
N
C
C N
CH2
OH
H
C C
C C
C C
OH
OH
OH
CH2
CH
CH
CH
N
N
N
C C
C
C N
O CH2
O
O
P
OH
OH
H
O
H
Vitamin A precursor: beta-carotene. Betacarotene is the carotenoid with the most vitamin A activity.
Flavin mononucleotide (FMN). FMN is a coenzyme that includes the riboflavin molecule as part of its structure.
Pyrophosphate
CH2
OH
OH
OH
CH
CH
CH
OH CH2
O
P O
P
O
H3C
C C
C C H
C C
N N
C C
N C
C N
O Riboflavin
O
H H HO
H
C
NH2
H
O
H H3C
FAD can pick up hydrogens and carry them to the electron transport chain.
H
OH O
OH
OH
O H Riboflavin. Riboflavin is a part of two coenzymes – flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).
CH3
CH
C
N
CH2 N
OH
CH3
H3C CH3 H C CH H C C H C C C H H H
C
CH3
H3C CH3 H C CH H C C
+
C
Thiamin pyrophosphate (TPP). TPP is a coenzyme that includes the thiamin molecule as part of its structure.
Vitamin A: retinoic acid. Retinoic acid is the acid form of vitamin A.
H C C C H H H
C
C
Thiamin. Thiamin is part of the coenzyme thiamin pyrophosphate (TPP).
CH3
H3C CH3 H C CH H C C
CH3
NH2
OH
C
C
H C
O
H C C
N C N C
H
C
N
H
N C
Adenine
C H
N
N
C
N
N
C
H
OH D-ribose
C
FAD (oxidised form)
Flavin adenine dinucleotide (FAD). FAD is a coenzyme that includes the riboflavin molecule as part of its structure.
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
FADH2 (reduced form)
722
Appendix C
H H
C C
H
O
C
C
C C
N
H
OH
H
H
Nicotinic acid
C C
H
O
C
C NH2
C C
N
H
Nicotinamide
Niacin (nicotinic acid and nicotinamide). These molecules are a part of two coenzymes – nicotinamide adenine dinucleotide (NAD1) and nicotinamide adenine dinucleotide phosphate (NADP1). Nicotinamide H H
C
C
Adenine NH2
O C
C NH2 H C
C + C H H N H HO
C H C H
N C
C
N
N C
H
H C
C O
HO
N C
D-ribose
H C OH D-ribose
O C
C
H
H C OH H
O CH2
O
O
P
O
P
OH
O
CH2
OH
Pyrophosphate
Nicotinamide adenine dinucleotide (NAD1) and nicotinamide adenine dinucleotide phosphate (NADP1). NADP has the same structure as NAD, but with a phosphate group attached to the O instead of to the H. H H
C
C
H
O C
H
C NH2
C + C H N
H
H H
H
H+
H
C C
C
C
N
C
O C NH2 H
NAD+
NADH Reduced NAD1. When NAD1 is reduced by the addition of H1 and two electrons, it becomes the coenzyme NADH. (The dots on the H entering this reaction represent electrons – see Appendix B.) H CH2 HO H3C
C C
C N
C C
Pyridoxine
OH CH2 H
CH2 NH2
C O OH
HO H3C
C C
C N
C C
Pyridoxal
CH2 H
OH
HO H3C
C C
C N
C C
CH2
OH
H
Pyridoxamine
Vitamin B6 (a general name for three compounds – pyridoxine, pyridoxal and pyridoxamine). These molecules are a part of two coenzymes: pyridoxal phosphate and pyridoxamine phosphate. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Appendix C
723
H C HO
H3C
C C
C N
O C C
CH2
O
P
OH
HO
O
NH3
OH
H
CH2
NH3
O
H3C
O
Pyridoxal phosphate
C C
C
C
N
C
NH2
O
CH2
O
P
OH
OH
H
Pyridoxamine phosphate
Pyridoxal phosphate (PLP) and pyridoxamine phosphate. These coenzymes include vitamin B6 as part of their structures.
N H2N
C
C N
H
H
OH C C
N N
H C C
CH2
C
N
C
C C
H
O O
C
C
C
H
H N
C
H
CH2
H
C
H3C H3C
OH
N H2N
C
C N
C C
N N
C C
H
H
CH2 H
N
H
C C
C C
H
C
C
H
O
N
C
H
CH2
H
C
H2N C
N
H2C
CH
O
H N
O H
Tetrahydrofolate. This active coenzyme form of folate has four added hydrogens. An intermediate form, dihydrofolate, has two added hydrogens.
CH3 H
O
CH3 CH2 CH2
C
NH2
CH3
H
O– P
OH
NH2
CH2 NH O
C
CH2 C
C O
CH3
CH2
H
NH2 O
C
CH2 H
N
H H2C CH3
OH
O CH2
Co+
CH2 O
C
N
O
H
H
H
H3C
H C
H2N C H2C
Folate (folacin or folic acid). This molecule consists of a double ring combined with a single ring and at least one glutamate (a non-essential amino acid marked in the box). Folate’s biologically active form is tetrahydrofolate.
CH3
CH2
O
C
OH
CH2
OH
CH2 O
C NH2
O
OH
O C
C H
C H O
CH2 OH
H
C
N
N
C C
C
C
CH3
C C
C
CH3
H
H
Vitamin B12 (cyanocobalamin). The arrows in this diagram indicate that the spare electron pairs on the nitrogens attract them to the cobalt. O
NH2
O OH CH3
HO C CH2 CH2 N C CH C H
CH2 OH
CH3
Pantothenic acid. This molecule is part of coenzyme A (CoA).
C
N C
H H O
O OH CH3
HS CH2 CH2 N C CH2 CH2 N C CH C H
O
N
C C
N C
H
N
O
CH2 O P O P O CH2
CH3
OH
OH O H
C
H C
H C H C
O
OH
HO P O OH
Coenzyme A (CoA). Coenzyme A is a coenzyme that includes pantothenic acid as part of its structure. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
724
Appendix C
H3C
O H H H H
C
H
7-dehydrocholesterol
N
N
C
C H O H C CH2 CH2 CH2 CH2 C OH
C
S
1 2
8
O HO
C
2H+
C
O C CH HO HO CH
+
2H
CH2OH Ascorbic acid (reduced form)
4
5
6
C
CH3
Carbon #7
C
Ultraviolet light on the skin
O O
25
CH3
Biotin HO 3
CH3
CH3
C
O C CH O HO CH CH2OH Dehydroascorbic acid (oxidised form)
Vitamin C. Two hydrogen atoms with their electrons are lost when ascorbic acid is oxidised and gained when it is reduced again.
H3C CH3
CH3
Vitamin D3 (also called cholecalciferol or calciol)
CH3
CH2
Hydroxylation in the liver
HO
H3C CH3 C OH CH3
CH3
Carbon #25
25-hydroxyvitamin D3 (also called calcidiol)
CH2
Hydroxylation in the kidneys
HO H3C CH3
CH3 C OH CH3
1,25-dihydroxyvitamin D3 (also called calcitriol) CH2
HO
C
OH
Carbon Vitamin D. The synthesis of active vitamin D #1 begins with 7-dehydrocholesterol. (The carbon atoms at which changes occur are numbered.)
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Appendix C
CH3 HO H3C
C C
C C
H C C
C O
H
H C H C CH2
CH3 CH2
CH2
CH
CH3 CH2
CH2
CH2 CH
CH3 CH2
CH2
CH2 CH
CH3
CH3
CH3 Tocotrienols contain double bonds here.
Vitamin E (alpha-tocopherol). The number and position of the methyl groups (CH3) bonded to the ring structure differentiate among the tocopherols.
H H H
C C
C C H
O C C
C C
C
CH3
CH3
C CH2
CH
C
CH3
CH2
CH2
CH2 CH
CH3 CH2
CH2
CH2 CH
CH3 CH2
CH2
CH2 CH
CH3
O
Vitamin K. Naturally occurring compounds with vitamin K activity include phylloquinones (from plants) and menaquinones (from bacteria). H H H OH HO P O
Cleavage
O Triphosphate
HO P O O
N H C
HO P O
N
C
C N
N C
CH2 C
H
H
C
C C
C C
CH3 H
OH
OH HO P O
Cleavage
O
O H C
C
C
Adenine
O Ribose
C
O
O H Menadione. This synthetic compound has the same activity as natural vitamin K.
NH2 C
C
C
H C H C
HO P O O
+ H O H (Water)
Glycolysis Figure C.1 depicts the events of glycolysis. The following text describes key steps as numbered on the figure: 1 A phosphate is attached to glucose at the carbon that chemists call number 6 (review the first diagram of glucose on page 717 to see how chemists number the carbons in a glucose molecule). The product is called, logically enough, glucose-6-phosphate. One ATP molecule is used to accomplish this. 2 Glucose-6-phosphate is rearranged by an enzyme. 3 A phosphate is added in another reaction that uses another molecule of ATP. The product this time is
O–
H+
Phosphate + OH HO P O
OH OH
Adenosine triphosphate (ATP), the energy carrier. The cleavage point marks the bond that is broken when ATP splits to become ADP 1 P.
HO P O
ADP
Adenosine diphosphate (ADP)
fructose-1,6-diphosphate. At this point, the 6-carbon sugar has a phosphate group on its first and sixth carbons and is ready to break apart. 4 When fructose-1,6-diphosphate breaks in half, the two three-carbon compounds are not identical. Each has a phosphate group attached, but only glyceraldehyde-3-phosphate converts directly to pyruvate. The other compound, however, converts easily to glyceraldehyde-3-phosphate. 5 In the next step, enough energy is released to convert NAD1 to NADH 1 H1. 6 In two of the following steps, ATP is regenerated.
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Appendix C
FIGURE C.1 Glycolysis Notice that galactose and fructose enter at different places but continue on the same pathway. Glycogen
Galactose
Glucose-1-phosphate
Glucose ATP 1 ADP Glucose-6-phosphate 2 Fructose
Fructose-6-phosphate ATP 3
ADP
Fructose-1,6-diphosphate 4 Dihydroxy acetone phosphate
Glyceraldehyde-3phosphate 2NAD+
5 Glycerol
2NADH + 2H+
1,3-diphosphoglyceric acid 2ADP
6
2ATP
3-phosphoglyceric acid
2-phosphoglyceric acid
Phosphoenol pyruvic acid 2ADP
6
2ATP
Pyruvate 2NADH + 2H+
Lactate 2NAD+
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Appendix C
Remember that, in effect, two molecules of glyceraldehyde-3-phosphate are produced from glucose; therefore, four ATP molecules are generated from each glucose molecule. Two ATP were needed to get the sequence started, so the net gain at this point is two ATP and two molecules of NADH 1 H1. As you will see later, each NADH 1 H1 moves to the electron transport chain to unload its hydrogens onto oxygen, producing more ATP.
FIGURE C.2 Fatty acid oxidation Palmitic acid (16C) ATP CoA
AMP + PP Activated palmitic acid FAD
Fatty acid oxidation Figure C.2 presents fatty acid oxidation. The sequence is as follows: 1 The fatty acid is activated by combining with coenzyme A (CoA). In this reaction, ATP loses two phosphorus atoms (PP, or pyrophosphate) and becomes AMP (adenosine monophosphate) – the equivalent of a loss of two ATP. 2 In the next reaction, two H1 with their electrons are removed and transferred to FAD, forming FADH2. 3 In a later reaction, two H1 are removed and go to NAD1 (forming NADH 1 H1). 4 The fatty acid is cleaved at the ‘beta’ carbon, the second carbon from the carboxyl (COOH) end. This break results in a fatty acid that is two carbons shorter than the previous one and a two-carbon molecule of acetyl CoA. At the same time, another CoA is attached to the fatty acid, thus activating it for its turn through the series of reactions. 5 The sequence is repeated with each cycle producing an acetyl CoA and a shorter fatty acid until only a two-carbon fatty acid remains – acetyl CoA. In the example shown in Figure C.2, palmitic acid (a 16-carbon fatty acid) will go through this series of reactions seven times, using the equivalent of two ATP for the initial activation and generating seven FADH2, seven NADH 1 H1, and eight acetyl CoA. As you will see later, each of the seven FADH2 will enter the electron transport chain to unload its hydrogens onto oxygen, yielding two ATP (for a total of 14). Similarly, each NADH 1 H1 will enter the electron transport chain to unload its hydrogens onto oxygen, yielding three ATP (for a total of 21). Thus the oxidation of a 16-carbon
1
2 FADH 2 H2O
5
NAD + 3 NADH + H
CoA
+
4
Activated myristic acid (14C) + Acetyl CoA (2C)
fatty acid uses two ATP and generates 35 ATP. When the eight acetyl CoAs enter the TCA cycle, even more ATP will be generated, as a later section describes.
Amino acid degradation The first step in amino acid degradation is the removal of the nitrogen-containing amino group through either deamination (Figure 7.14 on page 227) or transamination (Figure 7.16 on page 228) reactions. Then the remaining carbon skeletons may enter the metabolic pathways at different places, as shown in Figure C.3.
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Appendix C
FIGURE C.3 Amino acid degradation After losing their amino groups, carbon skeletons can be converted to one of seven molecules that can enter the TCA cycle (presented in Figure C.4). Pyruvate
Isoleucine Leucine Lysine Tryptophan
Asparagine Aspartate
Acetyl CoA
Alanine Cysteine Glysine Serine
Tryptophan Threonine
Acetoacetyl CoA
Leucine Phenylalanine Tyrosine
Oxaloacetate Citrate
Malate TCA cycle Aspartate Phenylalanine Tyrosine
Isocitrate
Fumarate
Alpha-ketoglutarate Succinate Succinyl CoA
Arginine Glutamate Glutamine Histidine Lysine Proline
Isoleucine Methionine Threonine Valine
The TCA cycle The tricarboxylic acid, or TCA, cycle is the set of reactions that breaks down acetyl CoA to carbon dioxide and hydrogens. To link glycolysis to the TCA cycle, pyruvate enters the mitochondrion, loses a carbon group and bonds with a molecule of CoA to become acetyl CoA. The TCA cycle uses any substance that can be converted to acetyl CoA directly or indirectly through pyruvate. The pathway from pyruvate to acetyl CoA is complex. We have included only those substances that will help you understand the transfer of energy from the nutrients. Pyruvate loses a carbon to carbon dioxide and is attached to a molecule of CoA. In the process, NAD1 picks up two hydrogens with their associated electrons, becoming NADH 1 H1.
Glucose Glycerol Some amino acids
Pyruvate
Lactate
Some amino acids
Acetyl CoA
Fatty acids
Some amino acids
TCA
Any substance that can be converted to acetyl CoA directly, or indirectly through pyruvate, may enter the TCA cycle.
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Appendix C
The step from pyruvate to acetyl CoA. (TPP and NAD are coenzymes containing the B vitamins thiamin and niacin, respectively.)
Let’s follow the steps of the TCA cycle (see the corresponding numbers in Figure C.4): 1 The 2-carbon acetyl CoA combines with a 4-carbon compound, oxaloacetate. The CoA comes off, and the product is a 6-carbon compound, citrate. 2 The atoms of citrate are rearranged to form isocitrate. 3 Now two H1 (with their two electrons) are removed from the isocitrate. One H1 becomes attached to the NAD1 with the two electrons; the other H1 is released as H1. Thus, NAD1 becomes NADH 1 H1. (Remember this NADH 1 H1, but let’s follow the carbons first.) A carbon is combined with two oxygens, forming carbon dioxide (which diffuses away into the blood and is exhaled). What is left is the 5-carbon compound alpha-ketoglutarate. 4 Now two compounds interact with alphaketoglutarate – a molecule of CoA and a molecule of NAD1. In this complex reaction, a carbon and two oxygens are removed (forming carbon dioxide); two hydrogens are removed and go to NAD1 (forming NADH 1 H1); and the remaining four-carbon compound is attached to the CoA, forming succinyl CoA. (Remember this NADH 1 H1 also. You will see later what happens to it.) 5 Now two molecules react with succinyl CoA – a molecule called guanosine diphosphate GDP and one of phosphate (P). The CoA comes off, the GDP and P combine to form the high-energy compound GTP (similar to ATP), and succinate remains. (Remember this GTP.) 6 In the next reaction, two H1 with their electrons are removed from succinate and are transferred to a molecule of flavin adenine dinucleotide FAD (a coenzyme like NAD1) to form FADH2. The product that remains is fumarate. (Remember this FADH2.)
7 Next, a molecule of water is added to fumarate, forming malate. 8 A molecule of NAD1 reacts with the malate; two H1 with their associated electrons are removed from the malate and form NADH 1 H1. The product that remains is the four-carbon compound oxaloacetate. (Remember this NADH 1 H1.) The cycle is complete and we are back where we started. The oxaloacetate formed in this process can combine with another molecule of acetyl CoA (step 1), and the cycle can begin again, as shown in Figure C.4. So far, we have seen two carbons brought in with acetyl CoA and two carbons ending up in carbon dioxide. But where are the energy and the ATP we promised? A review of the eight steps of the TCA cycle shows that the compounds NADH 1 H1 (three molecules), FADH2 and GTP capture energy originally found in acetyl CoA. To see how this energy ends up in ATP, we must follow the electrons further – into the electron transport chain.
The electron transport chain The six reactions described here are those of the electron transport chain, which is shown in Figure C.5 on page 731. Since oxygen is required for these reactions, and ADP and P are combined to form ATP in several of them (ADP is phosphorylated), these reactions are also called oxidative phosphorylation. An important concept to remember at this point is that an electron is not a fixed amount of energy. The electrons that bond the H1 to NAD1 in NADH have a relatively large amount of energy. In the series of reactions that follow, they release this energy in small amounts, until at the end they are attached (with H1) to oxygen (O) to make water (H2O). In some of the steps, the energy they release is captured into ATP in coupled reactions. 1 In the first step of the electron transport chain, NADH reacts with a molecule called a flavoprotein, losing its electrons (and their H1). The products are NAD1 and reduced flavoprotein. A little energy is released as heat in this reaction. 2 The flavoprotein passes on the electrons to a molecule called coenzyme Q. Again they release some energy as heat, but ADP and P bond together and form ATP, storing much of the energy. This is a coupled reaction: ADP 1 P → ATP 3 Coenzyme Q passes the electrons to cytochrome b. Again, the electrons release energy. 4 Cytochrome b passes the electrons to cytochrome c in a coupled reaction in which ATP is formed: ADP 1 P → ATP
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Appendix C
FIGURE C.4 The TCA cycle COOH C O With the assistance of a biotin coenzyme, pyruvate receives a carbon from carbon dioxide to regenerate oxaloacetate. This reaction is energetically costly.
CH3 Pyruvate TPP
CoA NAD+ NADH + H+ CO2
O H3C
C
(CoA)
Acetyl CoA
COOH
CoA
COOH
CH2
C O
1
CH2
NADH + H+
HO C
H2O
CH2
COOH Oxaloacetate
NAD+
COOH
COOH Citrate
H2O 2
8 COOH H C
COOH
OH
CH2
CH2
H C
COOH
COOH
H C OH
Malate
COOH Isocitrate
H2O
7
COOH
3
CH
NAD+ NADH + H+
CH COOH Fumarate
CO2 6 COOH
FADH2 FAD
COOH
CH2
CH2
CH2
CH2
5
COOH Succinate
COOH
4
CH2 CoA
CH2 O C (CoA) GTP GDP H2O + P Succinyl CoA
CO2
C O COOH AlphaCoA ketoglutarate NAD+ NADH + H+
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Appendix C
FIGURE C.5 The electron transport chain Acetyl CoA
Oxaloacetate
Citrate
Isocitrate Malate TCA cycle Alpha-ketoglutarate
Fumarate
Succinate 2H
Succinyl CoA
2H
2H
One energy-receiving compound of the TCA cycle (GTP) does not enter the electron transport chain but gives its energy directly to ADP in a simple phosphorylation reaction. This reaction yields one ATP. It is now possible to draw up a balance sheet of glucose metabolism (see Table C.3). Glycolysis has yielded four NADH 1 H1 and four ATP molecules and has spent two ATP. The two acetyl CoA going through the TCA cycle have yielded six NADH 1 H1, two FADH2 and two GTP molecules. After the NADH 1 H1 and FADH2 have gone through the electron transport chain, there are 28 ATP. Added to these are the four ATP from glycolysis and the two ATP from GTP, making the total 34 ATP generated from one molecule of glucose. After the expense of two ATP is subtracted, there is a net gain of 32 ATP.*
TABLE C.3 Balance sheet for glucose metabolism
2H
ATP
NAD+ 1
FAD
Flavoprotein ADP + P
ATP
2 Coenzyme Q
5 Cytochrome a ATP
6
2H + O
2
1 glucose to 2 pyruvate
2 NADH 1 H1
3−5a
2 pyruvate to 2 acetyl CoA
2 NADH 1 H1
5
2 isocitrate ATP
4 Cytochrome c
ADP + P
4 ATP – 2 ATP
TCA cycle and electron transport chain:
3 Cytochrome b ADP + P
Glycolysis
H2O
5 Cytochrome c passes the electrons to cytochrome a. 6 Cytochrome a passes them (with their H1) to an atom of oxygen (O), forming water (H2O). This is a coupled reaction in which ATP is formed: ADP 1 P → ATP At the end of the chain, the low-energy electrons are passed to oxygen, which combines with the free H+ ions to form water. Figure C.5 shows that each time NADH is oxidised (loses its electrons) by this means, the energy it releases is captured into three ATP molecules. When the electrons are passed on to water at the end, they are much lower in energy than they were originally. This completes the story of the electrons from NADH. As for FADH2, its electrons enter the electron transport chain at coenzyme Q. From coenzyme Q to water, ATP is generated in only two steps. Therefore, FADH2 coming out of the TCA cycle yields just two ATP molecules.
2 NADH 1 H1
5
1
2 alpha-ketoglutarate
2 NADH 1 H
5
2 succinyl CoA
2 GTP
2
2 succinate
2 FADH2
3
2 malate
2 NADH 1 H1
5
Total ATP collected from one molecule glucose:
30−32
Each NADH 1 H1 from glycolysis can yield 1.5 or 2.5 ATP. See the text.
a
A similar balance sheet from the complete breakdown of one 16-carbon fatty acid would show a net gain of 129 ATP. As mentioned earlier, 35 ATP were generated from the seven FADH2 and seven NADH 1 H1 produced during fatty acid oxidation. The eight acetyl CoA produced will each generate 12 ATP as they go through the TCA cycle and the electron transport chain, for a total of 96 more ATP. After subtracting the two ATP needed to activate the
*The total may sometimes be 30 ATP. The NADH 1 H1 generated in the cytoplasm during glycolysis pass their electrons on to shuttle molecules, which move them into the mitochondria. One shuttle, malate, contributes its electrons to the electron transport chain before the first site of ATP synthesis, yielding five ATP. Another, glycerol phosphate, adds its electrons into the chain beyond that first site, yielding three ATP. Thus sometimes five and sometimes three ATP result from the NADH 1 H1 that arise from glycolysis. The amount depends on the cell.
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Appendix C
fatty acid initially, the net yield from one 16-carbon fatty acid: 35 1 96 2 2 5 129 ATP These calculations help explain why fat yields more energy (measured as kilojoules) per gram than carbohydrate or protein. The more hydrogen atoms a fuel contains, the more ATP will be generated during oxidation. The 16-carbon fatty acid molecule, with its 32 hydrogen atoms, generates 129 ATP, whereas glucose, with its 12 hydrogen atoms, yields only 32 ATP. The TCA cycle and the electron transport chain are the body’s major means of capturing the energy from nutrients in ATP molecules. Other means, such as anaerobic glycolysis, contribute energy quickly, but the aerobic processes are the most efficient. Biologists and chemists understand much more about these processes than has been presented here.
FIGURE C.6 Ethanol enters the metabolic pathway This is a simplified version of the glucose-to-energy pathway showing the entry of ethanol. The coenzyme NAD1 (which is the active form of the B vitamin niacin) is the only one shown here; however, many others are involved. Glucose
NADH + H+ NAD+
Ethanol
NADH + H+
Highlight 7 provides an overview of how alcohol interferes with energy metabolism. With an understanding of the TCA cycle, a few more details may be appreciated. During alcohol metabolism, the enzyme alcohol dehydrogenase oxidises alcohol to acetaldehyde while it simultaneously reduces a molecule of NAD1 to NADH 1 H1. The related enzyme acetaldehyde dehydrogenase reduces another NAD1 to NADH 1 H1 while it oxidises acetaldehyde to acetyl CoA, the compound that enters the TCA cycle to generate energy. Thus, whenever alcohol is being metabolised in the body, NAD1 diminishes and NADH 1 H1 accumulates. Chemists say that the body’s ‘redox state’ is altered, because NAD1 can oxidise, and NADH 1 H1 can reduce, many other body compounds. During alcohol metabolism, NAD1 becomes unavailable for the multitude of reactions for which it is required. As the previous sections just explained, for glucose to be completely metabolised, the TCA cycle must be operating, and NAD1 must be present. If these conditions are not met (and when alcohol is present, they may not be), the pathway will be blocked and traffic will back up – or an alternative route will be taken. Think about this as you follow the pathway shown in Figure C.6. In each step of alcohol metabolism in which NAD1 is converted to NADH 1 H1, hydrogen ions accumulate, resulting in a dangerous shift of the acid–base balance towards acid (Chapter 12 explains acid–base balance). The accumulation of NADH 1 H1 slows TCA cycle activity, so pyruvate and acetyl CoA build up. This condition favours the conversion of pyruvate to lactate, which serves as a temporary storage place for hydrogens from NADH 1 H1. The conversion of pyruvate to lactate restores some NAD1, but a lactate build-up has serious
NAD+ Lactate
Pyruvate
NADH + H+
CO2
Acetaldehyde NAD+
NAD+
NADH + H+
Ketone bodies, fatty acids, and fat NAD+
NADH + H+
NADH + H+
Acetyl CoA NADH + H+
Alcohol’s interference with energy metabolism
NAD+
1 2
NAD+
3
8
NAD+ NADH + H+
TCA cycle
CO2 4
7
NAD+ NADH + H+ 6
5
CO2
Energy (ATP), CO2, H2O
consequences of its own. It adds to the body’s acid burden and interferes with the excretion of uric acid, causing gout-like symptoms. Molecules of acetyl CoA become building blocks for fatty acids or ketone bodies. The making of ketone bodies consumes acetyl CoA and generates NAD1, but some ketone bodies are acids, so they push the acid–base balance further towards acid. Thus, alcohol cascades through the metabolic pathways, wreaking havoc along the way. These consequences have physical effects, which Highlight 7 describes.
The urea cycle Chapter 7 sums up the process by which waste nitrogen is eliminated from the body by stating that ammonia molecules combine with carbon dioxide to produce urea. This is true, but it is not the whole story. Urea is produced in a multistep process within the cells of the liver.
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Appendix C
3 Argininosuccinate is split, forming another acid, fumarate, and the amino acid arginine. 4 Arginine loses its terminal carbon with two attached amino groups and picks up an oxygen from water. The end product is urea, which the kidneys excrete in the urine. The compound that remains is ornithine – identical to the ornithine with which this series of reactions began, and ready to react with another molecule of carbamyl phosphate and turn the cycle again.
Ammonia, freed from an amino acid or other compound during metabolism anywhere in the body, arrives at the liver by way of the bloodstream and is taken into a liver cell. There, it is first combined with carbon dioxide and a phosphate group from ATP to form carbamyl phosphate: 2 ATP CO2
+
2 ADP + P H2N
NH3
O
O C
O
O–
P O–
Carbon dioxide
Ammonia
Carbamyl phosphate
Formation of ketone bodies Normally, fatty acid oxidation proceeds all the way to carbon dioxide and water. However, in ketosis (as discussed in Chapter 7), an intermediate is formed from the condensation of two molecules of acetyl CoA: acetoacetyl CoA. Figure C.8 shows the formation of ketone bodies from that intermediate:
Figure C.7 shows the cycle of four reactions that follow: 1 Carbamyl phosphate combines with the amino acid ornithine, losing its phosphate group. The compound formed is citrulline. 2 Citrulline combines with the amino acid aspartic acid to form argininosuccinate. The reaction requires energy from ATP. (ATP was shown earlier losing one phosphorus atom in a phosphate group, P, to become ADP. In this reaction involving citrulline, ATP loses two phosphorus atoms joined together, PP, and becomes adenosine monophosphate, AMP.)
1 Acetoacetyl CoA condenses with acetyl CoA to form a six-carbon intermediate, beta-hydroxy-betamethylglutaryl CoA. 2 This intermediate is cleaved to acetyl CoA and acetoacetate. 3 Acetoacetate can be metabolised either to betahydroxybutyrate (step 3a) or to acetone (3b).
FIGURE C.7 The urea cycle O O
C H2N
NH2
Urea
H2N C
NH2
Phosphate
Carbamyl phosphate
CH2 CH2 CH2
4
H
1
H C NH2
Phosphate
COOH Ornithine
NH2
NH2
C NH
C
NH
N H
CH2
CH2
CH2
CH2
CH2
CH2
COOH
H C NH2
NH2
COOH Arginine COOH
O
H C NH2
CH2
COOH Citrulline
C N C H NH 3
COOH
CH2
CH
CH2
CH
CH2
COOH
H C NH2
Fumarate
COOH Argininosuccinate
COOH
2
CH2 ATP AMP + PP
H2N C H COOH Aspartic acid
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Appendix C
Acetoacetate, beta-hydroxybutyrate and acetone are the ketone bodies of ketosis. Two are real ketones (they have a C=O group between two carbons); the other is an alcohol that has been produced during ketone
formation – hence the term ketone bodies, rather than ketones, to describe the three of them. There are many other ketones in nature; these three are characteristic of ketosis in the body.
FIGURE C.8 The formation of ketone bodies O H3 C
O
C
CH2
O
C
CoA
+
H3C
Acetoacetyl CoA
C
CoA
+
H2O
Acetyl CoA
Water
1
HOOC
CH2
CH3
O
C
C
CH2
+
CoA
CoA
OH Beta-hydroxy-beta-methylglutaryl CoA
Coenzyme A
2
O H3C
NADH + H+
O
C
CH2
+
COOH
H3C
Acetoacetate (a ketone body)
C
CoA
Acetyl CoA
NAD+ OH H3C
C
3a CH2
3b COOH
H3C
O C
CH3
+
CO2
H Beta-hydroxybutyrate (a ketone body)
Acetone (a ketone body)
Carbon dioxide
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735
Appendix D CONTENTS Amino acid scoring
735
PDCAAS 736 Biological value
737
Net protein utilisation
737
Protein efficiency ratio
737
Measures of protein quality
In a world where food is scarce and many people’s diets contain marginal or inadequate amounts of protein, it is important to know which foods contain the highestquality protein. Chapter 6 describes protein quality, and this appendix presents different measures researchers use to assess the quality of a food protein.
TABLE D.1 A reference pattern for amino acid scoring of proteins ESSENTIAL AMINO ACIDS
Amino acid scoring Amino acid scoring evaluates a protein’s quality by determining its amino acid composition and comparing it with that of a reference protein. The advantages of amino acid scoring are that it is simple and inexpensive, it easily identifies the limiting amino acid and it can be used to score mixtures of different proportions of two or more proteins mathematically without having to make up a mixture and test it. Its chief weaknesses are that it fails to estimate the digestibility of a protein, which may strongly affect the protein’s quality; it relies on a chemical procedure in which certain amino acids may be destroyed, making the pattern that is analysed inaccurate; and it is blind to other features of the protein (such as the presence of substances that may inhibit the digestion or utilisation of the protein) that would only be revealed by a test in living animals. Table D.1 shows the reference pattern for the nine essential amino acids. To interpret the table, read, ‘For every 3210 units of essential amino acids, 145 must be histidine, 340 must be isoleucine, 540 must be leucine’, and so on. To compare a test protein with the reference protein, the experimenter first obtains a chemical analysis of the test protein’s amino acids. Then, taking 3210 units of the amino acids, the experimenter compares the amount of each amino acid to the amount found in 3210 units of essential amino acids in egg protein. For example, suppose the test protein contained (per 3210 units) 360 units of isoleucine, 500 units of
REFERENCE PROTEIN – WHOLE EGG (mg AMINO ACID PER g NITROGEN)
Histidine
145
Isoleucine
340
Leucine
540
Lysine
440
Methionine 1 cystinea
355
Phenylalanine 1 tyrosineb
580
Threonine
294
Tryptophan
106
Valine
410
Total
3210
Methionine is essential and is also used to make cystine. Thus the methionine requirement is lower if cystine is supplied. a
Phenylalanine is essential and is also used to make tyrosine if not enough of the latter is available. Thus the phenylalanine requirement is lower if tyrosine is also supplied.
b
leucine, 350 of lysine, and for each of the other amino acids, more units than egg protein contains. The two amino acids that are low are leucine (500 as compared with 540 in egg) and lysine (350 versus 440 in egg). The ratio – amino acid in the test protein divided by amino acid in egg – is 500:540 (or about 0.93) for leucine and 350:440 (or about 0.80) for lysine. Lysine is the limiting amino acid (the one that falls shortest compared with egg). If the protein’s limiting amino acid is 80 per cent of the amount found in the reference protein, it receives a score of 80.
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Appendix D
PDCAAS
TABLE D.2 PDCAAS values of selected foods
The protein digestibility–corrected amino acid score, or PDCAAS, compares the amino acid composition of a protein with human amino acid requirements and corrects for digestibility. First, the protein’s amino acid composition is determined, and then it is compared against the amino acid requirements of preschool-age children. This comparison reveals the most limiting amino acid – the one that falls shortest compared with the reference. If a food protein’s limiting amino acid is 70 per cent of the amount found in the reference protein, it receives a score of 70. The amino acid score is multiplied by the food’s protein digestibility percentage to determine the PDCAAS. The following ‘How to’ box provides an example of how to calculate the PDCAAS, and Table D.2 lists the PDCAAS values of selected foods.
Casein (milk protein)
1.00
Egg white
1.00
Soybean (isolate)
0.99
Beef
0.92
Chickpea flour
0.69
Kidney beans (canned)
0.68
Chickpeas (canned)
0.66
Pinto beans (canned)
0.66
Rolled oats
0.57
Lentils (canned)
0.52
Peanut meal
0.52
Whole wheat
0.40
NOTE: 1.0 is the maximum PDCAAS a food protein can receive.
MEASURE PROTEIN QUALITY USING PDCAAS
HOW TO:
To calculate the PDCAAS, researchers first determine the amino acid profile of the test protein (in this example, pinto beans). The second column of the table below presents the essential amino acid profile for pinto beans. The third column presents the amino acid reference pattern. To determine how well the food protein meets human needs, researchers calculate the ratio by dividing the second column by the third column (for example, 30 4 18 5 1.67). The amino acid with the lowest ratio is the most limiting amino acid – in this case, methionine. Its ratio is the amino acid score for the protein – in this case, 0.84. The amino acid score alone, however, does not account for digestibility. Protein digestibility, as determined by rat studies, yields a value of 79 per cent for pinto beans. Together, the amino acid score and the digestibility value determine the PDCAAS: PDCAAS 5 protein digestibility 3 amino acid score PDCAAS for pinto beans 5 0.79 3 0.84 5 0.66 Thus the PDCAAS for pinto beans is 0.66. Table D.2 lists the PDCAAS values of selected foods. AMINO ACID PROFILE OF PINTO BEANS (mg/g PROTEIN)
AMINO ACID REFERENCE PATTERN (mg/g PROTEIN)
AMINO ACID SCORE
Histidine
30.0
18
1.67
Isoleucine
42.5
25
1.70
Leucine
80.4
55
1.46
Lysine
69.0
51
1.35
Methionine 1 cystine
21.1
25
0.84
Phenylalanine 1 tyrosine
90.5
47
1.93
Threonine
43.7
27
1.62
Tryptophan
8.8
7
1.26
Valine
50.1
32
1.57
ESSENTIAL AMINO ACIDS
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Appendix D
Biological value The biological value (BV) of a protein measures its efficiency in supporting the body’s needs. In a test of biological value, two nitrogen balance studies are done. In the first, no protein is fed, and nitrogen (N) excretions in the urine and faeces are measured. It is assumed that under these conditions, N lost in the urine is the amount the body always necessarily loses by filtration into the urine each day, regardless of what protein is fed (endogenous N). The N lost in the faeces (called metabolic N) is the amount the body invariably loses into the intestine each day, whether or not food protein is fed. (To help you remember the terms: endogenous N is ‘urinary N on a zero-protein diet’; metabolic N is ‘faecal N on a zero-protein diet’.) In the second study, an amount of protein slightly below the requirement is fed. Intake and losses are measured; then the BV is derived using this formula:
BV 5
N retained N absorbed
3 100
The denominator of this equation expresses the amount of nitrogen absorbed: food N minus faecal N (excluding the metabolic N the body would lose in the faeces anyway, even without food). The numerator expresses the amount of N retained from the N absorbed: absorbed N (as in the denominator) minus the N excreted in the urine (excluding the endogenous N the body would lose in the urine anyway, even without food). The more nitrogen retained, the higher the protein quality. (Recall that when an essential amino acid is missing, protein synthesis stops, and the remaining amino acids are deaminated and the nitrogen excreted.) Egg protein has a BV of 100, indicating that 100 per cent of the nitrogen absorbed is retained. Supplied in adequate quantity, a protein with a BV of 70 or greater can support human growth as long as energy intake is adequate. Table D.3 presents the BV for selected foods.
of the subjects used for testing may not be similar to those for whom the test protein may ultimately be used. As another example, the retention of protein in the body does not necessarily mean that it is being well utilised. Considerable exchange of protein among tissues (protein turnover) occurs, but is hidden from view when only N intake and output are measured. The test of biological value would not detect if one tissue were shorted.
Net protein utilisation Like BV, net protein utilisation (NPU) measures how efficiently a protein is used by the body and involves two balance studies. The difference is that NPU measures retention of food nitrogen rather than food nitrogen absorbed (as in BV). The formula for NPU is:
NPU 5
100
Milk
93
Beef
75
Fish
75
Corn
72
NOTE: 100 is the maximum BV a food protein can receive.
This method has the advantages of being based on experiments with human beings (it can be done with animals, too, of course) and of measuring actual nitrogen retention. But it is also cumbersome, expensive and often impractical, and it is based on several assumptions that may not be valid. For example, the physiology, normal environment or typical food intake
N intake
3 100
The numerator is the same as for BV, but the denominator represents food N intake only – not N absorbed. This method offers advantages similar to those of BV determinations and is used more frequently, with animals as the test subjects. A drawback is that if a low NPU is obtained, the test results offer no help in distinguishing between two possible causes: a poor amino acid composition of the test protein or poor digestibility. There is also a limit to the extent to which animal test results can be assumed to be applicable to human beings.
Protein efficiency ratio The protein efficiency ratio (PER) measures the weight gain of a growing animal and compares it to the animal’s protein intake. Young rats are fed a measured amount of protein and weighed periodically as they grow. The PER is expressed as:
PER 5
TABLE D.3 Biological values (BVs) of selected foods Egg
N retained
weight gain (g) protein intake (g)
This method has the virtues of economy and simplicity, but it also has many drawbacks. The experiments are time-consuming, the amino acid needs of rats are not the same as those of human beings and the amino acid needs for growth are not the same as for the maintenance of adult animals (growing animals need more lysine, for example). Table D.4 presents PER values for selected foods.
TABLE D.4 Protein efficiency ratio (PER) values of selected proteins Casein (milk)
2.8
Soy
2.4
Gluten (wheat)
0.4
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Appendix E CONTENTS Historical information
738
Anthropometric measurements
741
Physical examinations
755
Biochemical analyses
755
Cautions about nutrition assessment
760
Nutrition assessment
Nutrition assessment evaluates a person’s health from a nutrition perspective. Many factors influence or reflect nutrition status. Consequently, the assessor, usually a dietitian assisted by other qualified healthcare professionals, gathers information from many sources, including: • historical information • anthropometric measurements • physical examinations • biochemical analyses (laboratory tests). Each of these methods involves collecting data in a variety of ways and interpreting each finding in relation to the others to create a total picture. The accurate gathering of this information and its careful interpretation are the basis for a meaningful evaluation. The more information gathered about a person, the more accurate the assessment will be. Gathering information is a time-consuming process, however, and time is often a rare commodity in the healthcare setting. Nutrition care is only one part of total care. It may not be practical or essential to collect detailed information on each person. A strategic compromise is to screen clients by collecting preliminary data. Data such as height–weight and haematocrit are easy to obtain and can alert healthcare workers to potential problems. Nutrition screening identifies clients who may require additional nutrition assessment. This appendix provides a sample of
the procedures, standards and charts commonly used in nutrition assessment.
Historical information Clues about present nutrition status become evident with a careful review of a person’s historical data (see Table E.1). Even when the data are subjective, they reveal important facts about a person. A thorough history identifies risk factors associated with poor nutrition status (see Table E.2) and provides a sense of the whole person. Many aspects of a person’s life influence nutrition status and provide clues to possible problems. An adept history taker uses the interview both to gather facts and to establish a rapport with the client. The major areas of nutrition concern in a person’s history are health, socioeconomic factors, drugs and diet.
Medical history
The assessor can obtain a medical history from records completed by the attending doctor, nurse or other healthcare professional. In addition, conversations with the client can uncover valuable information previously overlooked because no one thought to ask or because the client was not thinking clearly when asked. An accurate, complete health history can reveal conditions that increase a client’s risk for malnutrition
TABLE E.1 Historical data used in nutrition assessments TYPE OF HISTORY
WHAT IT IDENTIFIES
Health history
Current and previous health problems and family health history that affect nutrient needs, nutrition status or the need for intervention to prevent or alleviate health problems
Socioeconomic history
Personal, cultural, financial and environmental influences on food intake, nutrient needs and diet therapy options
Drug history
Medications (prescription and over-the-counter), illicit drugs, dietary supplements and alternative therapies that affect nutrition status
Diet history
Nutrient intake excesses or deficiencies and reasons for imbalances Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Appendix E
TABLE E.2 Risk factors for poor nutrition status HEALTH HISTORY • Acquired immune deficiency syndrome (AIDS) • Alcoholism • Anorexia (lack of appetite) • Anorexia nervosa • Bulimia nervosa • Burns • Cancer • Chewing or swallowing difficulties (including poorly fitted dentures, dental caries, missing teeth and mouth ulcers) • Chronic obstructive pulmonary disease • Circulatory problems • Constipation • Crohn’s disease • Cystic fibrosis • Decubitus ulcers (pressure sores) • Dementia • Depleted blood proteins • Depression • Diabetes mellitus
• Diarrhoea, prolonged or severe • Drug addiction • Dysphagia • Failure to thrive • Feeding disabilities • Fever • GI tract disorders or surgery • Heart disease • HIV infection • Hormonal imbalance • Hyperlipidaemia • Hypertension • Infections • Kidney disease • Liver disease • Lung disease • Malabsorption • Mental illness • Mental retardation • Multiple pregnancies
• Nausea • Neurologic disorders • Organ failure • Overweight • Pancreatic insufficiency • Paralysis • Physical disability • Pneumonia • Pregnancy • Radiation therapy • Recent major illness • Recent major surgery • Recent weight loss or gain • Tobacco use • Trauma • Ulcerative colitis • Ulcers • Underweight • Vomiting, prolonged or severe
• Ethnic identity • Income • Cooking facilities • Number of people in household
• Occupation • Religious affiliation
• Antidiarrhoeals • Antifungal agents • Antihyperlipidaemics • Antihypertensives • Antineoplastics • Antiulcer agents • Antiviral agents
• Catabolic steroids • Diuretics • Hormonal agents • Immunosuppressive agents • Laxatives • Oral contraceptives • Vitamin and other dietary supplements
• Monotonous diet (lacking variety) • No intake for seven or more days • Poor appetite • Restricted or fad diets
• Unbalanced diet (omitting any food group) • Recent weight gains or losses
SOCIOECONOMIC HISTORY • Access to food • Activities • Age • Education DRUG HISTORY • Amphetamines • Analgesics • Antacids • Antibiotics • Anticonvulsant agents • Antidepressant agents • Antidiabetic agents DIET HISTORY • Deficient or excessive food intakes • Frequently eating out • Intravenous fluids (other than total parenteral nutrition) for seven or more days
(review Table E.2). Diseases and their therapies can have either immediate or long-term effects on nutrition status by interfering with ingestion, digestion, absorption, metabolism or excretion of nutrients.
Personal and social history
A personal and social history reveals factors that can profoundly affect nutrition status. The ethnic background and educational level of both the client and the other members of the household can influence food availability and food choices. An understanding of the community environment is also important in assessing nutrition status. For example, the interviewer should be familiar with the food habits of the major ethnic groups within the local region, regional food preferences, and nutrition resources and programs available in the
community. Local councils and community health organisations can often provide such information. Financial concerns might restrict access to nutritious food and to healthcare. In general, the quality of the diet declines as income falls. At some point, the ability to purchase the foods required to meet nutrient needs is lost; an inadequate income puts an adequate diet out of reach. Low income affects not only the power to purchase foods but also the ability to shop for, store, and cook them; some individuals depend on others to procure and prepare meals. A person who lives alone or is depressed may eat poorly or be unable to follow complex dietary instructions. Use of alcohol, tobacco or illicit drugs interferes with good health and nutrition status. A skilled assessor will note such concerns in the history.
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Appendix E
Medication and supplement history The many interactions of foods and drugs require that healthcare professionals take a medication and supplement history and pay special attention to any client who takes drugs routinely. If a person is taking any drug, the assessor records the name of the drug; the dose, frequency and duration of intake; the reason for taking the drug; and signs of any adverse effects. The interactions of drugs and nutrients may take many forms: • Drugs can alter food intake and the absorption, metabolism and excretion of nutrients. • Foods and nutrients can alter the absorption, metabolism and excretion of drugs. Highlight 17 discusses nutrient–drug interactions in more detail, and Table H17.1 (on page 624) summarises the mechanisms by which these interactions occur and provides specific examples.
Diet history
A diet history provides a record of a person’s eating habits and food intake and can help identify possible nutrient imbalances. Food choices are an important part of lifestyle and often reflect a person’s philosophy. Asking non-judgemental questions about eating habits and food intake encourages trust and enhances the likelihood of obtaining accurate information. Assessors evaluate food intake using various tools such as the 24-hour recall, the usual intake record, the food record and the food frequency questionnaire. Food models or photos and measuring devices can help clients identify the types of foods and quantities consumed. The assessor also needs to know how the foods are prepared and when they are eaten. In addition to asking about foods, assessors ask about beverage consumption, including beverages containing alcohol or caffeine. Besides identifying possible nutrient imbalances, diet histories provide valuable clues about how a person will accept advice on dietary changes should it be necessary. Information about what and how a person eats provides the background for realistic and attainable nutrition goals.
24-hour recall
The 24-hour recall provides data for one day only and is commonly used in nutrition surveys to obtain estimates of the typical food intakes for a population. The assessor asks the client to recount everything eaten or drunk in the past 24 hours or for the previous day. The multiple-pass method is the most effective approach for obtaining an accurate 24-hour recall. In this procedure, the interview includes four or five separate passes through the 24‑hour period of interest. In the first pass, the person provides a ‘quick list’ of foods consumed without prompts from the interviewer. The second pass helps the person remember foods that are often forgotten, such as beverages, bread, additions
to foods (such as butter on toast), savoury snacks and sweets. Third and fourth passes elicit additional details about the foods consumed, such as the amounts eaten, preparation methods, and places where foods were obtained or consumed. A final pass provides an opportunity to recall foods and to probe for additional details. The entire multiple-pass interview can be conducted in about 30 to 45 minutes. An advantage of the 24-hour recall is that it is easy to obtain. It is also more likely to provide accurate data, at least about the past 24 hours, than estimates of average intakes over long periods. It does not, however, provide enough information to allow accurate generalisations about an individual’s usual food intake. The previous day’s intake may not be typical, for example, or the person may be unable to report portion sizes accurately or may conceal or forget information about foods eaten. This limitation is partially overcome when 24-hour recalls are collected on several non-consecutive days.
Usual intake To obtain data about a person’s usual intake, an inquiry might begin with, ‘What is the first thing you usually eat or drink during the day?’ Similar questions follow until a typical daily intake pattern emerges. This method can be useful, especially in verifying food intake when the past 24 hours have been atypical. It also helps the assessor verify food habits. For example, one person may always eat an afternoon snack; another may never eat breakfast. A person whose intake varies widely from day to day, however, may find it difficult to answer such general questions, and in that case, another food intake tool should be used to estimate nutrient intake.
Food record
Another tool for history taking is the food record, in which the person records food eaten, including the quantity and method of preparation. A food record may sometimes involve weighing food before it is eaten to give an accurate estimate of quantity. A food record can help both the assessor and the client to determine factors associated with eating that may affect dietary balance and adequacy. Food records work especially well with cooperative people, but require considerable time and effort on their part. A prime advantage is that the record keeper assumes an active role and may for the first time become aware of personal food habits and assume responsibility for them. It also provides the assessor with an accurate picture of the person’s lifestyle and factors that affect food intake. For these reasons, a food record can be particularly useful in outpatient counselling for such nutrition problems as overweight, underweight or food allergy. The major disadvantages stem from poor compliance in recording the data and conscious or unconscious changes in eating habits that may occur while the person is keeping the record.
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Appendix E
Food frequency questionnaire
An assessor uses a food frequency questionnaire to obtain information about a client’s usual food intake over a month or longer. Clients may be asked how many servings of each of the following they eat in a typical day: breads, cereals or grain products; vegetables; fruits; meat, poultry, fish and alternatives; milk, cheese and yoghurt; and fats, oils and sweets. This information helps pinpoint food groups, and therefore nutrients, that may be excessive or deficient in the diet. That a person ate no vegetables yesterday may not seem particularly significant, but never eating vegetables is a warning of possible nutrient deficiencies. When used with the usual intake or 24-hour recall approach, the food frequency questionnaire enables the assessor to double-check the accuracy of the information obtained.
Analysis of food intake data After collecting food intake data, the assessor estimates nutrient intakes, either informally by using food guides or formally by using food composition tables. The assessor compares these intakes with standards, usually nutrient recommendations or dietary guidelines, to determine how closely the person’s diet meets the standards. Are the types and amounts of proteins, carbohydrates (including fibre) and fats (including cholesterol) appropriate? Are all food groups included in appropriate amounts? Is caffeine or alcohol consumption excessive? Are intakes of any vitamins or minerals (including sodium and iron) excessive or deficient? An informal evaluation is possible only if the assessor has enough prior experience with formal calculations to ‘see’ nutrient amounts in reported food intakes without calculations. Even then, such an informal analysis is best followed by a spot check for key nutrients by actual calculation. Formal calculations can be performed either manually (by looking up each food in a table of food composition, recording its nutrients and adding them up) or by using a computer diet analysis program. The assessor then compares the intakes with standards such as the RDI.
Limitations of food intake analysis Diet histories can be superbly informative, but the skilful assessor also keeps their limitations in mind. For example, a computer diet analysis tends to imply greater accuracy than is possible to obtain from data as uncertain as the starting information. Nutrient contents of foods listed in tables of food composition or stored in computer databases are averages and, for some nutrients, incomplete. In addition, the available data on nutrient contents of foods do not reflect the amounts of nutrients a person actually absorbs. Iron is a case in point: its availability from a given meal may vary depending on the person’s iron status; the relative amounts of haem iron, non-haem iron, vitamin C, meat, fish and poultry
eaten at the meal; and the presence of inhibitors of iron absorption such as tea, coffee and nuts. (Chapter 13 describes the many factors that influence iron absorption from a meal.) Furthermore, reported portion sizes may not be correct. The person who reports eating ‘a serving’ of greens may not distinguish between ¼ cup and 2 whole cups; only trained individuals can accurately report serving sizes. Children tend to remember the serving sizes of foods they like as being larger than serving sizes of foods they dislike. An estimate of nutrient intakes from a diet history, combined with other sources of information, allows the assessor to confirm or eliminate the possibility of suspected food intake problems. The assessor must constantly remember that nutrient intakes in adequate amounts do not guarantee adequate nutrient status for an individual. Likewise, insufficient intakes do not always indicate deficiencies, but instead alert the assessor to possible problems. Each person digests, absorbs, metabolises and excretes nutrients in a unique way; individual needs vary. Intakes of nutrients identified by diet histories are only pieces of a puzzle that must be put together with other indicators of nutrition status in order to extract meaning.
Anthropometric measurements Anthropometrics are physical measurements that reflect body composition and development (see Table E.3). They serve three main purposes: first, to evaluate the progress of growth in pregnant women, infants, children and adolescents; second, to detect undernutrition and overnutrition in all age groups; and third, to measure changes in body composition over time.
TABLE E.3 Anthropometric measurements used in nutrition assessments TYPE OF MEASUREMENT
WHAT IT REFLECTS
Abdominal girth measurement
Abdominal fluid retention and abdominal organ size
Height–weight
Overnutrition and undernutrition; growth in children
Head circumference
Brain growth and development in infants and children under age two years
Skinfold
Subcutaneous and total body fat
Waist circumference
Body-fat distribution
Healthcare professionals compare anthropometric measurements taken on an individual with population standards specific for gender and age or with previous measures of the individual. Measurements taken
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741
742
Appendix E
periodically and compared with previous measurements reveal changes in an individual’s status. Mastering the techniques for taking anthropometric measurements requires proper instruction and practice to ensure reliability. Once the correct techniques are learned, taking measurements is easy and requires minimal equipment. Height and weight are well-recognised anthropometrics; other anthropometrics include skinfold measurements and various measures of lean tissue. Other measures are useful in specific situations. For example, a head circumference measurement may help to assess brain development in an infant, and an abdominal girth measurement supplies information about abdominal fluid retention in individuals with liver disease.
FIGURE E.2 Height measurement of an older child or adult Height is measured most accurately when the person stands against a flat wall to which a measuring tape has been affixed.
Measures of growth and development Height and weight are among the most common and useful anthropometric measurements. Length measurements for infants and children up to age three and height measurements for children over three are particularly valuable in assessing growth and therefore nutrition status. For adults, height measurements alone are not critical, but help to estimate healthy weight and to interpret other assessment data. Once adult height has been reached, changes in body weight provide useful information in assessing overnutrition and undernutrition.
Height For infants and children younger than three, healthcare professionals may use special equipment to measure length. The assessor lays the barefoot infant on a measuring board that has a fixed headboard and movable footboard attached at right angles to the surface (see Figure E.1). Often two people are needed to obtain an accurate measurement: one to hold the infant’s head against the headboard, and the other to keep the legs straight and do the measuring. This method provides the most accurate measure possible, but many healthcare professionals use a less exacting method. They may simply hold the infant straight with its head against the headboard or other vertical support, mark the blanket with a chalk or pen at the infant’s heel and then measure the distance from the headboard to the mark. Even more informally and less accurately, they may lay
FIGURE E.1 Length measurement of an infant An infant is measured lying down on a measuring board with a fixed headboard and a movable footboard. Note that two people are needed to measure the infant’s length.
the infant on a flat surface and extend a non-stretchable measuring tape along the side of the infant from the top of the head to the heel of the foot. The procedure for measuring a child who can stand erect and cooperate is the same as for an adult. The best way to measure standing height is with the person’s back against a flat wall to which a non-stretchable measuring tape or stick has been fixed (see Figure E.2). The person stands erect, without shoes, with heels together. The person’s line of sight should be horizontal, with the heels, buttocks, shoulders and head touching the wall. The assessor places a ruler, book or other inflexible object on top of the head at a right angle to the wall; carefully checks the height measurement; and records it immediately so that the correct measurement will not be forgotten. A measuring rod affixed to a set of weight scales is commonly used, but is less accurate because it bends easily. The assessor follows the same general procedure, asking the person to face away from the scale and to take extra care to stand erect. Unfortunately, many healthcare professionals merely ask clients how tall they are rather than measuring their height. Self-reported height is often inaccurate and should be used only as a last resort when measurement is impractical (for example, in the case of an uncooperative client, or in an emergency admission).
Weight Valid weight measurements require scales that have been carefully maintained, calibrated and checked for accuracy at regular intervals. Beam balance and electronic scales Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Appendix E
FIGURE E.3 Weight measurement of an infant Infants sit or lie down on scales that are designed to hold them while they are being weighed.
To measure head circumference, the assessor places a non-stretchable tape so that it encircles the largest part of the infant’s or child’s head: just above the eyebrow ridges, just above the point where the ears attach, and around the occipital prominence at the back of the head. To ensure accurate recording, the assessor immediately notes the measure.
Analysis of measures in infants and children
are the most accurate types of scales. To measure infants’ weight, assessors use special scales that allow infants to lie or sit (see Figure E.3). Weighing infants naked, without nappies, is standard procedure. Children who can stand are weighed in the same way as adults (see Figure E.4). To make repeated measures useful, standardised conditions are necessary. Each weighing should take place at the same time of day (preferably before breakfast), in the same amount of clothing (without shoes), after the person has voided and on the same scale. Special scales and hospital beds with built-in scales are available for weighing people who are bedridden. Bathroom scales are inaccurate and inappropriate in a professional setting. As with all measurements, the assessor records the observed weight immediately.
Head circumference Assessors may also measure head circumference to confirm that infant growth is proceeding normally or to help detect protein–energy malnutrition (PEM) and evaluate the extent of its impact on brain size.
FIGURE E.4 Weight measurement of an older child or adult Whenever possible, children and adults are measured on beam balance or electronic scales to ensure accuracy.
Growth retardation is a sign of poor nutrition status. Obesity is also a sign that dietary intervention may be needed. Health professionals generally evaluate physical development by monitoring the growth rate of a child and comparing this rate with standard charts. Standard charts compare weight to age, height to age and weight to height; ideally, height and weight are in roughly the same percentile. Although individual growth patterns may vary, a child’s growth curve will generally stay at about the same percentile throughout childhood. In children whose growth has been retarded, nutrition rehabilitation will ideally induce height and weight to increase to higher percentiles. In overweight children, the goal is for weight to remain stable as height increases, until weight becomes appropriate for height. To evaluate growth in infants, an assessor uses charts such Chapter 16 as those in Figure E.5 (A and B) presents BMI charts for children and to Figure E.10 (A and B). The adolescents. assessor follows these steps to plot a weight measurement on a percentile graph: • Select the appropriate chart based on age and gender. • Locate the child’s age along the horizontal axis on the bottom of the chart. • Locate the child’s weight in kilograms or pounds along the vertical axis. • Mark the chart where the age and weight lines intersect, and read off the percentile. To assess length, height or head circumference, the assessor follows the same procedure, using the appropriate chart. (When length is measured, use the chart for birth to 24 months; when height is measured, use the chart for two to 20 years.) Head circumference percentile should be similar to the child’s height and weight percentiles. With height, weight and head circumference measures plotted on growth percentile charts, a skilled clinician can begin to interpret the data. Percentile charts divide the measures of a population into 100 equal divisions. Thus, half of the population falls above the 50th percentile, and half falls below. The use of percentile measures allows for comparisons between people of the same age and gender. For example, a six-month-old female infant whose weight is at the 85 percentile weighs more than 85 per cent of the female infants her age.
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5
6
7
8
9
10
11
1 year
1
2
3
4
5
6
7
8
9
10
11
Age (completed months and years) WHO Child Growth Standards
2 years
2
2 4
3
3
3
4
4
2
5
5
1
6
6
Birth
7
7
Reprinted with permission from WHO Child Growth Standards (https://www.who.int/childgrowth/standards/en/)
Months
8
8
10
11
12
13
14
15
9
3rd
15th
50th
85th
97th
16
9
10
11
12
13
14
15
16
Birth to 2 years (percentiles)
Weight-for-age: BOYS
FIGURE E.5A Weight-for-age percentiles: boys, birth to 24 months
Weight (kg)
744 Appendix E
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5
6
7
8
9
10
11
1 year
1
2
3
4
5
6
7
8
9
10
11
Age (completed months and years) WHO Child Growth Standards
2 years
2
2 4
3
3
3
4
4
2
5
5
1
6
6
Birth
7
7
9
10
11
12
13
14
15
8
3rd
15th
50th
85th
97th
8
9
10
11
12
13
14
15
Birth to 2 years (percentiles)
Weight-for-age: GIRLS
Reprinted with permission from WHO Child Growth Standards (https://www.who.int/childgrowth/standards/en/)
Months
Weight (kg)
FIGURE E.5B Weight-for-age percentiles: girls, birth to 24 months`
Appendix E 745
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1
2
3
4
5
6
7
8
9
10
11
1 year
1
2
3
4
5
6
7
8
9
10
11
45
45
WHO Child Growth Standards
50
50
Age (completed months and years)
55
55
2 years
60
60
Birth
65
65
Reprinted with permission from WHO Child Growth Standards (https://www.who.int/childgrowth/standards/en/)
Months
70
70
75
75
85
90
95
80
3rd
15th
50th
85th
97th
80
85
90
95
Birth to 2 years (percentiles)
Length-for-age: BOYS
FIGURE E.6A Length-for-age percentiles: boys, birth to 24 months
Length (cm)
746 Appendix E
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6
7
8
9
10
11
1 year
1
2
3
4
5
6
7
8
9
10
11
2 years
Age (completed months and years) WHO Child Growth Standards
45
5
45 4
50
50
3
55
55
2
60
60
Birth
65
65
75
80
85
90
70
1
3rd
15th
50th
85th
97th
95
70
75
80
85
90
95
Birth to 2 years (percentiles)
Length-for-age: GIRLS
Reprinted with permission from WHO Child Growth Standards (https://www.who.int/childgrowth/standards/en/)
Months
Length (cm)
FIGURE E.6B Length-for-age percentiles: girls, birth to 24 months
Appendix E 747
70
75
80
85
90
95
100
105
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Reprinted with permission from WHO Child Growth Standards (https://www.who.int/childgrowth/standards/en/)
Length (cm) WHO Child Growth Standards
110
2
2 65
4
4
60
6
6
55
8
8
50
10
10
45
12
12
16
18
20
22
14
3rd
15th
50th
85th
97th
14
16
18
20
22
Birth to 2 years (percentiles)
Weight-for-length: BOYS
FIGURE E.7A Weight-for-length percentiles: boys, birth to 24 months
Weight (kg)
748 Appendix E
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70
75
80
85
90
95
100
105
Length (cm) WHO Child Growth Standards
110
2
2 65
4
4
60
6
6
55
8
8
50
10
10
45
12
12
16
18
20
22
14
3rd
15th
50th
85th
97th
14
16
18
20
22
Birth to 2 years (percentiles)
Weight-for-length: GIRLS
Reprinted with permission from WHO Child Growth Standards (https://www.who.int/childgrowth/standards/en/)
Weight (kg)
FIGURE E.7B Weight-for-length percentiles: girls, birth to 24 months
Appendix E 749
Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000).
FIGURE E.8A Weight-for-age percentiles: boys, 2 to 20 years
Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000).
FIGURE E.8B Weight-for-age percentiles: girls, 2 to 20 years
750 Appendix E
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000).
FIGURE E.9A Stature-for-age percentiles: boys, 2 to 20 years
Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000).
FIGURE E.9B Stature-for-age percentiles: girls, 2 to 20 years
Appendix E
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751
Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000).
FIGURE E.10A Weight-for-stature percentiles: boys, 2 to 20 years
Developed by the National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000).
FIGURE E.10B Weight-for-stature percentiles: girls, 2 to 20 years
752 Appendix E
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Appendix E
Head circumference is generally measured in children under two years of age. Since the brain grows rapidly before birth and during early infancy, extreme and chronic malnutrition during these times can impair brain development, curtailing the number of brain cells and the size of head circumference. Non-nutritional factors, such as certain disorders and genetic variation, can also influence head circumference.
Analysis of measures in adults Reminder: The body mass index (BMI) is an index of a person’s weight in relation to height, determined by dividing the weight in kilograms by the square of the height in metres: BMI =
weight (kg) height (m)2
For adults, healthcare professionals typically compare weights with weight-for-height standards. One such standard is the body mass index (BMI), described in Chapter 8 (page 267), which is useful for estimating the risk to health associated with overnutrition. The inside-front cover shows BMI for various heights and weights.
Measures of body fat and lean tissue Significant weight changes in both children and adults can reflect overnutrition and undernutrition with respect to energy and protein. To estimate the degree to which fat stores or lean tissues are affected by overnutrition or
malnutrition, several anthropometric measurements are useful (review Table E.3 on page 741). Clinicians use many other methods to estimate body fat and its distribution. Each has its advantages and disadvantages, as Table E.4 summarises.
Skinfold measures Skinfold measures provide a good estimate of total body fat and a fair assessment of the fat’s location. Approximately half the fat in the body lies directly beneath the skin, and the Common sites for thickness of this subcutaneous skinfold measures: fat reflects total body fat. In • triceps some parts of the body, such • biceps as the back and the back of the • subscapular (below arm over the triceps muscle, shoulder blade) this fat is loosely attached; a • suprailiac (above person can pull it up between hip bone) the thumb and forefinger to • abdomen obtain a measure of skinfold • upper thigh. thickness. To measure skinfold, a skilled assessor follows a standard procedure using reliable calipers (illustrated in Figure E.11) and then compares the measurement with standards. Triceps skinfold measures greater than 15 millimetres in men or 25 millimetres in women suggest excessive body fat.
TABLE E.4 Methods of estimating body fat and its distribution METHOD
COST
EASE OF USE
ACCURACY
MEASURES FAT DISTRIBUTION?
Height and weight
Low
Easy
High
No
Skinfolds
Low
Easy
Low
Yes
Circumferences
Low
Easy
Moderate
Yes
Moderate
Moderate
Moderate
Yes
Low
Moderate
High
No
Heavy water tritiated
Moderate
Moderate
High
No
Deuterium oxide, or heavy oxygen
High
Moderate
High
No
Very high
Difficult
High
No
Total body electrical conductivity (TOBEC)
High
Moderate
High
No
Bioelectric impedance (BIA)
Moderate
Easy
High
No
Dual energy X-ray absorptiometry (DEXA)
High
Easy
High
No
Computed tomography (CT)
Very high
Difficult
High
Yes
Magnetic resonance imaging (MRI)
Very high
Difficult
High
Yes
Ultrasound Hydrodensitometry
Potassium isotope (40K)
Adapted with permission from G. A. Bray, a handout presented at the North American Association for the Study of Obesity and Emory University School of Medicine Conference on Obesity Update: Pathophysiology, Clinical Consequences, and Therapeutic Options, Atlanta, Georgia, 31 August–2 September 1992. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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FIGURE E.11 How to measure the triceps skinfold A Find the midpoint of the arm: 1 Ask the subject to bend their arm at the elbow and lay the hand across the stomach. (If they are right-handed, measure the left arm, and vice versa.) 2 Feel the shoulder to locate the acromion process. It helps to slide your fingers along the clavicle to find the acromion process. The olecranon process is the tip of the elbow. 3 Place a measuring tape from the acromion process to the tip of the elbow. Divide this measurement by 2 and mark the midpoint of the arm with a pen. B Measure the skinfold: 1 Ask the subject to let their arm hang loosely to the side. 2 Grasp a fold of skin and subcutaneous fat between the thumb and forefinger slightly above the midpoint mark. Gently pull the skin away from the underlying muscle. (This step takes a lot of practice. If you want to be sure you don’t have muscle as well as fat, ask the subject to contract and relax the muscle. You should be able to feel if you are pinching muscle.) 3 Place the calipers over the skinfold at the midpoint mark and read the measurement to the nearest 1.0 millimetre in two to three seconds. (If using plastic calipers, align pressure lines, and read the measurement to the nearest 1.0 millimetre in two to three seconds.) 4 Repeat steps 2 and 3 twice more. Add the three readings, and then divide by 3 to find the average.
Clavicle Acromion process
Midpoint
Olecranon process
Skinfold measurements correlate directly with the risk of heart disease. They assess central obesity and its associated risks better than weight measures alone. If a person gains body fat, the skinfold increases proportionately; if the person loses fat, it decreases. Measurements taken from central-body sites (around the abdomen) better reflect changes in fatness than those taken from upper sites (arm and back). A major limitation of the skinfold test is that fat may be thicker under the skin in one area than in another. A pinch at the side of the waistline may not yield the same measurement as a pinch on the back of the arm. This limitation can be overcome by taking skinfold measurements at several (often seven) different places on the body (including upper-, central- and lower-body sites) and comparing each measurement with standards for that site. Multiple measures are not always practical in clinical settings, however, and most often the triceps skinfold measurement alone is used because it is easily accessible. Skinfold measures are not useful in assessing changes in body fat over time.
Waist circumference Chapter 8 describes how fat distribution correlates with health risks and mentions that the waist circumference is a valuable indicator of fat distribution. To measure waist circumference, the assessor places a nonstretchable tape around the person’s body, crossing just above the upper hip bones and making sure that the tape remains on a level horizontal plane on all sides (see Figure E.12). The tape is tightened slightly, but without compressing the skin.
Waist-to-hip ratio Alternatively, some clinicians measure both the waist and the hips. The waist-to-hip ratio also assesses abdominal obesity, but provides no more information than using the waist circumference alone. In general, women with a waist-tohip ratio of 0.80 or greater and
To calculate the waist-to-hip ratio, divide the waistline measurement by the hip measurement. For example, a woman with a 71-centimetre waist and 96-centimetre hips would have a ratio of 71 ÷ 96 = 0.74.
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Appendix E
FIGURE E.12 How to measure waist circumference Place the measuring tape, preferably a thin metal tape measure, around the waist just above the bony crest of the hip. The tape runs parallel to the floor and is snug (but does not compress the skin). The measurement is taken at the end of normal expiration.
results. Bioelectrical impedance is most accurate for people within a normal fat range; it tends to overestimate fat in lean people and underestimate fat in obese people.
Physical examinations An assessor can use a physical examination to search for signs of nutrient deficiency or toxicity. Like the other assessment methods, such an examination requires knowledge and skill. Many physical signs are non-specific; they can reflect any of several nutrient deficiencies as well as conditions not related to nutrition (see Table E.5). For example, cracked lips may be caused by sunburn, windburn, dehydration or any of several B vitamin deficiencies, to name just a few possible causes. For this reason, physical findings are most valuable in revealing problems for other assessment techniques to confirm or for confirming other assessment measures. With this limitation understood, physical symptoms can be most informative and communicate much information about nutrition health. Many tissues and organs can reflect signs of malnutrition. The signs appear most rapidly in parts of the body where cell replacement occurs at a high rate, such as in the hair, skin and digestive tract (including the mouth and tongue). The summary tables in Chapters 10 to 13 list additional physical signs of vitamin and mineral malnutrition.
National Institutes of Health Obesity Education Initiative, Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, Washington, DC: U.S. Department of Health and Human Services (1998): 59
men with a waist-to-hip ratio of 0.90 or greater have a high risk of health problems.
Hydrodensitometry
To estimate body density using Hydrodensitometry, the person is weighed twice – first on land and then again when submerged under water. Underwater weighing usually generates a good estimate of body fat and is useful in research, although the technique has drawbacks: it requires bulky, expensive and non-portable equipment. Furthermore, submerging some people (especially those who are very young, very old, ill or fearful) under water is not always practical.
Bioelectric impedance To measure body fat using the bioelectric impedance technique, a very-low-intensity electrical current is briefly sent through the body by way of electrodes placed on the wrist and ankle. As is true of other anthropometric techniques, bioelectrical impedance requires standardised procedures and calibrated instruments to provide reliable results. Recent food intake and hydration status, for example, influence
Biochemical analyses All of the approaches to nutrition The serum is the assessment discussed so far are watery portion of the external approaches. Biochemical blood that remains analyses or laboratory tests help after removal of the to determine what is happening cells and clot-forming to the body internally. Common material; plasma is tests are based on analysis of the fluid that remains when unclotted blood blood and urine samples, which is centrifuged. In most contain nutrients, enzymes and cases, serum and metabolites that reflect nutrition plasma concentrations status. Other tests, such as serum are similar, but plasma glucose, help pinpoint diseasesamples are more likely related problems with nutrition to clog mechanical implications. Tests that define blood analysers, so fluid and electrolyte balance, serum samples are acid–base balance and organ preferred. function also have nutrition implications. Table E.6 (on page 756) lists biochemical tests most useful for assessing vitamin and mineral status. The interpretation of biochemical data requires skill. Long metabolic sequences lead to the production of the end products and metabolites seen in blood and urine. No single test can reveal nutrition status because many factors influence test results. The low blood concentration of a nutrient may reflect a primary deficiency of that nutrient, but it may also be secondary
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TABLE E.5 Physical findings used in nutrition assessments BODY SYSTEM
HEALTHY FINDINGS
MALNUTRITION FINDINGS
WHAT THE FINDINGS REFLECT
Hair
Shiny, firm in the scalp
Dull, brittle, dry, loose; falls out
PEM (protein–energy malnutrition)
Eyes
Bright, clear pink membranes; adjust easily to light
Pale membranes; spots; redness; adjust slowly to darkness
Vitamin A, B vitamin, zinc and iron status
Teeth and gums
No pain or caries, gums firm, teeth bright
Missing, discoloured, decayed teeth; gums bleed easily and are swollen and spongy
Mineral and vitamin C status
Glands
No lumps
Swollen at front of neck
PEM and iodine status
Tongue
Red, bumpy, rough
Sore, smooth, purplish, swollen
B vitamin status
Skin
Smooth, firm, good colour
Off-colour, scaly, flaky, cracked, dry, rough, spotty; ‘sandpaper’ feel or sores; lack of fat under skin
PEM, essential fatty acid, vitamin A, B group vitamin and vitamin C status
Nails
Firm, pink
Spoon-shaped, brittle, ridged, pale
Iron status
Internal systems
Regular heart rhythm, heart rate and blood pressure; no impairment of digestive function, reflexes or mental status
Abnormal heart rate, heart rhythm or blood pressure; enlarged liver, spleen; abnormal digestion; burning, tingling of hands, feet; loss of balance, coordination; mental confusion, irritability, fatigue
PEM and mineral status
Muscles and bones
Muscle tone; posture, long bone development appropriate for age
‘Wasted’ appearance of muscles; swollen bumps on skull or ends of bones; small bumps on ribs; bowed legs or knock-knees
PEM, mineral and vitamin D status
TABLE E.6 Biochemical tests useful for assessing vitamin and mineral status NUTRIENT
ASSESSMENT TESTS
Vitamins Vitamin A Thiamin
Serum retinol, retinol-binding protein Erythrocyte (red blood cell) transketolase activity, erythrocyte thiamin pyrophosphate
a
Riboflavin
Erythrocyte glutathione reductase activity
a
Vitamin B6a
Urinary xanthurenic acid excretion after tryptophan load test, erythrocyte transaminase activity, plasma pyridoxal 5’-phosphate (PLP)
Niacin
Plasma or urinary metabolite NMN (N-methylnicotinamide) or 2-pyridone, or preferably both expressed as a ratio
Folateb
Serum folate, erythrocyte folate (reflects liver stores)
Vitamin B12
Serum vitamin B12, serum and urinary methylmalonic acid, Schilling test
Biotin
Urinary biotin, urinary 3-hydroxyisovaleric acid
Vitamin C
Plasma vitamin Cc, leucocyte vitamin C
Vitamin D
Serum vitamin D
Vitamin E
Serum alpha-tocopherol, erythrocyte haemolysis
Vitamin K
Serum vitamin K, plasma prothrombin; blood-clotting time (prothrombin time) is not an adequate indicator
b
Minerals Phosphorus
Serum phosphate
Sodium
Serum sodium
Chloride
Serum chloride
Potassium
Serum potassium
Magnesium
Serum magnesium, urinary magnesium Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
TABLE E-6
Appendix E
NUTRIENT
ASSESSMENT TESTS
Iron
Haemoglobin, haematocrit, serum ferritin, total iron-binding capacity (TIBC), erythrocyte protoporphyrin, serum iron, transferrin saturation
Iodine
Serum thyroxine or thyroid-stimulating hormone (TSH), urinary iodine
Zinc
Plasma zinc, hair zinc
Copper
Erythrocyte superoxide dismutase, serum copper, serum ceruloplasmin
Selenium
Erythrocyte selenium, glutathione peroxidase activity
Urinary measurements for these vitamins are common but may be of limited use. Urinary measurements reflect recent dietary intakes and may not provide reliable information concerning the severity of a deficiency. b Folate assessments should always be conducted in conjunction with vitamin B12 assessments (and vice versa) to help distinguish the cause of common deficiency symptoms. c Vitamin C shifts between the plasma and the white blood cells known as leucocytes; thus, a plasma determination may not accurately reflect the body’s pool. A measurement of leucocyte vitamin C can provide information about the body’s stores of vitamin C. A combination of both tests may be more reliable than either one alone. a
Adapted from H. E. Sauberlich, Laboratory Tests for the Assessment of Nutritional Status, Boca Raton, FL: CRC Press (1999).
to the deficiency of one or several other nutrients or to a disease. Taken together with other assessment data, however, laboratory test results help to create a picture that becomes clear with careful interpretation. They are especially useful in helping to detect subclinical malnutrition by uncovering early signs of malnutrition before the clinical signs of a classic deficiency disease appear. Laboratory tests used to assess vitamin and mineral status (review Table E.6) are particularly useful when combined with diet histories Reminder: A and physical findings. Vitamin subclinical deficiency is and mineral levels present in a nutrient deficiency the blood and urine sometimes in the early stages reflect recent rather than before the outward signs have appeared. long-term intakes. This makes detecting subclinical deficiencies difficult. Furthermore, many nutrients interact; therefore, the amounts of other nutrients in the body can affect a laboratory value for a particular nutrient. It is also important to remember that non-nutrient conditions such as diseases influence biochemical measures. It is beyond the scope of this text to describe all laboratory tests and their relations to nutrition status. Instead, the emphasis is on laboratory tests used to detect protein–energy malnutrition (PEM) and nutritional anaemias.
Protein–energy malnutrition No single biochemical analysis can adequately evaluate protein–energy malnutrition (PEM). Numerous procedures have been used over the years. This discussion focuses on the measures commonly used today – transthyretin, retinol-binding protein, serum transferrin and IGF-1 (insulin-like growth factor 1).
Table E.7 provides standards for these indicators. Although serum albumin is easily and routinely measured, it lacks the sensitivity to assess PEM because of its long turnover rate and the influence that non-nutritional factors such as chronic disease and inflammation can have on it.*
TABLE E.7 Normal values for serum proteins INDICATOR
REFERENCE RANGE
Albumin (g/L)
35−50
Transferrin (g/L)
2.0−4.0
Transthyretin (g/L)
190−430
Retinol-binding protein (mg/L) IGF-1 (µg/L)
30−70 300
NOTE: Levels less than normal suggest compromised protein status.
Transthyretin and retinol-binding protein Transthyretin and retinolbinding protein occur as Transthyretin is also a complex in the plasma. known as prealbumin They have a rapid turnover or thyroxine-binding and thus respond quickly to prealbumin. dietary protein inadequacy and therapy.** Conditions other than malnutrition that lower transthyretin include metabolic stress, haemodialysis and hypothyroidism; those that raise transthyretin include kidney disease and corticosteroid use. Conditions other than protein malnutrition that lower retinol-binding protein include vitamin A deficiency, metabolic stress, hyperthyroidism, liver disease and cystic fibrosis; kidney disease raises retinolbinding protein levels.
*The half-life of albumin is 18 days, an indication of a slow degradation rate. **The half-lives of transthyretin and retinol-binding protein are two days and 12 hours, respectively. Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
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Serum transferrin Serum transferrin transports iron; consequently, its concentrations reflect both protein and iron status. Using transferrin as an indicator of protein status is complicated when an iron deficiency is present. Transferrin rises as iron deficiency grows worse and falls as iron status improves. Markedly reduced transferrin levels indicate severe PEM; in mild-to-moderate PEM, transferrin levels may vary, limiting their usefulness. Conditions other than protein malnutrition that lower transferrin include liver disease, kidney disease and metabolic stress; those that raise transferrin include pregnancy, iron deficiency, hepatitis, blood loss and oral contraceptive use. Although transferrin breaks down in the body more quickly than albumin, with a half life of around 8 days, it is still relatively slow to respond to changes in protein intake and is not a sensitive indicator of the response to therapy.
TABLE E.8 Laboratory tests useful in evaluating nutrition-related anaemias TEST OR TEST RESULT Haemoglobin (Hb)
Total amount of haemoglobin in the red blood cells (RBC)
Haematocrit (Hct)
Percentage of RBC in the total blood volume
Red blood cell (RBC) count
Number of RBC
Mean corpuscular volume (MCV)
RBC size; helps to determine if anaemia is microcytic (iron deficiency) or macrocytic (folate or vitamin B12 deficiency)
Mean corpuscular haemoglobin concentration (MCHC)
Haemoglobin concentration within the average RBC; helps to determine if anaemia is hypochromic (iron deficiency) or normochromic (folate or vitamin B12 deficiency)
Bone marrow aspiration
The manufacture of blood cells in different developmental states
Insulin-like growth factor 1 Insulin-like growth factor 1 (IGF-1) declines in PEM. IGF-1 has a relatively short half-life of 12–15 hours and responds specifically to dietary protein rather than energy. For these reasons, it is a sensitive indicator of protein status and response to therapy. Conditions that decrease IGF-1 include anorexia nervosa, inflammatory bowel disease, coeliac disease, HIV infection and fasting.
Nutritional anaemias Anaemia, a symptom of a wide variety of nutrition- and non-nutrition-related disorders, is characterised by a reduced number of red blood cells. Iron, folate and vitamin B12 deficiencies caused by inadequate intake, poor absorption or abnormal metabolism of these nutrients are the most common nutritional anaemias. Some non-nutrition-related causes of anaemia include massive blood loss, infections, hereditary blood disorders such as sickle-cell anaemia, and chronic liver or kidney disease. Table E.8 shows which laboratory tests detect various nutrition-related anaemias.
Assessment of iron-deficiency anaemia Iron deficiency, a common Stages of iron mineral deficiency, develops in deficiency: stages. Chapter 13 describes iron • Iron stores deficiency in detail. This section diminish. describes tests used to uncover iron • Transport iron deficiency as it progresses. Table E.9 decreases. provides values used for assessing • Haemoglobin production falls. iron status. Although other tests are more specific in detecting early deficiencies, haemoglobin and haematocrit are the commonly available tests. • Haemoglobin. Iron forms an integral part of the haemoglobin molecule that transports oxygen to the cells. In iron deficiency, the body cannot synthesise haemoglobin. Low haemoglobin values signal
WHAT IT REFLECTS
For anaemia (general)
For iron-deficiency anaemia ↓ Serum ferritin
Early deficiency state with depleted iron stores
↓Transferrin saturation
Progressing deficiency state with diminished transport iron
↑Erythrocyte protoporphyrin
Later deficiency state with limited haemoglobin production
For folate-deficiency anaemia ↓Serum folate
Progressing deficiency state
↓RBC folate
Later deficiency state
For vitamin B12-deficiency anaemia ↓Serum vitamin B12
Progressing deficiency state
Schilling test
Absorption of vitamin B12
depleted iron stores. Table E.9 provides haemoglobin values used in nutrition assessment. Haemoglobin’s usefulness in evaluating iron status is limited, however, because haemoglobin concentrations drop fairly late in the development of iron deficiency, and other nutrient deficiencies and medical conditions can also alter haemoglobin concentrations. • Haematocrit. Haematocrit is commonly used to diagnose iron deficiency, even though it is an inconclusive measure of iron status. To measure the haematocrit, a laboratory technician spins a volume
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Appendix E
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TABLE E.9 Criteria for assessing iron status TEST Haemoglobin (g/L)
AGE (YEARS)
GENDER
DEFICIENCY VALUE
0.5−10
M and F
,110
11−15
M
,120
F
,115
M
,130
F
,120
.15
Pregnancy Haematocrit (%)
Serum ferritin (µg/L)
,110
0.5−4
M and F
,32
5−10
M and F
,33
11−15
M
,35
F
,34
.15
M
,40
F
,36
0.5−15
M and F
,10
.15
M and F
,12
Total iron-binding capacity (TIBC) (µmol/L)
.15
M and F
.75
Serum iron (µmol/L)
.15
M and F
,9
0.5−4
M and F
,12
5−10
M and F
,14
Transferrin saturation (%)
Erythrocyte protoporphyrin (µmol/L)
.10
M and F
,16
0.5−4
M and F
.1.42
.4
M and F
.1.24
of blood in a centrifuge to separate the red blood cells from the plasma. The haematocrit is the percentage of red blood cells in the total blood volume. Table E.9 includes values used to assess haematocrit status. Low values indicate incomplete haemoglobin formation, which is manifested by microcytic (abnormally smallcelled), hypochromic (abnormally lacking in colour) red blood cells. Low haemoglobin and haematocrit values alert the assessor to the possibility of iron deficiency. However, many nutrients and other conditions can affect haemoglobin and haematocrit. The other tests of iron status help pinpoint true iron deficiency. • Serum ferritin. In the first stage of iron deficiency, iron stores diminish. Measures of serum ferritin provide an estimate of iron stores. Such information is most valuable to iron assessment. Table E.9 shows serum ferritin cut-off values that indicate iron store depletion in children and adults. Serum ferritin is not reliable for diagnosing iron deficiency in infants, since normal serum ferritin values are often present in conjunction with iron-responsive anaemia. A decrease in transport iron characterises the second stage of iron deficiency. This is revealed by an increase in the iron-binding capacity of the protein transferrin and
a decrease in serum iron. These changes are reflected by the transferrin saturation, which is calculated from the ratio of the other two values as described in the following paragraphs. • Total iron-binding capacity (TIBC). Iron travels through the blood bound to the protein transferrin. TIBC is a measure of the total amount of iron that transferrin can carry. Laboratory technicians measure iron-binding capacity directly. Table E.9 gives the values for TIBC indicating anaemia. • Serum iron. Laboratory technicians can also measure serum iron directly. Elevated values indicate iron overload; reduced values indicate iron deficiency. Table E.9 shows the deficient value for serum iron. • Transferrin saturation. The percentage of transferrin that is saturated with iron is an indirect measure that is derived from the serum iron and total iron-binding capacity measures as follows:
Serum iron Transferrin saturation 5 3 100 Total iron 2 binding capacity Table E.9 shows deficient transferrin saturation values for various age groups.
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The third stage of iron deficiency occurs when the supply of transport iron diminishes to the point that it limits haemoglobin production. It is characterised by increases in erythrocyte protoporphyrin, a decrease in mean corpuscular volume, and decreased haemoglobin and haematocrit. • Erythrocyte protoporphyrin. The iron-containing portion of the haemoglobin molecule is haem. Haem is a combination of iron and protoporphyrin. Protoporphyrin accumulates in the blood when iron supplies are inadequate for the formation of haem. Laboratory technicians can measure erythrocyte protoporphyrin directly in a blood sample. The cut-offs for abnormal values of erythrocyte protoporphyrin are shown in Table E.9. • Mean corpuscular volume (MCV). A direct or calculated measure of the mean corpuscular volume (MCV) determines the average size of a red blood cell. Such a measure helps to classify the type of nutrient anaemia. In iron deficiency, the red blood cells are smaller (microcytic) than average.
Assessment of folate and vitamin B12 anaemias
Folate deficiency and vitamin B12 deficiency present a similar clinical picture – an anaemia characterised by abnormally large red blood cell precursors (megaloblasts) in the bone marrow and abnormally large, mature red blood cells (macrocytic cells) in the blood. Distinguishing between these two deficiencies is particularly important because their treatments differ. Giving folate to a person with vitamin B12 deficiency improves many of the laboratory test results indicative of vitamin B12 deficiency, but this is a dangerous error because vitamin B12 deficiency causes nerve damage that folate cannot correct. Thus, inappropriate folate administration masks vitamin B12-deficiency anaemia, and nerve damage worsens. For this reason, it is critical to determine whether the anaemia results from a folate deficiency or from a vitamin B12 deficiency. The following biochemical assessment techniques help to make this distinction (see also Tables E.8 and Table E.10):
TABLE E.10 Normal values for folate and vitamin B12 TEST Serum folate (ng/mL)
NORMAL VALUES a
Serum homocysteine (μmol/L)
3–16 5–14
Erythrocyte folate (ng/mL) a
140–628
Serum vitamin B12 (pg/mL)
200–835
Serum methylmalonic acid (nmol/L)
70–270
NOTE: A nanogram (ng) is one-billionth of a gram; a picogram (pg) is one-trillionth of a gram. To convert folate values (ng/mL) to international standard units (nmol/L), multiply by 2.266. a
• Mean corpuscular volume (MCV). The MCV is a measure of red blood cell size. In folate and vitamin B12 deficiencies, the red blood cells are larger than average (macrocytic). Additional tests must be performed to differentiate folate from vitamin B12 deficiency. Macrocytic cells may also result from a high alcohol intake, liver disease, and various medications. • Serum folate and vitamin B12 levels. Analyses of serum folate and vitamin B12 levels are usually among the first tests conducted to determine the cause of macrocytic red blood cells. A low serum level of either nutrient is consistent with a deficiency, whereas adequate levels can help rule out deficiency. Folate levels are not a specific measure of folate status, however; they increase with folate consumption and decrease with alcohol consumption, pregnancy, or use of anticonvulsant medications. Folate depletion is characterised by a fall in the folate concentrations of red blood cells (erythrocytes). As erythrocyte folate levels diminish, folate-deficiency anaemia develops. Because low erythrocyte folate concentrations also occur with vitamin B12 deficiency, serum vitamin B12 concentrations must also be measured. Table E.10 shows standards for folate and vitamin B12 assessment. • Methylmalonic acid and homocysteine levels. To determine whether a nutrient is deficient, measures are taken of substances that accumulate when the functions of the nutrient are impaired. For example, the amino acid homocysteine usually increases in both folate and vitamin B12 deficiencies because both nutrients are needed for its metabolism. Methylmalonic acid is a breakdown product of several amino acids and requires vitamin B12 for its metabolism; its concentrations are elevated in vitamin B12 deficiency, but not in folate deficiency. Thus this measure is useful in distinguishing folate and B12 deficiency. • Schilling test. Vitamin B12 deficiency usually arises from malabsorption, not from poor intake. To determine whether malabsorption is the cause, a small oral dose of radioactive vitamin B12 is given, and urinary excretion is measured. This test is rarely performed, but it measures vitamin B12 absorption and is called a Schilling test. • Antibodies to intrinsic factor. Serum antibodies for intrinsic factor can help confirm a diagnosis of pernicious anaemia, an autoimmune disease characterised by destruction of the cells that produce intrinsic factor. Intrinsic factor is a protein required for vitamin B12 absorption, as Chapter 10 explains.
Cautions about nutrition assessment The tests outlined in this appendix yield information that becomes meaningful only when conducted and
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Appendix E
interpreted by a skilled clinician. Potential sources of error may be introduced at any step, from the collection of samples and data to their reporting and analyses. Equipment must be regularly calibrated to ensure accuracy of measurements. In addition, the assessor must keep in mind that each assessment measure contributes only one piece of information that may be
useful in confirming or eliminating the possibility of suspected nutrition problems. Furthermore, the assessor must constantly remember that a sufficient intake of a nutrient does not guarantee adequate nutrient status for an individual. Conversely, the apparent inadequate intake of a nutrient does not, by itself, establish that a deficiency exists.
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761
762
Appendix F CONTENTS Using a shortcut to estimate total energy expenditure 763
Physical activity and energy requirements
Chapter 8 describes how to calculate the estimated energy requirement (EER) for adults by using an equation that accounts for gender, age, weight and physical activity level (PAL). Table F.1 presents the full equations to determine the basal metabolic rate (BMR) for people over 10 years of age using the Schofield equation, which is a widely used prediction equation. Once you have calculated BMR,
a multiplication factor can be applied to it to allow for PAL. Table F.2 provides estimates of PALs based on a range of daily activities, from bed rest up to heavy, vigorous activity. During the second trimester of pregnancy, an additional 1400 kilojoules should be added to estimated energy needs. During the third trimester of pregnancy, an additional 1900 kilojoules are required.
TABLE F.1 Equations to determine BMR in kJ/day
MALES
FEMALES
AGE (yrs)
EQUATION (WEIGHT IN KILOGRAMS)
10–17
(74 3 weight) 1 2754
18–29
(63 3 weight) 1 2896
30–59
(48 3 weight) 1 3653
.60
(49 3 weight) 1 2459
10–17
(56 3 weight) 1 2898
18–29
(62 3 weight) 1 2036
30–59
(34 3 weight) 1 3538
.60
(38 3 weight) 1 2755
W.N. Schofield, Predicting basal metabolic rate, new standards and review of previous work, Human Nutrition Clinical Nutrition 39C (Suppl 1) (1985): 5−41.
TABLE F.2 Energy expenditure levels for different lifestyles LIFESTYLE
DESCRIPTION
PHYSICAL ACTIVITY EQUIVALENTS
PHYSICAL ACTIVITY LEVEL (PAL) 1.2
Bed rest
At rest, exclusively sedentary or lying (chairbound or bed-bound)
Old, infirm individuals; unable to move around freely or earn a living
Very sedentary
Exclusively sedentary activity/seated work with little or no strenuous leisure activitya
Office employees, precision mechanics
1.4 to 1.5
Light activity
Sedentary activity/seated work with some requirement for occasional walking and standing, but little or no strenuous leisure activitya
Laboratory assistants, drivers, students, assembly line workers
1.6 to 1.7
Moderate activity
Predominantly standing or walking worka
Homemakers, salespersons, waiters, mechanics, traders
1.8 to 1.9
Heavy/ vigorous activity
Heavy occupational work or highly active leisure activitya
Construction workers, farmers, forest workers, miners, high-performance athletes
2.0 to 2.4
For sports and strenuous leisure activities (30−60 minutes, 4−5 times per week), add 0.3 PAL units per day.
a
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Appendix F
Using a shortcut to estimate total energy expenditure
763
in Table F.3 and Table F.4, which you can use as a guide to estimating energy requirements based on a fixed BMI across different PALs – that is, the number of kilojoules needed to maintain your current body weight. The tables have been adapted from the Nutrient Reference Values for Australia and New Zealand.
For those who prefer to bypass these steps, this appendix presents additional tables that provide a shortcut to estimating total energy expenditure for children, adolescents and adults. These estimates are presented
TABLE F.3 Estimated energy requirements of adults using predicted BMR and PAL AGE (yrs)
19–30
31–50
51–70
.70
BMI 5 22.0a
BMRb MJ/day
PHYSICAL ACTIVITY LEVEL (PAL)c MALES MJ/day
BMR MJ/day
PHYSICAL ACTIVITY LEVEL (PAL)c FEMALES MJ/day
Ht (m)
Wt (kg)
MALE
1.2
1.4
1.6
1.8
2
2.2
FEMALE
1.2
1.4
1.6
1.8
2
2.2
1.5
49.5
–
–
–
–
–
–
–
5.2
6.1
7.1
8.2
9.2
10.2
11.2
1.6
56.3
6.4
7.7
9.0
10.3
11.6
12.9
14.2
5.6
6.6
7.7
8.8
9.9
11.1
12.2
1.7
63.6
6.9
8.3
9.7
11.0
12.4
13.8
15.2
6.0
7.2
8.4
9.6
10.8
12.0
13.2
1.8
71.3
7.4
8.9
10.3
11.8
13.3
14.8
16.3
6.5
7.7
9.0
10.3
11.6
12.9
14.2
1.9
79.4
7.9
9.5
11.1
12.6
14.2
15.8
17.4
7.0
8.4
9.7
11.1
12.5
13.9
15.3
2.0
88.0
8.4
10.1
11.8
13.5
15.2
16.9
18.6
–
–
–
–
–
–
–
1.5
49.5
–
–
–
–
–
–
–
5.2
6.3
7.3
8.4
9.4
10.4
11.5
1.6
56.3
6.4
7.6
8.9
10.2
11.4
12.7
14.0
5.5
6.5
7.6
8.7
9.8
10.9
12.0
1.7
63.6
6.7
8.0
9.4
10.7
12.1
13.4
14.8
5.7
6.8
8.0
9.1
10.3
11.4
12.5
1.8
71.3
7.1
8.5
9.9
11.3
12.7
14.2
15.6
6.0
7.2
8.3
9.5
10.7
11.9
13.1
1.9
79.4
7.5
9.0
10.4
11.9
13.4
14.9
16.4
6.2
7.5
8.7
10.0
11.2
12.5
13.7
2.0
88.0
7.9
9.5
11.0
12.6
14.2
15.8
17.3
–
–
–
–
–
–
–
1.5
49.5
–
–
–
–
–
–
–
4.9
6.0
6.9
7.9
8.9
9.8
10.9
1.6
56.3
5.8
7.0
8.2
9.3
10.4
11.5
12.7
5.2
6.2
7.3
8.3
9.3
10.4
11.4
1.7
63.6
6.1
7.3
8.6
9.8
11.1
12.3
13.6
5.4
6.5
7.6
8.7
9.8
10.7
12.0
1.8
71.3
6.5
7.8
9.1
10.4
11.7
13.1
14.4
5.7
6.9
8.0
9.1
10.3
11.4
12.6
1.9
79.4
6.9
8.3
9.6
11.1
12.4
13.8
15.2
6.0
7.2
8.4
9.6
10.8
12.0
13.2
2.0
88.0
7.3
8.8
10.2
11.7
13.2
14.7
16.1
–
–
–
–
–
–
–
1.5
49.5
–
–
–
–
–
–
–
4.6
5.6
6.5
7.4
8.3
9.3
10.2
1.6
56.3
5.2
6.3
7.3
8.3
9.4
10.4
11.5
4.9
5.9
6.9
7.8
8.8
9.8
10.8
1.7
63.6
5.6
6.7
7.8
8.9
10.0
11.2
12.3
5.2
6.2
7.2
8.3
9.3
10.3
11.4
1.8
71.3
6.0
7.1
8.3
9.5
10.7
11.9
13.1
5.5
6.6
7.7
8.7
9.8
10.9
12.0
1.9
79.4
6.4
7.6
8.9
10.2
11.4
12.7
14.0
5.8
6.9
8.1
9.2
10.4
11.5
12.7
2.0
88.0
6.8
8.1
9.5
10.8
12.2
13.5
14.9
–
–
–
–
–
–
–
Note: The original Schofield equations from which these tables were derived used 601 years as the upper age category. For people aged 51−70 years, the estimates were derived by averaging those for the adults (31−50 years) and older (.70 years) adults. A BMI of 22.0 is approximately at the midpoint of the healthy weight range.
a
BMR is calculated according to Table F.1 formulas.
b
PALs incorporate relevant growth factor for age. They correspond to the following activities: 1.2 − bed rest; 1.4 – very sedentary; 1.6 − light activity; 1.8 − moderate activity; 2.0 − heavy activity; and 2.2 − vigorous activity.
c
Adapted from the Nutrient Reference Values for Australia and New Zealand. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand). Canberra, ACT: Commonwealth of Australia and New Zealand Government (2006).
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764
Appendix F
TABLE F.4 Estimated energy requirements (EERs) of children and adolescents (MJ/day) PHYSICAL ACTIVITY LEVEL (PAL) AGE GUIDE (yrs)a, b
REFERENCE WEIGHT (kg)
REFERENCE HEIGHT (m)
BMR (MJ/day)c
1.2 BED REST
1.4 VERY SEDENTARY
3
14.3
0.95
3.4
4.2
4.9
4
16.2
1.02
3.6
4.4
5.2
1.6 LIGHT
1.8 MODERATE
2 HEAVY
2.2 VIGOROUS
5.6
6.3
6.9
7.6
5.9
6.6
7.3
8.1
BOYS
5
18.4
1.09
3.8
4.7
5.5
6.2
7.0
7.8
8.5
6
20.7
1.15
4.1
5.0
5.8
6.6
7.4
8.2
9.0
7
23.1
1.22
4.3
5.2
6.1
7.0
7.8
8.7
9.5
8
25.6
1.28
4.5
5.5
6.4
7.3
8.2
9.2
10.1
9
28.6
1.34
4.8
5.9
6.8
7.8
8.8
9.7
10.7
10
31.9
1.39
5.1
6.3
7.3
8.3
9.3
10.4
11.4
11
35.9
1.44
5.4
6.6
7.7
8.8
9.9
11.0
12.0 12.8
12
40.5
1.49
5.8
7.0
8.2
9.3
10.5
11.6
13
45.6
1.56
6.2
7.5
8.7
10.0
11.2
12.4
13.6
14
51.0
1.64
6.6
8.0
9.3
10.6
11.9
13.2
14.6
15
56.3
1.74
7.0
8.5
9.9
11.2
12.6
14.0
15.4
16
60.9
1.74
7.3
8.9
10.3
11.8
13.2
14.7
16.2
17
64.6
1.75
7.6
9.2
10.7
12.2
13.7
15.2
16.7
18
67.2
1.76
7.7
9.4
10.9
12.5
14.0
15.6
17.1
GIRLS 3
13.9
0.94
3.2
3.9
4.5
5.3
5.8
6.4
7.1
4
15.8
1.01
3.4
4.1
4.8
5.5
6.1
6.8
7.5
5
17.9
1.08
3.6
4.4
5.1
5.7
6.5
7.2
7.9
6
20.2
1.15
3.8
4.6
5.4
6.1
6.9
7.6
8.4
7
22.8
1.21
4.0
4.9
5.7
6.5
7.3
8.1
8.9
8
25.6
1.28
4.2
5.2
6.0
6.9
7.7
8.6
9.4
9
29.0
1.33
4.5
5.5
6.4
7.3
8.2
9.1
10.0
10
32.9
1.38
4.7
5.7
6.7
7.6
8.5
9.5
10.4
11
37.2
1.44
4.9
6.0
7.0
8.0
9.0
10.0
11.0
12
41.6
1.51
5.2
6.4
7.4
8.5
9.5
10.6
11.6
13
45.8
1.57
5.5
6.7
7.8
8.9
10.0
11.1
12.2
14
49.4
1.60
5.7
6.9
8.1
9.2
10.3
11.5
12.6
15
52.0
1.62
5.8
7.1
8.2
9.4
10.6
11.7
12.9
16
53.9
1.63
5.9
7.2
8.4
9.5
10.7
11.9
13.1
17
55.1
1.63
5.9
7.2
8.4
9.6
10.8
12.0
13.2
18
56.2
1.63
6.0
7.3
8.5
9.7
10.9
12.1
13.3
EERs were calculated using BMR predicted from weight, height and age.
a
The height- and/or weight-to-age ratio may differ markedly in some ethnic groups. In this case, if BMI is in the acceptable range, it would be more relevant to use body weight as the main guide to current energy needs.
b
Estimated using Schofield equations for weight, height and age groups 3−10 and 10−18
c
Adapted from the Nutrient Reference Values for Australia and New Zealand. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand). Canberra, ACT: Commonwealth of Australia and New Zealand Government (2006).
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765
Appendix G CONTENTS Conversions 765 Percentages 765 Weights and measures
766
Aids to calculation
Many mathematical problems have been worked out in the ‘How to’ sections of the text, and practice problems have been provided in the ‘Nutrition calculations’ sections at the end of some chapters. These pages offer additional help and examples.
Conversions A conversion factor is a fraction that converts a measurement expressed in one unit to another unit – for example, from pounds to kilograms or from feet to metres. To create a conversion factor, an equality (such as 1 kilogram 5 2.2 pounds) is expressed as a fraction: 1kg 2.21b and 2.2 1b 1 kg To convert the units of a measurement, use the fraction with the desired unit in the numerator. Example 1 Convert a weight of 130 pounds to kilograms. Multiply 130 pounds by the conversion factor that includes both pounds and kilograms, with the desired unit (kilograms) in the numerator: 1kg 130 kg 5 5 59 kg 2.21b 2.2 Alternatively, to convert a measurement from one unit of measure to another, multiply the given measurement by the appropriate equivalent found in the conversion list on the following page. 1301b 3
Example 2 Convert 64 fluid ounces to litres. Locate the equivalent measure from the table (1 ounce 5 0.03 litre) and multiply the number of ounces by 0.03:
64 oz 3 0.03 oz/L 5 1.9 L
Percentages A percentage is a fraction whose denominator is 100. For example: 50 50% 5 100 Like other fractions, percentages are used to express a portion of a quantity. Fractions whose denominators are numbers other than 100 can be converted to percentages
by first dividing the numerator by the denominator and then multiplying the result by 100. Example 3 Express 5/8 as a percentage. 5 5 5 4 8 5 0.625 8
0.625 3 100 5 62.5%
The following examples show how to calculate specific percentages. Example 4 Suppose your energy intake for the day is 8400 kJ (2000 kcal) and your recommended energy intake is 10 080 kJ (2400 kcal). What percentage of the recommended energy intake did you consume? Divide your intake by the recommended intake:
8400 kJ (intake) 4 10 080 kJ (recommended) 5 0.83
Multiply by 100 to express the decimal as a percentage:
0.83 3 100 5 83%
Example 5 Suppose a person’s intake of vitamin C for the day is 120 mg and their RDI is 45 mg. What percentage of the RDI for vitamin C did they consume? Divide the intake by the recommended intake:
120 mg (intake) 4 45 mg (RDI) 5 2.67
Multiply by 100 to express the decimal as a percentage:
2.67 3 100 5 267%
Example 6 Dietary recommendations suggest that carbohydrates provide 45 to 65 per cent of the day’s energy intake. If your energy intake is 8400 kJ (2000 kcal), how much carbohydrate should you eat? Because this question has a range of acceptable answers, work the problem twice. First, use 45% to find the least amount you should eat: Divide 45 by 100 to convert to a decimal:
45 4 100 5 0.45
Multiply kilojoules by 0.45:
8400 kJ 3 0.45 5 3780 kJ
Divide kilojoules by 17 to convert carbohydrate kilojoules to grams:
3780 kJ 4 17 kJ/g 5 222 g
Now repeat the process using 65% to find the maximum number of grams of carbohydrates you should eat.
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766
Appendix G
Divide 65 by 100 to convert it to a decimal:
65 4 100 5 0.65
Multiply kilojoules by 0.65:
8400 kJ 3 0.65 5 5460 kJ
Divide kilojoules by 17 to convert carbohydrate kilojoules to grams:
5460 kJ 4 17 kJ/g 5 321 g
If you plan for between 45 and 65% of your 8400 kilojoule intake to be from carbohydrates, you should eat between 222 grams and 321 grams of carbohydrates.
Weights and measures Length 1 centimetre (cm) 5 0.39 inches (in) 1 foot (ft) 5 30.48 centimetres (cm) 1 inch (in) 5 2.54 centimetres (cm) 1 metre (m) 5 39.37 inches (in)
1 millilitre (mL) 5 0.001 litres (L) 5 0.035 fluid ounces (fl oz) 1 ounce (oz) 5 0.028 litres (L) 5 28 millilitres (mL) 1 pint (pt) 5 2 cups (c) 5 0.57 litres (L) 5 20 fluid ounces (oz) 1 quart (qt) 5 4 cups (c) 5 1.14 litres (L) 5 32 ounces (oz) 1 tablespoon (tbs or T) 5 4 teaspoons (tsp) 5 20 millilitres (mL) 1 teaspoon (tsp) 5 5 millilitres (mL) 1 gallon (gal) 5 8 pints (pt) 5 4.55 litres (L) 5 160 fluid ounces (oz)
Energy 1 megajoule (MJ) 5 240 kcalories (kcals)
Weight
1 kilojoule (kJ) 5 0.24 kcalories (kcals)
1 gram (g) 5 0.001 kilograms (kg) 5 1000 milligrams (mg) 5 0.035 ounces (oz) 1 kilogram (kg) 5 1000 grams (g) 5 2.2 pounds (lb) 1 microgram (µg) 5 0.001 milligrams (mg) 1 milligram (mg) 5 0.001 grams (g) 5 1000 micrograms (µg) 1 ounce (oz) 5 28 grams (g) 5 0.03 kilograms (kg) 1 pound (lb) 5 454 grams (g) 5 0.45 kilograms (kg) 5 16 ounces (oz)
Volume
Imperial measures are given, not US. 1 cup 5 12 tablespoons (tbs or T) 5 0.25 litres (L) 5 8 fluid ounces (oz) 1 litre (L) 5 35.1 fluid ounces (fl oz) 5 0.22 gallons (gal) 5 1.75 pints (pt) 5 0.88 quarts (qt) 5 1000 millilitres (mL)
1 kcalorie (kcals) 5 4.2 kilojoules (kJ) 1 g alcohol 5 7 kcals 5 29 kJ 1 g carbohydrate 5 4 kcals 5 17 kJ 1 g fat 5 9 kcals 5 37 kJ 1 g protein 5 4 kcals 5 17 kJ
Temperature To change from Fahrenheit (°F) to Celsius (°C), subtract 32 from the Fahrenheit measure and then multiply that result by 0.56. To change from Celsius (°C) to Fahrenheit (°F), multiply the Celsius measure by 1.8 and add 32 to that result. A comparison of some useful temperatures is given below. CELSIUS
FAHRENHEIT
Boiling point
100 °C
212 °F
Body temperature
37 °C
98.6 °F
Freezing point
0 °C
32 °F
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767
ANSWERS CHAPTER 1
Nutrition calculations
Study questions (multiple choice) 1. d 2. a 3. a 4. d 5. d 8. d 9. c 10. a
Nutrition calculations 1 a 5 g protein 3 17 kJ/g 5 85 kJ protein 30 g carbohydrate 3 17 kJ/g 5 510 kJ carbohydrate 11 fat 3 37 kJ/g 5 407 kJ fat Total 5 1002 kJ b 85 kJ 4 1002 kJ 3 100 5 8.5% kJ from protein 510 kJ 4 1002 kJ 3 100 5 50.9% kJ from carbohydrate 407 kJ 4 1002 kJ 3 100 5 40.6% kJ from fat Total 5 100% c 1 g protein 5 17 kJ protein 13 g carbohydrate 5 221 kJ carbohydrate 613 total kJ 2 238 kJ (protein 1 carbohydrate) 5 375 kJ alcohol 375 kJ alcohol 4 29 kJ/g 5 12.9 g alcohol 2 No. 20 g protein 3 17 kJ/g 5 340 kJ
1 a 0.7 3 8000 total kJ/day 5 5600 kJ from carbohydrate/day 5600 kJ from carbohydrate 4 17 kJ/g 5 329 g carbohydrate b 329 g carbohydrate 4 2 5 164.5 g carbohydrate/ day 164.5 g carbohydrate 3 17 kJ/g 5 2797 kJ from carbohydrate 2797 kJ from carbohydrate 4 8000 total kJ/day 5 0.35 0.35 3 100 5 35% kJ from carbohydrate c 329 g carbohydrate 3 2 5 658 g carbohydrate/day 658 g carbohydrate 3 17 kJ/g 5 11 186 kJ from carbohydrate 11 186 kJ from carbohydrate 4 15 000 total kJ/day 5 0.75 0.75 3 100 5 75% kJ from carbohydrate 2 150 g carbohydrate 3 17 kJ/g 5 2550 kJ from carbohydrate 2550 kJ from carbohydrate 4 4000 total kJ/day 5 0.64 0.64 3 100 5 64% kJ from carbohydrate
CHAPTER 2
CHAPTER 5
Study questions (multiple choice) 1. c 2. b 3. b 4. b 5. c
6. a
6. c
7. c
7. c
Nutrition calculations 1 a 150 g b 608 kilojoules c 7.4 g fat d 280 kilojoules e 280 kJ 4 608 kJ 5 0.46 0.46 3 100 5 46% f This product derives 46% of its kilojoules from fat g No h Whole milk i No
CHAPTER 3 Study questions (multiple choice) 1. c 2. c 3. a 4. d 5. b b 8. d 9. c 10. c
6. c
7.
6. d
7.
CHAPTER 4 Study questions (multiple choice) 1. b 2. c 3. a 4. a 5. d d 8. d 9. c 10. d
Study questions (multiple choice) 1. d 2. c 3. a 4. d 5. a 8. b 9. a 10. b
6. d
7. b
Nutrition calculations 1 a Milk A: 8 g fat 4 244 g total 5 0.03; 0.03 3 100 5 3% Milk B: 5 g fat 4 244 g total 5 0.02; 0.02 3 100 5 2% Milk C: 3 g fat 4 244 g total 5 0.01; 0.01 3 100 5 1% Milk D: 0 g fat 4 244 g total 5 0.00; 0.00 3 100 5 0% b Milk A: 8 g fat 3 37 kJ/g 5 296 kJ from fat Milk B: 5 g fat 3 37 kJ/g 5 185 kJ from fat Milk C: 3 g fat 3 37 kJ/g 5 111 kJ from fat Milk D: 0 g fat 3 37 kJ/g 5 0 kJ from fat c Milk A: (8 g fat 3 37 kJ/g) 1 (8 g prot 3 17 kJ/g) 1 (12 g carb 3 17 kJ/g) 5 636 kJ Milk B: (5 g fat 3 37 kJ/g) 1 (8 g prot 3 17 kJ/g) 1 (12 g carb 3 17 kJ /g) 5 525 kJ Milk C: (3 g fat 3 37 kJ/g) 1 (8 g prot 3 17 kJ/g) 1 (12 g carb 3 17 kJ/g) 5 451 kJ Milk D: (0 g fat 3 9 kJ/g) 1 (8 g prot 3 17 kJ/g) 1 (12 g carb 3 17 kJ/g) 5 340 kJ d Milk A: 296 kJ from fat 4 636 total kJ 5 0.47; 0.47 3 100 5 47%
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768
Answers
Milk B: 185 kJ from fat 4 525 total kJ 5 0.36; 0.36 3 100 5 36% Milk C: 114 kJ from fat 4 451 total kJ 5 0.25; 0.25 3 100 5 25% Milk D: 0 kJ from fat 4 340 total kJ 5 0.00; 0.00 3 100 5 0% e Milk A: whole Milk B: reduced-fat, 2% or less fat Milk C: low-fat or 1% Milk D: fat-free, non-fat, skim, zero-fat or no-fat 2 A 97% fat-free meal contains 3% fat (by weight). 3% of 275 g 5 8.25 g Energy content: 5 g fat 3 37 kJ 5 185 kJ
CHAPTER 6 Study questions (multiple choice) 1. a 2. c 3. a 4. b 5. c 8. c 9. c 10. d
6. c
7. a
Nutrition calculations 1 a 0.75 g/kg 3 70 kg 5 52.5 g protein per day b 0.84 g/kg 3 83 kg 5 69.7 g protein per day 2 a 50 g carbohydrate 3 17 kJ/g 5 850 kJ from carbohydrate 100 g fat 3 37 kJ/g 5 3700 kJ from fat 5200 kJ 2 (850 1 3700 kJ) 5 650 kJ from protein 650 kJ 4 17 kJ/g 5 38.2 g protein b Using the RDI guideline of 0.75 g/kg/day, an appropriate protein intake for this woman would be 39 g protein/day (0.75 g/kg 3 52 5 39 g/day). Her intake is slightly lower than her RDI. c Using the guideline that carbohydrate should contribute 45 to 65% and fat should contribute 20 to 35% of energy intake, her intake of 50 g carbohydrate is low (850 kJ carbohydrate 4 5200 total kJ 5 16.3%), and her intake of 100 g fat is high (3700 kJ fat 4 5200 total kJ 5 71%). The remaining 12.7% of her daily energy is supplied by protein.
CHAPTER 7 Study questions (multiple choice) 1. c 2. d 3. c 4. c 5. b 8. c 9. b 10. b
6. c
7. d
6. c
7. b
CHAPTER 8 Study questions (multiple choice) 1. d 2. b 3. b 4. a 5. a 8. b 9. a 10. d
Nutrition calculations 1 a 0.416 kJ/kg/min 3 64 kg 5 26.6 kJ/min 26.6 kJ/min 3 120 min 5 3195 kJ b 0.953 kJ/kg/min 3 64 kg 5 61 kJ/min 61 kJ/min 3 20 min 5 1220 kJ
c 0.523 kJ/kg/min 3 64 kg 5 33.5 kJ/min 33.5 kJ/min 3 45 min 5 1508 kJ d 0.345 kJ/kg/min 3 64 kg 5 22 kJ/min 22 kJ/min 3 60 min 5 1320 kJ 2 The infant has the faster BMR (2100 kJ/day 4 9 kg 5 233 kJ/kg/day and 6300 kJ/day 4 77 kg 5 81.8 kJ/ kg/day). Because the infant has a BMR of 233 kJ/ kg, whereas the adult has a BMR of 81.8 kJ/kg, the infant’s BMR is almost three times faster than the adult’s based on body weight. 3 BMR 5 (63 3 weight) 1 2896 5 (63 3 59 kg) 1 896 5 6613 kJ. Physical activity level is lightly active 5 1.6 multiplication factor EER 5 6613 3 1.6 5 10 581 kJ/day 4 57 kilograms
CHAPTER 9 Study questions (multiple choice) 1. a 2. d 3. a 4. b 5. c 8. d 9. d 10. d
6. c
7. c
Nutrition calculations 1 a Three milk shakes provide 2 3 1100 kJ 5 2200 kJ 2 3 35 g carbohydrate 5 70 g carbohydrate 2 3 15 g protein 5 30 g protein 2 3 2 g fat 5 4 g fat b Of course, there are many possible dinners that you could plan. One might be: Salad made with 1 cup lettuce, 1 cup chopped tomatoes and onions, ¼ cup three-bean mix, and 2 tbs low-fat dressing -- 100 g grilled chicken -- 1 medium baked potato -- 1 cup squash and zucchini -- 1 cup melon cubes This meal brings the day’s totals to 4100 kilojoules, 90 g of protein, 166 g of carbohydrate and 14 g of fat, which meets the goals for kilojoules, protein and carbohydrate. Because the milk shake has been fortified, all vitamin and mineral needs are covered as well. The only possible dietary shortcoming is that the day’s percentage of kilojoules from fat is low (only 10%), but because energy and nutrient recommendations have been met and the goal is weight loss, this may be acceptable. c This weight-loss plan uses a liquid formula rather than foods, making clients dependent on a special device (the formula) rather than teaching them how to make good choices from the conventional food supply. It provides no information about drop-out rates, the long-term success of clients or weight maintenance after the program ends.
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Answers
2 a b
1920 kJ 4 442 g 5 4.34 kJ/g Almost another whole salad (2100 kJ 4 4.34 kJ/g 5 485 g) ITEM NO./FOOD Original totals:
ENERGY (kJ)
442
1920
Minus: Lettuce, 1 cup
55
25
Plus: Roast ham
30
157
Cheddar cheese
30
507
Totals:
d e
WEIGHT (g)
447 g
2559 kJ
2559 kJ 2 1920 kJ 5 639 kJ added 447 g 2 442 g 5 5 g added
Study questions (multiple choice) 1. d 2. a 3. b 4. c 5. c 8. b 9. b 10. d 6. b
7. c
Nutrition calculations 1 a Thiamin: mg Riboflavin: mg Niacin: mg NE Vitamin B6: mg Folate: µg DFE Vitamin B12: µg Vitamin C: mg b 1 g 5 1000 mg; 1 mg 5 1000 µg (1000 3 1000 5 1 000 000); 1 million µg 5 1 g 1 tsp 5 5 g 5 3 1 000 000 µg 5 5 000 000 µg/tsp See inside front cover for your RDI based on age and gender. 2 a She eats 90 g protein. Assume she uses 46 g as protein. This leaves 90 g 2 46 g 5 44 g protein ‘leftover’. 44 g protein 4 100 5 0.44 g tryptophan 0.44 g tryptophan 3 1000 5 440 mg tryptophan 440 mg tryptophan 4 60 5 7.3 mg NE 7.3 mg NE 1 9 mg niacin 5 16.3 mg NE b Yes
CHAPTER 11 Study questions (multiple choice) 1. c 2. a 3. c 4. b 5. c 8. d 9. d 10. c Nutrition calculations 1 Vitamin A: µg RE Vitamin E: mg Vitamin D: µg Vitamin K: µg
2 Thiamin: legumes and grains Riboflavin: milks, grains and meats Niacin: meats and grains Vitamin B6: meats Folate: legumes and vegetables Vitamin B12: meats and milks Vitamin C: vegetables and fruits Vitamin A: vegetables, fruits and milks Vitamin D: milks Vitamin E: legumes and oils Taken together, ‘the most’ groups form healthy eating according to the Australian Guide to Healthy Eating – grains, vegetables, legumes, fruits, milks, meats and oils.
CHAPTER 12
CHAPTER 10 Study questions (multiple choice) 1. c 2. a 3. a 4. c 5. b 8. d 9. c 10. a
769
6. c
7. a
6. a
7. d
Nutrition calculations 1 Calcium: mg; Magnesium: mg; Phosphorus: mg; Potassium: mg; Sodium: mg 2
a
b
c
FOOD
CALCIUM IN FOOD (mg) 3 ABSORPTION RATE (%) 5 CALCIUM IN THE BODY (mg)
Cauliflower, ½ cup cooked, fresh
10 mg 3 0.50 5 5 mg (or more)
Kale, ½ cup cooked, fresh
40 mg 3 0.50 5 20 mg (or more)
Milk, 1 cup, 1% low-fat
300 mg 3 0.30 5 90 mg
Sweet potatoes, 60 g
150 mg 3 0.20 5 30 mg
Spinach, 1 cup raw
55 mg 3 0.05 5 3 mg (or less)
The sweet potatoes offer more than twice as much calcium per serving, but an equivalent amount after absorption. To equal the 300 milligrams provided by milk, a person would need to eat 15 cups of cauliflower (300 mg/cup milk 4 10 mg/½ cup cauliflower 5 30 half-cups or 15 cups). After considering the better absorption rate of cauliflower, a person would need to eat 9 cups of cauliflower (5 mg/½ cup or 10 mg/cup; 90 mg 4 10 mg/cup 5 9 cups) to match the 90 milligrams available to the body from milk after absorption. The better absorption rate reduced the quantity of cauliflower significantly, but that’s still a lot of cauliflower.
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Answers
CHAPTER 13
CHAPTER 14
Study questions (multiple choice) 1. b 2. c 3. c 4. a 5. d 8. d 9. a 10. c Nutrition calculations 1 Iron: mg Zinc: mg Iodine: µg Selenium: µg Copper: mg Manganese: mg Fluoride: mg Chromium: µg Molybdenum: µg 2 a
6. d
7. c
Study questions (multiple choice) 1. d 2. b 3. a 4. d 5. c 8. b 9. a 10. d
6. c
7. c
6. c
7. b
6. c
7. c
6. b
7. a
6. b
7. c
6. d
7. a
CHAPTER 15 Study questions (multiple choice) 1. c 2. c 3. c 4. b 5. c 8. a 9. c 10. c
CHAPTER 16 Study questions (multiple choice) 1. c 2. a 3. c 4. c 5. a 8. a 9. c 10. c
FOOD
IRON DENSITY (mg/1000 kJ)
Milk, full-fat, 1 cup
0.10 mg 4 357 kJ 3 1000 5 0.28 mg/1000 kJ
Cheddar cheese, 30 g
0.19 mg 4 479 kJ 3 1000 5 0.39 mg/1000 kJ
Kale, cooked from fresh, chopped, 1 cup
1.31 mg 4 184 kJ 3 1000 5 7.12 mg/1000 kJ
Sweet potato, baked in skin, 1 whole
0.51 mg 4 491 kJ 3 1000 5 1.03 mg/1000 kJ
Lamb chop, 100 g
2.50 mg 4 900 kJ 3 1000 5 2.78 mg/1000 kJ
Carrots, fresh, ½ cup
0.48 mg 4 147 kJ 3 1000 5 3.26 mg/1000 kJ
CHAPTER 19
Whole wheat bread, 1 slice
0.87 mg 4 269 kJ 3 1000 5 3.23 mg/1000 kJ
Green peas, cooked from frozen, ½ cup
1.26 mg 4 260 kJ 3 1000 5 4.84 mg/1000 kJ
Study questions (multiple choice) 1. b 2. b 3. d 4. b 5. c 8. b 9. d 10. c
Apple, 1 medium
0.38 mg 4 525 kJ 3 1000 5 0.72 mg/1000 kJ
Sirloin steak, lean, 115 g
3.81 mg 4 958 kJ 3 1000 5 3.97 mg/1000 kJ
CHAPTER 17 Study questions (multiple choice) 1. c 2. a 3. c 4. d 5. a 8. d 9. b 10. b
CHAPTER 18 Study questions (multiple choice) 1. a 2. d 3. d 4. c 5. d 8. d 9. a 10. c
Ranked by iron density (iron per kilojoule): kale. green peas . sirloin steak . carrots . bread . lamb chop . sweet potato . apple . cheese . milk
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771
GLOSSARY 24-hour recall
base concentrations (see Chapter 12)
nutrient intake when an RDI cannot be determined
acidosis
adipokines
above-normal acidity in the blood and body fluids
proteins synthesised and secreted by adipose cells
the uptake of nutrients by the cells of the small intestine for transport into either the blood or the lymph
acids
adiponectin
compounds that release hydrogen ions in a solution
Acceptable Macronutrient Distribution Ranges (AMDR)
a chronic inflammation of the skin’s follicles and oil-producing glands, which leads to an accumulation of oils inside the ducts that surround hairs; usually associated with the maturation of young adults
a protein produced by adipose cells that inhibits inflammation and protects against insulin resistance, type 2 diabetes, and cardiovascular disease
a record of foods eaten by a person for one 24-hour period
absorption
ranges of intakes for the energy nutrients that provide adequate energy and nutrients and reduce the risk of chronic diseases
accredited approved; in the case of healthcare facilities or universities, certified by an agency recognised by government
Accredited Practising Dietitian (APD) program a credentialling program administered by the Dietitians Association of Australia (DAA), and the only credential for dietitians recognised by the Australian Government (for Medicare purposes), many State governments and many private health insurers. Only individuals with recognised tertiary-level qualifications in dietetics who are eligible to join as full members of the DAA are able to take part in the APD program
acesulphame-K an artificial sweetener composed of an organic salt; K is the chemical symbol for potassium
acne
acupuncture a technique that involves piercing the skin with long thin needles at specific anatomical points to relieve pain or illness. Acupuncture sometimes uses heat, pressure, friction, suction or electromagnetic energy to stimulate the points
acute PEM protein–energy malnutrition caused by recent severe food restriction; characterised in children by thinness for height (wasting)
adaptive thermogenesis adjustments in energy expenditure related to changes in environment such as extreme cold and to physiological events such as overfeeding, trauma and changes in hormone status
added sugars
an intermediary in alcohol metabolism
sugars and syrups used as an ingredient in the processing and preparation of foods such as breads, cakes, beverages, jellies and ice-cream, as well as sugars eaten separately or added to foods at the table
acetyl CoA
additives
acetaldehyde
a 2-carbon compound (acetate, or acetic acid) to which a molecule of CoA is attached
acid controllers medications used to prevent or relieve indigestion by suppressing production of acid in the stomach; also called H2 blockers. Common brands include Zantac (ranitidine) and Pepcidine (famotidine)
acid–base balance the equilibrium in the body between acid and
substances not normally consumed as foods but added to food either intentionally or by accident
adequacy (dietary) providing all the essential nutrients, fibre and energy in amounts sufficient to maintain health
Adequate Intake (AI) the average daily amount of a nutrient that appears sufficient to maintain a specified criterion; a value used as a guide for
adipose tissue the body’s fat tissue; consists of masses of triglyceride-storing cells
adolescence
drinking despite ongoing social problems that are caused by or worsened by alcohol
alcohol dehydrogenase an enzyme active in the stomach and the liver that converts ethanol to acetaldehyde
alcoholism a pattern of drinking that includes a strong craving for alcohol, a loss of control and an inability to stop drinking once begun, withdrawal symptoms (nausea, sweating, shakiness and anxiety) after heavy drinking, and the need for increasing amounts of alcohol to feel ‘high’
the period from the beginning of puberty until maturity
alcohol-related birth defects (ARBD)
adrenal glands
malformations in the skeletal and organ systems (heart, kidneys, eyes, ears) associated with prenatal alcohol exposure
glands adjacent to, and just above, each kidney
adrenaline a hormone of the adrenal gland that modulates the stress response; also called epinephrine. When administered by injection, adrenaline counteracts anaphylactic shock by opening the airways and maintaining heartbeat and blood pressure
adrenocorticotropin or ACTH
alcohol-related neurodevelopmental disorder (ARND) abnormalities in the central nervous system and cognitive development associated with prenatal alcohol exposure
alkalosis above-normal alkalinity (base) in the blood and body fluids
a hormone, so named because it stimulates the adrenal cortex. The adrenal gland, like the pituitary, has two parts, in this case an outer portion (cortex) and an inner core (medulla). The release of ACTH is mediated by corticotropin-releasing hormone (CRH)
alpha-lactalbumin
adverse reactions
alpha-tocopherol
unusual responses to food (including intolerances and allergies)
the active vitamin E compound
aerobic requiring oxygen
alcohol a class of organic compounds containing hydroxyl (OH) groups
alcohol abuse a pattern of drinking that includes failure to fulfil work, school or home responsibilities; drinking in situations that are physically dangerous (as in driving while intoxicated); recurring alcohol-related legal problems (as in aggravated assault charges); or continued
the major protein in human breast milk, as opposed to casein, the major protein in cow’s milk
alpha-linolenic acid an essential fatty acid with 18 carbons and three double bonds
Alzheimer’s disease a degenerative disease of the brain involving memory loss and major structural changes in neuron networks; also known as senile dementia of the Alzheimer’s type (SDAT), primary degenerative dementia of senile onset, or chronic brain syndrome
amenorrhoea the absence of or cessation of menstruation. Primary amenorrhoea is menarche delayed beyond 16 years of age. Secondary amenorrhoea is the absence of three to six consecutive menstrual cycles
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Glossary
amino acid pool
androstenedione
antibodies
the supply of amino acids derived from either food proteins or body proteins that collect in the cells and circulating blood and stand ready to be incorporated in proteins and other compounds or used for energy
a hormone made in the adrenal glands that serves as a precursor to the male hormone testosterone; falsely promoted as burning fat, building muscle and slowing ageing. Side effects include acne, aggressiveness and liver enlargement
large proteins of the blood and body fluids, produced by the immune system in response to the invasion of the body by foreign molecules (usually proteins called antigens). Antibodies combine with and deactivate the foreign invaders, thus protecting the body
a measure of protein quality assessed by comparing a protein’s amino acid pattern with that of a reference protein; sometimes called chemical scoring
anencephaly
antidiuretic hormone (ADH)
an uncommon and always fatal type of neural tube defect; characterised by the absence of a brain
amino acids
aneurysm
building blocks of proteins. Each contains an amino group, an acid group, a hydrogen atom and a distinctive side group, all attached to a central carbon atom
an abnormal enlargement or bulging of a blood vessel (usually an artery) caused by damage to or weakness in the blood vessel wall
ammonia
a painful feeling of tightness or pressure in and around the heart, often radiating to the back, neck and arms; caused by a lack of oxygen to an area of heart muscle
a hormone produced by the pituitary gland in response to dehydration (or a high sodium concentration in the blood). It stimulates the kidneys to reabsorb more water and therefore prevents water loss in urine (also called vasopressin). (This ADH should not be confused with the enzyme alcohol dehydrogenase, which is also sometimes abbreviated ADH)
amino acid scoring
a compound with the chemical formula NH3; produced during the deamination of amino acids
amniotic sac the ‘bag of waters’ in the uterus, in which the foetus floats
amylase an enzyme that hydrolyses amylose (a form of starch). Amylase is a carbohydrase, an enzyme that breaks down carbohydrates
anabolic steroids drugs related to the male sex hormone, testosterone, that stimulate the development of lean body mass
anabolism reactions in which small molecules are put together to build larger ones. Anabolic reactions require energy
anaemia literally, ‘without blood’. Anaemia is any condition in which too few red blood cells are present, or the red blood cells are immature (and therefore large) or too small or contain too little haemoglobin to carry the normal amount of oxygen to the tissues. It is not a disease itself but can be a symptom of many different disease conditions, including many nutrient deficiencies, bleeding, excessive red blood cell destruction and defective red blood cell formation
anaerobic not requiring oxygen
anaphylaxis a life-threatening, whole-body allergic reaction to an offending substance
angina
angiotensin a hormone involved in blood pressure regulation. Its precursor protein is called angiotensinogen; it is activated by renin, an enzyme from the kidneys
angiotensin I an inactive precursor that is converted by an enzyme to yield active angiotensin II
angiotensin II a hormone involved in blood pressure regulation
anions negatively charged ions
anorexia nervosa
antigens substances that elicit the formation of antibodies or an inflammation reaction from the immune system. A bacterium, a virus, a toxin and a protein in food that causes allergy are all examples of antigens
antioxidant a substance in foods that significantly decreases the adverse effects of free radicals on normal physiological functions in the human body. As a food additive, preserves or delays rancidity of fats in foods and other damage to food caused by oxygen
relating to measurement of the physical characteristics of the body, such as height and weight
water drawn from a well that taps a confined aquifer in which the water is under pressure
arthritis inflammation of a joint, usually accompanied by pain, swelling and structural changes
artificial sweeteners sugar substitutes that provide negligible, if any, energy; sometimes called non-nutritive sweeteners
ascorbic acid one of the two active forms of vitamin C (see Figure 10.13). Vitamin C is often referred to by this name
-ase a word ending denoting an enzyme. The word beginning often identifies the compounds the enzyme works on. Examples include carbohydrase, an enzyme that hydrolyses carbohydrates; lipase, an enzyme that hydrolyses lipids (fats); and protease, an enzyme that hydrolyses proteins
aspartame
atherosclerosis
anus
a type of artery disease characterised by plaques (accumulations of lipid-containing material) on the inner walls of the arteries (see Chapter 18)
the terminal outlet of the GI tract
a narrow blind sac extending from the beginning of the colon; it stores lymph cells
anthropometric
artesian water
the original name for vitamin C
antacids
a competing factor that counteracts the action of another factor. When a drug displaces a vitamin from its site of action, the drug renders the vitamin ineffective and thus acts as a vitamin antagonist
vessels that carry blood from the heart to the tissues
antiscorbutic factor
aorta
antagonist
arteries
an artificial sweetener composed of two amino acids (phenylalanine and aspartic acid)
an eating disorder characterised by a refusal to maintain a minimally normal body weight and a distortion in perception of body shape and weight medications used to relieve indigestion by neutralising acid in the stomach. Common brands include Mylanta, Gaviscon, AlkaSeltzer, Rennie and Tums
applied by massage or baths) to enhance physical, psychological and spiritual health
the large, primary artery that conducts blood from the heart to the body’s smaller arteries
appendix
appetite the integrated response to the sight, smell, thought or taste of food that initiates or delays eating
arachidonic acid an omega-6-polyunsaturated fatty acid with 20 carbons and four double bonds; it is present in small amounts in meat and other animal products and is synthesised in the body from linoleic acid
aroma therapy a technique that uses oil extracts from plants and flowers (usually
atoms the smallest components of an element that still have all of the properties of the element
ATP or adenosine triphosphate a common high-energy compound composed of a purine (adenine), a sugar (ribose) and three phosphate groups
atrophic gastritis chronic inflammation of the stomach accompanied by a diminished size and functioning of the mucous membrane and glands
atrophy becoming smaller; with regard to muscles, a decrease in size (and strength) because of disuse, undernutrition or a wasting disease
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Glossary
autoimmune disorder
beta-alanine
biofeedback
a condition in which the body develops antibodies to its own proteins and then proceeds to destroy cells containing these proteins. In type 1 diabetes, the body develops antibodies to its insulin and destroys the pancreatic cells that produce the insulin, creating an insulin deficiency
a nonessential amino acid that is the rate-limiting precursor for the synthesis of the dipeptide carnosine. Carnosine acts primarily as a buffer in skeletal muscle. Beta-alanine supplements raise carnosine concentrations, which enhance the muscles’ buffering capacity
the use of special devices to convey information about heart rate, blood pressure, skin temperature, muscle relaxation and the like to enable a person to learn how to consciously control these medically important functions
autonomic nervous system
beta-carotene
the division of the nervous system that controls the body’s automatic responses. Its two branches are the sympathetic branch, which helps the body respond to stressors from the outside environment, and the parasympathetic branch, which regulates normal body activities between stressful times
one of the carotenoids; an orange pigment and vitamin A precursor found in plants
Ayurveda
an alkaline compound with the formula HCO321 that is secreted from the pancreas as part of the pancreatic juice. (Bicarbonate is also produced in all cell fluids from the dissociation of carbonic acid to help maintain the body’s acid–base balance)
a traditional Hindu system of improving health by using herbs, diet, meditation, massage and yoga to stimulate the body, mind and spirit to prevent and treat disease
beta-hydroxymethylbutyrate (HMB) a metabolite of the amino acid leucine promoted to increase muscle mass and strength
bicarbonate
bifidus factors
B-cells lymphocytes that produce antibodies. B stands for bone marrow, where the B-cells develop and mature
balance (dietary) providing foods in proportion to each other and in proportion to the body’s needs
basal metabolic rate (BMR) the rate of energy use for metabolism under specified conditions
basal metabolism the energy needed to maintain life when a body is at complete digestive, physical and emotional rest
bases compounds that accept hydrogen ions in a solution
factors in colostrum and breast milk that favour the growth of the ‘friendly’ bacterium Lactobacillus bifidus in the infant’s intestinal tract, so that other, less desirable intestinal inhabitants will not flourish
bile an emulsifier that prepares fats and oils for digestion; an exocrine secretion made by the liver, stored in the gall bladder and released into the small intestine when needed
binders chemical compounds in foods that combine with nutrients (especially minerals) to form complexes the body cannot absorb. Examples are phytates and oxalates
binge-eating disorder
biological value (BV) a measure of protein quality assessed by measuring the amount of protein nitrogen that is retained from a given amount of protein nitrogen absorbed
biotechnology the use of biological systems or organisms to create or modify products. Examples are the use of bacteria to make yoghurt, yeast to make beer, and cross-breeding to enhance crop production
bioterrorism the intentional spreading of disease-causing microorganisms or toxins
biotin a B vitamin that functions as a coenzyme in metabolism
blind experiment an experiment in which the subjects do not know whether they are members of the experimental group or the control group
blood lipid profile results of blood tests that reveal a person’s total cholesterol, triglycerides and various lipoproteins
body composition the proportions of muscle, bone, fat and other tissue that make up a person’s total body weight
body mass index (BMI) an index of a person’s weight in relation to height; determined by dividing the weight (in kilograms) by the square of the height (in metres)
bolus
an alcoholic beverage brewed by fermenting malt and hops
an eating disorder with criteria similar to those of bulimia nervosa, excluding purging or other compensatory behaviours
behaviour modification
bioaccumulation
an instrument that measures the heat energy released when foods are burned, thus providing an estimate of the potential energy of the foods
beer
the changing of behaviour by the manipulation of antecedents (cues or environmental factors that trigger behaviour), the behaviour itself, and consequences (the penalties or rewards attached to behaviour)
belching the expulsion of gas from the stomach through the mouth
beriberi the thiamin-deficiency disease
the accumulation of contaminants in the flesh of animals high on the food chain
bioavailability the rate at and the extent to which a nutrient is absorbed and used
bioelectromagnetic medical applications the use of electrical energy, magnetic energy or both to stimulate bone repair, wound healing and tissue regeneration
a portion; with respect to food, the amount swallowed at one time
bomb calorimeter
773
calcium to the diet. Calcium from bone is not well absorbed and is often contaminated with toxic minerals such as arsenic, mercury, lead and cadmium
boron a non-essential mineral that is promoted to increase muscle mass
bottled water drinking water sold in bottles
botulism an often fatal food-borne illness caused by the ingestion of foods containing a toxin produced by bacteria that grow without oxygen (see Chapter 19 for details)
branched-chain amino acids the essential amino acids leucine, isoleucine and valine, which are present in large amounts in skeletal muscle tissue; falsely promoted as fuel for exercising muscles
brite adipocytes white fat cells with brown fat cell characteristics; also called beige adipocytes
brown adipose tissue masses of specialised fat cells packed with pigmented mitochondria that produce heat instead of ATP
brown sugar refined white sugar crystals to which manufacturers have added molasses syrup with natural flavour and colour; 91 to 96 per cent pure sucrose
bulimia nervosa an eating disorder characterised by repeated episodes of binge eating usually followed by selfinduced vomiting, misuse of laxatives or diuretics, fasting or excessive exercise
caesarean section a surgically assisted birth involving removal of the foetus by an incision into the uterus, usually by way of the abdominal wall
caffeine
a measure of bone strength. When minerals fill the bone matrix (making it dense), they give it strength
a natural stimulant found in many common foods and beverages, including coffee, tea and chocolate; may enhance endurance by stimulating fatty acid release. High doses cause headaches, trembling, rapid heart rate and other undesirable side effects
bone meal or powdered bone
calbindin
bone density
crushed or ground bone preparations intended to supply
a protein in the intestinal cells, made with the help of vitamin D,
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774
Glossary
carcinogenesis
cations
chlorophyll
the process of cancer development
positively charged ions
a hormone secreted by the thyroid gland that regulates blood calcium by lowering it when levels rise too high
carcinogens
the basic structural unit of all living things
the green pigment of plants, which absorbs light and transfers the energy to other molecules, thereby initiating photosynthesis
calcium
the volume of blood discharged by the heart each minute; determined by multiplying the stroke volume by the heart rate. The stroke volume is the amount of oxygenated blood the heart ejects towards the tissues at each beat
that facilitates calcium binding and absorption
calcitonin
the most abundant mineral in the body; found primarily in the body’s bones and teeth
calcium rigor hardness or stiffness of the muscles caused by high blood calcium concentrations
substances that can cause cancer (the adjective is carcinogenic)
cardiac output
cardiorespiratory conditioning
calcium tetany intermittent spasm of the extremities due to nervous and muscular excitability caused by low blood calcium concentrations
cancers malignant growths or tumours that result from abnormal and uncontrolled cell division
improvements in heart and lung function and increased blood volume, brought about by aerobic training
cardiorespiratory endurance the ability to perform largemuscle, dynamic exercise of moderate-to-high intensity for prolonged periods
cardiovascular disease (CVD)
capillaries small vessels that branch from an artery. Capillaries connect arteries to veins. Exchange of oxygen, nutrients and waste materials takes place across capillary walls
carbohydrate loading a regimen of moderate exercise followed by the consumption of a highcarbohydrate diet that enables muscles to store glycogen beyond their normal capacities; also called glycogen loading or glycogen super compensation
carbohydrates compounds composed of carbon, oxygen and hydrogen arranged as monosaccharides or multiples of monosaccharides. Most, but not all, carbohydrates have a ratio of one carbon molecule to one water molecule
carbonated water water that contains carbon dioxide gas, either naturally occurring or added, that causes bubbles to form in it; also called bubbling or sparkling water. Seltzer, soda and tonic waters are legally soft drinks and are not regulated as water
carbonic acid a compound with the formula H2CO3 that results from the combination of carbon dioxide (CO2) and water (H2O); of particular importance in maintaining the body’s acid–base balance
a general term for all diseases of the heart and blood vessels. Atherosclerosis is the main cause of CVD. When the arteries that carry blood to the heart muscle become blocked, the heart suffers damage known as coronary heart disease (CHD)
carnitine a non-essential, non-protein amino acid made in the body from lysine; it helps transport fatty acids across the mitochondrial membrane
carotenoids pigments commonly found in plants and animals, some of which have vitamin A activity. The carotenoid with the greatest vitamin A activity is beta-carotene
cell
cell differentiation the process by which immature cells develop specific functions different from those of the original that are characteristic of their mature cell type
cell membrane the thin layer of tissue that surrounds the cell and encloses its contents; made primarily of lipid and protein
cellulite supposedly a lumpy form of fat; actually, a fraud. Fatty areas of the body may appear lumpy when the strands of connective tissue that attach the skin to underlying muscles pull tight where the fat is thick. The fat itself is the same as fat anywhere else in the body. If the fat in these areas is lost, the lumpy appearance disappears
central nervous system the central part of the nervous system; the brain and spinal cord
central obesity excess fat around the trunk of the body; also called abdominal fat or upper-body fat
CHD risk equivalents disorders that raise the risk of heart attacks, strokes and other complications associated with cardiovascular disease to the same degree as existing CHD. These disorders include symptomatic carotid artery disease, peripheral arterial disease, abdominal aortic aneurysm and diabetes mellitus
cholecystokinin, or CCK a hormone produced by cells of the intestinal wall. Target organ: the gall bladder. Response: release of bile and slowing of GI motility
cholesterol one of the sterols containing a four-ring carbon structure with a carbon side chain
choline a nitrogen-containing compound found in foods and made in the body from the amino acid methionine. Choline is part of the phospholipid lecithin and the neurotransmitter acetylcholine
chromium picolinate a trace mineral supplement; falsely promoted as building muscle, enhancing energy and burning fat. Picolinate is a derivative of the amino acid tryptophan that seems to enhance chromium absorption
chromosomes structures within the nucleus of a cell made of DNA and associated proteins. Human beings have 46 chromosomes in 23 pairs. Each chromosome has many genes
chronic diseases diseases characterised by a slow progression and long duration. Examples include heart disease, cancer and diabetes
chronic PEM protein–energy malnutrition caused by long-term food deprivation; characterised in children by short height for age (stunting)
chelate
chronological age
a substance that can grasp the positive ions of a mineral
a person’s age in years from their date of birth
chelation therapy
chylomicrons
reactions in which large molecules are broken down to smaller ones; catabolic reactions release energy
the use of ethylenediaminetetraacetic acid (EDTA) to bind with metallic ions, thus healing the body by removing toxic metals
the class of lipoproteins that transport lipids from the intestinal cells to the rest of the body
catalyst
chiropractic
a compound that facilitates chemical reactions without itself being changed in the process
a manual healing method of manipulating the spine to restore health
cataract
chloride
thickening of the eye lens that impairs vision and can lead to blindness
the major anion in the extracellular fluids of the body. Chloride is the ionic form of chlorine, Cl2. See Appendix B for a description of the chlorine-tochloride conversion
cartilage therapy the use of cleaned and powdered connective tissue, such as collagen, to improve health
catabolism
cathartic an agent that promotes evacuation of the bowel
chyme the semiliquid mass of partly digested food expelled by the stomach into the duodenum
cirrhosis advanced liver disease in which liver cells turn orange, die and harden, permanently losing their function; often associated with alcoholism
cis on the near side of; refers to a chemical configuration in which
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Glossary
the hydrogen atoms are located on the same side of a double bond
missing from one are supplied by the other
clinically severe obesity
complex carbohydrates (starches and fibres)
a BMI of 40 kg/m2 or greater or a BMI of 35 kg/m2 or greater with additional medical problems. A less preferred term used to describe the same condition is morbid obesity
CoA coenzyme A; the coenzyme derived from the B vitamin pantothenic acid and central to energy metabolism
coenzyme Q10 a lipid found in cells (mitochondria) shown to improve exercise performance in patients with heart disease, but not effective in improving the performance of healthy athletes
coenzymes complex organic molecules that work with enzymes to facilitate the enzymes’ activity. Many coenzymes have B vitamins as part of their structures
colitis inflammation of the colon
collagen the protein from which connective tissues such as scars, tendons, ligaments and the foundations of bones and teeth are made
colonic irrigation
polysaccharides composed of straight or branched chains of monosaccharides
compound a substance composed of two or more different atoms; for example, water (H2O)
conception the union of the male sperm and the female ovum; fertilisation
condensation a chemical reaction in which two reactants combine to yield a larger product
conditionally essential amino acid an amino acid that is normally non-essential but must be supplied by the diet in special circumstances when the need for it exceeds the body’s ability to produce it
conditionally essential nutrient a nutrient that is normally non-essential, but must be supplied by the diet in special circumstances when the need for it exceeds the body’s ability to produce it
conjugated linoleic acid
the popular but potentially harmful practice of ‘washing’ the large intestine with a powerful enema machine
a collective term for several fatty acids that have the same chemical formula as linoleic acid (18 carbons, two double bonds) but with different configurations
colostrum
constipation
a milk-like secretion from the breast, present during the first day or so after delivery before milk appears; rich in protective factors
the condition of having infrequent or difficult bowel movements
complementary and alternative medicine (CAM) diverse medical and healthcare systems, practices and products that are not currently considered part of conventional medicine; also called adjunctive, unconventional or unorthodox therapies
complementary medicine an approach that uses alternative therapies as an adjunct to, and not simply a replacement for, conventional medicine
complementary proteins two or more dietary proteins whose amino acid assortments complement each other in such a way that the essential amino acids
contaminants substances that make a food impure and unsuitable for ingestion
contamination iron iron found in foods as the result of contamination by inorganic iron salts from iron cookware, ironcontaining soils and the like
control group a group of individuals similar in all possible respects to the experimental group except for the treatment. Ideally, the control group receives a placebo while the experimental group receives a real treatment
conventional medicine diagnosis and treatment of diseases as practised by medical doctors (MBBS) and allied health professionals such as physical
therapists and registered nurses; also called Western, mainstream, orthodox or regular medicine
cool-down 5 to 10 minutes of light activity, such as walking or stretching, following a vigorous workout to gradually return the body’s core to near-normal temperature
Cori cycle the path from muscle glycogen to glucose to pyruvate to lactate (which travels to the liver) to glucose (which can travel back to the muscle) to glycogen; named after the scientist who elucidated this pathway
corn sweeteners corn syrup and sugars derived from corn
corn syrup a syrup made from cornstarch that has been treated with acid, high temperatures and enzymes that produce glucose, maltose and dextrins (see also high fructose corn syrup [HFCS])
cornea the transparent membrane covering the outside of the eye
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CP, creatine phosphate (also called phosphocreatine) a high-energy compound in muscle cells that acts as a reservoir of energy that can maintain a steady supply of ATP; CP provides the energy for short bursts of activity
C-reactive protein (CRP) a protein released during the acute phase of infection or inflammation that enhances immunity by promoting phagocytosis and activating platelets. Its presence may be used to assess a person’s risk of an impending heart attack or stroke
creatine a nitrogen-containing compound that combines with phosphate to form the highenergy compound creatine phosphate (or phosphocreatine) in muscles. Claims that creatine enhances energy use and muscle strength need further confirmation
cretinism
blood vessels that supply blood to the heart
a congenital disease characterised by mental and physical retardation and commonly caused by maternal iodine deficiency during pregnancy
coronary heart disease (CHD)
critical periods
coronary arteries
the damage that occurs when the blood vessels carrying blood to the heart (the coronary arteries) become narrow and occluded
correlation the simultaneous increase, decrease or change in two variables. If A increases as B increases, or if A decreases as B decreases, the correlation is positive. (This does not mean that A causes B or vice versa.) If A increases as B decreases, or if A decreases as B increases, the correlation is negative. (This does not mean that A prevents B or vice versa.) Some third factor may account for both A and B
cortical bone
finite periods during development in which certain events occur that will have irreversible effects on later developmental stages; usually a period of rapid cell division
cross-contamination (of food) the contamination of food by bacteria that occurs when the food comes into contact with surfaces previously touched by raw meat, poultry or seafood
cruciferous vegetables vegetables of the cabbage family, including cauliflower, broccoli and brussels sprouts
crypts
the very dense bone tissue that forms the outer shell surrounding trabecular bone and comprises the shaft of a long bone
tubular glands that lie between the intestinal villi and secrete intestinal juices into the small intestine
coupled reactions
cyclamate
pairs of chemical reactions in which some of the energy released from the breakdown of one compound is used to create a bond in the formation of another compound
covert hidden, as if under covers
an artificial sweetener that has been approved for use in Australia and New Zealand
cytokines special proteins that direct immune and inflammatory responses
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776
Glossary
cytoplasm
diarrhoea
distilled liquor or hard liquor
dysphagia
the cell contents, except for the nucleus
the frequent passage of watery bowel movements
difficulty in swallowing
cytosol
diet
an alcoholic beverage made by fermenting and distilling grains; sometimes called distilled spirits
the fluid of cytoplasm; contains water, ions, nutrients and enzymes
the foods and beverages a person eats and drinks
diet history a record of eating behaviours and the foods a person eats
deamination removal of the amino (NH2) group from a compound such as an amino acid
defecate to move the bowels and eliminate waste
deficient (nutrient) the amount of a nutrient below which almost all healthy people can be expected, over time, to experience deficiency symptoms
dehydration the condition in which body water output exceeds water input. Symptoms include thirst, dry skin and mucous membranes, rapid heartbeat, low blood pressure and weakness
denaturation the change in a protein’s shape and consequent loss of its function brought about by heat, agitation, acid, base, alcohol, heavy metals or other agents
dietary fibres in plant foods, the non-starch polysaccharides that are not digested by human digestive enzymes, although some are digested by GI tract bacteria. Dietary fibres include cellulose, hemicelluloses, pectins, gums and mucilages, and the nonpolysaccharides lignins, cutins and tannins
dietary folate equivalents (DFE) the amount of folate available to the body from naturally occurring sources, fortified foods and supplements, accounting for differences in the bioavailability from each source
dietitian a person trained in nutrition, food science and diet therapy. See also Accredited Practising Dietitian (APD)
Dietitians Association of Australia (DAA)
decay of teeth
the professional organisation representing dietitians in Australia
dental plaque
digestion
dental caries
a gummy mass of bacteria that grows on teeth and can lead to dental caries and gum disease
the process by which food is broken down into absorbable units
dextrose
proteins found in digestive juices that act on food substances, causing them to break down into simpler compounds
an older name for glucose
DHEA (dehydroepiandrosterone) hormone made in the adrenal glands that serve as precursors to the male hormone testosterone; falsely promoted as burning fat, building muscle and slowing ageing. Side effects include acne, aggressiveness and liver enlargement
diabetes a chronic disorder of carbohydrate metabolism, usually resulting from insufficient or ineffective insulin
diabetes mellitus a group of metabolic diseases characterised by hyperglycaemia and resulting from defects in insulin secretion, insulin action or both
digestive enzymes
digestive system all the organs and glands associated with the ingestion and digestion of food
dipeptide
distilled water water that has been vaporised and recondensed, leaving it free of dissolved minerals
diverticula sacs or pouches that develop in the weakened areas of the intestinal wall (like bulges in an inner tube where the tyre wall is weak)
diverticulitis infected or inflamed diverticula; the condition of having diverticula. About one in every six people in Western countries develops diverticulitis in middle or later life
DNA (deoxyribonucleic acid) the double helix molecules of which genes are made
docosahexaenoic acid (DHA) an omega-3 polyunsaturated fatty acid with 22 carbons and six double bonds; present in fish and synthesised in limited amounts in the body from alpha-linolenic acid
dolomite a compound of minerals (calcium magnesium carbonate) found in limestone and marble. Dolomite is powdered and is sold as a calcium–magnesium supplement. However, it may be contaminated with toxic minerals, is not well absorbed, and interacts adversely with absorption of other essential minerals
double-blind experiment an experiment in which neither the subjects nor the researchers know which subjects are members of the experimental group and which are serving as control subjects, until after the experiment is over
Down syndrome a genetic abnormality that causes mental retardation, short stature and flattened facial features
two amino acids bonded together
drink (one standard)
disaccharides
a dose of any alcoholic beverage that delivers 10 g of pure ethanol
pairs of monosaccharides linked together (see Appendix C for the chemical structures of the disaccharides)
disordered eating eating behaviours that are neither normal nor healthy, including restrained eating, fasting, binge eating and purging
dissociates physically separates
eating disorders disturbances in eating behaviour that jeopardise a person’s physical or psychological health
eclampsia a severe stage of pre-eclampsia characterised by convulsions
ectopic fat excess fat in locations other than adipose tissue
eicosanoids derivatives of 20-carbon fatty acids; biologically active compounds that help to regulate blood pressure, blood clotting and other body functions. They include prostaglandins, thromboxanes and leukotrienes
eicosapentaenoic acid (EPA) an omega-3 polyunsaturated fatty acid with 20 carbons and five double bonds; present in fish and synthesised in limited amounts in the body from alphalinolenic acid
electrolyte solutions solutions that can conduct electricity
electrolytes salts that dissolve in water and dissociate into charged particles called ions
electron transport chain the final pathway in energy metabolism that transports electrons from hydrogen to oxygen and captures the energy released in the bonds of ATP
element a substance composed of atoms that are alike; for example, iron (Fe)
embolism the obstruction of a blood vessel by an embolus, or travelling clot, causing sudden tissue death
embryo the developing infant from two to eight weeks after conception
emerging risk factors
a substance that can modify one or more of the body’s functions
recently identified factors that enhance the ability to predict disease risk in an individual
duodenum
emetic
the first portion of the small intestine (about ‘12 fingers’ breadth’ long in ancient terminology)
empty-kilojoule foods
drug
dysentery an infection of the digestive tract that causes diarrhoea
an agent that causes vomiting a popular term used to denote foods that contribute energy but lack protein, vitamins and minerals
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Glossary
emulsifier a substance with both watersoluble and fat-soluble portions that promotes the mixing of oils and fats in a watery solution
endogenous from within the body
endoplasmic reticulum a complex network of intracellular membranes. The rough endoplasmic reticulum is dotted with ribosomes, where protein synthesis takes place; the smooth endoplasmic reticulum bears no ribosomes
enemas solutions inserted into the rectum and colon to stimulate a bowel movement and empty the lower large intestine
energy the capacity to do work. The energy in food is chemical energy. The body can convert this chemical energy to mechanical, electrical or heat energy
that attacks many people at the same time in the same region
epigenetics the study of heritable changes in gene function that occur without a change in the DNA sequence
epiglottis cartilage in the throat that guards the entrance to the trachea and prevents fluid or food from entering it when a person swallows
epithelial cells cells on the surface of the skin and mucous membranes
epithelial tissue the layer of the body that serves as a selective barrier between the body’s interior and the environment; examples are the cornea of the eyes, the skin, the respiratory lining of the lungs, and the lining of the digestive tract.
ergogenic aids
management of food energy intake
substances or techniques used in an attempt to enhance physical performance
energy density
erythrocyte haemolysis
energy (kilojoule) control
a measure of the energy a food provides relative to the amount of food (kilojoules per gram)
energy-yielding nutrients
the breaking open of red blood cells (erythrocytes); a symptom of vitamin E-deficiency disease in human beings
the nutrients that break down to yield energy the body can use
erythrocyte protoporphyrin
enhanced water
erythropoietin
water that is fortified with ingredients such as vitamins, minerals, protein, oxygen, or herbs. Enhanced water is marketed as vitamin water, sports water, oxygenated water and protein water
a precursor to haemoglobin a hormone that stimulates red blood cell production
essential amino acids amino acids that the body cannot synthesise in amounts sufficient to meet physiological needs
essential fatty acids
enriched the addition to a food of nutrients that were lost during processing so that the food will meet a specified standard
enteropancreatic circulation the circulatory route from the pancreas to the intestine and back to the pancreas
enzymes proteins that facilitate chemical reactions without being changed in the process; protein catalysts
EPA (Environmental Protection Agency) each Australian state has its own EPA that is responsible for, among other things, water quality
epidemic the appearance of a disease (usually infectious) or condition
fatty acids needed by the body but not made by it in amounts sufficient to meet physiological needs
essential nutrients nutrients a person must obtain from food because the body cannot make them for itself in sufficient quantity to meet physiological needs; also called indispensable nutrients. About 40 nutrients are currently known to be essential for human beings
Estimated Average Requirement (EAR) the average daily amount of a nutrient that will maintain a specific biochemical or physiological function in half the healthy people of a given age and gender group
Estimated Energy Requirement (EER) the average dietary energy intake that maintains energy balance and good health in a person of a given age, gender, weight, height and level of physical activity
ethanol a particular type of alcohol found in beer, wine and distilled liquor; also called ethyl alcohol (see Figure H7.1). Ethanol is the most widely used – and abused – drug in our society. It is also the only legal, non-prescription drug that produces euphoria
exercise planned, structured and repetitive body movements that promote or maintain physical fitness
exogenous from outside the body
experimental group a group of individuals similar in all possible respects to the control group except for the treatment. The experimental group receives the real treatment
extracellular fluid fluid outside the cells. It includes two main components – the interstitial fluid and the plasma – and accounts for approximately one-third of the body’s water
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fat replacers ingredients that replace some or all of the functions of fat and may or may not provide energy
fats lipids that are solid at room temperature (25 °C)
fatty acid an organic compound composed of a carbon chain with hydrogens attached and an acid group (COOH) at one end and a methyl group (CH3) at the other end
fatty acid oxidation the metabolic breakdown of fatty acids to acetyl CoA; also called beta oxidation
fatty liver an early stage of liver deterioration seen in several diseases, including kwashiorkor and alcoholic liver disease. Fatty liver is characterised by an accumulation of fat in the liver cells
fatty streaks accumulations of cholesterol and other lipids along the walls of the arteries
female athlete triad a potentially fatal combination of three medical problems – disordered eating, amenorrhea and osteoporosis
fermentable fad diets popular eating plans that promise quick weight loss. Most fad diets severely limit certain foods or overemphasise others (for example, never eat potatoes or pasta, or eat cabbage soup daily)
faith healing healing by invoking divine intervention without the use of medical, surgical or other traditional therapy
false negative a test result indicating that a condition is not present (negative) when in fact it is present (therefore false)
false positive a test result indicating that a condition is present (positive) when in fact it is not (therefore false)
FAO (Food and Agriculture Organization) an international agency (part of the United Nations) that has adopted standards to regulate pesticide use, among other responsibilities (www.fao.org)
the extent to which bacteria in the GI tract can break down fibre into fragments that the body can use
ferritin the iron storage protein
fertility the capacity of a woman to produce and release a normal ovum periodically and of a man to produce normal sperm; the ability to reproduce
fibrocystic breast disease a harmless condition in which the breasts develop lumps, sometimes associated with caffeine consumption. In some, it responds to abstinence from caffeine; in others, it can be treated with vitamin E
fibrosis an intermediate stage of liver deterioration seen in several diseases, including viral hepatitis and alcoholic liver disease. In fibrosis, the liver cells lose their function and assume the characteristics of connective tissue cells (fibres)
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778
Glossary
filtered water
folate
water treated by filtration, usually through activated carbon filters that reduce the lead in tap water, or by reverse osmosis units that force pressurised water across a membrane removing lead, arsenic and some microorganisms from tap water
a B vitamin; also known as folic acid, folacin or pteroylglutamic acid (PGA). The coenzyme forms are DHF (dihydrofolate) and THF (tetrahydrofolate)
fitness the characteristics that enable the body to perform physical activity; more broadly, the ability to meet routine physical demands with enough reserve energy to rise to a physical challenge; or the body’s ability to withstand stress of all kinds
flavonoids yellow pigments in foods; phytochemicals that may exert physiological effects on the body
flaxseeds the small brown seeds of the flax plant; valued as a source of linseed oil, fibre and omega-3 fatty acids
follicle-stimulating hormone (FSH) a hormone that stimulates maturation of the ovarian follicles in females and the production of sperm in males. (The ovarian follicles are part of the female reproductive system where the eggs are produced.) The release of FSH is mediated by folliclestimulating hormone releasing hormone (FSH-RH)
food allergy an adverse reaction to food that involves an immune response
food aversions strong desires to avoid particular foods
body to yield energy and nutrients for the maintenance of life and the growth and repair of tissues
contracts and squirts bile through the bile duct into the duodenum
fortified
a plant sterol that supposedly provides the same physical responses as anabolic steroids without the adverse side effects; also known as ferulic acid, ferulate or FRAC
the addition to a food of nutrients that were either not originally present or present in insignificant amounts. Fortification can be used to correct or prevent a widespread nutrient deficiency or to balance the total nutrient profile of a food
fraudulent the promotion, for financial gain, of devices, treatments, services, plans or products (including diets and supplements) that alter or claim to alter a human condition without proof of safety or effectiveness. (The word quackery comes from the term quacksalver, meaning a person who quacks loudly about a miracle product – a lotion or a salve)
free radicals
flexibility
food chain
the capacity of the joints to move through a full range of motion; the ability to bend and recover without injury
the sequence in which living things depend on other living things for food
unstable and highly reactive atoms or molecules that have one or more unpaired electrons in the outer orbit. (See Appendix B for a review of basic chemistry concepts)
fluid balance
food cravings strong desires to eat particular foods
fructose
maintenance of the proper types and amounts of fluid in each compartment of the body fluids (see Chapter 12)
fluorapatite the stabilised form of bone and tooth crystal, in which fluoride has replaced the hydroxyl groups of hydroxyapatite
fluorosis discoloration and pitting of tooth enamel caused by excess fluoride during tooth development
foetal alcohol spectrum disorder a range of physical, behavioural and cognitive abnormalities caused by prenatal alcohol exposure
foetal alcohol syndrome (FAS) a cluster of physical, behavioural and cognitive abnormalities associated with prenatal alcohol exposure, including facial malformations, growth retardation and central nervous disorders
food frequency questionnaire a checklist of foods on which a person can record the frequency with which they eat each food
gastric glands exocrine glands in the stomach wall that secrete gastric juice into the stomach
gastric juice the digestive secretion of the gastric glands of the stomach
gastrin a hormone secreted by cells in the stomach wall. Target organ: the glands of the stomach. Response: secretion of gastric acid
gastrointestinal (GI) tract the digestive tract; the principal organs are the stomach and intestines
gastro-oesophageal reflux the backflow of stomach acid into the oesophagus, causing damage to the cells of the oesophagus and the sensation of heartburn. Gastro-oesophageal reflux disease (GORD) is characterised by symptoms of reflux occurring two or more times a week
FSANZ (Food Standards Australia New Zealand)
gene expression
diet-planning tools that sort foods into groups based on nutrient content and then specify that people should eat certain amounts of foods from each group
a bi-national government agency that develops and administers the Australia New Zealand Food Standards Code, which lists requirements for foods (www. foodstandards.gov.au)
gene pool
food intolerances
fuel
food group plans
adverse reactions to foods that do not involve the immune system
food record an extensive, accurate log of all foods eaten over a period of several days or weeks. A food record that includes associated information such as when, where and with whom each food is eaten is sometimes called a food diary
food-borne illness
the influence of substances during foetal growth on the development of diseases in later life
illness transmitted to human beings through food and water, caused by either an infectious agent (food-borne infection) or a poisonous substance (food toxin); commonly known as food poisoning
foetus
foods
the developing infant from eight weeks after conception until birth
products derived from plants or animals that can be taken into the
foetal programming
a monosaccharide; sometimes known as fruit sugar or levulose. Fructose is found abundantly in fruits, honey and saps
gamma-oryzanol
compounds that cells can use for energy. The major fuels include glucose, fatty acids and amino acids; other fuels include ketone bodies, lactate, glycerol and alcohol
functional foods foods that contain physiologically active compounds that provide health benefits beyond their nutrient contributions; sometimes called designer foods or nutraceuticals
galactose a monosaccharide; part of the disaccharide lactose
gall bladder the organ that stores and concentrates bile. When it receives the signal that fat is present in the duodenum, the gall bladder
the process by which a cell converts the genetic code into RNA and protein all the genetic information of a population at a given time
genes sections of chromosomes that contain the instructions needed to make one or more proteins
genetic engineering the use of biotechnology to modify the genetic material of living cells so that they will produce new substances or perform new functions. Foods produced via this technology are called genetically modified (GM) or genetically engineered (GE) foods
genome the full complement of genetic material (DNA) in the chromosomes of a cell. In human beings, the genome consists of 46 chromosomes. The study of genomes is called genomics
genomics the study of all the genes in an organism and their interactions with environmental factors
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Glossary
gestation
manufactured and stored in the liver and muscles as a storage form of glucose. Glycogen is not a significant food source of carbohydrate and is not counted as one of the complex carbohydrates in foods
haemochromatosis
the period from conception to birth. For human beings, the average length of a healthy gestation is 40 weeks. Pregnancy is often measured in three-month periods, called trimesters
gestational diabetes
glycolysis
the globular protein of the red blood cells that carries oxygen from the lungs to the cells throughout the body
abnormal glucose tolerance during pregnancy
ghrelin a protein produced by the stomach cells that enhances appetite and decreases energy expenditure
ginseng a plant whose extract supposedly boosts energy. Side effects of chronic use include nervousness, confusion and depression
glands cells or groups of cells that secrete materials for special uses in the body. Glands may be exocrine glands, secreting their materials ‘out’ (into the digestive tract or onto the surface of the skin), or endocrine glands, secreting their materials ‘in’ (into the blood)
the metabolic breakdown of glucose to pyruvate. Glycolysis does not require oxygen (anaerobic)
goblet cells
a hormone that is secreted by special cells in the pancreas in response to low blood glucose concentration and elicits the release of glucose from liver glycogen stores
gluconeogenesis the making of glucose from a noncarbohydrate source
glucose a monosaccharide; sometimes known as blood sugar or dextrose
glucose polymers compounds that supply glucose, not as single molecules, but linked in chains somewhat like starch. The objective is to attract less water from the body into the digestive tract (osmotic attraction depends on the number, not the size, of particles)
glycaemic index a method of classifying foods according to their potential for raising blood glucose
glycaemic response the extent to which a food raises the blood glucose concentration and elicits an insulin response
glycerol an alcohol composed of a threecarbon chain, which can serve as the backbone for a triglyceride
glycogen an animal polysaccharide composed of glucose;
haemoglobin
haemolytic anaemia
cells of the GI tract (and lungs) that secrete mucus
the condition of having too few red blood cells as a result of erythrocyte haemolysis
goitre
haemophilia
an enlargement of the thyroid gland due to an iodine deficiency, malfunction of the gland, or overconsumption of a goitrogen. Goitre caused by iodine deficiency is simple goitre
goitrogen a substance that enlarges the thyroid gland and causes toxic goitre. Goitrogens occur naturally in foods such as cabbage, kale, brussels sprouts, cauliflower and broccoli
Golgi apparatus
glucagon
a genetically determined failure to prevent absorption of unneeded dietary iron that is characterised by iron overload and tissue damage
a set of membranes within the cell where secretory materials are packaged for export
good source of fibre the food must not contain less than 4 g of dietary fibre per serving of food
gout a common form of arthritis characterised by deposits of uric acid crystals in the joints
granulated sugar crystalline sucrose; 99.9 per cent pure
growth hormone (GH) a hormone secreted by the pituitary that regulates the cell division and protein synthesis needed for normal growth (also called somatotropin). The release of GH is mediated by GH releasing hormone (GHRH) and GH inhibiting hormone (GHIH)
haem the iron-holding part of the haemoglobin and myoglobin proteins. About 40% of the iron in meat, fish and poultry is bound into haem; the other 60% is nonhaem iron
haematocrit measurement of the volume of the red blood cells packed by centrifuge in a given volume of blood
a hereditary disease in which the blood is unable to clot because it lacks the ability to synthesise certain clotting factors
haemorrhagic disease a disease characterised by excessive bleeding
haemorrhoids painful swelling of the veins surrounding the rectum
haemosiderin an iron-storage protein primarily made in times of iron overload
haemosiderosis a condition characterised by the deposition of haemosiderin in the liver and other tissues
hard water water with a high calcium and magnesium content
hazard a source of danger; used to refer to circumstances in which harm is possible under normal conditions of use
Hazard Analysis Critical Control Points (HACCP) a systematic plan to identify and correct potential microbial hazards in the manufacturing, distribution and commercial use of food products (pronounced ‘hassip’)
HDL (high-density lipoprotein) the type of lipoprotein that transports cholesterol back to the liver from the cells; composed primarily of protein
health claims statements that may characterise the relationship between a nutrient or other substance in a food and a disease or healthrelated condition
heart attack sudden tissue death caused by blockages of vessels that feed
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the heart muscle; also called myocardial infarction
heartburn a burning sensation in the chest area caused by backflow of stomach acid into the oesophagus
heat stroke a dangerous accumulation of body heat with accompanying loss of body fluid
heavy metals mineral ions such as mercury and lead, so called because they are of relatively high atomic weight. Many heavy metals are poisonous
hepatic portal vein the vein that collects blood from the GI tract and conducts it to capillaries in the liver
hepatic vein the vein that collects blood from the liver capillaries and returns it to the heart
hepcidin a hormone produced by the liver that regulates iron balance
herbal medicine the use of plants to treat disease or improve health; also known as botanical medicine or phytotherapy
hGH (human growth hormone) a hormone produced by the brain’s pituitary gland that regulates normal growth and development; also called somatotropin. Some athletes misuse this hormone to increase their height and strength
hiccups repeated cough-like sounds and jerks that are produced when an involuntary spasm of the diaphragm muscle sucks air down the windpipe (also spelled hiccoughs)
high potency (of a supplement) contains 100% or more of the RDI for the nutrient in a single supplement and at least twothirds of the nutrients in a multinutrient supplement
high-fructose corn syrup (HFCS) a syrup made from cornstarch that has been treated with an enzyme that converts some of the glucose to the sweeter fructose; made especially for use in processed foods and beverages, where it is the predominant sweetener. With a chemical structure similar to sucrose, HFCS has a fructose content of 42, 55 or 90 per cent, with glucose making up the remainder
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780
Glossary
high-quality proteins dietary proteins containing all the essential amino acids in relatively the same amounts that human beings require. They may also contain non-essential amino acids
high-risk pregnancy a pregnancy characterised by indicators that make it likely the birth will be surrounded by problems such as premature delivery, difficult birth, retarded growth, birth defects and early infant death
histamine a substance produced by cells of the immune system as part of a local immune reaction to an antigen; participates in causing inflammation
HMB (beta-hydroxy-betamethylbutyrate) a metabolite of the branchedchain amino acid leucine. Claims that HMB increases muscle mass and strength are based on the results of two studies from the lab that developed HMB as a supplement
homoeopathy a practice based on the theory that ‘like cures like’; that is, that substances that cause symptoms in healthy people can cure those symptoms when given in very diluted amounts
homeostasis the maintenance of constant internal conditions (such as blood chemistry, temperature and blood pressure) by the body’s control systems. A homeostatic system is constantly reacting to external forces to maintain limits set by the body’s needs
honey sugar (mostly sucrose) formed from nectar gathered by bees. An enzyme splits the sucrose into glucose and fructose. Composition and flavour vary, but honey always contains a mixture of sucrose, fructose and glucose
hormones chemical messengers. Hormones are secreted by a variety of glands in response to altered conditions in the body. Each hormone travels to one or more specific target tissues or organs, where it elicits a specific response to maintain homeostasis
hormone-sensitive lipase an enzyme inside adipose cells that responds to the body’s need for fuel by hydrolysing triglycerides so that their parts
(glycerol and fatty acids) escape into the general circulation and thus become available to other cells for fuel. The signals to which this enzyme responds include adrenaline and glucagon, which oppose insulin (see Chapter 4)
hourly sweat rate the amount of weight lost plus fluid consumed during exercise per hour
human genome
hyperglycaemia elevated blood glucose concentrations
emotional or spiritual state by visualising themselves in that state
hypertension
immune system
higher-than-normal blood pressure. Hypertension that develops without an identifiable cause is known as essential or primary hypertension; hypertension that is caused by a specific disorder such as kidney disease is known as secondary hypertension
the full complement of genetic material in the chromosomes of a person’s cells
hyperthermia
hunger
hypertrophy
the painful sensation caused by a lack of food that initiates foodseeking behaviour
hydrochloric acid an acid composed of hydrogen and chloride atoms (HCl); it is normally produced by the gastric glands
hydrogenation a chemical process by which hydrogens are added to monounsaturated or polyunsaturated fatty acids to reduce the number of double bonds, making the fats more saturated (solid) and more resistant to oxidation (protecting against rancidity). Hydrogenation produces transfatty acids
hydrolysis a chemical reaction in which a major reactant is split into two products, with the addition of a hydrogen atom (H) to one and a hydroxyl group (OH) to the other (from water, H2O) (The noun is hydrolysis; the verb is hydrolyse)
hydrophilic a term referring to water-loving, or water-soluble, substances
an above-normal body temperature growing larger; with regard to muscles, an increase in size (and strength) in response to use
hypnotherapy a technique that uses hypnosis and the power of suggestion to improve health behaviours, relieve pain and heal
hypoallergenic formulas clinically tested infant formulas that support infant growth and development but do not provoke reactions in 90% of infants or children with confirmed cow’s milk allergy
hypoglycaemia an abnormally low blood glucose concentration
hyponatraemia a decreased concentration of sodium in the blood
hypothalamus a brain centre that controls activities such as maintenance of water balance, regulation of body temperature and control of appetite
hypothermia
hydrophobic
a below-normal body temperature
a term referring to water-fearing, or non-water-soluble, substances; also known as lipophilic (fatloving)
hypothesis
hydrotherapy the use of water (in whirlpools, as douches or packed as ice, for example) to promote relaxation and healing
hydroxyapatite crystals made of calcium and phosphorus
hyperactivity inattentive and impulsive behaviour that is more frequent and severe than is typical of others a similar age; professionally called attention-deficit/hyperactivity disorder (ADHD)
an unproven statement that tentatively explains the relationships between two or more variables
icing sugar finely powdered sucrose, 99.9 per cent pure
ileocaecal valve the sphincter separating the small and large intestines
the body’s natural defence against foreign materials that have penetrated the skin or mucous membranes
immunity the body’s ability to defend itself against diseases (see Chapter 18)
immunoglobulins proteins capable of acting as antibodies
implantation the stage of development in which the zygote embeds itself in the wall of the uterus and begins to develop; occurs during the first two weeks after conception
indigestion incomplete or uncomfortable digestion, usually accompanied by pain, nausea, vomiting, heartburn, intestinal gas or belching
indirect or incidental additives substances that can get into food as a result of contact during growing, processing, packaging, storing, cooking or some other stage before the foods are consumed; sometimes called accidental additives
infectious diseases diseases caused by bacteria, viruses, parasites or other microorganisms that can be transmitted from one person to another through air, water or food; by contact; or through vector organisms such as mosquitoes
inflammaging characterised as a chronic, lowgrade inflammation that occurs as a person ages
inflammation an immunological response to cellular injury characterised by an increase in white blood cells
initiators factors that cause mutations that give rise to cancer, such as radiation and carcinogens
inorganic not containing carbon or pertaining to living things
inositol
the last segment of the small intestine
a non-essential nutrient that can be made in the body from glucose. Inositol is apart of cell membrane structures
imagery
insoluble fibre
ileum
a technique that guides clients to achieve a desired physical,
indigestible food components that do not dissolve in water; examples
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Glossary
are the tough, fibrous structures found in the strings of celery and the skins of corn kernels
(Cl2). (For a closer look at ions, see Appendix B)
insulin
the study of changes in the iris of the eye and their relationships to disease
a hormone secreted by special cells in the pancreas in response to (among other things) increased blood glucose concentration. The primary role of insulin is to control the transport of glucose from the bloodstream into the muscle and fat cells
insulin resistance the condition in which a normal amount of insulin produces a subnormal effect in muscle, adipose and liver cells, resulting in an elevated fasting glucose; a metabolic consequence of obesity that precedes type 2 diabetes
intentional food additives additives intentionally added to foods, such as nutrients, colours, and preservatives
intermittent claudication severe calf pain caused by inadequate blood supply. It occurs when walking and subsides during rest
iridology
iron deficiency the state of having depleted iron stores
iron overload toxicity from excess iron
iron-deficiency anaemia severe depletion of iron stores that results in low haemoglobin and small, pale red blood cells. Anaemias that impair haemoglobin synthesis are microcytic (small cell)
irradiation sterilising a food by exposure to energy waves, similar to ultraviolet light and microwaves
irritable bowel syndrome an intestinal disorder of unknown cause. Symptoms include abdominal discomfort and cramping, diarrhoea, constipation, or alternating diarrhoea and constipation
intestinal ischaemia a diminished blood flow to the intestines that is characterised by abdominal pain, forceful bowel movements, and blood in the stool
intra-abdominal fat fat stored within the abdominal cavity in association with the internal abdominal organs, as opposed to the fat stored directly under the skin (subcutaneous fat)
intracellular fluid fluid within the cells, usually high in potassium and phosphate. Intracellular fluid accounts for approximately two-thirds of the body’s water
intrinsic factor a glycoprotein (a protein with short polysaccharide chains attached) secreted by the stomach cells that binds with vitamin B12 in the small intestine to aid in the absorption of vitamin B12
ions atoms or molecules that have gained or lost electrons and therefore have electrical charges. Examples include the positively charged sodium ion (Na1) and the negatively charged chloride ion
an undesirably high concentration of ketone bodies in the blood and urine
kwashiorkor a form of PEM that results either from inadequate protein intake or, more commonly, from infections
lactadherin a protein in breast milk that attacks diarrhoea-causing viruses
lactase an enzyme that hydrolyses lactose
lactase deficiency a lack of the enzyme required to digest the disaccharide lactose into its component monosaccharides (glucose and galactose)
lactate a 3-carbon compound produced from pyruvate during anaerobic metabolism
lactation production and secretion of breast milk for the purpose of nourishing an infant
vocal cords; also called the voice box
laxatives substances that loosen the bowels and thereby prevent or treat constipation
LDL (low-density lipoprotein) the type of lipoprotein derived from very-low-density lipoproteins (VLDL) as VLDL triglycerides are removed and broken down; composed primarily of cholesterol
lean body mass the body minus its fat content
lecithin one of the phospholipids. Both nature and the food industry use lecithin as an emulsifier to combine water-soluble and fat-soluble ingredients that do not ordinarily mix, such as water and oil
legumes plants of the bean and pea family, with seeds that are rich in protein compared with other plant-derived foods
leptin
the first two-fifths of the small intestine beyond the duodenum
a protein in breast milk that binds iron and keeps it from supporting the growth of the infant’s intestinal bacteria
a protein produced by fat cells under direction of the ob gene that decreases appetite and increases energy expenditure; sometimes called the ob protein
joules
lacto-ovo-vegetarians
let-down reflex
lactoferrin
interstitial fluid fluid between the cells (intercellular), usually high in sodium and chloride. Interstitial fluid is a large component of extracellular fluid
ketosis
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jejunum
units by which energy is measured. Food energy is measured in kilojoules (1000 joules equals 1 kilojoule), abbreviated to kJ; 4.2 kilojoules (or 1 kcalorie) is the amount of heat necessary to raise the temperature of 1 kilogram (kg) of water 1°C
keratin a water-insoluble protein; the normal protein of hair and nails
keratinisation accumulation of keratin in a tissue; a sign of vitamin A deficiency
keratomalacia softening of the cornea that leads to irreversible blindness; seen in severe vitamin A deficiency
keto acid an organic acid that contains a carbonyl group (C−O)
ketone bodies the product of the incomplete breakdown of fat when glucose is not available in the cells
people who include milk, milk products and eggs, but exclude meat, poultry, fish and seafood from their diets
the reflex that forces milk to the front of the breast when the infant begins to nurse
lactose a disaccharide composed of glucose and galactose; commonly known as milk sugar
products of eicosanoid metabolism with several physiologic roles, such as mediation of inflammation
lactose intolerance
levulose
a condition that results from inability to digest the milk sugar lactose; characterised by bloating, gas, abdominal discomfort and diarrhoea. Lactose intolerance differs from milk allergy, which is caused by an immune reaction to the protein in milk
lacto-vegetarians people who include milk and milk products, but exclude meat, poultry, fish, seafood and eggs from their diets
large intestine or colon the lower portion of intestine that completes the digestive process. Its segments are the ascending colon, the transverse colon, the descending colon and the sigmoid colon
larynx the upper part of the air passageway that contains the
leukotrienes
an older name for fructose
life expectancy the average number of years lived by people in a given society
life span the maximum number of years of life attainable by a member of a species
lignans phytochemicals present in flaxseed, but not in flax oil, that are converted to phytosterols by intestinal bacteria and are under study as possible anticancer agents
limiting amino acid the essential amino acid found in the shortest supply relative to the amounts needed for protein synthesis in the body. Four amino acids are most likely to be limiting:
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Glossary
lysine, methionine, threonine and tryptophan
linoleic acid an essential fatty acid with 18 carbons and two double bonds
lipase enzymes that hydrolyse lipids. Lingual lipase is a fat-digesting enzyme secreted from the salivary gland at the base of the tongue; gastric lipase is a fat-digesting enzyme secreted from the cells of the stomach
lipids a family of compounds that includes triglycerides, phospholipids and sterols; characterised by their insolubility in water
lipoprotein lipase (LPL) an enzyme that hydrolyses triglycerides passing by in the bloodstream and directs their parts into the cells, where they can be metabolised for energy or reassembled for storage
lipoproteins clusters of lipids associated with proteins that serve as transport vehicles for lipids in the lymph and blood
listeriosis an infection caused by eating food contaminated with the bacterium Listeria monocytogenes, which can be killed by pasteurisation and cooking but can survive at refrigerated temperatures; certain ready to-eat foods, such as soft cheeses and deli meats, may become contaminated after cooking or processing, but before packaging
liver the organ that manufactures bile. (The liver’s many other functions are described in Chapter 7)
longevity long duration of life
lorcaserin a prescription drug used for weight loss in those who are obese. It acts through the serotonin uptake system in the brain
low birth weight (LBW) a birth weight of 2500 g or less; indicates probable poor health in the newborn and poor nutrition status in the mother during pregnancy, before pregnancy or both. Normal birth weight for a full-term baby is about 3000 to 4000 g
low cholesterol or low in cholesterol The food must not contain more than 20 mg cholesterol per 100 g
of solid food or 10 mg per 100 ml of liquid food and must meet the conditions for a nutrition content claim about low saturated fatty acids
lymphocytes
low fat or low in fat
cellular organelles; membraneenclosed sacs of degradative enzymes
the food must not contain more than 3 g of fat per 100 g of solid food (or 1.5 g of fat per 100 mL of liquid food)
low in salt low in salt means the food contains less than 120 mg of sodium per100 g or 100 mL
low sugar or low in sugar the food must not contain more than 5 g of sugar per 100 g of solid food or 2.5 g of fat per 100 mL of liquid food
low-risk pregnancy a pregnancy characterised by indicators that make a normal outcome likely
lumen the space within a vessel, such as the intestine
lutein a plant pigment of yellow hue; a phytochemical believed to play roles in eye functioning and health
luteinising hormone (LH) a hormone that stimulates ovulation and the development of the corpus luteum (the small tissue that develops from a ruptured ovarian follicle and secretes hormones); so called because the follicle turns yellow as it matures. In men, LH stimulates testosterone secretion. The release of LH is mediated by luteinising hormone-releasing hormone (LH-RH)
lycopene a pigment responsible for the red colour of tomatoes and other redhued vegetables; a phytochemical that may act as an antioxidant in the body
lymph a clear yellowish fluid that is similar to blood except that it contains no red blood cells or platelets. Lymph from the GI tract transports fat and fat-soluble vitamins to the bloodstream via lymphatic vessels
lymphatic system a loosely organised system of vessels and ducts that convey fluids towards the heart. The GI part of the lymphatic system carries the products of fat digestion into the bloodstream
white blood cells that participate in acquired immunity; B-cells and T-cells
salt, for example, the margin of safety is one-fifth (five times the amount normally used would be hazardous)
lysosomes
massage therapy
macrobiotic diets extremely restrictive diets limited to a few grains and vegetables; based on metaphysical beliefs and not on nutrition. A macrobiotic diet might consist of brown rice, miso soup and sea vegetables, for example
macular degeneration deterioration of the macular area of the eye that can lead to loss of central vision and eventual blindness. The macula is a small, oval, yellowish region in the centre of the retina that provides the sharp, straight-ahead vision so critical to reading and driving
magnesium a cation within the body’s cells, active in many enzyme systems
major minerals essential mineral nutrients found in the human body in amounts larger than 5 g; sometimes called macrominerals
malignant
a healing method in which the therapist manually kneads muscles to reduce tension, increase blood circulation, improve joint mobility and promote the healing of injuries
matrix the basic substance that gives form to a developing structure; in the body, the formative cells from which teeth and bones grow
matter anything that takes up space and has mass
meat replacements products formulated to look and taste like meat, fish or poultry; usually made of textured vegetable protein
medical history an account of a client’s current and past health status and disease risks
medication and supplement history a record of all the drugs, overthe-counter and prescribed, as well as dietary and herbal supplements that a person takes routinely
describes a cancerous cell or tumour, which can injure healthy tissue and spread cancer to other regions of the body
meditation
malnutrition
MEOS or microsomal ethanoloxidising system
any condition caused by excess or deficient food energy or nutrient intake or by an imbalance of nutrients
maltase an enzyme that hydrolyses maltose
maltose a disaccharide composed of two glucose units; sometimes known as malt sugar
mammary glands glands of the female breast that secrete milk
marasmus a form of PEM that results from a severe deprivation, or impaired absorption, of energy, protein, vitamins and minerals
margin of safety when speaking of food additives, a zone between the concentration normally used and that at which a hazard exists. For common table
a self-directed technique of relaxing the body and calming the mind
a system of enzymes in the liver that oxidise not only alcohol but also several classes of drugs
metabolic syndrome a combination of risk factors – insulin resistance, hypertension, abnormal blood lipids and abdominal obesity – that greatly increase a person’s risk of developing coronary heart disease; also called Syndrome X, insulin resistance syndrome or dysmetabolic syndrome
metabolism the sum total of all the chemical reactions that go on in living cells. Energy metabolism includes all the reactions by which the body obtains and expends the energy from food
metalloenzymes enzymes that contain one or more minerals as part of their structures
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Glossary
metallothionein a sulphur-rich protein that avidly binds with and transports metals such as zinc
per million (ppm) of minerals. Minerals give water a distinctive flavour. Many mineral waters are high in sodium
metastasis
mineralisation
the spread of cancer from one part of the body to another
MFP factor a peptide released during the digestion of meat, fish and poultry that enhances non-haem iron absorption
micelles tiny spherical complexes of emulsified fat that arise during digestion; most contain bile salts and the products of lipid digestion, including fatty acids, monoglycerides and cholesterol
microarray technology research tools that analyse the expression of thousands of genes simultaneously and search for particular gene changes associated with a disease. DNA microarrays are also called DNA chips
microbes microscopically small organisms including bacteria, viruses, fungi, and protozoa; also called microorganisms.
microbiome the full collection of genes of all microbes in a community. The human microbiome can be considered a counterpart to the human genome
microvilli tiny, hair-like projections on each cell of every villus that can trap nutrient particles and transport them into the cells; singular microvillus
milk anaemia iron-deficiency anaemia that develops when an excessive milk intake displaces iron-rich foods from the diet
milliequivalents (mEq) the concentration of electrolytes in a volume of solution. Milliequivalents are a useful measure when considering ions because the number of charges reveals characteristics about the solution that are not evident when the concentration is expressed in terms of weight
mineral oil a purified liquid derived from petroleum and used to treat constipation
mineral water water from a spring or well that typically contains 250 to 500 parts
the process in which calcium, phosphorus and other minerals crystallise on the collagen matrix of a growing bone, hardening the bone
minerals inorganic elements. Some minerals are essential nutrients required in small amounts by the body for health
misinformation false or misleading information
mitochondria the cellular organelles responsible for producing ATP aerobically; made of membranes (lipid and protein) with enzymes mounted on them; singular mitochondrion
moderate exercise activity equivalent to the rate of exertion reached when walking at a speed of just over 6 kilometres per hour (15 minutes to walk 1.5 kilometres)
moderation (dietary) providing enough but not too much of a substance
molasses the thick brown syrup produced during sugar refining. Molasses retains residual sugar and other by-products and a few minerals; blackstrap molasses contains significant amounts of calcium and iron
molecule two or more atoms of the same or different elements joined by chemical bonds. Examples are molecules of the element oxygen, composed of two oxygen atoms (O2), and molecules of the compound water, composed of two hydrogen atoms and one oxygen atom (H2O).
molybdenum a trace element
monoglycerides molecules of glycerol with one fatty acid attached
monosaccharides carbohydrates of the general formula CnH2nOn that typically form a single ring. See Appendix C for the chemical structures of the monosaccharides
monosodium glutamate (MSG) a sodium salt of the amino acid glutamic acid commonly used as a flavour enhancer
mono-unsaturated fatty acid (MUFA) a fatty acid that lacks two hydrogen atoms and has one double bond between carbons – for example, oleic acid. A monounsaturated fat is composed of triglycerides in which most of the fatty acids are mono-unsaturated
mouth the oral cavity containing the tongue and teeth
mucous membranes composed of mucus-secreting cells, that line the surfaces of body tissues
mucus a slippery substance secreted by cells of the GI lining (and other body linings) that protects the cells from exposure to digestive juices (and other destructive agents). The lining of the GI tract with its coat of mucus is a mucous membrane (The noun is mucus; the adjective is mucous)
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natural water water obtained from a spring or well that is certified to be safe and sanitary. The mineral content may not be changed, but the water may be treated in other ways such as with ozone or by filtration
naturopathic medicine a system that taps the natural healing forces within the body by integrating several practices, including traditional medicine, herbal medicine, clinical nutrition, homoeopathy, acupuncture, East Asian medicine, hydrotherapy and manipulative therapy
net protein utilisation (NPU) a measure of protein quality assessed by measuring the amount of protein nitrogen that is retained from a given amount of protein nitrogen eaten
neural tube the embryonic tissue that forms the brain and spinal cord
muscle dysmorphia
neural tube defects
a psychiatric disorder characterised by a preoccupation with building body mass
malformations of the brain, spinal cord or both during embryonic development that often result in lifelong disability or death
muscle endurance the ability of a muscle to contract repeatedly without becoming exhausted
muscle power the product of force generation (strength) and movement velocity (speed); the speed at which a given amount of exertion is completed
muscle strength the ability of muscles to work against resistance
muscular dystrophy a hereditary disease in which the muscles gradually weaken. Its most debilitating effects arise in the lungs
mutations a permanent change in the DNA that can be inherited
myoglobin the oxygen-holding protein of the muscle cells
NAD (nicotinamide adenine dinucleotide) the main coenzyme form of the vitamin niacin. Its reduced form is NADH
narcotic a drug that dulls the senses, induces sleep and becomes addictive with prolonged use
neurofibrillary tangles snarls of the thread-like strands that extend from the nerve cells; commonly found in the brains of people with Alzheimer’s dementia
neurons nerve cells; the structural and functional units of the nervous system. Neurons initiate and conduct nerve impulse transmissions
neuropeptide Y a chemical produced in the brain that stimulates appetite, diminishes energy expenditure and increases fat storage
neurotransmitters chemicals that are released at the end of a nerve cell when a nerve impulse arrives there. They diffuse across the gap to the next cell and alter the membrane of that second cell to either inhibit or excite it
New Zealand Dietetic Association (NZDA) the professional association for registered dietitians and associated nutrition professionals in New Zealand
niacin a B vitamin. The coenzyme forms are NAD (nicotinamide adenine dinucleotide) and NADP (the phosphate form of NAD). Niacin
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784
Glossary
can be eaten preformed or made in the body from its precursor, tryptophan, one of the amino acids
niacin equivalents (NE) the amount of niacin present in food, including the niacin that can theoretically be made from its precursor, tryptophan, present in the food
niacin flush a temporary burning, tingling and itching sensation that occurs when a person takes a large dose of nicotinic acid; often accompanied by a headache and reddened face, arms and chest
night blindness slow recovery of vision after flashes of bright light at night or an inability to see in dim light; an early symptom of vitamin A deficiency
nitrites salts added to food to prevent botulism. One example is sodium nitrite, which is used to preserve meats
nitrogen balance the amount of nitrogen consumed (N in) as compared with the amount of nitrogen excreted (N out) in a given period of time
nitrosamines derivatives of nitrites that may be formed in the stomach when nitrites combine with amines. Nitrosamines are carcinogenic in animals
no artificial colourings or flavours negative claims are statements that claim the non-addition or absence of a substance in a food. Such claims, especially referring to food additives, are a quick and effective way of communicating to consumers. Negative claims are commonly made about no artificial colourings or flavourings, no flavour enhancers or preservatives, or no added sugar
non-essential amino acids amino acids that the body can synthesise
non-nutritive sweeteners sweeteners that yield no energy (or insignificant energy in the case of aspartame)
nucleotide bases the nitrogen-containing building blocks of DNA and RNA – cytosine (C), thymine (T), uracil (U), guanine (G) and adenine (A). In DNA, the base pairs are A–T and C–G, and in RNA, the base pairs are A–U and C–G
nucleotides the sub-units of DNA and RNA molecules, composed of a phosphate group, a 5-carbon sugar (deoxyribose for DNA and ribose for RNA), and a nitrogencontaining base
nucleus a major membrane-enclosed body within every cell, which contains the cell’s genetic material, DNA, embedded in chromosomes
nursing bottle tooth decay extensive tooth decay due to prolonged tooth contact with formula, milk, fruit juice or other carbohydrate-rich liquid offered to an infant in a bottle
nutrient claims statements that characterise the quantity of a nutrient in a food
nutrient density a measure of the nutrients a food provides relative to the energy it provides. The more nutrients and the fewer kilojoules, the higher the nutrient density
Nutrient Reference Values (NRV) a set of nutrient intake values for healthy people in Australia and New Zealand. These values are used for planning and assessing diets
nutrients chemical substances obtained from food and used in the body to provide energy, structural materials and regulating agents to support growth, maintenance and repair of the body’s tissues. Nutrients may also reduce the risks of some diseases
nutrition the science of foods and the nutrients and other substances they contain, and of their actions within the body (including ingestion, digestion, absorption, transport, metabolism and excretion). A broader definition includes the social, economic, cultural and psychological implications of food and eating
nutrition assessment a comprehensive analysis of a person’s nutrition status that uses health, socioeconomic, medication and diet histories; anthropometric measurements; physical examinations; and laboratory tests
nutrition screening the use of preliminary nutritionassessment techniques to identify
people who are malnourished or are at risk for malnutrition
double bond from the methyl (CH3) end of a fatty acid
nutritional genomics
omega-3 fatty acid
the science of how food (and its components) interacts with the genome. The study of how nutrients affect the activities of genes is called nutrigenomics. The study of how genes affect the activities of nutrients is called nutrigenetics
a polyunsaturated fatty acid in which the first double bond is three carbons away from the methyl (CH3) end of the carbon chain
nutritionist a person who specialises in the study of nutrition. Note that this definition does not specify qualifications and may apply not only to dietitians but also to selfdescribed experts whose training is questionable
nutritive sweeteners sweeteners that yield energy, including both sugars and sugar replacers
NZFSA (New Zealand Food Safety Authority) the agency responsible for the administration of the Australia New Zealand Food Standards Code in New Zealand (www.nzfsa. govt.nz)
obese overweight with adverse health effects; BMI 30 or higher
oedema the swelling of body tissue caused by excessive amounts of fluid in the interstitial spaces; seen in protein deficiency (among other conditions)
oesophageal sphincter a sphincter muscle at the upper or lower end of the oesophagus. The lower oesophageal sphincter is also called the cardiac sphincter
oesophagus the food pipe; the conduit from the mouth to the stomach
oestrogens hormones responsible for the menstrual cycle and other female characteristics
oils lipids that are liquid at room temperature (approximately 25 ºC)
olestra a synthetic fat made from sucrose and fatty acids that provides 0 kJ per gram; also known as sucrose polyester
omega the last letter of the Greek alphabet; it is used by chemists to refer to the position of the first
omega-6 fatty acid a polyunsaturated fatty acid in which the first double bond is six carbons from the methyl (CH3) end of the carbon chain
opsin the protein portion of the visual pigment molecule
organelles subcellular structures such as ribosomes, mitochondria and lysosomes
organic in agriculture, crops grown and processed according to regulations defining the use of synthetic chemicals or genetically modified components
organic in chemistry, a substance or molecule containing carbon– carbon bonds or carbon–hydrogen bonds. This definition excludes coal, diamonds and a few carboncontaining compounds that contain only a single carbon and no hydrogen, such as carbon dioxide (CO2), calcium carbonate (CaCO3), magnesium carbonate (MgCO3) and sodium cyanide (NaCN)
organic halogens an organic compound containing one or more atoms of a halogen – fluorine, chlorine, iodine or bromine
orlistat a drug used in the treatment of obesity that inhibits the absorption of fat in the GI tract, thus limiting kilojoule intake
orthomolecular medicine the use of large doses of vitamins to treat chronic disease
orthorexia nervosa an obsession with good nutrition to improve health that is characterised by restrictive diets, ritualised patterns of eating, and rigid avoidance of foods believed to be unhealthy
osmosis the movement of water across a membrane towards the side where the solutes are more concentrated
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Glossary
osmotic pressure
oxidants
the amount of pressure needed to prevent the movement of water across a membrane
compounds (such as oxygen itself) that oxidise other compounds. Compounds that prevent oxidation are called antioxidants, whereas those that promote it are called prooxidants
osteoarthritis a painful, degenerative disease of the joints that occurs when the cartilage in a joint deteriorates; joint structures damaged, with loss of function; also called degenerative arthritis
oxidation the process of a substance combining with oxygen; oxidation reactions involve the loss of electrons
osteocalcin
oxidative stress
a calcium-binding protein in bones, essential for normal mineralisation
a condition in which the production of oxidants and free radicals exceeds the body’s ability to handle them and prevent damage
osteomalacia a bone disease characterised by softening of the bones. Symptoms include bending of the spine and bowing of the legs. The disease occurs most often in adult women
osteoporosis a disease in which the bones become porous and fragile due to a loss of minerals; also called adult bone loss
overload an extra physical demand placed on the body; an increase in the frequency, duration or intensity of an activity. A principle of training which states that for a body system to improve, it must be worked at frequencies, durations or intensities that increase by increments
overnutrition excess energy or nutrients
overt out in the open and easy to observe
overweight body weight above some standard of acceptable weight that is usually defined in relation to height (such as BMI); BMI 25 to 29.9
ovum the female reproductive cell, capable of developing into a new organism upon fertilisation; commonly referred to as an egg
oxaloacetate a carbohydrate intermediate of the TCA cycle
oxytocin a hormone that stimulates the mammary glands to eject milk during lactation and the uterus to contract during childbirth
oyster shell a product made from the powdered shells of oysters that is sold as a calcium supplement; however, it is not well absorbed by the digestive system
ozone therapy the use of ozone gas to enhance the body’s immune system
pancreas a gland that secretes digestive enzymes and juices into the duodenum (The pancreas also secretes hormones into the blood that help to maintain glucose homeostasis)
pancreatic juice
coenzyme A, called ‘CoA’ throughout Chapter 7
parathyroid hormone a hormone from the parathyroid glands that regulates blood calcium by raising it when levels fall too low; also known as parathormone
pasteurisation heat processing of food that inactivates some, but not all, microorganisms in the food; not a sterilisation process. Bacteria that cause spoilage are still present
pathogen a micro-organism capable of producing disease
PBB (polybrominated biphenyl) and PCB (polychlorinated biphenyl) toxic organic compounds used in pesticides, paints, and flame retardants
PDCAAS (protein digestibility-corrected amino acid score) a measure of protein quality assessed by comparing the amino acid score of a food protein with the amino acid requirements of preschool-age children and then correcting for the true digestibility of the protein; recommended by the FAO/WHO
peak bone mass the highest attainable bone density for an individual, developed during the first three decades of life
peer review a process in which a panel of scientists rigorously evaluates a research study to assure that the scientific method was followed
the exocrine secretion of the pancreas, containing enzymes for the digestion of carbohydrate, fat and protein as well as bicarbonate, a neutralising agent. The juice flows from the pancreas into the small intestine through the pancreatic duct (The pancreas also has an endocrine function, the secretion of insulin and other hormones)
a gastric enzyme that hydrolyses protein. Pepsin is secreted in an inactive form, pepsinogen, which is activated by hydrochloric acid in the stomach
pantothenic acid
peptic ulcer
a B vitamin. The principal active form is part of
pellagra the niacin-deficiency disease
pepsin
a lesion in the mucous membrane of either the
785
stomach (a gastric ulcer) or the duodenum (a duodenal ulcer)
background, including such factors as education, income and ethnic identity
peptidase
pesticides
a digestive enzyme that hydrolyses peptide bonds. Tripeptidases cleave tripeptides; dipeptidases cleave peptides. Endopeptidases cleave peptide bonds within the chain to create smaller fragments, whereas exopeptidases cleave bonds at the ends to release free amino acids
chemicals used to control insects, weeds, fungi and other pests on plants, vegetables, fruits and animals. Used broadly, the term includes herbicides (to kill weeds), insecticides (to kill insects) and fungicides (to kill fungi)
peptide bond a bond that connects the acid end of one amino acid with the amino end of another, forming a link in a protein chain
peripheral nervous system the peripheral (outermost) part of the nervous system; the vast complex of wiring that extends from the central nervous system to the body’s outermost areas. It contains both somatic and autonomic components
peripheral resistance the resistance to pumped blood in the small arterial branches (arterioles) that carry blood to tissues
peristalsis wave-like muscular contractions of the GI tract that push its contents along
pernicious anaemia a blood disorder that reflects a vitamin B12 deficiency caused by lack of intrinsic factor and characterised by abnormally large and immature red blood cells. Other symptoms include muscle weakness and irreversible neurological damage
persistence stubborn or enduring continuance; with respect to food contaminants, the quality of persisting, rather than breaking down, in the bodies of animals and human beings
personal and social history a record of a person’s social and economic
pH the unit of measure expressing a substance’s acidity or alkalinity
phagocytes white blood cells (neutrophils and macrophages) that have the ability to ingest and destroy foreign substances
phagocytosis the process by which phagocytes engulf and destroy foreign materials
pharynx the passageway leading from the nose and mouth to the larynx and oesophagus, respectively
phentermine a prescription drug used for weight loss in those who are obese. It works by reducing food intake and possibly stimulating energy expenditure
phenylketonuria or PKU an inherited disorder characterised by failure to metabolise the amino acid phenylalanine to tyrosine
phospholipid a compound similar to a triglyceride but having a phosphate group (a phosphorus-containing salt) and choline (or another nitrogencontaining compound) in place of one of the fatty acids
phosphorus a major mineral found mostly in the body’s bones and teeth
photosynthesis the process by which green plants use the sun’s energy to make carbohydrates from carbon dioxide and water
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Glossary
physical activity
plant-pesticides
prediabetes
proof
bodily movement produced by muscle contractions that substantially increase energy expenditure
pesticides made by the plants themselves
condition in which blood glucose levels are higher than normal but not high enough to be diagnosed as diabetes; considered a major risk factor for future diabetes and cardiovascular diseases
a way of stating the percentage of alcohol in distilled liquor. Liquor that is 100 proof is 50% alcohol, 90 proof is 45%, and so on
physiological age a person’s age as estimated from their body’s health and probable life expectancy
phytic acid a non-nutrient component of plant seeds; also called phytate. Phytic acid occurs in the husks of grains, legumes and seeds and is capable of binding minerals such as zinc, iron, calcium, magnesium and copper in insoluble complexes in the intestine, which the body excretes unused
phytochemicals non-nutrient compounds found in plant-derived foods that have biological activity in the body
plaque an accumulation of fatty deposits, smooth muscle cells and fibrous connective tissue that develops in the artery walls in atherosclerosis. Plaque associated with atherosclerosis is known as atheromatous plaque
platelets tiny, disc-shaped bodies in the blood, important in blood clot formation
point of unsaturation the double bond of a fatty acid, where hydrogen atoms can easily be added to the structure
polypeptide many (10 or more) amino acids bonded together
polysaccharides
phytoestrogens plant-derived compounds that have structural and functional similarities to human oestrogen. Phytoestrogens include the isoflavones genistein, daidzein and glycitein
phytosterols plant-derived compounds that have structural similarities to cholesterol and lower blood cholesterol by competing with cholesterol for absorption. Phytosterols include sterol esters and stanol esters
pica a craving for non-food substances. Also known as geophagia when referring to clay eating and pagophagia when referring to ice craving
pigment a molecule capable of absorbing certain wavelengths of light so that it reflects only those that we perceive as a certain colour
compounds composed of many monosaccharides linked together. An intermediate string of three to 10 monosaccharides is an oligosaccharide
polyunsaturated fatty acid (PUFA) a fatty acid that lacks four or more hydrogen atoms and has two or more double bonds between carbons – for example, linoleic acid (two double bonds) and alpha-linolenic acid (three double bonds). A polyunsaturated fat is composed of triglycerides in which most of the fatty acids are polyunsaturated
postpartum amenorrhea the normal temporary absence of menstrual periods immediately following childbirth
post-term (infant) an infant born after the 42nd week of pregnancy
potassium
placebo an inert, harmless medication given to provide comfort and hope; a sham treatment used in controlled research studies
placebo effect a change that occurs in response to expectations in the effectiveness of a treatment that actually has no pharmaceutical effects
placenta the organ that develops inside the uterus early in pregnancy, through which the foetus receives nutrients and oxygen and returns carbon dioxide and other waste products to be excreted
the principal cation within the body’s cells; critical to the maintenance of fluid balance, nerve impulse transmissions, and muscle contractions
prebiotics food components (such as fibres) that are not digested by the human body but are used as food by the GI bacteria to promote their growth and activity
precursors substances that precede others; with regard to vitamins, compounds that can be converted into active vitamins; also known as provitamins
pre-eclampsia a condition characterised by hypertension, fluid retention and protein in the urine; formerly known as pregnancy-induced hypertension
preformed vitamin A dietary vitamin A in its active form
preservatives antimicrobial agents, antioxidants and other additives that retard spoilage or maintain desired qualities, such as softness in baked goods
pressure ulcers damage to the skin and underlying tissues as a result of compression and poor circulation; commonly seen in people who are bedridden or chair-bound
preterm (infant) an infant born prior to the 38th week of pregnancy; also called a premature infant. A term infant is born between the 38th and 42nd week of pregnancy
primary deficiency a nutrient deficiency caused by inadequate dietary intake of a nutrient
probiotics living micro-organisms found in foods that, when consumed in sufficient quantities, are beneficial to health
processed foods foods that have been intentionally changed by the addition of substances, or a method of cooking, preserving, milling, or such foods that have been treated to change their physical, chemical, microbiological or sensory properties
progesterone the hormone of gestation (pregnancy)
prolactin a hormone secreted from the anterior pituitary gland that acts on the mammary glands to promote the production of milk. The release of prolactin is mediated by prolactin-inhibiting hormone (PIH)
promoters factors that favour the development of cancers once they have begun
prooxidants substances that significantly induce oxidative stress
proteases enzymes that hydrolyse protein
protective effect factors that oppose the development of cancer
protein digestibility a measure of the amount of amino acids absorbed from a given protein intake
protein efficiency ratio (PER) a measure of protein quality assessed by determining how well a given protein supports weight gain in growing rats; used to establish the protein quality for infant formulas and baby foods
protein turnover the degradation and synthesis of protein
protein-energy malnutrition (PEM) a deficiency of protein, energy or both, including kwashiorkor, marasmus and instances in which they overlap
proteins compounds composed of carbon, hydrogen, oxygen and nitrogen atoms, arranged into amino acids linked in a chain. Some amino acids also contain sulphur atoms
protein-sparing action the action of carbohydrate (and fat) in providing energy that allows protein to be used for other purposes
puberty the period in life in which a person becomes physically capable of reproduction
public health nutritionists dietitians or nutritionists who specialise in providing nutrition services through organised community efforts
public water water from a municipal water system that has been treated and disinfected
purified water water that has been treated by distillation or other physical or chemical processes that remove dissolved solids. Because purified water contains no
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Glossary
minerals or contaminants, it is useful for medical and research purposes
purines compounds of nitrogen-containing bases such as adenine, guanine and caffeine. Purines that originate from the body are endogenous and those that derive from foods are exogenous
pyloric sphincter the circular muscle that separates the stomach from the small intestine and regulates the flow of partially digested food into the small intestine; also called pylorus or pyloric valve
pyruvate a 3-carbon compound that plays a key role in energy metabolism
refined the process by which the coarse parts of a food are removed. When wheat is refined into flour, the bran, germ and husk are removed, leaving only the endosperm
reflux a backward flow
registered nutritionist a credentialling scheme overseen by the Nutrition Society of Australia for the recognition of individuals with relevant nutrition qualifications and professional work experience. In New Zealand, individuals with relevant qualifications can apply for professional registration through the New Zealand Register of Nutritionists
relative energy deficiency in sport (RE D-S)
qi gong a Chinese system that combines movement, meditation and breathing techniques to enhance the flow of qi (vital energy) in the body
quality of life a person’s perceived physical and mental wellbeing
randomisation a process of choosing the members of the experimental and control groups without bias
raw sugar partially refined crystals harvested during sugar processing
Recommended Dietary Intake (RDI) the average daily amount of a nutrient considered adequate to meet the known nutrient needs of practically all healthy people; a goal for dietary intake by individuals
rectum the muscular terminal part of the intestine, extending from the sigmoid colon to the anus
reduced fat or less fat the food contains at least 25 per cent less fat than in the same quantity of reference food
reduced salt/sodium the food must contain at least 25 per cent less sodium than the same quantity of reference food
reference protein a standard against which to measure the quality of other proteins
a syndrome of impaired physiological functions caused by relative energy deficiency (too little energy intake for the energy expended)
relaxin the hormone of late pregnancy
remodelling the dismantling and reformation of a structure; for example, bone
person does push-ups, pull-ups, or abdominal crunches
resistant starches starches that escape digestion and absorption in the small intestine of healthy people
resistin protein produced by adipose cells that promotes inflammation and causes insulin resistance
resting metabolic rate (RMR) similar to the basal metabolic rate (BMR), a measure of the energy use of a person at rest in a comfortable setting, but with less stringent criteria for recent food intake and physical activity. Consequently, the RMR is slightly higher than the BMR
retina the layer of light-sensitive nerve cells lining the back of the inside of the eye; consists of rods and cones
retinoids chemically related compounds with biological activity similar to that of retinol; metabolites of retinol
retinol equivalent (RE)
an enzyme from the kidneys that activates angiotensin
a measure of vitamin A activity; the amount of retinol that the body will derive from a food containing preformed retinol or its precursor betacarotene
rennin
retinol-binding protein (RBP)
renin
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bone (manifested in bowed legs or knock-knees, outward-bowed chest, and knobs on ribs). A rare type of rickets, not caused by vitamin D deficiency, is known as vitamin D-refractory rickets
risk a measure of the probability and severity of harm
risk factor a condition or behaviour associated with an elevated frequency of a disease but not proved to be causal. Leading risk factors for chronic diseases include obesity, cigarette smoking, high blood pressure, high blood cholesterol, physical inactivity and a diet high in saturated fats and low in vegetables, fruits and wholegrain
RNA (ribonucleic acid) a compound similar to DNA, but RNA is a single strand with a ribose sugar instead of a deoxyribose sugar and uracil instead of thymine as one of its bases
royal jelly the substance produced by worker bees and fed to the queen bee; falsely promoted as increasing strength and enhancing performance
saccharin
an enzyme that coagulates milk; found in the gastric juice of cows, but not human beings
the specific protein responsible for transporting retinol
an artificial sweetener that has been approved for use in Australia and New Zealand
replication
rheumatoid arthritis a disease of the immune system involving painful inflammation of the joints and related structures
safety
repeating an experiment and getting the same results. The sceptical scientist, on hearing of a new, exciting finding, will ask, ‘Has it been replicated yet?’ If it hasn’t, the scientist will withhold judgement regarding the finding’s validity
requirement the lowest continuing intake of a nutrient that will maintain a specified criterion of adequacy
residues whatever remains. In the case of pesticides, those amounts that remain on or in foods when people buy and use them
resistance training the use of free weights or weight machines to provide resistance for developing muscle strength, power, and endurance; also called weight training. A person’s own body weight may also be used to provide resistance such as when a
rhodopsin a light-sensitive pigment of the retina; contains the retinal form of vitamin A and the protein opsin
riboflavin a B vitamin. The coenzyme forms are FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide)
ribose a 5-carbon sugar falsely promoted as improving the regeneration of ATP and thereby the speed of recovery after high power exercise
the condition of being free from harm or danger
saliva the secretion of the salivary glands. Its principal enzyme begins carbohydrate digestion
salivary glands exocrine glands that secrete saliva into the mouth
salt a compound composed of a positive ion other than H1 and a negative ion other than OH2. An example is sodium chloride (Na1 Cl2)
salt sensitivity
protein-making organelles in cells; composed of RNA and protein
a characteristic of individuals who respond to a high salt intake with an increase in blood pressure or to a low salt intake with a decrease in blood pressure
rickets
sarcopenia
ribosomes
the vitamin D-deficiency disease in children characterised by inadequate mineralisation of
loss of skeletal muscle mass, strength and quality
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788
Glossary
satiating having the power to suppress hunger and inhibit eating
synthesised in the body from the amino acid tryptophan with the help of vitamin B6
example is pectin from fruit, which is used to thicken jellies
responsibility for many food safety aspects falls
satiation
set point
solutes
sterile
the substances that are dissolved in a solution. The number of molecules in a given volume of fluid is the solute concentration
free of microorganisms, such as bacteria
the feeling of satisfaction and fullness that occurs during a meal and halts eating. Satiation determines how much food is consumed during a meal
satiety the feeling of fullness and satisfaction that occurs after a meal and inhibits eating until the next meal. Satiety determines how much time passes between meals
the point at which controls are set (for example, on a thermostat). The set point theory that relates to body weight proposes that the body tends to maintain a certain weight by means of its own internal controls
sickle-cell anaemia
a fatty acid carrying the maximum possible number of hydrogen atoms; for example, stearic acid. A saturated fat is composed of triglycerides in which most of the fatty acids are saturated
a hereditary form of anaemia characterised by abnormal sickle or crescent-shaped red blood cells. Sickled cells interfere with oxygen transport and blood flow. Symptoms are precipitated by dehydration and insufficient oxygen (as may occur at high altitudes) and include haemolytic anaemia (red blood cells burst), fever and severe pain in the joints and abdomen
scurvy
simple carbohydrates (sugars)
saturated fatty acid
the vitamin C-deficiency disease
secondary deficiency a nutrient deficiency caused by something other than an inadequate intake, such as a disease condition or drug interaction that reduces absorption, accelerates use, hastens excretion or destroys the nutrient
secretin
monosaccharides and disaccharides
small intestine a 3-metre length of small diameter intestine that is the major site of digestion of food and absorption of nutrients. Its segments are the duodenum, jejunum and ileum
sodium
a hormone produced by cells in the duodenum wall. Target organ: the pancreas. Response: secretion of bicarbonate rich pancreatic juice
the principal cation in the extracellular fluids of the body; critical to the maintenance of fluid balance, nerve impulse transmissions and muscle contractions
sedentary
sodium bicarbonate
physically inactive (literally, sitting down a lot) a periodic squeezing or partitioning of the intestine at intervals along its length by its circular muscles
baking soda; an alkaline salt believed to neutralise blood lactic acid and thereby to reduce pain and enhance possible workload. ‘Soda loading’ may cause intestinal bloating and diarrhoea
selenium
soft water
segmentation
water with a high sodium or potassium content
a trace element
senile dementia the loss of brain function beyond the normal loss of physical adeptness and memory that occurs with ageing
solanine
senile plaques
solid fats
clumps of the protein fragment beta-amyloid on the nerve cells, commonly found in the brains of people with Alzheimer’s dementia
serotonin a neurotransmitter important in sleep regulation, appetite control and sensory perception, among other roles. Serotonin is
a poisonous narcotic-like substance present in potato peels and sprouts fats that are solid at room temperature; examples are animal fat and butter. Solid fats mainly come from animal foods but can also be made from vegetable oils through a process called hydrogenation
soluble fibre indigestible food components that dissolve in water to form a gel. An
somatic nervous system the division of the nervous system that controls the voluntary muscles, as distinguished from the autonomic nervous system, which controls involuntary functions
somatostatin (GHIH) a hormone that inhibits the release of growth hormone; the opposite of somatotropin (GH)
source of fibre or contains fibre the food must not contain less than 1.5 g of dietary fibre per serving of food
sperm the male reproductive cell, capable of fertilising an ovum
sphincter a circular muscle surrounding, and able to close, a body opening. Sphincters are found at specific points along the GI tract and regulate the flow of food particles
spina bifida the most common type of neural tube defect; characterised by the incomplete closure of the spinal cord and its bony encasement
spirulina a kind of alga (‘blue-green manna’) that supposedly contains large amounts of protein and vitamin B12, suppresses appetite and improves athletic performance. It actually does none of these things and is potentially toxic
sports anaemia a transient condition of low haemoglobin in the blood, associated with the early stages of sports training or other strenuous activity
spring water water originating from an underground spring or well. It may be carbonated, or ‘flat’ or ‘still’, meaning not carbonated. Brand names such as ‘Spring Pure’ do not necessarily mean that the water comes from a spring
starches plant polysaccharides composed of glucose
State and territory health services each Australian state and territory has its own health department under which the
sterols compounds containing a four-ring carbon structure with any of a variety of side chains attached
stomach a muscular, elastic, sac-like portion of the digestive tract that grinds and churns swallowed food, mixing it with acid and enzymes to form chyme
stools waste matter discharged from the colon; also called faeces
stress any threat to a person’s wellbeing; a demand placed on the body to adapt
stress fractures bone damage or breaks caused by stress on bone surfaces during exercise
stress response the body’s response to stress, mediated by both nerves and hormones
stressors environmental elements, physical or psychological, that cause stress
stroke an event in which the blood flow to a part of the brain is cut off; also called cerebrovascular accident (CVA)
subclavian vein the vein that provides passageway from the lymphatic system to the vascular system
subclinical deficiency a deficiency in the early stages, before the outward signs have appeared
subjects the people or animals participating in a research project successful weight-loss maintenance achieving a weight loss of at least 10 per cent of initial body weight and maintaining the loss for at least one year
sucralose an artificial sweetener approved for use in Australia and New Zealand
sucrase an enzyme that hydrolyses sucrose
sucrose a disaccharide composed of glucose and fructose; commonly
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Glossary
known as table sugar or cane sugar. Sucrose also occurs in many fruits and some vegetables and grains
sudden infant death syndrome (SIDS) the unexpected and unexplained death of an apparently well infant; the most common cause of death of infants between the second week and the end of the first year of life; also called cot death
sugar alcohols commonly found in foods; they are sorbitol, mannitol and xylitol. They generally come from plant products such as fruits and berries where the carbohydrate in these plant products is chemically altered
Suggested Dietary Targets (SDTs) a daily average intake from food and beverages for certain nutrients that that may help in prevention of chronic disease. Average intake may be based on the mean or median depending on the nutrient and available data
sulphate the oxidised form of sulphur
sulphites salts containing sulphur that are added to foods to prevent spoilage
sulphur a mineral present in the body as part of some proteins
supplement any pill, capsule, tablet, liquid or powder that contains vitamins, minerals, herbs or amino acids; intended to increase dietary intake of these substances
sushi vinegar-flavoured rice and seafood, typically wrapped in seaweed and stuffed with colourful vegetables. Some sushi is stuffed with raw fish; other varieties contain cooked seafood
synergistic multiple factors operating together in such a way that their combined effects are greater than the sum of their individual effects
TCA cycle or tricarboxylic acid cycle a series of metabolic reactions that break down molecules of acetyl CoA to carbon dioxide and hydrogen atoms; also called the Krebs cycle after the biochemist who elucidated its reactions
T-cells lymphocytes that attack antigens. T stands for the thymus gland, where the T-cells mature
tempeh a fermented soybean food, rich in protein and fibre
teratogenic causing abnormal foetal development and birth defects
testosterone a steroid hormone from the testicles, or testes. The steroids, as explained in Chapter 5, are chemically related to, and some are derived from, the lipid cholesterol
textured vegetable protein
a blood vessel, causing gradual tissue death
thromboxanes products of eicosanoid metabolism that causes blood clotting and constriction of blood vessels. It also encourages platelet aggregation
thyroid-stimulating hormone (TSH) a hormone secreted by the pituitary that stimulates the thyroid gland to secrete its hormones – thyroxine and triiodothyronine. The release of TSH is mediated by TSH releasing hormone (TRH)
tocopherol
processed soybean protein used in vegetarian products such as soy burgers; see also meat replacements
a general term for several chemically related compounds, one of which has vitamin E activity (See Appendix C for chemical structures)
TGA (Therapeutic Goods Administration)
tocotrienols
a part of the Australian Government Department of Health and Ageing that is responsible for ensuring the safety of all vitamin, mineral and dietary supplements, and their labelling
theory a tentative explanation that integrates many and diverse findings to further the understanding of a defined topic
thermic effect of food (TEF) an estimation of the energy required to process food (digest, absorb, transport, metabolise and store ingested nutrients); also called the specific dynamic effect (SDE) of food or the specific dynamic activity (SDA) of food. The sum of the TEF and any increase in the metabolic rate due to overeating is known as diet-induced thermogenesis (DIT)
thermogenesis the generation of heat; used in physiology and nutrition studies as an index of how much energy the body is expending
thiamin a B vitamin. The coenzyme form is TPP (thiamin pyrophosphate) thirst a conscious desire to drink
thoracic duct the main lymphatic vessel that collects lymph and drains into the left subclavian vein
thrombosis the formation of a thrombus, or a blood clot, that may obstruct
members of the vitamin E family having the chemical structure of a complex ring structure with a long unsaturated side chain
tofu a food made by coagulating soy milk and then pressing the resulting curds into soft white blocks; also known as bean curd
tolerance level the maximum amount of a residue permitted in a food when a pesticide is used according to label directions
toxicity the ability of a substance to harm living organisms. All substances are toxic if high enough concentrations are used
trabecular bone the lacy inner structure of calcium crystals that supports the bone’s structure and provides a calcium storage bank
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acid, producing a new nonessential amino acid and a new keto acid
trans-fatty acids fatty acids with hydrogens on opposite sides of the double bond.
transferrin the iron transport protein
transient hypertension of pregnancy high blood pressure that develops in the second half of pregnancy and resolves after childbirth, usually without affecting the outcome of the pregnancy
transient ischaemic attack (TIA) a temporary reduction in blood flow to the brain, which causes temporary symptoms that vary depending on the part of the brain affected. Common symptoms include light-headedness, visual disturbances, paralysis, staggering, numbness and inability to swallow
travellers’ diarrhoea nausea, vomiting and diarrhoea caused by consuming food or water contaminated by any of several organisms, most commonly, E. coli, Shigella, Campylobacter jejuni and Salmonella
triglycerides the chief form of fat in the diet and the major storage form of fat in the body, composed of a molecule of glycerol with three fatty acids attached; also called triacylglycerols
tripeptide three amino acids bonded together
tumour an abnormal tissue mass with no physiological function; also called a neoplasm
type 1 diabetes
essential mineral nutrients found in the human body in amounts smaller than 5 g; sometimes called microminerals
the type of diabetes that accounts for 5 to 10 per cent of diabetes cases and usually results from autoimmune destruction of pancreatic beta cells. In this type of diabetes, the pancreas produces little or no insulin
trachea
type 2 diabetes
the air passageway from the larynx to the lungs; also called the windpipe
the type of diabetes that accounts for 90 to 95 per cent of diabetes cases and usually results from insulin resistance coupled with insufficient insulin secretion. Obesity is present in 80 to 90 per cent of cases
trace minerals
trans on the other side of; refers to a chemical configuration in which the hydrogen atoms are located on opposite sides of a double bond
transamination the transfer of an amino group from one amino acid to a keto
type I osteoporosis osteoporosis characterised by rapid bone losses, primarily of trabecular bone
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790
Glossary
type II osteoporosis osteoporosis characterised by gradual losses of both trabecular and cortical bone
ulcer a lesion of the skin or mucous membranes characterised by inflammation and damaged tissues. See also peptic ulcer
ultrahigh temperature (UHT) treatment sterilising a food by brief exposure to temperatures above those normally used
ultra-processed foods foods that have been made from substances that are typically used in food preparation, but not consumed as foods by themselves (such as oils, fats, flours, refined starches and sugars) that undergo further processing by adding a little, if any, minimally processed foods, salt and other preservatives, and additives such as flavours and colours
umbilical cord the rope-like structure through which the foetus’s veins and arteries reach the placenta; the route of nourishment and oxygen to the foetus and the route of waste disposal from the foetus. The scar in the middle of the abdomen that marks the former attachment of the umbilical cord is the umbilicus, commonly known as the belly button
undernutrition when an individual receives suboptimal nutrition. This may occur with respect to macronutrients or micronutrients or both
underweight body weight below some standard of acceptable weight that is usually defined in relation to height (such as BMI); BMI below 18.5
unsaturated fatty acid a fatty acid that lacks hydrogen atoms and has at least one double bond between carbons (includes mono-unsaturated and polyunsaturated fatty acids). An unsaturated fat is composed of triglycerides in which most of the fatty acids are unsaturated
unspecified eating disorders eating disorders that do not meet the defined criteria for specific eating disorders
Upper Level of Intake (UL) the maximum daily amount of a nutrient that appears safe for
most healthy people and beyond which there is an increased risk of adverse health effects
precursor forms in foods without distinguishing between them
urea
a family of compounds – pyridoxal, pyridoxine and pyridoxamine. The primary active coenzyme form is PLP (pyridoxal phosphate)
the principal nitrogen-excretion product of protein metabolism. Two ammonia fragments are combined with carbon dioxide to form urea
uterus the muscular organ within which the infant develops before birth
validity having the quality of being founded on fact or evidence
variables factors that change. A variable may depend on another variable (for example, a child’s height depends on their age), or it may be independent (for example, a child’s height does not depend on the colour of their eyes). Sometimes both variables correlate with a third variable (a child’s height and eye colour both depend on genetics)
variety (dietary) eating a wide selection of foods within and among the major food groups
vasoconstrictor a substance that constricts or narrows the blood vessels
vegans people who exclude all animal derived foods (including meat, poultry, fish, eggs and dairy products) from their diets; also called pure vegetarians, strict vegetarians or total vegetarians
vegetarians a general term used to describe people who exclude meat, poultry, fish or other animal-derived foods from their diets
veins vessels that carry blood to the heart
villi finger-like projections from the folds of the small intestine; singular villus
viscous a gel-like consistency
vitamin A all naturally occurring compounds with the biological activity of retinol, the alcohol form of vitamin A
vitamin A activity a term referring to both the active forms of vitamin A and the
vitamin B6
vitamin B12
a B vitamin characterised by the presence of cobalt (see Figure 13.11). The active forms of coenzyme B12 are methylcobalamin and deoxyadenosylcobalamin
vitamins organic, essential nutrients required in small amounts by the body for health
VLDL (very-low-density lipoprotein) the type of lipoprotein made primarily by liver cells to transport lipids to various tissues in the body; composed primarily of triglycerides
VO2max
the maximum rate of oxygen consumption by an individual at sea level
vomiting expulsion of the contents of the stomach up through the oesophagus to the mouth
waist circumference an anthropometric measurement used to assess a person’s abdominal fat
warm-up
Wernicke-Korsakoff syndrome a neurological disorder typically associated with chronic alcoholism and caused by a deficiency of the B vitamin thiamin; also called alcoholrelated dementia
whey protein a by-product of cheese production; falsely promoted as increasing muscle mass. Whey is the watery part of milk that separates from the curds
white sugar pure sucrose or ‘table sugar’, produced by dissolving, concentrating and recrystallising raw sugar
WHO (World Health Organization) an international agency concerned with promoting health and eradicating disease (www.who.int)
whole foods fresh foods such as vegetables, grains, legumes, meats and milk that are unprocessed or minimally processed
whole grain a grain milled in its entirety (all but the husk); not refined
wine an alcoholic beverage made by fermenting grape juice
xanthophylls pigments found in plants; responsible for the colour changes seen in autumn leaves
Five to 10 minutes of light activity, such as easy jogging or cycling, prior to a workout to prepare the body for more vigorous activity
xerophthalmia
water balance
abnormal drying of the skin and mucous membranes; a sign of vitamin A deficiency
the balance between water intake and output (losses)
progressive blindness caused by severe vitamin A deficiency
xerosis
water intoxication the rare condition in which body water contents are too high in all body fluid compartments
wean to gradually replace breast milk with infant formula or other foods appropriate to an infant’s diet
weight management maintaining body weight in a healthy range by preventing gradual weight gain over time and losing weight if overweight
yoghurt milk product that results from the fermentation of lactic acid in milk by Lactobacillus bulgaricus and Streptococcus thermophilus
zygote the product of the union of ovum and sperm; so-called for the first two weeks after fertilisation
well water water drawn from ground water by tapping into an aquifer
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791
INDEX A
abdominal cramps 363, 619 abdominal discomfort 88–90, 105 abdominal girth 741–2 abdominal obesity 648 absorption 10, 67–77, 88, 362, 373, 378, 396, 420, 430, 653, 739 of carbohydrates 102–6 of fat 148 of iron 63, 454–7 of lipids 147–8 of monosaccharides 105 of nitrogen 737 of protein 182–3 of zinc 63, 464–5 absorption enhancers 375 absorption-enhancing factors 456 absorption-inhibiting factors 456 absorptive systems, anatomy 75–6 abstract 16 abstracts 32 acceptable daily intake (ADI) 119, 686 Acceptable Macronutrient Distribution Ranges (AMDR) 20 accidental spills 681 acclimatisation 416 accreditation 35 accredited exercise physiologist (AEP) 34 accredited practising dietitian (APD) 34 accuracy 32, 664, 740, 743, 761 Accutane (isotretinoin) 383 acetaldehyde 245, 249 acetyl CoA 219, 222–4, 226, 229–30, 236, 245, 335, 359, 617 alternative route to fat 246 options 222–3 paths 223 acetylcholine 617 acid 73, 92–3 acid controllers 91, 93 acid group (COOH) 135, 178, 238 see also keto acids acid–base balance 108, 226, 245, 413–15, 421, 425 acid–base regulators 188 acidity 72–3, 88, 222, 413, 415, 626, 689, 714 acidosis 188, 664 acids 101–2, 188, 413–14, 714 acne 383, 588 acromegaly 523 acrylamide 654 activated carbon filters 691 active people 507–8 active transport 75, 104 activity 62, 310–11, 417, 495, 498–508, 515–16, 589 choosing 311–12 coordinated 67 glucose before, during and after 502–5 intensity/duration affects 501, 505,507 nutrient-supported 5–6, 40 training affects fat use 506 of vitamin A 378
activity statements 44 acute PEM (recent severe food deprivation) 195, 197–8 adaptations (body) 238, 492–517, 522, 540 adaptive mechanisms 88 adaptive thermogenesis 263 added energy 248 added fats 47, 50–1, 124 added salt 43, 50–1, 422 added sugars 42–3, 47, 50–1, 112–13, 115, 124 addictions 130, 372 addictive behaviours 283 additives 5, 653, 686 in food see food additives regulations governing 686–7 risks versus benefits 687 adenomas 652 adequacy 40, 84, 306, 515, 740 Adequate Intake (AI) 1–3, 17–19, 330, 336–7, 393–4, 417–18, 426, 472 adipokines 151 adiponectin 151, 292 adipose tissue 151, 235, 304, 402, 648 adiposity 71 adolescence 564–91 energy intake and activity 589 nutrition during 588–91 adolescent growth spurt 588–9 adolescents 388 eating away from home 591 estimated energy requirements for 764 growth and development 588–9 pregnancy in 547 recommended dietary patterns for 48 adrenal glands 361, 411, 413 adrenaline 109, 191, 209, 580 ‘adult diseases’ 594 Adult Nutrition Surveys 25 adulthood 601–20 adults 636 analysis of measures in 753 diabetes incidents 646–7 estimated energy requirements for 763 groups at risk of vitamin D deficiency 401 heart rate, respiration rate and energy needs compared 564 height measurements 742 weight measurements 743 adverse effects 118, 331, 363, 625 adverse health consequences 199 adverse reactions 580, 665 advertising 333, 524, 583 advice 34, 111, 515, 656, 740 aerobic activity 596 aerobic energy pathway 221 aerobic system 499–500 aflatoxins 197 age 17, 23, 28, 244, 263, 446–8, 630, 636–7, 763–5 ageing 389, 445, 601, 605, 644, 648 nutrient concerns of 611–12 process 605–8
ageing brain 614–17 agents 5, 402, 646, 687–8 age-related factors 448, 615–16 aggression 522 agriculture alternative farming methods 685 genetically assisted 698 see also biopharming AIDS 554, 624 AIDS drugs 698 air 67, 90, 653 air passages 87 air pollution 477 albumin 758 alcohol 5, 7–8, 11, 28, 43, 93, 199, 383, 449, 514, 548, 555, 644, 653, 676, 688, 739–40 abstinence from 246 blood levels 248 in the body 242–51 consequences of use 249 consumption 650, 741 disruptions to liver 245–6 lethal dose 247 malnutrition and 247 myths and truths 251 short- and long-term effects 249–50 sugar alcohols 119–20 tolerances for 244 alcohol abuse 242, 245, 248, 449 chronic 248 alcohol consumption 249, 555, 558 heavy 249 alcohol dehydrogenase enzyme 244–5, 250 alcohol dependency 372 alcohol metabolism 245 alcohol toxicity 248 alcoholism 248, 653 alcohol-related birth defects (ARBD) 558 alcohol-related neurodevelopmental disorder (ARND) 558 aldosterone 143, 410–13 alkaline 73, 82, 626 alkalosis 188 allergenicity 701 allergens 573 introduction of 699 allergic reactions 580 allergies 81, 569–70, 573, 740 alpha-lactalbumin 568 alpha-tocopherol 392 alternative sweeteners 116–20 alternative therapies 373, 660, 662–7 advice and precautions on 663 examples 661 Alzheimer’s disease 615–17 amenorrhoea 279, 281, 544 American Academy of Paediatrics 521 American College of Sports Medicine (ACSM) guidelines 493–4 American Heart Association 325
American Journal of Clinical Nutrition 524 amino acid chains 180 amino acid metabolism 246, 345 amino acid pool 191 amino acid scoring 735 amino acid sequences 180 amino acid supplements 201–2 amino acids 146, 178–202, 218, 226–9, 237, 371, 646, 688–9, 720 to acetyl CoA 226 chains 361 common 179 degradation 727–8 destruction 735 to glucose 226 limiting 735–6 to make proteins/nonessential amino acids 191 sequencing errors 184–5 side groups 178 ammonia 192, 202, 228, 711, 714 conversion to urea 192 to urea in liver 226–7 amniotic sac 407 amphetamines 624 amylase 102 amylopectin 100 amylose 100 anabolic steroids 522–3 anabolism 216 anaemia 184–5, 198, 352, 362, 393, 575, 757–60 anaerobic energy pathway 221 anaerobic versus aerobic systems 500 anaesthetic 247, 249 analysis 5, 15, 735 biochemical 755–60 of food intake data 741 of measures 743–53 of research findings 15–16 anaphylaxis 580 anatomy 87 of gastrointestinal tract 67–9 androstenedione 522 anencephaly 532 angina 635 angiotensin (I and II) 410–12 animal fats 62,160 animal protein 199–200 animal studies 202, 477, 655, 689 laboratory-based 13–14 animal-based foods 28 animal-protein intake 199 animals 384 cloning 698 energy restriction in 603–4 foods derived from 160 anions 408–9, 713 anorexia nervosa 196, 200, 277, 279–80, 292–3, 316, 448 physical consequences 280–1 treatment 281 antacids 91, 450, 625, 627 antagonistic actions 373–4 anthropometric data 23 anthropometric measurements 23, 375, 741–55 antibiotics 624, 627, 630, 690
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792
Index
antibodies 189, 198, 569, 580, 631–2, 760 anticlotting effect 623 anticoagulant drugs 396 antidiuretic hormone (ADH) 247, 410–11 antigens 189, 631 antihypertensive agents 646 anti-inflammatory drugs 92 antimicrobial agents 687–8 antimicrobial plastic wrap 679 antineoplastic drugs 624 antioxidant vitamins 62 antioxidants 140, 360–1, 381, 483, 509, 655, 687–8, 716 antiretroviral drugs 624 antiscorbutic factor 360 antispasmodic drugs 89 anus 68–9 anxiety 3, 110, 238, 247, 284, 590, 665 aorta 78 apathy 460 appendix 68–9 appetite 71, 131, 255, 313, 316, 587, 608, 662 irregularities 316 regulation 208 suppression 238 appetite control 130–1, 311 appetite-stimulating hormone see ghrelin aquifiers 693 arachidonic acid (AA) 152, 568 area 75 arginine 199 aroma 483 aromatherapy products 375 arrhythmias 626 arsenic 691 arteries 78–80, 83, 389, 595, 635 hardening see atherosclerosis arterioles 643 arthritis 613–14 articles 16, 201, 660 artificial flavours 56, 688 artificial sweeteners 116, 118 ascending colon 70 ascorbic acid 360–1 aspartame 689 aspirin 623 assessment 458 data 742 of food additives 686 of food safety 701 of iron-deficiency anaemia 758–60 of nutrition see nutrition assessment of risk see risk assessment techniques 23 of vitamin B12 anaemias 760 assessment techniques 24 associations 2–3 assumptions 737 asthma 158, 583, 688–9 atherogenic diet 638 atheromatous plaque 634 atherosclerosis 144, 171, 594–5, 634–5, 642, 648 athletes 201–2, 372, 506–8, 511, 516, 520 carbohydrate intake guidelines 503 disordered eating in 277–9 iron recommendations 510 power 521
athletic performance see performance athletic prowess 588 Atkins diet 322 atom 135 atomic numbers 709–11 atomic weight 711 atoms 4–5, 96–7, 409, 708 electron sharing 711 identity 708 maximum stability 710–11 nature of 708 ATP (adenosine triphosphate) 217, 221, 294, 437, 499–500 synthesis 231 atrophic gastritis 355, 372, 610 atrophy 494 attitude 312–13 Australia ageing population 601 ‘Australian diet’ 2, 646 deaths from obesity-related diseases 271–2 gene technology regulations 701 incidence of FAS in 558 neural tube defects 531 NRVs for 1–3, 332, 430–1, 609 obesity and overweight in 288 PEM statistics 196 as skin cancer capital 403 Australia New Zealand Food Standards Code 701 Australian and New Zealand Food Authority (FSANZ) 118 Australian Diabetes Council 120 Australian Dietary Approaches to Stop Hypertension study 645–6 Australian Dietary Guidelines 22, 42–6, 115, 122, 129, 156, 421, 550, 574, 612, 650 Australian Government 692 Australian Guide to Healthy Eating 22, 42, 44–9, 62, 124, 160, 336–7, 645–6 diet plan example 50 dietary framework 609 Australian Guidelines to Reduce the Health Risks from Drinking Alcohol 242 Australian Medical Association 113 Australian National Health Survey 492 Australian Quarantine and Inspection Service (AQIS) 685 Australian Sports Anti-Doping Authority 523 Australian standards 690 Australian Total Diet Survey 684 autoimmune diseases 89, 401, 403, 760 autoimmune disorder 647 autonomic nervous system 704–5 averages 21 avocados 160, 164, 169, 396, 515 awareness 33
B
B group vitamins 47, 51, 199, 239, 245, 330–67 in concert 358–60 as individuals 333–58 roles 358–9
bacteria 72–3, 83, 101, 362, 394, 396, 569, 626, 672–3, 675, 685, 688, 690–1 species and subspecies 80 bacterial infections 92, 634, 678–9 bad breath 239 balance 20, 40, 84, 114, 402, 413–19, 573–4 balanced diet 2, 61, 64, 528, 609, 663 balanced fitness program 497–8 balanced meals 110 barbiturates 79 bariatric surgery 303 barley 89, 101, 392 Barrett’s oesophagus 92 basal metabolic rate (BMR) 260–1, 763–5 factors affecting 261, 263–4 basal metabolism 260–1 bases 188, 414, 714 basic 73, 88 B-cells 631 beaded ribs 388 beam balances 743 beans 45 beast health 554–5 beer 242 ‘beer belly’ 248 behaviour 312–13, 577, 579 addictive 283 inappropriate eating behaviours 596 potentially harmful 249 behaviour abnormalities 208 behaviour modification 312 behavioural change 312, 585 belching 87, 90 beliefs 4, 619 benefits 4, 61–2, 158, 161, 171, 174, 492–4, 551, 566, 570, 596, 660–3, 687 see also health benefits beriberi 335, 371 ‘best before’ date 674 best practice 683 beta cells 533–4, 647–8 beta-amyloid 616 beta-carotene 374, 378–86 as antioxidant 381 beta-hydroxymethylbutyrate (HMB) 522 beverages 46, 93, 417–18, 590, 740 alcohol in 242 carbonated 90 poor choices 514 bias 15 bicarbonate–carbonic acid buffer system 415 bicarbonates 73, 82, 414–15, 689 bifidus factors 569 bile 73, 88, 146, 378 destination 147 bile duct 68–9 binders 374, 420 binge drinking 249 binge eating 282–4 binge–purge cycles 284 bioaccumulation 680–1 bioavailability 330–1, 373–4, 384, 396, 432, 438, 521–2 of calcium 432 variable 420 biochemical analyses 755–60 biochemical assessment techniques 760
biochemical structures and pathways 717–34 biochemical tests 756–7 bioelectric impedance 755 bioelectrical impedance 755 biofortification 697 biological value (BV) 737 biological weapons 699 biomarkers 488 biopharming 698 biopsy 89 biotechnology 385, 696–701 possibilities 698 biotin 81, 333–4, 343–4, 366 food sources 344 recommendations 344 biotin deficiency 344 biotin toxicity 344 biphenyls 681 birth defects 11, 383, 543–5, 558 Birth to 2 years (percentiles) 744–9 birth trauma 535 birth weight 543, 545–6 bitter 69 bleeding 92, 158, 363, 572, 623, 635 blind experiment 15 blindness 385, 648–9 blindness (xerophthalmia) 381–2 bloating 89, 105 blood 77–8, 104, 331, 371, 413, 643, 755 blood samples 435 fuels from 647 oxygenated 79 pH ranges 414 production 539 route travelled see blood flow blood alcohol 559–60 blood calcium 389 blood cells 352 blood cholesterol 209–10, 595–6, 656 blood clots/clotting 83, 393–4, 396, 623, 634–5, 638, 664, 666 disorders 374 process 395 blood flow 78, 83, 412, 595 blood glucose 238, 646, 651 balancing 109–10 levels 650 blood indicators 449 blood lipid profile 154, 656 blood lipid profiles 114, 209 blood lipids 62, 111–12, 161, 209, 238, 596, 640 blood loss 458, 758 blood pH 414 blood pressure 27, 62, 81, 174, 239, 272, 410, 421, 594–5, 626, 635, 643, 656 determinants 643 modifications 644 blood sugar 97 blood tests 209, 510 blood transferrin 455 blood vessels 389, 411, 528–9, 566, 635, 646 diseases of the large/small blood vessels 648–9 integrity of 362 permeability of walls 634 blood volume 410, 537 blood volume regulation 412 bloodstream 77, 80, 107, 354, 631, 704
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Index
BMI-for-age percentiles 581 body, the 110 adaptations of see body adaptations alcohol in 242–51 blood concentration maintenance 378 capabilities 77 challenges 67 chemical reactions in 214–18 composition 5 coordinated activities of 67 defences see defence systems elemental composition 712 energy in 8 equilibrium 88 glucose in 107–12 growth, maintenance and repair of 5, 7 handling of minerals 420 nutrient support 5–6, 40 over-enlarged 523–4 power of mind over 524 protein in 184–93 roles of substances in 151–4, 421–2, 425–6, 428–30, 435–8, 454, 464, 468, 470, 472, 474–5 systemic operations see systems total acid burden 415 body adaptations 492–517 body builders 522 body cells 348 body composition 5, 200, 244, 254–70, 310, 314, 495, 606–7, 637 body dysmorphia 279 body fat 11,153, 228, 271, 289, 753–5 body weight, distinction 200 distribution 267–70, 573 estimates 753 health risks 271–3 loss 197 body fat stores 505 body fluids 428, 666 calcium in 428–9 distribution and movement of 407–10 body heat 231 body image 266, 288 body mass 522 body mass index (BMI) 271, 273, 298, 580–1, 753 body shapes and 267 body shapes 267 ‘apple’ and ‘pear’ shapes 269 body size 263–4 body temperature 146, 416, 707 body tissues 23–4, 237–8 body weight 61–2, 129, 131, 174, 238, 265–71, 277, 314, 388, 416, 449, 528, 566, 606, 617 body fat, distinction 200 health risks 271–3 losses or gains 41, 742 statements 44 water components 407 bolus 69, 102 bomb calorimeter 255 bonding requirements 96 bonds 187, 232, 255, 392, 711 lines representing 97 bone calcium 446–8 bone defects 382 bone density 389, 401–2, 445–6, 448–9, 553, 590
bone development 590 phases throughout life 434 bone loss 63,279, 422, 434, 446, 448–9, 590 adult see osteoporosis comparison over time 448 minimising 447–8 bone mass 446 maximising 446–7 bone mineral density 450 bone mineralisation 401 bone remodelling 448 bones 89, 151, 361, 589 bone proteins 396 calcium in 428 development and disintegration 445–6 formation 71 growth 381, 387 rebuilding 362 role of vitamin D in 387, 401–2 boredom 3 boron 522 bottled water 691 safety 419 botulinum toxin 687 botulism 574, 671, 673 bowed legs 388 bowel movements 83, 87, 89 bowing ribs 391 boys BMI-for-age percentiles 581 calcium intake 449 energy needs 589 brain, the 71, 83, 108, 259, 379, 560, 595, 706, 753 alcohol in 247 chemistry of 3 damage to 681, 689 development 159, 197 function 159 glucose for 236–7 brain cells 108 brain disorders 388 brain function 614–15 branched-chain amino acids 202 brands 374 brand loyalty 3 breads and cereals 7, 50–1, 124, 162, 620, 641 refined, enriched or wholegrain 50 breakdown reactions 217 breakfast 590 breast cancer 11, 402, 448, 653 breast milk 550, 564, 566–70, 572, 577 allergy and disease protection 569–70 immunological protection 568–9 nutrients in 569 vitamin and mineral content of 568 breastfeeding 371, 388, 566 benefits of 551 data 550 encourage, support and promote 43 frequency and duration of 566–7 a learned behaviour 551–2 steps 552 breathing 67, 87 deeply 87–8 breeding 697
brite adipocytes 294 broccoli 655 brown adipose tissue (BAT) 231,294 brown sugar 113 browning 294 brussels sprouts 655 bubbles 418 buffer systems 435 buffers 413–14 building reactions 216 bulimia nervosa 88, 277, 281–3 characteristics 281–2 treatment 283 ‘burning feet’ syndrome 345 burns 361, 413 butter 51, 384 ‘buyer beware’ 36 by-product 91
C
cabbage 655 cadmium 361, 477 caesarean section 535 caffeine 93, 250, 418, 514, 550, 555, 590, 741 calbindin 430 calciferol see vitamin D calcification 389 calcitonin 429, 448 calcitriol 387 calcium 40, 52, 63, 106, 371–3, 382, 389, 401, 418, 420, 428–35, 441, 445–8, 541, 590, 611, 691 in body fluids 428–9 in bones 428 dietary 449 food sources 431 recommendations and sources 430–4 roles in the body 428–30 from supplements 433–4 calcium absorption 430 calcium balance 429 growth 387 calcium binders 432 calcium carbonate 450 calcium deficiency 434–5 calcium intake 433–4 calcium metabolism 200 calcium rigor 430 calcium supplements 433 calcium tetany 430 calcium-to-protein ratio 199 calculation 741 energy available from foods 9 calculation aids 765–6 cancer 2, 28, 62, 71, 92, 121, 155, 158, 169, 198–9, 208, 272–3, 303, 351, 401, 439, 624, 652–5, 663, 665, 691 accumulation in blood/ tissue 652 classifications 652 defending against 483, 485 development 652–5 risk-reducing recommendations 655–7 role of vitamin D as preventative agent 402 selenium and 470–1 sites 654 canola oil 170 capillaries 78–80, 188, 361, 648–9 carbohydrate intake 503
793
carbohydrate loading 504 carbohydrate metabolism preview 107–8 carbohydrate-rich foods 516 carbohydrates 5–9, 20, 61, 72, 74–5, 82–3, 96–125, 129, 236, 515, 610, 717–18 ‘bad’ and ‘good’ 129–30 carbs, kilojoules and controversies 129–31 chemist’s view of 96 digestion and absorption of 102–6 digestive enzymes for 67 energy contributions 129–30 excess 235 load 11 selecting 308 sources 650 carbon 6, 96, 135, 226, 378, 710–11 carbon chains 136 length 135–6 carbon dioxide 78, 90, 107, 214, 222, 414–15, 521, 689 carbon–hydrogen bonds 232 carbonic acid 414 carcinogenesis 652–3 carcinogens 653 carcinomas 652 cardiac output 496, 643 cardiorespiratory conditioning 496–7 cardiorespiratory endurance 496–8 cardiorespiratory endurance training 496 cardiovascular disease (CVD) 28, 154, 272, 389, 401, 403, 594, 634–42, 648, 651–2 caregivers 596 carnitine 357, 361, 374, 522 carnosine 521 carotenoids 378–9, 485 carriers 375 cascades 715 case-control studies 13–14 catabolism 217 final steps 229–32 catalyst 72 cataracts 612–13 catchment areas 692 cathartics 282 cations 408–9, 478, 713 cauliflower 655 causation 61 cause 15, 289 cause and effect 14, 208 causal roles of vitamin D 402 cell differentiation 380 cell distension 648 cell division 529 cell membrane 143, 149, 151, 153–4, 242, 408–10, 613, 703 cells 4, 10, 75–7, 206, 215, 248–9, 331, 402, 409, 566, 631, 646, 652, 703–4 continuous nutrient supply 67 coordinated actions 704 structure 703 cellulite 302 cellulose 718 Celsius (°C) 766 central nervous system 246, 704 central obesity 268 cereals 45, 50–1, 84, 124, 162, 620, 641 cerebrovascular disease 633
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
794
Index
certification systems 6 chain reactions 715 chance 14 change 608 dietary 656, 740 environmental 691–2 lifestyle changes 640–2, 644 charts 576 growth charts 565 standard charts 743 CHD risk equivalents 637 cheating 522, 524 cheese 41, 46, 106, 201, 741 chelate 463 chelating agents 472 chelation therapy 660 chemical analysis 5 chemical bonds/bonding 96, 711–12 chemical composition 708 chemical compounds 704 chemical formula 98 chemical identity 419 chemical pollution 678 chemical properties 708 chemical reactions 250, 708, 714–15 in the body 214–18 chemical structure 348 chemical symbols 96, 409, 709–10 chemicals 680, 691 hazardous 683 chemistry, basic concepts 708–16 chemists 96 chewing 74 ‘chicken blindness’ 382 child health and survival 381 childhood 564–91 nutrition during 576–88 childhood adiposity 582 childhood obesity 580–5, 594–6 children 88, 291, 681 analysis of measures in 743–53 diabetes incidents 646 dietary recommendations for 596 energy intake and activity 576 estimated energy requirements for 764 features of marasmus and kwashiorkor in 196 hunger in 577–9 length/height measurements 742 with PKU 209 recommended dietary patterns for 48 signs of malnutrition in 578–9 vitamin A deficiencies 381 weight measurements 743 ‘children’s menus’ 596 children’s preferences 585 chlordane 681 chloride 409, 420, 425–6, 440 deficiency and toxicity 425–6 recommendations and intakes 425 roles in the body 425 chloride deficiency 425–6 chlorine 691, 713 chlorophyll 385, 438 choice dietary choice continuum 61 of foods see food choices healthy 53, 63–4 choking 69, 87–8, 608 prevention 586
cholecystokinin (CCK) 82–3, 146, 258, 293 actions 83 cholesterol 81, 160, 163–4, 208, 634, 637–8, 656 ‘good’ 143 health effects and recommended intakes 154–6 cholesterol degradation 209 cholesterol screening 640 choline 142, 333–4, 357, 617 chondroitin 614 chromium 10, 475–6 overview 476 recommendations and sources 476 roles in the body 475 chromium picolinate 522 chromium supplements 476 chromosomes 206, 703 chronic conditions management 528 chronic disease 2, 20, 26, 40, 63, 113–14, 198, 208, 372, 393, 533–4, 757 early development of 594–6 ‘rich countries’ problems’ 25 risk factors for 26–8 chronic diseases 594, 632–4 chronic inflammation 272–3, 653 chronic kidney disease 421 chronic PEM (long-term food deprivation) 195, 197 chronological age 602 churning 74 chylomicron 147 chylomicrons 77, 148 chyme 69–70, 73, 82, 146 cigarette smoking see smoking circle (plate) 49 circulation 464–5, 648–9 circulatory system 77–80, 635 cirrhosis 471 cis configuration 141, 379–80 cis fatty acids 141 citrus fruits 364–5 claims 54–7, 155, 362, 373–5, 488 of fad diets 321–2 herbs, effectiveness 664 cleavage 378 climate 692 clinical concerns 209–10 clinical studies 209 clinical syndromes 196–7 clinical trials 13–14, 170, 402, 660 clinically severe obesity 302 cloning 698 Clostridium botulinum 671 clustering of food by nutrient content 44 of risk factors 27 clusters, of symptoms 594 CoA 219, 359 cobalt 477 coconuts 160 codes/coding 697 Australia New Zealand Food Standards Code 701 DNA encoding 703 Food Standards Code 571 coeliac disease 89 coenzyme NAD (nicotinamide adenine dinucleotide) 245–6 coenzyme PLP (pyridoxal phosphate) 345–6, 360 coenzyme Q10 522
coenzyme thiamin pyrophosphate (TPP) 334 coenzymes 218, 239, 333, 338, 721–5 actions 334 cofactor 454 cofactors 361 coffee 93, 250, 740–1 cognitive decline 11 cognitive skills 313 cohorts 13–14 coins, flipping 14 see also randomisation colitis 88–9 collaboration 17 collagen 186, 361 colon see large intestine colon cancer 402, 653 colonic irrigation 90 colorectal cancer 26, 248 colostrum 569 colours 52, 687–8, 708 artificial 56 of urine in relation to hydration 416 of vitamin A foods 384–5 coma 188, 373 common cold 466 communication 16, 71 networks 707 community 198 community environment 739 community health organisations 739 community public water systems 691 companionship 2 comparison 124, 307, 459, 538 of body composition 268 bone loss over time 448 of chemical structures 232 of cis- and trans-fatty acids 141 EAR–RDI comparison 18 of food nutrient density 41, 53 of foods of differing sizes see nutritional information/facts glycogen and starch molecules compared 100 of GM food with conventional food 701 of healthy eating guides/plans 645 of intake against standards 741 of meals – saturated and unsaturated fats 172 of nutrient recommendations 21 of omega-3 and omega-6 fatty acids 138 of popular diets 322–3 of saturated and unsaturated fatty acids 139 selective breeding–genetic engineering 697 of skinfold measures with standards 754 compensatory behaviours 282 competition 516–17 complementary and alternative medicine (CAM) 660–7 defining 660 sound research, loud controversy 660–2 complementary medicines 375 complementary proteins 195 complementary therapies 660 complex carbohydrates 61, 96, 100–2
compliance testing 683 complications 92, 648–9, 651 compounds 5–6, 160, 200, 361, 392, 473, 653, 682–3, 704, 708 amino acids to make 191 stable 715 compromised intestinal function 470 conception 528 weight prior to 534–5 conclusions 16 cautious 15–16 condensation 98–9, 107, 139 conditionally essential amino acid 179 conditions mutually aggravating 637 optimal systems 83–4 real life 670 as risk factors 633 confectionary 488 confusion 280, 461, 617 conjugated linoleic acids 142 connective tissues 361 consignment testing 684 constipation 81, 87, 89–90, 106, 239, 542–3, 610 consumer awareness 674 consumer concerns about food and water 670–93 about irradiation 679 about pesticides 684–5 consumer groups 35 consumer guidelines 674, 681–2 consumers 165, 666 environmental considerations 691 food dollars 3 hesitation of 699 misleading information for 33, 169 perspectives 665–7 preventive measures–food-borne illness 674 consumption 19, 365, 740 of alcohol 650, 741 of pesticides 700 contaminant minerals 477–8 contaminants 10, 79, 197, 549, 691 ‘bad guys’ 477–8 environmental 680–2 persistence and clustering quality 680 contaminated water 690 contamination 90, 171, 462–3, 690 points of 674 contamination iron 462 contraction 89 control 14 for biotechnology 701 of diabetes 651 energy (kilojoule) control 40 industry controls–food-borne illness 674 nervous system control 704 of weight see weight control control group 14–15 controversy 660–2 convenience foods 3 conventional medicine 660 conversions 765 of carotenes 383–4 of retinol and retinal 378–9 reversible and irreversible 379 of vitamin A compounds 379
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Index
cooking (food) 52, 160, 170, 420, 540–1, 608, 653, 682 creatively 620 see also food preparation cool-down activities 495 coping 282 copper 10, 472–3, 691 overview 472–3 recommendations and sources 472 roles in the body 472 copper deficiency 472 copper toxicity 472 Cori cycle 222 corn 101, 698 GM 701 Cornish diet 323 corn sugar 112 corn sweeteners 113 corn syrup 113 corn syrups and solids 112 cornea 379 coronary arteries 634, 636 coronary heart disease (CHD) 11, 26, 634 recommendations for reducing risk 638–42 risk factors 636–8 coronary thrombosis 635 corpuscular volume 760 corrective therapy 88 correlation 15, 61, 199, 271, 402–3, 596 cortical bone 445 corticosteroids 757 cortisol 143 cortisone 143 cough 87 Council of Australian Governments (COAG) 692 counselling 740 coupled reactions 217 covalent bonds 711, 713–14 covert condition 24 cow’s milk 572 introducing 572 cramping 300, 393 cravings 130, 543 C-reactive protein (CRP) 635 creatine phosphate (CP) 499–500, 521 credentials 34–5 cretinism 469 critical periods 530–4 critical thinking 32 crop resistance 700 crop yields 685, 696–8 crops 488 cross-contamination 675–6 cross-sectional studies 13–14 cruciferous vegetables 655 crying 567 Cryptosporidium 690 crypts 75–6 cues 71, 257, 306 culture 172 customs 2–3 cyanide poisoning 662, 682 cyanogens 682–3 Cyclospora 690 cysteine 440 cystic fibrosis 393, 395 cystine 735 cytokines 631 cytoplasm 703 cytosol 703
D
daily intakes 44–5, 165 average 21 patterns 740 daily meals 81 regular 317 Daily Value 165 dairy foods 50 dairy products 28, 106, 112, 431 dams 692 dangerous products and procedures 299–302, 662–3 DASH (Dietary Approaches to Stop Hypertension) diet 325, 421–2 data 438, 742 anthropometric 23 historical 738 interpretation 21 preliminary 738 data collection 12, 22, 24, 738 DDT 681 deamination 192, 226–7 death 25–6, 62, 90, 153, 188, 282, 371, 373, 389, 416, 594, 635 from alcohol-related events 242 leading causes of Australian deaths 26, 632–3 death rates 170 debate 699–700 decaffeinated coffee 93 decaffeinated coffee beans 698 decision making, about food 2–3, 49 defecation 69, 89 defence systems (body) 630–2 deficiency 18, 23, 202, 334, 346, 362–3, 381–2, 386, 388–9, 393, 395–6, 424–7, 439, 457–60, 465, 468–70, 646, 648, 697, 761 classical 371–2 overt deficiency disease correction 371 subclinical 372 symptoms 21, 40 see also requirement dehydration 410, 416, 609, 619, 626 signs and symptoms 416 dehydroascorbic acid 361 de-ionisation 691 delirium 280, 416 dementia 615 denaturation 181 denominators 737, 765–6 dental caries 88, 115, 282, 474, 656 prevention 588 dental plaque 115 dentition 316 dentures 607–8 Department of Agriculture and Water Resources 683–4, 690 Department of Health and Ageing 44 depressant 247 depression 3, 238, 282, 284, 363 deprivation 305 dermatitis 89 desalinated seawater 693 desalination 692 descending colon 70 ‘designer’ therapies 209–10 desserts 155, 574, 642 detoxification 79 development and growth measures 742–53 dextrose 113 DHEA (dehydroepiandrosterone) 522–3
diabetes 11, 26, 62, 110–12, 114, 121, 169, 272, 388, 401, 403, 421, 439, 554, 633, 637, 656 complications 648–9 development 646–7 recommendations 649–51 underlying/contributing to other diseases 646 untreated 649 diabetes mellitus 646–51 diagnosis 89, 93 diagnostic criteria 277, 281 diaphragm 67 diarrhoea 81, 87–9, 105–6, 202, 300, 363, 373, 381, 413, 521, 569, 574, 619, 678 diet 2, 11, 17, 20, 22, 25–8, 61, 77, 80, 89, 93, 208, 417, 421, 430, 584, 626, 645–6, 738 affects on glycogen storage and use 501 affects protein use during activity 506–7 central role of meat 201 choosing diet to support fitness 515–16 delaying cognitive decline by 11 for diabetes 649–51 exclusions/inclusions 61–2 of father and children 582 healthy 40–57, 170 to lower blood pressure 421 manipulation of 603–5 for physically active people 515–17 poor 388 popular 322–3 vegetarian 61–4 also under specific diet see also heart-healthy diets diet analysis program 22 diet history 738–41 diet plans/planning 40–53, 62–3, 124–5, 160–5, 296, 324–5 dietary advice 34, 111, 656 dietary calcium 449 dietary changes 656, 740 dietary factors 625, 654–5 dietary fat 650 dietary fibre 90, 96–123, 164, 516 diabetes link 651 health effects and recommended intakes of 116–20 dietary folate equivalents (DFE) 348 estimates 349–50 dietary guides/guidelines 42–50 dietary intake 23, 122 dietary intervention trials 392 dietary nitrate 521–2 dietary patterns 28, 47–8, 61 dietary recommendations 169, 545–6, 596 dietary status 25 dietary strategy 641 dietary supplements 508, 520 that do, do not, may not perform as claimed 520–2 dietitians 34, 209, 371, 663, 738 Dietitians Association of Australia (DAA) 34–5 diet-related disease 26, 630–57 diffusion 75, 104 digestibility 194 corrections for 736 lower digestibility of plant proteins 62
795
digestion 8, 67–84, 739 of carbohydrates 102–6 easily digested meals 516 final stage 73–4 inhibitors 735 of lipids 144–7 muscular action of 67, 69–71 preparation for absorption 67 of protein 182–3 see also hydrolysis digestive enzymes 71–2, 82–3, 182 for carbohydrate, fat and protein 67 digestive fibre 73–4 digestive glands 72 digestive problems/disorders 77 common 87–93 digestive secretions 71–3 digestive system 69 digestive tract see gastrointestinal (GI) tract digoxin 625, 664, 666 dinner 641–2 dioxin 691 dioxins 681 dipeptides 180 disaccharides 7, 96, 98–9, 102, 717 disadvantaged groups 371 discretionary kilojoule allowance 310–11 discretionary kJ 164 discussion 16 disease 20, 62, 80–1, 158, 208–9, 372, 381, 672–3 chronic see chronic disease diet-related 630–57 genetic component 633 heart see heart disease hereditary susceptibility to 656 immunity to 698 introduction of 699 reduced risk of 372 water-borne 691 also under specific disease 403 disease burden 27 disease prevention 483 disease risk profile 298 disease-causing bacteria 569 disinfectant 691 disinfectants 242 disordered eating 278–9 in athletes 277–9 disorders 88, 196, 208–9, 388, 395, 647, 676 dissociation 407, 714 dissolving 409, 450 distillation 691 distilled liquor (hard liquor) 242, 244 distractions 296 distress signals 87 disulphide bridges 440 diuretics 418, 427, 646 diverticula 90, 121 diverticular disease 62 diverticulitis 90 dizziness 461 DNA (deoxyribonucleic acid) 184, 208, 346, 351, 354, 464, 655, 657, 703, 714 DNA methylation 208 DNA molecules 206 DNA sequence 206, 208 docosahexaenoic acid (DHA) 152, 568, 570
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796
Index
doctors 34, 371, 662, 666 see also healthcare professionals documentation 373 dolomite 450 dopamine 284 dosage/dose levels 19, 374, 465, 488, 521, 664, 686 megadoses 549–50 therapeutic 371 double bonds 136–8, 141 double-blind experiments 15 ‘dowager’s hump’ 445–6 Down syndrome 548 ‘downhill’ reactions 715 drinking 67, 88 drinking patterns 560 drinking water 410, 413, 417, 474 sources 690–1 drinks 244 see also beverages; standard drinks guide drought 692 drug absorption 625 drug history 22, 738–9 drug testing 520 drug therapy 644, 646 drug toxicities 626 drugs 70, 79, 89, 92, 242, 302–3, 393, 396, 487, 548, 555, 617, 662, 696, 698, 738 actions 623 drugs–nutrients interactions 623–6 efficient delivery 698 inactive ingredients in 626–7 dukan diet 323, 325 duodenal ulcers 92 duodenum 69–70, 73, 88 dysentery 198 dysmorphia 279 dysphagia 607
E
early pregnancy 545 early puberty 289 Eat Right 4 Your Type 323 eating 49, 67, 172, 236, 259 away from home 591 good eating habits 2, 373, 596 Healthy Eating Pyramid 49 overeating 3–4 a scientific experiment see genetically modified foods slowly 294 triggering desire see ghrelin see also binge eating; eating patterns Eating and Activity Guidelines for New Zealand Adults 43–4 eating disorders 196, 277–84, 427 combating 280 preventing in athletes 279 in society 284 eating habits 296, 582, 590, 740 of older adults 617–20 eating patterns 172, 238, 283, 305–9, 433 healthy 49, 172 eating plans 63 eating statements 43–4 eclampsia 546 economic changes 608 economic circumstances 22 ecosystems 699
ectopic fat 272 education 34 educational level 22, 739 eggs 45, 49, 125, 160–1, 201, 384, 390, 620, 735 enriched 163 eicosanoids 152, 635 eicosapentaenoic acid (EPA) 152 18-carbon fatty acids 137, 218 elderly people 88, 316, 372, 389, 402, 416, 671 electrical impulses 379 electrolyte abnormalities 90 electrolyte balances 278 electrolyte deficiencies 437 electrolyte imbalance 413 electrolyte loss/replacement 512–14 electrolyte solutions 408, 566 electrolytes 407–9, 512 attract water 408–9 important body electrolytes 408 to support activity 510–14 electron carriers 454 electron transport chain 219–20, 222–4, 230–1, 338, 340, 704, 729–31 electronic media 32 electronic scales 743 electrons 361, 708, 713 exchange 715 shells 709–11 unpaired 392 elements 6, 419–20, 708 chemical symbols for 709–10 configuration 713 elimination 71, 74, 89 embarrassment 90, 299 embolism 635 embryo 529–30 embryonic developmental stages 530 emergency assistance 87–8 emerging risk factors 638 emetics 282 emotional comfort 3–4 emotional health 555 emotions 3 empty-kilojoule foods 42 emulsification 82–3, 146 emulsifiers 73, 687, 689 encouragement 43 end products 715 endangered species 664 endergonic reactions 715 endocrine organs 11 endocrine system 81, 705 endocrinology 704 endogenous cholesterol 144 endogenous N 737 endoplasmic reticulum 704 rough and smooth 704 endurance training 261, 449, 509 enema 90 energy 5, 20, 107, 129, 214, 248, 375, 538–9, 552–4, 566–70, 576–7, 589–90, 609–10, 708, 766 in alcohol 248 amino acid use for 191–2 in the body 8 breaking down nutrients for 218–33 concentrated form of 52 cuts 160 energy-yielding nutrients 6–9 excess 234–5 facilitating release of see vitamins
from foods 7–8 measured in kilojoules 7 sources 190 sufficient to meet needs 40, 43 using glucose for 107 energy (kilojoule) control 40 energy allowances 42, 62, 114, 609, 611 energy balance 154, 234–9, 254–73, 294 energy bars 520 energy budgets 239, 254 energy density 7, 258, 306–7 energy drinks 520 energy expenditure 197, 262–3, 291–2, 310, 762–5 components 260–3 energy fitness shakes 427 energy gels 520 energy homeostasis 71 energy in 255–9 energy intake 11, 197, 235, 305, 324, 576, 589 energy metabolism 8, 214, 361, 460, 703–4 alcohol’s interference with 732 central pathways of 233 machinery 237 energy needs 564 energy nutrients 553, 565–8, 609–10 energy out 260–5 energy pathways 223 amino acid entry 227 fats entry 225 glucose entry 226 energy recommendations EERs 19 establishing 20 energy regulation 131 energy requirements 53, 762–5 energy restriction 603–5 energy systems ATP and CP 499–500 to support activity 498–508 energy-balance equation 254–5 energy-dense foods 316–17 energy-yielding nutrients 6–9, 72–4, 218–19, 228–9, 232, 255, 330, 417, 568, 647 roles 8–9 enforcement agencies 56 enhanced water 514 enriched products 50 enterohepatic circulation 147, 354 enteropancreatic circulation 464–5 environment 197, 255, 295–7, 415, 739 abnormal 11 cellular interactions with 703 contaminant entry 681 costs to 691 environment–genes interaction 653 preserving 478 residues in the 683 environmental change 691–2 environmental concerns 4, 700 environmental considerations 691 environmental contaminants 10, 549, 680–2 harmfulness of 680–1 environmental factors 209, 390, 582, 653 environmental protection 700–1 Environmental Protection Authority (EPA) 171, 701
environmental temperature 417 enzymes 186–7, 218, 244, 374, 413, 454 actions 187 degradative 381 digestive 67, 71–2, 82 inactive form of 82 intestinal 73 mucus protection from 73 ‘softening’ 697 vitamin C assistance 360 ephedrine 300 epidemics 289, 583 epidemiological studies 13, 209, 392, 655 epigenetics 207, 291–4 epiglottis 68–9 epinephrine 109 EpiPen 580 epithelial cells 380 epithelial tissue 380 equations 254–5, 264, 643, 762–4 equivalents 348, 637 ergogenic aids 520–4 error 671, 761 erythrocyte haemolysis 393 erythrocyte protoporphyrin 459, 760 erythrocytes see red blood cells essential amino acids 179, 200, 209, 720 essential fatty acids 151–3, 539 essential minerals 10, 52–3 essential nutrients 6, 40, 407 essential oils 688 Estimated Average Requirement (EAR) 17–18, 330 Estimated Energy Requirement (EER) 20, 763–5 estimated energy requirements (EER) 263–5 estimation 20, 23, 342–3, 349–50, 740, 753, 763–5 of calcium intake 433–4 ethanol 97, 242, 245, 249–50, 732 ethical dilemma 699 ethical issues 699 ethnic background 22, 739 ethnic groups 105 ethnic heritage 2 ethnic populations 648 ethyl alcohol 242 euphoria 244 evacuation, periodic and voluntary 67 evaluation 336–7, 738, 743 informal 741 of reliability of research 16 evaporation 693 events, happy occasions 3 evidence 15–16, 19, 129, 198, 372, 403, 520 examinations, physical 23–4, 755 excitatory nerves 247 exclusions (food) 61 excretion 67, 228, 331, 739 of drugs 626 of fat in GI tract 164 in the kidneys 413, 415 of urea 193 exercise 34, 42, 291, 373, 492 to build muscles 317 intensities 522 during pregnancy 536–7 Exercise and Sports Science Australia (ESSA) 34 exercise guidelines 537, 604
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Index
exergonic reactions 715 exhalation 78 exhaustion 416 exogenous cholesterol 144 experimental designs 403 experimental group 14–15 experimental studies 13, 737 experiments 12, 14–16, 699 nutrition experiment 360 ‘extra’ foods 46, 50 extracellular fluid 187, 407, 410, 428 extremes 17–18 eyelids 380 eyes 88, 249, 379, 407
F
facilitated diffusion 75, 104 facts 53–4, 56 FAD (flavin adenine dinucleotide) 338, 360 fad diets 28, 200, 239, 300, 588 appeal 324 claims and truths of 321–2 identifying 325–6 rating 325–6 faeces 90, 147, 191, 415, 737 faeces sweat 191 Fahrenheit (°F) 766 fainting 300 fake credentials 34–5 falls 402, 603 false positive/negative 363 family history 22, 244, 633, 636–7 farming 698 fashion 266 fast diet 323 fast food 3 fast-food restaurants 591 fasting 4, 153, 245, 649 inadequate energy 236–9 intermittent 238 special requirements for glucose during 237 transition from feasting to 235–6 fasting blood glucose 647, 651 fat and fit 298 fat breakdown 224, 237 fat cells 292, 294 development 289 metabolism 289–90 fat digestion 146, 395 in the mouth, stomach and small intestine 146 fat distribution 268 fat emulsification 82–3 fat intake guidelines for 169 moderation strategies 52–3 reducing 161–5 fat malabsorption 393 fat metabolism 209 fat replacement 169 fat replacers 165 fat synthesis 647 fat use 505–6 fatigue 24, 40, 239, 460, 494, 666 fatness 295 fats 3–9, 20, 42–3, 46–7, 50–1, 72–5, 82–4, 107, 163–4, 236, 505–6, 577, 610, 642, 650, 741, 753–5 amino acid use for making 192 digestive enzymes for 67
excess 235 fat fragments 108 location of fat 290 making from glucose 108 selecting 308 storing fat as fat 153 using for energy 153–4 fat-soluble vitamins 77, 80, 90, 160, 331–3, 378–98 deficiency 395 overview 398 versus water-soluble 378 fatty acid deficiencies 153 fatty acid oxidation 727 fatty acid profile 701 fatty acids 11, 62–3, 104, 135–9, 144, 161–3, 171, 218, 223–5, 235–6, 242, 244–5, 379, 392, 577, 635, 638, 646, 682 to acetyl CoA 223–4 chemical structures of 232 chemist’s view of 135–42 composition 140 inability to synthesise glucose 225 stockpiles 245 fatty deposits 595 fatty fish 161, 390 fatty liver 197, 245 fatty meats 171 fatty streaks 595 feasting excess energy 234–5 transition to fasting 235–6 feedback 704 feedback mechanisms 81 feet 649 female athlete triad 277 female growth patterns 588 fermentable quality 101 ferric iron 454 ferritin 455, 458 ferrous iron 454, 713 fertilisers 696 fertility 544, 681 fertility problems 316 fever 261, 619 fever, fluid imbalances 198 fibre 5, 46, 62, 73–4, 81, 90, 96–102, 164, 307–8, 577, 591, 610, 651, 655, 703 fibrocystic breast disease 393 fibrosis 246 fibrous connective tissue 595, 634 Fight Bac! 675 fight-or-flight hormone 109 fight-or-flight response 605–6 financial concerns 739 findings see research findings first aid 87 fish 45, 50, 52–3, 63, 160, 162, 171, 549, 596, 680–1, 741 alternatives 741 raw 366 fish liver oils 384 fish oil 394 fish oil supplements 158–9 fit and fat versus sedentary and slim 273 fitness 492–517 benefits of 492–4 components 495 developing 494–5 supportive diets 515–16 fitness programs 495 flatulence 89–91
flavonoids 485 flavour 2, 52, 160, 687–8 flavour enhancers 688 flaxseeds 483 flexibility 312, 495 flexitarians 61 floods 692 flours 4 fluid balance 197, 247, 415, 418 regulation of 410–12 regulators 187 fluid imbalances anaemia 198 fluid intake 415 fluid loss 88, 413, 511, 566 fluid needs 515 fluid replacement 515 via hydration 511–12 fluid retention 643, 741–2 fluids 67, 90, 278, 413, 713 of cells 703 dripping 69 imbalances 88 to support activity 510–14 fluorapatite 474 fluoride 10, 371, 474–5, 656, 690 overview 475 recommendations and sources 475 roles in the body 474 fluoride toxicity 474–5 fluorosis 474–5 FMN (flavin mononucleotide) 338 foam cells 634 FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) 89, 106 foetal alcohol spectrum disorder 558 foetal alcohol syndrome (FAS) 558–60 facial characteristics of 559 foetal development 545, 560 foetal growth and development 529–30 stages and critical periods 530–4 foetal programming 534 foetus 407, 530, 553 preterm and premature 571 folacin 348 folate 47, 62, 81, 199, 333–4, 348–54, 367, 591, 625, 760 absorption and activation 349 food sources 353 normal values for 760 recommendations 348–9 folate deficiency 248, 352, 625 folate supplements 350, 533 folate toxicity 353 folic acid 51, 348, 371, 533 supplements 11 folk remedies 664 folklore 660 food additives 686–9 for texture and stability 689 food allergy 573, 579–80, 740 detecting 580 Food and Agriculture Organization (FAO) 384, 679 Food and Nutrition Guidelines for Healthy Infants and Toddlers 550 food availability 2–3, 739 food aversions 543, 623 food biotechnology 696–701 debates regarding genetic engineering 699–700 food chain 680
797
food choices 2–4, 63–4, 308, 364, 538–9, 573–4, 590–1, 601, 617–20, 739 behavioural or social motives 2 health and nutritional benefits of 4 healthy 63–4, 160, 162–3 heart-healthy 160, 162–3 influences on 22 poor 40 sound 64 food composition tables 741 food consumption 617 food cravings 543 food crops 488 food deprivation 195, 197–8, 238 food faddism 196 food frequency questionnaire 741 food group plans 44 food groups 43, 45–6, 741 nutrient-dense options within 47 also under specific food group food habits 21, 739–40 food intake 255–9, 316, 740 analysis and limitations 741 reducing/limiting 2–3 food intolerance 579–80 food intolerances 580 food labels 53–7, 142, 685, 701 protein regulations for 195 read 125, 165 see also labels/labelling food packaging 53, 57, 679 food poisoning 671, 678 food preferences 739 food preparation 2–3, 43, 420, 653 to minimise pesticide residues 684 food preservatives see preservatives food processing 4, 696 effect on content 423 efficient 697–8 food production 698 food records 740 food safety 43, 670–9 advances in 679 concerns 670–93 from farms to consumers 674 keeping hot food hot; cold food cold 675–7 limits 684 food scarcity 735 food security 297 food shortages 696 food skills 586 Food Standards Australia New Zealand (FSANZ) 51, 53–4, 171, 350, 375, 422, 469, 570–1, 670, 683–4, 686, 701 FSANZ Model List of preapproved statements 56 Food Standards Code 571 food storage safe refrigerator storage times 678 see also food safety food supply 670 food toxins 671, 673 food-borne illness 549, 619, 671–3, 678–9, 687 food-borne infections 630, 671–3 food-handling techniques 570 food-related dreams 238
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Index
foods 2, 4, 49, 67, 84, 142–3, 662–3, 670–93 accessibility, ease and convenience 295 additives in see food additives appropriateness 741 availability, convenience and economy 2–3 breast milk and 554 calcium in 431 clusters 44 colours of 487 combinations 40, 77, 322 composition 5, 255, 417 consistency 689 empty-kilojoule 42 in the fields 683–4 ‘If in doubt, throw it out’ 677 keep hot food hot; cold food cold 676 magnesium in 438 metabolic consequences of eating 324 ‘natural’ 682 natural toxins in 682–3 nutrients in 5–6 to omit for infants 574 as pharmacy 487–8 phosphorus in 436 on the plate 684 potassium in 427 protein in 194–5 versus supplements 392–3 temperatures 675–7 to use sparingly 423 visual appearance 686 vitamin D in 390 water content 417 also under specific food types formaldehyde 689 formula (infant) 565–6, 568 composition 570 special, inappropriate 571 standards for 570–1 fortified foods 50, 53, 62, 384, 390, 430, 656 mandatory fortification 51 foxglove 664 fractions 765–6 fractures 362, 382, 389, 396, 401–2, 434, 449–50 Framingham Heart Study 639–40 ‘Frankenfoods’ 698 fraud 206, 630 free iron 363 free radicals 360–2, 392, 470, 509, 634 formation 715–16 fructose 96, 98, 104, 106, 130–1, 219, 645 fruit drinks 112 fruit juices 582, 688 fruits 3, 40, 45, 49–50, 52, 61–2, 90, 112, 120, 125, 160, 162, 164, 351, 360, 364, 392, 396, 422, 638, 641, 655, 688, 690, 741 raw 365 FSANZ Model List of pre-approved statements 56 fuels 214, 236, 500, 506 sources 8 to support activity 498–508 fullness 83 functional foods 483–8 functional magnetic resonance imaging (fMRI) 259
fungi 80, 690 future foods 488
G
galactose 96, 98, 104, 219 gall bladder 68–9, 71–3, 82 gall stones 62 gamma-oryzanol 522 gamma-tocopherol 392 gangrene 649 gases 90–1, 104, 708 gastric acid 83, 249 gastric juices 71–3, 378 gastric surgery 303–4 gastric ulcers 92 gastrin 81 actions 83 gastrointestinal (GI) tract 5, 82, 88, 103, 144–5, 183, 197, 382, 418, 572, 607, 631–2, 755 anatomy 67–9 carbohydrate, fat and protein constituents 67 digestive stages and process 67–74 distress 373, 434 fat digestion in 145 fat excretion 164 health and regulation of 80–4 lining of 9, 380 microbiome, hormones and nerve pathways 80–3 muscular layers 70 optimal system conditions 83–4 gastrointestinal health 121 gastrointestinal hormones 259 gastrointestinal motility 112 gastro-oesophageal reflux 91–2 gels 689 gender 17, 23, 28, 244, 263, 448, 630, 636–7, 763–5 gender difference 290, 637 gene expression 186, 206–7, 464 nutrient regulation of 208 gene pool 295, 700 gene technology 488 Gene Technology Act 2000 701 gene technology regulations 701 gene transcription 11 general level health claims 56–7 generalising 14, 740 genes 206–7, 272, 696 environment–genes interaction 653 influences on 379 switching on and off 207–8 unwanted 701 genetic abnormality 363 genetic ammunition 698 genetic contributions 528 genetic disorders 472 genetic engineering 198, 696–8 comparison with selective breeding 697 debates 699–700 potential problems and concerns 698–701 genetic factors 582 genetic markers 210 genetic pollution/improvements 700 genetic profile 206, 210 genetic research 698 genetic tendencies 316 genetic tendency 22
genetic traits 207–8 genetic variation 206, 208–9 genetically modified foods 4, 385, 696–701 genetically modified (GM) organisms 701 genetics 2, 20, 28, 244, 255, 291–4, 448–9, 594, 630–1, 633, 644 genetic predisposition 634 genome 10 genomics 206–10 genomics primers 206–8 germanium 664 germs 679 gestation 530, 571 gestational diabetes 545–6 ghrelin 71, 292–3 GI contractions 89 GI motility 83 Giardia 691 gimmicks 302 Ginkgo biloba 664 ginseng 522 ginseng pyruvate 522 girls BMI-for-age percentiles 581 calcium intake 449 energy needs 589 glands 72, 75–6, 81, 247, 698, 704 glass 689 gliomas 652 global food system 289 glucagon 108–9 gluconeogenesis 108, 503 glucosamine 614 glucose 88, 96–8, 104, 107, 218–23, 225–6, 500–5, 646, 708 amino acid use for 191–2 balancing within normal range 109–10 in the body 107–12 for the brain 236–7 chemical structures of 232 falling outside normal range 110 making fat from 108 making from protein 108 to pyruvate see glycolysis sources 190 storing as glycogen 107 using for energy 107 glucose homeostasis 108, 475 glucose metabolism 731 glucose synthesis 225 glutamate 348 glutathione peroxidase 338, 470 gluten 89 gluten-free diets 89 gluttony 284 glycaemic control 535 glycaemic effect 650 glycaemic index (GI) 111–12, 131, 324, 505, 650 glycaemic load 11 glycaemic response 110–12, 119 glycerol 138–9, 144, 218, 223–5, 242 to pyruvate 223 glycobiology 107 glycogen 96, 100, 107, 235–6, 500, 718 amino acid use for making 192 storing glucose as 107 glycogen breakdown 108 glycogen depletion 236, 239 glycogen stores 239, 501, 515, 517 maximising 504
glycogen synthesis 647 glycogen use 501–2 glycolipids 107 glycolysis 219–20, 222, 725–7 glycoproteins 107 glycosylated haemoglobin 651 goblet cells 75–6, 380, 382 goitre 468 goitrogen 468 goitrogen-containing vegetables 682–3 golden rice 385, 697 Golgi apparatus 704 good eating habits 2 good source of, source of, contains fibre 56 goose bumps 707 gout 363, 614 government intergovernmental agreement 692 monitoring systems 25 oversight (of industry) 700 see also Australian Government government agencies 35 grain foods 45 grains 49–50, 101, 164, 201, 392, 420 see also whole grains grams 419 granulated sugar 113 grapefruit juice–drug interactions 626 graphs 18 Greek alphabet 392 green bile 88 ‘green’ pills 374 green tea 664 grey water 692 grief 3–4 groundwater 690–1 reserves 692 group therapy 280 growth 263, 466, 564, 574, 583 growth and development/measures 528, 742–53 growth charts 565, 576 growth hormones 293 growth patterns 588, 743 growth retardation 388, 465–6, 558, 560 gums 687 gut bacteria 394
H
habit 2, 90, 296, 313–14, 316, 373, 528, 537, 582, 656, 739–40 good eating habits 2, 373, 596 habits 21, 740 habitual diet patterns 81 haem 346, 478, 760 haem iron 63, 454–5, 741 haematocrit 738, 758–60 haematocrit values 459 haemochromatosis 460 haemodialysis 757 haemoglobin 184, 188–9, 346, 454, 460, 758, 760 haemolysis 393 haemolytic anaemia 393 haemophilia 395 haemorrhage 362–3, 393 haemorrhagic disease 395–6 haemorrhoids 90, 121, 542–3
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Index
haemosiderin 457 haemosiderosis 460 hairs 75–6 handwashing 678 hard water 418, 439, 691 harm 122, 372–3, 528, 666 environmental contaminants, harmfulness of 680–1 potential for 249, 682 Harris Benedict equation 264 Hazard Analysis Critical Control Points (HACCP) 674, 678 hazardous chemicals 683 Hazardous Substances and New Organisms (HSNO) Act 1996 701 hazards 660, 686 of fasting 238 of food 670 hazardous waste sites 691 of pesticides 683 HDL (high-density lipoproteins) 149 health implications 150 HDL cholesterol 170, 637 head circumference 741–3, 753 headaches 24, 460, 626 headboard 742 healing effect 661 health 173, 210, 244, 265–7, 297–8, 583, 738 diet and 25–8 of gastrointestinal tract 80–4 optimal 324 paediatric health issues 388 promoting 61 see also heart health health advantages 62 health agencies/departments 678–9 health benefits 4, 61–2, 161, 171, 174, 596, 660–3 health claims 54–7, 373, 488 health concerns 316 health consequences 199 health effects 8, 195–202 of dietary fibre 116–20 of heavy alcohol consumption 250 of mono-unsaturated and polyunsaturated fats 156–9 of protein 198–200 of saturated fats, trans fats and cholesterol 154–6 of starch 116–20 of sugars 112–15 of water 418–19 health goals 24 health history 738–9 health problems 594, 680 health promotion 666 health recommendations 28 health risks 271–3, 288, 298–9, 308, 683 health status 22, 25, 602 healthcare professionals 34, 77, 298, 372–3, 560, 662, 738, 742–3 healthcare setting 738 ‘health-food beverages’ 196 health-promoting habits 594 healthy body weight 20, 62, 110, 528, 655 accepting 266 defining 265–7 healthy choices 53, 63–4 healthy diet 234 planning principles and guidelines 40–57 see also diet planning
healthy eating habits 596 Healthy Eating Pyramid 49, 62 healthy food choices 63–4 healthy habits 590–1, 602 healthy lifestyle 612 healthy weight 5 heart 78–9, 389, 418, 560 workload 638 heart attack 83, 150, 171, 199, 303, 623, 635, 648 heart disease 2, 11, 22, 62, 111, 114, 120, 154–5, 157–8, 169–71, 198–9, 208, 248, 351, 388, 421, 439, 522, 595, 663, 682 defending against 485 early development of 595–6 prevention strategies 393 risk assessment 639–40 heart failure 90 heart health 169–71, 174 heart muscles 197 heart rate 564 heartbeat 110 heartburn 72, 91, 543 heart-healthy diets 160, 162–3, 170, 641–2, 645 heat 231, 294 heat conservation 707 heat processing 394 heat stroke 510–11 heavy metals 361, 477, 681, 691 height 23, 564, 741–2 asking versus measuring 742 loss due to osteoporosis 447 Helicobacter pylori 92–3, 355 hepatic artery 79 hepatic portal vein 79 hepatitis 79, 676, 758 hepcidin 457, 509 herbal laxatives 300 herbal products 116, 119 precautions 664–7 herbal remedies 662–4 examples 662 herbal supplements 548 herb–drug interactions 666 herbicides 700 herbs 371, 522, 665, 688 adverse reactions/toxicity 665 purity, uses, contra-indications 664 hereditary muscular dystrophy 393 heredity 656 HGH (human growth hormone) 522–4 high blood pressure (hypertension) 27, 594, 637 high infant birth weight 545–6 high LDL cholesterol 634, 637 ‘high potency’ claims 374 high-carbohydrate liquid supplements 515 high-fat foods 2, 169–74 high-fructose corn syrup (HFCS) 112–13, 130 high-level health claims 56–7 high-protein diet 199 high-quality proteins 194, 508 high-risk pregnancies 543–50 factors 544 histidine 735 histories/historical information 22–3, 633, 636–7, 738–41 HIV (human immunodeficiency virus) 381 HIV infection 554
home water filters 691 homeostasis 71, 81, 108, 290, 293, 410, 414–15, 454, 704, 706–7 homocysteine 199, 248, 351, 634, 637 levels 760 homoeopathic medicines 375 honey 97, 112–14 hormonal (endocrine) system 81 hormonal growth promotants 690 hormones 81, 187–8, 361, 410–11, 448, 551, 653, 690, 704 gastrointestinal 81–3 major 705–6 regulating 108–9 secretion of 71 stomach 71 vitamin D 387 hormone-sensitive lipase 153 hospitalisation 281 hospitality industry 2–3 hostility 522 hourly sweat rate 511 household measures 54 human beings, energy restriction in 604–5 human body see body, the human genome 10, 206–7, 209, 291 understandings 209–10 Human Genome Project 206 human intervention 13–14 human tampering 700 humidity 416–17 hundreds of milligrams 419 hunger 71, 110, 121, 255–6, 284, 567, 576–9, 698 irregularities 316 overriding 257 hydration 416, 511–12 hydration status 755 hydrochloric acid 81, 425, 714 hydrodensitometry 755 hydrogen 6, 90, 96–7, 135–6, 221, 409, 708, 714–15 hydrogen bonds 714 hydrogen gas 708 hydrogen ions 413, 421 hydrogenation 140–1, 156, 379 hydrolysis 72, 99, 106–7, 146–7, 217 hydrophilic phosphate group 142 hydrophobic fatty acids 142 hydroponics 698 hydroxyapatite 428, 474 hydroxyl 474 hydroxyl (OH) groups 242 hydroxylates 361 hydroxylation reactions 386 hydroxylysine 361 hydroxyproline 361 ‘hyper’ behaviour 579 hyperactivity 579 hypercalcaemia 389 hypercarotenaemia 386 hyperglycaemia 646, 648 hyperinsulinaemia 648 hypertension 62, 114, 272, 388, 403, 411, 419, 421, 426–7, 439, 595, 634, 637, 642–6 development 643 potassium and 426 risk factors 644 hyperthermia 510–11 hypertrophy 494 hyperventilation 414 hypoglycaemia 110, 545, 650–1 hyponatraemia 417, 512
799
hypothalamus 71, 256, 258–9, 290, 410, 412, 416 hypothermia 511 hypothesis 12, 16 hypothyroidism 757 hysteria 363
I
ice 708 icing sugar 113 identical twins 295 IGF-1 (insulin-like growth factor 1) 757–8 ileocaecal valve 68–9, 71 ileum 69 illegal substances 520 illicit drugs 548, 555, 739 illness 70, 196–7, 316, 465, 662, 671–9 food-borne see food-borne illness see also infection imaging 259 immune response 631 immune system 107, 361–2, 385, 403, 438, 607, 630–1 person with a compromised immune system 88 weakened 671 immunisation 630 immunity 189, 631–2, 698 impaired 631–2 immunoglobulins 631 immunological protection 568–9 impaired immunity 631–2 impaired vision 393 imperial measures 766 implantation 529 incentives 54–5 incidental additives 689–90 income 608 inconsistent findings 200 Indigenous Australians 272, 648 Indigenous communities 334 Indigenous populations 371, 638 indigestion 91, 93 indirect food additives 689–90 individual variation 456–7 individuals fitting the needs of each individual 208 less-mobile 402 nutrient goals for 18, 21 nutrition assessment of 22–4 recommendations for 656–7 industrialised countries 198, 295, 466 industry controls 674 infancy 564–91 nutrition during 564–75 infant birth weight 534–5 infant colic 81 infant deaths 534 infant formula 550, 570–1 infants 88, 551, 596 analysis of measures in 743–53 birth weight 543 development and recommended foods 573 energy intake and activity 564 energy nutrients 565–6 heart rate, respiration rate and energy needs compared 564 length measurements 742 weight measurements 743
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800
Index
infection 88, 90, 92, 196, 198, 282, 361–2, 366, 382, 690 food-borne 630, 671–2 also under specific infection see also illness infectious diseases 381, 630–2 inflammaging 612 inflammation 81–2, 114, 197, 239, 249, 272–3, 388, 403, 439, 485, 612, 623, 634, 757 chronic 653 influenza virus 630 role of vitamin D 402–3 information 704 from food packaging 53 found on the Internet 16 health-related 32 historical 22–3, 738–41 nutritional see nutritional information ingestion 68, 739 ingredient lists 53, 88, 701 inhibitions 247 inhibitors 735 inhibitory nerves 247 initiators 653 injury 495 inner ear 382 inorganic elements 419–20 inorganic nutrients 6 inositol 357, 374 insoluble fibre 101 insomnia 664–5 insulin 108–9, 129–31, 324, 594, 646–7, 651 demand for 648 insulin deficiency 648 insulin resistance 11, 114, 272, 533 insulin response 111 insulin-resistant cells 594 intelligence 570, 577 intensive training 515 intentional food additives 687–9 interactions 22, 210, 478, 623–7, 740 of carbohydrate/glycaemic load with insulin resistance 11 of cells 703 drugs–nutrients interactions 623–6 enhancing or impairing immunity 632 environment–genes interaction 653 herb–drug interactions 664, 666 of metabolism 214–39 of multiple polypeptides 181 mutually beneficial 77 nutrient interactions 420 sodium–calcium interactions 420 trace minerals 453–4 intermittent claudication 393 intermittent fasting 238 International Code of Marketing of Breast-milk Substitutes 1981 (WHO Code) 571 International Olympic Committee 523 International Organic Accreditation Service 685 Internet 16, 206, 321, 374, 524, 583 nutrition on 32–3 interpretation 12 interstitial fluid 407 interstitial spaces 197, 411
intervention 13–14, 27, 88, 196, 208–9, 249, 413, 487, 594, 607, 614, 638 dangerous 299–302 intestinal bleeding 572 intestinal cells 76–7, 249, 388, 455 intestinal contents 69 intestinal enzymes 73 intestinal gas 87, 90 intestinal ischaemia 83 intestinal perforation 90 intoxication 244 intra-abdominal fat 268 intracellular fluid 187, 407, 428 intravascular fluid 407 intravenous feedings 88 intrinsic factor 354, 760 introduction 16 invaders 631 invert sugar 112 in-vitro studies, laboratory-based 13–14 iodide, roles in the body 468 iodine 10, 371, 457–60, 468–70, 540–1 overview 470 recommendations and sources 469 roles in the body 468 iodine deficiency 468–9 iodine toxicity 469 iodised salt 540–1 ion exchange 691 ionic states 454 ions 407, 713 formation 712–13 iron 6, 10, 24, 46–7, 52, 62–3, 188–9, 361, 373, 419, 454–63, 540, 589, 611, 741, 760 absorption and metabolism 454–7 contamination and supplementation 462–3 food sources 461–2 foods providing 574 meat alternatives for 40 recommendations and sources 461–2 recycling 457–8 roles in the body 454 transport and storage 457 iron absorption 454–5, 741 maximising 461–2 iron chelate 463 iron deficiency 92, 457–60, 509, 572, 578, 611, 758–9 assessment of 458 iron homeostasis 454 iron overload 363, 460 iron poisoning 461 iron status 758 assessment criteria 759 iron supplements 462–3 iron supplements, high-potency 373 iron toxicity 460–1 iron-binding capacity 759 iron-binding protein 569 iron-containing electrons 454 iron-deficiency anaemia 459, 509, 577–8, 758–60 iron-fortified foods 461 iron-responsive anaemia 759 irradiation 4, 339, 678–9 irrigation 696 irritable bowel syndrome 80, 88–9, 106
irritation 88, 282 ischaemia 635 ischaemic heart disease 62, 633 isocaloric exchange 645 isoleucine 735
J
jejunum 69 jin bu huan 664 joints 407 joules 7–8 Journal of the American Medical Association 524 journals 16, 56 reviewed 660 judgement 19, 250 judgementality 740 juices 52, 317, 582 protective effect 393
K
kale 396 keratin 382 keratinisation 382 keratomalacia 382 keto acids 192, 238 keto diet 322, 325 ketonaemia 238 ketone bodies 108, 237–8 formation 733–4 making from fat fragments 108 ketones 649 ketonuria 238 ketosis 108, 239, 246 shift to 237 ketosis-producing diets 238 kidney damage 648, 665 kidney disease 200, 363, 594, 651, 758 kidney failure 90, 648 kidney stones 198, 363, 389 kidneys 193, 228, 248, 331, 335, 410, 412, 418, 421, 560, 568, 650 excretion in 413, 415 functional loss 648 functioning units 411 kilograms 5 kilojoules 7–8, 40, 113, 129–31, 164, 538–9 don’t count 324 empty 308 expended 260–5 from foods 255–9 restricted 130 kilojoules-per-gram secret 232 kitchens clean and safe 675–6 food safety in 674–8 kiwi fruit 396 Kombucha tea 664 kwashiorkor 196–8
L
labels/labelling 11, 53–7, 119, 124, 142, 158–9, 164, 195, 375, 533, 664, 685, 691, 700–1 mandatory labelling requirements – ‘genetically modified’ 701 warning labels 689
see also food labels; product tracking laboratory tests 23, 757 for evaluating nutrition-related anaemias 758 laboratory-based studies 13–14 labour and delivery 535 lactadherin 569 lactase 104, 698 lactase activity 104 lactase deficiency 105 lactate 221–2, 501–2 lactating women 681 lactation 528–54 nutrition during 550–5 a physiological process 551 practices incompatible with 555 vegetarian diets during 541–2 lactic acid system 499 lactoferrin 569 lacto-ovo-vegetarians 63 lactose 97, 99, 626–7 lactose intolerance 81, 105–6, 432, 698 dietary changes 106 symptoms, causes, prevalence 105 lactovegetarians 63 landfill 691 large intestine 67–70, 73, 101, 104 later years 601–20 lateral chest thrusts 87 laxatives 90, 119, 300 LDL (low-density lipoproteins) 149 health implications 150 LDL cholesterol 154–5, 164, 170–1, 208–9, 583, 634, 637 receptors 11 leaching 420 lead 361, 450, 477–8, 691 lead toxicity 478 lean body mass 495, 589 lean choices 161 lean meats 45, 50, 201 lean tissue 235, 238, 254, 407, 741–2, 753–5 lecithin 142–3, 346 legislation mandatory fortification 51, 335, 390, 469 mandatory labelling requirements 701 also under specific Act see also standards legumes 45, 47, 49–50, 61, 84, 101, 112, 120, 125, 147, 162–3, 201, 420, 438, 655 length 766 length-for-age percentiles, boys/ girls 746–7 Lent 4 leptin 291–3 lesions 595–6 let-down reflex 551 lethal dose 247 lethargy 280 leucine 735 leucovorin 625 leukaemia 652 levulose 113 licences 701 life 708 life processes 407 life-threatening complications 92 vulnerable stages of 458
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Index
life cycle nutrition adulthood and the later years 601–20 infancy, childhood and adolescence 564–91 pregnancy and lactation 528–55 life expectancy 61, 271, 594, 601 life span 601 lifestyle 93, 594, 630, 638 misperceptions about 552 lifestyle changes 640–2, 644 lifestyle choices 210, 373, 641 lifestyle factors 11, 62, 83, 89, 199, 210, 631 lifestyle habits 656 lifestyle modifications 644–6 lignans 485 limestone 450 limiting amino acids 194 lingual lipase 146 linoleic acid 152 linolenic acid 137 lipase 146 lipid metabolism 11, 153–4 lipid profiles 596, 651 lipids 5–6, 62, 114, 135–65, 242, 392, 436, 539, 634, 640, 719 in the body 151–4 diet-derived 148 digestion, absorption and transport of 144–51 hydrophobic 331 sources 157 lipoprotein lipase (LPL) 153, 289–90 lipoproteins 148–9, 637 liposuction 304 liquids 67, 88, 394, 708 lithium 626 liver 68, 70–3, 77, 107, 193, 226–7, 244–5, 378–9, 381, 384, 647, 653 alcohol in 244–5 disruptions from alcohol 245–6 metabolic work 215–16 nutrient transport role 79 priority treatment of alcohol 246 vitamin A-rich 385 liver cells 250 liver damage 373, 522 liver disease 758 livestock 680, 683, 690 lollies 130, 488 loneliness 608 long-chain fatty acids 11, 361 longevity 210, 601–5 Lorcaserin 303 low birth weight 543 low blood pressure 239 low glycaemic diet 131 low HDL cholesterol 637 low-carbohydrate diets 239 low-fat alternatives 160 low-fat milk products 50, 596 low/low in 56 low-risk pregnancy 543 lubricants/lubrication 67, 407 lumen 68 lunch 591, 641–2 lung cancer 401 lungs 67, 389, 413–15 lycopene 485 lymph 79–80, 331, 632 lymphatic system 80, 378 lymphocytes 631
lymphomas 652 lysine 361, 735 lysosomes 703–4
M
ma huang 665 macrocytic anaemia 352 macrocytic cells 760 macronutrients 6, 20 macrophages 634–5 macular degeneration 388, 612–13 magazines 201, 524 magnesium 373–4, 409, 418, 420, 433, 437–9, 441, 691 in foods 438 intakes 438 roles in the body 437–8 magnesium deficiency 439 magnesium salts 439 magnetic resonance imaging 270 mains water 693 major minerals 407–41 malabsorption diseases 90 malaria 381 male growth patterns 588 male sex hormone 522 malignant growths 652 malnourishment 20, 22, 206, 238, 316, 413, 671 malnutrition 23, 89, 196, 249, 366, 385, 465, 533–4, 578–9, 617–18, 631, 743, 757–8 pregnancy and 544–5 maltase 104 maltose 97–9 mammary glands 551, 698 managed aquifer recharge 692–3 manganese 10, 473–4, 691 overview 473–4 recommendations and sources 473 manganese toxicity 473 Manufacturers and Importers Agreement 1992 (MAIF Agreement) 571 manure 685 marasmus 196–7, 280 marasmus–kwashiorkor mix 198 margarine 384, 390, 394, 487–8 margin of safety 686 marijuana 662 marital status 22 markers 635 marketing 3, 301, 488 ploys 374 marketplace, food safety in 671, 674 mass 446–7 maternal energy 552–4 maternal health 545–7, 554–5 maternal weight 534–7 matrix 186, 428, 445 matter 708–11 maximal oxygen uptake (VO2 max) 496–7, 516 Mayo Clinic Diet 325 meal replacers 520 meals/mealtimes 84, 89, 91, 172, 284, 516–17, 575, 617, 651 before and after competition 516–17 balanced 110 at home 585–8 liquid 516
participation 585–6 for singles 619–20 stir-fries 620 with toddlers 575 mean corpuscular volume (MCV) 760 measles 381 measurement/measuring 565 anthropometric 741–55 of energy intake 11 of growth and development 742–53 household and metric measures 54 measured portions 48 periodically 23 quality measures 735–7 also under specific measurement meat 741 meat alternatives 40, 47 meat substitute 487 meats 28, 45, 50, 52–3, 63, 160–3, 201, 235, 366, 394, 422, 680, 687 cooking methods 52 NZ reduction trends 2 raw meat versus cooked meat weight 52 safe handling of 675 trimming 161 media 28 medical aid 88 medical conditions 666 medical history 738–9 medical intervention 413, 614 medical procedures 304 Medical Research Council of Australia 242 medication 22, 88–91, 106, 246, 316, 361, 372, 413, 434, 614, 623–5 self-medicating 93 use 22 medication and supplement history 740 medicinal drugs 548, 555 Mediterranean diet 171–4, 325 pyramid 173 Medsafe 375 megaloblastic anaemia 352 megaloblasts 760 melanin 197–8 melanomas 652 Melbourne Collaborative Cohort Study 173 membranes 380, 703–4 men body composition 5 bone loss 590 bone loss in 448 CHD risk 636 healthy-weight 5 iron needs 611 iron overload 460 recommended dietary patterns for 47 requirement 17 retinol for 380 standard drinks 244 stress response 606 total water needs 417 ‘trouble spot’ 312 two standard drinks limit 650 menadione 394 menaquinones 394, 396 Menkes disease 472 menopause 448, 637, 653, 663
801
menstruation 271, 279, 281, 371, 457–8 mental alertness 238 mental retardation 208 MEOS (microsomal ethanoloxidising system) 246 mercury 161, 171, 361, 477, 549, 681, 691 mercury poisoning 681 messages 16, 81, 258–9, 706–7 fat messages 169 hormonal ‘release energy’ 100 point-to-point 707 messenger RNA 184, 206–7 metabolic consequences 324 metabolic diseases 80 metabolic factors 316 metabolic harmony 372 metabolic N 737 metabolic pathway 108 metabolic pathways 196, 235, 359, 732 metabolic rate 361 metabolic reactions 10 cells 214–15 helpers 218 metabolic stress 758 metabolic studies 392 metabolic syndrome 272, 638 metabolism 71, 81, 107–8, 214, 361, 374, 417, 647, 689, 703–4, 739 of bone proteins 396 disruptions 239 energy 8 favours fat formation 234 of iron 454–7 slowing 238 transformations and interactions 214–39 transformations of 214–39 of zinc 464–5 metabolites 522, 755 metalloenzymes 464 metallothionein 464 metals 681 metastasis 652 methane 90, 711 methionine 248, 735 methodology 16, 570 methotrexate 625 methyl alcohol (methanol) 689 methyl groups 135, 207, 354, 392 methylmalonic acid 760 methylmercury 681 MFP factor 455 micelles 147 microarray technology 207 microbes 80, 630, 679 microbial contamination 678 microbiome gastrointestinal 80–1 stability, disturbance, and resilience of 80 microcytic cells 760 micrograms 419 microorganisms 630, 680, 690–1 disease-producing 701 microvilli 75–8, 703 middle age 242 midpoint 17–18 migraine headaches 660 migrants 2, 4 milk alternatives 46 milk anaemia 575 milk intolerance 196 milk sugar 99
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
802
Index
milk/milk products 40, 46, 49, 53, 106, 125, 162, 164, 201, 317, 384, 389, 417, 422, 432, 642, 680, 741 low-fat 41 skimming 161 millet 101 milliequivalents 408 mindful eating 296 mineral losses 102 mineral oil 90 mineral waters 432 mineralisation 401, 428 minerals 3, 5–6, 9–10, 19, 46, 73, 84, 161, 538, 553, 566, 577, 610–11 arrays 9 in the body 419 contaminant 10 essential 10, 52–3 intakes – RDIs and AIs 2–3 non-destruction of 419–20 overview 419–20 roles 420 supplements 371–5, 663 to support activity 508–10 also under specific mineral see also trace minerals; vitamins Ministry of Health 25 misbehaviour 579 misinformation 32–6 life-threatening 373 misleading claims 373–4 mitochondria 221, 231, 361, 506, 703–4 moderate exercise program 495 moderate intensity aerobic exercise 537 moderation 42, 52–3, 84, 114, 122, 165, 242, 244, 250, 573–4, 605, 689 not deprivation 596 molasses 113 mole 714 molecules 4, 72, 77, 96, 379, 407, 708, 711–12, 714 from digestion 75 relinking of 715 molybdenum 10, 476–7 monitoring 683 food supply, agencies monitoring 670 monitoring systems 25 of pesticides 683–4 water monitoring 682, 693 monoamine oxidase (MAO) inhibitors 626–7 monoglycerides 144, 146–7 monosaccharides 7, 96–8, 102, 105, 107, 219, 717 monosodium glutamate (MSG) 688–9 monounsaturated fats 62, 156–7, 160, 170 mono-unsaturated fatty acids 137 moral issues 699 morbidity 612 morning sickness 542 mortality 11, 62–3, 271, 381, 612, 681 early 389 mothers 551 age of 547–8 energy intake and exercise 552–3 motility 112 motivation 298
mouths 67, 69, 102, 104, 146, 239 movement 70 body fluids 407–10 of digestive content through tract 67, 69–71, 89 MSG 688–9 mucous membranes 631 integrity of 380 mucus 72–3, 75–6, 83, 382 multigene disorders 209 multiple sclerosis 401 multiple-pass method 740 multivitamin–mineral supplements 374 muscle cells 454 muscle conditioning 497 muscle contraction 437, 707 muscle dysmorphia 279 muscle endurance 495, 498 muscle mass 603 loss 316 muscle power 498 muscle strength 495, 603 muscles 8, 197, 235, 362, 494, 506, 589, 647, 704 building 317, 522 cells 402 circular, longitudinal and diagonal 70 healthy muscle tone 83 muscular action of digestion 67, 69–71 muscular layers of GI tract 70 rectal 69–71 role of vitamin D in health of 401–2 sheets 75–6 stomach muscles 70 see also sphincter muscles muscular contractions 88 muscular dystrophy 393 mutations 208, 653 mycoprotein 487 myoglobin 454 myrrh 664
N
narcotics 22, 247 National Association for Sustainable Agriculture, Australia (NASAA) 685 National Children’s Nutrition Survey 25 National Cholesterol Education Program Expert Panel 638 National Health and Medical Research Council (NHMRC) 42, 558 national health goals 24 National Health Survey 25 National Institutes of Health National Cholesterol Education Program 325 National Nutrition Survey 25 National Residue Survey (NRS) 683, 690 National Water Commission 692 National Water Commission Act 2004 692 National Water Initiative 692 natural compounds 392 natural ecosystems 699 natural flavours 688 natural science 708
natural toxins 682–3 nausea 88, 239, 300, 363, 373, 466, 542, 662 needs 19, 375, 515, 611, 713, 737 energy 40, 43, 609–12 nutritional 40, 43, 371, 609–12 special needs of preterm infants 571–2 for supplements 372 support for 371 negative feedback 704 negative feedback loop 82 negative ions 714 negatively charged particles 407–9, 708 nephrons 411 nerve cells 108, 247, 379 nerve damage 760 nerves 416, 646, 704–7 diseases of 649 functional loss 648 nerve pathways 81–3, 706 nervous system 81, 89, 108, 549, 643, 704–7 general functions 704 organisation of 707 net protein utilisation (NPU) 737 networking 3 neural tube defects 51, 349–50, 371, 531 neurofibrillary tangles 616 neuromuscular dysfunction 393 neurones 614 neuropeptide Y 258 neurotransmitters 191, 209, 361, 614 neutrons 708 New Zealand ageing population 601 deaths from obesity-related diseases 271–2 diet 2 gene technology regulations 701 government 350, 533 incidence of FAS in 558 neural tube defects 531 NRVs for 1–3, 22, 332, 430–1, 609 obesity and overweight in 288 PEM statistics 196 regulatory framework 375 New Zealand Dietetic Association (NZDA) 34–5 New Zealand Food and Nutrition Guidelines 22 New Zealand Health Survey 288 New Zealand Medicines and Medical Devices Safety Authority 375 newborn infants 396 news, nutrition in 33–4 niacin 223–4, 333–4, 340–3, 366 food sources 341–2 recommendations 340 niacin coenzyme NAD 358–9 niacin deficiency 340–1 niacin equivalents (NE) 340 estimated 342–3 niacin flush 341 niacin toxicity 341 nicotinamide adenine dinucleotide (NAD and NADP) 340 nicotine 555 night blindness 381–2 nitrate 521–2 nitric oxide 521–2
nitric oxide bioavailability 521–2 nitrite 521–2 nitrites 687–8 nitrogen 6, 90, 96, 710–11, 737 nitrogen balance 191 nitrogen-containing compounds 200 nitrosamines 688 no artificial colourings or flavours 56 ‘no-meat diet’ 199 non-alcoholic beverages 250 non–B group vitamins 357–8 non-coeliac gluten sensitivity 89 non-essential amino acids 179, 191, 200, 227–8, 345 amino acid use for making 192 non-food cravings 543 non-haem iron 63, 454–5, 741 non-judgemental questions 740 non-nutrients 625 non-nutritive sweeteners 118 non-starch polysaccharides 101 non-steroidal anti-inflammatory drugs (NSAIDs) 624 noodles 124 noradrenaline 191 norepinephrine 361 normal weight obesity syndrome 273 nourishment 2, 4 optimal 67 nucleic acids 346 nucleotide bases 206, 208 nucleus 206, 703 numerators 737, 765–6 nursing bottle tooth decay 571 nursing home residents 610 nutrient absorption 624–5 Nutrient Australia 49 nutrient claims 54, 375 nutrient composition 696 improved 697 nutrient deficiencies 578 nutrient deficiency 114, 614–15 development stages 24 see also deficiency nutrient density 41–2, 47, 307, 515 nutrient goals 18, 20–1 nutrient intake 19, 564 nutrient loss 331 nutrient malabsorption 624 nutrient metabolism 625–6 nutrient needs 371, 566–70, 576–7, 589–90 increased 371 during lactation 552–4 nutrient recommendations 538, 741 comparing 21 establishing 17–19 using 20–1 Nutrient Reference Values (NRVs) 17–23, 122–3, 330, 332, 392, 417–18, 425, 430, 449, 533, 609 for Australia and New Zealand 1–3 NRV Working Party 17, 390, 432, 473 nutrient requirements 17–18 nutrient supplements 541, 553, 611 nutrient-dense foods 304, 372, 516, 538–9, 619 see also nutrient density nutrient–drug interactions 623–7, 740
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Index
nutrients 4–10, 78, 84, 248, 407, 449–50, 478, 492–517, 655, 696, 741 binding 624 for blood production and cell growth 539–41 for bone development 541 breaking down for energy 218–33 chemical composition 5–6 classes 6–7 of concern 509–10 documentation of absorption effects 373 dose levels 19 drugs–nutrients interactions 623–6 excesses 23, 25 ‘good guys’ 477–8 increased/decreased with GM 700 intakes – RDIs and AIs 1 interdependence of 84 key food group nutrients 47 macronutrients 20 notable 45–6 nutrient-dense foods 50 overconsumption of 19 preparing for transport 77 sufficient to meet needs 40, 43 yielding energy see energyyielding nutrients ‘nutrimedicine’ 34–5 nutrition 2–28, 107, 602–5, 630–4 during adolescence 588–91 during childhood 576–88 field of 16 during infancy 564–75 life cycle 528–55, 564–91, 601–20 national surveys of 25 prior to pregnancy 528 resources 739 science of 10–16 nutrition assessment 371, 738–61 anthropometric measurements used in 741–2 cautions 760–1 historical data used in 738 of individuals 22–4 physical findings used in 756 of population 24–5 Nutrition Australia 49, 62 nutrition buzzwords 374 nutrition content claims/terms 54, 56–7 nutrition education 34 nutrition experts 34 nutrition information 32–6, 422 credible sources of 35 Nutrition Information Panel 422 nutrition intervention 196 nutrition misinformation 32–6 nutrition problems 740 nutrition quackery 36 nutrition references 33 nutrition research 11 nutrition screening 22, 738 nutrition status 22–3, 25, 385, 477, 608, 761 improvement 371–2 influencing factors 738 personal line of defence 630–1 nutrition surveys 740 nutritional adequacy 306 nutritional anaemias 757–60
nutritional genomics 11, 206–10 nutritional ignorance 196 nutritional information 11, 53–4, 56 nutritional value 687 nutritionists 34 nutrition-related alternative therapies 662–5 nutrition-related anaemias 758 nutrition-related concerns 542–3, 612–17 nutritive sweeteners 119 nuts 45, 61, 125, 170, 392, 438, 515, 596, 741
O
oats 89, 101, 124 ob gene 292 obese 267 obesity 3–4, 11, 20, 28, 61–2, 80, 83, 110, 113–14, 130–1, 154–5, 158, 169, 198, 248, 256, 288–317, 401, 534–5, 580, 589, 594, 606, 637, 644, 648, 653 aggressive treatments for 302–4 causes of 291–7 controlling 11 with a life-threatening condition 299 onset prevention 585 perceptions and prejudices 299 prevention and treatment of 302, 584 problems of 297–302 rates 288 with risk factors 298–9 susceptibility to 291 obesity epidemic 583 observation 12, 602–3 observational designs 403 observational studies 402 odour 238, 678, 691, 708 oedema 188, 197, 335, 411, 471 oesophageal sphincter 68–9 oesophagus 67–70, 72, 88, 92, 249 oestrogen 272, 279, 290, 448, 637, 653 oestrogen therapy 448 of world hunger 698 Office of the Gene Technology Regulator 701 oils 4, 8, 46–7, 163–4, 170, 485, 596, 642, 741 older adults 389, 402, 619, 671 eating habits of 617–20 energy and nutrient needs of 609–12 nutrition-related concerns 612–17 olestra 88, 165 olive oil 155, 170, 485, 613 olives 164 omega number 138 omega-3 fatty acids 62–3, 135, 158, 161–4, 171–2, 549, 617, 635, 638, 682 family 152 omega-3 supplements 158–9 omega-6 fatty acids 135, 161 family 152 pathways 152 omega-6 to omega-3 ratio 153 omega-9 group 138 opsin 379–80
optimal health 488 oral contraceptives 758 organic compounds 6 organic contaminants 691 organic foods 685 organic halogens 681 organically grown crops 685 organisms, disease-causing 672–3 organs 4, 11 over-enlarged 523–4 target 704 vital 151 Orlistat 302–3 orthorexia nervosa 279 osmosis 409–10, 691 osmotic pressure 409 osteoarthritis 613–14 osteocalcin 396 osteomalacia 389, 401 osteoporosis 62, 198–9, 271, 279, 372, 382, 389, 401–2, 422, 434, 445–50 outpatient counselling 740 overconsumption 19 Overeaters Anonymous (OA) 313 overeating 3–4, 111, 236, 295 see also feasting overload 494 overnutrition 741, 753 over-the-counter medications 22, 106, 623, 627 overweight 26, 28, 111, 154, 239, 267, 288–317, 534–5, 576, 581, 589–90, 594, 606, 613, 656, 740 causes of 291–7 in good health 298 health risks 271–2 with a life-threatening condition 299 problems of 297–302 with risk factors 298–9 ovum 529 oxalate 363 oxaloacetate 229, 359 oxidants 362 oxidation 140, 235, 361, 379, 392–4, 634, 688, 715–16 oxidative stress 361, 485, 546, 613, 637 oxygen 6, 24, 78, 87, 90, 96–7, 135, 222, 361, 365, 409, 454, 497, 680, 688, 710, 714–15 oxygen consumption 521–2, 604 oxygen gas 708 oxytocin 551, 555 oyster shell 450 oysters 676, 690 OZDASH diet 421–2, 645–6 ozone 691
P
Pacific Islanders 648 packaging see food packaging paediatric health issues 388 paediatricians 596 pain 83, 89, 91, 93, 434, 660, 662, 664, 666 pairs (electron) 712 palatability 160 paleo diet 323 pallor 24, 460 pallor headaches 24 pancreas 68–9, 82, 131, 403, 647 secretions 82
803
pancreatic bicarbonate 82 pancreatic duct 68 pancreatic juice 73 pancreatitis 90 pantothenic acid 81, 333–4, 344–5, 366 food sources 345 pantothenic acid deficiency 345 paper 689 Paraguay tea 664 parasites 672, 676 parasympathetic nervous system 706–7 parathyroid hormone 429, 448 parents 197, 291, 582, 585, 596 participation, learning through 585–6 particles 407–9, 703, 708 part-time vegetarians 61 pasta 2, 124, 641 pasteurisation 671, 676, 679 cold pasteurisation see irradiation pathogen 671 pathways 80–3, 717–34 patterns 172, 238, 283, 291, 305–9, 433, 535–6, 560, 740, 743 compulsive 284 dietary 28, 47–8, 61 inaccurate pattern analysis 735 male and female 588 see also eating patterns PCBs (polychlorinated biphenyls) 681 peak bone mass 388, 430, 434, 449 peer influence 591 peer review 16 pellagra 340–1, 371 penicillamine 472 peppermint oil 89 pepsin 182 peptic ulcers 92 peptidase enzymes 182 peptide bond 180 peptide YY (PYY) 293 peptides 341 % Daily Intake per serving 165 % RDI per serve 195 percentages 765–6 energy-yielding nutrients 568 of water in foods 417 percentiles 580–1, 743–52 performance 516, 524 enhancing 521 performance diet example 516 peripheral nervous system 704 peripheral resistance 643 peristalsis 70, 73, 80, 90 permeability 83 pernicious anaemia 355, 760 peroxides 716 persistence 27, 680 personal and social history 739 personal Daily Intake 165 personal line of defence 630–1 personal preference 2 pesticides 79, 653, 683–5, 696 alternatives to 685 consumption 700 producing own 698 pH 80, 115, 182, 413–14 pH scale 73, 82, 414, 714 phagocytes 631 phagocytosis 631 pharynx 68–9, 88 Phentermine 302
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
804
Index
phenylalanine 209, 689, 735 phenylketonuria (PKU) 119, 208–9, 689 philosophy 740 phosphagen system 499 phosphate 401, 409 phosphates 435 phospholipids 135–43, 395, 436 chemist’s view of 142–4 in foods 142 roles 142–3 phosphoric acid 435 phosphorus 420, 435–7, 441 in foods 436 recommendations and intakes 436 roles in the body 435–6 photosynthesis 214 phyates 456, 625 phylloquinone 394, 396 physical activity 27, 42–3, 62, 83, 90, 208, 261, 263, 304, 309–12, 402, 449, 492–517, 528, 584, 596, 602–3, 651, 763–5 energy requirements for 762–4 energy systems – ATP and CP 499–500 fat use during 505–6 glucose use during 500–5 intense 553 patterns 291 protein use during 506–8 physical activity level (PAL) 763–5 physical development 743 physical endurance 501 physical examinations 23–4, 755 physical fitness 637 physical inactivity 297, 582, 637–8, 648 physical problems 608 physical traits 583 physiologic tolerance 374 physiological age 602 physiological changes 606–8 physiology 87 phytates 420 phytic acid 101–2 phytochemicals 5, 46, 61–2, 64, 163–4, 170, 373, 483–8, 655, 663, 685, 696–8 defending against cancer 483, 485 food sources 484–5 in foods and beverages 486 in perspective 485 phytoestrogens 483, 663 phytosterols 485 pica 460 pigeon breast 391 pigments 5, 379, 381, 390 pinpoint haemorrhages 363 ‘pins and needles’ sensation 521 pituitary gland 247, 410 placebo 15, 660, 666 placebo effect 14, 524, 660–1 placenta 528, 559–60, 571 structures 529 placental development 528–9 plankton 680 plant stanols/sterols 11, 522 plant-based foods 28, 121, 160 plant-pesticides 698 plants 214, 392, 680, 688 plaques 144, 150, 595, 634–5 plasma 187, 759 plasma ammonia 202
plasma prothrombin 396 plastic 689 plastic wrap 679 platelets 635, 638 play 586 pneumonia 381 poisoning/poisons 662, 682 poisonous mushrooms 682 poisonous gases 425 polar bonds 714 policy 552 political views 4 pollutants 171 pollution 477, 653, 678, 692, 698, 700 polyglutamate 348 polypeptides 180 interactions – quaternary structure 181 shapes – secondary structure 181 tangles – tertiary structure 181 polysaccharides 96–7, 100, 718 polyunsaturated fats 62, 156–7 polyunsaturated fatty acids 137, 160, 209, 392, 539 population 403, 678 Indigenous 638 M¯aori and Pacific populations 110 nutrition assessment of 24–5 recommendations for 656 population groups 401 population studies 199, 654 portion creep 8 portion sizes 22, 235, 258, 306, 317, 741 positive correlation 15 positive ions 714 positively charged particles 407–9, 708, 713–14 post-term births 535 potassium 46, 78, 409, 413, 420, 422, 426–8, 440 absorption 420 deficiency and toxicity 426–8 effect of food processing on content 423 in foods 427 hypertension and 426 recommendations and intakes 426 roles in the body 426 potassium deficiency 646 potassium-to-sodium ratio 423 potatoes 2, 101, 366, 654, 682, 698 poultry 2, 45, 50, 52–3, 63, 125, 160–1, 741 cooking methods 52 safe handling of 675 poverty 196, 699 power struggles 586 practice best practice 683 incompatible with lactation 555 prebiotics 81, 612 precautions and procedures, for food safety 678 precursors 331 prediabetes 646 prediction 12 predisposition 208, 609 pre-eclampsia 546 pre-existing diabetes 545 pre-existing hypertension 546 preferences 2, 585
preformed vitamin A 383 pre-game meals 516–17 pregnancy 51, 380, 383, 407, 528–55, 558, 758 in adolescents 547 drinking during 559–60 energy and nutrient needs during 538–41 exercise during 536–7 growth and development during 528–34 malnutrition and 544–5 nutrition during 537–43 nutrition prior to 528 nutrition-related concerns 542–3 practices incompatible with 548–50 vegetarian diets during 541–2 weight gain during 535–6 in women over age 29 years 547–8 pregnant women 244, 371, 671, 681 should not drink alcohol 249 vitamin A and 385 prenatal weight-gain grid 535–6 pre-pregnancy weight 535 prescribed medications 22, 106, 623 preservatives 686–8 pressure ulcers 609 preterm births 534 preterm infants, special needs of 571–2 prevention 314 preventive measures 670, 676–8 preventive strategies 630 see also handwashing price food prices 2 for potential competitive edge 522 primary deficiency 24, 755 primary structure 180 probiotics 81, 456, 612 problem drinkers 249 processed foods 4, 50, 423, 486 producers 680 product tracking 700 professional organisations 35 profiles 298, 596, 651, 656, 701 profit motive 699–700 prolactin 551, 704 prolactin-inhibiting hormone (PIH) 704 proline 361 promoters 653–5 proof 244 pro-oxidant 363, 374 prostaglandins 623, 635 prostate cancer 402 proteases 182 protective effect 171, 555, 637, 653, 655 protective factors 447, 654 protein 5–9, 20, 46–7, 62, 72, 74–5, 82–3, 89, 178–81, 236, 293, 395, 506–8, 515–16, 539, 577, 610, 631, 650 in abundance 201 amino acid use for making 192 attracts water 410 in the body 184–93 chemist’s view of 178–81 digestion and absorption of 182–3 digestive enzymes for 67 excess 234–5
in foods 194–5 as fuel 506 health effects of 198–200 high-quality 161, 163 hydrophilic 331 instructions for making 696 making glucose from 108 meets glucose needs 237 in muscle building 506 quality measures of 735–7 recommendations 507 recommended intakes of 195–201 roles 186–90 synthesis 704 transporters 188–9 uncoupling 294 see also food labels protein deficiency 191, 195 protein denaturation 181 protein digestibility–corrected amino acid score (PDCAAS) 736 protein digestion 183 protein efficiency ratio (PER) 737 protein foods 161–3 fat options 161 protein intake 197, 200, 228 protein metabolism 190–3, 246 protein powders 201–2 protein quality 194–5 protein RDI 200–1 protein replacement 200 protein status 758 protein supplements 201–2 protein synthesis 184–6, 206, 380, 402, 647 protein turnover 191, 737 protein use 506–7 protein–energy malnutrition (PEM) 195–8, 280, 632, 743, 757–8 classifying 196 protein-sparing action 108 protons 708, 710–11, 713–14 exchange 715 protoporphyrin 760 protozoa 80, 690 provitamins 331 psychological benefits 311 psychological changes 608 psychological development 583–4 psychological effects 299 psychological support 584–5 psychological traits 316 pteroyl glutamic acid (PGA) 348 puberty 289, 589 public health nutritionists 34 public health programs 314–15 public health strategies 314–15 public relations 25 PubMed 32–3, 660 pumps 189, 426 punishment, food as 3 purging 282–3 purified protein preparations 202 purines 614 pyloric sphincter 68–9, 71, 82, 146 pyruvate 219, 237, 245, 335, 359, 522 to lactate 221–2 options 221 paths 223 pyruvate-to-acetyl CoA 222
Q
quackery 36, 524 quality 194–5
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Index
quality measures 735–7 quality of life 602 quantity 740, 765–6 questionnaires 11, 741 questions 12 non-judgemental 740 quinidine 626 Quorn 487
R
rachitic rosary 388, 391 radiation 653 rainfall 692 Ramadan 4 rancidity 140, 686–8 randomisation 14 randomised controlled trials 401 raw sugar 113 real-life conditions 670 reasoning 259 recall 674 receptors 704 recombinant DNA technology 699 recommendations 20, 28, 169, 200, 305, 417–18, 422–3, 430–4, 493, 566, 649–51, 741 for chronic disease prevention 656–7 confidence to make 16 dietary 324 FAO/WHO recommendations 21 personalised 208 for reducing risk 638–42, 655 specific 657 targeting ‘most’ 20 for vitamins 383–4, 390–1, 393–4, 396–7 also under specific recommendations recommended amounts 44–6 Recommended Dietary Intake (RDI) 1–3, 17–18, 195, 200–1, 330, 336–7, 341, 362, 371, 418, 473, 533, 539, 589, 611, 651 recommended intakes 415–19, 425–6, 436, 449 body weight comparison 567 of dietary fibre 116–20 of iron 461 of mono-unsaturated and polyunsaturated fats 156–9 of saturated fats, trans fats and cholesterol 154–6 of starch 116–20 of sugars 112–15 records/recording 129, 740 recovery meals 517 rectum 68–70, 89 recycling 4, 457–8, 692–3 red blood cells 5–6, 9, 24, 108, 236–7, 393, 454, 457, 539, 758–60 hypochromic and microcytic 459 reduced/less catch-cry 56 reduction reactions 715 refeeding syndrome 437 reference patterns 735 reference proteins 194 references 16, 33, 374 see also Nutrient Reference Values refined foods 50 refined starches 4 reflexes 393
reflux 70–2 refrigeration 678 refuelling 236 registered nutritionist 34 regulating agents 5 regulation 208, 419, 700 blood volume regulation by water 412 by the buffers 414 energy regulation 131 of fluid balance 410–12 fluid regulation 67 of gastrointestinal tract 80–4 gene technology regulations 701 of gene transcription 11 of GI tract 80–4 governing additives 686–7 in the lungs 414–15 by negative feedback 704 of pesticides 683, 685 protein regulations for food labels 195 regulating hormones 108–9 regulatory frameworks (NZ) 375 self-correcting systems 81–3 state and local 674 temperature regulation 510–11 of water systems 691 rehydration 88, 413 relationships 16, 25, 28 alcohol–accidents relationship 246 among fat types 169 body weight–carbohydrate inverse relationship 129 excess protein–chronic disease 199 risk–benefit 662–3 risk–diet 636 Relative Energy Deficiency in Sport (RED-S) 277–8 consequences 277 relaxation 88, 247 reliability 16 religious beliefs 4 remodelling 381, 704 renin 410–12 rennin 697–8 replication 16 reports/reporting 33–4, 660, 761 reproduction 380, 699 requirement (nutrient) 17–18 research 16, 273, 321, 362, 401, 403, 522, 660–3, 699 conducting 11–14 emerging areas 402 genetic 698 in nutrition 8 private and public control of 11 reliability of 16 using animals 477 research designs 12–14 research findings 16, 111, 113, 169, 660 analysis of 15–16 generalising 14 ‘surprising new findings’ 34 research papers 32 research studies 550 reservoirs 692 residue prevention 683 residues 683 of antibiotics 690 excretion from the body see excretion pesticide 79, 684 undigested 73
resistance 101 insulin resistance 11 resistance training 498 resistant starches 101 resistin 151 resources 739 respiration 413 respiration rate 414, 564 respiratory disease 401 respiratory distress 545 resting metabolic rate (RMR) 260–1 results 12, 16 retina 379–80, 393 retinal 378–9 retinoic acid 249, 379 retinoids 378–9 retinol 378 retinol equivalents (RE) 383 retinol-binding protein (RBP) 379, 757 reusing/recharging 4, 692–3 reverse osmosis 691 review 660, 738 review findings 28 reward 284, 586 food as 3 rheumatoid arthritis 62, 613–14 rhodopsin 379–80 riboflavin 81, 106, 223–4, 333–4, 338, 359, 366 deficiency and toxicity 338 food sources 338–9 functions 339–40 recommendations 338 ribosomes 703 rice 2, 101, 124, 335 polishing 335 rickets 388 rip-offs 313 risk 51, 62, 92, 111, 242, 383, 396, 549, 670, 682–3, 687, 698, 701 versus benefits 660–2, 687 of formula feeding 570 to health see health risks of toxicity 378 risk assessment 639–40 risk equivalents 637 risk factors 26, 199, 278–9, 298–9, 402, 446–7, 594, 618, 633, 638, 654, 738 for CHD 636–8 for chronic disease 26–8 emerging 638 for hypertension 644 modifiable 636 persistance and clustering quality 27 in perspective 27–8 for poor nutrition status 739 risk minimisation 64, 161 of pesticide residue ingestion 684 risk profiles 298 risk–benefit relationship 662–3 RNA (ribonucleic acid) 206, 346, 354, 464, 703 role models 582 room temperature 679 rye 89, 101
S
sabotage 308 saccharin 689
805
safe handling 630, 675–8 safety 419, 570 of foods see food safety safe refrigerator storage times 678 safety assessments 701 safety limits 684, 686 safety procedures 674 safety standards 670 safety testing 700–1 salad dressings 394 salicylates, naturally occurring 664 saline 88 saliva 72, 74, 83, 115 salivary amylase 102 salivary glands 68–9, 71–2, 88, 146 Salmonella 671 salt 2, 43, 50–1, 409, 420–2, 540–1, 687, 713 reduce intake 421–3 salt tolerance 698 water desalination 692 salt sensitivity 421, 644 salt-restricted diet 421 salts 70, 72, 407, 419, 439 imbalances 88 water-dissolved 409 salty 69, 409, 688 sample size 14 samples 23, 761 sarcomas 652 sarcopenia 202, 606–7 satiation 83, 256, 259, 416 sustaining 258 satiety 104, 200, 256, 291, 375, 416, 576 irregularities 316 overriding 257 sustaining 258 saturated fat 43, 62, 154, 160, 164, 172, 174, 199, 596, 613, 634, 638, 650 health effects and recommended intakes 154–6 replacing with unsaturated 158 swapping 169, 172 saturated fatty acids 136, 160, 719 sauces 617 savouriness 2 saw palmetto 392 scales 742–3 scar tissue 362 scepticism 16 Schilling test 760 schizophrenia 401 Schofield equation 264, 762–4 science 34, 708 forward thrust of 699 of nutrition 10–16 scientific evidence 19, 56, 129, 520, 660, 663 scientific findings 62 scientific journals 16, 32 scientific judgements 19 scientific method 12, 16 scientific nutrition references 33 scientific research 16, 36 scorbutic gums 363 screening 22, 545, 638, 640, 738 scurvy 360, 362–3, 366, 371 seafood 63, 162, 682 safe handling of 676–8 seafood poisoning 678 seasonings 160, 617, 642 secondary deficiency 24, 755–6
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806
Index
second-hand smoke 640 secretin 82 actions 83 secretions 71–3, 81–3, 93 of digestion see digestive secretions of hormones 71 see also evacuation sedentary activities 297 sedentary lifestyle 492, 594 sediment 691 seeds 45, 49, 61, 392, 438 segmentation 70 seizures 208–9 selective breeding, comparison with genetic engineering 697 selenium 10, 470–1 overview 471 recommendations and sources 471 roles in the body 470 selenium deficiency 470 selenium toxicity 471 self-denial 316 self-diagnosis 89, 373 self-esteem 279, 311 self-induced vomiting 88 self-medicating 93 self-starvation 280 semi-prepared foods 3 semi-vegetarians 61 senile cataracts 613 senile plaques 616 senna 664 sensation 649 senses 69 sensitivity 421, 585, 644, 648, 757 sensory loss 608 sensory stimuli 704 serotonin 191, 361 serum 569 serum albumin 757 serum antibodies 760 serum ferritin 460, 759 serum folate 760 serum iron 759 serum proteins, normal values for 757 serum transferrin 757–8 serves/servings 41, 243, 248 recommended average daily number of serves 47–8 sizes 53–4, 295, 336, 339, 347, 365, 384, 427, 431, 438, 467, 741 serving containers 296 serving equivalents 48 servings 741 set point 290 set-point theory 290 Seven Countries Study 170 sex hormones 9 shelf-life 696–7 shift work 256 shock 151, 373, 461 short-chain fatty acids 81, 104 sickle-cell anaemia 184–5 side effects 375, 522–3 signals/signalling 71, 90, 257, 290 distress signals 87 of hormones 704 significance 16 simple carbohydrates 96–9, 102 simple diffusion 75 single nucleotide polymorphisms (SNPs) 209
single-gene disorders 208–9 sinus passageways 380 16-carbon fatty acids 218 skeletal abnormalities 388 skeletal growth 589 skin 4–5, 8, 362, 383, 631–2, 755 skinfold measurements 741–2 skinfold measures 753–4 sleep 83, 460 small intestine 67–72, 89, 104, 146, 182, 625 villi 75–7 smell 678–9 smog 390 smoking 28, 62, 91, 199, 208, 271–2, 361–2, 381, 383, 449, 548–9, 555, 594, 631, 634, 638 passive 362 smooth muscle 595 snacks 3, 244, 317, 590, 642, 651 ideas 587 soap 418, 691 social anaesthetic 247 social changes 608 social consequences 299 social inequalities 297 social interactions 2–3 social networks 3 socioeconomic factors 738–9 socioeconomic groups 297 socioeconomic status 22 sodium 51, 53, 409, 413, 418, 420–4, 440, 627, 691, 712–13, 741 deficiency and toxicity 424 effect of food processing on content 423 excessive intakes 424 recommendations and sources 422–3 reduce intake 422–3 retention 643 roles in the body 421–2 sodium bicarbonate 73, 626 sodium deficiency 424 sodium ions 421 sodium reabsorption 411 sodium–potassium pump 410 sodium-to-water ratio 421 soft drink 42 soft drinks 28, 112, 590–1 soft tissues 437 soft water 418–19 soil 469, 471, 477, 540–1, 698 solanine 682 solid fats/oils 154, 161, 164 characteristics 139–42 firmness and stability 139–40 solid foods, introducing 572–5 solids 67, 394, 708 solubility 331 soluble fibre 101 solutes 409–10, 413 attract water 409–10 solutions 408, 566 concentration of 409 solvents 691 somatic nervous system 704 sorbitol 88, 626–7 sores 198 sour 69, 688 South Beach diet 323 soy 448 soy products 62 soy protein 62–3 soybean oil 396 specialisation cells 77
species 80, 664 sphincter see ileocaecal valve sphincter contractions 70–1 sphincter muscles 71, 91 spices 642, 688 spina bifida 532 spinach 396 spinal cord 357, 393, 407, 532, 706 spleen 70 spoilage 686–7 spontaneous abortion 560 sports anaemia 510 sports drinks 513 spot reducing 312 stability 687 standard drinks guide 242–3 standardised conditions 743 standardised tests 589 standards Australia New Zealand Food Standards Code 701 Australian standards 690 of cleanliness 679 infant formula standards 570–1 intake against comparison 741 minimum 691 New Zealand standards 701 safety standards 670 setting for older people 609 of skinfold measures 754 standard charts 743 standard procedure 753 see also codes/coding; Food Standards Australia New Zealand stanols 11 Staphylococcus aureus 671, 673 starches 7, 96–101, 654, 718 health effects and recommended intakes of 116–20 starvation 236, 238, 279–81, 316, 544–5, 605, 607, 698, 701 symptoms 238 starving 197 state 708 state of mind 83 statements 16, 43–4, 56 states/territories monitoring systems 25 regulations 674 residue monitoring 683 water monitoring 682, 693 statistical methods 14 statistical significance 16 statistical studies 26 stature-for-age percentiles, boys/ girls 751 stature-for-stature percentiles, boys/ girls 752 steam 691, 708 stearic acid 136, 155 sterile intestinal tract 396 steroids 520, 522 sterols 11, 135–44 chemist’s view of 142–4 in foods 143 roles 143–4 stevia 119 stimulants 665 stimuli 704 stomach 67–9, 71–2, 81, 88, 102–4, 146, 182 circular, longitudinal and diagonal muscles 70 lining 92 muscles 70
stomach action 70 stomach cancer 93 stomach glands 81 stomach hormones 71 stones 389 stool softeners 90 stools 73, 83, 88, 90, 104, 121 stormwater 692–3 strategy for ageing healthily 617–18 to alleviate maternal discomforts 542 to build fitness and prevent injuries 495 to cut salt intake 422–3 diet strategies for combating bulimia nervosa 283 disease prevention strategies 393, 656 for obesity 584 personal 250–1 portion-control 8 to prevent/alleviate common GI problems 92 preventive 630 risk reduction 641 weight-gain strategies 316–17 weight-loss strategies 304–15 strength training 312 strength-training activities 261 stress 70, 89, 109, 261, 311, 361–2, 372, 434, 445, 566, 605, 637 stress fractures 279 stress response 605 stressors 605, 707 stroke 26, 83, 170–1, 303, 439, 595, 623, 635, 642 structures 5, 717–34 studies 13, 15, 26, 170, 199, 202, 209, 392, 395, 401, 477, 550, 639–40, 645–6, 654–5, 664 meta-analysis of 582 also under specific study study findings 16 stunted growth 466 subatomic particles 708 subclavian vein 80 subclinical deficiency 24 subcutaneous fat 290, 753 subjects assignation 14 substance abuse 282 substances 708 substituted energy 248 successful weight-loss maintenance 313–14 sucrase 104 sucrose 7, 97, 99, 112 sudden death 199 sudden infant death syndrome (SIDS) 549, 555 sugar 2, 8, 130–1, 626–7, 650, 687 sugar alcohols 116, 119–20, 648 sugar alternatives 88, 688–9 on food labels 119 sugar recommendations 650 sugars 2–4, 42–3, 47, 50–1, 96–125 health effects and recommended intakes of 112–15 Suggested Dietary Targets (SDTs) 17 suicide 281 sulphate 409, 440–1 sulphites 688 sulphur 440, 691 sun exposure 401, 653 sun protection factors (SPFs) 390
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Index
sunlight 386, 390, 402, 447–8, 610, 680 lack of 388 sunscreens 390 supplements 11, 300–1, 371–5, 382, 420, 433–4, 439, 450, 611, 646, 663–4 arguments against 372–4 arguments for 371–2 contents 374 costs 375 dangerous, banned and illegal 522–4 dietary 508 as ergogenic aids 520–4 false sense of security 373 versus food 392–3 history 740 ‘ideal’ 373 invalid reasons for taking 373 people who should avoid 372–3 perspective on 450 regulation of 375 selection 374–5 support for activity 498–516 for breastfeeding 43 for increased nutrient needs 371 psychological support 584–5 support groups 313 surface area 75 surgery 89, 303–4, 372–3, 445, 614 surveys 24–5, 156, 373, 472, 492, 683–4, 690, 740 sushi 676 suspensions 67, 73 see also gases; liquids; solids; solutions swallowing 67, 69, 74, 87–8, 90 simple 130 sweat 110, 191, 413, 510, 512, 590 sweeteners 113, 116–18 sweetness 2, 69, 97, 688 sweets 130, 587, 741 symbols 96, 409, 709–10 sympathetic nervous system 706–7 synergistic downward spiral 631 synergy 631, 633 synthesising drugs 664 synthetic 374 systems 6, 418 absorptive 75–6 circulatory see circulatory system coordination and integration of 67 defence systems, body 630–2 digestive system 69 distillation 691 lymphatic 80, 378 self-correcting regulatory systems 81–3 vascular 77–9 also under specific system
T
Take off Weight Naturally (TOWN) 313 takeaway foods 596 targeted monitoring 683 taste 2, 165, 483, 619, 679, 686, 691, 708 taste buds 69 taxation 113
Taxol 664 TCA cycle 219, 223, 229–30, 245–6, 338, 359, 473, 704, 728–30 T-cells 631 tea 28, 418, 664, 741 teams/teamwork 387 technological advances 53, 601, 679, 692, 699 technology 206, 297 gene technology 701 imperfect 699 teenagers see adolescents teeth 361–2, 428 television 583 tempeh 62–3 temperature 417, 707–8, 766 of the body see body temperature extremes 151, 361 of foods 675–7 of room see room temperature safe 675 temperature regulation 510–11 tens of milligrams 419 tension 590, 660 teratogenic risk 383 terminology 54 overweight and obese 581 preterm and premature 571 words ending in -ase see enzymes territories see states/territories testimonial accounts 660 testosterone 290, 522 tests/testing 209, 510, 589, 683–4 animal test results applicability to human being 737 drug testing 520 laboratory tests 23 safety testing 700–1 tetrahydrofolate (THF) 348, 360 texture 52, 160, 165, 687, 708 textured vegetable protein 63 theory 12 Therapeutic Goods Act 1989 375 Therapeutic Goods Administration (TGA) 375, 488 Therapeutic Lifestyle Changes (TLC) diet 325 therapeutic trials 362 therapists 663 therapy 660 thermic effect of food (TEF) 263 thermogenesis 260 thermometers 675–6 thiamin 62, 81, 249, 333–5, 337, 359, 366, 437 deficiency and toxicity 334 food sources 335–6 recommendations 334 thiamin supplements 249 thinking 259 thinness 277, 295 thirst 410, 416, 515 thoracic duct 80 threonine 735 thrombin 395 thromboplastin 395 thrombosis 635 thromboxanes 635 thyroid 682 thyroid-stimulating hormone (TSH) 468 thyroxine 361 tin 689 tissue 4, 82, 206, 237–8, 361–2, 380, 407, 632, 753–5 body tissues 78, 753–5
exchange of protein among see protein turnover fat tissue 11, 753–5 growth, maintenance and repair of 5, 704 loss 278 remodelling 704 tissues 646 tobacco 653, 739 tocopherols 392 tocotrienols 392 toddlers 596 foods at one year 575 recommended dietary patterns for 48 tofu 61–2 tolerance level 683 tolerances 19 tomatoes 696–7 hydroponically grown 698 tongue 69 tooth decay 113, 571 tooth loss 607–8 total blood cholesterol 637 total blood volume 759 total carbohydrate intake 650 total energy expenditure 763–5 total fat 62, 160 total iron-binding capacity (TIBC) 759 toxic effects 249 toxicity 23, 171, 202, 244, 332, 334, 346, 362–3, 372–3, 383, 389, 393, 396, 425–8, 439, 460–1, 466, 469, 471, 474–5, 478, 522, 648, 665, 670, 698, 701 toxins 79, 361, 522, 634, 638, 673, 680, 687 food 671 introduction of 699 natural 682–3 toxicity 383 trabecular bone 445–6 trace mineral deficiency 453 trace mineral toxicities 453 trace minerals 419, 453–79 food sources 453 other 477–9 overview 453–4 trachea 68, 87 tradition 2, 172, 660 training 496–8, 502, 522 heavy 515 traits 105, 316, 583, 696 trans configuration 379 trans fats 154–6, 160, 164, 169, 171, 638 health effects and recommended intakes 154–6 trans fatty acids 11, 141–2 transamination reactions 192, 228 transfer RNA 184 transferrin 455 iron-binding capacity 759 saturation 759 transferrin saturation 460 transient hypertension of pregnancy 546 transient ischaemic attack (TIA) 635 transport 67–84 of lipids 148–51 of nutrients 75 preparing nutrients for 77 transportation costs 693 transporters 188–9 transthyretin 757
807
transverse colon 70 traumatic wounds 413 travellers’ diarrhoea 678–9 travelling 678–9 treatment 83, 93, 303, 614, 638, 640, 660–1 of anorexia nervosa 281 of choking 87 comprehensive treatment plans 666 of hypertension 644–6 of irritable bowel syndrome 89 self-treatment 89, 93 see also surgery treatment plans 199 tremors 209 trends 33, 110, 129, 295, 488, 630 international food trends 2 national 25 trials 13–14, 402 triceps skinfold 753–4 triglyceride 108 triglycerides 135–9, 153, 165, 223, 225–6, 234–5, 242, 244–5, 289, 638 chemist’s view of 135–42 formation 139 roles 151 tripeptides 180 tropical oil 171 trust 740 tryptophan 340–3, 359, 735 tryptophan and tyrosine 361 tuberculosis 630 tubers 101 tubes 703 tumour 652, 654 20-carbon omega-6 635 24-hour recall 740 type 1 diabetes 110, 131, 403, 554, 647 features 647 recommendations 651 type 2 diabetes 28, 110–12, 121, 388, 533–4, 594, 648 early development of 594–5 features 647 prevalence rates for 594 recommendations 651 typhoid fever 691 tyramine 626–7 tyrosine 197–8, 208–9, 735
U
ulcers 81, 92–3, 249 ultrahigh temperature [UHT] treatment 679 ultra-processed foods 4 ultraviolet (UV) rays 331, 339, 386, 403 umami 69, 688 umbilical cord 528 undernutrition 575, 620, 741, 753 underweight 239, 267, 271, 288–317, 740 health risks 271 problems of 316 women 534 United Nations International Children’s Emergency Fund (UNICEF) 381 United States National Health and Nutrition Examination Survey (NHANES) records 129
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808
Index
units 73, 765 unsaturated fats 63, 164, 172, 174 swapping to 169, 172 unsaturated fatty acids 135, 209, 719 unsaturation degree of 139 point of 137 unspecified eating disorders 283 ‘uphill’ reactions 715 Upper Level of Intake (UL) 1–3, 17, 19, 198, 330, 332, 372, 374, 383, 389, 393, 439, 453, 466, 473, 686 urea 192, 226–7 excretion via the kidneys 228 synthesis 193 urea cycle 732–3 urea synthesis 227 urethra 380 uric acid 239, 614 urinary bladder 380 urinary tract 382 urine 191, 209, 239, 415–16, 626, 737, 755 ‘use by’ date 674 usual intake 740 uterus 380, 528, 537
V
vaccination/vaccine 107, 656, 698 vagina 380, 382 valerian 664 validity 16 valine 735 values 4 variable bioavailability 420 variables 14–15 variation 14, 208–9, 456–7 variety 42–3, 84, 114, 122, 124, 296, 325, 573–4, 663, 682 vascular system 77–9 vasoconstriction 643 vasoconstrictors 411 vasodilators 335 vasopressin 410 vegan diets 122, 355 vegans 63, 339, 458, 542 vegetable oils 392, 396, 596 vegetables 3–4, 40, 45, 49–52, 61–2, 84, 90, 112, 120, 125, 160, 162, 164, 201, 351, 360, 364, 392, 422, 613, 638, 641, 655, 663, 690, 741 fresh, canned or frozen 51–2, 619 goitrogen-containing 682–3 green leafy 62, 338–9, 432, 438 raw 365, 516 vegetarian diet planning 62–3 vegetarian diets 61–4, 432–3, 516 health benefits of 61–2 during infancy 574–5 during pregnancy and lactation 541–2 vegetarian food guide 49 vegetarians 61–2, 199, 372, 458 veins 78–80 venous pooling 335 Vibrio vulnificus 690 villi 75–8, 89, 105 viral infections 634 viral intestinal disorders 676 viruses 80, 362, 470, 671–2, 676 visceral fat 290 viscous quality 101
vision 63, 249, 379–80, 393, 612–13 vision loss 648–9 visual activity 379 vitamin A 42, 53, 62, 160, 249, 331, 373, 378–86, 488, 553, 591 activity 378 deficiency 381–2, 697 in foods 384–6 forms 378 overview 386, 398 precursors see beta-carotene preformed 383 in protein synthesis and cell differentiation 380 recommendations 383–4 in reproduction and growth 380–1 role in vision 379–80 roles in the body 379–81 toxicity 383 vitamin B6 62, 81, 199, 249, 333–4, 367, 373, 553 food sources 346–7 recommendations 346 vitamin B6 deficiency 346 vitamin B6 toxicity 346 vitamin B12 62–3, 81, 199, 333–4, 354–6, 367, 516, 539, 553, 610, 760 deficiency and toxicity 355 food sources 356 normal values for 760 recommendations 355 vitamin B12 anaemias 760 vitamin C 42, 52, 62–3, 330–65, 367, 373, 591, 663, 741 as cofactor in collagen formation/other reactions 361 common cold and 362 deficiency and toxicity 362–3 food sources 364–6 foods providing 574 recommendations 362 roles 360–2 in stress 361–2 vitamin D 53, 63, 106, 160, 331, 386–91, 433, 447–8, 541, 547, 553, 589, 610–11 deficiency 388–9 multisystemic role 11 overview 391, 398 recommendations and sources 390–1 roles 401–3 roles in the body 387–8 sunshine vitamin 401–2 synthesis 390 synthesis and activation 387 toxicity 389 vitamin D–fortified foods 63 vitamin E 62, 160, 331, 374, 392–4, 470, 509 as an antioxidant 392–3 deficiency and toxicity 393 overview 394, 398 recommendations and sources 393–4 subgroups 392 supplements 11 vitamin impostors 358 vitamin K 81, 160, 331, 394–8 deficiency and toxicity 396 overview 397–8 recommendations and sources 396–7 synthesis 396
vitamin–mineral megadoses 549–50 vitamin–mineral supplements 371–5 vitamins 3, 5–6, 9, 19, 46, 73, 80, 90, 161, 330–67, 538, 553, 566, 577, 589, 610–11, 721–5 carbohydrates, fats and proteins, distinction 330 chewable 373 fat-soluble 378–98 intakes – RDIs and AIs 2–3 organic nature 331 overview 330–3 supplements 11, 371–5, 663 to support activity 508–10 also under specific vitamin see also minerals VLDL (very-low-density lipoproteins) 149 ‘volatile’ gases 90 volume 766 voluntary food folic acid fortification 350 volunteer associations 35 vomiting 88, 282, 300, 413, 425, 427, 619, 662, 678 vulnerable people 403, 671
W
waist circumference 268–9, 271, 298, 754–5 waist-to-hip ratio 754–5 warfarin 396, 625 warm-up activities 495 warning labels 689 waste elimination 89 waste products 10, 78, 420 hazardous waste sites 691 wasting 197, 238, 610 water 5–6, 10, 53, 67, 70–3, 90, 104, 107, 214, 307, 515, 554, 566, 609, 666, 670–93, 708, 713–14 attractions of 408–10 blood volume regulation 412 consumer concerns about 690–3 contaminated 690 daily ‘eight glasses of water’? 418 doubly labelled 11 for drinking see drinking water filters 691 fluoridated 656 intakes – RDIs and AIs 1 major minerals and 407–41 mineral content of 691 purification 630 recommendations 417–18 re-use, recharge and recycling 692–3 water balance 407, 415–19 water intake 416–17 excessive 417 water loss 247, 415–16, 510 excessive 416 water pollution 653 water restrictions 692 water retention 411–12, 643 water shortages 692 water sources 416–17 water supply 653 fluoridated 474 issues and options 691–3 water systems/regulations 691 water-borne diseases 691 water-conserving hormones 410
water-soluble nutrients 77 water-soluble substances 361 water-soluble vitamins 330–67 versus fat-soluble 378 waterways health 693 weakness 24, 110, 197, 416, 437, 460, 603 weaning 570 websites 32–3, 201 weight 23, 515, 564, 711, 741–3, 763–6 desirable 596 from food ingredients 53 healthy 5 maternal 534–7 weight control 61–2, 111, 200, 214, 644 weight gain 20, 42, 297, 314, 589 components 536 during pregnancy 535–6 prevention 310 recommended 535 weight loss 3, 8, 27, 42, 161, 197, 208, 238, 288, 292, 296–8, 309, 515, 651, 665 versus fat loss 325 identifying scams 325–6 latest and greatest diet for 321–6 postpartum 553 post-pregnancy 536 unhealthy 279 weight-loss diet 89 weight maintenance 313–14 weight management 111, 121, 254–73, 288, 309, 594–5 weight training 449 Weight Watchers (WW) 313, 325 weight-bearing endurance activities 449 weight-bearing physical activity 279 weight-for-age percentiles, boys/girls 744–5, 750 weight-for-length percentiles, boys/ girls 748–9 weight-gain patterns 535–6 weight-gain strategies 316–17 weight-loss dieting 550 weight-loss diets 305 weight-loss products 300 weight-loss strategies 304–15 weights and measures 766 Wernicke-Korsakoff syndrome 248, 335 Western diet 28 wheat 89, 101 Wheat Belly 323 wheat germ 392 wheatgerm oil 394 whey protein 201 white blood cells 569, 631 white fat cells 294 white sugar 113 whole foods 4, 52, 63 whole grains 28, 40, 50, 61, 90, 112, 120, 147, 160, 596, 655 Whole30 diet 325 wholegrain cereals 84 wholegrain products 50–1 whole-milk products 171 wiggle room 310 willpower 299 Wilson disease 472 wine 242 women body composition 5 bone loss 590
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Index
bone loss in 448 CHD risk 636–7 of child-bearing age 371 healthy-weight 5 iron needs 611 iron overload 460 postmenopausal 372–3 pregnancy in women over age 29 years 547–8 recommended dietary patterns for 47 requirement 17 retinol for 380 standard drinks 244 stress response 606 total water needs 417 ‘trouble spot’ 312 two standard drinks limit 650 World Anti-Doping Agency 522 World Health Organization (WHO) 381, 571, 679, 744–9 world malnutrition 385 World Wide Web 32
worms 676 wounds 361–2, 413
X
xanthophylls 385 xerophthalmia 381–2 xerosis 382
Y
yoghurt 46, 81, 106, 125, 155, 164, 741 young children 88, 196 feeding guidelines 575 young people 671 ‘yo-yo’ dieting 300
Z
zinc 10, 47, 52, 63, 373, 464–8, 540 absorption and metabolism 464–5 in foods 467 overview 467–8 recommendations and sources 466 roles in the body 464 supplementation 466–7 zinc absorption 464 zinc deficiency 465 zinc toxicity 466 zinc transport 464–5 zone diet 323 zygote 529–30
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809
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Nutrient Reference Values (NRV) for Australia and New Zealand (http://www.nrv.gov.au)
determine an RDI, an AI is set. AI is more tentative than RDI, but both may be used as goals for nutrient intakes. (Chapter 1 provides more details.) In addition to the values that serve as goals for nutrient intakes (presented in the tables on the following pages), the NRV include a set of values called Upper Level of Intake (UL). The UL represent the maximum amount of a nutrient that appears safe for most healthy people to consume on a regular basis. A listing of the UL for selected vitamins and minerals follows.
The Nutrient Reference Values (NRV) include two sets of values that serve as goals for nutrient intake – Recommended Dietary Intake (RDI) and Adequate Intake (AI). The RDI reflects the average daily amount of a nutrient considered adequate to meet the needs of most healthy people. If there is insufficient evidence to
Age (yrs)
Reference weight (kg)
Watera AI (L/day)
Carbohydrate AI (g/day)
Dietary fibre AI (g/day)
Total fat AI (g/day)
Linoleic acid (n-6) AI (g/day)
Alpha-linolenic acid (n-3) AI (g/day)
Long-chain n-3b AI (mg/day)
Protein RDI (g/day)
Protein RDI (g/kg body weight/day)
RECOMMENDED DIETARY INTAKES (RDI) AND ADEQUATE INTAKES (AI) FOR WATER AND THE ENERGY NUTRIENTS
Males 0–0.5 0.5–1 1–3 4–8 9–13 14–18 19–30 31–50 51–70 >70
7 9 13 22 40 64 76 76 76 76
0.7c 0.8d 1.4 1.6 2.2 2.7 3.4 3.4 3.4 3.4
60 95 – – – – – – – –
– – 14 18 24 28 30 30 30 30
31 30 – – – – – – – –
4.4 4.6 5 8 10 12 13 13 13 13
0.5 0.5 0.5 0.8 1.0 1.2 1.3 1.3 1.3 1.3
– – 40 55 70 125 160 160 160 160
10 14 14 20 40 65 64 64 64 81
1.43 1.60 1.08 0.91 0.94 0.99 0.84 0.84 0.84 1.07
Females 0–0.5 0.5–1 1–3 4–8 9–13 14–18 19–30 31–50 51–70 >70
7 9 13 22 40 57 61 61 61 61
0.7c 0.8d 1.4 1.6 1.9 2.2 2.8 2.8 2.8 2.8
60 95 – – – – – – – –
– – 14 18 20 22 25 25 25 25
31 30 – – – – – – – –
4.4 4.6 5 8 8 8 8 8 8 8
0.5 0.5 0.5 0.8 0.8 0.8 0.8 0.8 0.8 0.8
– – 40 55 70 85 90 90 90 90
10 14 14 20 35 45 46 46 46 57
1.43 1.60 1.08 0.91 0.87 0.77 0.75 0.75 0.75 0.94
Pregnancy 14–18 19–30 31–50
2.4 3.1 3.1
– – –
25 28 28
– – –
10 10 10
1.0 1.0 1.0
110 115 115
58e 60e 60e
1.02e 1.00e 1.00e
Lactation 14–18 19–30 31–50
2.9 3.5 3.5
– – –
27 30 30
– – –
12 12 12
1.2 1.2 1.2
140 145 145
63 67 67
1.1 1.1 1.1
NOTE: For all nutrients, values for infants are AI. Dashes indicate that values have not been determined. a
b
he water AI includes drinking water, water in beverages such as milk, and water in foods; in general, drinking water and other beverages contribute about 70 to T 80 per cent to water intake, and foods, the remainder.
Long-chain n-3 fatty acids include eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA).
From breast milk or formula
c
d e
From breast milk, formula, food, plain water and other beverages (including 0.6 L as fluids)
In second and third trimesters only Adapted from the Nutrient Reference Values for Australia and New Zealand. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand). Canberra, ACT: Commonwealth of Australia and New Zealand Government (2006). Available from: http://www.nhmrc.gov.au/publications/synopses/n35syn.htm
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Age (yrs)
Thiamin RDI (mg/day)
Riboflavin RDI (mg/day)
Niacin RDI (mg/day)a
Biotin AI (mg/day)
Pantothenic acid AI (mg/day)
Vitamin B6 RDI (mg/day)
Folate RDI (mg/day)b
Vitamin B12 RDI (mg/day)
Choline AI (mg/day)
Vitamin C RDI (mg/day)
Vitamin A RDI (mg/day)c
Vitamin D AI (mg/day)d
Vitamin E AI (mg/day)e
Vitamin K AI (mg/day)
RECOMMENDED DIETARY INTAKES (RDI) AND ADEQUATE INTAKES (AI) FOR VITAMINS
Infants 0–0.5 0.5–1
0.2 0.3
0.3 0.4
2 4
5 6
1.7 2.2
0.1 0.3
65 80
0.4 0.5
125 150
25 30
250 430
5 5
4 5
2.0 2.5
Children 1–3 4–8
0.5 0.6
0.5 0.6
6 8
8 12
3.5 4.0
0.5 0.6
150 200
0.9 1.2
200 250
35 35
300 400
5 5
5 6
25 35
Males 9–13 14–18 19–30 31–50 51–70 >70
0.9 1.2 1.2 1.2 1.2 1.2
0.9 1.3 1.3 1.3 1.3 1.6
12 16 16 16 16 16
20 30 30 30 30 30
5 6 6 6 6 6
1.0 1.3 1.3 1.3 1.7 1.7
300 400 400 400 400 400
1.8 2.4 2.4 2.4 2.4 2.4
375 550 550 550 550 550
40 40 45 45 45 45
600 900 900 900 900 900
5 5 5 5 10 15
9 10 10 10 10 10
45 55 70 70 70 70
Females 9–13 14–18 19–30 31–50 51–70 >70
0.9 1.1 1.1 1.1 1.1 1.1
0.9 1.1 1.1 1.1 1.1 1.3
12 14 14 14 14 14
20 25 25 25 25 25
4 4 4 4 4 4
1.0 1.2 1.3 1.3 1.5 1.5
300 400 400 400 400 400
1.8 2.4 2.4 2.4 2.4 2.4
375 400 425 425 425 425
40 40 45 45 45 45
600 700 700 700 700 700
5 5 5 5 10 15
8 8 7 7 7 7
45 55 60 60 60 60
Pregnancy 14–18 19–50
1.4 1.4
1.4 1.4
18 18
30 30
5 5
1.9 1.9
600 600
2.6 2.6
415 440
55 60
700 800
5 5
8 7
60 60
Lactation 14–18 19–50
1.4 1.4
1.6 1.6
17 17
35 35
6 6
2.0 2.0
500 500
2.8 2.8
550 550
80 85
1100 1100
5 5
12 11
60 60
NOTE: For all nutrients, values for infants are AI. Niacin recommendations are expressed as niacin equivalents (NE), except for recommendations for infants younger than 6 months, which are expressed as preformed niacin.
a
Folate recommendations are expressed as dietary folate equivalents (DFE).
b
Vitamin A recommendations are expressed as retinol equivalents (RE).
c
Vitamin D recommendations are expressed as cholecalciferol and assume no or minimal exposure to sunlight.
d e
Vitamin E recommendations are expressed as alpha-tocopherol equivalents. Adapted from the Nutrient Reference Values for Australia and New Zealand. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand). Canberra, ACT: Commonwealth of Australia and New Zealand Government (2006). Available from: www.nhmrc.gov.au/publications/synopses/n35syn.htm
Age (yrs)
Sodium AI (mg/day)
Potassium AI (mg/day)
Calcium RDI (mg/day)
Phosphorus RDI (mg/day)
Magnesium RDI (mg/day)
Iron RDI (mg/day)
Zinc RDI (mg/day)
Iodine RDI (mg/day)
Selenium RDI (mg/day)
Copper AI (mg/day)
Manganese AI (mg/day)
Fluoride AI (mg/day)
Chromium AI (mg/day)
Molybdenum RDI (mg/day)
RECOMMENDED DIETARY INTAKES (RDI) AND ADEQUATE INTAKES (AI) FOR MINERALS
Infants 0–0.5 0.5–1
120 170
400 700
210 270
100 275
30 75
0.2 11
2 3
90 110
12 15
0.2 0.22
0.003 0.6
– 0.5
0.2 5.5
2 3
Children 1–3 4–8
200–400 300–600
2000 2300
500 700
460 500
80 130
9 10
3 4
90 90
25 30
0.7 1.0
2.0 2.5
0.6 1.1
11 15
17 22
Males 9–13 14–18 19–30 31–50 51–70 >70
400–800 460–920 460–920 460–920 460–920 460–920
3000 3600 3800 3800 3800 3800
1000–1300 1300 1000 1000 1000 1300
1250 1250 1000 1000 1000 1000
240 410 400 420 420 420
8 11 8 8 8 8
6 13 14 14 14 14
120 150 150 150 150 150
50 70 70 70 70 70
1.3 1.5 1.7 1.7 1.7 1.7
3.0 3.5 5.5 5.5 5.5 5.5
2 3 4 4 4 4
25 35 35 35 35 35
34 43 45 45 45 45
Females 9–13 14–18 19–30 31–50 51–70 >70
400–800 460–920 460–920 460–920 460–920 460–920
2500 2600 2800 2800 2800 2800
1000–1300 1300 1000 1000 1300 1300
1250 1250 1000 1000 1000 1000
240 360 310 320 320 320
8 15 18 18 8 8
6 7 8 8 8 8
120 150 150 150 150 150
50 60 60 60 60 60
1.1 1.1 1.2 1.2 1.2 1.2
2.5 3.0 5.0 5.0 5.0 5.0
2 3 3 3 3 3
21 24 25 25 25 25
34 43 45 45 45 45
Pregnancy 14–18 19–50
460–920 460–920
2800 2800
1300 1000
1250 1000
400 350
27 27
10 11
220 220
65 65
1.2 1.3
5 5
3 3
30 30
50 50
Lactation 14–18 19–50
460–920 460–920
3200 3200
1300 1000
1250 1000
360 310
10 9
11 12
270 270
75 75
1.4 1.5
5 5
3 3
45 45
50 50
Adapted from the Nutrient Reference Values for Australia and New Zealand. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand). Canberra, ACT: Commonwealth of Australia and New Zealand Government (2006). Available from: www.nhmrc.gov.au/publications/synopses/n35syn.htm Copyright Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-202
Age (yrs)
Niacin (mg/day)a
Vitamin B6 (mg/day)
Folate (µg/day)a
Choline (mg/day)
Vitamin A (µg/day)b
Vitamin D (µg/day)
Vitamin E (mg/day)c
UPPER LEVEL OF INTAKE (UL) FOR VITAMINS
Infants 0–0.5 0.5–1
BM B/F
BM B/F
BM B/F
BM B/F
600 600
25 25
BM B/F
Children 1–3 4–8 9–13
10 15 20
15 20 30
300 400 600
1000 1000 1000
600 900 1700
80 80 80
70 100 180
Adolescents 30
40
800
3000
2800
80
250
Adults 19–70 >70
35 35
50 50
1000 1000
3500 3500
3000 3000
80 80
300 300
Pregnancy 14–18 19–50
30 35
40 50
800 1000
3000 3500
2800 3000
80 80
300 300
Lactation 14–18 19–50
30 35
40 50
800 1000
3000 3500
2800 3000
80 80
300 300
BM = amount normally received in breast milk; B/F = amount in breast milk and food NOTE: An UL was not established for vitamins not listed because of a lack of data, not because these nutrients are safe to consume at any level of intake. All nutrients can have adverse effects when intakes are excessive. The UL for niacin and folate apply to synthetic forms obtained from supplements, fortified foods or a combination of the two.
a
The UL for vitamin A applies to the preformed vitamin only.
b
The UL for vitamin E applies to any form of supplemental alpha-tocopherol, fortified foods, or a combination of the two.
c
Adapted from the Nutrient Reference Values for Australia and New Zealand. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand). Canberra, ACT: Commonwealth of Australia and New Zealand Government (2006). Available from: www.nhmrc.gov.au/publications/synopses/n35syn.htm
Molybdenum (µg/day)
14–18 19–50
Fluoride (mg/day)
Lactation
Manganesec (mg/day)
14–18 19–50
Copper (mg/day)
Pregnancy
Selenium (µg/day)
19–70 >70
Iodine (µg/day)
14–18
Adults
Zinc (mg/day)
Adolescents
Iron (mg/day)
1–3 4–8 9–13
Magnesium (mg/day)b
Children
Phosphorus (mg/day)
0–0.5 0.5–1
Calcium (mg/day)
Infants
Sodiuma (mg/day)
Age (yrs)
UPPER LEVEL OF INTAKE (UL) FOR MINERALS
– –
BM B/F
BM B/F
BM B/F
20 20
4 5
BM B/F
45 60
BM B/F
BM B/F
1.2 1.8
BM B/F
1000 1400 2000
2500 2500 2500
3000 3000 4000
65 110 350
20 40 40
7 12 25
200 300 600
90 150 280
1 3 5
– – –
2.4 4.4 10
300 600 1100
2300
2500
4000
350
45
35
900
400
8
–
10
1700
Not determined Not determined
2500 2500
4000 3000
350 350
45 45
40 40
1100 1100
400 400
10 10
– –
10 10
2000 2000
Not determined Not determined
2500 2500
3500 3500
350 350
45 45
35 40
900 1100
400 400
8 10
– –
10 10
1700 2000
Not determined Not determined
2500 2500
4000 4000
350 350
45 45
35 40
900 1100
400 400
8 10
– –
10 10
1700 2000
BM = amount normally received in breast milk; B/F = amount in breast milk and food NOTE: An UL was not established for minerals not listed and for those age groups listed with a dash (–) because of a lack of data, not because these nutrients are safe to consume at any level of intake. All nutrients can have adverse effects when intakes are excessive. a
A level of no more than 1600 mg (70 mmol) of sodium per day is recommended for older, overweight hypertensives and for those wishing to maintain low blood pressure over the lifespan The UL for magnesium applies to synthetic forms obtained from supplements.
b
Intake of manganese beyond that normally found in food and beverages could represent a health risk, but there is insufficient data to set a UL.
c
Adapted from the Nutrient Reference Values for Australia and New Zealand. Australian Government Department of Health and Ageing, National Health and Medical Research Council (Australia), Ministry of Health (New Zealand). Canberra, ACT: Commonwealth of Australia and New Zealand Government (2006). Available from: www.nhmrc.gov.au/publications/synopses/n35syn.htm
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