Phytonutrients

In many Western diets, the role of plants has been reduced in favour of more animal-based products and this is now being cited more widely as being the cause of increases in the incidence of diseases such as cancer and cardiovascular disease. This important book covers the biochemistry and nutritional importance of a wide range of phytonutrients, including all the major macronutrients as well as the micronutrients and 'non-essential' nutrients. Phytonutrients is divided into three parts. The first deals with the role of plants in the human diet. Part II, representing the major part of the book covers in turn each of the major phytonutrient groups. Chapters include: non-lipid micronutrients, lipids and steroids, carotenoids, phenolics, vitamins C, E, folate/vitamin B12, phytoestrogens, other phytonutrients and minerals, and anti-nutritional factors. The final part of the book covers the methods used to manipulate levels of phytonutrients in the diet, such as fortification, supplementation and the use of genetically modified plants. Phytonutrients is an essential purchase for nutritionists, food scientists and plant biochemists, particularly those dealing with nutrients from plants, and their use in the human diet. Andrew Salter is Professor of Nutritional Biochemistry in the School of Biosciences at the University of Nottingham. Helen Wiseman is Lecturer in Nutritional Sciences in the Diabetes and Nutritional Sciences Division at King's College London. Gregory Tucker is Professor of Plant Biochemistry in the School of Biosciences at the University of Nottingham CONTENTS Plant foods and health 1 Judith Buttriss Introduction 1 Historical changes in the plant content of the human diet 1 Changing composition of dietary constituents in the past 50 years 5 Plants – nutrients and other constituents 6 A summary of the evidence linking plant food intake and health 6 Coronary heart disease and stroke 9 Fruits and vegetables 9 Pulses and nuts 13 Cereals 15 Antioxidant nutrients 17 Other bioactive substances 18 Antioxidant hypothesis 20 Phytosterols and –stanols 20 Conclusions for coronary heart disease and stroke 21 Cancer 21 Fruit and vegetables 21 Legumes and nuts 26 Foods containing fibre 26 Vitamins 26 Other plant-derived substances 28 Conclusions for cancer 28 Type 2 diabetes 29 Age-related macular degeneration and cataract 29 Age-related cognitive decline 30 Chronic obstructive pulmonary disease 31 Osteoporosis and bone health 31 Plant foods and health: overall conclusions 32 Recommendations and current policy on plant food intake 33 Fruit and vegetables 33 Wholegrain foods 35 Current consumption patterns 35 Conclusions 39 Acknowledgement 40 2 Carbohydrates and lipids 52 Andrew Salter and Gregory Tucker Introduction 52 Major carbohydrates 53 Sugars 54 Polysaccharides 55 Starch 55 Cell wall polymers 58 Biosynthesis of cell wall polymers 60 Cell wall turnover 62 Nutritional benefits of plant carbohydrates 64 Major sources of dietary fibre within the diet and recommended intakes 64 Definition and measurement of dietary fibre 65 Physiological effects of dietary fibre 66 Lipids 68 Synthesis of fatty acids in plants 69 Synthesis of glycerolipids in plants 70 Modification of plant lipids 73 Fatty acid composition of plant foods 76 Vegetables 76 Cereals 77 Fruit 77 Oil seeds 77 Dietary lipids and human health 79 Phytosterols 80 3 Carotenoids 89 Úrsula Flores-Perez and Manuel Rodriguez-Concepcion Introduction 89 Structure, biosynthesis and function of plant carotenoids 90 Dietary sources and health benefits 93 Absorption and bioavailability of dietary carotenoids 97 Carotenoid type 98 Food matrix 98 Carotenoid metabolism in humans 99 Meeting the dietary demand and consequences for imbalance 101 Acknowledgements 102 4 Polyphenols 110 David Vauzour, Katerina Vafeiadou and Jeremy P. E. Spencer Introduction 110 Polyphenol structure 110 Phenolic acids and stilbenes 110 Flavonoids 113 Biosynthetic routes within the plant 115 Shikimic precursor and benzoic acid biosynthesis 115 Cinnamic acid biosynthesis 115 Stilbene biosynthesis 119 Flavonoid biosynthesis 119 Major sources within the diet 121 Phenolic acids and stilbenes 121 Flavonoids 121 Flavonols 121 Flavanones 122 Flavanols 123 Flavones 123 Anthocyanins 123 Isoflavones 123 Metabolic fate of dietary polyphenols 124 Gastrointestinal tract metabolism 124 Colonic metabolism 126 Role in human health 127 Flavonoids as classical antioxidants 128 Non-antioxidant activities of fl avonoids 130 Interactions with cell signalling pathways 131 Other potential mechanisms of action 133 Conclusion 133 Summary 134 Acknowledgements 134 5 Vitamins C and E 146 David Gray, John Brameld and Gregory Tucker Introduction 146 Vitamin C: structure and chemistry 146 Dietary sources of vitamin C 147 Vitamin C: biosynthesis and metabolism in plants 148 Vitamin C functions in plants 152 Vitamin C manipulation in plants 154 Absorption and transport of vitamin C in mammals 155 Vitamin E: structure and chemistry 156 Dietary sources of vitamin E 159 Vitamin E: biosynthetic pathways 159 Roles of tocochromanols in plants 161 Manipulation of tocochromanol concentration 162 Absorption and transport of vitamin E in mammals 164 Antioxidant functions of vitamin E 164 6 Folate 173 Stéphane Ravanel and Fabrice Rébeillé Introduction 173 One-carbon metabolism 174 Generation and interconversion of C1-units 176 Serine–glycine metabolism 176 Formate activation 176 Histidine catabolism 177 Interconvertion of C1-substituted folates 178 Utilisation of C1-units 179 Methionine synthesis 179 Purine ring formation 179 Formylation of methionyl-tRNA 180 Thymidylate synthesis 180 Pantothenate synthesis 180 Folate synthesis and distribution in plants 181 Biosynthesis of tetrahydrofolate in plants 181 Pterin branch 182 pABA branch 183 Assembly of the pterin, pABA and glutamate moieties 183 Reduction and polyglutamylation 184 Catabolism and salvage pathway 185 Compartmentation and transport of folates 185 Subcellular location of folates 185 Folate transporters 186 Folates distribution in plants 186 Physiology of folate in human health and disease 188 Absorption 188 Transport, storage, catabolism and excretion 189 Metabolic and clinical manifestations of folate deficiency 189 Diagnosis of folate deficiency 190 Folate bioavailability, requirements and food fortification 191 Bioavailability 191 Dietary intake recommendations 192 Dietary sources of folate 192 Food fortification 194 Prospects for plant foods biofortification 195 7 Phytoestrogens 203 Helen Wiseman Introduction 203 Biosynthesis of phytoestrogens 203 Introduction 203 Isoflavonoids 203 Prenylated flavonoids 205 Stilbenes 205 Lignans 205 Genetic engineering 205 Isoflavonoids 206 Introduction 206 Dietary sources and intakes 206 Metabolism and bioavailability 208 Isoflavonoids and cancer prevention 211 Hormone-dependent cancer prevention by isoflavonoids 211 Oestrogens and risk of breast cancer 213 Oestrogen receptor-mediated events 213 Animal models 215 Mechanisms of anticancer action of isoflavonoids 217 Clinical studies 219 Protection by isoflavonoids against cardiovascular disease 220 Cholesterol-lowering and isoflavonoids 220 Antioxidant action 222 Arterial function 225 Cellular effects 226 Protection by isoflavonoids against osteoporosis, cognitive decline and menopausal symptoms? 226 Osteoporosis 226 Menopausal symptoms and cognitive decline 227 Isoflavonoids: potential risks 228 Lignans 229 Introduction 229 Production of mammalian lignans 230 Cardiovascular disease 230 Breast cancer prevention 230 Prostate cancer prevention 230 Prevention of other types of cancer 231 Other health benefits 231 Prenylflavonoids 231 Stilbenes 233 Miroestrol 235 Deoxybenzoins 235 Coumestans 236 Phytoestrogens and human health: conclusions 236 8 Plant minerals 254 Martin R. Broadley and Philip J. White Introduction 254 Genetic variation in plant mineral concentration 258 Introduction 258 Between-species genetic variation in plant mineral concentration 258 Within-species genetic variation in plant mineral concentration 259 Iron and zinc 260 Iodine and selenium 263 Calcium and magnesium 264 Copper 266 Has the mineral concentration of crops declined due to breeding for increased yield? 266 Evidence for a decline in mineral concentration of horticultural crops 266 Is there evidence for a decline in mineral concentration of staple crops? 267 A case study on potatoes; a précis of White et al. (2009) 268 Index 278