Chapter abstracts for “Nutrition: Maintaining and Improving Health” 5th edition

Anyone who follows this blog may have noted the absence of new posts for several months. This is because I have been finishing the draft of a 5th edition of my large nutrition text published by Taylor and Francis. To give a taster of this new edition, the chapter abstracts are shown below

Chapter 1           Changing priorities in nutrition

This chapter traces changes in the priorities for nutrition education during the 20th century. In the first half of the century, most micronutrients were identified and shown to cure serious illnesses like pellagra, rickets and beriberi. Nutrition education guides used food groups to point consumers towards a diet that was adequate for all essential nutrients. As deficiency diseases all but disappeared in developed countries, the priority changed to guiding consumers towards a diet that was not only adequate but also reduced the risk of chronic diseases like cancer, cardiovascular disease, type 2 diabetes and tooth decay.  New food guides using images of plates and pyramids were designed to reflect this additional aim. The characteristics of diets that meet these twin aims were established four decades ago and much of current nutrition research seems to have limited useful purpose. The chapter ends with a case study of a putative link between yogurt consumption and ovarian cancer. This was based upon very flimsy preliminary evidence but has generated forty years of ongoing research which has not established, nor is it likely to establish, such a link but has wasted large amounts of time, money and effort.

Chapter 2            Food selection

This chapter aims to remind science-focused nutrition students that food is not just a source of nutrients but has many non-nutritional roles. Nutrient content has not traditionally been a major influence on food choices; people eat food not nutrients. The author’s “hierarchy of availabilities” model of food selection is used as a framework to discuss the many varied influences upon food selection. This model was created from the concepts in Abraham Maslow’s famous hierarchy of human needs. To be selected a food must be physically available, affordable, culturally acceptable, provided by an individual’s gatekeeper and be personally acceptable to the individual e.g. they should like it and must be able to tolerate it. Under the umbrella of “economic availability, the role of poverty in causing malnutrition in developing countries is discussed as is the influence of income upon diet in the UK. Under the umbrella of “cultural availability” there is a discussion of dietary taboos and of migration as a driver of dietary change. The chapter ends with a brief discussion of a more recent social ecological framework for decision making for nutrition and physical activity developed by the USDA.

Chapter 3         Methods of nutritional assessment and surveillance

This chapter critically reviews the methods used to assess and monitor nutritional wellbeing of individuals and populations. These methods either assess whether energy and nutrient intakes are sufficient to satisfy estimated requirements or assess the nutritional status of subjects using clinical, anthropometric or biochemical indicators. A range of methods of measuring food intake of individuals or populations are discussed. Food tables on electronic databases are used to convert food intakes into energy and nutrient intakes and these estimates are then compared to yardsticks of adequacy and diet quality called dietary reference values (e.g. RDA). In the UK, the rolling National Diet and Nutrition Survey gives estimated food and nutrient intakes of a representative sample of the population and a household budget survey now called Family Food monitors variation in food purchasing practices of different groups and how these change over time. There is a body of convincing evidence which suggests that all self-reporting methods significantly underestimate actual energy and food intakes as measured objectively by the doubly-labelled- water (DLW) method. A range of clinical, anthropometric and biochemical indicators of nutritional status are discussed and the strengths and limitations of these three approaches reviewed. Methods of measuring energy expenditure are reviewed including long term expenditure in free-living subjects using DLW.

Chapter 4            Investigating links between diet and health outcomes

This chapter discusses, with illustrative examples, all of the various observational and experimental approaches that are available to enable nutritionists to determine how nutritional and lifestyle factors influence health. These methods are used by researchers across the biomedical sciences to determine the causes of ill-health and the efficacy of treatments. The observational/epidemiological methods range from relatively simple descriptive methods (e.g. correlating death rates or risk factor levels to dietary characteristics across cultures) to more sophisticated analytical methods like cohort studies that may involve monitoring tens or hundreds of thousands of people for decades to see if measured dietary intakes or risk factor levels predict disease or mortality risk. No matter how large or sophisticated observational studies are, they cannot conclusively demonstrate cause and effect although the Bradford Hill tests of causality indicate the likelihood that any association is due to cause and effect. The experimental methods range from animal or in vitro studies, through short term human experiments testing the effects of dietary change upon risk factors, to randomised controlled trials which are seen as the “gold standard” of evidence in the biomedical sciences.

Chapter 5       Investigating links between diet and health – amalgamation, synthesis   and decision making

This chapter examines how the evidence from multiple and varied studies can be amalgamated and synthesised to allow decisions about treatment and health promotion advice to be made. Meta-analysis is a way of amalgamating studies with similar methodology and outcome measures into effectively a single larger study of greater statistical power. A meta-analysis of randomised controlled trials is seen to be at the very top of the hierarchy in biomedical decision making and a meta-analysis of any category of studies is seen as a notch higher than an individual study. The role of pyramids or numerical grading hierarchies in the decision making process are discussed. The National Institute for Health and Care Excellence (NICE) is an independent government financed body that is charged with making decisions about best practice in medical and social care. Many published studies are never reproduced or cannot be independently verified; this is especially true for the observational studies which are so prominent in nutrition research. Some of the likely causes for this lack of reproducibility are outlined and its implications discussed. The chapter ends with a brief discussion of research fraud including a brief summary of some known fraudulent researchers in nutrition-related research.

Chapter 6   Dietary guidelines and recommendations

Some of the most influential sets of dietary guidelines issued in the UK, USA and by the WHO are outlined and synthesised. There is a very high level of agreement between these sources and a high level of consistency over time. Despite claims to the contrary, these guidelines have had a profound effect upon food choices in industrialised countries like the UK. Some of the barriers that may impede the implementation of dietary guidelines are identified and discussed. Current UK alcohol guidelines are discussed in depth and there is a critical evaluation of the evidence upon which they are based. The chapter ends with a brief summary of the food selection guides discussed in chapter 1 i.e. food group systems and food guide plates and pyramids.

Chapter 7   Introduction to energy aspects of nutrition

The chapter starts with definitions of the main units for energy used in nutrition, the kilocalorie and the kilojoule. There is a review of the ways in which energy requirements are estimated and thus how the dietary reference values for energy are set. Methods used to determine the energy contents of foods are summarised. The contribution of the three major macronutrients and of the different foods groups to the total energy content of the UK diet are estimated using data from the National Diet and Nutrition Survey. The changes in these values over time are also summarised and how these changes have been partly driven by the dietary guidelines discussed in chapter 6. The concepts of energy density and nutrient density are explained. The effects of energy deficit and starvation upon the body are summarised including the metabolic adaptations that occur during prolonged starvation. Eating disorders like anorexia nervosa and bulimia are briefly reviewed along with the cachexia seen in serious illnesses especially the severe cachexia produced by some forms of cancer.

Chapter 8   Energy balance and its regulation

The concept of energy balance is introduced. Growth, convalescence and increasing fatness are associated with positive energy balance; dieting, serious illness and starvation are associated with negative energy balance. Long term weight stability requires that either energy intake or output or both are regulated. The physiological regulation of appetite and energy intake is mainly mediated through centres in the hypothalamus. A variety of inputs to the hypothalamus like signals from the gut and blood substrate levels influence short term appetite. It is difficult to envisage how such short-term inputs could enable there to be long term accurate control of body weight. The lipostat theory of the 1950s envisaged a factor released from adipose tissue in proportion to its mass that would indicate to the hypothalamus the total level of body fat and give a plausible mechanism for long term weight control; in 1994, this previously hypothetical hormone was identified and called leptin.  Genetic leptin or leptin receptor deficiency leads to severe obesity in animal models and in people. During the 1980s, it was widely held that brown fat thermogenesis played a major role in the regulation of body weight and that some defect in brown fat might be a major cause of human obesity. The origins and decline of this brown fat theory of obesity are critically discussed.

Chapter 9            Obesity

Obesity, overweight and underweight are defined using the body mass index (BMI). The prevalence of obesity in different world populations and in various sectors of the UK and US populations are summarised. There is an increasing prevalence of overweight and obesity across the world and the consequences and probable causes of this major and increasing public health problem are reviewed. There is a particular focus upon the rising tide of obesity and overweight in children. High fat and sugar diets and increasing levels of inactivity have been proposed as major drivers of the increasing obesity prevalence; the evidence implicating these factors is evaluated. There is an overview of the ways in which obesity is treated in individuals and some of the measures that governments could take that might be expected to reduce the prevalence of obesity in populations especially the prevalence of obesity in children. Guidelines are presented to aid in the selection of the appropriate level of intervention for overweight and obese patients that use the patient’s BMI and the presence or absence of additional risk factors. Strategies range from diet and exercise up to the use of bariatric surgery.

Chapter 10           Carbohydrates

The chemical nature of carbohydrates is outlined and the carbohydrates are classified into sugars, starches and non-starch polysaccharides or dietary fibre. The main food sources of the different carbohydrate fractions in the UK diet are identified using data from the National Diet and Nutrition Survey. The nutritional issues associated with the individual carbohydrate fractions are discussed. There is an outline review of the various artificial sweeteners that are used as sugar substitutes. The new UK tax upon sugary drinks and its immediate impact upon sales is explained and the anticipated long term effects of this tax and their likely realisation are discussed. The glycaemic index and the glycaemic load are defined and their nutritional significance discussed. The chapter ends with a review of the evidence that high fibre intakes may have protective effect against bowel cancer and cardiovascular disease.

Chapter 11          Protein and amino acids

The first half of this chapter covers the traditional scientific aspects of protein found in most nutrition books. The nature, dietary sources, requirements and typical UK intakes are reviewed along with a brief summary of the digestion of protein and metabolism of amino acids. The concept of nitrogen balance is explained and the likely reasons why a person would be in positive or negative balance identified. Protein quality and the concept of a limiting amino acid are also covered. In the second half of the chapter there is extended discussion of the historical belief that there was a crisis of world protein supply and that primary protein deficiency was the most common nutritional problem in the world – “the protein gap”. The origins, causes and some of the major and persistent consequences of this now discredited belief in a protein gap are reviewed. Measures taken to try close the illusory protein gap cost billions of pounds and had a lasting effect upon attitudes to protein-rich foods.

Chapter 12          Fat

The nature, sources and roles of dietary fats are explained as is the difference between saturated and the different types of unsaturated fatty acids. The relative prominence of saturated, monounsaturated and polyunsaturated fatty acids in food fats is compared as is the effect of these different categories of fatty acids upon blood lipid levels and especially upon blood cholesterol concentration. There is a brief summary of the digestion, absorption, transport and metabolism of fats. There is an extended analysis of the effect of statins upon blood cholesterol level and cardiovascular disease risk; mass use of statins has had major population impact upon levels of blood cholesterol in middle-aged and older people in countries like the UK. The generally accepted role of dietary saturated fats in raising blood cholesterol levels and increasing cardiovascular disease risk is explained along with a review of the evidence supporting this “diet-heart hypothesis”. The nature and nutritional aspects of fish oils and oily fish are discussed and the probable requirement and nutritional impact of n-3 polyunsaturated fatty acids overviewed.

Chapter 13                    Dietary supplements and food fortification

There is an overview of food fortification and dietary supplements and their likely value as strategies for increasing intakes in those likely to benefit from higher micronutrient intakes. Over-the counter supplements tend to be taken by those who need them least and are rarely taken by those most likely to benefit from them. Current UK food fortification policy was essentially designed in World War II (1943) and the case for an updated and more rational food fortification policy is made. Dietary supplements are loosely defined and classified into five major categories: essential micronutrients, natural metabolites, natural fats and oils, natural plant extract and antioxidants. Each of these five categories is overviewed. The range of phytochemicals found in natural plant extract are classified and their physiological effects and likely therapeutic benefits evaluated. Many natural extracts like Agnus Castus, Echinacea, St John’s wort, and Milk Thistle that have no authentic culinary use were previously sold as dietary supplements in the UK but are now sold as Traditional Herbal Remedies; they are still sold as supplements in the USA. Some issues are discussed more fully such as: the case for fortification of UK flour with folic acid; the likely benefits of fish oil supplements; the antioxidant theory of disease and indications that antioxidant supplements are more likely to do net harm than good.

Chapter 14          Food as medicine

The common theme running through this chapter is discussion of foods where consumption is promoted as having specific disease-preventing or curative benefits. The WHO considered that there was sufficient evidence to recommend five daily portions (5x80g) of fruit and vegetables in 1990 but there are still many studies published that test this hypothesis. A spate of headlines in recent years have suggested that even more than five portions might be needed for optimal benefits. The methodology behind these headlines claims is critiqued and it is questioned whether higher recommendations are justified for small hypothetical extra benefits if most of the population do not get close to five a day. The concept of “superfoods” is critically discussed and the claims for a number of the most popular superfoods evaluated. The idea that a single food can transform a diet, which the title superfood implies, seems innately flawed and unrealistic. The chapter ends with a discussion of so-called functional foods and an evaluation of the claims made for three classes of functional food: foods like soy which are rich in phytoestrogens (substances with weak oestrogenic activity); foods with live probiotic bacteria; and, finally foods rich in cholesterol–like plant sterols (phytosterols) than have a demonstrable, if limited, cholesterol-lowering effect.

Chapter 15           The Vitamins

The chapter begins with a general overview of vitamins. Vitamins are defined and classified into fat and water soluble vitamins. Vitamins fulfill specific biochemical roles and deficiency of a vitamin leads to a characteristic set of symptoms, a deficiency disease. Some vitamins must be consumed ready made but others can be synthesised from specific dietary precursors (e.g. vitamin A from β-carotene) and vitamin D can be synthesised in skin that is adequately exposed to summer sunlight. Vitamin deficiency diseases tend to occur under specific dietary circumstances e.g. pellagra is usually associated with a maize-based diet, beriberi with a diet based upon white rice and scurvy is precipitated by lengthy deprivation of fruit and vegetables. There follows a review of each of the 13 individual vitamins that includes: its chemical forms, dietary requirements, food sources, biochemical measures of adequacy, functions, the effects of deficiency and the current levels of adequacy/inadequacy especially in the UK.  There is a more extended discussion of a number of vitamin-related issues: the worldwide prevalence and consequences of vitamin A deficiency; the extent of vitamin D deficiency in the UK and its implications for bone health, muscle function and immunity; the historical importance of pellagra and beriberi; and, the claim that high doses of vitamin C prevents colds.

Chapter 16           The Minerals

Nine individual minerals are briefly reviewed with information about: requirements and dietary sources; biochemical functions; toxicity and guidance on high intakes; the prevalence, causes and effects of deficiency. The following four mineral-related issues are discussed more fully. Iodine deficiency and iodine deficiency diseases is discussed in a world context and there is also discussion of the extent of marginal iodine deficiency in the UK and its likely consequences especially during pregnancy and lactation; the effect of increased levels of veganism and the widespread use of unfortified milk substitutes is also discussed. Worldwide, iron deficiency anaemia is the most prevalent nutritional deficiency and is also prevalent amongst UK girls and women. The implications and possible strategies for coping with this problem are reviewed. Calcium homeostasis is explained and there is extended discussion of the relationship between calcium intakes, vitamin D status and bone health including the risk of osteoporosis.  High salt intake is an aetiological factor for the development of hypertension and the evidence that implicates salt in the development of hypertension is evaluated. The dietary recommendations and guidelines aimed at reducing the prevalence of hypertension and of the health problems like strokes, heart disease and renal disease that accompany it.

Chapter 17             Nutrition and the human life-cycle

This chapter reviews the changes in nutritional needs and priorities of different lifecycle groups. The extra energy and nutrient needs of pregnancy are relatively modest and these are summarised. There is discussion of the effects of malnutrition during pregnancy as well as the results of studies that have assessed the impact of supplementation programmes. The increased nutritional requirements of lactation are also summarised as is the effect of low nutrient intakes upon milk composition. Breastfeeding is the ideal way to feed new-born babies and trends in the prevalence and duration of breastfeeding in the UK are summarised. International comparisons suggest that the UK has the lowest percentage of women who wholly breastfeed their babies for the recommended six months. Nutritional aspects of weaning, infancy and adolescence are summarised. The increase in the number of elderly people and recent changes in their living circumstances and wealth are charted. The physiological effects of ageing and their nutritional implications are described. The current diets and nutritional status of elderly UK people is compared to that of other adults. As people get older and frailer so maintaining dietary adequacy re-assumes a higher priority but the general dietary guidelines for chronic disease and risk factor reduction are appropriate for both younger and older adults.

Chapter 18           Nutrition as treatment

This chapter deals with the role of nutrition in the clinical management of injury and illness. Dietary restriction can completely eliminate the symptoms and consequences of some illnesses where they are triggered by allergy or other intolerance to particular foods or dietary components. Food allergy, coeliac disease and phenylketonuria are used as case-studies to illustrate some of the issues and difficulties of managing conditions that require total avoidance of some foods or severe regulation of an essential and ubiquitous nutrient. Diet can also be a substantial and specific component of the therapy of some diseases; diabetes mellitus, cystic fibrosis and chronic renal failure are used as case-studies of such conditions. The final part of the chapter deals with the prevalence, effects, causes and means of avoiding/treating malnutrition in the general hospital population. Key elements in reducing this problem are better nutritional training and awareness of medical and nursing staff, high levels of vigilance and monitoring and the supply of food that is both nutritious and appetising.

Chapter 19           Some other groups and circumstances

This chapter covers vegetarianism, the nutrition of minority ethnic groups and the interactions between diet, health and physical activity. The prevalence of varying degrees of vegetarianism has grown recently in the UK. There has been a particular increase in veganism and the avoidance of dairy foods. Meat, fish, eggs, and milk are major sources of some nutrients; the likely effects of varying levels of vegetarianism upon adequacy are identified and strategies for managing any likely problems suggested. Affluent white vegetarians generally have lower chronic disease risk than the general population; the likely extent to which this is due to avoiding meat per se is discussed. There is an analysis of the current ethnic make-up of the UK population. The diets, nutritional status and health statistics of the major ethnic groups in the UK are compared. Under the umbrella title “nutrition and physical activity”, there is: an explanation of the term fitness and the activity and the fitness levels of the UK population are compared to guidelines and recommendations. There is overwhelming evidence that increased physical activity and fitness has many benefits upon physical and mental health and enables older people to remain independent. Many of these benefits are summarised and sample evidence of these benefits presented. There is a brief review of the use of diet as a means to improving athletic performance; a topic that occupies whole textbooks of sport’s nutrition.

Chapter 20           The safety and quality of food

The basic tenets of UK food law are listed and their origins, aims and enforcement methods overviewed. UK and US food labelling regulations are compared and their aims and objectives discussed; there is also consideration of how health claims relating to food are manage in these two countries. Under the umbrella title “microbiological safety of food” there is a review of the prevalence and causes of food borne disease along with some practical measures for minimising the risk of foodborne disease. The way in which the source and cause of a foodborne disease outbreak can be pinpointed is explained. The nature and characteristics of the most common micro-organisms responsible for foodborne diseases are summarised. There is an extended discussion of the recent bovine spongiform encephalopathy (BSE) or “mad cow disease” crisis in the UK and its impact. Even though this BSE crisis is essentially over it had profound economic and political impact and has left a legacy of mistrust of government’s ability and willingness to ensure food safety. The main methods of food processing are reviewed and their benefits and potential problems identified. The chapter ends with a discussion of the three main potential sources of chemical hazard in food; natural toxicants, contaminants and food additives.

 

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