CHAPTER 1
NUTRITION THROUGH THE LIFE CYCLE
Prakash Shetty
1.1 Approaches to the Study of Human Nutrition
Most texts on the subject of nutrition approach it from the viewpoint of the various nutrients present in food in our daily diet; provide information on the chemical structure of the nutrient, its important biological actions and their physiological role in the body; highlight the important sources of these nutrients in the foods that compose our daily diet; explain how the nutrients are made available to the body from the food ingested; and provide descriptions of the various pathological conditions that are associated with their deficiency or excess.
Another approach would be to characterise the stages of life through the cycle of life from conception to death, with the reproduction of the species, through this cycle (see Fig. 1.1). This approach provides a detailed account of the nutritional needs throughout the life cycle and highlights the special nutritional features of each of these stages. It also provides an opportunity to highlight the nutritional problems (related to both deficiency and excess) that characterise that particular phase in the life cycle and gives an opportunity to suggest ways and means to intervene during these phases taking into consideration the special problems that one needs to be aware of during this period in the individual's life. It also enables one to look at the promotion of good nutrition, taking care of identified vulnerabilities during each of these periods and thus helping to ensure the nutritional well-being and good health of the population as a whole.
The expectation is that the latter approach to the study of nutrition is more holistic and puts the individual at the various life stages of growth, development and the continuing ageing process at the centre rather than the nutrients in our daily diet. A subtle but important distinction that needs to be made when one approaches the study of human nutrition through the life cycle is to recognise that health and nutritional problems that manifest at the various life stages are not wholly dependent on inadequate or poor nutrition during that phase, although several nutrients may affect the individual during these critical periods in growth and development. The appreciation that what has happened in the past may continue to affect the individual and will interact with events and nutritional stresses later in life provides a life course perspective to nutritional problems that manifest at the various life stages throughout the life cycle. The life cycle approach to nutrition enables one to discuss these important interactions in a more meaningful manner than a didactic and reductionist approach to the science of human nutrition.
It would not be out of place to state that, just as one may consider the various life stages through one's life cycle, one has to acknowledge that the food industry that caters to us as consumers recognises us as several life style groups, which are specifically researched and targeted, such as for instance teenagers, young free and single, traditional families and retirees. On the other hand, organisations involved with promoting good nutrition and health may specifically target identified stages in the life cycle, such as pregnant mothers, babies, toddlers, school children, adolescents, adults (early, middle and late), elderly, etc.
1.2 Nutrition through the Life Cycle
The life cycle approach to nutrition provides an opportunity to look at the individual as she or he passes through the various life stages (the main stages of the life cycle are outlined in Fig. 1.1), as well as enabling the student to look at the entire population distributed at any given time throughout the various stages in the life cycle.
This approach has several advantages (1). It helps recognise age-specific vulnerability throughout the life cycle. Bartley et al. (2) summarise the various critical transitions and life events in human development, which occur side by side with the biological growth and development of the individual and may characterise periods of vulnerability of an individual in society (Fig. 1.2).
The life cycle approach helps us to understand that maximum benefits in one age group at a particular stage in the life cycle can best be derived from interventions made in an earlier stage or age group of individuals. For instance, it helps us to recognise that better nutrition and health during pregnancy will improve intra-uterine growth, improve birth outcomes and result in fewer complications related to pregnancy outcome; or that improved physical growth and development in infancy translates into improved cognitive function and intellectual development during childhood and leads to better economic prospects both for the individual in adulthood and in turn for society; or that improved birth weights mean less risk of chronic disease and premature death in adulthood.
This approach also reinforces the view that interventions at several points across the life cycle are needed to sustain improvements in health and nutritional outcomes. For instance, one will find it easy to consider that, for good health outcomes, the importance of good nutrition begins in the diet and nutrition during pregnancy, and continues in exclusive breast feeding at birth and the timely and adequate provision of complementary feeds, and good nutrition and diets during childhood, adolescence and adulthood to ensure healthy ageing and a good quality of life in the last stage of one's life.
The life cycle approach also enables us to consider risks and benefits through the entire life cycle and across generations and thus provides an opportunity to understand the importance of the increasingly popular life course approach to health and nutritional well-being.
Thus, a life cycle approach can help us to assess risks at various life stages, recognise important environmental influences that may be inimical to good nutrition and health, and identify key interventions at the various stages in the life cycle to prevent or deal with these external factors. An understanding of the importance of the life cycle approach implies that we recognise that ensuring good nutrition and healthy lifestyles is a life-long function. An elderly individual is unlikely to benefit much from a change in diet and life style late in life; nor does the pursuit of good nutrition and healthy lifestyles come easy to someone who has not followed this course in the earlier phases of life.
1.3 Nutrition over the Last Century in the United Kingdom
Childhood malnutrition and nutritional deficiencies are now things of the past in the developed industrialised west – in the United Kingdom and the rest of Western Europe and in the USA. However, it may not be out of place to remind ourselves that at the end of the 19th and around the beginning of the 20th century, malnutrition was a serious problem in Victorian England. Over 1 in 10 children attending London schools were habitually going hungry, while between 40 and 60% of young men presenting for military service at the time of the Boer war were rejected on medical grounds, much of this attributable to malnutrition (3). It was reported that many from the labouring classes in Edinburgh did not have the income to obtain sufficient food and at the same time lacked the education to make correct food choices (4). These and other subsequent reports resulted in the mandated national policy for feeding needy children at school and, in 1907, in London alone, 27,000 children received school meals, with the numbers doubling 2 years later (5). Between the war years, a report published in 1936 by John Boyd Orr indicated that the poorest in the country (then numbering about 4.5 million) were on diets deficient in all vitamins and minerals, while the next poorest (about 9 million) had a diet adequate in macronutrients (protein, carbohydrates and fat) but deficient in all vitamins and minerals (6). Only 50% of the population who were surveyed had a diet adequate in all dietary nutrients. This situation existed in Great Britain in 1936 despite the fact that the per capita consumption of dairy products and fruits and vegetables had dramatically increased between the years 1909 and 1934. The recognition of the nutritional value of milk in improving body weights and heights of children resulted in 46% of the school children being provided with milk at school by the year 1945, while about 40% of the children were having school meals in the same year.
The nutritional situation of the population of the UK after World War II was a completely different story (7). Despite the rationing and shortage of food in the early post-war years, food supply began to increase, and, when rationing was withdrawn completely by the year 1954, meat consumption began to increase. In 1950, school lunches were provided for over half of all school children, which rose to 70% in 1966. The years of austerity of the early 1950s were replaced by rising incomes and increased consumption of meat and sugar, almost as though it was a reaction to the years of rationing of these commodities. Fruit and vegetable consumption began to decline from the 1970s and consumption patterns and the food culture began to alter along with other social, economic and technological changes that occurred over the next two decades or so.
Changes in the way in which society processed food, purchased and consumed it, and responded to changing tastes and conveniences obviously left their mark on the food and nutrition of the population as a whole over the same period of almost half a century after World War II. Meat, dairy products, bread and potatoes remain important constituents of the daily diet in the UK, while the consumption of fruits and vegetables continues to be relatively low compared with that in other parts of Europe. Since the 1970s, milk and egg consumption has dropped and so has the consumption of meat (beef, pork and lamb), while the popularity of white meat from poultry has increased. These and other dietary changes have reduced the amount of fat and sugar we consume in the daily diet as compared with the early post-war years. However, the consumption of fats and sugars in processed food is high. The purchase and consumption of processed foods are also reflected in a nearly 70% drop in the purchase of flour since the 1950s. A disturbing trend is the drop in the consumption of fresh vegetables over the same period, although the consumption of fresh fruits may be increasing and a particular feature of this may be that many of them are available all the year round.
The overall nutritional change resulting from these changes in our food choices over time is that energy intakes have decreased. The proportional contribution from fat to the total energy in the diet, which increased right up to the early 1980s, has now reversed and, on average, about 35% of food energy is from fat, with about 11% from saturated fat intakes (8). For a healthy diet, the UK population may need to further reduce consumption of fat and sugar, as well as salt in the diet – much of this from the consumption of processed food. The consumption of a varied and balanced diet rich in fruit, vegetables and starchy foods, with fewer foods high in fat or sugar, needs to be the goal for a healthy and nutritious diet.
1.4 Diet and Nutrition Related Problems in the United Kingdom
Given the brief historical outline of how dietary patterns and food consumption have changed over the last several decades in the UK, perhaps the question to ask is how does this translate into diet and nutrition related problems currently in the UK?
1.4.1 Anaemia in childhood and adolescent years
Iron deficiency and possibly anaemia have been recognised to be a problem in the UK, particularly among adolescents and young adults. In girls, with the onset of the menstruation, the already high demands for daily iron requirements associated with rapid growth are further exaggerated. Since much of haem iron – a main source of iron in the diet – is obtained from meat and other related products, the tendency among adolescent females to vegetarianism, particularly the avoidance of meat, also adds to the problem. Iron absorption is also relatively poor among those on a meat-free diet. Associations between iron deficiency and poor cognitive function are well known. Although in the UK iron deficiency is generally mild, the increasing evidence that borderline iron status in this age group can have adverse effects on cognitive function may have important implications in terms of learning ability and academic performance.
1.4.2 Obesity
Obesity is a major risk factor for cardiovascular disease, diabetes, hypertension and premature death, and is increasing amongst adults in the UK. Abdominal or android type obesity is recognised as a specific risk factor in relation to these chronic diseases. The prevalence of obesity increased gradually in most age groups in both sexes in the 1990s (9). The increase was greater in women than in men, and in those aged 45 years and over than in those aged 16-44 years. The prevalence of obesity in men was 17.3% and in women 21.2% in 1998. Several environmental factors, both diet- and lifestyle-related, contribute to increased obesity in communities. Social and environmental factors that either increase energy intake and/or reduce physical activity are critical. Changes both in the food consumed and in the patterns of eating behaviour may have contributed to increasing risk of obesity. Patterns of eating, particularly snacking between meals and frequent snacks, may be significant contributors. However, the overwhelming evidence seems to support the view that much of the energy imbalance that is responsible for the epidemic of obesity in modern societies such as the UK is largely the result of dramatic reductions in physical activity, both occupational and leisure time, when food availability is more than adequate and unrestricted.
1.4.3 Cardiovascular diseases
The commonest cardiovascular diseases that are diet-related are coronary heart disease (CHD) and hypertension. CHD emerged as a burgeoning public health problem in UK after World War II, and by the end of the 1950s, had become the single major cause of adult death. The risk of CHD in individuals is dominated by three major factors: (i) high serum total cholesterol, (ii) high blood pressure, and (iii) cigarette smoking (10). Obesity resulting from dietary and lifestyle changes is strongly related to changes in serum total cholesterol, high blood pressure and diabetes mellitus, which are risk factors for CHD. The increase in consumption of animal fat and the reduced intakes of fruits and vegetables noted earlier have contributed to the increase in CHD in the UK since the 1950s. The appropriate dietary recommendations would include lowering total fat intake to between 30 and 35% of total calories, restricting saturated fat intake to a maximum of 10% of total calories, and increasing intakes of fruits and vegetables. Translated into food components, this would mean reducing animal fat intake in particular and intake of hydrogenated and hardened vegetable oils, and increasing the consumption of cereals, vegetables and fruits.
Statistics from the Department of Health (11) indicate that CHD prevalence increases with age in both sexes, with men having a higher prevalence than women. In particular, the prevalence of angina (5.3% vs 3.9%) and heart attack (4.2% vs 1.8%) was higher in men than in women (respectively) in the survey. CHD continued to increase with age and showed a gradient according to social class and income in both sexes. For instance, the age-standardised prevalence was 5.2% in men in Social Class I and 11.3% in Social Class IV. There is also evidence to suggest that there are significant associations between greater sodium intake in the daily diet and high blood pressure. A diet rich in fruits, vegetables, and low-fat dairy foods and with reduced saturated and total fat can substantially lower blood pressure – a major risk factor for CHD. The White Paper 'Our Healthier Nation' (12) states that a good diet is important in protecting health and the target is to improve the diet of the population by educating and providing information about diet and health to groups at risk, and to ensure that there is adequate access to, and availability of a wide range of healthy foods. An increase in the intake of fruits and vegetables and a reduction in the consumption of fats and salt can have a beneficial influence on health.
1.4.4 Non-insulin-dependent diabetes mellitus (NIDDM)
NIDDM is a chronic metabolic disorder, which occurs in adulthood and is strongly associated with an increased risk of CHD. Obesity is a major risk factor for the occurrence of NIDDM and the risk in a community appears to be triggered by a number of environmental factors such as sedentary lifestyle and dietary factors. Ethnic minorities in the UK from South Asia (i.e. Indians, Pakistanis and Bangladeshis) have a higher incidence of NIDDM. The cause of NIDDM is unclear, but it seems to involve both an impaired pancreatic secretion of insulin and the development of tissue resistance to insulin. Overweight and obesity, particularly the central or truncal distribution of fat, accompanied by a high waist/hip ratio and a high waist circumference, seem to be invariably present with NIDDM. The most rational and promising approach to preventing NIDDM is to prevent obesity. Physical activity also helps improve glucose tolerance by weight reduction and also by its beneficial effects on insulin resistance. Diets high in plant foods are associated with a lower incidence, and vegetarians have a substantially lower risk than non-vegetarians of having NIDDM. The age-standardised death rates due to NIDDM in the UK are 10.2 and 11.3 per 100,000, respectively for men and women for the year 2000 (11).
