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In millennia past, and until recently, among hunter-gatherers and like populations, in all populations, in measure, down through the ages, the securing of sufficient food was life's primary purpose. Virtually all people were physically very active during early life and later in their everyday occupations. In contrast, nowadays, in Western populations, with relative abundance of food, the way of life is mainly one of enjoyment of meals, of work, and of leisure time, in a context of as few as one child per family, and with long survival times of about 75 to 80 y, due in large part to much reduced child mortality and the effective treatments of disorders and diseases. As to changes in food consumption, compared with the erratic and often monotonous fares of the past, both far and not so distant, everyday diets have changed tremendously in variety, nutritional value, and palatability such that, inter alia, overeating is almost inevitable. Compounding the latter, sedentariness is the rule, in contrast to the previously very high level of everyday physical activity in the masses of populations. In consequence, one speculation is that, by 2230, "all Americans will be obese." Although the living of much longer lives is highly gratifying, understandably, all wish to have longer "healthy life expectancy," i.e. to suffer as little as possible before death. However, with regard to the present-day "passive consumer," although the practical recommendations for leading still healthier lives, dietarily and non-dietarily, are well known, very few are interested, and still fewer practice them. Nevertheless, for the few who, with determination, are eager to improve their lifestyles, there could be highly profitable lengthening of years of "healthy life expectancy" by eating less, eating more plant foods, being much more physically active, and restricting non-dietary risk factors (smoking, alcohol consumption).

In South Africa, with changes in environmental factors, varyingly, there have been measures of westernization of diet, with slight rises in intakes of energy and fat, with more of animal, but less of plant foods, being eaten, and with a fall in dietary fibre intake. Smoking practice has increased, particularly in males, likewise alcohol consumption. Physical activity has fallen, especially in urban dwellers. Changes in cancer incidence rates, as reported in the South African Cancer Registry for the periods 1986 and 1993-1995 have been investigated. Additionally, changes in percentages of cancers in hospitals in Johannesburg during 1953-1955 and in Durban during 1994-1996, have been looked into. The high occurrences of oesophageal and cervix cancers have fallen slightly, although more so in respect of liver cancer. But there have been rises, widely varying, in the cases of cancers of the lung, prostate and breast. While some of these changes would be expected from the changes in environmental factors, many cancer occurrence situations remain problematical, e.g. the continuing low occurrence of colorectal cancer. Recently, the rapidly rising epidemic of HIV/AIDS has slightly increased the occurrence of certain cancers, particularly Kaposi's sarcoma and non-Hodgkin's lymphoma. Regarding prevention, chances of cancer control in Africans, through lessening personal risk factors, are very remote, which unfortunately also prevails in large measure in western populations, regarding their reluctance to make the recommended beneficial changes.

Coronary heart disease (CHD), rare in the early 1900s, in the 1970s was responsible for almost a third of deaths in Western populations. Although its mortality rate has fallen in the last 20 years, considerably in certain populations, it remains the leading cause of death, and there is little evidence of any fall in its incidence rate. The primary risk factors, which include pattern of diet, smoking practice, and level of physical activity, are well known, but explain only approximately 50% of variation in its occurrence. Despite the numerous health improvement recommendations made, alterations in diet have been relatively slight. Although smoking practice has halved in some populations, its prevalence is now rising in the young. The extent of physical activity is low, compared with that in the past, and may even be decreasing in the young. With the general ageing of populations, the near absence of strong encouragement from the state, and individuals' general failure to reduce risk factors significantly, the chances of decreases in the incidence of CHD appear remote.

In emigrants from less to more developed countries, consequent changes in environmental factors are associated, inter alia, with changes in occurrences of the chronic diseases of lifestyle. In South Africa, most immigrants from India arrived in the early 1900s. To learn of the current pattern of cancer in the descendants of these people, enquiries were made on several series of patients admitted to RK Khan Hospital in Durban. The results were then compared with those of patients admitted to Ambojogai Hospital, North West India, the ancestral home of the majority of South African Indians. The most prominent differences were the lower percentages in South African Indians in respect of cancers of the mouth/pharynx in both sexes and of cervical cancer, and their considerably higher percentages, principally in the cases of stomach cancer in both sexes, of prostate cancer in males and of breast cancer in females. Discussion of risk factors indicates that in such populations there could be some control over the rises in some cancers, and on reductions in others. However, endeavours at prevention are hindered not only by the lack of knowledge prevailing, but also by their general indifference; likewise, this is the case with western populations.

In all Third World populations, among preschool and schoolchildren, low weight- and height-for-age, i.e. below the 5th centile of US NCHS reference standards, are common, affecting 10-50%. Orthodoxly, shortfalls are attributed largely to insufficiency of food. In an attempt to throw more light on the situation regarding African schoolchildren, studies have been made on series of pupils, aged 10-12 years, at three rural schools in North West Province, South Africa. Of 396 pupils, 126 (31.8%) were below, and 270 (68.2%) above the 5th centile. Enquiries were made on each pupil's diet and meal pattern, their class position and games aptitude, and, regarding home characteristics, their family size, Parent(s) working, and the latter's interest in education. With minor exceptions, no significant differences in odds ratios were found between respective groups below and above the 5th centile. Evidently, there are multiple influencing factors. Hence, among children of school-age, there must be caution against overblaming undernutrition, and of overrating the health disadvantages from mild to moderate malnutrition. For definition clarification, long-term observations are necessary.

In Western populations, historically, from early times until the 19th century, diets were composed largely of plant foods-cereals, beans, vegetables and fruit. The huge majority of populations were very poor with restricted food choices. The same situation prevails with most present-day Third World populations, although principally with rural dwellers. In Western populations, in recent times, stemming largely from urbanization and rise in prosperity, and accompanying increased partiality to animal foods, there have been falls in the intake of some plant foods yet rises in others. Potato intake has halved, whereas vegetable consumption has increased only slightly, although that of fruit more so. National consumptions of these foodstuffs vary widely, those in the United Kingdom and United States of American being only about half of those in Mediterranean countries, Spain, Portugal and Greece. In the former countries, present dietary guidelines urge that vegetable consumption be doubled, with fruit up by a half. In southern Africa, consumption of vegetables and fruit by the white population appears similar to those in The USA and UK. Yet in African cities, intake is low due to their cost. In view of the protective role of high vegetable and fruit intake in the combating of coronary heart disease and many forms of cancer, the relatively low consumption of these foodstuffs, especially in the poorer populations, is disappointing, and alas, appears unlikely to rise in the near future.

Many countries have folklore beliefs about the use of foodstuffs to remedy ill health and to promote long life. Many of the beliefs and practices of the ancients and, more recently, "mothers's views of health" have a basic soundness and are in harmony with present-day advice on the attainment of a prudent diet and life-style.

In Africa, with poverty rising, and health care diminishing, a nutritional question is-what are the limits of successful physiological adaptation to low dietary intakes? In this review the practice of lactation is discussed, from both past and present viewpoints. Orthodox Recommended Allowances for lactation are scarcely ever met. Yet, through various adaptations, the huge majority of African and similarly placed mothers lactate successfully and produce milk of good quantity and quality. The benefits from supplements are discussed; broadly, results have been disappointing. Some good and adverse non-dietary practices are considered. Benefits for infant and mother from lactation, even for protracted periods, far exceed drawbacks.

Colon cancer, rare in the past, and in developing populations, currently accounts for 2 to 4% of all deaths in Western populations. Evidence suggests the primary cause to be changes in diet, which affect the bowel milieu intérieur. It is possible that in sophisticated populations, the higher concentrations of fecal bile acids and sterols, and longer transit time, favor the production of potentially carcinogenic metabolites. Of secular changes in diet, evidence suggests that the following may have etiological importance: 1) the fall in intake of fiber-containing foods with its effects on bowel physiology, and 2) the decreased fiber but increased fat intakes, in their respective capacities to raise concentrations of fecal bile acids, sterols, and other noxious substances. For possible prophylaxis against colon cancer, recommendations for a lower fat intake, or a higher intake of fiber-containing foods (apart from fiber ingestion from bran) are extremely unlikely to be adopted. For future research, western populations with considerably lower than average mortality rates, e.g., Seventh Day Adventists, Mormons, the rural Finnish population, as well as developing populations, demand intensive study. Also requiring elucidation are the respective roles of diet and of genetic constitution on concentrations of fecal bile acids, etc., and on transit time, in prone and nonprone populations.

Bowel behaviour was investigated in 81 rural black, 117 urban black, and 77 white children aged 1 to 4 years. The study was undertaken principally because intake of dietary fibre by urban blacks is now lower than that of whites: moreover, that of rural blacks has also fallen. Average daily defecation frequencies in rural and urban black children and white children were 1.9, 1.8, and 1.5, respectively. Black children voided smaller stools and more frequently than white children. In both ethnic groups most stools were soft. Median transit times, determined in 55 rural black, 80 urban black, and 45 white children, were approximately 6.5, 7, and 27 hours, respectively. Median transit times increased little with age in black compared with white children. The higher defecation frequency and the much shorter transit time in black children are not explicable in terms of the levels of fibre intake.

Compared with our ancestor's diet, that consumed by present-day Western populations is higher in intake of energy, of protein (especially animal protein) and of fat (especially animal fat), but lower in intake of fibre-containing cereal foods; this diet is associated with high rates of morbidity and mortality from degenerative diseases. In the USA, the Dietary Goals report has recommended partial reversion to our ancestors' diet, including decreased intake of animal fat and protein, cholesterol, salt, sugar and alcohol--hopefully to reduce mortality from the six leading causes of death. 'Dietary goals', 'sensible eating' and the extreme 'longevity diet' are discussed. It is concluded that the general public will not voluntarily accept dietary changes of the magnitude required to promote a meaningful decrease in the burden of ill-health from degenerative diseases, because of: (i) conservativeness of dietary habits; and (ii) uncertainties about the extent of benefits likely to accrue. It is speculated, however, that in the distant future dietary changes of the type recommended will gradually but compulsorily be introduced, because of: (i) increases in population numbers; and (ii) the far greater economy of land usage linked with production of a near-vegetarian diet.

Published values on glycaemic indices of foods are based on studies made on subjects in diabetes-prone populations. Values have therefore been determined in South African black rural adolescents--a population at very low risk to the disease. While the profile of responses evoked by common foodstuffs on blood glucose levels was similar in blacks to that reported for white subjects, mean levels in blacks were 1 mmol/l or more lower. The glycaemic indices of legumes, particularly that of gram dal, were much lower than those for cereal products, vegetables and fruit.

Epidemiological evidence suggests that the incidence and death rate from prostatic cancer, an endocrine-associated disease, are related to environmental factors including diet. In this study, a comparison of serum and urinary levels of steroid hormones was carried out in healthy elderly rural vegetarian South African black men, a low-risk population, and a comparable group of men with prostatic cancer. In these prostatic cancer patients, plasma androgen levels decreased, while estrogen levels increased. Concomitantly, the androsterone:etiocholanolone ratio increased, and a greater proportion of estrogens was excreted as estriol. When transferred to a Western diet, plasma androgens showed a further decrease and a greater increase in estrone in prostatic cancer patients. In prostatic cancer patients, the total urinary androgen and estrogen levels were unaltered. However, in elderly healthy men, the Western diet decreased the excretion of estrogens and androgens. Thus, a Western diet supplemented the decrease in plasma androgens initially present in these patients. Evidence suggests that the decrease in plasma androgens increases the estrogen: androgen ratio, which may lead to hyperplasia of the prostatic ductal epithelia, a change enhanced by a Western diet. Changes in urinary steroid hormone levels in South African black patients comparable to those reported in white prostatic cancer patients indicate that hormonal changes must be related to several environmental factors, apart from diet. A simultaneous study of the steroid hormone composition of blood and prostatic fluid in this low-risk population is suggested.

Mean faecal pH values did not differ significantly in groups of rural South African Black schoolchildren of 10--12 years who ate their traditional high-fibre low-fat diet, and urban dwellers who consumed a partially westernized diet. However, both means were significantly lower than those of groups of White schoolchildren. In feeding studies of 5 days' duration, mean faecal pH value of Black children became significantly less acid when white bread replaced maize meal, and became significantly more acid when a supplement of 6 oranges was consumed daily. Supplements which consisted of skim milk, butter, and sugar had no significant effect on mean faecal pH value. In White children in an institution, the mean pH value of faeces became significantly more acid when a supplement of 6 oranges, although not of bran 'crunchies', was consumed daily.

The effect of a habitual high cholesterol intake on serum cholesterol and other lipid levels against the background of a moderate fat intake was investigated in 30 rural coloured volunteers (16 men, 14 women) working on an egg farm. Protein contributed approximately 11%, fat 31%, carbohydrate 58% (sucrose 21%) of energy intake. Daily cholesterol intake averaged 575 mg. In men, although not in women, cholesterol intake correlated negatively with serum cholesterol and low-density lipoprotein cholesterol levels, indicating that a high consumption of eggs in the study population did not prejudice lipid homeostasis. The population exhibited a high profile of coronary heart disease risk factors.

Coronary heart disease (CHD) is rare in South African Blacks, even in urban dwellers, but very common in Whites. The disease is multifactorial in causation. Habitual pattern of diet undoubtedly is strongly involved. Epidemiological and other evidence suggests that for the primary and secondary dietary prevention of CHD, intake of fat (also cholesterol) should be reduced, with an increase in the polyunsaturated moiety, and obesity should be controlled. Less specific general recommendations are increased consumptions of unrefined or partially refined grain products, and fruit and vegetables. Controversies over interpretations of evidence, over dietary recommendations, and also over the changes of their adoption, are discussed.

Urinary steroid hormone content was determined in Black and White North American men and in rural Black South African men between 40 and 55 years of age and in Black South African men over 60 years of age when maintained on their customary diets or when transferred to a vegetarian or Western diet, respectively. When eating their customary diets, Black South African men had lower levels of urinary estrogens and androgens than did Black and White North American men. The total androgen content decreased significantly in Black North American men on the vegetarian diet and increased in Black South African men fed a Western diet. Urinary excretion of estrogens was higher in older than in younger rural Black South African men. Data indicated that a vegetarian diet modified androgen and estrogen metabolism in North American men and that a Western diet was associated with higher levels of urinary steroid hormones in young Black South African men. Diet-related changes in steroid metabolism in rural Black South African men were age dependent. The relationship of the increased urinary excretion of steroid hormones in Black South African men, a low-risk group fed a Western diet, and the decreased excretion in Black and White North American men, high-risk groups fed a vegetarian diet, to the development of prostatic cancer remains to be clarified.

Changes in diet from ancient times until the present are described. Previously relatively low in energy and animal products yet high in fibre-containing foods, diets are now high in energy and animal products (particularly fat), yet contain less fibre. The changing incidences of bowel disorders and diseases are described, with assessments of the role of diet. Clearly, diet is implicated as regards predisposition to constipation, appendicitis, colorectal cancer and diverticular disease; however, a meaningful dietary role in irritable bowel syndrome, ulcerative colitis and Crohn's disease is doubtful. In South Africa the rarity of bowel diseases in rural blacks compared with whites affords valuable aetiological information about some bowel diseases. The low occurrence thereof (except inflammatory bowel disease) in Indian and coloured populations is not readily explicable. While dietary changes in whites are being widely urged in order to combat degenerative diseases, the magnitude of changes made is unlikely to reduce the occurrence of bowel diseases. The progressive westernization of the diets and lifestyles of less-privileged populations is likely to be associated with increases in the incidences of these diseases.

Although prostatic cancer is evident late in life, pathological evidence suggests this disease is initiated earlier in life. As prostatic cancer is an endocrine associated disease and as adult hormone profiles are established during puberty, it was of interest whether difference in pubertal hormone levels occurred in populations at low or high risk for prostatic cancer. Accordingly we have investigated the hormone profiles in rural Black South African and urban white boys during puberty. It has been suggested that the timing of puberty is modified by environmental factors and that there is a concomitant control of gonadotrophin release and food intake by CNS-peptide hormones. It is therefore postulated that dietary factors during puberty modify the gut-CNS peptide hormones which in turn control the hypothalamic-pituitary-testicular axis. Distinct difference in plasma androgen and gonadotrophins between the two races are in part concordant with a modification of CNS-peptide hormones by environmental factors during puberty.