What We Eat And Why

Ask yourself why you ate what you did last week and you will probably answer that you ate the foods you liked so far as it was convenient to get them. And then you may add that you ate what was "good" for you. Human diets are always compromises between what appeals to our appetites, what foods we have available, and what we think we should eat for strength and health.

All peoples have strong convictions about what foods are "good" for them. The notions of primitive peoples on this point are compounded of the accumulated experience of the tribe, in which observations of short-term effects are prominent, distorted by all sorts of taboos and superstitions. Our own opinions about what we should or should not eat have the same basis plus the influence of advertising and an increasing reflection of the reports from modern scientific studies on nutrition. We are bombarded with nutritional propaganda which, whether commercial or truly educational by intent, purports to be "scientific". And it unquestionably influences our choice of what we buy and eat.

One thing is certain. Our diets have changed greatly from those of our ancestors and they will continue to evolve, not only because of the growth of nutritional knowledge, but perhaps even more as a result of advancing technology and the related economic pressures it produces. The most obvious influence on our diet is food availability; our current dietary trend reflects a superabundance of foods in variety undreamed of not long ago and this is also true in many other lands, particularly among the more prosperous members of the community.

Sunday dinner is no longer special because of the Sunday joint; we have Sunday every day. We tend to grow fat on luxurious foods or we attempt to combat obesity by omitting all but the most luxurious items from the table. The fat of the land (literally) is ours. But how good, actually, is the result?

Gastronomically, one may argue interminably because tastes differ and too often are shaped by one or another variety of snobbery. The trend is to favour the most expensive foods. But now that the food heaven of the teenager is at hand - unlimited steak and foods fried in deep fat, more butter than bread and ice cream between meals - many adults obviously are not content, as witness the almost frantic search for more and more exotic foods, the flood of books and articles on foreign cookery. Foods that are simply fatter and more expensive still leave us vaguely dissatisfied.

As to health, our luxurious modern diets seem to prevent the classical deficiency diseases but there are plenty of populations whose diets are low in meat and dairy fats and who are not plagued with deficiency diseases either. We praise our modern diet because our children grow bigger than their parents, ignoring the fact that the same trend is apparent in populations all over the world. Anyway, it is naïve to insist that body size is a reliable measure of health in youth, let alone in later life. And our big health problem today is with our adults. Even if we have evolved a fine diet for infants and young children, we must seriously ask whether the same pattern is ideal for older children and adults. The needs of the body, as well as the dangers of disease, are very different after physical growth is completed.

The Work Of Nutritionists

Until lately the main concern of nutritionists has been to discover and correct dietary deficiencies and their advice has been to make sure we get enough, without worrying about excesses, of each of the nutrients they identify as useful in experiments on growing animals. Their most popular measure of nutritional value has been the rate of growth and weight gain of young rats, because the rapidly growing animal is particularly sensitive to dietary lack. Better diets for human infants have resulted from this work, but pediatricians are not sure that the quality of babies, and the adults they are to become, is accurately gauged by the rate of growth. In any case the diet that best adds weight to a baby rat is not necessarily best suited to maintain human health after the years of growth have passed.

Most experimental work on nutrition has necessarily been limited to short-term studies on animals. Laboratory animals and man alike have similar basic nutritional needs, but quantitatively they differ greatly. The human counterpart of a rat diet (or vice versa) is difficult to specify, and it is not easy to decide on optimal proportions of nutrients even for rats beyond the period of early growth. There are special difficulties when we ask about the role of the diet in preventing or promoting the diseases that now pose the most serious problems for human health. Some of these diseases, such as cancer, seem to be remarkably independent of the diet, and others, such as the major human heart diseases, almost never occur spontaneously in the animals used in dietary experiments.

Nevertheless, dietary experiments on animals have produced some notable findings that have relevance to our concern about adult human health. One is that underfed rats (and other species too) live longer than full-fed animals. Another is that diets that raise the cholesterol in the blood lead to a disease of the arteries which, in man, is basic to coronary heart disease. About cholesterol and atherosclerosis much more will be said later.

Dietary experiments on man are far more troublesome and expensive and can never be carried to the extremes possible with animals. But more and more nutritionists are conducting experiments and observations on man himself. The extension beyond the laboratory experiment is to inquire whether a relationship between the diet and heart disease can be found in human populations. Nutritionists, collaborating with heart specialists and other scientists, are seeking out populations that differ in their diets so as to study experiments of nature that cannot be made in their laboratories. We ourselves started such work in 1951 and the results are the main reason for writing this book.