Our primitive forefathers ate plant or animal food which might be raw or cooked, but which was otherwise unprocessed. Shortage was usual between harvests, and when food was abundant it was difficult to store the surplus. The diet was monotonous, and often contaminated with bacteria or parasites.
Today in affluent countries we have plentiful food in great variety available every day of the year. Contamination with infective agents is rare, and most of the food we eat has been processed and packaged to enhance its appearance, flavour and keeping qualities. Obesity, arising from an intake of food which is more than that required for the sedentary lifestyle of modern man, is by far the commonest nutritional disease. Diseases due to nutrient deficiencies are rare except in special groups, such as neglected old people, alcoholics, and people who, as a result of disease or drug treatment, have abnormal dietary requirements. Ironically, another group in whom nutrient deficiencies occur are dieters: people who deliberately avoid particular types of food, or who severely restrict their total food intake. This may be done for religious or philosophical reasons, or in an attempt to achieve greater health or beauty.
A vegetarian diet (which excludes meat) is adopted by an increasing number of people for various reasons, such as concern for animal welfare, conservation of global resources, or avoidance of saturated fat, which is found in animal products and which may increase the risk of cardiovascular disease. Such a diet is certainly compatible with excellent health if appropriate plant foods are chosen to supply the protein, and minerals such as iron, which are normally provided by meat in omnivorous diets. Diets which exclude not only meat but also milk and dairy products, eggs, fish and poultry have to be selected with great care if all nutrient requirements are to be met, since plants foods are not good sources of calcium, and the iron in vegetables is less well absorbed in the human intestine than iron in meat. Reliable advice on these problems is available from the Vegetarian Society.
The attraction of organically farmed food is that it will not be contaminated by synthetic weedkillers, pesticides, fertilizers or additives: the disadvantage is that crop yield is somewhat lower than normal, and consequently the price tends to be higher, and produce may show more blemishes. There is little evidence that organic food is nutritionally superior, or that agrochemicals are a significant cause of human disease, but many people are convinced that organic, free-range, stone-ground and generally "natural" foods taste better, and are ecologically superior.
There is strong scientific evidence that a diet which contains wholegrain cereals and fresh fruit and vegetables is healthier than one in which the grain has been milled to produce white flour, and fruit and vegetables are either cooked, or not eaten at all. The outer part of cereal grains (bran, in the case of wheat), and fruits and vegetables, contain dietary fibre which has a beneficial effect on bowel function, and probably also reduces risk of cardiovascular disease by improving blood cholesterol concentrations. Fresh fruit and vegetables are important sources of protective vitamins which may be destroyed by prolonged cooking. However claims for health benefits have been carried too far by some popular authors who advocate that a large proportion of the diet should be raw food which rids the body of "toxins". The nature of these toxins is never explained, not is it clear why raw food should remove them. The idea that raw food confers special benefits because it is "living food" has no scientific foundation: by the time the food is digested and absorbed into the body it is as "dead" as it would have been if it had been cooked.
The dieters who are in greatest danger are young women (usually) who are trying to achieve abnormal thinness for aesthetic reasons. The table below shows the range of weight (from A to B) which is medically desirable in young adults of a given height, and the (C) the weight at which obesity begins significantly to impair health. People whose weight is between B and C should take care not to gain more weight, and people whose weight is greater than C should seek to reduce it at a rate of about 1-2 lb /week by appropriate dieting. More rapid weight loss may involve excessive loss of lean tissue, and it is unlikely that people who lose weight too rapidly will be able to sustain the weight reduction.
The problem arises with people who weigh less than B, but who try to lose weight. "Slimming supplements" which provide compounds such as free amino acids, lecithin, choline or vitamins do not make weight loss by dieting more effective or safer. Diuretics cause water loss (and hence weight loss) but this is transient. Bulk fillers (such as guar gum) do not aid weight loss unless taken in such large amounts that they impair appetite.
It is particularly important that people near to weight A do not attempt to become even thinner, since this would probably be injurious to health.
This position paper by J Garrow
endorsed for the Executive Committee, July 1994