It is probable that the question of diet in training has been considerably over-discussed. Certain it is that diet will not produce muscular efficiency, whereas regular graduated exercise upon an ordinary sufficient diet may do so. The constant practising of any series of movements such as running, walking, rowing, or bicycling is likely in itself to lead to a more economical performance of the mechanical work involved, so that the store of energy available will last a longer time. The heart and circulation are of prime importance, for the smooth working of a muscle is dependent upon the removal of waste products by the blood, and upon the regular absorption of sufficient oxygen and elimination of carbon dioxide by the lungs. The enforced rests, the regular meals, and the general discipline of a period of training is also of very great value in bringing the neuromuscular system into a perfectly healthy condition. The diet in training must be an easily digested one, for indigestion in any form is fatal to success. This is one reason why a large amount of protein is preferred by athletes. Carbo-hydrate foods are often bulky, though not necessarily so, and fatty foods in excess are liable to be borne badly by the stomach. It appears also from the most recent work that protein is not converted into fat, and one object of the athlete is to have as little fat in his body as possible. The amount of food should always be increased : this is found to be so in dietary studies on training, with the exception of those of Chittenden, and according to Benedict, the athletes observed by Chittenden have returned to their former and more usual diet. We have already considered the relation of food to muscular work, and have given on p. 135 the diets taken by football men, rowing men, and professional bicyclists.
A number of experimental studies (Mosso, Harley) has shown that sugar is of great value when muscular exertion is severe. Locke has demonstrated the beneficial effect which dextrose has upon the perfused heart; when it is added to the perfusing solution the force of contraction is favourably influenced within a few seconds. In training, sugar should be freely taken, either dissolved in fluids such as cocoa, or in such a form as chocolate.
During the performance of prolonged feats of muscular exertion the diet should be such as to call for a minimum of digestive work on the part of the alimentary canal; fluid, easily assimilable foods will be readily absorbed and rapidly available for use. In his six days' ride, the bicyclist Miller, referred to on page 135, took his food in the form of eggs, milk, meat extract, boiled rice, boiled oatmeal, Charlotte russe, custard pie, tomato soup, sugar, apples and oranges, with a little bread on one day.
Intellectual work has not been found to have any demonstrable quantitative effect upon the metabolism of man : the energy of cerebral activity is not measurable by the most accurate calorimetric methods. A man doing hard mental work in Atwater's respiration chamber gave the same results as when he was resting. Neither has mental activity been found in health to produce any qualitative change in the metabolism. The diet of such workers does not, therefore, need special consideration in this chapter.
In advanced age the amount of food required is less than in the more active years of life. Various studies of the metabolism in old people have shown a food value of 21-38 calories per kilogramme (von Noorden). The proportion of protein varied from 7 to 2 grammes per kilogramme. The diet should be simple, and of a nature which can be properly masticated; and the less digestible foods should be avoided.