Amount Of Food Required

The amount of food required varies under different conditions. Thus, the growing child requires relatively more than the adult, old people need less than the middle-aged, and the food requirements of a stout muscular subject engaged in active physical work are greater than those of a thin weakly subject leading a sedentary life. We will here consider the minimum diet required for a man of average build and weight, doing a moderate amount of muscular work - in other words, the standard amount of the different nutritive constituents required daily. At the outset it must be clearly indicated that no final statement can yet be made on this important point, since the results of recent researches have thrown considerable doubt on the correctness of the teaching that has long been regarded as definitely established.

A healthy man of average weight and doing a moderate amount of muscular work, excretes from 16 to 20 grammes of nitrogen and about 320 grammes of carbon daily. The investigations of Atwater, Rubner, Voit, and others, until lately regarded as classical, established the standard amounts of the nutritive constituents required to make good this loss daily, as follows: -

These yield the following amount of heat in calories: -

If expressed in terms of nitrogen and carbon: -

Or, in the proportion of 1 gramme N to 15 grammes of carbon. No single article of food contains these elements in a proper proportion, and for this reason a mixed diet is necessary, as by that means only can we avoid taking too largely of one or other ingredients.

Expressed in terms of ordinary foods, the above dietary is approximately as follows: -

Or, if expressed in meals: -

Breakfast

2 slices of thick bread and butter. 2 eggs.

Dinner

1 plateful of potato soup.

Large helping of meat with fat (about 6 ounces of cooked meat).

4 moderate-sized potatoes (2/3 lb.).

I thick slice of bread and butter.

Tea

Glass of milk and 2 thick slices of bread and butter.

Supper

2 thick slices of bread and butter and 2 ounces of cheese.

In the case of subjects engaged in severe muscular work, it has long been taught that the amount of food required is greater than the above, the increase being shared by all three food constituents so as to furnish an energy value of 4500 to 5000 calories.

Daily Amount Of Food Required

In recent years the researches of Chittenden have thrown considerable doubt on the correctness of these views. Chittenden's observations were made on three classes of subjects:

(1) Men engaged in mental work,

(2) Soldiers engaged in moderate exercises, and;

(3) Highly skilled athletes, his experiments being conducted with great care and over long periods. Chittenden's work has rightly attracted a very large amount of attention, because of the very large number of persons simultaneously experimented upon, and the completeness of the experiment from the point of view of chemical analysis. Chittenden found that a state of nitrogenous equilibrium and good bodily health was maintained on a diet which contained from 1/2 to 1/3 of the protein in the standard diet.

It will be seen that Chittenden's results throw much doubt on the correctness of the teaching hitherto regarded as well established. There is no question that the ideal diet consists in the smallest amount of protein food, together with non-nitrogenous food, that will keep the body in a state of vigour. The question is whether it is right to accept as correct, for protein consumption,

(1) The minimum of 100 to 120 grammes of the commonly accepted standard dietary; or

(2) The minimum of 50 to 70 grammes of the Chittenden standard.

These figures refer to men of average size and weight. Strictly speaking, the amount of proteins should be indicated in terms of so many grammes per kilogram of body-weight, since we must recognise the need for varying the amount of food taken with the size of the body to be nourished.

Chittenden's explanation of the advantages of a low protein is that the protein food when metabolised yields a number of crystalline nitrogenous products which are excreted through the kidneys. If proteins are taken in excess, the kidneys are overworked, and the end-products of protein metabolism cither surcharge the blood or are deposited in the tissues, giving rise to various diseased states (see Auto-intoxication, p. 346). Reviewing the position as a whole, it may be said that further observations are required before we can finally accept Chittenden's results as giving a standard for universal application. There is, in the author's opinion, however, no doubt whatever as to the correctness of Chittenden's main contention that the amount of protein required daily to maintain the body in a satisfactory state of health is considerably less than the amount hitherto regarded as essential; and secondly, that some at least of the excess is injurious to health. This view is now very largely held by clinicians. Some of the directions in which excess of protein may injuriously effect the tissues are indicated in the results of the author's investigations (see Appendix).

With regard to the amount of carbohydratcs and fats, it has to be borne in mind that the more fat and carbohydrates in the diet, the less is the protein of the food used up for the production of energy. Carbohydrates and fats are both protein-sparers; and one cannot replace the other in a mixed diet as a source of energy. Any excess of protein-sparers in the diet may produce similar results to an excess of protein itself, by protecting the latter from complete oxidation.