Having discussed in a fairly comprehensive manner the most ancient of all theories of diet, we have paved the way for a consideration of the most recent arrival, viz., the low-protein theory, and as in many respects there is a notable degree of similarity between the two, our deliberations upon it need not be at any great length.

It has always been known that moderation in eating and drinking was decidedly advantageous, but whilst admitted in theory its practice was confined to a few. The classical case of Cornaro will occur to every one. A physical wreck at the age of forty, he adopted a system of extreme temperance in eating and moderation in drinking, partaking of only 12 ounces of mixed food daily and 14 ounces of red wine, gradually diminishing this quantity as he grew older, and died peacefully in his own armchair at the age of one hundred and three.

Even before the days of Cornaro there are many examples of parsimony in diet, for Cyrus, the creator of the Persian Empire, subsisted from childhood on the simplest and plainest diet of vegetable food and water, whilst his soldiers adhered to the same rigorous fare. Coming to our own day, we find Edison telling us that for two months he lived on 12 ounces of food per day, taking absolutely no exercise and retaining his weight at 185 lbs., while Dr. Rabagliati in our own country has been preaching for many years that no man should eat more than a pound and a half of food per day, and he, personally, restricts his allowance to nearer 12 ounces- These, however, have been looked upon as exceptional cases, and as there was no scientific precision used in the measurement of their diet, they can hardly be recognised officially.

Besides, until the last few years, it was always considered that however much the total quantity of the food might be diminished it was dangerous or at least risky to curtail the allowance of the tissue building and repairing protein. Voit's diet of 118 grams protein (105 grams of which must be absorbable), 56 grams of fat, and 500 grams of carbohydrates with a total fuel or caloric value of 3,050 large calories, was considered essential to keep the body in equilibrium. Moreover, under conditions of hard work the Voit standard increased the daily allowance to 145 grams of protein, with fat and carbohydrate sufficient to yield a total fuel value of 3,370 calories. Other experimenters in various countries, notably Atwater in America, who fixed the daily protein requirement at 125 grams, with sufficient fat and carbohydrate to produce 3,500 calories, obtained very similar results, and emphasis was laid upon the fact that it was hazardous to transgress below these limits if health and strength were to be maintained. These deductions were made from observations on the customs and habits of mankind, which - even in highly civilised countries - are by no means always in accordance with physiological laws, but "orthodox physiological faith" was soon established on the pronouncement, and it was considered that this settled the matter. This, of course, it did, so far as it showed the dietetic standards arrived at empirically by mankind, but it in no way demonstrated what were the actual requirements of the body. As a matter of fact, in 1887 Hirschfield remained in nitrogenous equilibrium for nearly a fortnight on about 6 grams of nitrogen, as opposed to his usual diet of 16 to 20 grams per day. The diet on which he subsisted was practically of the lacto-vegetarian type, and the above amount represented about 40 grams of protein with, in addition, proportionally increased quantities of fat and carbohydrates. In 1889 E. Voit, studying the diet of vegetarians, found that with 8 grams of nitrogen or about 50 grams of protein and augmented allowances of starch and fats, it was possible to maintain nitrogenous equilibrium. Klemperer, Caspari, Breisacher, Siven and other workers have made similar experiments and arrived at similar conclusions, all deliberately proving that it is quite unnecessary to consume a diet of high protein-content in order to establish, nitrogenous equilibrium.

Such experimental diets having demonstrated that life was perfectly possible on a smaller quantity of nitrogenous food than was contained in the standard diet, the question then arose as to whether it might not be more advantageous to the health thus to subsist, Voit himself having enunciated the principle that the smallest amount of protein with the addition of fats and carbohydrates that would maintain the body in health and vigour is the best conceivable diet. He recognised that an excess of non-nitrogenous food would be unlikely to damage the tissues because its end-products, being carbonic acid and water, were comparatively harmless, whereas the ultimate results of protein metabolism were highly irritating products, which were liable to injure the body both functionally and organically. The chief reason, however, for concentrating the attention upon the protein requirement was that it is now known that it is not a variable modified by the amount of bodily activity, as is the case with fats and carbohydrates, but a constant for the individual, dependent mainly upon the weight of the protein-containing tissues of the body and the waste of their protoplasm. The amount of nitrogen excreted is, of course, a measure of this tissue waste, but the problem is complicated by the fact that it is increased in accordance with the quantity of protein food consumed, and hardly at all influenced by the degree of bodily activity. These two facts clearly demonstrate that protein is not the source of the energy of muscle work, and that it" is incapable of being stored up in the body to any appreciable extent; and a reasonable' deduction to be inferred from these statements is that any excess of protein food above the quantity actually required for the repair of the waste of the tissue cells is superfluous and uneconomical, expending the energies of the body in an entirely unnecessary manner, and exposing the tissues to wanton damage from an excess of nitrogenous waste products.