It has frequently been asserted that the people at large do as a matter of fact consume on the average about 118 grams of protein per 70 kilos of weight. But I venture to insist that the question of average protein consumption has little or nothing to do with the problem before us. To argue that the customary or the average consumption of protein is the necessary consumption suggests that the necessary potein consumption is after all far more flexible than is indicated by the standard diets. It also implies that the people have solved the problem without the aid of science, and further that their average health and vigor is now all that we can hope for in so far as the protein contents of the food have anything to do with it.
Voit, himself, remained, I think, somewhat under the strong influence of Liebig's teachings concerning the peculiar value of protein as a food. It is difficult to see how he could otherwise have failed to find that it is possible to maintain nitrogen equilibrium on a comparatively small fraction of the protein which he declared to be the minimum. It was right and natural that Voit should not put the necessary protein requirement at too low a figure; its great practical import demanded cautiousness. But the minimum protein requirement for man could of course not be found except by studying the metabolism of man under the influence of smaller and smaller quantities of protein. This is clearly demonstrated by the results of the modern low nitrogen equilibrium experiments.
The disciples of Voit can not and do not question the accuracy of the results recorded from the low protein feeding experiments. But it is now rightly enough held that to prove that a person can maintain nitrogen equilibrium for a limited length of time, as for a few days, on a very small amount of protein does not at all prove that he can permanently do so with advantage or even with impunity. The correctness of this position must be granted, and it is, in fact, the position taken by the more conservative experimenters on low nitrogen equilibrium, as for example by Siven. But while freely admitting this, it must, in my opinon, be insisted that the low protein experiments of even such short duration, as a few days, have completely destroyed the scientific basis on which the protein prescriptions of Voit and his disciples are supposed to rest.
As far as we yet know there is no reason for assuming that a diet capable of maintaining nitrogen equilibrium for a week should fail to do so at the end of a month or any other time. In fact, investigations of the last three or four years clearly indicate that nitrogen equilibrium can be maintained for long as well as for short periods on very small quantities of protein.
In 1902 Dr. R. O. Neumann, privatdocent in the Hygiene Institute at Kiel, published an account of metabolism experiments with himself covering a period of over two years. The average composition of his diet during that time corresponded to 117 grams fat, 213 grams carbohydrates, and 74.2 grams protein per 70 kilos of body weight. Neumann's experiments covering such a long period would certainly seem to constitute definite proof that Voit's so-called minimum protein requirement is at least half again as large as is really necessary for the permanent maintenance of nitrogen equilibrium, physical vigor, and efficiency.
More striking still are the metabolism records published last year by Professor Chittenden. I shall not go into details of this work, as Mrs. Richards is on the program for a report on it. But I must cite the fact that Chittenden maintained a body weight of 57 kilos as well as nitrogen equilibrium from July, 1903, until the publication of his book in the fall of 1904, on an average protein consumption of less than 35 grams a day.