Benedict argued that general experience in animal feeding favors the use of liberal quantities of protein, and that "while men may for some months reduce the proportion of protein in their diet very markedly and apparently suffer no deleterious consequences, yet, nevertheless, a permanent reduction of the protein beyond that found to be the normal amount for man is not without possible danger. The fact that a subject can so adjust an artificial diet as to obtain nitrogenous equilibrium with an excretion of nitrogen amounting to about 2 or 3 grams per day is no logical argument for the permanent reduction of the nitrogen in food for the period of a lifetime. . . . Dietary studies all over the world show that in those communities where productive power, enterprise, and civilization are at their highest, man has instinctively and independently selected liberal rather than small quantities of protein" (American Journal of Physiology, Vol. 16, page 409).

A similar position was taken by Meltzer, who compared the appetite for a liberal surplus of protein with the liberal way in which the body is provided with organs and tissues for nearly all of its functions, and concludes that" valuable as the facts which Chittenden and his colaborer found may be, they do not make obvious their theory that the minimum supply is the optimum -the ideal. The bodily health and vigor which people with one kidney still enjoy does not make the possession of only one kidney an ideal condition. The finding that the accepted standard of protein diet can be reduced to one half can be compared with the finding that the inspired oxygen can be reduced to one half without affecting the health and comfort of the individual, but no one deduces from the latter fact that the breathing of air so rarefied would be the ideal. . . . The storing away of protein, like the storing away of glycogen and fat, for use in expected and unexpected exceptional conditions is exactly like the superabundance of tissues in an organ of an animal, or like an extra beam in the support of a building or a bridge - a factor of safety" (Science, Vol. 25, page 481).

In view of the arguments of Benedict and of Meltzer, it is of especial interest that in his later book Chittenden says: "It is certainly just as plausible to assume that increase in the consumption of protein food follows in the footsteps of commercial and other forms of prosperity, as to argue that prosperity or mental and physical development are the result of an increased intake of protein food. Protein foods are usually costly and the ability of a community to indulge freely in this form of dietetic luxury depends in large measure upon its commercial prosperity." Moreover, Chittenden contends that his allowance of 60 grams of protein per day for a man of average size is a perfectly trustworthy figure, with a reasonable margin of safety; that "dietetic requirements, and standard dietaries, are not to be founded upon the so-called cravings of appetite, but upon reason and intelligence reenforced by definite knowledge of the real necessities of the bodily machinery"; that "we must be ever mindful of the fact, so many times expressed, that protein does not undergo complete oxidation in the body to simple gaseous products like the non-nitrogenous foods, but that there is left behind a residue not so easily disposed of "; and that "there are many suggestions of improvement in bodily health, of greater efficiency in working power, and of greater freedom from disease, in a system of dietetics which aims to meet the physiological needs of the body without undue waste of energy and unnecessary drain upon the functions of digestion, absorption, excretion, and metabolism in general . . . " (The Nutrition of Man, pages 160, 164, 227, 269).

Plainly the dietary habit of well-to-do people and the dietary standards which have been generally accepted in the past tend to be decidedly liberal with respect to protein, and to prescribe it in quantities which may be believed to be beneficial but certainly are not known to be necessary. It does not seem advisable, however, to adopt as a standard the lowest amount of protein to which the body can adjust itself, but rather to regard as the normal requirement an amount which will enable the body to maintain not only its equilibrium, but also some such reserve store of protein as we are accustomed to carry. An allowance of about 75 grams of protein per man per day, which is 50 per cent above the average estimate of actual requirement (page 220), seems fully adequate in view of our present knowledge.

A reasonable surplus of protein, from suitable food materials, can hardly be injurious and may be advantageous. Whether such a surplus should be especially recommended or not is largely an economic question. Where little can be spent for food and there is danger that too little food may be eaten, it would be a mistake to use a surplus of protein which could economically be replaced by other food of greater fuel value. In such cases one must not be misled by the popular statement that "protein builds tissue" into supposing that a liberal amount of protein can keep the body strong in spite of a deficiency in the total food. This impression is still somewhat prevalent, but is certainly incorrect.

The body is weakened through getting too little food, because body material must then be burned for fuel. So long as the total food be deficient, the loss of body substance will continue, because not only the food protein, but body tissues as well, must be burned to meet the energy requirement. To strengthen the body through the diet we must increase, not the protein alone, but primarily the total calories.

Strengthening or weakening of the body by feeding ordinarily depends much more upon the sufficiency or insufficiency of the energy value of the total food than upon the amount of protein which it contains.