A more recent investigator, Professor W. O. Atwater, places the daily requirement for proteid at 125 grams or 41/6 ounces, with sufficient fats and carbohydrates to give a total fuel value of 3,500 large calories for a man doing moderate work; while for a man at hard work he increases the daily diet to 150 grams or 5 ounces of proteid, with fats and carbohydrates to yield a total fuel value of 4,500 large calories.

16Chittenden: "Physiological Economy in Nutrition," p. 8. 17 Chittenden: " Nutrition of Man," pp. 98-99.

Through his experiments Professor Chittenden has shown conclusively that mental and bodily vigor are maintained and even tend to be greatly increased on a much smaller quantity of all classes of foods, but of proteid foods in particular, than are called for by these standards. Furthermore, he has shown that not only is there no advantage in the consumption of these quantities of food, but that their presence in the body may be directly injurious.

In the first place, Professor Chittenden's experiments indicate that, contrary to general opinion, the body cannot lay up flesh - that is, lean meat - by the consumption of large quantities of proteid. "It is generally considered as a settled fact," he says, "that in man it is impossible to accomplish any large permanent storing or deposition of flesh by overfeeding. Similarly, it is understood, that the muscular strength of man cannot be greatly increased by an excessive intake of food. The only conditions under which there is ordinarily any marked and permanent flesh deposition are such as are connected with the regenerative energy of living cells. Thus, as van Noorden has stated, an accumulation or storing of tissue proteid is seen especially in the growing body, where new cells are being rapidly constructed; also in the adult where growth may have ceased, but where increased muscular work has resulted in an hypertrophy or enlargement of the muscular tissue; and lastly in those cases where, owing to previous insufficient food or to the wasting away of the body, incidental to disease, the proteid content of the tissues has been more or less diminished, and consequently an abundance of proteid food is called for and duly utilized to make good the loss." 18

The experiments seem to prove conclusively that the intake and outgo of nitrogen - the important element of proteid - tend to run in exactly parallel lines - that is to say, that "increase of proteid income is followed at once by an increase in the metabolism of proteid with a corresponding outgo of nitrogen."19

18 Chittenden: "Nutrition of Man," p. 131.

"A meal rich in proteid leads at once - within a few hours," - he says, " to an excretion of urea equivalent to full 50 per cent, of the nitrogen of the ingested proteid, while a few hours later finds practically all the nitrogen of the intake eliminated from the body. Further, it is to be remembered that in a general way this occurs no matter what the condition of the body may be at the time and no matter how large or small the amount of proteid consumed. In other words, there is practically no appreciable storing of nitrogen or proteid for future needs, - at least none that is proportional to the increase in nitrogen intake, even though the body be in a condition approximating to nitrogen starvation."

19 Chittenden: "Nutrition of Man," p. 151.

Therefore all but the very small quantity of proteid food that is required by the tissues for development or repairs, is left floating in the blood along with the other food material which is to be oxidized for the furnishing of heat and energy. Professor Chittenden questions whether this can be regarded as an advantage. "We all recognize that an excessive accumulation of fat is distinctly disadvantageous to the welfare of the body," he says, "and there is, physiologically speaking, equally good ground for considering that the storage of unorganized proteid in amounts beyond all possible requirements of the body may be equally undesirable. Because less tangible to the eye, the accumulation of unnecessary proteid is not so easily recognizable, but this fact does not Diminish the possible danger which such accumulation may constitute." 20

Formerly it was thought that the combustion of proteid matter in the blood was the main source of energy for muscle work, but it is now known that while proteid matter is capable of yielding a certain amount of heat and energy in oxidation, it is inferior for this purpose to the fats and carbohydrates, and also that proteid, in burning, yields certain deleterious products which may be a serious evil to the body and which throws upon the liver and kidneys an amount of unnecessary labor that is likely to weaken and throw them open to the attacks of disease.

20 Chittenden: "Nutrition of Man," p. 131.

"Therefore," says Professor Chittenden, "in the nourishment of the body for vigorous muscular work, there is reason in a diet which shall provide an abundance of carbohydrate and fat; proteid being added thereto only in amounts sufficient to meet the ordinary requirements of the body for nitrogen and to furnish, it may be, proper pabulum for the development of fresh muscle fibres, where, as in training, effort is being made to strengthen the muscle tissue and so enable it to do more work. Increase in proteid food may help to make new tissue, but the source of the energy of muscle work is to be found mainly in the breaking down of the non-nitrogenous materials, carbohydrate and fat." 21

Furthermore, Professor Chittenden also points out that proteid decomposition products are a constant menace to the well-being of the body. "Proteid foods," he says, "when oxidized, yield a row of crystalline nitrogenous products which ultimately pass out of the body through the kidneys. Prior to their excretion, however, these products - frequently spoken of as toxins - float about through the body and may exercise more or less of a deleterious influence upon the system, or, being temporarily deposited, may exert some specific or local influence that calls for their speedy removal. Hence, the importance of restricting the production of these bodies to the minimal amount, owing to their possible physiological effect and the part they are liable to play in the causation of many diseased conditions. Further, the elimination of excessive amounts of these crystalline nitrogenous bodies through the kidneys places upon these organs an unnecessary burden which is liable to endanger their integrity and possibly result in serious injury, to say nothing of an early impairment of function.22

21 Chittenden: "Physiological Economy in Nutrition," pp. 16-17.

22 Chittenden: "Nutrition of Man," p. 269.