GENERAL METHODS HISTORY OF PROTEIN FOOD. 899 



and in a normal state of efficiency upon a diet containing only 

 30 to 50 gms. of protein per day, according to the weight of the 

 individual or, expressed in more general terms, the daily quota 

 of protein per kilo of weight may be reduced from 1.5 gms. 

 (0.23 gm. N.) to about one-half, that is, 0.75 gm. of protein or 

 0.12 gm. of nitrogen per kilo. This general result has been 

 confirmed on a large scale by the studies made by McCay* of 

 the metabolism of the Bengalis of India. He finds that the 

 average Bengali metabolizes in his body, so far as may be judged 

 from the nitrogen excreted in the urine, only about 37.5 gms. of 

 protein daily, corresponding to a consumption per kilo of 0.7 gm. 

 of protein or 0.113 gm. of nitrogen. A corresponding average 

 amount of protein is, of course, eaten daily, and on this low pro- 

 tein diet they exist in apparent health. Rubnerf also empha- 

 sizes the fact that milk, which forms the sole diet of the infant, is 

 a protein poor food. The usual daily diet of the adult has a heat 

 value of from 2400 to 3000 calories (see p. 940). Of this total 

 heat value the protein food in the diets usually recommended 

 forms about 15 to 20 per cent. In milk, however, according to 

 Rubner's estimates, the protein constitutes only about 10 per 

 cent, of the total heat value. As the result of these and similar 

 investigations, the practical question presents itself as to what 

 constitutes the optimum daily quota of protein. If the body can 

 be kept in good condition upon 0.75 gm. per kilo per day, will an 

 ingest ion of more than this, say twice as much, prove injurious 

 or beneficial or indifferent to the body? Outside its hygienic 

 aspect the question is important from an economical standpoint, 

 since the proteins are the most expensive foods, and in the feeding 

 of large masses of individuals armies, schools, asylums, etc. 

 it is not desirable to waste money on protein food if it is not 

 needed. The full and satisfactory answer to this question must 

 be deferred until more experience is obtained. The report upon 

 the Bengalis, noted above, would seem at first to constitute a 

 satisfactory demonstration of the practicability of a low protein 

 diet, but McCay states that the Bengali is inferior physically to 

 the average European, and is particularly deficient in capacity 

 for muscular work, and he is inclined to attribute this inferiority 

 to the diet. Moreover, the Bengali is quite susceptible to kidney 

 troubles, a fact which seems to destroy one prediction often 

 made by those who advocate a low protein diet, namely, that the 

 smaller amount of work thus thrown on the kidneys would result 



* McCay, "The Metabolism of the Bengalis, Calcutta," 1908. (Scientific 

 Memoirs, Medical Department Government of India, No. 34.) Also later 

 report upon Jail Dietaries, ibid., No. 37, 1910. 



f Rubner, "Das Problem des Lebensdauer," 1908; Cohnheim, "Die 

 Physiologic der Verdauung u. Ernahrung," 1908. 



