A NORMAL DIET 401 



said to be an uneconomical manner of distribution, milk is, for most people 

 in this country, a comparatively cheap food. 



Protein Minimum and Optimum 



The question of the protein minimum and optimum has engaged the 

 attention of physiologists for many years. While the necessity of a cer- 

 tain amount of protein has been recognized from the beginning, it has 

 been believed that the optimum could be, and was, readily exceeded and 

 that the excess was distinctly injurious. This belief has been due chiefly 

 to the fact that protein is not completely oxidized to carbon dioxid and 

 water, as are carbohydrates and fats, but leaves a non-combustible residue 

 which must be excreted by the kidneys. Other objections are the high 

 cost of protein foods, their ready susceptibility to putrefaction in the in- 

 testine and the fact -that only a small part of the potential energy in pro- 

 tein is available for work, the remainder being excreted as urea, etc., or 

 useful only as heat. Since, as a rule, the latter is produced in excess of 

 requirements, this part of the protein energy may also be regarded as 

 lost. 



There have been many experiments on the so-called nitrogen minimum 

 the minimum amount of nitrogen in the food required to maintain an 

 equilibrium with that of the excretions. Sherman(/) (1920) has collected 

 the results of 109 experiments in 25 different investigations of this nature 

 and has calculated the values found to a uniform basis of 70 kilos body 

 weight. There is no difference in the per kilo requirements of men and 

 women. The average of all 109 experiments is 44.4 grams. The range of 

 values is very considerable, from 21 to 65 grams, but out of the 109 values, 

 94 fell between 29 and 56 grams, with an average of 42.8 grams, and 76, 

 derived from 19 investigations and including 20 men and 4 women as sub- 

 jects, fell between 30 and 50 grams, with an average of 40.6 grams. Ex- 

 pressed in terms per kilo body weight, these averages become 0.635, 0.61 

 and 0.58 respectively. Most of these experiments were of comparatively 

 short duration and consequently the values obtained must be regarded as 

 absolute minima and not as satisfactory and altogether sufficient amounts. 



The apparently low protein intake of the Japanese and other Oriental 

 peoples has long been noted but the earliest observations of any degree 

 of accuracy seem to have been those of Eijkman on the diet of Japanese 

 prisoners and those of Nagase on the diet of a military colonist in Formosa. 

 (Both cited from Oshima.) In the latter, the content of protein was about 

 one gram per kilo body weight. It was about the same in the diets of 

 the prisoners doing no work but was higher (1.18 grams) in the diets of 

 those doing light work and still higher (probably 1.5 grams or more) in 

 the diets of those at hard work. These diets were not "freely chosen" 



