6i2 METABOLISM, NUTRITION AND DIETETICS 



records, to cut and handle timber, to mine^coal, and to make war, 

 the diet on which these things are accomplished is very variable. 



Recent observations tend to reduce the amount of protein con- 

 sidered necessary for a person under ordinary conditions. Siven 

 remained in nitrogen equilibrium, for a time at least, with an intake 

 of only 0-07 to 0-08 gramme of nitrogen (0-4 to 0-5 gramme of 

 protein) per kilo of body-weight, or not much more than one-third 

 of the amount in Ranke's diet. It is obvious that the endogenous 

 protein katabolism sets the limit below which it must be impossible 

 permanently to reduce the allowance of protein. But it would be 

 very hazardous to assume that this theoretical minimum limit 

 corresponds with the permissible physiological limit. From ex- 

 periments on men of various callings extending over many months, 

 Chittenden has concluded that the average man eats at least twice 

 as much protein as he really requires. We have already seen that 

 the amount of nitrogen required to repair the actual waste of the 

 tissues is comparatively small, and that with the ordinary amount 

 of protein in the food a very large fraction of the total nitrogen is 

 rapidly excreted as urea. There is no doubt, also, that many 

 persons consume too much protein, at any rate in the form of 

 animal food, and would feel better, work better, and probably live 

 longer, if they restricted themselves in this regard. But there is 

 no evidence that the digestion of such quantities of protein as the 

 average healthy man eats, or the elaboration and excretion of the 

 corresponding amounts of urea, ' strain ' in the least the digestive 

 apparatus, the liver, or the kidneys. And it may just as well be 

 argued that it is advantageous that much more than the minimum 

 protein requirement should be offered to the tissues, so that the 

 appropriate amino-acids, even the scarcest of them, may be sure 

 to be present in sufficient amount, rather than that the organs 

 should be subjected to the unnecessary ' strain ' of reconstructing 

 some of the amino-acids themselves, supposing that they possess 

 this power. In a question of this sort the immemorial experience 

 and instinct of mankind cannot be lightly waved aside. 



McCay points out that while Bengalis in Lower Bengal subsist on 

 food containing only about one-third the amount of protein in such 

 a ' standard ' diet as Voit's (6 to 7 grammes of nitrogen a day), and 

 may therefore be supposed to be immune from the dangers of an 

 excessive protein metabolism, the large intake of carbo-hydrate 

 rendered necessary by the poverty of the food in protein is associated 

 with perhaps g reater evils, among them a marked predisposition to 

 diabetes and renal troubles. Their weight, chest measurement, and 

 muscular development are inferior to those of other Asiatics living 

 in the same climate, but with dietetic habits or economic conditions 

 which ensure them a larger supply of protein. Thus the natives of 

 Behar, with a larger intake of nitrogen, derived from wheat, and the 

 natives of Eastern Bengal with a larger intake of nitrogen, derived 



