DIETETICS 625 



from wheat and fish, are physically much superior to the rice-eating 

 Bengalis of Lower Bengal, although all belong to the same race. 



If we decide the matter merely on physiological grounds, we may 

 say that for a man of 70 kilos, doing fairly hard, but not excessive, 

 work, 15 grammes nitrogen and 250 grammes carbon are a sufficient 

 allowance. The 15 grammes nitrogen will be contained in 95 

 grammes dry protein, which will also yield 50 grammes of the 

 required carbon. The balance of 200 grammes carbon could 

 theoretically ~ be supplied either in 450 grammes starch or in 

 260 grammes fat. But it has been found by experiment and by 

 experience (which is indeed a very complex and proverbially expen- 

 sive form of experiment) that for civilized man a mixture of these 

 is necessary for health, although the nomads of the Asian steppes, 

 and the herdsmen of the Pampas, are said to subsist for long periods 

 on flesh alone, and a dog can live very well on proteins* and fat. 

 The proportion of fat and carbo-hydrates in a diet may, however, 

 be varied within wide limits. Probably no ' work ' diet should 

 contain much less than 40 grammes of fat, but twice this amount 

 would be better; 80 grammes fat give about 60 grammes carbon, 

 so that from proteins and fat we have now got no grammes of the 

 necessary 250, leaving 140 grammes carbon to be taken in about 

 310 grammes starch, or an equivalent amount of cane-sugar or 

 dextrose. Adding 30 grammes inorganic salts, we can put down as 

 the solid portion of a normal diet sufficient from the physiological 

 point of view for a man of 70 kilos : 



95 grammes proteins - - =T&<J f body-weight. 



80 fat - - =jj, 



310 ,, carbo-hydrates =2^5 ,, 



30 salts. 



515 solid food - = t j ff 



Now, knowing the composition of the various food-stuffs, we can 

 easily construct a diet containing the proper quantities of nitrogen 

 and carbon, by using a table such as appears on p. 626. 



Economic and social influences prices and habits and not 

 purely physiological rules, fix the diet of populations. The Chinese 

 labourer in a rice district, for example, is apt to live on a diet which 

 no physiologist would commend. In order to obtain 15 grammes 

 nitrogen or 95 grammes protein, he must consume more than 

 1,500 grammes rice, which will yield 700 grammes carbon, or twice 

 as much as is required. But if many of the Chinese labourers could 

 not live on rice, or often on grains cheaper than rice, they could not 

 live at all. The Irish peasant, in the days when the potato was his 

 staple, was even in worse case; he would have been obliged to 

 consume nearly 4 kilos of potatoes to obtain his 15 grammes nitrogen, 

 while little more than half this amount would have furnished the 



* A little glycogen is, of course, supplied in the meat. 



4 



