FOOD AND DIET. 373 



His views have not met with general acceptance. In the first place, 

 individuals living on such a low protein diet often suffer in general 

 health, and in their ability to resist infection. Secondly, the diet of 

 the infant contains much more protein than the minimum which would 

 be necessary according to Chittenden's view, and, since nature provides 

 more than the minimum of protein, the minimum is probably not the 

 optimum. Thirdly, the protein taken in the food does not merely 

 replace tissue waste, but supplies certain complex chemical groupings 

 which the body cannot make for itself ; and it may be necessary that, 

 in order to obtain a sufficient amount of these groups, the body should 

 be supplied with a quantity of protein considerably in excess of the 

 minimum required to replace tissue waste. Such a grouping, for 

 instance, might be tryptophane. Although Chittenden's work has 

 been of value in showing that many people eat too much protein, yet 

 the actual amount needed by the body is probably much higher than 

 that taken in his experiments; and we may regard 110 to 120 grams 

 of protein daily as representing the optimum intake for most men. 

 The protein requirements of women are rather less, being from 90 to 

 100 grams. Under conditions of severe muscular stress, for example 

 in soldiers during war time, considerably larger amounts of protein 

 may be necessary to maintain health. 



Although the diet in man usually conforms in a general way to the 

 principles just laid down, it must be remembered that wide individual 

 variations occur and are compatible with health ; and it is impossible 

 to formulate any arbitrary laws as to diet.^ 



In addition to serving as a source of energy and to supplying a 

 sufficiency of protein, the food normally contains certain substances, 

 essential to health and even to life, which have been called vitamines. 

 Their existence was first shown in connection with the disease known 

 as beri-beri, which is characterised by nervous symptoms and by 

 wasting ; it occurs in individuals whose diet consists solely, or almost 

 solely, of "polished" rice, that is rice from which the husk has been 

 removed. A similar condition is produced in fowls, when placed on 

 this diet, and can be cured by the addition to the diet of a substance 

 extracted from the husk of rice ; this substance is not a protein, but is 

 probably a basic nitrogenous body, and very small amounts of it are 

 sufficient to relieve the symptoms in birds. In man, beri-beri is cured 

 or prevented by a diet of unpolished rice, or by the addition of yeast, 

 meat juice, or other substances to the food. 



It is probable, though not proved, that other diseases, such as 

 scurvy, are also brought about by the absence from the food of 

 vitamines which are present in fresh milk, lemon juice, and meat juice. 



