PKOTEINS IN THE DIET — MITCHELL 231 



paratively rich in sulphur, would supplement the proteins of beans 

 better than milk proteins, since casein, the main protein of milk, is 

 known to be very poor in respect to its content of cystine. Recently 

 the value of the proteins of nuts has been demonstrated (12). Their 

 high content of protein, of fairly high digestibility and apparently 

 of good biological value, should commend them as a good source of 

 dietary protein. 



Any complete survey of the place of proteins in the diet must 

 include some consideration of the conclusion so frequently expressed, 

 that protein consumed in amounts much above the actual require- 

 ments of the body may exert harmful physiological effects. In sup- 

 port of this conclusion, reference is often made to the well-known 

 work of Chittenden on the low protein dietary. However, in these 

 classical experiments, the absence of control groups maintained upon 

 the usual level of protein renders questionable the deduction that the 

 observed benefits of the low protein dietaries adopted were due 

 solely, if at all, to the reduction in protein intake. In fact, the 

 recent success of McCollum in raising rats on diets containing as 

 high as 70 per cent of protein certainly is a strong argument against 

 ascribing to protein deleterious physiological effects when fed even 

 in great excess. Several instances in recorded human experience 

 may be cited to the same purpose. However, while it is probably 

 true that protein may be indulged in to great excess without any 

 immediate ill effects, or even with no pronounced ill effects at all, 

 the wisdom of so doing may be questioned. The comfort of an in- 

 dividual, as well as his mental and physical efficiency, are undoubt- 

 edly adversely affected under certain conditions by a high-protein 

 dietary. The degree and type of activity of the individual should 

 be considered, and the protein intake graded in direct proportion to 

 the muscular activity. The well-known stimulating action of pro- 

 tein foods on metabolism probably is related to vitality and stamina, 

 and should be numbered among the favorable effects of protein as 

 a nutrient. At the same time the pronounced heating effect of pro- 

 tein, associated with its stimulating action on metabolism, will 

 naturally and rightly lead to a seasonal variation in the popularity 

 of protein-rich foods. 



This abbreviated consideration of the importance of protein in 

 the dietary, involving a study of the waste incidental to its utiliza- 

 tion by the body, its proper function in the body, and its physiologi- 

 cal effects, illustrates how complicated the problem of protein re- 

 quirements has become and how difficult it is to make hard and fast 

 recommendations. In pedagogy the subject of protein requirements 

 is still the despair of the teacher of the physiology of nutrition. 



