THE FASTING KATABOLISM 



251 



i. THE PROTEIN KATABOLISM IN FASTING 



335. Protein katabolism normally small. In view of the 

 structural functions of the proteins (264), it is of some im- 

 portance to inquire what proportion of the total energy require- 

 ment is supplied by these substances. 



This aspect of the subject has been considered especially by 

 E. Voit, 1 who has compiled and discussed the results of a con- 

 siderable number of experiments upon fasting. While some of 

 his computations are based on estimates, they are sufficiently 

 accurate to outline definitely the main features of the fasting 

 katabolism. They show that in what may be spoken of as the 

 normal fasting animal, in which the influence of the previous 

 feeding has disappeared and in which, on the other hand, the 

 fat reserve has not been exhausted, the protein katabolism sup- 

 plies a rather small proportion of the total energy transformed, 

 the percentage with dogs, e.g., ranging in the majority of cases 

 between 10 and 17. 



336. Fasting protein katabolism variable. It is not true, 

 however, as has sometimes been loosely stated on the basis of 

 C. Voit's experiments (338), that the protein katabolism of a 

 fasting animal becomes constant within a short time. On the 

 contrary, in the presence of an adequate amount of body fat, 

 its amount tends to diminish with the progress of fasting. For 

 example, in one of Benedict's fasting experiments (Table 29), 

 the total urinary nitrogen upon the several days of the experi- 

 ment was : 



TABLE 30. PROTEIN KATABOLISM OF A FASTING MAN BENEDICT 



Ztschr. Biol., 41 (1901), 167. 



