94 General Aspects of Fasting [Sept 



The muscular disintegration is influenced by the factors already 

 mentioned; the nutritive condition and the experience of previous 

 fasts, or repeated fasting. The diet just before the fast influences 

 the nitrogen excretion for a number of days. This has been demon- 

 strated in the classical experiments of Voit (26), in which he fed 

 varying amounts of meat and bread to a dog and showed that, when 

 fasted the rate of nitrogen excretion varied, but that in each case 

 the animal came to the same level of catabolism on about the seventh 

 day of fasting. 



The fat available in the body exerts a marked efTect upon the 

 protein metabolism and the Hfe of an animal. So long as there is 

 sufficient fat in the organism to supply the energy requirements, 

 the protein metabolism will remain at a minimum. When, how- 

 ever, the fat deposits are depleted, the body is forced to use protein 

 to furnish the necessary energy. The result is a more rapid protein 

 consumption and an earlier death. This increased protein con- 

 sumption, is, of course, accompanied by an increased nitrogen excre- 

 tion, which has been designated as the " premortal rise." The feed- 

 ing of carbohydrate or fat sufficient to supply the energy require- 

 ment of the body would prevent this increased consumption of pro- 

 tein and thus lengthen the life. 



Repeated fasting will also modify the rate of metabolism. This 

 point is well illustrated by the results obtained on a subject in a 

 repeated fast (10), in which there was a rapid and increasing con- 

 sumption of the protein reserves of the body during the first fast, 

 but a more gradual and uniform consumption during the second 

 fast. The total body weight and nitrogen losses were practically 

 identical in the two fasts and the data f rom the intermediate feeding 

 period would indicate that an increased fat störe was not the cause 

 of the more gradual utilization of the body resources. 



A study of the differential distribution of the nitrogen in the 

 urine serves to bring out certain points with regard to the protein 

 metabolism of fasting animals. The percentage of total nitrogen 

 occurring as urea-nitrogen decreases in man and is accompanied by 

 an increased ammonia-nitrogen excretion. This has been explained 

 as due to the condition of acidosis, which may result, at least in 

 part, from the accelerated utilization of the fat deposits and the 

 decreased oxidative powers of the animal. 



