CHAPTER VI. 

 PROTEIN REQUIREMENTS. 



A QUESTION which must now be considered is that of the minimum 

 amount of protein required daily by the body. The subject is one 

 not merely of scientific, but also of economic importance. Two 

 questions require answers, (i) Can the organism not only subsist but 

 also thrive on an intake of protein nitrogen equal to that which is ex- 

 creted during starvation? (2) Is there a single protein minimum 

 intake? 



The Protein Minimum. 



The physiological protein minimum is the quantity of protein 

 which must be ingested in order to prevent loss of protein from the 

 body. 



Voit and Korkunoff (410) were amongst the earliest workers who 

 investigated this question. Taking the output of nitrogen of a dog 

 on the third day of fasting as the standard for the amount of protein 

 catabolized daily, they found that the amount of nitrogen required to 

 prevent loss of nitrogen from the body varied very markedly with the 

 nature of the diet, i.e. whether it consisted of pure protein (washed 

 flesh), or protein plus carbohydrate, or protein plus fat. The physio- 

 logical protein minimum was always found to be greater than the 

 amount of protein catabolized in the tissues during hunger. Thus 

 for every 100 grms. protein catabolized in starvation 368 grms. of pure 

 protein, 157-193 grms. of protein when mixed with fat, and 108-134 

 grms. of protein when mixed with carbohydrate, had to be consumed 

 in order to prevent loss of nitrogen. Thus the addition of fat lowered 

 the amount of protein required from 368 grms. to 1 57 grms., a decrease 

 of 57 per cent, and the addition of carbohydrate reduced it from 368 

 grms. to 108 grms., a decrease of 70-6 percent. Cremer and Hender- 

 son (101) repeated some of this work, but they were unable to obtain 



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