THE PROTEINS AND THEIR METABOLISM 119 



The Question of Optimum Versus Minimum Protein Diet 



When protein, in amounts corresponding to the "wear and tear" quota 

 (0.045 grams per kg. of body weight), is added to a diet consisting of 

 carbohydrates and fats sufficient to cover all the caloric requirements of an 

 individual, he will not maintain nitrogenous equilibrium. For short 

 periods of time, Siven (1900) was able to maintain himself in nitro- 

 genous equilibrium on a level of 0.08 gram per kg. of body weight (almost 

 double the "wear and tear" quota). 



When Voit studied the nitrogen excretion of a number of individuals, 

 who lived on general diets following the dictates of their appetites, he 

 found the average excretion for a man of 70 kg. in body weight was 19 

 grams of nitrogen per twenty-four hours. He therefore came to the con- 

 clusion that for a normal man to keep himself in a good condition of 

 nutrition a supply of 118 grams of protein per day was necessary. This 

 corresponds to 0.271 gram per kg. of body weight or six times as much 

 as the "wear and tear" quota. 



These figures of Voit's were obtained after a statistical and not after 

 a physiological study, and therefore caused considerable discussion and 

 inquiry into their justification. The literature is filled with series of 

 experiments, of shorter or longer duration, tending to prove that physical 

 comfort and nitrogenous equilibrium can be maintained at much lower 

 levels of protein metabolism than Voit's figures. 2 The most convincing of 

 these are the ones reported by Chittenden and Hindhede. In a series 

 of well-planned experiments on different individuals, representing different 

 classes of workers, and carried on for a period of eight months, Chitten- 

 den (1904) obtained results which led him to the conclusion that normal 

 adults can maintain themselves in nitrogenous equilibrium, and in good 

 health, on levels from 0.093 to 0.171 gram of nitrogen per kg. of body 

 weight, 3 with the greatest number maintaining equilibrium with 0.120 to 

 0.140 gram per kg., which is approximately three times the "wear and 

 tear" quota. Taking the mean of the greatest number 0.130 grams 

 per kg. of body weight a man of 70 kg. would require 9.1 grams of 

 nitrogen per day, which is equivalent to 57 grains of protein or one-half of 

 Voit's figures. 



Hindhede went a step further than Chittenden. His life for twenty- 

 one years has been practically one continuous experiment. He and his 

 family lived on an average of 50 grams of protein per person per day as 

 the maximum. The nitrogen output in his urine kept close to 7.0 grams. 



2 For a complete review of the literature, see "Theorien des EiweissHtoffwechsels 

 nebst cinigen praktisehen Konseqiienx-en derselben." L. H. Mendel. Krgebnis.se der 

 Physiologic, 1911, Vol. XI, pp. 418-525. 



Of the twenty-six men studied one maintained equilibrium on a level of 0.003. 

 three between 0.100 and 0.109, three between 0.114 and 0.119, sixteen between 0.120 

 and 0.147, two at 0.150 and 0.151 and one at 0.171. 



