304 ORGANIC AGRICULTURAL CHEMISTRY 



might be easily supplied by carbohydrates and fats alone, yet, 

 except for a brief period, such non-protein food is unable to 

 supply the needs of the body because torn-down body protein 

 is impossible of reconstruction. In adult man or in non-fatten- 

 ing or non-producing mature animals the amount of protein in 

 the body does not increase. All of the protein food is thus 

 indirectly converted into energy, but in the process it first serves 

 as a constructing substance and cannot be wholly replaced by 

 either of the other food constituents. 



The amount of the protein requirement in man is a question 

 over which there has been considerable controversy. The 

 standard usually accepted from studies of normal diets and of 

 the nitrogen income and outgo of normal men has been 100 

 grams of protein per day for a man of 150 pounds. Some in- 

 vestigators, however, especially Chittenden, reduce this amount 

 to as low as 70 grams or even less. 



We have given figures showing the effect of increased muscular 

 activity upon the energy requirement of the body, raising the 

 amount from 2000 Cal. per day for maintenance to 5000 Cal. 

 per day under severe muscular exertion. In contrast to this is 

 the fact that increased muscular activity has only a slight effect 

 upon the amount of protein metaboHsm. On the other hand, 

 while increased food supply raises the energy metabolism of the 

 body only slightly, it has the direct and marked effect of increas- 

 ing the protein metabolism. That is, an increase in protein 

 food increases the amount of protein metabolized, there being 

 no appreciable increase in the amount of body protein. An in- 

 crease in carbohydrate and fat food increases the general 

 metabolic action, which in turn increases the amount of body 

 protein torn down in the muscular activity of the accompanying 

 physiological processes. 



In the foregoing discussion we have considered only the main 

 facts in regard to the value of foods and the food requirements 

 of the body. The actual value and economic use of foods, the 

 effect of varying conditions upon the food requirements and the 

 fixing of standard or feeding rations have all been omitted as 



