1058 



ABSORPTION 



considerably, while the nitrogen content remains practically the same. 

 Obviously, a gain in carbon means a gain in fat, and vice versa. In 

 the carnivorous animals, the carbon-equilibrium is retained on an 

 abundant protein diet, but this foodstuff must be supplied in excessive 

 amounts. Thus, Voit has shown that the larger carnivora need at 

 least 1500 grm. of meat daily to prevent a loss of carbon. For a 

 man weighing 70 kilos, this would mean an ingestion of 2000 grm. 

 of lean meat, and a combustion and elimination of nitrogen about three 

 times greater than normal. Obviously, a metabolism of this kind 

 could not be continued for any length of time. This again shows the 

 necessity of a mixed diet, as being more beneficial and economical. 



CHAPTER LXXXVIII 



THE NUTRITIVE VALUE OF FOOD 



The Normal Diet of Man. — The quantity of food which is required 

 to keep a person in a condition of health is determined by its power 

 of sustaining the energy which he is called upon to liberate. While 

 the latter must vary considerably with the activities of the body, 

 we may adhere rather closely to the data of Rubner which show the 

 following energy requirements: 



Thus, it will be seen that a vigorous man weighing 70 kilos necessi- 

 tates close to 37 calories for each kilogram of weight, or about 2600 

 calories in all. During starvation this same person needs 32 calories 

 per kilogram, or 2200 calories in all. Consequently, the ordinary re- 

 quirement is about 14 per cent, above that of starvation. In order to 

 supply this energy, Voit gives the following ration for the use of work- 

 men performing 8 to 9 hours of work: proteins 118 grm., fat 50 grm., 

 and carbohydrate 500 grm. This would yield 3055 calories which, 

 owing to a certain non-utilization, may be reduced to about 2700 

 calories. Rubner allows 127 grm. of protein and Atwater^ 125 grm. 

 for this class of workmen. Furthermore, in the case of severe work 



1 Physiologie des Stoffwechsels, 1881. 



2 Mem. of the Nat. Acad, of Sciences, Washington, 1902. 



