CHAPTER V 

 THE PROTEIN REQUIREMENTS OF MANKIND 



IN an earlier chapter we examined the twofold function of food, 

 and saw that it is essential for the growth and repair of the proto- 

 plasmic tissues, and necessary to furnish energy for the muscular 

 and other work the body has to perform, and yield heat for the 

 maintenance of the body temperature at a proper level. 



Leaving aside for the present the question of mineral matters 

 and water, the above requirements are met by the protein 

 element on the one hand, and the total potential energy of the 

 dietary on the other. Protein alone of the constituents of a 

 diet is able to perform both functions ; carbohydrates and fat 

 are only capable of providing heat and potential energy. 

 Dietaries may therefore be considered from the standpoint of 

 the protein element and total energy or heat value. The nutri- 

 tive values of the fats and carbohydrates are almost proportional 

 to the amount of energy they can furnish ; consequently, it is 

 only important that the quantity of either, or both, be such that 

 their total energy, when added to that of the protein of a diet, 

 shall supply the total amount required by the body, due allow- 

 ance being made for the decrease in the energy value, caused 

 by the loss of a certain amount of the potential energy in the 

 corresponding urine and faeces.* 



In the present connection it is not necessary to discuss in 

 detail the heat values of the dietaries examined, not because 

 they are relatively of small importance, but for the reason that 

 ordinarily the caloric value is quite sufficient to meet the demands 

 of the body, if the diet is otherwise satisfactory. Further, as in 

 the present volume, we are dealing more particularly with the 

 light that may be thrown on the problems of nutrition from 

 observations on the effects of tropical dietaries ; the caloric 



* Benedict, " The Nutritive Requirements of the Body." 

 96 



