37 2 ESSENTIALS OF PHYSIOLOGY. 



4000-5000 calories or even more. As we have seen (p. 339), the 

 average physiological calorie value of the food-stuffs is as follows : 



1 gram fat = 9'3 calories 



1 carbohydrate = 4*1 

 1 protein = 4'1 



From these data it is easy to draw up a diet containing the food-stuffs 

 in such amount that, when oxidised in the body, they will furnish 

 sufficient energy to replace the daily loss. Such diets have been 

 constructed as the result of observations on individuals living in 

 institutions under similar conditions of work and surroundings. The 

 following represents the proportions of the different alimentary prin- 

 ciples which have been found most suitable : 



Protein 120 grams = 492 calories 



Fat 60 = 558 



Carbohydrate 500 =2050 ,, 



3100 



The calorie value of this diet is 3100, but a deduction of at least 

 5 per cent, must be made for food which, though taken by the mouth, 

 is not absorbed from the digestive tract, being lost to the body in the 

 excreta. The same calorie value could be obtained by combinations of 

 these three food-stuffs in other proportions, and, regarded merely as a 

 source of energy, it seems to be a matter of indifference in what form 

 the calorie value is supplied to the body. 



(2) The Replacement of Wear and Tear. In order to replace the 

 breaking down of the tissue proteins, the diet must contain a certain 

 minimum of protein, and much discussion has arisen as to the amount 

 of protein in the food which is most suitable for the needs of the body. 

 Chittenden has put forward the view that the amount of protein 

 consumed by most people is excessive. He considers that it can be 

 largely replaced by fat and carbohydrate as a source of energy, and 

 that a comparatively small amount of protein is needed to repair tissue 

 waste and to maintain nitrogenous equilibrium. Any excess of protein 

 beyond this minimum is regarded by him merely as throwing additional 

 work on the liver and kidneys in excreting its nitrogen. Chittenden 

 found by observation on himself and others that it was possible to 

 maintain health and nitrogenous equilibrium for six to eighteen months, 

 and to carry out muscular work, on a diet containing much less protein 

 than that in the dietary mentioned above ; in many cases the daily 

 intake of protein did not exceed 40 to 60 grams. 



