DIETETICS. 953 



terms of its heat value, varies chiefly with the amount of muscular 

 work to be done. Persons who lead a very muscular life require 

 a correspondingly large amount of energy in the diet, and this 

 demand is met usually by augmenting the proportion of carbo- 

 hydrate and fat, especially the carbohydrate. Since the amount 

 of protein is not varied greatly in such cases the diet is relatively 

 poor in this foodstuff. On the contrary, those who lead a sedentary 

 life, including, broadly speaking, all the well-to-do class, require 

 less energy in their diet, and they can afford to reduce the pro- 

 portion of carbohydrate and fat. The diet in such cases may be 

 relatively rich in protein, although the amount per kilogram of 

 body weight is not increased, in fact, is usually diminished some- 

 what. These facts are illustrated in Atwater's estimate of the 

 diet necessary for men performing different amounts of muscular 

 work. 



PROTEIN. CARBOHYDRATE 

 AND FAT. 



Man doing hard muscular work 600 cal. 3550 cal. 



Man doing moderate muscular work 500 " 2900 ; 



Man doing no muscular work 360 ' 2040 ' 



On comparing these diets it will be observed that in per- 

 forming hard muscular work the diet contained 1700 Calories of 

 energy beyond that used when no work was done. About six- 

 sevenths of this increase was provided for by the carbohydrates 

 and fats. It will be seen also that in this case the proportion 

 of the total energy obtained from protein remained practically 

 unchanged. 



In the dietetics of large groups of persons, that of a nation, 

 for example, it is important to know not only the amount of energy 

 needed daily by each individual and the proportion of this energy 

 that should be obtained respectively from proteins, fats, and carbo- 

 hydrates, but also from what naturally occurring foods these 

 supplies of energy are actually drawn. Thus in an interesting 

 report published by an English commission it is shown that in 

 Great "Britain in the years 1909-13, 30.8 per cent, of the energy 

 in the diets of the inhabitants was derived from wheat alone. 

 Meat furnished 17.4 per cent.; sugar, 13 per cent., and fish, only 

 1 per cent.* 



Munk gives an interesting table showing how much of certain 

 familiar articles of food would be necessary, if taken alone, to supply 

 the requisite daily amount of protein or non-protein material; his 

 estimates are based upon the percentage composition of the foods 

 and upon experimental data showing the extent of absorption of the 



* See Lusk, "Science," April 13, 1917. 



