378 HUMAN PHYSIOLOGY 



observations Atwater concludes that the energy requirements 

 of the diet varies as follows : 



Calories. 



Man without muscular work . 2700 



with light muscular work . 3000 



moderate muscular work 3500 



severe muscular work . 4500 



It must, of course, be remembered that all the energy of 

 the constituents of the diet is not available, since a consider- 

 able and varying proportion of the food is not digested or 

 absorbed (p. 381). The gross energy of the diet must there- 

 fore be well above the nett energy requirements of the body. 



A rough idea of these nett requirements may be arrived at 

 by considering the average expenditure of energy in different 

 forms. Taking the case of a man doing a moderate day's 

 muscular work equivalent to 150,000 kgms. or 350 Calories 

 (see p. 73), he gives off, according to N. Stewart's calcula- 

 tions (Manual of Physiology, p. 425), 2590 Calories of heat. 

 The loss of energy is thus 



Calories. 



In external muscular work, equivalent to 350 

 As heat 2600 



Total . . . 2950 



To make good this loss of energy the diet should contain 

 more than 3000 gross Calories, and the results of Zuntz 

 clearly show that, when muscular work is large in amount, 

 a greater supply of energy must be forthcoming, while in 

 individuals leading a sedentary life the energy requirement 

 will be smaller. In the case of a labourer it is safe to allow 

 at least 3500 Calories. 



II. Proteid Requirements. Many experiments have been 

 made to determine the smallest amount of proteids upon 

 which life can be maintained, and conflicting results have 

 been arrived at. Various investigators have succeeded in 

 maintaining a nitrogenous equilibrium for short periods on 

 an intake of proteid no greater than that metabolised in 

 fasting. 



