SECTION .VI 

 THE NORMAL DIET OF MAN 



HAVING learnt the significance of food in general and of the different food- 

 stuffs in the animal economy, we are in a position to examine the actual 

 requirements of the normal human individual. This involves a considera- 

 tion not only of the total energy requirements of man according to age, 

 size, sex and occupation, but also of the proper distribution of the foodstuffs 

 in the diet. 



We have seen that the energy requirements of a warm-blooded animal 

 are a function of its surface. Knowing the weight and height of a man 

 we can determine his surface by Du Bois' formula (p. 676). The average 

 height and weight of English adults is 171 cm. and 70-3 kilos, corresponding 

 to a surface of 1*772 square metres. The basal metabolism of a man is 

 equal to 40 Calories per square metre per hour, so that the average man will 

 have an hourly basal metabolism of 71 Calories. This is the energy output 

 in bed and during sleep. When he is taking food this amount must be 

 increased by about 10 per cent., and if he is up and about a further increase 

 in metabolism will be evoked by the muscular movements, exposure to 

 cold, etc. If we divide the twenty-four hours into three portions eight 

 hours' sleep, eight hours awake and eight hours' work we must allow the 

 basal metabolism for the eight hours' sleep, basal metabolism increased by 

 about 30 per cent, for the eight hours during which the man is up and about 

 and taking meals, and the basal metabolism plus an additional amount 

 for work during the eight working hours. It is by no means easy to decide 

 what figure should be accepted as representing the average work of an 

 adult man. It is usual to take this as involving an energy output of 1000 

 Calories. Of these Calories 20 per cent., or even more, may under favourable 

 conditions be transmuted into mechanical work, so that 1000 Calories would 

 be sufficient to provide for the performance of about 100,000 kilogrammetres 

 of external work. With these assumptions we arrive at the following energy 

 requirements for an adult working man : 



8 hours' sleep at 71 (Basal Metabolism) . . . 568 Calories. 



8 hours awake at 92 (Basal Metabolism plus 30 per cent.) 736 

 8 hours' work (Basal Metabolism plus 1000 Calories) . 1568 



Total 2872 



Some additional expenditure of energy will be involved in travelling, 

 so that we are justified in accepting the figure usually given for the energy 



695 



