698 PHYSIOLOGY 



from the alimentary canal in order to make good the loss. No food under- 

 goes complete digestion, the average loss being about 10 per cent, with an 

 ordinary mixed diet, as is shown in the following Table : 



Percentage of Foodstuffs Absorbed 



Protein Fat Carbohydrate Ash Total Energy 



Average of 5 experiments 92-6 94 97-7 774 90-5 



Three thousand net Calories (i. e. energy requirements) require therefore 

 an intake of food with a Calorie value of 3300. If the food consists mainly 

 of vegetable products it may be necessary to increase still further the allow- 

 ance for loss in digestion, since on a diet such as rye bread as much as 33 

 per cent, of the total energy of the food may be lost in the faeces. The 

 Table of food requirements for various ages and sexes will be as follows : 



Children 0-6 ... 1650 Calories. 



6-10 . . . 2300 



10-14 . . 2750 



Females 14 and upwards . . 2750 



Males 14 and upwards . . 3300 



These values are for average well-nourished individuals. It has already been 

 pointed out that in a state of semi -starvation, accompanied by loss of weight, the basal 

 requirements may be reduced considerably. As a result of a number of experiments 

 Chittenden came to the conclusion that there was a definite advantage to be gained 

 by reducing not only the protein intake of the body but also the total food. For a 

 prolonged period Chittenden himself lived on a diet containing about 6 grm. of nitrogen 

 daily with a heat value of about 1600 Calories, and in another individual the intake 

 of nitrogen was 9-9 grm. and the heat value of the food 2500 Calories. Although 

 such a limitation of the diet may be advantageous in a certain number of cases, there 

 is no evidence which would warrant its general application; and the experience of 

 Germany during the last three years of wer has shown that a forced limitation of food 

 to about two-thirds of what we have put down as normal has resulted finally in a 

 decrease of efficiency of mind and body and in a marked diminution in the resistance 

 to infection, especially tuberculosis. 



DISTRIBUTION OF FOODSTUFFS IN A NORMAL DIET 



A Committe of the Royal Society has laid down the following as a proper 

 diet for the ' average man ' : 



Protein Fat Carbohydrate Total energy value 



100 grammes 100 grammes 500 grammes 3400 Calories. 



Since the energy for muscular work and that necessary to maintain the 

 body temperature may be furnished by any of the three classes of food- 

 stuffs, wide variations are possible in the relative proportions of the food- 

 stuffs without injury to health. It is important however to consider the 

 limits within which these variations are permissible. 



Proteins. As a rule an average mixed diet with a Calorie value of 3300 

 will contain about 100 grm. of protein. If the diet is mainly vegetable the 

 proportion of protein will tend to fall. We have already seen -that a certain 

 amount of protein is essential to replace tissue waste. This amount may be 



