THE NORMAL DIET OF MAN 649 



action of the vegetable diet on the movements of the alimentary canal, so 

 that the food is hurried through the intestine before the processes of digestion 

 and absorption have had time to attain their limit. This last factor may 

 interfere also with the digestion of animal protein on a mixed diet. The 

 fats and carbohydrates of the ordinary diet of man are also utilised to a 

 very large extent. The faeces passed on a fat-free diet always contain 

 between 3 and 6 grm. of ethereal extract which is reckoned as fat. When the 

 fat of the food consists largely of olein and is fluid at the temperature of the 

 body, it is almost totally absorbed, the absorption becoming less as the 

 melting-point of the fat rises. Ordinary carbohydrates are also very well 

 absorbed, but here very large variations may be produced by altering the 

 condition in which they are presented in the food. The following Table 

 shows the relative digestibility of the different food- stuffs in a healthy 

 individual on a normal diet : 



PERCENTAGE OF FOOD -STUFF ABSORBED 



Protein Fat Carbohydrate Ash Total energy 

 Average of five j ^ ^ ^ ?7 . 4 9Q>5 



experiments J 



In judging therefore of the sufficiency of any given dietary, it is important 

 to remember that on the average only about 90 per cent, of the total energy 

 of the food is available for use by the body. If, for instance, the body 

 requires an amount of energy equivalent to 3000 calories per day, it would 

 be necessary to give food corresponding to 3333 calories per day. If, as 

 is the case with the poorer classes, the food consists mainly of vegetable pro- 

 ducts it may be necessary to increase still further this allowance, since on 

 a diet such as rye bread the loss of energy in the faeces may amount to as 

 much as 35 per cent, of the total energy of the food. 



The quantity of food which is necessary to keep an adult man in a state 

 of health, without loss or gain of weight, is represented by that amount which 

 is sufficient after absorption to supply the total daily output of energy. This 

 output will vary considerably not only from individual to individual but also 

 with the weight and size of the man, and above all with his state of muscular 

 activity. Thus in the case of a woman weighing 4945 kilos, in a state of 

 hysterical sleep, the total output of energy during twenty-four hours 

 amounted to 1228 calories, i.e. 24*8 calories per kilo body weight. Under 

 more normal conditions, with the increased tone of muscle which is present 

 during waking hours, the evolution of energy by the body is increased above 

 this amount. Pettenkofer and Voit found that a resting individual had an 

 output of 2300 calories during starvation and 2670 calories on a normal diet. 

 A series of experiments by Tigerstedt on individuals kept in a state of rest, 

 but on normal diet, gave results varying between 26 and 36 calories per kilo 

 for the twenty- four hours. We may take therefore 30 calories per kilo body 

 weight as the average requirements of a man in a state of rest. This would 

 correspond to 2100 calories for a man weighing 70 kilos. When muscular 

 work is performed the energy output is at once largely increased, and with 

 it the food requirements of the body. The attempts which have been 



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