194 NUTRITIONAL PHYSIOLOGY 



terval of fasting the metabolism responds by rising more 

 than in the first case. Instead of the 6 per cent, increase 

 about 14 per cent, is to be anticipated. Hence, to insure 

 equality of income and outgo from the energy standpoint 

 114 Calories must be furnished in the form of fat to corre- 

 spond with a fasting production of 100 Calories. The 

 specific dynamic effect of protein is much more decisive. 

 If pure protein is the only food the metabolism may in- 

 crease by as much as 40 per cent, over the fasting standard. 

 The selection of much protein at a meal will be followed, 

 during the next few hours, by a definite rise in heat pro- 

 duction which may be a really wasteful operation. A 

 quantity of heat may be generated entirely apart from the 

 performance of muscular movements and have to be re- 

 moved as a useless excess. 



Foods rich in protein have the name of being "heating," 

 and here as in many another instance the popular impres- 

 sion has been supported by scientific findings. We can 

 see that the eating of much meat in warm weather must 

 add to the discomfort of the eater. The effect is some- 

 thing like the opening of a furnace draft when the house is 

 already too hot for the pleasure of its tenant. A distinc- 

 tion must be made between the heating influence of protein 

 and the high fuel value of fat. It is true that fat, gram 

 for gram, can liberate more energy in the body than can 

 protein. But it is less likely to be destroyed when there is 

 no useful application to be made of its energy content. 



Age and Sex as Influencing Metabolism. Young and 

 growing individuals whether human or otherwise have 

 relatively more heat production than is the case with 

 adults. Thus an infant weighing 10 kilograms (22 pounds) 

 may be expected to have a metabolism of 600 or 700 Cal- 

 ories. That is to say, that with a weight only one-sixth 

 or one-seventh of that of a grown man, it has a heat pro- 

 duction one-third or one-fourth as great. It has been 

 shown, however, that if the metabolism of both the infant 

 and the adult is calculated for the surface of the body there 

 is a reasonable proportionality between them. The area 



