FATS AS ESSENTIAL DIETARY fOMrONEXTS 845 



Table 1 



The Partition ok the Average Daily Intake 



OF Energy per Rat during 70 Days" 



» R. W. Swift and A. Black, /. Am. Oil Chemists' Assoc, 26, 171-176 (1949). 



low-fat diets are fed. Although the authors do not propose an explanation 

 of this divergent effect on specific dynamic action, it is possible that the 

 prolongation of the absorption time resulting from the increased fat con- 

 tent in the diet might reduce the period during ^vhich an excess of amino 

 acids and of carbohydrate occurs in the animal body, inasmuch as the 

 specific dynamic action of protein and that of carbohydrate are both re- 

 garded as plethora phenomena. It is possible that extending the period 

 of absorption over a longer time interval would effectively decrease the 

 concentration present in the body at a given time, and thus lessen the total 

 specific dynamic action produced. According to Forbes and Swift, -^ 

 these data suggest that it is unnecessary to diminish the protein content of 

 the diet during hot weather in order to insure a low heat increment re- 

 sulting from specific dynamic action; one need only substitute an addi- 

 tional proportion of fat for some of the carbohydrate in the diet. There 

 is no evidence as yet that the so-called associative dynamic action observed 

 in the rat also occurs in man or in other animals. ^^ 



{2) The Effect of Dietary Fat upon the Time of Sexual Maturity 



Sexual maturity is not so obvious an indication of nutritional value as 

 is growth, nevertheless it is a factor which can be used to assess the nu- 

 tritional value of a foodstuff. The age at which sexual maturity develops 

 in the female rat can be determined with considerable accuracy from the 

 opening of the vagina. Diets which induce the completion of this change 



