FATS AS ESSENTIAL DIETARY COMPONENTS 843 



tory effect upon heat production, and this is followed in turn by carbo- 

 hydrate and fat. Other foodstuffs such as vitamins and water apparently 

 exert no similar calorigenic action. Although it was shown by Rulmer" 

 that the extra heat produced due to specific djniamic action may be used 

 by the body in lieu of a stimulation of metabolism by shivering, the extra 

 heat produced by the metabolism of the foodstuffs usually represents 

 waste heat. Any condition which will reduce the output of this waste 

 heat Avill obviously result in a greater efficiency of food utilization. 



The earlier experimental work indicated that the specific dynamic 

 action of the several foodstuffs is a result of different types of stimulation. 

 It has been generally believed that these different types of specific dynamic 

 action are completely additi^'e. Thus Murlin and Lusk-^ demonstrated by 

 experiments on dogs that the total heat produced when 20 g. glycocoll 

 was fed together ^\^.th 70 g. glucose and 75 g. fat over a two-hour period 

 was identical with the sum of extra heats produced during the same interval 

 when the foodstuffs were fed separately (20 g. glycocoll and 50 g. glucose 

 four hours after the administration of 75 g. fat). However, in these data 

 the calculations were based only upon the short period following the in- 

 gestion of the several foodstuffs, at which time the specific dynamic action 

 was at the maximum. It is possible, however, that variations may have 

 l)een caused by the action of one foodstuff or another on the specific dy- 

 namic action produced at a time remote from the period at which the 

 materials were fed. 



In the studies by Forbes and Swift -^ on the rat, heat production as 

 effected by the various combinations of foodstuffs was followed during the 

 entire twenty-four-hour period after the ingestion of the several diets. 

 When the several foodstuffs were fed to the rats the amounts of extra heat 

 produced were 323 calories per 1,000 calories of beef protein, 202 calories 

 per 1,000 calories of carbohydrate (cerelose), and 160 calories for 1,000 

 calories of fat (lard) . When glucose and protein were given simultaneously, 

 the response calculated from the proportion of each of the foodstuffs fed 

 agi'eed closely with the value actually found. However, when lard was 

 included in the diet, either with beef protein or with cerelose, the calculated 

 values exceeded those actually observed by a considerable amount. Thus, 

 when the fat was administered wdth beef protein, only 113 extra calories 

 were produced, as compared with a theoretical value more than trwdce as 



^' M. Rubner, Die Gesetze des Energieverbrauchs bei der Erndhrung, Leipzig & Vienna, 

 1902, p. 109; cited by G. Lusk, The Elements of the Science of Nutrition, 4th ed., Saun- 

 ders, Philadelphia & London, 1928, p. 278. 



28 J. R. Murhn and G. Lusk, /. Biol. Chem., 22, 15-29 (1915). 



