THE BODY'S UTILIZATION OF FAT 425 



THE BODY'S UTILIZATION" OF FAT 



BY FRANK S. MATHEWS, M.D. 

 COLUMBIA UNIVERSITY 



T3 ECENT physiology has considerably advanced our knowledge of 

 -*- * fatty metabolism. Some of the recent work has had an im- 

 portant bearing on metabolism in general, as well as on the special 

 metabolism of fats. This article aims to outline the results of some 

 of the more important experimental work on the subject. 



Fat is the form in which the body lays up its greatest supply of 

 potential energy. Plants also store energy, but they do it chiefly in 

 the form of sugar and starch or, to give these substances a single name, 

 carbohydrate. As the animal kingdom is parasitic directly or in- 

 directly upon the vegetable, it results that the animal's food is largely 

 composed of carbohydrate. Thus Voit's figures, expressing the needs 

 of an adult man, are 118 grams of proteid, 1 50 grams of fat and 500 

 grams of carbohydrate food in twenty-four hours. 



But there are good reasons why carbohydrate, which is our most 

 abundant and cheapest food, would not be an economical store of 

 energy for the animal body. Chief among these is the fact that 

 animals are for the most part motile and hence the advantage of having 

 their store of energy-producing compounds in small compass and of 

 light weight. Fat fulfils the indications admirably, since its atoms, 

 carbon and hydrogen, are light, since a given weight is capable of com- 

 bining with a large amount of oxygen and since it can be completely 

 oxidized in the body, i. e., the body is able to utilize all its potential 

 energy. 



Not all our fat comes from the fat of our food, but is made in the 

 body from other substances. There are two theories — one that it is 

 made from carbohydrate, the other that it is made from proteid. 



An animal can be fattened without giving it any fat in its food, 

 in fact, the usual method of fattening animals is by increasing their 

 carbohydrate food. Though there is some question of the origin of fat 

 from proteid, there can be little or none as to the transformation of 

 carbohydrate into fat. This knowledge that fat can be so made upsets 

 one of the notions largely held till recently as to the kind of chemistry 



1 Chittenden has investigated our proteid needs very carefully and would 

 probably agree that these figures fairly well represent what the average man 

 does consume, but he finds that such a quantity of proteid is much beyond 

 actual needs. He found men able to do work of all kinds, both mental and 

 physical, and retain good health on one third to one half this quantity of proteid. 



