196 III. DIGESTIBILITY OF FATS 



2. Methods for the Study of Digestibility of Lipids 



Most procedures for the study of digestibility are quite similar and in- 

 volve variations in the type of diet employed, the length of the test period, 

 or the method of analysis of feces. Several of the more widely employed 

 procedures for the study of the digestibility of fat and of other lipids are 

 described below. 



(1) Procedure of Atwater Used in U.S.D.A. Studies 



The methods employed in a long series of tests on a wide variety of 

 fats by Langworthy and Holmes, on human subjects, are typical of those 

 in general use. These workers followed the procedure originally described 

 by Atwater 1 for testing feces by means of various markers. 



The tests were carried out on young adult male subjects over three- 

 day periods. This interval was considered to be of sufficient length for 

 an accurate collection of feces, but not too long for the diet to become 

 monotonous. During this period, the subjects partook exclusively of the 

 test diet, which was given to them ad libitum. The weight of each food 

 constituent eaten at each meal w r as recorded; from this figure the weight 

 of the test substance ingested could be calculated. 



The diet employed in the tests of fat digestibility consisted of several 

 common foods which are practically fat-free, together with a cornstarch 

 blanc-mange pudding into which the test fat was incorporated. The diet 

 included oranges, whole-wheat biscuits, sugar, and coffee or tea without 

 cream. The blanc-mange w^as prepared with cornstarch, sugar, skimmed 

 milk, caramel (to mask the flavor of the fat) and the fat under investiga- 

 tion. After cooling, the blanc-mange was thoroughly mixed and put 

 through a potato ricer to insure equal distribution of the fat throughout 

 the mixture. 



The feces passed during the diet period were separated by the use of 

 markers. The markers consisted of non-absorbable materials which 

 imparted a characteristic color to the feces. Charcoal is the substance 

 most frequently employed for such tests, w T hile carmine or vital red may 

 also be used. The subjects were instructed to take one or two gelatin 

 capsules containing the marker with the first meal of the test diet, and with 

 the first meal following the conclusion of the experiment. The feces 

 showing the color of the first marker, and all material excreted until the 



1 H. C. Atwater, U. S. Dept. Agr. Office Exvt. Sta., Bull. No. 143, 12-13, 58-60, 

 66-77 (1904). 



