FACTORS ALTERING NUTRITIONAL VALUE 905 



tion is obviousl}^ important in assessing to what extent the fat can be uti- 

 Uzed by the animal. 



b. The Digestibility of Fats and Oils. The extent of digestibility pro- 

 vides one of the most exacting indices of the nutritional value. The so- 

 called coefficient of digestibility is a constant which ser^Ts as a criterion of 

 the extent of utilization of a foodstuff. It is the ratio of the absorbed 

 material to the total amount ingested; in the case of fat, corrections are 

 made for the "metabolic fat" in the feces. This latter fraction represents 

 the lipid-like material which would be excreted irrespective of the diet. 

 For a complete discussion on the digestibility of fats, the reader is referred 

 to The Lipids, Vol. II, pages 195-246. 



(a) The Digestibility of Vegetable and of Animal Fats in Man. With 

 very few^ exceptions, all natural animal and vegetable fats melting l^elow 

 50°C. (122°F.) are practically completely digested bj^ the normal individ- 

 ual. In a comprehensive study made by the author and by the late Dr. 

 C. F. LangW'Orthy and Dr. A. D. Holmes and others of the Office of Home 

 Economics of the U. S. Dept. of Agriculture,^^*'"^^^ it was found that the 

 coefficients of digestibihty of thirty-four vegetable fats ingested with a 

 fat-free diet in amounts of 50 to 100 g. daily, varied between 94 and 99; 

 the only exceptions were avocado fat and teaseed oil, in which the co- 

 efficients of digestibility were 88 and 91, respectively."^^^ The figures 

 for digestibihty of some common vegetable fats are as follows:-^- cocoa 

 butter, 95; coconut oil, 98; corn oil, 97; cottonseed oil, 98; Enghsh 

 walnut oil, 98; hempseed oil, 96; olive oil, 98; peanut oil, 98; poppyseed 

 oil, 96; rapeseed oil, 99 ; sesame oil, 98; soybean oil, 98; and sunflowerseed 

 oil, 96. In the studies w^hich were made mth eighteen different animal 

 fats, the digestibility figures varied between 93 and 99. Some of these 

 values for animal fats are as follow^s:^^^ beef fat, 93; butter, 97; chicken 

 fat, 97; cod-hver oil, 98; egg yolk fat, 94; goose fat, 95; lard, 97; oleo oil, 

 97 ; ox-marrow fat, 94. One criticism of the earlier work is that no account 

 was taken of the fat excreted in the form of soap in the feces. It is possible 

 bhat, had this factor been taken into consideration, the calculated coeffi- 

 cients of digestibility might have been somewhat lower. However, Deuel 

 et al.^^^ have reinvestigated the digestibility of cottonseed and rapeseed oil 



"« H. J. Deuel, Jr., and A. D. Holmes, U. S. Dept. Agr. Bull. No. 1033, 1-15 (July 27, 

 1922). 



291 C. F. Langworthv and A. D. Holmes, U. S. Dept. Agr. Bull. No. 505, 1-20 (Feb. 13, 

 1917). 



"2 C. F. Langworthv, hid. Eng. Chem., 15, 276-278 (1923). 



2" H. J. Deuel, Jr., R. M. Johnson, C. E. Calbert, J. Gardner, and B. Thomas, J. 

 Nutrition, 38, 309-379 (1949). 



