STUDIES ON FATS, OILS, AND FATTY ACIDS 225 



lipolysis was noted in the tests by Deuel et al., To the low digestibility was 

 ascribed to the failure to absorb erucic acid. 



On the other hand, Holmes 79 had reported earlier that the digestibility 

 of rapeseed oil in man was 99%. This high figure for utilization cannot 

 be attributed to the fact that the investigator failed to take into con- 

 sideration the excretion of fat in the form of soaps inasmuch as, in later 

 experiments of Deuel and associates, 4 a coefficient of digestibility was 

 found for human subjects identical with that reported by Holmes. In 

 these later tests, 4 the excretion of fecal soap was determined. One must- 

 conclude that a fundamental difference in the utilization of rapeseed oil 

 obtains between the rat and man; at the present time, there is no ade- 

 quate explanation for this variation. 



Another difference in fat utilization is noted when one compares the 

 digestibility of fats by the guinea pig and by other species. Although 

 cod-liver, olive, and soybean oils are utilized approximately as well in 

 the guinea pig as in other species, the coefficient of digestibility of corn, 

 cottonseed, and peanut oils appears to be somewhat depressed in this 

 rodent. 70 Moreover, Cook and Thomson 72 reported a coefficient of 

 digestibility for olive oil of only 77 in the guinea pig when this vegetable 

 oil was fed at a comparatively high level (3 g. per day) . Lard was found 

 to be digested only to the extent of 75.2% by the guinea pig, 70 as con- 

 trasted with 96.6% in the rat 62 and 97.0% in man. 2 



b. Digestibility of Simple Triglycerides and Fatty Acids. A number of 

 pertinent studies on the digestibility of simple triglycerides and of fatty 

 acids have been made for several species. These are recorded in Table 14. 



Several interesting factors are noted when one considers the digestibility 

 of the higher simple triglycerides. In the first place, when no other fats 

 were present in the diet, trilaurin was found to be practically completely 

 digested, while trimyristin, tripalmitin, and tristearin were progressively 

 less efficiently utilized in the rat. 5 In the experiments of Hoagland and 

 Snider, 80 in which the triglycerides were fed in 5 or 10% solutions in olive 

 oil, trilaurin and trimyristin were highly utilized and only about 15% 

 of the tripalmitin failed to be absorbed. The coefficients of digestibility 

 of the entire fat mixtures when the triglycerides made up 5 or 10% of the 

 total fat, respectively, were as follows: trilaurin, 98.2 and 99.9; tri- 

 myristin, 96.4, 99.0; tripalmitin, 95.8, 95.6; and tristearin, 92.7 and 89.2. 

 However, the digestibility of tristearin was not increased by its solution 

 in olive oil. The coefficients of digestibility calculated for this triglyc- 



79 A. D. Holmes, U. S. Dept. Agr., Bull. No. 687, 1-20 (1918). 



80 R. Hoagland and G. G. Snider, /. Nutrition, 26, 219-225 (1943). 



