NORMAL FACTORS ALTERING DIGESTIBILITY OF FATS 227 



In general, the higher saturated fatty acids are poorly absorbed, even 

 when fed in solution in olive oil. Both lauric and myristic acids were 

 found to be only approximately 80% utilized by the rat, while the co- 

 efficients of digestibility of palmitic and stearic acids are approximately 

 the same when they are fed alone and when they are administered in 5 to 

 25% solutions in olive oil. The high digestibility reported by Lyman 81 

 for palmitic acid in the dog is in line with the high utilization of tripalmitin 

 in this species, but it stands out in sharp contrast to the results on rats. 



Paul and McCay 73 demonstrated an interesting species variation in the 

 utilization of oleic acid and its trans isomer, elaidic acid. Whereas the 

 rat is able to utilize both of these acids to the extent of 95%, the guinea 

 pig can digest only the oleic acid efficiently. Elaidic acid was found to 

 have the low coefficient of digestibility of 56 in the latter species. 



The hen presents an interesting species variation in the case of tri- 

 butyrin. Although digestibility experiments of the usual type have not 

 been recorded in rats, it has been found that 100% of tributyrin fed had 

 disappeared from the gut of the rat within eight hours after feeding. 83 

 In all probability, this triglyceride is practically completely absorbed by 

 the rat. Davis 84 reported an average coefficient of digestibility of 91.9 for 

 tributyrin in hens, except in two tests in which a coefficient of 86.9 was 

 found; in these latter cases toxicity apparently obtained. McClure and 

 Carr 85 have found that the lower fatty acids are also toxic for pigeons. 

 Cook 86 has reviewed the comparative aspects of lipid absorption and ex- 

 cretion. 



4. Normal Factors Altering the Digestibility of Fats 



(1) The Effect of Age 



No systematic studies have been made to determine the effect of age 

 on the digestibility of fats. However, it is evident from the studies of 

 Holt and collaborators 87,88 that the digestibility of fat is less efficient in 



83 H. J. Deuel, Jr., J. S. Butts, H. Blunden, C. H. Cutler, and L. Knott, /. Biol. Chem., 

 117, 119-129 (1937). 

 • 84 R. E. Davis, J. Biol. Chem., 88, 67-75 (1930). 

 86 F. J. McClure and R. H. Carr, Am. J. Physiol., 74, 70-78 (1925). 



86 R. P. Cook, "Comparative Aspects of Lipid Absorption and Excretion," in R. T. 

 Williams, Lipid Metabolism, Biochem. Soc. Symposia, No. 9, Cambridge Univ. Press, 

 14-29 (1952). 



87 L. E. Holt, A. M. Courtney, and H. L. Fales, Am. J. Diseases Children, 17, 241-250 

 (1919). 



88 L. E. Holt, A. M. Courtney, and H. L. Fales, Am. J. Diseases Children, 18, 107-126 

 (1919). 



