FACTORS AFFECTING RATE OF ABSORPTION 181 



Table 25 gives a summary of absorption tests on simple triglycerides 

 composed of C2 to C ]2 acids. 



Two interesting variations are immediately evident from the results 

 with the simple triglycerides. In the first place, the most rapid absorption 

 rate is found in the case of triacetin and tributyrin. As the number of 

 carbons on the acid component increases, a regular decrease in absorption 

 occurs when one compares the values for the fats having C6, Cg, and C12 

 acids. The second striking phenomenon is the marked retardation in 

 absorption rates of the triglycerides having the odd-chain carbon fatty 

 acids as compared with the triglycerides having the even-chain acids. 

 However, tripropionin (C 3 ), trivalerin (C 5 ), and triheptylin (C7) all have 

 practically identical absorption rates, and do not show the decrease noted 

 between tributyrin (C 4 ) and tricaprylin (C 8 ). Triisovalerin gives results 

 considerably higher than those for trivalerin, but lower than the figures 

 for tributyrin. It is provisionally classified with the even-chain fats, 

 but might be considered as belonging to the odd-chain series. 



b. The Rate of Absorption of Fatty Acids. The variations in the rate of 

 absorption of the simple triglycerides might be the result of differences in 

 the rate of hydrolysis of the triglycerides or in the rate of absorption of the 

 resultant fatty acids. The results in Table 26 (p. 182) on the rate of absorp- 

 tion of fatty acids (or their salts in the case of the short-chain acids) would 

 seem to indicate that the rate of absorption of the triglycerides is a function 

 of the rate of absorption of the fatty acids. This finding does not support 

 either the Lipolytic or the Partition Theory, inasmuch as both Verzar 

 and Frazer postulate the hydrolysis of the triglycerides which contain 

 water-soluble acids. 



The results in general support the thesis that the variations in absorption 

 rate of the simple triglycerides are related to the speed of absorption of 

 their constituent fatty acids. Some alterations are brought about in the 

 case of the short-chain fatty acids by the use of their sodium salts rather 

 than of the free acids, which are too irritating to be used. This may ac- 

 count for the poor showing for acetate, since sodium acetate is known to be 

 an intestinal irritant. 823 The reduced rate of absorption of the lower odd- 

 chain fatty acids, as compared with the even-chain acids, can be noted for 

 propionic, valeric, and heptylic acids when they are fed as their sodium 

 salts. 



c. The Absorption of Short-Chain Acids. There has been some question 

 as to the fate of the volatile fatty acids when ingested by animals. In 

 spite of the fact that acetic, propionic, and butyric acids disappear from the 



823 H. J. Deuel, Jr., and A. T. Milhorat, J. Biol. Chem., 78, 299-309 (1928). 



