The Effects of Chain Length on the Metabolism of Saturated Fatty Acids by the Rat

Abstract

Four randomly mixed triglycerides containing either butyric-1-C¹⁴, caprylic-1-C¹⁴, lauric-1-C¹⁴ or palmitic-1-C¹⁴ acid were administered to young adult rats by stomach tube. Radioactivity measurements were made on samples of breath collected at timed intervals during 48 hours and on samples of urine, feces and colon contents collected during 48 hours. Activity measurements on fecal samples indicated that the efficiency of absorption of palmitic acid (86%) from the intestinal tract was significantly lower than that of the three shorter-chain fatty acids (98 to 100%). The rates of metabolism of butyric and caprylic acids to respired C¹⁴O₂ were highest and similar, that of lauric acid was intermediate, and that of palmitic acid was lowest. The differences observed in the expired C¹⁴O₂, an end product of fatty acid metabolism, were probably due, at least in part, to differences in the route of transport of the fatty acids to the tissues following absorption from the gastrointestinal tract. The rapid excretion of C¹⁴O₂ observed when the shorter-chain fatty acids were fed indicates that they were oxidized instead of entering the fat depots.