In vivo absorption of medium-chain fatty acids by the rat colon exceeds that of short-chain fatty acids

Background & Aims: Short-chain fatty acids (SCFAs) are main fuels of the co lonic epithelium, and are avidly absorbed by the colon of animal and man. T he current knowledge on colonic metabolism and absorption of medium-chain f atty acids (MCFAs) is limited, In some clinical situations, colonic absorpt ion of high-energy substances could compensate for reduced absorptive capac ity because of a shortened or malfunctioning small bowel, We evaluated and compared colonic absorption and metabolism of MCFAs (octanoate, decanoate, and dodecanoate), SCFAs (acetate and butyrate), and long-chain fatty acids (LCFAs) (oleate), Methods: Rats were surgically operated on to cannulate a 7-cm segment of proximal colon, isolate the vasculature, and cannulate the right colic vein draining this segment. The lumen was perfused with C-14-la beled substrates for 100 minutes, Right colic vein blood was analyzed for t otal C-14, (CO2)-C-14, and metabolites by scintillation counting and high-p erformance liquid chromatography, Results: The transport from the colonic l umen to mesenteric blood of substrate carbon from MCFAs exceeded by 2-13-fo ld that of SCFAs and LCFAs, The CO2 production from the oxidation of MCFAs was as high as or higher than that from SCFAs, CO2 produced from the LCFA, oleate, was lower than from SCFAs or MCFAs. In addition to CO2, ketone bodi es were major metabolites of SCFAs and MCFAs. Ketogenesis from butyrate and the MCFAs was significantly higher than from acetate and oleate, A substan tial proportion (50%-90%) of all substrates was absorbed without being meta bolized, Conclusions: The colonic epithelium serves to absorb and partially metabolize MCFAs. For patients with a compromised small-bowel function, co lonic absorption of MCFAs could represent an important way of receiving cal ories.