Metabolic Consequences of Dietary Medium-chain Triglycerides in the Rat

Abstract

Some metabolic effects of feeding rats medium-chain triglyceride (MCT), triglyceride containing primarily C₈ and C₁₀ fatty acids, were compared to the effects of feeding triglycerides composed of long-chain fatty acids. In vitro rates of lipogenesis in liver and adipose tissue of animals receiving long-chain triglycerides were significantly depressed relative to rates in tissues of rats receiving a low fat diet. MCT was markedly less effective in depressing lipogenesis. Malic enzyme, citrate cleavage enzyme and glucose-6-phosphate dehydrogenase + 6-phosphogluconate dehydrogenase enzyme activities were depressed in rat liver as a result of adding triglycerides containing either long- or medium-chain fatty acids to a low fat diet. In adipose tissue MCT was much less effective than were triglycerides containing long-chain fatty acids in depressing the activity of these enzymes. Circulating levels of β-hydroxybutyrate were markedly elevated by MCT feeding. Adding corn oil or MCT to the low fat diet appeared to increase circulating insulin levels, whereas only corn oil elevated circulating triglycerides. The lack of effect of MCT on lipogenesis is attributed to its portal absorption and rapid uptake and oxidation by the liver. Results support the theory that long-chain fatty acids or their CoA derivatives are involved in the regulation of fat synthesis in both liver and adipose tissue.