Metabolic effects induced by long-term feeding of medium-chain triglycerides in the rat

Abstract

Energy intake, weight gain, carcass composition, plasma hormones and fuels, hepatic metabolites and the activities of phosphoenolpyruvate carboxykinase (PEPCK), malic enzyme, and glucose 6-phosphate dehydrogenase (G6P-DH) were examined in adult rats during a 44-day period of low fat, high carbohydrate (LF) feeding or of consumption of one or two high (70% metabolizable energy) fat diets composed of 63% (metabolizable energy) long-chain (LCT) or medium-chain (MCT) triglycerides. Energy intake was similar in the LCT and MCT groups but was less than that of LF group. The weight gain of rats fed MCT diet was 30% less than that of rats fed LF or LCT diets. Energy retention was less when the diet provided MCT than LCT or LF, and that resulted in a 60% decrease in the daily lipids deposition. Plasma glucose, free fatty acids, glycerol, and insulin/glucagon ratio were similar in the three groups. Blood ketone body (KB) concentrations in rats fed the high fat diets were extremely elevate, particularly in the MCT group, but declined throughout the experiment and by the 44 th day hyperketonemia decreased by 50% but remained higher than in the LF diet. The blood β-hydroxybutyrate/acetoacetate ( B A ) ratio remained slightly elevated in rats fed the high fat diets. Similar changes were observed in liver KB concentration and in the B A ratio. Liver lactate/pyruvate ratio elevated in the LCT and MCT groups at the initiation of the diets decreased by 50% at the end of the experiment. The consumption of high fat diets led to a 1.5-fold increase in liver PEPCK activity. Malic enzyme activity was not altered by the MCT diet, while feeding the LCT diet decreased by 40% malic enzyme activity. By the end of experiment, G6P-DH activity was 25% and 85% lower in MCT and LCT rats than in LF rats. The decrease of ketonemia throughout the experiment in the MCT rats which is associated with a decrease in B A ratio might be due to an adaptation of the rats to the MCT diet (ie, decrease hepatic ketone body production and/or peripheral ketone body utilization).