Influence of medium-chain and long-chain triacylglycerols on the control of food intake in men

Hunger may be delayed and food intake reduced under metabolic conditions that spare carbohydrate oxidation, especially during oxidation of medium-chain triacylglycerols (MCTs) or monounsaturated triacylglycerols. In 12 healthy, adult, male volunteers isolated and deprived of any time cues, we compared the effects of 4 high-carbohydrate breakfasts (1670 kJ) supplemented either with a fat substitute (Sub; 70 kJ) or with 1460 kJ fat as monounsaturated long-chain triacylglycerols (LCT-U), saturated long-chain triacylglycerols (LCT-S), or MCTs. In the first session we investigated the effects of these breakfasts on the following food intake variables: hunger ratings at repeated intervals, the time until the spontaneous request for the next 2 free-choice meals, and the amount of food consumed. In a second session with fixed lunches, we studied the effects of the same breakfasts on plasma glucose, insulin, triacylglycerol, fatty acid, and beta-hydroxybutyrate concentrations. The addition of any of the fats to the high-carbohydrate breakfasts did not alter hunger ratings, but significantly delayed the request for lunch compared with the low-fat breakfast. The free-choice lunch eaten after the MCT breakfast was also significantly smaller. Blood glucose and insulin concentrations were lower after the 3 fat breakfasts, followed by larger increases in glucose and enhanced insulin responses 30 min after the lunch. No differences were observed between the LCT-U and LCT-S conditions. We conclude that MCTs decreased food intake by a postabsorptive mechanism, although the exact effect of these lipids on carbohydrate oxidation will require further studies involving nutrient balance measurements.