Background: Different dietary fats are metabolized differently in humans and may influence energy expenditure, substrate oxidation, appetite regulation, and body weight regulation.
Objective: We examined the short-term effects of 4 triacylglycerols (test fats) on subjective appetite, ad libitum energy intake, meal-induced thermogenesis, and postprandial substrate oxidation.
Design: Eleven healthy, normal-weight men (mean age: 25.1 +/- 0.5 y) consumed 4 different test fats [conventional fat (rapeseed oil) and 3 modified fats (lipase-structured fat, chemically structured fat, and physically mixed fat)] in a randomized, double-blind, crossover design.
Results: No significant differences in appetite sensations or ad libitum energy intakes were observed between the 4 test fats. Overall, the 4 fats exerted different effects on energy expenditure (meal effect: P < 0.01) and substrate oxidation (interaction between meal and time: P < 0.05). In post hoc tests, the 3 modified fats resulted in significantly higher postprandial energy expenditure and fat oxidation than did the conventional fat (P < 0.008, Bonferroni adjusted); no significant differences were observed between the 3 modified fats.
Conclusions: Structured fats do not change short-term postprandial appetite sensations or ad libitum energy intakes but do result in higher postprandial energy expenditure and fat oxidation than do conventional fats and hence promote negative energy and fat balance. In humans, a physically mixed fat (trioctanoate + rapeseed oil) is metabolized as quickly as are structured fats. The position of medium-chain fatty acids on the glycerol backbone of triacylglycerols does not seem to affect energy expenditure or appetite.