Reduced oxidation of dietary fat after a short term high-carbohydrate diet

Background: Short-term high-carbohydrate (HC) diets induce metabolic alterations, including hypertriacylglycerolemia, in both the fasting and postprandial states. The underlying tissue-specific alterations in fatty acid metabolism are not well understood. Objective: We investigated alterations in exogenous and endogenous fatty acid metabolism by using stable isotope tracers to label meal triacylglycerol and plasma fatty acids. Design: Eight healthy subjects consumed isocaloric diets containing a high percentage of energy from carbohydrates or a higher percentage of energy from fat for 3 d in a randomized crossover dietary intervention study. A test meal containing [U-C-13] palmitate was combined with intravenous infusion of [H-2(2)]palmitate to label plasma fatty acids and VLDL triacylglycerol. Blood and breath samples were taken before the meal and for 6 h postprandially. Blood samples were drawn from the femoral artery and from veins draining subcutaneous adipose tissue and forearm muscle for monitoring of tissue-specific metabolic substrate partitioning. Results: Systemic triacylglycerol concentrations were increased in both fasting (P = 0.02) and postprandial (P = 0.02) periods, and a greater amount of infused labeled fatty acid appeared in VLDL triacylglycerol after the HC diet than after the higher-fat diet (P = 0.05). Significantly less (CO2)-C-13 was exhaled after the HC diet (P 0.04) and significantly less production of (CO2)-C-13, was seen across forearm muscle (P = 0.04). Systemic 3-hydroxybutyrate was significantly lower, postprandially, after the HC diet (P = 0.02). Conclusion: Metabolic alterations suggestive of repartitioning of fatty acids away from oxidation toward esterification in both liver and muscle occur in response to short-term adaptation to a HC diet.