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Reduced oxidation of dietary fat after a short term high-carbohydrate diet^1,2,3

¹ From the Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, United Kingdom (RR, ASB, BAF, MF-FC, MG, FK, and KNF); the Department of Human Biology, Maastricht University and University Hospital, Maastricht, Netherlands (EEB); and the School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom (AJW)

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-¹³C]palmitate was combined with intravenous infusion of [²H₂]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 ¹³CO₂ was exhaled after the HC diet (P = 0.04) and significantly less production of ¹³CO₂ 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.