Mechanism for the increase in plasma triacylglycerol concentrations after consumption of short-term, high-carbohydrate diets

Background: High-carbohydrate (HC) diets are recommended for lowering the r isk of coronary heart disease because they decrease plasma LDL-cholesterol concentrations. However, an unfavorable effect of HC diets is an increase i n plasma triacylglycerol concentrations. The underlying mechanisms of this effect are still unclear. Objective: We examined the effect of diet composition on VLDL-triacylglycer ol metabolism using in vivo isotopically labeled VLDL-triacylglycerol trace rs. Design: Six healthy subjects were studied on 2 occasions: after 2 wk of an HC diet (75% carbohydrates, 10% Fat, and 15% protein) and after 2 wk of an isoenergetic high-fat (HF) diet (30% carbohydrates, 55% fat, and 15% protei n). Results: The plasma VLDL-triacylglycerol concentration was higher after the HC diet than after the HF diet (690 +/- 186 compared with 287 +/- 104 mu m ol/L; P < 0.05) because of higher rates: of VLDL-triacylglycerol production (0.76 +/- 0.12 compared with 0.45 +/- 0.15 mu mol.kg(-1).min(-1); P < 0.05 ) rather than diminished VLDL-triacylglycerol clearance (1.5 +/- 0.5 compar ed with 1.7 +/- 0.5 mL.kg(-1).min(-1) after the HC diet than after the HF d iet, respectively). The increase in VLDL-triacylglycerol production was pro bably mediated by a decrease in hepatic fatty acid oxidation after the HC d iet (0.13 +/- 0.02 compared with 0.69 +/- 0.13 mu mol.kg(-1).min(-1); P < 0 .05), which presumably increased hepatic fatty acid availability for triacy lglycerol synthesis. Conclusions: The increase in fasting plasma triacylglycerol concentrations in response to short-term HC diets is due to accelerated VLDL-triacylglycer ol secretion. Increased hepatic fatty acid availability, resulting from red uced hepatic fatty acid oxidation, is most likely responsible for the obser ved increase in VLDL-triacylglycerol secretion.