Infusion of long-chain or medium-chain triglycerides inhibits peripheral glucose metabolism in men

To investigate whether increased availability of lipids affects glucose metabolism in healthy postabsorptive men when lipid and glucose are infused in amounts used in parenteral nutrition, we infused glucose (4 mg/kg.min-1) for 6 hours and clamped plasma glucose at basal level during the first 3 hours. After 3 hours, either long-chain triglycerides (LCTs) (0.07 g/kg.h-1) (n = 7) or a mixture of LCTs and medium-chain triglycerides (MCTs) (MCTs/LCTs, 50/50%, 0.07 g/kg.h-1) (n = 7) was administered, and the infusion rates of glucose and insulin were unchanged compared with the first 3 hours. In a control study, glucose was infused for a period of 6 hours without the lipid infusion (n = 5). After 6 hours, the plasma glucose concentration and glucose tissue uptake were not affected by LCT or MCT/LCT infusion. Nonetheless, glucose oxidation decreased in the LCT group (from 6.42 +/- 1.04 to 2.31 +/- 0.85 mumol/kg.min-1, p < .001) and in the MCT/LCT group (from 7.62 +/- 1.50 to 5.50 +/- 0.76 mumol/kg.min-1, p < .01) but not in the control group. Concentrations of the glucoregulatory hormones were not different among the three groups. In conclusion, MCTs/LCTs administered concomitantly with glucose infusion, in amounts similar to those used in total parenteral nutrition, inhibit glucose oxidation without affecting glucose tissue uptake, just as LCTs do.