Dietary medium-chain triglycerides (MCT) may improve insulin-mediated glucose metabolism. To examine this possibility, 10 non-insulin-dependent diabetes mellitus (NIDDM) patients, 4 hypertriglyceridemic, and 6 normotriglyceridemic nondiabetic control subjects were examined with a 5-day cross-over design, in which the short-term metabolic effects of a 40% fat diet containing 77.5% of fat calories as MCT were compared with an isocaloric long-chain triglyceride-containing diet. In diabetic patients, MCT failed to alter fasting serum glucose concentrations but reduced preprandial glycemic excursions by 45% (F = 7.9, P < 0.01). On MCT, the amount of glucose needed to maintain euglycemia during an intravenous insulin infusion was increased in diabetic subjects by 30%, in hypertriglyceridemic subjects by 30%, and in normotriglyceridemic control subjects by 17%. MCT increased mean ± SE insulin-mediated glucose disposal (4.52 ± 0.56 vs. 2.89 ± 0.21−1 · min−1; n = 3, P < 0.05) but failed to alter basal glucose metabolism or insulin-mediated suppression of hepatic glucose output. Metabolic responses to MCT were observed independent of sulfonylurea therapy or severity of fasting hyperglycemia. No change in fasting serum insulin or triglyceride concentrations were seen with MCT administration. Although MCT increased mean fasting serum β-hydroxybutyrate levels from 0.10 ± 0.03 to 0.26 ± 0.06 mM (P < 0.05) in normotriglyceridemic nondiabetic subjects, no change was seen in diabetic patients. Thus, MCT-containing diets increased insulin-mediated glucose metabolism in both diabetic patients and nondiabetic subjects. In diabetic subjects, this effect appears to be mediated by increases in insulin-mediated glucose disposal. MCT may be a promising adjunct to conventional dietary and sulfonylurea treatment in NIDDM.

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