Impaired oxidation of plasma-derived fatty acids in type 2 diabetic subjects during moderate-intensity exercise

The present study was intended to investigate the different components of fatty acid utilization during a 60-min period of moderate-intensity cycling exercise (50% of Vo(2max)) in eight male type 2 diabetic subjects (aged 52.6 +/- 3.1 years, body fat 35.8 +/- 1.3%) and eight male obese control subjects (aged 45.1 +/- 1.4 years, body fat 34.2 +/- 1.3%) matched for age, body composition, and maximal aerobic capacity. To quantitate the different components of fatty acid metabolism, an isotope infusion of [U-C-13]-palmitate was used in combination with indirect calorimetry. In separate experiments, the C-13 label recovery in expired air was determined during infusion of [1,2-C-13]-acetate (acetate recovery factor). There mere no differences in energy expenditure of carbohydrate and total fat oxidation between the groups. The rate of appearance (R-a) of free fatty acid (FFA) (P < 0.05) and the exercise-induced increase in R-a of FFA were significantly lower (P < 0.05) in type 2 diabetic subjects compared with control subjects (baseline vs. exercise [40-60 min]; type 2 diabetes 11.9 +/- 0.9 vs. 19.6 +/- 2.2 mu mol.k(-1) fat-free mass [FFM].min(-1) and control 15.8 +/- 1.8 vs. 28.6 +/- 2.1 mu mol.kg(-1) FFM.min(-1)). The oxidation of plasma-derived fatty acids was significantly lower in type 2 diabetic subjects during both conditions (P < 0.05, baseline vs. exercise [40-60 min]; type 2 diabetes 4.2 +/- 0.5 vs. 14.1 +/- 1.9 mol.kg(-1) FFM.min(-1) and control 6.2 +/- 0.6 vs. 20.4 +/- 1.9 mu mol.kg(-1) FFM.min(-1)), whereas the oxidation of triglyceride-derived fatty acids was higher (P < 0.05). It is hypothesized that these impairments in fatty acid utilization may play a role in the etiology of skeletal muscle and hepatic insulin resistance.