Substrate oxidation during exercise: type 2 diabetes is associated with a decrease in lipid oxidation and an earlier shift towards carbohydrate utilization

Objectives: Exercise is a recommended treatment for type 2 diabetes but the actual pattern of metabolic adaptation to exercise in this disease is poorly known and not taken in account in the protocols used. Metabolic defects involved in the pathways of substrate oxidation were described in type 2 diabetes. We hypothesized that type 2 diabetes, regardless of age, gender, training status and weight, could influence by its own the balance of substrates at exercise. Methods: 30 sedentary type 2 diabetic subjects and 38 sedentary matched control subjects were recruited. We used exercise calorimetry to determine lipid and carbohydrate oxidation rates. We calculated two parameters quantifying the balance of substrates induced by increasing exercise intensity: the maximal lipid oxidation point (PLipoxMax) and the Crossover point (COP), intensity from which the part of carbohydrate utilization providing energy becomes predominant on lipid oxidation. Results: Lipid oxidation was lower in the diabetic group, independent of exercise intensity. PLipoxMax and COP were lower in the diabetic group [PLipoxMax=25.3 +/- 1.4% vs. 36.6 +/- 1.7% %Wmax (P < 0.0001)] - COP =24.2 +/- 2.2% vs. 38.8 +/- 1.9% %Wmax (P < 0.0001). Conclusions: Type 2 diabetes is associated with a decrease in lipid oxidation at exercise and a shift towards a predominance of carbohydrate oxidation for exercise intensities lower than in control subjects. Taking into account these alterations could provide a basis for personalizing training intensity.