Carbohydrate Supplementation and Sex Differences in Fuel Selection during Exercise

TREMBLAY, J., F. PERONNET, D. MASSICOTTE, and C. LAVOIE. Carbohydrate Supplementation and Sex Differences in Fuel Selection during Exercise. Med. Sci. Sports Exerc., Vol. 42, No. 7, pp. 1314-1323, 2010. Purpose: To compare the effects of a high-CHO diet (80% CHO) and glucose ingestion (2 g.kg(-1)) during exercise (120 min, 57% (V) over dotO(2max)) on fuel selection in women taking (W+OC) or not (W-OC) oral contraceptives and in men (six in each group). Methods: Substrate oxidation was measured using indirect respiratory calorimetry in combination with a tracer technique to compute the oxidation of exogenous (C-13-glucose) and endogenous CHO. Results: In the control situation (mixed diet with water ingestion during exercise), the percent contribution to the energy yield (%En) of CHO oxidation was higher in men than in women (62 vs 53 %En). The high-CHO diet and glucose ingestion during exercise separately increased the %En from CHO oxidation in both men (+12%) and women (+24%), and the sex difference observed in the control situation disappeared. However, the increase in the % En from total CHO oxidation observed when glucose was ingested during exercise and when combined with a high-CHO diet was larger in women than in men (+47 vs +17 %En). This was not attributable to a higher % En from exogenous glucose oxidation in women, for which no sex difference was observed (25 and 27 % En in men and women), but was attributable to a smaller decrease in endogenous glucose oxidation. No significant difference in fuel selection was observed between W+OC and W-OC. Conclusions: The increase in total CHO oxidation after the high-CHO diet was not different between sexes. Glucose ingestion during exercise, separately and combined to the high-CHO diet, had a greater effect in women than in men; this was mostly attributable to the smaller reduction in endogenous CHO oxidation.