To compare the effects of a high-CHO diet (80% CHO) and glucose ingestion (2 g·kg−1) during exercise (120 min, 57% V˙O2max) on fuel selection in women taking (W+OC) or not (W−OC) oral contraceptives and in men (six in each group).
Substrate oxidation was measured using indirect respiratory calorimetry in combination with a tracer technique to compute the oxidation of exogenous (13C-glucose) and endogenous CHO.
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.
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.
1Department of Kinesiology, University of Montreal, Montreal, Quebec, CANADA; 2Department of Kinanthropology, University of Quebec in Montreal, Montreal, Quebec, CANADA; and 3Department of Exercise Sciences, University of Quebec in Trois-Rivieres, Trois-Rivieres, Quebec, CANADA
Address for correspondence: Jonathan Tremblay, PhD, Department of Kinesiology, University of Montreal, CP 6128, Succursale Centre-Ville, Montreal, Quebec, Canada H3C 3J7; E-mail: email@example.com.
Submitted for publication February 2009.
Accepted for publication November 2009.