Metabolic response to carbohydrate ingestion during exercise in males and females

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Abstract
The present study investigated potential sex-related differences in the metabolic response to carbohydrate (CHO) ingestion during exercise. Moderately endurance-trained men and women ( n = 8 for each sex) performed 2 h of cycling at ∼67% V̇o2 max with water (WAT) or CHO ingestion (1.5 g of glucose/min). Substrate oxidation and kinetics were quantified during exercise using indirect calorimetry and stable isotope techniques ([13C]glucose ingestion, [6,6-2H2]glucose, and [2H5]glycerol infusion). In both sexes, CHO ingestion significantly increased the rates of appearance (Ra) and disappearance (Rd) of glucose during exercise compared with WAT ingestion [males: WAT, ∼28–29 μmol·kg lean body mass (LBM)−1·min−1; CHO, ∼53 μmol·kg LBM−1·min−1; females: WAT, ∼28–29 μmol·kg LBM−1·min−1; CHO, ∼61 μmol·kg LBM−1·min−1; main effect of trial, P < 0.05]. The contribution of plasma glucose oxidation to the energy yield was significantly increased with CHO ingestion in both sexes (from ∼10% to ∼20% of energy expenditure; main effect of trial, P < 0.05). Liver-derived glucose oxidation was reduced, although the rate of muscle glycogen oxidation was unaffected with CHO ingestion (males: WAT, 108 ± 12 μmol·kg LBM−1·min−1; CHO, 108 ± 11 μmol·kg LBM−1·min−1; females: WAT, 89 ± 10 μmol·kg LBM−1·min−1; CHO, 93 ± 11 μmol·kg LBM−1·min−1). CHO ingestion reduced fat oxidation and lipolytic rate (Ra glycerol) to a similar extent in both sexes. Finally, ingested CHO was oxidized at similar rates in men and women during exercise (peak rates of 0.70 ± 0.08 and 0.65 ± 0.06 g/min, respectively). The present investigation suggests that the metabolic response to CHO ingestion during exercise is largely similar in men and women.