Metabolic response to carbohydrate ingestion during exercise in males and females

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 similar to 67% (V) over dot O-2 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 ([C-13] glucose ingestion, [6,6-H-2(2)] glucose, and [H-2(5)] glycerol infusion). In both sexes, CHO ingestion significantly increased the rates of appearance (R-a) and disappearance (R-d) of glucose during exercise compared with WAT ingestion [ males: WAT, similar to 28 - 29 mu mol . kg lean body mass (LBM)(-1) . min(-1); CHO, similar to 53 mu mol . kg LBM-1 . min(-1); females: WAT, similar to 28 - 29 mu mol . kg LBM-1 . min(-1); CHO, similar to 61 mu mol . 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 similar to 10% to similar 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 mu mol . kg LBM-1 . min(-1); CHO, 108 +/- 11 mu mol . kg LBM-1 . min(-1); females: WAT, 89 +/- 10 mu mol . kg LBM-1 . min(-1); CHO, 93 +/- 11 mu mol . 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.