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Metabolic response to carbohydrate ingestion during exercise in males and females

¹School of Sport and Exercise Sciences, University of Birmingham; and ²Diabetes Centre, Selly Oak Hospital, Birmingham, United Kingdom

Submitted 2 August 2005 ; accepted in final form 4 November 2005

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% 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 ([¹³C]glucose ingestion, [6,6-²H₂]glucose, and [²H₅]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, 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 (R_a 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.

stable isotopes; substrate utilization; glucose ingestion; sex-related differences

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