Carbohydrate supplementation and sex differences in fuel selection during exercise.
OBJECTIVE
To compare the effects of a high-CHO diet (80% CHO) and glucose ingestion (2 g x kg(-1)) during exercise (120 min, 57% VO2max) 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 (13C-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.
Tremblay
Jonathan
J
Department of Kinesiology, University of Montreal, Montreal, Quebec, Canada. jonathan.tremblay@umontreal.ca
Peronnet
Francois
F
Massicotte
Denis
D
Lavoie
Carole
C
D000328:Adult; D002153:Calorimetry, Indirect; D050260:Carbohydrate Metabolism / Q000502:physiology*; D003279:Contraceptives, Oral, Sequential; D015444:Exercise / Q000502:physiology*; D005260:Female; D005518:Food Preferences; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D008297:Male; D010101:Oxygen Consumption; D012737:Sex Factors; D055815:Young Adult
D003279:Contraceptives, Oral, Sequential; D005947:Glucose