Oral contraception and energy intake in women: Impact on substrate oxidation during exercise

Oral contraception (OC) and energy intake may play a role in fuel selection during exercise. The aim of this study was to investigate the effect of OCs (OC+ vs. OC-) in fed and fasting conditions on substrate oxidation and metabolic and hormonal responses in women during exercise. Substrate oxidation (respiratory exchange ratio and lipid and carbohydrates oxidation rates), metabolic (glycerol, free fatty acids (FFA), and glucose), and hormonal (insulin, adrenaline, and noradrenaline) responses were determined in 21 women: 10 regularly menstruating women (OC-) and 11 women using OCs (OC+: low-dose monophasic pill; ethinyl estradiol <= 30 mu g) during 45 min at 65% of maximal oxygen consumption in fasting and postprandial states. At rest, OC+ presented higher low-density lipoprotein cholesterol, total cholesterol, and triglyceride plasma concentrations as compared with OC-. OC status had no influence on substrate oxidation and metabolic and hormonal responses during exercise. In the fasting state, whatever the OC status, women exhibited greater reliance on fat than in postprandial condition. This occurred in the presence of lower plasma insulin concentrations and higher plasma FFA and glycerol levels. The results indicated that the use of low-dose monophasic combined with OCs did not modify fuel selection and metabolic and hormonal responses during exercise in women. The fasting condition, compared with the fed condition, decreased carbohydrate oxidation during exercise, leading to a greater lipid mobilization and utilization whatever the OC status. Thus, in women, the realization of an exercise in either the fed or fasting conditions had a greater impact on substrate oxidation than OC status.