Fatty acid reesterification but not oxidation is increased by oral contraceptive use in women

We evaluated the hypothesis that fatty acid reesterification would be increased during rest and exercise in the midluteal menstrual cycle phase and during oral contraceptive use, when ovarian hormone concentrations are high, compared with the early follicular phase. Subjects were eight moderately active, weight-stable, eumenorrheic women (24.8 ± 1.2 yr, peak oxygen consumption = 42.0 ± 2.3 ml·kg^-1·min ^-1) who had not taken oral contraceptives for at least 6 mo. Plasma free fatty acid (FFA) kinetics were assessed in the 3-h postprandial state by continuous infusion of [1-¹³C]palmitate and [1,1,2,3,3- ²H]glycerol during 90 min of rest and 60 min of exercise at 45% and 65% peak oxygen consumption in the early follicular and midluteal menstrual cycle phases and during the inactive- and high-dose phases following 4 mo of oral contraceptive use. Plasma FFA rates of appearance, disappearance, and oxidation increased significantly from rest to exercise with no differences noted between menstrual cycle or oral contraceptive phases or exercise intensities. Compared with either menstrual cycle phase, oral contraceptive use resulted in an increase in plasma-derived fatty acid reesterification and a decrease in the proportion of plasma FFA rate of disappearance that was oxidized at rest and during exercise. Endogenous and exogenous synthetic ovarian hormones do not exert a measurable influence on plasma FFA turnover or oxidation at rest or during moderate-intensity exercise in the 3-h postprandial state when carbohydrate use predominates. The increase in whole body lipolytic rate during exercise noted previously with oral contraceptive use is not matched by an increase in fatty acid oxidation and results in an increase in reesterification. Synthetic ovarian hormones contained in oral contraceptives increase lipolytic rate, but fatty acid oxidation during exercise is determined by exercise intensity and its metabolic and endocrine consequences.