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  • Title: The effect of oral contraceptive agents on the basal metabolic rate of young women.
    Author: Diffey B, Piers LS, Soares MJ, O'Dea K.
    Journal: Br J Nutr; 1997 Jun; 77(6):853-62. PubMed ID: 9227183.
    Abstract:
    The use of oral contraceptive agents by women may be a factor that contributes to the observed inter-individual variability in the BMR. We, therefore, measured the BMR, body build and composition in two groups of young women and also assessed their self-reported level of physical activity. One group had been using oral contraceptive agents for a period of 6 months or more (OCA, n 24), while the other group had never used oral contraceptives (NOCA, n 22). There were no significant differences in age, body build or composition. The absolute BMR in the groups were not significantly different when compared using an unpaired t test (OCA: 5841 (SD 471) v. NOCA: 5633 (SD 615) kJ/d). However, using an analysis of covariance, with either body weight or a combination of fat and fat free mass as covariates, the OCA group had a BMR almost 5% higher than that of the NOCA group (OCA: 5871 v. NOCA: 5601 kJ/d; P = 0.002). When those subjects with high self-reported levels of physical activity were excluded, the difference in BMR between the two groups persisted (P = 0.001). An ANOVA of oral contraceptives use and phase of menstrual cycle showed significant differences in BMR with use of oral contraceptives (P = 0.004) but no difference in BMR between phases of the menstrual cycle. In conclusion, the use of oral contraceptive agents deserves consideration when conducting and analysing data from studies on energy metabolism in young women, as it results in a significantly higher BMR. The contribution of oral contraceptive (OC) use to inter-individual variation in the basal metabolic rate (BMR) was investigated in two groups of Australian women, 18-31 years old: 24 women who had been using OCs for 6 months or more and 22 women who had never used OCs. There were no significant differences between the groups in terms of age, body mass index, or body composition. BMR was significantly higher in OC users than never-users, even when women with high levels of physical activity (presumed to increase BMR) were excluded from the analysis. In the analysis of covariance, with either body weight or a combination of fat and fat-free mass as covariates, the OC users had a BMR almost 5% higher than never-users (5871 and 5601 kJ/d, respectively). There were no significant differences in BMR between phases of the menstrual cycle. The stimulatory effect of catecholamines on energy expenditure may be responsible, in part, for the observed difference. The stimulatory effect of OCs on BMR was accompanied by a small but significant pressor effect. OC use should be considered in all studies on energy metabolism in women.
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