Impact Of Menstrual Cycle On Resting And Postprandial Metabolism In Recreationally Active, Eumenorrheic Females

PURPOSE: Changes in estrogen and progesterone across the menstrual cycle impact many biological systems including resting and postprandial metabolism. The purpose of this study was to investigate whether menstrual cycle phase impacted resting and postprandial energy expenditure (EE) and substrate utilization in recreationally active, eumenorrheic females. METHODS: In this study, 8 eumenorrheic females (mean ± SD age: 33 ± 8 years, BMI: 22.5 ± 2.2 kg/m2; VO2max: 36.9 ± 3.8 ml/kg/min) had resting energy expenditure (REE) and substrate utilization continuously measured with indirect calorimetry for 45 min at rest after an overnight fast, and for 3 h after a mixed meal (490 kcal, 53% carbohydrate, 31% fat, 20% protein) during three distinct phases of the menstrual cycle (early follicular, late follicular, and mid luteal). Menstrual cycle phase was determined using calendar-based counting, ovulation test strips, and confirmed via serum hormone levels (estrogen and progesterone). REE (kcal/day) was calculated using the abbreviated Weir Equation. Diet-induced thermogenesis (DIT) was calculated by subtracting REE (kcal/min) from postprandial EE (kcal/min). This value (kcal/min) was then multiplied by the testing time (180 min) to obtain DIT (kcal) for the 3-h postprandial period. A one-way, repeated measures ANOVA was used to assess differences in REE, respiratory quotient (RQ), and DIT across menstrual cycle phase. All data reported as mean ± SD. RESULTS: REE was higher during mid luteal (1486 ± 178 kcal/day) compared to early follicular (1409 ± 108 kcal/day) and late follicular (1390 ± 103 kcal/day) phases (F[2,14] = 2.28, p = 0.14; effect size = 0.25). Resting RQ did not differ across menstrual cycle phase. DIT was higher during early follicular (34 ± 8 kcal) and late follicular (32 ± 12 kcal) than mid-luteal (23 ± 12 kcal) phase (F[2,14] = 3.02, p = 0.08; effect size = 0.30). Postprandial RQ was higher during early follicular (0.87 ± 0.04) and late follicular (0.87 ± 0.03) than mid-luteal (0.85 ± 0.04) phase (F[2,14] = 3.22, p = 0.07; effect size = 0.32). CONCLUSIONS: These preliminary results on 8 recreationally active, eumenorrheic females suggest that resting and postprandial metabolism may differ across the menstrual cycle. It is unclear whether the magnitude of these differences is clinically meaningful. Texas Woman's University ORSP Small Grant