Energy expenditure by indirect calorimetry in premenopausal women: variation within one menstrual cycle

Abstract

Energy expenditure in relation to the menstrual cycle was determined by indirect calorimetry in premenopausal women. For each subject, three measurements were made within a single menstrual cycle. Energy expenditure measurements coincided with the subject's expected hormonal fluxes of estradiol and progesterone: menstrual phase-both hormones at basal levels; follicular phase-elevated estradiol; and luteal phase-elevated progesterone. In experiment I, resting energy expenditure of 14 women was determined for 1 hour using a canopy system for calorimetry; in experiment 2, 24-hour energy expenditures of 12 subjects were measured in a room-size calorimeter. Blood from fasted (12 hours) subjects was collected following measurements of energy expenditure and analyzed for serum estradiol-17B and progesterone by radioimmunoassay. In experiment 1, resting energy expenditure did not differ within one menstrual cycle; neither estradiol nor progesterone affected resting energy expenditure. In experiment 2, 24-hour energy expenditure was significantly lower ( P < 0.013) during the follicular phase when compared with the menstrual (−3.8%) and luteal (−4.9%) phases. Lowered 24-hour energy expenditure during the follicular phase may in part be due to a decrease in spontaneous activity and exercise. Energy expenditure during sleep, an indicator of metabolic energy expenditure, was significantly greater ( P < 0.0001) during the luteal phase than during the menstrual (+6.7%) and follicular (+5.4%) phases; this was a reflection of increased progesterone ( P < 0.0001). Twenty-four hour energy expenditure (mean ± SEM) during the menstrual, follicular, and luteal phases was 8.86 ± 0.26, 8.52 ± 0.22, and 8.96 ± 0.21 MJ/d, respectively. Corresponding values for energy expenditure during sleep were 5.49 ± 0.09, 5.56 ± 0.10, and 5.86 ± 0.11 MJ/d. The menstrual cycle is a significant contributor to variation in energy expenditure through progesterone-mediated increases in metabolic rate. Variation in metabolic energy expenditure was detectable when the contributory components of 24-hour energy expenditure were measured.