Early menstrual cycle phases do not change the energy metabolism and physical performance of young women

BACKGROUND: During the menstrual cycle (MC) changes in the secretion of hormones that perform physiological functions related to metabolism occur. This study aimed to evaluate the resting metabolic rate (RMR), substrate oxidation, peak of oxygen uptake (VO2peak), and body composition in the early follicular (EF) and early luteal (EL) phases of young women.METHODS: Cross-sectional study, with 21 eumenorrheic women, aged 24±4, which started the project and should be evaluated in both EF and EL. Data are expressed as mean and standard deviation, T, Wilcoxon and Spearman tests were used after the normality was checked by Shapiro-Wilk Test. Also, the Rout test was used (Q=1%), in GraphPad Prism 8 (P<0.05).RESULTS: Sixteen women completed both phases, with Body Mass Index (BMI) 24±3 kg/m². They had a RMR (kcal) of 1355±229 EF and 1392±262 EL (P=0.580). Also, no differences were found in physical performance, with the VO2peak (mLO2/kg/min) of 35±5 EF and 36±6 EL (P=0.256). The rate of extracellular water 0.375±0.009 EF and 0.373±0.007 EL (P=0.029) and waist circumference (cm) 73±7 EF and 71±6 EL (P=0.035) were lower in EL.CONCLUSIONS: The results may demonstrate that physiological changes in the MC do not affect the energy metabolism of young women. In the EF and EL phases, women can be evaluated in clinical studies.