Impact of Follicular Menstrual Phase on Body Composition Measures and Resting Metabolism.

Purpose To identify the effects of early follicular (EF) and mid-follicular (MF) menstrual phases on body composition, metabolic rate (RMR), and respiratory quotient (RQ) assessment accuracy to identify an optimal testing period. Methods Body composition was obtained from a 4-compartment (4C) criterion model (fat mass [FM], fat-free mass [FFM], body fat percent [%fat] and dual-energy X-ray absorptiometry (DXA; FM, lean mass [LM], trunk FM [TFM], and trunk LM [TLM]) in 19 eumenorrheic females (Mean±Standard Deviation [SD]: Age 21.3±3.1 yrs, Body Mass Index 23.6±1.8 kg/m2). RMR (kcal/day) and RQ (a.u.) were measured via indirect calorimetry for 25 minutes. Body composition, RMR, and RQ were measured during the EF and MF phases. Dependent samples t-tests were used to compare outcomes between EF and MF. Results 4C outcomes were similar between phases (p>0.05). During EF, the following 4C components were significantly greater (p 0.05), however, DXA FM was significantly greater during EF (MD±SD: 0.29±0.40 kg; p=0.005), yet within measurement error of the device. While RMR was not significantly different between phases (MD±SD: 6.0±190.93 kcal/day; p>0.05), RQ was significantly higher during EF (Mean±SD: 0.03±0.06 a.u.; p=0.029) compared to MF. Conclusions Body composition from 4C and DXA do not appear to be impacted beyond measurement error as a result of compartmental changes from the menstrual cycle. During MF, women oxidized more fat as demonstrated by a lower RQ. Researchers should aim to be more inclusive and schedule testing for females within 11-12 days from the onset of menstruation.