Knowledge Bank

The menstrual cycle’s hormonal fluctuations significantly impact women’s physiology, influencing metabolism, body composition, and physical performance. Resting energy expenditure (REE), accounting for 60–75% of daily energy expenditure, tends to increase during the luteal phase compared to the follicular phase. However, inconsistent methods for identifying menstrual phases have limited the validation of these findings. Respiratory Quotient (RQ) is a measure of carbohydrate and fat oxidation, and provides further insight into metabolic changes across the cycle. Research suggests that body composition and substrate oxidation vary, particularly during the luteal phase, though individual responses differ. Fluid retention, a common menstrual symptom, peaks on the first day of menses when estradiol and progesterone levels are lowest, highlighting the dynamic relationship between hormones and physiological changes. The Strategic Hormonal Evaluation and Instrument-Reliability Study (SHE IS) examines these relationships by analyzing hormonal blood markers (follicle stimulating hormone, Luteinizing Hormone, estrogen, progesterone) and their effects on body composition, REE, RQ, fluid retention (via InBody), and muscle strength/endurance (using Biodex). The study integrates femtech devices (Mira, OvuSense, Femometer) for precise cycle tracking. Eleven women (27.4 ± 7 years) are enrolled, with most completing at least two monitored cycles. A one-way repeated-measures ANOVA was conducted to evaluate changes across menstrual phases (α=0.05). Analysis revealed trends toward significance for total body water weight (p=0.065) and REE (p=0.052). Total fat mass changes were not significant (p=0.191), but RQ showed significant variation across phases (p=0.041). No post hoc significance was found, though the luteal phase exhibited the greatest variation. These findings suggest promising trends, emphasizing the need for more participants to enhance statistical power. Preliminary SHE IS data aligns with prior research, indicating increased REE and body composition changes during the luteal phase. This study highlights the scarcity of longitudinal, high-quality research in this field and underscores the value of femtech for precise cycle tracking. Continued funding and innovation are crucial to advancing menstrual health research and improving personalized health solutions for women.