Appetite and Energy Intake in Laboratory and Free-Living Conditions Remain Consistent Across Menstrual Cycle Phases when Using Precise Measurement Methods

Self-reported dietary intake varies across menstrual cycle phases, but objective assessments of dietary intake together with appetite and resting metabolic rate (RMR) are limited. This study aimed to assess differences in appetite, dietary intake, and RMR during two hormonally-distinct menstrual cycle phases in laboratory and free-living settings. Healthy premenopausal females with predictable normal-length menstrual cycles completed two study visits: one in the late-follicular and one in the mid-luteal phase. Menstrual cycle phases were identified using urinary luteinizing hormone surge and cycle days. Participants consumed a 2-day energy- and macronutrient-balanced run-in diet prior to each visit. RMR was measured with indirect calorimetry, followed by appetite ratings before and after a standardized breakfast, and completed a food cravings questionnaire. Appetite was also tracked for 2.5 days post-visit in a free-living environment. Ad libitum energy and macronutrient intake were measured using pre-weighed plus weighing of uneaten food at an in-laboratory lunch meal, as well as during the 2.5-day free-living period. Eighteen participants were included (age: 21±4 years; body mass index: 21.2±1.5 kg/m 2 ). There were no differences between in-laboratory ad libitum energy or macronutrient intakes, appetite, or food cravings between phases. RMR did not differ between phases, although the mid-luteal phase RMR trended toward higher (104±218 kcal/day higher ; P =0.074). No main nor interaction effects for phase and time were observed for free-living dietary intake nor appetite ratings. Accurate measurements show no differences in appetite or energy intake between menstrual cycle phases, though RMR may be slightly elevated in the luteal phase.