Role of Lifestyle and Nutrition in Menstrual Cycle Regularity: Associations with Body Composition and Dietary Habits

Background: Nutritional status and lifestyle factors are increasingly recognized as relevant modulators of women’s reproductive health. However, data remain limited on the relationship between body composition, dietary habits, and menstrual cycle characteristics in apparently healthy young women. This study aimed to assess nutritional status, body composition, and lifestyle behaviors in young women and to explore their associations with menstrual cycle regularity. Methods: This cross-sectional study included 49 apparently healthy women aged 19–30 years. Anthropometric measurements and body composition were assessed using bioelectrical impedance analysis. Dietary habits were evaluated through a simplified food frequency questionnaire, and adherence to the Mediterranean diet was assessed using the PREDIMED score. Physical activity was estimated using MET values based on the Compendium of Physical Activities. Menstrual cycle characteristics were collected via questionnaire. Group comparisons were performed between women with regular and irregular menstrual cycles. Results: The sample was predominantly normal-weight (mean BMI 22.36 ± 4.26 kg/m2). Anthropometric and bioelectrical impedance parameters did not differ significantly between women with regular and irregular cycles. Women with irregular cycles showed higher resistance and extracellular water and lower phase angle and body cell mass, although differences were not statistically significant. A significant association was found for meat consumption, which was lower in women with irregular cycles (p = 0.007). No associations were observed for other dietary variables, physical activity, or meal frequency. Conclusions: Menstrual regularity in young women was not associated with major anthropometric differences but may be linked to subtle aspects of nutritional status and dietary habits. Lower meat consumption emerged as a potential dietary factor associated with menstrual irregularity. Although associations were modest, these findings support the relevance of nutritional and lifestyle factors in menstrual health. Larger longitudinal studies are needed to clarify these relationships.