Association of Exercise and Dietary Habits With Muscle and Fat Mass in Healthy Working-Age Adults: A Cross-Sectional Study.

Introduction Age-related changes in body composition, particularly sarcopenia and fat accumulation, have been widely studied in older adults, but data on healthy working-age populations remain limited. This study aimed to investigate the associations between exercise habits, dietary intake, and body composition in healthy adults aged 20-59 years. Methods A cross-sectional study was conducted among 1,738 employees undergoing health checkups. Body composition was assessed using bioelectrical impedance analysis (BIA). Exercise frequency and dietary habits were evaluated via questionnaire. Skeletal muscle mass index (SMI) and body fat mass index (BFMI) were calculated, and associations were analyzed by sex. Results SMI remained stable across age groups in men but increased with age in women; BFMI increased with age in both sexes. Regular exercise was significantly associated with higher SMI but not with BFMI. Intake of fish, soy products, and dairy products correlated with higher SMI, while higher fat intake was associated with increased BFMI. Conclusion Exercise habits and protein-rich diets were associated with greater skeletal muscle mass, while fat mass appeared to be more influenced by age and dietary fat intake. Further longitudinal studies are needed to clarify the causal pathways for sarcopenia prevention in working-age populations.