Reduced skeletal muscle mass and elevated phase angle are linked to metabolic dysfunction-associated steatotic liver disease in Japanese males

• The effect of body composition on metabolic dysfunction-associated steatotic liver disease (MASLD) remains unclear. • In our study, which included a Japanese health checkup population, reduced skeletal muscle mass and elevated phase angle were independent factors for the presence of MASLD in males, whereas no such association was found in females. • Our findings expand the existing knowledge regarding the pathophysiological role of body composition in MASLD in the general population. This study aimed to elucidate the effects of body composition, particularly muscle mass, on metabolic dysfunction-associated steatotic liver disease (MASLD). Additionally, the association between phase angle (PhA) and MASLD was evaluated. This cross-sectional study recruited university staff and faculty members at Gifu University who underwent annual health checkups. Health checkup data and liver ultrasonography findings were used to diagnose MASLD. Skeletal muscle mass index (SMI), fat mass index (FMI), and PhA were measured using bioelectrical impedance analysis. A sex-stratified multivariable logistic regression model was used to investigate independent factors for the presence of MASLD, and the restricted cubic spline (RCS) model demonstrated the influence of body composition on MASLD. Among the 624 participants (median age, 46 years), 320 (51%) were males. The prevalence of MASLD was 27% in total, 38% in males, and 16% in females. In sex-stratified multivariable logistic regression models, SMI (odds ratio [OR], 0.33; 95% confidence interval [CI], 0.13–0.82; p = 0.018) and PhA (OR, 5.11; 95% CI, 2.14–12.77; p < 0.001) were independent factors for the presence of MASLD in males, whereas this relationship was not observed in females. The adjusted RCS models demonstrated an inverse linear relationship between SMI and MASLD and a positive association between SMI and MASLD in males but not in females. Skeletal muscle loss and elevated PhA affect the presence of MASLD in Japanese male adults. Further investigations are required to elucidate the sex-specific effects of body composition on MASLD.