Association of skeletal muscle mass indices and adiposity with ultrasonography-detected hepatic steatosis in Tibetan and Han adults: a cross-sectional study

Abstract Background Low muscle mass with adiposity has been linked to steatotic liver disease, but classification depends on how skeletal muscle mass is normalized. Evidence including Tibetan adults remains limited. Methods We conducted a retrospective cross-sectional study enrolling 2,070 adults (1,563 Tibetans, 507 Han) undergoing a health examination. Body composition was assessed using bioelectrical impedance analysis (BIA). Body-composition phenotypes were defined using appendicular skeletal muscle mass index (ASMI) combined with sex-specific body fat percentage (BFP) cut-offs; weight-standardized skeletal muscle index (SMI) and predicted skeletal muscle mass percentage served as supplementary analyses. The outcome measures were ultrasonography-detected hepatic steatosis (HS) and metabolic dysfunction-associated steatotic liver disease (MASLD). Logistic regression and modified Poisson regression models were used to estimate odds ratios (ORs) and adjusted prevalence ratios (aPRs); ethnic interactions and exploratory FIB-4/VCTE analyses were also evaluated. Results Under the ASMI-based definition, low ASMI with adiposity was uncommon (7.9% Tibetan; 9.1% Han), whereas HA only was common (58.7%; 48.9%). HS prevalence was 52.1% and 48.1%; MASLD prevalence was 50.7% and 46.4%. In age- and sex-adjusted models, HA only showed the strongest associations with HS (Tibetan OR 6.89, aPR 2.50; Han OR 5.65, aPR 2.30) and MASLD (Tibetan OR 8.41, aPR 2.92; Han OR 6.26, aPR 2.46). The ASMI-based combined phenotype was not associated with either outcome. Weight-normalized SMI classified more participants as low relative muscle mass with adiposity and produced stronger apparent associations. Ethnicity × phenotype interactions were not significant. FIB-4 findings were attenuated after adjustment and not corroborated by VCTE liver stiffness. Conclusions In adults undergoing urban health examination, high adiposity was the most consistent body-composition correlate of prevalent HS and MASLD. Apparent low muscle mass with adiposity signals were highly sensitive to muscle mass normalization. Prospective studies should include functional muscle measures and fibrosis staging.