Appendicular skeletal muscle mass is associated with metabolic dysfunction-associated steatotic liver disease severity in young men: a cross-sectional and longitudinal study.

Background and aim: Although appendicular skeletal muscle mass (ASM) has been linked to the severity of hepatic steatosis, investigations of its correlation among younger age groups are lacking. We aimed to elucidate the role of ASM in determining the severity of metabolic dysfunction-associated steatotic liver disease (MASLD) in younger patients.

Methods: Retrospective data were collected from patients younger than 35 years who visited the Armed Forces Goyang Hospital between June 2022 and February 2024. Steatosis presence was determined by a controlled attenuation parameter score ≥ 250 dB/m, and significant fibrosis was identified with liver stiffness measurement > 8.0 kPa. ASM was measured using multifrequency bioelectrical impedance analysis (InBody 620).

Results: Of 910 participants, 630 were diagnosed with MASLD. Patients with MASLD had lower ASM/fat mass (ASM/F) (1.02 vs. 1.91; p < 0.001), ASM/body mass index (BMI) (0.91 vs. 1.04/m²; p < 0.001), and ASM/body weight (ASM/W) (29.5% vs. 33.8%; p < 0.001) than non-MASLD patients. Additionally, ASM/F, ASM/BMI, and ASM/W significantly decreased with worsening steatosis severity and were notably lower in patients with significant fibrosis. Among 107 patients with MASLD who underwent two examinations with a median interval of 6.0 months, those with increased ASM/F showed a higher proportion of steatosis regression and a lower proportion of steatosis worsening than those with decreased ASM/F (steatosis regression, 43.1% vs. 22.9%; worsening, 11.1% vs. 28.6%; p = 0.031). All three ASM indices were significant factors in steatosis regression during the study period.

Conclusions: ASM is associated with the severity of steatosis and significant fibrosis in MASLD in young adults < 35 years.