Muscle fat content is strongly associated with NASH: A longitudinal study in patients with morbid obesity

Studies exploring the relationship between muscle fat content and non-alcoholic fatty liver disease (NAFLD) are scarce. Herein, we aimed to evaluate the association of muscle mass and fatty infiltration with biopsy-assessed NAFLD in patients with obesity.

At inclusion (n = 184) and 12 months after a dietary intervention (n = 15) or bariatric surgery (n = 24), we evaluated NAFLD by liver biopsy, and skeletal muscle mass index (SMI) by CT (CT-SMI) or bioelectrical impedance analysis (BIA-SMI). We developed an index to evaluate absolute fat content in muscle (skeletal muscle fat index [SMFI]) from CT-based psoas muscle density (SMFI_Psoas).

Muscle mass was higher in patients with NAFLD than in those without (CT-SMI 56.8 ± 9.9 vs. 47.4 ± 6.5 cm²/m², p <0.0001). There was no association between sarcopenia and non-alcoholic steatohepatitis (NASH). SMFI_Psoas was higher in NASH ≥F2 and early NASH F0-1 than in NAFL (78.5 ± 23.6 and 73.1 ± 15.6 vs. 61.2 ± 12.6, p <0.001). A 1-point change in the score for any of the individual cardinal NASH features (i.e. steatosis, inflammation or ballooning) was associated with an increase in SMFI_Psoas (all p <0.05). The association between SMFI_Psoas and NASH was highly significant even after adjustment for multiple confounders (all p <0.025). After intervention (n = 39), NASH improvement, defined by NAFLD activity score <3 or a 2-point score reduction, was achieved in more than 75% of patients (n = 25 or n = 27, respectively) that had pre-established NASH at inclusion (n = 32) and was associated with a significant decrease in SMFI_Psoas (p <0.001). Strikingly, all patients who had ≥11% reduction in SMFI_Psoas achieved NASH improvement (14/14, p <0.05).

Muscle fat content, but not muscle mass, is strongly and independently associated with NASH. All individuals who achieved a ≥11% decrease in SMFI_Psoas after intervention improved their NASH. These data indicate that muscle fatty infiltration could be a potential marker for (and perhaps a pathophysiological contributor to) NASH.

The fat content in skeletal muscles is highly reflective of the severity of non-alcoholic fatty liver disease (NAFLD) in patients with morbid obesity. In particular, muscle fat content is strongly associated with non-alcoholic steatohepatitis (NASH) and decreases upon NASH improvement. These data indicate that muscle fatty infiltration could be a marker and possible pathophysiological contributor to NASH.