Association Between Skeletal Muscle Mass and Fatty Liver Index; Insights From NHANES (2017–2020)

Background: Skeletal muscle reduction has been linked to adverse metabolic outcomes, but its association with fatty liver index (FLI) remains unclear. Objective: This study investigates the association between skeletal muscle and FLI, exploring subgroup differences based on demographic and metabolic characteristics. Methods: We conducted a cross-sectional analysis of 1,121 participants aged ≥20 years using NHANES 2017–2020 data. Skeletal muscle was assessed via appendicular skeletal muscle mass index (ASM/BMI), and FLI was calculated using validated equations. Logistic regression and restricted cubic spline (RCS) analysis were used to examine linear and nonlinear associations, while subgroup analyses stratified the results by sex, age, and other covariates. Results: Skeletal muscle reduction was significantly associated with elevated FLI risk (OR=1.27, 95% CI: 1.01–1.60, P =0.047) in fully adjusted models. The association was stronger in males (OR=1.54, P =0.016), older adults (>56 years; OR=1.28, P =0.047), and non-diabetic participants (OR=1.38, P =0.048). RCS analysis revealed a near-linear relationship ( P for non-linearity=0.056). Conclusion: Skeletal muscle reduction independently predicts high FLI, particularly in specific subgroups. Interventions targeting muscle preservation may mitigate FLI-related metabolic risks.