Potential mediating role of triglycerides in the nonlinear association between body roundness index and MASLD in nondiabetic adults

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most prevalent chronic liver disease globally, with visceral adiposity and dyslipidemia as key drivers. The body roundness index (BRI) is a novel anthropometric marker of visceral adiposity. Still, its nonlinear association with MASLD—including potential threshold effects and mechanistic mediators—remains underexplored in non-diabetic populations. We conducted a cross-sectional analysis of 15,464 non-diabetic participants from the 2004–2015 NAGALA cohort. Multivariable logistic regression evaluated the independent association between BRI and MASLD, generalized additive models (GAMs) characterized nonlinearity and threshold effects, and formal mediation analysis quantified the mediating role of serum triglycerides (TG). A total of 2,427 (15.7%) participants were diagnosed with MASLD. After full adjustment for confounders, higher BRI was independently associated with increased MASLD risk (OR = 2.56, 95% CI: 2.31–2.84), with stronger associations observed in women, individuals < 40 years, those with BMI < 25 kg/m², and non-hypertensive participants. GAM analysis revealed an inverted-U-shaped relationship between BRI and MASLD, with a saturation threshold at BRI = 4.80. Mediation analysis suggested a potential partial mediating effect of TG in this association, accounting for 12.08% of the total statistical effect (indirect effect = 0.013; 95% CI: 0.010–0.015). In non-diabetic adults, elevated BRI is strongly and nonlinearly associated with MASLD risk in a threshold-dependent manner, even in traditionally low-risk subgroups. Serum TG may serve as a potential mediator in the pathway from visceral adiposity (as reflected by BRI) to hepatic steatosis, providing observational association evidence for MASLD pathological pathways requiring further prospective research.