Cross-Sectional Associations of Metabolically Healthy Obesity, Lifestyle Factors, and Steatotic Liver Disease in Adults from the Fels Longitudinal Study

Objective: To examine the associations of metabolic health and obesity phenotypes with liver fat accumulation and hepatic steatosis in adults. Methods: We analyzed 676 non-Hispanic white adults (18–95 years; 55.8% female) from the Fels Longitudinal Study using a cross-sectional design. Participants were classified into metabolically healthy normal weight (MHNW), metabolically healthy obesity (MHO), metabolically unhealthy normal weight (MUNW), and metabolically unhealthy obesity (MUO) phenotypes. Metabolically unhealthy status was defined as the presence of ≥1 metabolic dysfunction, consistent with prior epidemiological definitions; secondary analyses using ≥2 were also performed. Obesity was defined using DXA-derived body fat percentage. Liver fat (%) was quantified using magnetic resonance imaging, and hepatic steatosis was defined as liver fat > 5.56%. Multivariable linear and probit regression models were used to evaluate associations, adjusting for demographic and lifestyle covariates; secondary models additionally examined dietary intake. Results: Mean liver fat was 5.95% (SE = 0.23), and steatosis was present in 29.8% of participants. Compared to MHNW individuals, liver fat was significantly higher in MHO (mean 3.77% vs. 2.67%), MUNW (4.63%), and MUO (8.47%) phenotypes. After covariate adjustment, liver fat was 33.8% (95% CI: 13.7–57.5%) higher in MHO, 28.1% (10.1–49.0%) higher in MUNW, and 113.0% (85.3–144.7%) higher in MUO relative to MHNW. Corresponding increases in steatosis probabilities were observed across phenotypes. No individual dietary component or dietary pattern was significantly associated with liver fat after adjustment. Conclusions: Metabolically healthy obesity was associated with higher liver fat and steatosis probability compared with metabolically healthy normal weight, with levels comparable to metabolically unhealthy normal weight individuals. These findings suggest that the absence of overt metabolic abnormalities does not necessarily indicate a metabolically benign state with respect to liver fat accumulation. Given the cross-sectional design, these results should be interpreted as associations rather than causal relationships.