Waist-to-Height Ratio as a Simple Anthropometric Marker for Identifying Individuals at High Risk of MASLD: A Large Population-Based Analysis Using the Fatty Liver Index

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease worldwide and represents a major component of the global burden of metabolic disorders. Simple anthropometric markers capable of identifying individuals at increased risk of hepatic steatosis are of considerable interest for population-level screening. Methods: In this cross-sectional population-based study, we evaluated the performance of waist-to-height ratio (WtHR) for identifying individuals with a high Fatty Liver Index (FLI ≥ 60), a widely used surrogate marker of hepatic steatosis. The study included 146,318 adult participants with available anthropometric and biochemical data. Discriminatory performance was assessed using receiver operating characteristic (ROC) curve analysis. Optimal WtHR thresholds were determined using the Youden index. Associations between WtHR and high FLI were evaluated using age-adjusted logistic regression models. Non-linear relationships were explored using restricted cubic spline models. Additional analyses included a comparison with body mass index (BMI) and waist circumference, decision curve analysis, and subgroup analyses across age and BMI strata. Results: The prevalence of high FLI in the study population was 18.1%. WtHR demonstrated excellent discriminatory performance, with area under the ROC curve (AUC) values of 0.908 (95% CI 0.906–0.910) in men and 0.972 (95% CI 0.971–0.974) in women. Optimal WtHR thresholds for identifying individuals with high FLI were 0.52 in men and 0.53 in women. Each 0.01 increase in WtHR was strongly associated with higher odds of high FLI (OR 1.56 in men and 1.69 in women). Restricted cubic spline analysis demonstrated a non-linear relationship, with a marked increase in predicted probability of high FLI above WtHR values of approximately 0.50–0.52. WtHR showed discriminatory performance comparable to BMI and waist circumference and maintained strong associations with high FLI across age groups and BMI categories. Conclusions: Waist-to-height ratio is a simple anthropometric marker strongly associated with a high Fatty Liver Index in a large population-based cohort. Given its simplicity, low cost, and ease of calculation, WtHR may represent a practical screening indicator for identifying individuals at increased risk of MASLD-related phenotypes in both clinical practice and population health strategies.