Waist-to-Height Ratio Reveals Hidden Metabolic Risk in Lean Individuals with MASLD.

BACKGROUND: Lean metabolic dysfunction-associated steatotic liver disease (MASLD) can be overlooked in adults with a normal body mass index (BMI). We examined whether waist-to-height ratio (WHtR), a simple marker of central adiposity, was associated with prevalent lean MASLD and explored its relative contribution within an anthropometric and metabolic feature set. METHODS: This cross-sectional study used National Health and Nutrition Examination Survey (NHANES) 2021-2023 data for exploratory model development (n = 770) and NHANES 2017-2020 data for independent validation (n = 809). Lean MASLD was defined as controlled attenuation parameter-based steatosis plus at least one cardiometabolic risk factor after excluding participants whose classification depended only on waist circumference. Machine-learning models were used for exploratory feature ranking; the validation analysis used survey-weighted logistic regression and restricted cubic splines. RESULTS: In exploratory model comparison, gradient boosting had the highest discrimination (area under the receiver operating characteristic curve 0.762), and WHtR had the largest mean absolute SHAP value in that model. In the validation cohort, weighted lean MASLD prevalence increased from 2.15% in the lowest WHtR quartile to 36.93% in the highest (P for trend < 0.001). Each 0.01 increase in WHtR was associated with higher odds of prevalent lean MASLD after multivariable adjustment (odds ratio 1.16, 95% confidence interval 1.10-1.22; P = 0.009). CONCLUSIONS: Higher WHtR was independently associated with prevalent lean MASLD in a representative sample of adults with normal BMI. WHtR may be useful as a simple marker for identifying lean adults who warrant further assessment.