Beyond BMI : Reassessing the Prevalence of Obesity in Patients With MASLD Under the Lancet Commission Diagnostic Criteria

Aims To examine obesity prevalence and reclassification under the new Lancet Commission on Obesity criteria among adults aged 18–59 years with metabolic dysfunction–associated steatotic liver disease (MASLD), including BMI‐defined lean‐MASLD. Methods We analysed NHANES 2017–2018 data from adults aged 18–59 years with MASLD, the age range available for dual‐energy X‐ray absorptiometry (DEXA) in adults of NHANES. Obesity was defined using the new Lancet Commission criteria and the traditional BMI‐based criteria. The new criteria incorporated waist circumference, waist‐to‐hip ratio, waist‐to‐height ratio and body fat percentage measured by DEXA. Individuals were classified as having obesity if any of the following conditions were met: (1) BMI ≥ 40 kg/m 2 ; (2) elevated BMI in combination with at least one elevated anthropometric measure; (3) at least two elevated anthropometric measures, irrespective of BMI; (4) excess body fat assessed by DEXA. Elevated BMI and traditional obesity was defined as BMI ≥ 27.5 kg/m 2 for Asian and BMI ≥ 30 kg/m 2 for other ethnicities. Results (1) The new criteria increased the estimated prevalence of obesity among patients with MASLD from 66.8% (95% CI, 60.6%–72.4%) to 98.3% (95% CI, 97.3%–99.0%). (2) Among MASLD patients classified as non‐obese by traditional criteria, 94.9% were reclassified as obese under the new criteria. (3) Among BMI‐defined lean‐MASLD, 84.2% met the new obesity criteria. Conclusion Among adults aged 18–59 years with MASLD, the new obesity criteria increased the estimated prevalence of obesity to 98.3%. Moreover, 94.9% of individuals considered non‐obese by traditional BMI criteria and 84.2% of those with BMI‐defined lean MASLD met the new obesity criteria.