Body weight categories and fat distribution in relation to all-cause mortality among adults with metabolic dysfunction-associated steatotic liver disease: a population-based analysis of NHANES, 2007–2018

OBJECTIVE: Although body mass index (BMI)-defined non-obesity metabolic dysfunction-associated steatotic liver disease (MASLD) predicts poor prognosis, the role of visceral adiposity and weight-based phenotypes is unclear. This study aimed to examine the clinical correlates of four unique MASLD phenotypes based on BMI and waist-to-height ratio (WHtR) and to assess the prognostic value of this classification with respect to mortality. DESIGN: Population-based cross-sectional study with prospective mortality follow-up. SETTING: Nationally representative US population derived from the National Health and Nutrition Examination Survey (NHANES), 2007-2018. PARTICIPANTS: 6300 adults with MASLD, sampled from NHANES 2007 to 2018. METHODS: Participants were allocated into four phenotypes based on obesity/lean and central adiposity status. Obesity was defined as BMI≥30 kg/m², while those without obesity were determined as lean. High central adiposity was defined as WHtR≥0.6. PRIMARY OUTCOME MEASURE: The primary outcome was all-cause mortality. This was ascertained through National Death Index linkage with follow-up censored at 31 December 2019. RESULTS: Among adults with MASLD, 72.1% had obesity with high central adiposity (mean follow-up: 6.9±3.5 years). The non-obesity, high central adiposity phenotype (9.6%) exhibited the highest rates of hypertension (60.2%), type 2 diabetes (31.8%) and chronic kidney disease (23.3%). This phenotype portended the poorest 6-year survival (p<0.001) and was independently associated with higher all-cause mortality (adjusted HR (aHR) 3.1, 95% CI 1.3 to 7.7). A J-shaped association was observed between BMI and mortality, with increasing WHtR linked to elevated risk. CONCLUSION: Non-obesity MASLD with high central adiposity confers the poorest survival and cardiometabolic burden.