Severe obesity is associated with worse outcomes than lean metabolic dysfunction-associated steatotic liver disease.

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) is highly prevalent in people with obesity. We aimed to study the association of body mass index (BMI) with clinical outcomes in patients with MASLD.

Methods: A retrospective cohort of 32,900 patients with MASLD, identified through the International Classification of Diseases-9 and 10 codes within the electronic health records of a large US-based health system, with a mean follow-up of 5.5 years (range: 1-15 y), was stratified into 6 BMI categories, <25, 25-<30, 30-<40, 40-<50, and ≥50 kg/m2.

Results: The risk of liver decompensation and extrahepatic obesity-associated cancers had a J-shaped profile (both ps for linear and quadratic terms <0.05). Compared to patients with BMI 25-<30 kg/m2, the adjusted HRs (95% CIs) for liver decompensation of patients with BMI <25 and BMI ≥50 kg/m2 were 1.44 (1.17-1.77) and 2.27 (1.66-3.00), respectively. The corresponding figures for obesity-associated extrahepatic cancer were 1.15 (0.97-1.36) and 1.29 (1.00-1.76). There was an inverse association for BMI with liver transplantation and non-obesity-associated cancer (both ps for linear terms <0.05), but no association with HCC or all types of cancers combined. A similar J-shaped association between BMI and all-cause mortality was observed; adjusted HRs (95% CIs) for BMI <25 and ≥50 kg/m2 were 1.51 (1.32-1.72) and 3.24 (2.67-3.83), respectively, compared with BMI 25-<30 kg/m2 (both ps for linear and quadratic terms <0.001).

Conclusions: Patients with MASLD and very severe obesity (BMI ≥50 kg/m2) had the highest risk, exceeding that of patients with lean MASLD, for developing liver decompensation, obesity-associated extrahepatic cancers, or dying from any cause.