Introduction
Metabolic dysfunction–associated steatotic liver disease (MASLD) has traditionally been linked with obesity and metabolic syndrome. However, an emerging subset—lean MASLD—is increasingly recognised, particularly in Asian populations. Despite having a normal body mass index, these patients exhibit metabolic dysfunction and hepatic steatosis. The long-term clinical implications of lean MASLD have remained unclear, with conflicting data regarding whether it represents a milder or equally aggressive phenotype compared to non-lean MASLD.
Problem Statement
Current clinical paradigms often underestimate lean MASLD due to the absence of obesity, leading to delayed diagnosis and risk stratification. There is a major gap in understanding whether lean MASLD carries similar, lower, or higher risks of liver-related events, mortality, and cardiovascular outcomes compared to non-lean MASLD.
Summary
This large multicohort prospective study involving over 180,000 patients across Western and Asian populations provides important clarity. Lean MASLD was associated with significantly higher risks of liver-related events, liver-related mortality, and overall mortality, highlighting a more aggressive hepatic phenotype despite normal BMI. Interestingly, lean MASLD showed similar risks of hepatocellular carcinoma and extrahepatic cancers, but lower cardiovascular disease risk compared to non-lean MASLD.
These findings redefine lean MASLD as a high-risk but under-recognized clinical entity, emphasizing that absence of obesity does not imply a benign course. Clinicians must adopt a metabolic and liver-focused approach rather than BMI-based risk assessment, ensuring early detection, monitoring, and targeted management in this overlooked population.