A large multinational retrospective study of more than 18,000 adults with metabolic dysfunction-associated steatotic liver disease (MASLD) found that being lean offered no protective benefit. Patients with lean MASLD had similar risks of all-cause mortality and clinical events—such as hepatocellular carcinoma, hepatic decompensation, or liver transplant—compared with those who were overweight or obese. The findings held whether leanness was defined by body mass index or waist circumference.
The strongest predictor of poor outcomes was advanced histologic fibrosis, which was associated with more than double the risk of death and more than triple the risk of clinical events. Although advanced fibrosis was slightly less common in lean patients (29.3% vs 37.2%), the authors concluded that normal body weight should not be interpreted as indicating lower risk in established MASLD. They emphasized that risk stratification should focus on fibrosis severity rather than anthropometric phenotype.
An accompanying editorial noted that lean MASLD may be missed in primary care and specialty settings because clinicians often do not suspect liver disease in patients with normal BMI. The editorial also suggested that management of lean MASLD may require different lifestyle goals, including attention to diet quality, insulin sensitivity, and muscle mass preservation, and that lean patients with advanced fibrosis should not be excluded from pharmacologic treatment solely because they lack obesity.
The study had limitations, including a lack of detailed data on diet, physical activity, genetics, alcohol exposure, and body composition, which could introduce residual confounding. Nevertheless, the findings reinforce that fibrosis assessment, not body size, should guide clinical decisions in MASLD.