Lean MASLD: Histologic Severity and Prognostic Outcomes
Global Study Insights on Lean MASLD
Clinicians traditionally associate metabolic dysfunction-associated steatotic liver disease with excess body weight. However, normal-weight individuals also develop lean MASLD across global populations. A multinational team analyzed data from 41 countries involving 18,326 adults with biopsy-proven disease. Consequently, this study provides vital clarity on histologic disease severity and long-term prognosis.
Histologic Features and Asian Prevalence
Notably, lean MASLD showed the highest prevalence in Asia, exceeding 11% by body mass index and waist circumference. In contrast, overall prevalence was 6.7% by body mass index across the global cohort. Patients with lean disease exhibited a lower prevalence of type 2 diabetes than overweight individuals. Furthermore, lean patients demonstrated significantly lower Non-Alcoholic Fatty Liver Disease Activity Scores. Advanced fibrosis also occurred less frequently in lean individuals compared to those with obesity. Therefore, lean patients generally present with a milder histologic profile at initial biopsy.
Diagnostic Accuracy of Noninvasive Tests
Accurate noninvasive fibrosis assessment remains essential for routine clinical risk stratification. Interestingly, the commonly used FIB-4 score showed lower accuracy in lean individuals than in obese patients. In contrast, liver stiffness measurement via transient elastography performed with superior diagnostic accuracy. Specifically, elastography achieved an area under the curve of 0.87 in the lean group. Therefore, clinicians should prioritize elastography over blood-based scores when evaluating lean patients.
Prognostic Significance of Fibrosis Severity
Despite milder baseline histology, clinical outcomes showed important nuances during follow-up. For instance, lean status itself was not an independent predictor of all-cause mortality or adverse clinical events. Instead, advanced fibrosis independently predicted severe liver decompensation and death across all weight classes. Patients with stage F3 or F4 fibrosis faced more than three times the risk of clinical events. Thus, fibrosis stage remains the primary driver of long-term prognosis regardless of body habitus. Ultimately, clinicians must look beyond body weight when assessing overall disease risk.
Frequently Asked Questions
Q1: What defines lean MASLD in clinical practice?
Clinicians define lean MASLD when hepatic steatosis and cardiometabolic risk factors occur in individuals with a normal body mass index.
Q2: Is lean MASLD associated with lower long-term mortality?
No, evidence indicates that lean patients experience similar long-term mortality and clinical event rates compared to overweight individuals with comparable fibrosis.
Q3: Which noninvasive test is preferred for assessing fibrosis in lean MASLD?
Liver stiffness measurement by transient elastography provides superior diagnostic accuracy compared to the FIB-4 score in lean patients.
References
- de Avila L et al. Histologic Features and Clinical Outcomes of Lean Metabolic Dysfunction-Associated Steatotic Liver Disease. JAMA. 2026 Sep 30. doi: 10.1001/jama.2026.18491. PMID: 42814439.
- Rinella ME, Lazarus JV, Ratziu V, et al. A multi-society Delphi consensus statement on new fatty liver disease nomenclature. Hepatology. 2023;78(6):1966-1986.
- Chan KE, Koh TJL, Tang ASP, et al. Global Prevalence, Characteristics, and Clinical Outcomes of Lean Non-alcoholic Fatty Liver Disease: A Systematic Review and Meta-analysis. Lancet Gastroenterol Hepatol. 2023;8(6):534-547.
