Natural History of Nonalcoholic Fatty Liver Disease With Normal Body Mass Index: A Population-Based Study

Background & Aims: The natural history of lean nonalcoholic fatty liver disease (NAFLD) is not well-understood. Consequently, patient counseling and disease management are limited. We aimed to compare the natural history of lean, overweight, and obese NAFLD in a U.S. population with long-term follow-up. Methods: All adults diagnosed with NAFLD in Olmsted County, MN between 1996 and 2016 were identified, and all subsequent medical events were ascertained using a medical record linkage system. Subjects were divided on the basis of body mass index (BMI) at NAFLD diagnosis into 3 groups: normal, overweight, and obese. The probability to develop cirrhosis, decompensation, malignancies, cardiovascular events, or death among the 3 groups was estimated by using the Aalen-Johansen method, treating death as a competing risk. The impact of BMI categories on these outcomes was explored by using Cox proportional hazards regression analysis. Results: A total of 4834 NAFLD individuals were identified: 414 normal BMI, 1189 overweight, and 3231 obese. Normal BMI NAFLD individuals were characterized by a higher proportion of women (66% vs 47%) and lower prevalence of metabolic comorbidities than the other 2 groups. In reference to obese, those with normal BMI NAFLD had a nonsignificant trend toward lower risk of cirrhosis (hazard ratio [HR], 0.33, 95% confidence interval [CI], 0.1–1.05). There were no significant differences in the risk of decompensation (HR, 0.79; 95% CI, 0.11–5.79), cardiovascular events (HR, 1.05; 95% CI, 0.73–1.51), or malignancy (HR, 0.87; 95% CI, 0.51–1.48). Compared with obese, normal BMI NAFLD had higher risk of all-cause mortality (HR, 1.96; 95% CI, 1.52–2.51). Conclusions: NAFLD with normal BMI is associated with a healthier metabolic profile and possibly a lower risk of liver disease progression but similar risk of cardiovascular disease and malignancy than obese NAFLD.