ABSTRACT
This chapter discusses the definitions of obesity and leanness and then reviews the epidemiology, pathogenesis, clinical features and outcomes of nonalcoholic fatty liver disease (NAFLD) in lean patients. Despite its more conventionally recognized clinical phenotype, NAFLD is also reported in nonobese populations. A Korean prospective cohort study with biopsy-proven NAFLD showed no significant difference in histology between nonobese NAFLD and obese NAFLD except for higher severity of hepatic fibrosis in nonobese nonalcoholic steatohepatitis (NASH). Although visceral adiposity accounts for only 7–15% of the total body fat, it carries significant prognostic value, consequential to the pathogenesis of NAFLD and insulin resistance. Several studies showed an increased risk of NAFLD, NASH and fibrosis among individuals with sarcopenia, independent of obesity, insulin resistance and inflammatory marker. In lean individuals, various metabolic risk factors in NAFLD are consistent with obese NAFLD. Whether NAFLD in lean individuals is a distinct entity with an increased risk of adverse clinical outcomes is a matter of hot debate.
