Non-alcoholic fatty liver disease (NAFLD) is fatty inflammation of the liver when this is not due to excessive alcohol use. It is related to insulin resistance and the metabolic syndrome, and may respond to treatments originally developed for other insulin resistant states (e.g. diabetes mellitus type 2), such as weight loss, metformin and thiazolidinediones. Adams LA, Angulo P. Treatment of non-alcoholic fatty liver disease. Postgrad Med J 2006;82:315-22. PMID 16679470. Non-alcoholic steatohepatitis (NASH) is the most extreme form of NAFLD, which is regarded as a major cause of cryptogenic cirrhosis of the liver. Clark JM, Diehl AM. Nonalcoholic fatty liver disease: an underrecognized cause of cryptogenic cirrhosis. JAMA 2003;289:3000-4. PMID 12799409.

NASH was first described in 1980 in a series of patients of the Mayo Clinic. Its relevance and high prevalence were recognized mainly in the 1990s.