Metabolic dysfunction–associated steatotic liver disease (MASLD), previously known as non-alcoholic fatty liver disease (NAFLD), is a type of chronic liver disease. This condition is diagnosed when there is excessive fat build-up in the liver (hepatic steatosis), and at least one metabolic risk factor. When there is also increased alcohol intake, the term MetALD, or metabolic dysfunction and alcohol associated/related liver disease is used, and differentiated from alcohol-related liver disease (ALD) where alcohol is the predominant cause of the steatotic liver disease. The terms non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH, now known as metabolic dysfunction associated steatohepatitis (MASH)) have been used to describe different severities, the latter indicating the presence of further liver inflammation. MASLD may progress to MASH, with the risk of progression estimated as 7-35% per year. MASH may also regress to MASLD, especially with healthy diet, exercise and medications. Both MASLD and MASH have liver related complications such as cirrhosis, liver cancer, liver failure, as well as liver independent complications such as cardiovascular disease. These complications are much more common with MASH.
Obesity and type 2 diabetes are strong risk factors for MASLD. Other risks include being overweight, metabolic syndrome (defined as at least three of the five following medical conditions: abdominal obesity, high blood pressure, high blood sugar, high serum triglycerides, and low serum HDL cholesterol), a diet high in fructose, and older age. Obtaining a sample of the liver after excluding other potential causes of fatty liver can confirm the diagnosis.