1. Fatty liver and non-alcoholic steatohepatitis

Although steatohepatitis can be induced by an excessive intake of alcohol, it can also arise through various other causes, in which case it is known as non-alcoholic fatty liver disease (NAFLD). NAFLD is classified into two categories:simple fatty liver with a favorable clinical outcome, and non-alcoholic steatohepatitis (NASH), which is intractable and progressive. Recently in Japan, there has been an increase in the number of individuals at risk of lifestyle-related diseases, due to increased insulin resistance and visceral fat obesity. The metabolic syndrome (MS) is associated with several risk factors for atherosclerosis, including diabetes mellitus (DM), hypertension, and hyperlipidemia. Visceral fat obesity is the prime cause of NASH in the liver, and is therefore considered to be one of the phenotypic features of MS. Furthermore, most chronic liver diseases are associated with hepatitis C virus (HCV) infection. Fatty degeneration of hepatocytes is often observed in the liver of HCV-infected individuals, and results from viral suppression of mitochondrial beta-oxidation of fatty acid. The natural outcome of HCV infection is worse in patients with lifestyle-related high insulin resistance and visceral fat obesity. In this review, we describe the recent advances in research on progressive liver diseases that are the result of fat accumulation in the liver, with special reference to MS.