Non alcoholic fatty liver: epidemiology and natural history.

Non Alcoholic Fatty Liver Disease (NAFLD), defined as the presence of a significant amount of lipid accumulation in the liver (at least in 5% of hepatocytes), represents a challenging issue for the Hepatologists. NAFLD is not represented by a single entity, but rather by two different entities that have different natural history and evolution that range from simple fat accumulation in the liver (without any consequence), to necroinflammation, fibrosis, cirrhosis and hepatocellular carcinoma (HCC). The reason of these differences has to be found in the host characteristics and associated risk factors. Globally, its prevalence among liver diseases, and in the general population, is rising in the recent years along with its associated conditions: obesity, insulin resistance, metabolic syndrome and diabetes. This increment, together with the reported clinical conditions, may be accounted for changes in dietary habits and the increase of sedentary lifestyle. Its diffusion seems to be pandemic, given that it is beginning to affect the populations in the developing world due to the spread of Western lifestyle. This is particularly worrying in young adults and children in what seems to have become the main cause of liver disease. Even if the real rate of global incidence of NAFLD are not known, its worldwide prevalence in general population is estimated to be 20-30% in Western Countries and 5-18% in Asia and it is increasing over time. In this review we will report on the global and regional prevalence of NAFLD, the principal risk factors and the natural history of its different presentations.