Obesity and fatty liver are 'grease' for the machinery of hepatic fibrosis.

Nonalcoholic fatty liver disease (NAFLD) starts with hepatic steatosis, which can progress with inflammation to nonalcoholic steatohepatitis, and a subset of patients develop progressive fibrosis and ultimately cirrhosis. In the majority of cases, NAFLD is associated with (components of) the metabolic syndrome. Obesity, diabetes and hepatic steatosis are also independent risk factors for hepatic fibrosis in different chronic liver diseases. However, the question is whether it is actually nonalcoholic steatohepatitis and not 'simple' steatosis that promotes fibrosis progression based on hepatocellular injury. In this review, the concept will be put forward that (1) hepatic steatosis per se is profibrogenic, and (2) that in NAFLD development and progression of hepatic fibrosis is not simply determined by (the degree of) hepatic inflammation. In addition to the liver, this view is expanded to other organs affected by the metabolic syndrome, which affects hepatic injury and fibrosis also via extrahepatic pathophysiological alterations. In conclusion, fatty liver and the metabolic syndrome, respectively, have to be recognized as significant lubricants of hepatic fibrosis, and simple hepatic steatosis cannot be considered as benign.