Fatty liver is simply the build-up of fat in the liver. Fat in the liver usually does not cause liver damage. However, certain other conditions and diseases can be associated with the development of fatty liver.
Nutritional causes of fatty liver are starvation, obesity, protein malnutrition and intestinal bypass operations for obesity. The endocrine disorder diabetes mellitus often leads to fatty liver. In juvenile diabetes the fat may be rapidly deposited leading to tenderness in the upper right of the abdomen. In all of these conditions the fatty deposits are occasionally accompanied by some inflammatory changes and scarring of the liver - so-called non-alcoholic steatohepatitis or NASH.