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.
Alcohol abuse can lead to the accumulation of fat within hepatocytes, the predominant cell type in the liver. A similar condition can also be seen in some obese people who are not alcohol abusers. Fatty liver is reversible if the patient stops drinking, however, fatty liver can lead to steatohepatitis. Steatohepatitis is fatty liver accompanied by inflammation and this condition can lead to scarring of the liver and cirrhosis.