Fatty liver is a condition in which fat accumulates in the liver cells. However simple fatty liver does not damage the liver. Fat accumulation in the liver can be caused by weight gain or diabetes mellitus. Fatty liver can occur with a lean diet and ailments such as tuberculosis and intestinal bypass surgery for obesity. It can also occur while certain drugs like corticosteroids. The condition is also caused by heavy alcohol use. A patient is diagnosed as having a fatty liver when fat makes up at least 10% of the liver.

Fatty food does not cause a fatty liver. It is a common condition that is seen in people who are overweight or suffer from diabetes. Explanations for a fatty liver include the transfer of fat from other parts of the body, or a spurt in the extraction of fat presented to the liver from the intestine. Another argument is that the fat accumulates because the liver is unable to change it into a form that can be removed.

Fatty liver is diagnosed by eliminating the chances of chronic liver disease, particularly from alcohol abuse. Images of the liver obtained through an ultrasound test, a CT scan or a magnetic resonance imaging (MRI) scan can diagnose a fatty liver. In an ultrasound test, a fatty liver produces a bright image in a ripple pattern. A CT scan will show a picture in which the liver will appear less dense than normal.

The treatment of fatty liver is linked with the cause. A simple fatty liver does not need treatment, because it does not damage the liver cells. Overweight patients with fatty liver will have to reduce their weight. Control of diabetes also decreases the fat content in the liver.

Another condition that causes fat deposit in the liver is the nonalcoholic steatohepatitis (NASH). But, unlike a simple fatty liver, it causes damage to the liver cells. It is not linked to other causes of chronic liver disease, like hepatitis B and C viruses, autoimmune disorders, alcohol, drug toxicity, and the accumulation of copper (Wilson's Disease) or iron (hemochromatosis).