Fatty liver disease involves the buildup of fat in the liver. This triggers inflammation, which over time can lead to serious complications, including cirrhosis, liver cancer and the need for a liver transplant. There are currently no approved medications for fatty liver disease, and its prevention and management rely on lifestyle changes, such as weight loss and exercise.

Fat accumulation in liver cells, known as steatosis, can have several causes. People who drink heavily may develop alcoholic fatty liver disease. Certain drugs and environmental toxins can also lead to steatosis. When it occurs in people who do not drink much, the condition is known as non-alcoholic fatty liver disease (NAFLD) or its more severe form, non-alcoholic steatohepatitis (NASH).

Fatty liver disease is increasingly recognized as part of metabolic syndrome, a cluster of conditions that raise the risk of cardiovascular disease. It is commonly linked to obesity, though some lean people develop NAFLD too. People with fatty liver disease often also have insulin resistance, type 2 diabetes, abnormal cholesterol and triglyceride levels, and high blood pressure. Lifestyle factors, including being overweight—especially having excess fat around the waistline—eating an unhealthy diet and lack of physical activity, play a role in the development of NAFLD. People with genotype 3 of hepatitis C virus are more likely to develop fatty liver disease than those with other strains of the virus.

NAFLD and NASH are responsible for a growing proportion of advanced liver disease in the United States and worldwide. Experts estimate that up to a third of Americans have fatty liver disease, and the proportion is rising. The condition is also becoming more common among children and adolescents. Latinos have a higher rate of fatty liver disease than African Americans or whites. Now that hepatitis B can be prevented with a vaccine and hepatitis C can easily be cured with antivirals, NAFLD and NASH are expected to become the leading reason for liver transplants in the U.S.