Nonalcoholic fatty liver disease, often called NAFLD, is a liver problem that affects people who drink little to no alcohol. In NAFLD, too much fat builds up in the liver. It is seen most often in people who are overweight or obese.

NAFLD is becoming more common around the world, especially in Middle Eastern and Western nations as the number of people with obesity rises. It is the most common form of chronic liver disease, affecting about 25% of the world's population. In the United States, about 100 million people have NAFLD.

Some people with NAFLD can get nonalcoholic steatohepatitis, also called NASH. NASH is a serious form of fatty liver disease that causes the liver to swell and become damaged due to the fat deposits in the liver. NASH may get worse and may lead to serious liver scarring, called cirrhosis, and even liver cancer. This damage is like the damage caused by heavy alcohol use.

A move is currently underway to change the name nonalcoholic fatty liver disease to metabolic dysfunction-associated steatotic liver disease (MASLD). Experts also have recommended changing the name nonalcoholic steatohepatitis to metabolic dysfunction-associated steatohepatitis (MASH).