Nonalcoholic fatty liver disease (NAFLD) is a liver problem that affects people who drink little to no alcohol. NAFLD is the most common form of liver disease in the world and is becoming increasingly prevalent, especially in Western nations, as the number of people with obesity rises. NAFLD ranges in severity from simple fatty liver, where fat collects in the liver without inflammation, to nonalcoholic steatohepatitis (NASH). NASH causes the liver to swell and become damaged due to the fat deposits in the liver. Over time, NAFLD can progress to a more serious condition known as nonalcoholic steatohepatitis (NASH).