As of February 2015, scientists do not know exactly what causes nonalcoholic fatty liver disease, explains Mayo Clinic. People with alcoholic fatty liver develop the condition due the effects of enzymes involved in alcohol metabolism, notes the Cleveland Clinic.
Nonalcoholic fatty liver disease causes extra fat to accumulate in the liver tissue, states Mayo Clinic. There are several forms of the disease. Nonalcoholic fatty liver is an accumulation of fat that does not cause any complications. Nonalcoholic fatty liver disease-associated hepatitis results in scarring of the tissue, causing some people to develop liver failure due to a loss of liver function. In people with nonalcoholic steatohepatitis, extra fat triggers inflammation in the liver, which can eventually lead to scarring.
Alcoholic fatty liver develops due to the effects of alcohol dehydrogenase and acetaldehyde dehydrogenase, reports the Cleveland Clinic. These enzymes change nicotinamide adenine dinucleotide, commonly called NAD, to its oxidized form, NADH. When there is an abnormal ratio of NAD to NADH, fatty acid oxidation is inhibited, causing excess fat to build up in the liver. If a person with alcoholic fatty liver stops drinking, the liver usually returns to normal.
People with nonalcoholic fatty liver disease usually do not have any symptoms, notes Mayo Clinic. If symptoms develop, they include weight loss, fatigue and abdominal pain. Someone with alcoholic fatty liver may have an enlarged liver upon physical examination, but the condition usually causes no symptoms, states the Cleveland Clinic.