Fatty liver, or hepatic steatosis, is caused by the accumulation of excess lipids within the cells of the liver. Steatosis is the liver's most common response to injury, and it can occur during pregnancy, as a result of alcohol abuse or toxin exposure or in individuals who are overweight or obese. Due to the increasing incidence of obesity, metabolic syndrome and diabetes in developed countries, non-alcoholic fatty liver disease, or NAFLD, is becoming more prevalent.
The full health impact of fatty liver in overweight persons is still unfolding. In "Nonalcoholic Fatty Liver Disease" in the June 2006 issue of "American Family Physician," scientists report that NAFLD is the primary cause of elevated liver enzymes in American adults. According to the National Institutes of Health, if you are obese or overweight you are at an increased risk for premature death. Diabetes, heart disease, degenerative arthritis, cancer, high blood pressure, gallbladder disease and stroke are all more common in obese individuals, and these conditions decrease your quality of life and your longevity. NAFLD may eventually be added to this list.
NAFLD can be divided into two types. The first, benign fatty infiltration without inflammation, involves the collection of lipid molecules within the liver's cells, or hepatocytes. This may represent a preliminary stage that later develops into the second type, called non-alcoholic steatohepatitis, or NASH. NASH is an inflammatory liver condition which can progress to cirrhosis.
NAFLD can occur in individuals of all ages and both sexes, but it is most commonly diagnosed in women between the ages of 40 and 60 who are obese and who have either type 2 diabetes or high lipid levels. Fatty infiltration could be due to increased delivery of dietary fatty acids to the liver or to decreased metabolism and removal of fatty acids from the liver.
Lipid molecules within the liver cells undergo oxidation, which then damages surrounding cell membranes. This cellular injury triggers a physiologic response that involves the production of inflammatory chemicals and the recruitment of specialized immune cells that cull out injured hepatocytes and attempt to repair the damage. Inflammation is the hallmark of NASH.
As immune cells remove injured hepatocytes, another type of cell called a stellate cell moves into the damaged area and initiates repairs. Although the liver has a remarkable regenerative capacity, the repair process does not always result in replacement of dead hepatocytes with new, healthy ones. Some scarring, or fibrosis, occurs in damaged areas. If not arrested, NASH can cause progressive fibrosis and, eventually, advanced cirrhosis.
Signs and Symptoms
Most people with NASH do not exhibit the classic symptoms that are usually associated with liver disease until their illness becomes advanced. Some may complain of fatigue or abdominal discomfort, and about three-quarters will eventually develop enlargement of the liver. In advanced cases, the spleen may enlarge as well. Laboratory tests frequently reveal elevated liver enzyme levels, and an abdominal ultrasound often demonstrates abnormalities in the liver's texture. A liver biopsy shows changes that are similar to those found in alcoholic hepatitis.
Fatty liver disease is treated by addressing the conditions that cause it. Weight loss and control of other underlying medical problems, such as diabetes or high lipid levels, are important management tools. It is also advisable to avoid drugs or toxins that can potentially damage the liver.
Is This an Emergency?
- “The Merck Manual of Diagnosis and Therapy, 18th Edition: Fatty Liver”; Mark H. Beers, M.D., Editor in Chief; 2006
- “American Family Physician”; Nonalcoholic Fatty Liver Disease; Bayard, M, et al; 2006
- The National Institutes of Health: Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults