Fat in the liver: good for fois gras, but very bad for people (and geese)!
Remember when the Super Size Me guy gets told he has evidence of liver damage from pigging out at McDonald’s? Well, it turns out that overeating and weight gain are associated with the accumulation of fat in the liver. This shouldn’t really be a surprise -- the folks who help create foie gras by force feeding geese have known this all along.
It is not eating fat that causes obesity-related fatty liver. It is getting fat that causes it. The condition is called “nonalcoholic fatty liver disease” or NAFLD. This is to distinguish it from fatty liver related to drinking too many alcoholic beverages.
Fatty deposits in liver cells without inflammation is called “simple fatty liver” or steatosis. Simple fatty liver does not permanently damage liver cells. However, inflammation of the liver does occur, in some people, when fat accumulates in the liver. When this occurs, we call the condition “nonalcoholic steatohepatitis,” or NASH. Some people who develop NASH will end up with irreversible, advanced scarring of the liver (cirrhosis) which can lead to liver failure.
NAFLD is one of the most common types of liver disease in the United States. It is estimated that somewhere between 6 and 14% of the population has NAFLD and 3% have the more serious form, NASH. The increase in prevalence appears to be tied to the epidemic of obesity in this country, and indeed around the globe.
NAFLD, like obesity, is associated with insulin resistance. Individuals in populations have a spectrum of sensitivity to this important hormone. Weight gain, particularly when fat accumulates in the abdominal area, increases insulin resistance. Therefore, NAFLD is linked (via the development of insulin resistance) to obesity. It is important to note, however, that not everyone who is insulin resistant is obese and not all obese people are insulin resistant. The Super Size guy most likely had a genetically determined predisposition to become insulin resistant when he gained weight.
Although we do not yet have good prospective, randomized clinical trials (the gold standard in medical research) to prove it, most experts recommend weight loss as the primary treatment for uncomplicated NAFLD. It makes sense that this would work given what we know about the relationship between abdominal obesity, insulin resistance and NAFLD. There are some medications that are used in diabetes, such as metformin and the TZDs (known as the thiazolinediones) that increase sensitivity to insulin, that may eventually prove to have value as well.
For now, I think it is safe to say that the best approach is prevention – obtain and maintain a healthy weight for life -- give your liver some respect and it will surely work hard for you in return.