If you eat too much fat, it can go straight to your liver and damage it

May 3 2005

A University of Minnesota study is the first to show that if you eat too much fat, it can go straight to your liver and damage it.

In obese people with nonalcoholic fatty liver disease (NAFLD), fat from the diet ends up "stuck" in the liver, where it doesn't belong. It was known that the livers of NAFLD patients accumulated fat, but its origin was unknown. The new work implicates fat from the diet as one cause of NAFLD and shows that fat buildup in the liver results when the liver loses its ability to manage the various influxes of fat that occur during transitions between the fasted and fed states. Identifying the origins of accumulated fat in the livers of NAFLD patients will be important in preventing and reversing this condition, which can lead to more serious liver trouble. The work will be published May 2 in the Journal of Clinical Investigation.

"This is the first scientific proof of dietary fat stored in the liver in humans," said Elizabeth Parks, an associate professor of human nutrition, who led the study. "In health, it's the liver's job to store glycogen--a storage form of carbohydrates--not fat." The clear implication is that too much dietary fat leads the liver to fail in its mission as the body's central shipping and receiving center for fat. No longer does it take in dietary fat, repackage it and send it on its way back out into the blood. In obesity, fat builds up in the liver. The fat comes both straight from the diet and also from sugars that the liver turns into fat. As a result, the liver functions poorly.

In healthy people, about half the fat from a meal is burned for energy, and the rest is shunted to adipose tissue, where it is stored until needed during fasting. Very little fat is normally stored in the liver.

Working with obese subjects who had NAFLD, Parks and her colleagues fed the subjects food containing fats labeled with deuterium, a rare but stable form of hydrogen that can be used to trace fats as they move through the body. The subjects were already scheduled for liver biopsies, and Parks' team gave the patients labeled fat for five days before their biopsy. The researchers analyzed the waste liver tissue from the biopsies and found that these patients' livers had globules of fat--about 20 percent of it from the diet. Furthermore, the liver's synthesis of fat from dietary carbohydrates was also elevated.

Once thought benign, fatty liver is now considered a component of a condition called metabolic syndrome, which occurs most often in overweight people and whose features include insulin resistance and cholesterol abnormalities. Fatty liver is also a precursor to the more advanced liver disease nonalcoholic steatohepatitis, which may progress to cirrhosis of the liver in up to 25 percent of patients, said Parks.

"The bottom line is, this is a clear implication that if one eats too much fat, as in the film 'Super Size Me,' fat becomes deposited in the liver. This leads to a kind of liver toxicity that would be good to avoid," said Parks.

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