The finding comes from a study of the diet drug orlistat (also known as Xenical and Alli), which did not itself improve liver disease.

Brent Neuschwander-Tetri, M.D., a hepatologist at Saint Louis University Liver Center and study researcher said, "It's a helpful study because we can now give patients a benchmark, a line they need to cross to see improvement."

The study looked at patients with NASH, which is a type of liver disease characterized by excessive fat, causing inflammation and damage in the liver. Researchers set out to see if orlistat, which limits fat absorption, along with calorie restriction would lead to weight loss and improve liver disease in overweight patients with NASH, which was determined by a liver biopsy.

Fifty patients participated in the study, with all instructed to consume a 1,400 calorie diet and vitamin E, and half also receiving orlistat for 36 weeks, at which time liver biopsies were repeated.

While orlistat itself was not linked directly to improved liver health, weight loss was, and, further, researchers were able to pin-point the percentage of weight loss needed to improve liver damage.

Patients who lost 5 percent or more of body weight over nine months showed improvement in insulin resistance and steatosis (fat accumulation in the liver), and those who lost at least 9 percent showed reversal of their liver damage.

The data about the drug orlistat was less clear. Those in the orlistat group lost 8.3 percent body weight and those in the other group lost 6 percent body weight, not a statistically significant difference. As for liver disease, orlistat did not itself improve liver enzymes, measures of insulin resistance or reverse liver damage.

"The bottom line is that weight loss can help improve fatty liver disease," said Neuschwander-Tetri, who is a professor of internal medicine at Saint Louis University. "Now we know how much weight loss is needed for improvement, and we can give patients specific goals as they work to improve their health."

Published in the January edition of Hepatology , the study was conducted at Saint Louis University and Brooke Army Medical Center and was funded by Roche Pharmaceuticals, the maker of orlistat.

Established in 1836, Saint Louis University School of Medicine has the distinction of awarding the first medical degree west of the Mississippi River. The school educates physicians and biomedical scientists, conducts medical research, and provides health care on a local, national and international level. Research at the school seeks new cures and treatments in five key areas: cancer, liver disease, heart/lung disease, aging and brain disease, and infectious disease.

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