Heart attack patients who undergo an intestinal operation to lower their cholesterol significantly reduce their risk of suffering another heart attack or dying from heart disease, a study shows.

The surgery, called a partial ileal bypass, reroutes the bowel to bypass about one-third of the small intestine. This reduces the amount of cholesterol that is absorbed into the bloodstream.Dr. Henry Buchwald of the University of Minnesota, who directed the study, said this surgery should be considered as a possible treatment for people with high cholesterol who cannot bring it down enough by changing what they eat.

An important drawback, however, is diarrhea, which afflicts virtually everyone to some degree after having the operation. Other possible side effects include a higher risk of gallstones, kidney stones and intestinal obstruction.

The study is called the Program on the Surgical Control of the Hyperlipidemias, or high cholesterol. Published in Thursday's New England Journal of Medicine, it was conducted in Minneapolis; Los Angeles; Philadelphia, and Little Rock, Ark.

Despite the wide acceptance of cholesterol lowering, doubts remain about whether it actually helps people live longer if they already have healthy hearts. Although the latest study was conducted exclusively on people who had suffered heart attacks, Buchwald said he believes the research should settle that question.

It found that among people whose hearts were still healthy because their heart attacks had caused minimal damage, lowering cholesterol saved lives. Twenty-four percent of these people died during the 10 years after their cholesterol-lowering operations, compared with 39 percent in a comparison group who tried to lower their cholesterol through diet alone.