BOSTON -- Worried that fish oil has become this year's snake oil, scientists meeting here last week warned there would be no shortcuts out of America's epidemic of heart disease.

Ever since researchers reported that Eskimos who consumed enormous quantities of fatty fish had almost no heart disease, Americans have looked to fish oil supplements as a way to ward off the nation's No. 1 killer.

There is no question that eating fish is healthful. But at a Massachusetts Institute of Technology conference to discuss the health effects of the fats present in fish oil, called omega-3 fatty acids, doctors said that Americans must change their diets to combat heart disease. Fish oil supplements are not harmful, but unless consumption of other fatty foods is curbed, they will have no significant beneficial effect, researchers said.

"The barrage of advertising {for fish oil capsules} is essentially without any scientific evidence," said Dr. Robert Lees, professor of cardiovascular diseases at MIT.

Researchers at the conference said that too much remains unknown about the consumption of omega-3 to warrant a rush to take the pills. They added, however, that doctors might wish to prescribe fish oil supplements for a small group with extremely high cholesterol levels.

Many studies have shown the link between increased fish consumption and a reduction in deaths from heart disease. One of the first and most compelling occurred in Scandinavia during World War II. When Scandinavians were forced by wartime shortages to substitute fish for their normally high intake of red meat, their rate of heart disease plummeted. After the war, when meat returned to their diet, the heart disease death rate rose dramatically.

"We still do not know how much to ingest and what is the best form to do it," said Marcus Karel, MIT professor of food engineering. "And we can see that people who dose themselves as a supplement without making other changes in their diets will at the least be deceiving themselves."

Omega-3 is an unsaturated fat found primarily in deep-sea saltwater fish, such as tuna and salmon. Unsaturated fat is much healthier than the saturated fat found in meats and dairy products. A diet that contains omega-3 helps to thin blood, and that reduces the deadly cholesterol buildup that has been linked to heart disease. It also appears to lower the level of fats called triglycerides in the blood.

The National Heart, Lung and Blood Institute estimates that one of every four Americans has dangerously high blood cholesterol.

More than 90 firms have marketed fish oil capsules in the past two years. Sales this year are expected to exceed $50 million, pharmaceutical industry analysts said.

But many questions remain about the consumption of fish oil, particularly in capsule form. Scientists are concerned that environmental pollutants found in some fish are also turning up in some capsules.

And research has shown that while large doses of fish oil appear to have beneficial effects, particularly on lowering tryglicerides, low doses also lower HDL, the type of cholesterol that protects against heart disease by removing fat from arteries. Although many experts suspect that fish oil is what makes eating fish healthful, there is not yet conclusive proof.

And not all fish oil is alike. Sardines have 10 times the omega-3 content of haddock. It would take more than three pounds of daily flounder consumption to get a useful dose of omega-3, according to Dr. John Kinsella, professor of food science at Cornell University.

Supplements have fans among doctors who believe Americans will never eat enough fish. In one Chicago study, 200 patients with severely elevated cholesterol took pills and experienced large reductions in total cholesterol and even bigger drops in triglycerides, according to Dr. Michael Davidson, assistant professor of preventive medicine at the Rush Presbyterian-St. Luke's Medical Center.

Participants at the meeting voiced concern that people would simply add fish oil pills to a diet that for most Americans includes too much fat. In interviews, several conference participants criticized the aggressive marketing many companies have undertaken.

"We are not trying to snow anyone," said Lori Versaci, marketing director for consumer products at E.R. Squibb, a maker of fish oil capsules. "Obviously we had hoped for more conclusive evidence that omega-3 supplements had benefits. But one thing we did hear loud and clear is that fish is good for you."