Oat bran's reputation as a cholesterol fighter, exalted and then sullied by conflicting scientific studies, is on the rebound.

In the 18 months since a controversial and highly publicized Harvard University report concluded that the high-fiber breakfast food played no significant role in reducing cholesterol, medical journals have published at least three major new studies reaching the opposite conclusion. The latest, a 156-person study that found a cholesterol reduction of almost 16 percent among some oat bran eaters, is being reported in today's issue of the Journal of the American Medical Association.

A number of scientists in the field also have become increasingly outspoken in their criticism of the design and conclusions of the Harvard research, which was published in the usually rigorous New England Journal of Medicine. The report landed its authors on major television news and talk shows and is credited with almost single-handedly dashing one of the biggest health food fads in years.

The new consensus on oat bran does not go as far as before in celebrating oat bran's ability to reduce the level of artery-clogging cholesterol in blood. Some scientists concede that in the rush to cash in on the oat bran boom -- which resulted at its peak in what industry analysts estimate was a 450 percent increase in the sales of ready-to-eat oat and bran cereals -- the product's cholesterol-lowering properties were oversold. But weighing the spate of more recent oat bran studies, many researchers say that it is now increasingly clear that the fiber in oat bran can play a modest but important role in lowering the risk of coronary heart disease.

"Science speaks from numbers," said Linda Van Horn, a cholesterol researcher at Northwestern University Medical School. "And the overall interpretation of all the dietary information on this subject would continue to suggest that there is definite benefit to including oats in a diet."

"News reports of the death of the fiber-cholesterol hypothesis were greatly exaggerated," concluded University of North Carolina epidemiologist Charles Humble, in a review of the oat bran literature published in a recent issue of the American Journal of Public Health.

The now-challenged Harvard study was based on 20 healthy young women who were fed five high-fiber oat bran muffins every day for six weeks and then ate, for comparison purposes, five low-fiber wheat muffins every day for another six weeks. Like virtually every other oat bran study, the Harvard group found that those eating oat bran significantly lowered the amount of the harmful form cholesterol, known as LDL, in their blood.

However, when the subjects switched to wheat muffins they had exactly the same reduction in cholesterol. In other words, the Harvard group concluded, it wasn't that oat bran was doing anything special, it was cutting cholesterol simply by filling people up and displacing the high-fat foods that raise cholesterol. Any number of starchy, filling carbohydrates -- including relatively low fiber foods such as rice, potatoes or pasta -- thus would be equally effective in fighting high cholesterol.

Since that study appeared, however, a number of other researchers have challenged its finding. For example, at the American Heart Association last fall in Dallas, a group from the University of Minnesota reported on a trial involving 149 people who were fed equally low-fat diets. Then, one group was given wheat cereal to eat in the morning, one group ready-to-eat oat bran, and a third group was used as a control.

The results showed that the oat bran group's LDL level dropped 7.7 percent while the other two groups remained unchanged. This led the researchers to conclude that oat bran indeed has an independent effect on cholesterol.

The JAMA study published today, which was paid for by the Quaker Oats Co., looked at the issue even more closely. The report, submitted by a group from the Chicago Center for Clinical Research, compared the effects of eating oat bran to eating oatmeal, which contains about half as much fiber. Had the results supported the Harvard report, people eating equal amounts of oat bran and oatmeal would have identical reductions in cholesterol, because both diets would displace just as much high-fat, cholesterol-raising foods.

But that is not what the study found. Instead, those eating oat bran had a 15.9 percent reduction in cholesterol compared to a 2.7 percent reduction for those eating oatmeal, a change the researchers attributed to the independent, cholesterol-fighting effects of the extra fiber in oat bran.

Why were the conclusions of the Harvard study, which was funded by the National Institutes of Health, so different from those of subsequent studies? One reason, researchers said, is that the Harvard group chose as its subjects healthy, young, female dieticians who all had better than average levels of LDL to begin with. Many researchers say that they believe that oat bran's beneficial effects are far more pronounced among people who have high levels of blood cholesterol.

"He chose the least representative group in society to study," said Joseph Keenan, a researcher at the University of Minnesota. "What relevance does the experience of {young women with low cholesterol} have to the people we are really concerned about: older men and women with high cholesterol."

By contrast, all the studies that contradict the Harvard results were done in people under a doctor's order to reduce their cholesterol levels.

This weakness is conceded by the authors of the Harvard study.

"I think it is legitimate to be asked to limit the validity of your findings to your own study groups," said Frank Sacks, a researcher at the Harvard School of Public Health. "That's a limitation of our study."

However, Sacks said he stands by his results.

"The true effect of oat bran rests somewhere between zero and 'doing a little,' " he said. The only reason that the issue continues to be debated, he added, is that many of the studies "are being funded by industry."