Study Doubts Oat Bran’s Cholesterol-Cutting Effect
Oat bran, much ballyhooed as a cholesterol-fighting food, appears to have little specific cholesterol-lowering effect in people with normal cholesterol levels, researchers at Harvard Medical School and the Brigham and Women’s Hospital in Boston reported today in the New England Journal of Medicine.
The researchers found that large amounts of high-fiber oat bran are no more effective in a cholesterol-lowering diet than low-fiber refined wheat. This suggests that people’s cholesterol levels are lowered not by any unique property of oat bran but simply because people eat less fatty food when they are full with carbohydrates.
Moreover, a wide variety of starchy carbohydrates, ranging from cereals to rice, potatoes, bread, beans, pasta, fruits and vegetables, could be equally effective, the findings suggest. Previously, oat bran, because of its fiber content, was believed to have direct cholesterol-lowering properties.
“There is nothing special about oat bran,” said Dr. Frank Sacks, an assistant professor of medicine at the Harvard Medical School and the leader of the research team. “It is like any other cereal product that does not have any cholesterol or saturated fat in it.”
Oat bran consumption has taken off in recent years after promising preliminary studies, heavy promotion by cereal manufacturers and a general public health emphasis on cholesterol reduction as a way to prevent heart disease.
Oat bran products have been the fastest-growing segment of the $6.5-billion cereal industry. In 1989 alone, 218 new oat bran products were launched, including cookies, cereals, pretzels and muffins.
The new study is likely to dampen this enthusiasm.
In an editorial for the medical journal, Dr. William E. Connor of the Oregon Health Sciences University in Portland wrote: “Clearly, people who eat large quantities of oat bran or other similar cereals for breakfast have little room for bacon and eggs, and that may all be to the good.” Connor called the research “superbly conducted.”
Sacks, Connor and other nutrition experts said that fundamental dietary changes, not magic bullets such as oat bran, remain the best way to control cholesterol. Such changes include reducing consumption of cholesterol and the saturated fats found in such foods as meat, pork and butter and replacing them with a variety of starchy carbohydrates.
Nevertheless, substantial interest in the potential cholesterol-lowering role of dietary fiber will continue.
For example, Dr. Larry P. Bell of the Hennepin County Medical Center in Minneapolis and other researchers have shown that psyllium, a fiber that is the active ingredient in several bulk-forming laxatives, appears to have cholesterol-lowering effects when taken in significant amounts--two to three teaspoons a day.
And after reviewing the new study, Bell and another nutrition expert, Dr. Edwin L. Bierman of the University of Washington School of Medicine in Seattle, noted that the study did not examine people with high cholesterol levels. These researchers believe that large amounts of oat bran may still have direct cholesterol-lowering effects in people with high cholesterol levels--a possibility that Sacks and his colleagues said was unlikely.
But Bierman, who served as vice chairman of a National Research Council committee that issued a massive report in 1989 on diet and health, and other physicians not connected with the study also praised the Boston researchers for placing oat bran in perspective.
Dr. Myron L. Weisfeldt, director of cardiology at Johns Hopkins and the president of the American Heart Assn., said the message “before, during and after the oat bran craze is always the same: It is the whole diet (that determines cholesterol levels). It is the overall choices that you do and do not make.”
Dr. Rodman D. Starke, a heart association senior vice president, said the organization is “not convinced that there is satisfying scientific data supporting significant cholesterol reductions through oat bran-containing foods.”
The Boston study involved 20 healthy adults--four men and 16 women--who were dietitians or other hospital employees. The researchers said it was more carefully conducted and less prone to error than previous oat bran research that suggested a direct cholesterol-lowering effect. Many of these studies, they said, lacked appropriate control groups or the participants were told what diet supplements they were receiving, possibly influencing the results.
While continuing on their usual diets, the participants ate diet supplements containing either 100 grams (3.5 ounces) of oat bran or low-fiber wheat for separate, six-week periods. This was the equivalent of five high-fiber oat bran muffins or five low-fiber refined wheat muffins a day. Their complete dietary intake, cholesterol levels, blood pressure and diet-related symptoms were closely monitored.
To avoid bias, neither the researchers nor the participants were told which supplement was prescribed when. All of the subjects took part in both the high-fiber and low-fiber phases to “minimize non-specific effects” and the effect of changes in the intake of foods other than oat bran and refined wheat.
The cholesterol levels of participants “decreased significantly from base line during both the high-fiber and low-fiber dietary periods,” according to the report. The average decrease was 7.5% during the oat bran period and 7.1% during the wheat period, indicating that the effects of the two food products were virtually identical. These changes mirrored decreases in the consumption of saturated fats and cholesterol, as subjects became full after consuming the additional oat bran or wheat.
The researchers also found that oat bran did not lower blood pressure, another of its reputed health benefits. The study was funded by the National Institutes of Health, unlike much dietary fiber research, which has been sponsored by cereal manufactures or pharmaceutical manufacturers.
Eighteen of the 20 subjects reported gastrointestinal side-effects while taking the oat bran supplements, such as excess gas, cramps and diarrhea. By comparison, only one subject experienced a gastrointestinal reaction--constipation--while taking the wheat supplements.
This led the researchers to conclude that while people could “benefit from diets that are rich in oat bran if their dietary fat intake decreases to compensate for the calories of the oat bran . . . low-fiber products can achieve the same result with fewer gastrointestinal side-effects.”
Although people with high cholesterol levels were not studied, Sacks said there “is really no precedent” for a dietary factor or drug to be effective in such individuals if no significant reduction was seen in patients with normal cholesterol levels. But Sacks and other nutrition experts said it was important to study people with high cholesterol levels before this conclusion could be reached with certainty.
Sacks also said there was “no question” that certain water-soluble fibers, such as fruit pectin, certain gums and “probably” psyllium, are effective cholesterol-lowering agents. But he cautioned that relatively large amounts of the fibers must to be taken, that products such as gums may not be palatable and that potential side-effects, such as the laxative effects of psyllium, need to be considered.
Times staff writers Linda Roach Monroe in San Antonio and Maria L. LaGanga in Los Angeles contributed to this story.
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