Fiber Reduces Risk of Heart Disease, Researchers Say

By William J. Cromie

Gazette Staff

When it comes to cereals, fruits, and vegetables, you don't have to worry about eating your heart out. The fiber in these foods has absolutely no nutritional value, but evidence continues to accumulate that it protects against heart disease.

As a result of following the diets of 43,757 men for six years, researchers at the School of Public Health (SPH) conclude that diets high in fiber, especially from cereals and grains, can cut the risk of coronary heart disease in half.

"Our results show that a high-fiber diet is as important, or more important, for prevention of heart disease than a low-fat diet," said Eric Rimm, assistant professor of epidemiology and nutrition. "It is more protective to adhere to national guidelines for fiber intake than to only eat low-fat foods, which often have the fiber processed out."

Government guidelines advise eating at least five or more portions of fruits and vegetables a day, and six or more helpings of beans, whole-grain breads, and cereals.

Women Also Protected

The SPH investigation, the largest and most current, confirms the results of several smaller and shorter studies. Rimm and his colleagues found that men who included the most fiber in their diets enjoyed a 35 percent reduction in the risk of heart attacks over those who ate the least.

There's every reason to believe that women receive the same protection. Evidence from an ongoing study of more than 100,000 women verifies this, as do findings from earlier, smaller investigations.

Rimm and his colleagues calculated that men get a 29 percent reduction in heart disease for every 10-gram increase in cereal fiber. An apple or banana contains about 3 grams, as does a serving of peas or nuts. Breakfast cereals have anywhere from 1 to 14 grams per serving. A slice of whole-grain bread provides 1 to 3 grams. Therefore, a man, and probably a women, can cut his or her risk of heart disease significantly by eating high-fiber cereal for breakfast, plus a couple of slices of whole-grain bread, and several pieces of fruit and servings of vegetables a day.

Researchers can't explain why. Fiber is the digestive-resistant part of plant food that passes through the stomach and intestines pretty much intact. One theory holds that soluble fiber, found in fruits, vegetables, and beans, inhibits the absorption of fats. That, in turn, reduces the amount of "bad" cholesterol that gets into the blood.

But, Rimm says, "that's only a small part of the explanation. Fiber also slows [blood] clotting. Another possibility is that people who eat more fiber eat less food overall, because fiber makes you feel fuller quicker. Those in our study with the highest fiber intake had the lowest fat consumption."

However, Rimm admits he and his colleagues don't know where all of the protection comes from. "It could be a combination of several unknown factors," he says.

More than 200 studies credit fruits and vegetables with protecting people against heart disease and various cancers, but no one knows exactly how this happens. Vitamins may play a key role.

Fiber also protects against colon and breast cancer, helps control diabetes, suppresses the appetite, and controls constipation. In the case of colon cancer, it sops up bile acids, which are thought to contribute to tumors. Fiber also hurries the gastrointestinal journey of cancer-causing substances, such as compounds produced by meat cooked at high temperatures and byproducts of intestinal bacteria. The less time these things spend in the gut, the less harm they can do.

Fiber is believed to protect against breast cancer by lowering estrogen, a hormone that promotes the growth of breast tumors. For diabetics, it fosters a slower more regular release of sugar into the blood. This action may also explain some of the protection against heart disease.

Nutritionists seldom recommend the heavily advertised supplements as a way to increase fiber. They advise gradually substituting high-fiber for high-fat foods. Adding just a few grams a day helps control the inevitable intestinal gas and that bloated feeling.

People who eat 20 to 25 grams a day of fiber showed the lowest risk of heart disease in our study, Rimm said. He and his coresearchers from the School of Public Health and the Medical School reported these results in yesterday's Journal of the American Medical Association.