Diets low in saturated fat and cholesterol and high in fiber are associated with a reduced risk of certain cancers, diabetes, digestive disorders, and heart disease. Diets low in fat and rich in fiber-containing grain products, fruits, and vegetables may reduce
risk of some types of cancer.
Diets low in saturated fat and cholesterol and rich in fruits, vegetables, and grain products that contain fiber, particularly soluble fiber, may reduce risk of coronary heart disease.
Diets low in fat and rich in fruits and vegetables, which are low-fat foods and may contain fiber or vitamin A (as beta-carotene) and vitamin C, may reduce risk of some cancers.
Found only in plant foods, such as whole grains, fruits, vegetables, beans, nuts, and seeds, fiber is composed of complex carbohydrates. Some fibers are soluble in water and others are insoluble. Most plant foods contain some of each kind.
Some foods containing high levels of soluble fiber are dried beans, oats, barley, and some fruits, notably apples and citrus, and vegetables, such as potatoes. Foods high in insoluble fiber are wheat bran, whole grains, cereals, seeds, and skins of many fruits and vegetables.
Fiber's Health Benefits
What can fiber do for you? Numerous epidemiologic (population-based) studies have found that diets low in saturated fat and cholesterol and high in fiber are associated with a reduced risk of certain cancers, diabetes, digestive disorders, and heart disease. However, since high-fiber foods may also contain antioxidant vitamins, phytochemicals, and other substances that may offer protection against these diseases, researchers can't say for certain that fiber alone is responsible for reduced health risks they observe, notes Joyce Saltsman, a nutritionist with FDA's Office of Food Labeling. "Moreover, no one knows whether one specific type of fiber is more beneficial than another since fiber-rich foods tend to contain various types," she adds.
Recent findings on health effects of fiber show it may play a role in:
Cancer: Epidemiologic studies have consistently noted an association between low total fat and high fiber intakes and reduced incidence of colon cancer. A 1992 study by researchers at Harvard Medical School found that men who consumed 12 grams of fiber a day were twice as likely to develop precancerous colon changes as men whose daily fiber intake was about 30 grams. The exact mechanism for reducing risk is not known, but scientists theorize that insoluble fiber adds bulk to stool, which in turn dilutes carcinogens and speeds their transit through lower intestines and out of body.
The evidence that a high-fiber diet can protect against breast cancer is equivocal. Researchers analyzing data from Nurses' Health Study, which tracked 89,494 women for eight years, concluded in 1992 that fiber intake has no influence on breast cancer risk in middle-aged women. Previously, a review and analysis of 12 studies found a link between high fiber intake and reduced risk.
In early stages, some breast tumors are stimulated by excess amounts of estrogen circulating in bloodstream. Some scientists believe that fiber may hamper growth of such tumors by binding with estrogen in intestine. This prevents excess estrogen from being reabsorbed into bloodstream.
Digestive disorders: Because insoluble fiber aids digestion and adds bulk to stool, it hastens passage of fecal material through gut, thus helping to prevent or alleviate constipation. Fiber also may help reduce risk of diverticulosis, a condition in which small pouches form in colon wall (usually from pressure of straining during bowel movements). People who already have diverticulosis often find that increased fiber consumption can alleviate symptoms, which include constipation and/or diarrhea, abdominal pain, flatulence, and mucus or blood in stool.
Diabetes: As with cholesterol, soluble fiber traps carbohydrates to slow their digestion and absorption. In theory, this may help prevent wide swings in blood sugar level throughout day. Additionally, a new study from Harvard School of Public Health, published in Feb. 12 issue of Journal of American Medical Association, suggests that a high-sugar, low-fiber diet more than doubles women's risk of Type II (non-insulin-dependent) diabetes. In study, cereal fiber was associated with a 28 percent decreased risk, with fiber from fruits and vegetables having no effect. In comparison, cola beverages, white bread, white rice, and french fries increased risk.
High-fiber diets may help blunt effects of smoking and other risk factors for heart disease.
Heart Disease: Clinical studies show that a heart-healthy diet (low in saturated fat and cholesterol, and high in fruits, vegetables and grain products that contain soluble fiber) can lower blood cholesterol. In these studies, cholesterol levels dropped between 0.5 percent and 2 percent for every gram of soluble fiber eaten per day.
