The benefits of fiber

It seems that your mom's nagging you to eat your fruits and vegetables was justified. Getting your "roughage" is important. Roughage, what we now refer to as fiber, is the indigestible portion of food that travels through the digestive system virtually intact. While dietary fiber has no nutritional value, it can have a profound impact on health, including lowering the risk for certain types of cancer, lowering blood cholesterol levels and minimizing the complications of diabetes. In addition, it may even aid appetite control.

Fiber can be classified into two categories--soluble and insoluble, depending on its ability to bond with water molecules. The loosely knit chemical bonds of fiber molecules allow them to pick up water molecules in the course of their journey through the digestive system. "Soluble" fiber molecules readily accept and retain water, whereas "insoluble" fibers are more rigid and crystalline in structure and have few available bonds for water molecules.

Not only can fiber bond with water, but fiber molecules also bond with substances such as hormones, bile acids and potential carcinogens. Because of this, fiber plays an important role in preventing the following:

Colon cancer

Research has shown that diets high in fiber, particularly insoluble fiber, protect against colon cancer. By binding with bile acids, which in high concentrations are thought to contribute to the development of malignancies, fiber appears to protect the inner lining of the colon. Furthermore, fiber hastens the amount of time it takes for feces to be eliminated, thereby minimizing the colon's exposure to naturally occurring carcinogens--including byproducts of intestinal bacteria, substances derived from the breakdown of cholesterol, and compounds produced by meat cooked at high temperatures.

Elevated cholesterol

Numerous studies have confirmed soluble fiber's ability to lower blood cholesterol levels, specifically LDL-cholesterol. Bile acids, once again the culprit, are thought to play a role in lipid absorption. By attaching themselves to fiber molecules, bile acids are eliminated, decreasing the rate of lipid absorption and the rate at which LDL-cholesterol enters the bloodstream.


Soluble fiber forms a protective coating in the stomach and small intestine, which shields starches and sugars in unrefined foods from digestive enzymes. Thus, sugars are released more gradually into the bloodstream, helping to modulate a person's blood sugar levels.

Appetite control

Because fiber absorbs water, it takes up a considerable amount of room in the stomach, creating a feeling of fullness.

No one agrees on exactly how much fiber is needed for good health. The American Dietetic Association recommends 20-35 grams of fiber a day, while the National Cancer Institute advises consuming 25-30 grams.

To increase fiber intake, it is best to do so by changing your diet, not relying on supplements. A reasonable goal is adding one to two grams of fiber a day. Also, remember that fiber absorbs water, so increase your fluid intake to at least eight eight-ounce glasses a day. The chart below gives examples of foods high in dietary fiber.

Sources of dietary fiber


Wheat bran

Navy, kidney, pinto and lima beans

Skins of fruits and vegetables

Raspberries and strawberries

Sesame and poppy seeds


Oat bran

Navy, pinto and lima beans


Fruits and vegetables

Nancy Anderson is coordinator of the Emory HeartWise Program. The publication of the Wellness column is coordinated by the Seretean Center for Health Promotion.

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