Fiber is the structural material of plants and is found in all fruits, vegetables, whole grains, beans, nuts and other seeds. It is a type of carbohydrate that your body cannot break down, so you can't absorb it. There are two types: soluble and insoluble. Insoluble fiber adds bulk to your stool and helps to prevent constipation. Soluble fiber binds to fat in the intestines and keeps some fat from being absorbed.

Insoluble fiber may help to prevent colon cancer by speeding cancer-causing agents through the digestive system. It helps with weight control because it binds to water, creating bulk that makes you feel full. It can help control diabetes because it slows the rate at which your body absorbs glucose.

Soluble fiber has an added benefit. When you add more soluble fiber to your diet, it lowers blood levels of the plaque-forming LDL cholesterol. Soluble fiber is degraded by bacteria in the colon to form types of fatty acids that are absorbed into the bloodstream and help to block the synthesis of cholesterol by the liver. This is the only food component we know will lower blood cholesterol when you add more to your diet. However, people who have high blood levels of cholesterol must do a lot more than just add soluble fiber to their diet. They also should not smoke, not be overweight, and exercise regularly.

You should eat at least 30 grams of fiber per day, and the average North American gets only 11 grams. There's very little fiber in the typical diet of hamburgers, pizza, fried chicken and coke. Foods made from animal products never have any fiber, and processed foods made from grains, vegetables or fruit frequently have most of the fiber removed. Wheat berries, baked potatoes, apples and oranges contain many times more fiber than bread, potato chips, apple jelly or orange juice.

Don't worry about whether you are getting soluble or insoluble fiber; you need both kinds, and both are found in fruits, vegetables, whole grains and beans. If you're not getting enough fiber, don't try to correct the situation by adding fiber supplements, lots of bran cereal or foods made with added ground-up fiber. When you eat whole fruits, vegetables, whole grains and beans, you get all of the vitamins, minerals and phytochemicals nature packages with the fiber. Introduce more high-fiber whole foods into your diet gradually to avoid digestive discomfort.

Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in four specialties, including sports medicine. Read or listen to hundreds of his fitness and health reports at http://www.DrMirkin.com

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