Diseases & Conditions


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Fiber


Some foods contain fiber, which is a tough complex carbohydrate. Fiber may be partly soluble: It dissolves in water, and the body may be able to digest some of it. Or it may be insoluble: It does not dissolve in water, and the body cannot digest it. Eating too much insoluble fiber can interfere with absorption of certain vitamins and minerals.

Authorities generally recommend that about 30 grams of fiber be consumed daily. In the United States, the average amount of fiber consumed daily is about 12 grams because people tend to eat products made with highly refined wheat flour and do not eat many fruits and vegetables. An average serving of fruit, a vegetable, or cereal contains 2 to 4 grams of fiber. Meat and dairy foods do not contain fiber.

Did You Know...

Eating a lot of insoluble fiber (in such foods as brown rice, prunes, and many vegetables) can reduce the absorption of certain vitamins and minerals.

Comparing Soluble and Insoluble Fiber

Type of Fiber

Sources

Functions

Soluble

Apples

Barley

Beans

Citrus fruits

Lentils

Oat bran

Oatmeal

Pectin (from fruit)

Psyllium

Rice bran

Strawberries

Helps moderate the changes in blood sugar and insulin levels that occur after eating a meal

Helps reduce cholesterol levels

May reduce the risk of coronary artery disease

Insoluble

Apples

Brown rice

Pears

Prunes

Many vegetables, including cabbage, root vegetables, and zucchini

Whole grains and whole-grain breads and pastas

Provides bulk to feces and thus helps food move through the digestive tract, preventing constipation

Helps eliminate cancer-causing substances produced by the bacteria in the large intestine

Reduces pressure in the intestine, helping prevent diverticular disease

Is helpful in losing weight because the body processes it slowly

Last full review/revision July 2008 by Margaret-Mary G. Wilson, MD

Source: The Merck Manual Home Edition