A common misconception about fiber is that it is not digested by enzymes in the body and therefore provides no calories or nutrients. But the category "fiber" includes chemicals that are not fibrous, materials that can be dissolved, and some substances that can be digested partially. We eat quite a complex mixture of fibers.

Dietary fiber is a broad generic term; it includes the following chemicals, which form the structural components of plants, including many of the plant foods we eat:

cellulose
hemicellulose
lignin
pectins
mucilages
gums

The first three are insoluble fibers which can absorb and hold water in the digestive system. The others are soluble fibers, which are partially broken down in digestion to a gel-like substance, which also retains water.

What does it do?

Fiber's ability to hold water and to bind minerals and cholesterol-like materials results in a number of physiological effects which vary depending on the type of fiber and/or where it is in the digestive tract.

In the mouth, fiber stimulates the flow of saliva.
In the stomach and small intestine, fiber dilutes the contents and delays the emptying of food and the absorption of nutrients; this promotes a feeling of fullness.
In the large intestine, fiber dilutes the contents and provides a place for bacterial growth and digestion. The water-holding capacity of insoluble fiber in the lower intestine softens the stool and increases stool size, so that the process of elimination is easier and faster.
In the large intestine, fiber also acts to bind certain chemicals. Different kinds of fiber have different binding capacities: when fiber binds cholesterol-like compounds, it lowers cholesterol, a healthy result; when fiber binds minerals, it decreases their absorption, a less desirable result.

Because of these physiological effects, fiber is considered beneficial in preventing, alleviating or curing a number of diseases and conditions, including:

arteriosclerosis (hardening of the arteries)
excess food intake
diverticular disease
irritable bowel syndrome
Crohn's disease
gallstone formation
constipation

Where do you get it?

Recent recommendations suggest that we should be getting fiber from a variety of foods high in different types of fibers, rather than from dietary supplements. A healthy diet should provide a mixture of both soluble and insoluble fibers.

About eight grams of daily fiber intake should be in the form of soluble fibers, such as:

fruits, especially apples and citrus
vegetables, especially leafy green varieties
oats

Major sources of insoluble fibers include:

wheat bran
whole grains
legumes
most fruits and vegetables

A good source of fiber should have at least three grams of fiber. High-fiber foods provide five grams or more. The accompanying chart lists a variety of foods and their fiber content.

Sources of Fiber

Food	Amount	Fiber (grams)

Fiber One	4 oz. (1/2 cup)	13
All Bran	4 oz. (1/2 cup)	10
Beans, cooked	4 oz. (1/2 cup)	5-8
Lentils, cooked	8 oz. (1 cup)	7
Shredded Wheat	2	6
Peanuts	4 oz. (1/2 cup)	6
Raspberries	8 oz. (1 cup)	6
Whole wheat bread, 100%	2 slices	6
Harvest burger	1 burger	5
Sunflower seeds	1 oz.	5
Apple	1 apple	4
Blueberries, raw	8 oz. (1 cup)	4
Green peas	4 oz. (1/2 cup)	4
Pear	1 pear	4
Pumpkin, canned	4 oz. (1/2 cup)	4
Strawberries, fresh	8 oz. (1 cup)	4
Sweet potato w/skin, baked	1 potato	4
White potato w/skin, baked	1 potato	4
Banana	1 banana	3
Brown rice, cooked	8 oz. (1 cup)	3
Carrots	4 oz. (1/2 cup)	3
Orange	1 orange	3
Total cereal	6 oz. (3/4 cup)	3
Pumpernickel bread	2 slices	2
Asparagus	4 oz. (1/2 cup)	2
Broccoli	4 oz. (1/2 cup)	2
Corn	1 corn	2
Jewish rye bread	2 slices	2
Nectarine	1 nectarine	2
Peach	1 peach	2
Cantaloupe	8 oz. (1 cup)	1
Corn flakes	8 oz. (1 cup)	1
Rice Krispies	8 oz. (1 cup)	1
Tomato, fresh	1/2 tomato	1
White, French or Vienna bread	2 slices	1

How much do we need?

A healthy adult should get 20-25 grams of fiber a day, based on the assumption that we need 10-13 grams of fiber a day for every 1,000 calories consumed. Unfortunately, most Americans consume only about 10 grams.

Children ages 3-18 need less fiber than adults, and they need different amounts at different ages. To calculate a child's daily fiber requirements, add the child's age to the number five (for five grams). For example, a four-year-old needs nine grams of fiber a day.

To get the appropriate amount of fiber, adults should include the following in their diets:

two to three servings of whole grains (as part of the 6-11 recommended daily servings)
five servings of fruits and vegetables a day
one or two servings of legumes every week

Is it safe?

Yes. However, increasing your fiber intake to recommended levels may cause some unpleasant effects unless you do it gradually and drink plenty of water. This can help you avoid:

gas, distention and/or diarrhea resulting from increases in fiber intake
colon obstruction caused by very large intakes of fiber
interference with the absorption of some minerals (though this should not be a problem if you eat a healthy diet.)

Fiber

What is it?

Dietary fibers are structural components of plants. The type and amount of fiber in plants vary from species to species.