Diet - fiber

Alternative names
Fiber; Roughage; Bulk

Dietary fiber is found in plant foods. Fiber cannot be digested by humans. It has no calories because the body cannot absorb it.

Dietary fiber provides a feeling of fullness and adds bulk in the diet. This assists digestion and elimination.

Including fiber in your daily diet helps prevent many problems and brings many benefits. It may be helpful in controlling weight by making you feel full sooner. It helps prevent constipation. It may be helpful in the prevention or treatment of diverticulosis, diabetes, and heart disease (ask your health care provider or registered dietician about recommendations for these conditions).

Food Sources
There are two forms of fiber: soluble and insoluble. Soluble fiber attracts water and turns to gel during digestion. This slows digestion and the rate of nutrient absorption from the stomach and intestine. It is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. Insoluble fiber is found in foods such as wheat bran, vegetables and whole grains. It appears to speed the passage of foods through the stomach and intestines and adds bulk to the stool.

Side Effects
Eating a large amount of fiber in a short period of time can cause intestinal gas (flatulence), bloating, and abdominal cramps. This subsides once the natural bacteria in the digestive system get used to the increase in fiber in the diet. The problem with gas or diarrhea can be reduced considerably by adding fiber gradually to the diet.

Too much fiber may interfere with the absorption of trace minerals including iron, zinc, magnesium, and calcium. This effect is minimal because high-fiber foods are usually rich in minerals.


The average American now eats 10 to 15 grams of fiber per day. The recommendation for older children, adolescents and adults is 20 to 35 grams per day. Younger children will not be able to eat enough calories to achieve this, but introducing whole grains, fresh fruits and other high fiber foods is suggested.

To ensure adequate fiber intake, eat a variety of foods, including more fruits, vegetables, whole grains, cereals, and dried beans and peas. Add fiber gradually over a period of a few weeks to avoid abdominal discomfort. Water aids the passage of fiber through the digestive system. Drink plenty of fluids (approximately 8 glasses of water or noncaloric fluid a day).

Peeling can reduce the amount of fiber in a food. Cooking may actually increase your intake by decreasing the volume of the food that is prepared. Therefore, eating fiber-containing food is beneficial either cooked or raw.

Johns Hopkins patient information

Last revised: December 3, 2012
by Martin A. Harms, M.D.

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