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Diet - fiber; Roughage; Bulk

Fiber is a substance found in plants. Dietary fiber, which is the type of fiber you can eat, is found in fruits, vegetables, and grains. It is an important part of a healthy diet.

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  • Function

    Dietary fiber adds bulk to your diet. Because it makes you feel full faster, it can help with weight control. Fiber aids digestion and helps prevent constipation. It is sometimes used for the treatment of diverticulosis, diabetes, and heart disease.

  • Food Sources

    There are two forms of fiber: soluble and insoluble.

    Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. Research has shown that soluble fiber lowers cholesterol, which can help prevent heart disease.

    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 problem often goes away once the natural bacteria in the digestive system get used to the increase in fiber. Adding fiber to the diet slowly, instead of all at one time, can help reduce gas or diarrhea.

    Too much fiber may interfere with the absorption of minerals such as iron, zinc, magnesium, and calcium. In most cases, this is not a cause for too much concern because high-fiber foods tend to be rich in minerals.

  • Recommendations

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

    To ensure that you get enough fiber, eat a variety of foods, including:

    • Cereals
    • Dried beans and peas
    • Fruits
    • Vegetables
    • Whole grains

    Add fiber gradually over a period of a few weeks to avoid stomach distress. Water helps fiber pass through the digestive system. Drink plenty of fluids (about 8 glasses of water or noncaloric fluid a day).

    Taking the peels off fruits and vegetables reduces the amount of fiber you get from the food. Fiber-rich foods offer health benefits when eaten raw or cooked.


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National Research Council. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). The National Academies Press. Washington, DC; 2005:chap 7.

Noel MB, Thompson M, Wadland WC. Nutrition and family medicine. In: Rakel RE, ed. Textbook of Family Medicine. 8th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 37.

Nutrition's interface with health and disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 220.

U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th ed, Washington, DC: U.S. Government Printing Office; 2010.



Review Date: 8/17/2014  

Reviewed By: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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