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.
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.
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.
On average, Americans now eat about 16 grams of fiber per day. The recommendation for older children, adolescents, and adults is to eat 21 to 38 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:
- Dried beans and peas
- 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.
Diet - fiber; Roughage; Bulk; Constipation - fiber
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Heimburger DC. Nutrition's interface with health and disease. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 213.
Thompson M, Noel MB. Nutrition and family medicine. In: Rakel RE, Rakel DP, eds. Textbook of Family Medicine. 9th ed. Philadelphia, PA: Elsevier; 2016:chap 37.
US Department of Health and Human Services. US Department of Agriculture. 2015-2020 Dietary Guidelines for Americans. 8th ed. health.gov/dietaryguidelines/2015/guidelines/. Accessed July 25, 2018.
Review Date 6/28/2018
Updated by: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.