Other name(s):

b-glucan, cellulose, chitosan, gellan, guar gum, gum, hemicellulose, konjac mannan, lignin, mucilage pectin

General description

Fiber is a type of carbohydrate found in plant foods. It's not digested or absorbed by the body. Fiber is often referred to as soluble or insoluble. This depends on whether it dissolves in water. Food sources include bran, whole grains, vegetables, fruits, and seaweed.

Soluble fiber can interfere with the absorption of dietary fat and cholesterol. This can help lower low-density lipoprotein (LDL or “bad”) cholesterol levels in the blood. It can also help control blood sugar after a meal. Insoluble fiber can speed up the movement of food through the large intestine and relieve constipation.

Studies suggest that fiber may help prevent colon cancer.

Medically valid uses

Some large studies have suggested that fiber in the diet, especially from whole grains, may lower colorectal cancer risk. Research in this area is still ongoing. Many studies have shown that people and cultures whose diet is made up largely of fruits and vegetables have a lower rate of colon cancer. This is compared to those whose diet contains large amounts of meat and animal fats.

Fiber is also used to:

  • Improve the taste and texture of food

  • Improve retention of water in foods

  • Prevent constipation

  • Bulk up some liquid medicines

Fiber is also used as a no-calorie or low-calorie meat expander in foods such as hamburger. It’s also used as a low-calorie fat substitute. Fiber can also be used as a surgical dressing for wounds.

Unsubstantiated claims

There may be benefits that haven't yet been proven through research.

Fiber may help treat diverticulosis and diabetes. It may also help treat high cholesterol and high blood pressure.

Dosing format

The Adequate Intake (AI) for total fiber in foods is shown below:


Grams (g) of fiber per day

Children ages 1 to 3 years

19 g

Children ages 4 to 8 years

25 g

Males 9 to 13 years

31 g

Females 9 to 13 years

26 g

Males 14 to 18 years

38 g

Females 14 to 18 years

26 g

Males 19 to years

38 g

Females 19 to 50 years

25 g

Males 50 years and older

30 g

Females 50 years and older

21 g

Pregnant women

28 g

Lactating women

29 g

Many people in the U.S. don’t get enough fiber in their diet. When adding more fiber to your diet, increase it slowly over time. Make sure to drink plenty of water. This can reduce the risk of gastrointestinal issues.

Side effects, toxicity, and interactions

Some fiber sources can cause diarrhea. Others can cause constipation.

There are no known food or medicine interactions linked with fiber.

Online Medical Reviewer: Brittany Poulson MDA RDN CD CDE
Online Medical Reviewer: Heather M Trevino BSN RNC
Date Last Reviewed: 8/1/2023