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Fiber is the general name for certain carbohydrates -- usually parts of vegetables, plants, and grains -- that the body can't fully digest. While fiber isn't broken down and absorbed like nutrients, it still plays a key role in good health.

There are two main types of fiber. They are soluble fiber (which dissolves in water) and insoluble fiber (which does not). Combined, they're called total fiber.

Why do people take fiber?

A number of studies have found that a high intake of total fiber, from foods and supplements, lowers the risk of heart disease. High-fiber diets have also been associated with a reduced risk of type 2 diabetes.

Insoluble fiber adds bulk to stools. It helps treat constipation and diverticular disease and may benefit people with some types of IBS ( irritable bowel syndrome). Some studies seem to show that insoluble fiber can reduce the risk of colon cancer. However, larger and more recent studies have shown no benefit.

Soluble fiber seems to lower cholesterol levels. It binds with cholesterol in the intestines and prevents it from being absorbed. Soluble fiber may also be useful in treating diabetes and insulin resistance ( prediabetes). It can slow the absorption of carbohydrates, helping to improve blood sugar levels.

Since fiber is filling and has very few calories, high-fiber foods may also help with weight loss.

How much fiber should you take?

Fiber that comes from whole foods is called dietary fiber. Fiber that's sold in supplements, or added to fortified foods, is called functional fiber. The Institute of Medicine has set an adequate intake (AI) for total fiber, which includes all sources. Getting this amount of fiber should be enough to stay healthy. Doctors may recommend higher doses of fiber.

Adequate Intake (AI)
1-3 years 19 g/day
4-8 years 25 g/day
9-18 years 26 g/day
19-50 years 25 g/day
51 years and up 21 g/day
Pregnant 28 g/day
Breastfeeding 29 g/day
9-13 years 31 g/day
14-50 years 38 g/day
51 years and up 30 g/day

Even in high amounts, fiber appears to be safe. Experts have not discovered an amount of fiber that's harmful.

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