Dietary Fiber Fiber

Overview & Description

There is no official definition of dietary fiber. Experts in the field of food chemistry are currently debating an appropriate definition. Presently, the most accepted definition of dietary fiber is that it is the part of plant foods that cannot be digested or absorbed by humans.

There are two types of dietary fiber, soluble and insoluble. They both have very different functions in the body. Nearly all fiber-containing foods have more insoluble fiber than soluble fiber.


Increased fiber intake in the diet should be done gradually. Fiber can cause increased gas and bloating. It is also important to drink lots of water when on a higher fiber diet or when increasing fiber in the diet. Water helps to move the fiber through the system. Aim for at least eight 8-ounce glasses per day.

There are many things people can do to increase the fiber in their daily diet:

  • Read food labels and choose foods high in fiber.
  • Choose fiber-rich breakfast cereals and eat a bowl every morning. Look for cereal that contains at least 5 grams or more of fiber per serving.
  • Switch to whole-grains breads, pasta, and rice.
  • Eat dried beans at least two to three times per week. They are great in soups or salads.
  • Eat at least five servings of fruits and vegetables daily.
  • Eat the edible skin on fruits and vegetables.
  • Choose whole fruit rather than fruit juice as often as possible. Fiber is found in the peel and pulp, both of which are usually removed when the fruit is made into juice.
  • Functions and Sources

    What food source is the nutrient found in?

    There is no RDA for fiber. However, the National Cancer Institute recommends consuming 20 to 30 grams of dietary fiber per day, with an upper limit of 35 grams. This should include a mix of soluble and insoluble fiber. Most Americans eat about 14 to 15 grams of fiber per day.

    Following are some common sources of soluble fiber:

  • apples
  • barley
  • beans
  • citrus fruits
  • many vegetables
  • oats
  • peas
  • psyllium seed
  • squash
  • strawberries
  • Common sources of insoluble fiber are as follows:

  • bran
  • breakfast cereals
  • corn
  • flaxseed
  • peppers
  • potatoes
  • skins of fruits and vegetables
  • whole-wheat and whole-grain products
  • Most popular American foods are not high in dietary fiber. When choosing a cereal, check the food labels for a cereal with 5 or more grams of fiber per serving. Use whole grain breads such as:

  • corn bread from whole, ground cornmeal
  • cracked wheat bread
  • oatmeal bread
  • pumpernickel bread
  • rye bread
  • whole-wheat bread
  • Grains that have been refined have had the fiber removed. White flour, for example, is whole-wheat flour that has had the fiber removed during refining. Whole-wheat flour is a good source of fiber. White flour is not. Be aware that just because bread is brown does not mean it is high in fiber. Look for the words “whole-wheat” or “whole-grain” to make sure the product is made with wheat flour and has fiber in it.

    Legumes are the best source of fiber. This food group includes dried peas and beans.

    How does the nutrient affect the body?

    Some studies suggest that an intake of fiber-rich foods may decrease the risk of colorectal cancer. It is estimated that the risk of colorectal cancer in the United States population could be reduced by about 31% if fiber intake from food sources were increased by an average of about 13 grams per day. Clinical trials using the incidence of colorectal polyps as a marker for colon cancer risk have not supported these studies. However, these studies did not measure fiber intake adequately.

    A diet rich in fiber can be helpful with weight management. Fiber can provide more volume with fewer calories. It may help a person feel satisfied for a longer period of time between meals.

    Fiber has a role in the treatment of diabetes because it slows the absorption of glucose from the small intestine. If blood glucose levels after meals are elevated, adding soluble fiber to the diet can minimize this abnormal glucose spike.

    When included in a diet low in saturated fat and cholesterol, soluble fiber can help reduce blood cholesterol levels. In the body, these fibers bind with bile acids. Bile acids are made in the liver from cholesterol. When bile acids are bound to fiber, they are excreted in the stool. This causes more cholesterol to be used to make bile acids. This leads to an overall lowering of blood cholesterol levels. The effect may be subtle, but even a small drop in blood cholesterol levels can protect against heart disease.

    Fiber has been used for many years to treat constipation and promote regularity. Fiber does this by increasing the bulk of stools, which hurries the stool through the gastrointestinal, or GI, tract. Fiber can also help prevent hemorrhoids and diverticulosis.

    Article type: xmedgeneral