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How Fiber is Digested by the Body

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Instructor: Donna Ricketts

Donna Ricketts is a health educator with 15 years of professional experience designing health and wellness programs for adults and children.

The body digests fiber through a process called fermentation. Learn about the benefits of consuming fiber, foods high in fiber, and the course of digestion in the human body. Updated: 10/21/2021

What Is Fiber?

Dietary fiber is a type of carbohydrate found in the portion of plants that is not digested by enzymes in the small intestine. While you may have heard other names for fiber that include 'bulk' and 'roughage,' be aware that these labels can be misleading because some forms of fiber are not bulky or rough at all.

There are two main types of fiber: soluble fiber, which dissolves in water, and insoluble fiber, which does not dissolve in water. Foods with soluble fiber include oatmeal, beans, apples and blueberries. Examples of insoluble fiber are whole grains, carrots, cucumbers and tomatoes. Both types are important in maintaining optimal health.

There is one more type of fiber, called fermentable fiber. Fermentable fiber is fiber that is resistant to digestion and absorption in your small intestine, just like soluble and insoluble fiber, but is broken down partially or completely by bacteria in the large intestine. Fermentable fibers are also called prebiotics.

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  • 0:01 What is Fiber?
  • 1:17 Digestion of Fiber
  • 2:35 Benefits of Fiber
  • 3:48 Lesson Summary
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Digestion of Fiber

Many types of soluble fiber can act as prebiotics, a food fiber that grows in plants that feed healthy bacteria. Onions, garlic and bananas are examples of where prebiotic soluble fiber can be found. Soluble fiber passes through the small intestine relatively unchanged until it reaches the colon, or large intestine, which is the part of your digestive system responsible for absorbing water from indigestible parts of food. It is here where fermentation of fiber occurs. Fermentation is the action of bacteria on prebiotic fiber, producing gases and short-chain fatty acids.

When the friendly bacteria called probiotics, bacteria that keeps disease-promoting microorganisms from infecting your colon, ferments or digests the probiotic fiber, it produces many nutrients that help keep your colon healthy. The products of the fermentation stimulate your bowels, retain water in your stool and bulk up your stool. Insoluble fiber passes through the colon relatively unchanged and helps bulk your stool.

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