Fiber: Its Importance In Your Diet

How Does The Body Use Fiber?

Fiber has numerous effects in the large intestine:

  • Fiber is attacked and broken down by the huge population of bacteria that live in the colon.
  • The breakdown products are acids and gases. This process is called fermentation. Dietary fiber is only partly fermented, because some plant cell walls resist bacterial attack.
  • The simple organic acids produced by fermentation are mostly absorbed, and in doing so they nourish the lining of the colon. They also provide fuel for the rest of the body, especially the liver. This may have important consequences for metabolism; half the calories in fiber are made available to the body.
  • The gases arising from fermentation soften and enlarge the stool. They are also passed as wind (flatus) and can contribute to bloated feelings in some people.

Here is a summary of the actions of dietary fiber at different levels of the digestive system:


Makes work, slows ingestion, cleans teeth


Dilutes contents, distends, prolongs retention of food

Small intestine

Dilutes contents, distends, slows absorption

Right colon

Dilutes, distends, feeds bacteria and so acidifies contents

Left colon

Nourishes the colon, speeds up passage, lowers pressures

Rectum, anus

Softens and enlarges stool, prevents trauma to the body,

reduces strain of defecation

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