Definition of Fiber

fiber sourcesFiber, the indigestible residue of plant-based foods, adds bulk to the gastrointestinal contents.

This bulk helps stimulate peristalsis, the rhythmic muscle contractions of the intestinal wall that move gastrointestinal contents through the digestive process.

In the small intestine where digestive juices work to break down food particles into molecules of nutrients, the consistency fiber adds to the chyme (the thick, liquid mixture the stomach sends to the intestines) helps keep the food in the small intestine long enough for complete digestion to take place.

In the colon, fiber helps maintain more fluid in the stool, keeping this digestive waste soft enough to pass easily from the body during a bowel movement.


A number of studies suggest a diet high in fiber and low in saturated fats measurably reduces the risk for intestinal polyps as well as for colorectal cancer. Good sources of dietary fiber include fruits, vegetables, and whole grains and whole grain products. Products such as methylcellulose (Citrucel) and psyllium (Metamucil) can supplement dietary fiber.

Drinking plenty of water is also important to keep the body hydrated, which reduces the amount of water the colon extracts from digestive waste.


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