For centuries, dietary fiber has been reported to improve the movement of food/fluid through the intestinal tract, improve overall health and prolong life. The “fiber hypothesis” put forth by Hugh Trowell, proposed that a diet high in fiber and unrefined carbohydrate would help protect people against many Western diseases such as colon cancer, diverticular disease (where outpouchings occur in the wall of the large intestine), constipation and obesity. Over the past several years, there has been much data to support the beneficial effects of fiber on the GI tract and health.

Dietary fiber is a complex mixture of substances which play different roles in the digestive tract. What is most important clinically is whether these substances are soluble (able to be broken down by water in the body) or insoluble. Generally, cellulose, (the main component in plant cell walls), lignin, (a non-carbohydrate material very resistant to being broken down) and some hemicellulose are insoluble. Plants with high concentrations of insoluble fibers include unrefined vegetables and grain fibers like unprocessed whole wheat bran. Most soluble fibers include pectin, gums, mucilage, and hemicellulose. Examples of plants with a lot of soluble fibers include fruits and oat bran.

In your GI tract, specifically your colon, there are bacteria that cause the fiber to ferment, with the by-products of this process helping with water and electrolyte absorption. Fiber itself can hold a significant amount of water, with fiber from cereal grains holding more water than fruits and vegetables. Fiber increases stool size which results in stool moving through your colon faster. One way to think of fiber is that it’s like a sponge; it can pull in more fluid if needed or get rid of excess fluid.

So, what role does fiber play in various colonic diseases? It reverses mild constipation in most people, but the results aren’t as consistent in people who have severe constipation. It’s important to remember that a low fiber diet is only one of the many causes of constipation. It does seem that the patients who experience incomplete evacuation didn’t respond as well to increasing their fiber intake. Dr. Lembo recommends that patients have a trial of fiber therapy before having any diagnostic testing done.

For people with IBS, Dr. Lembo writes that there is no convincing evidence that exists to support the effectiveness of using it in the treatment of most patients with moderate to severe symptoms of IBS. IBS patients and normal subjects have been found to consume similar amounts of dietary fiber, and in certain groups of patients, it may even make the symptoms worse. It does seem that fiber may have a helpful effect on the sensations of discomfort/pain.

For those suffering from Diverticulosis, most studies suggest that diverticular disease is associated with a low intake of dietary fiber and that treating the disease by increasing your fiber may relieve symptoms and improve the function of the colon. There is also some evidence suggesting that less surgery is performed for the complications of diverticular disease when a high fiber diet is followed.

Studies have also shown that eating vegetables is associated with a decreased risk of colon cancer and that consumption of meat is positively associated with an increased risk of colon cancer. A study that looked at several other studies found a lower risk of colon cancer with higher fiber intake, especially the insoluble fibers. There are lots of ideas about why fiber helps protect against colon cancer including: diluting potential cancer causing agents by absorption, reducing the time it takes for stool to move through the intestines, or changing the bacterial composition of the by-products of fermentation.

In Dr. Lembo’s conclusion, he writes that dietary fiber is important to help maintain the normal functioning of your colon. Its role in the treatment and prevention of diseases of the colon is not completely understood, but there is general agreement that dietary fiber should be part of a healthy diet.

At the Neuroenteric Disease program, we believe that every patient should have an adequate trial of fiber in their diet, which means starting with a small amount, building up your dosage very slowly (to allow your system to adapt and prevent/minimize bloating) and taking it on a daily basis with your meals. You may also need to try different foods or different commercial brands to find out what combination is right for you. Fiber is not just for problems with constipation. Many people aren’t aware of the importance of the sponge-like role that fiber can play in helping your body’s digestive system to function optimally.

If you would like to learn more about possible involvement in our research studies and/or our IBS class, please call (310) 268-3432.

Summarized from "FIBER AND ITS EFFECT ON COLONIC FUNCTION IN HEALTH AND DISEASE" by Tony Lembo, MD