DEAR MAYO CLINIC:

I recently had a hernia operation and frequently find myself constipated. My physician recommended taking a powdered fiber supplement. Are there any long-term side effects from taking this type of product? If so, how long can I continue to take it safely?

ANSWER:

Constipation is a common problem. Doctors often recommend fiber supplements, also called bulk laxatives, for people with chronic constipation. In general, these powdered fiber supplements are gentle on your body and are safe to use long term.

Normally, the waste products of digestion (stool) are propelled through the intestines by muscle contractions. In the large intestine (colon), most of the water and salt in this waste mixture are reabsorbed because they're essential for many body functions. When the colon absorbs too much water, though, or if the colon's muscle contractions are slow, the stool becomes hard and dry and passes through the colon too slowly, causing constipation.

A high-fiber diet can help relieve constipation. Consuming at least 20 to 35 grams of fiber each day helps your body form soft, bulky stool. High-fiber foods include beans, whole grains and fresh fruits and vegetables. If you can't get enough fiber from the foods you eat to reduce constipation, a powdered fiber supplement may help.

Examples of fiber supplements available over-the-counter include FiberCon, Metamucil, Konsyl, Serutan and Citrucel. These products work by absorbing water to form soft, bulky stool, prompting normal contractions of the intestinal muscles. In general, fiber supplements have less effect on stool consistency than other laxatives.

There's no evidence that long-term use of fiber supplements is harmful. Make sure you take them with plenty of water, though. Otherwise, they can actually make constipation worse. Other side effects may include bloating, gas and cramping. Adding supplemental fiber to your diet slowly can usually reduce these side effects. If you experience bothersome side effects with a fiber supplement, try switching to a different brand. You may tolerate it better. Don't exceed the recommended dose of a fiber supplement unless your doctor tells you otherwise.

Also, ask your doctor or a pharmacist whether a fiber supplement may interact with any medications you take. Fiber supplements can decrease the absorption of certain medications, such as aspirin, warfarin and carbamazepine. Fiber supplements can also reduce blood sugar levels, which may require an adjustment in insulin dosage if you have diabetes.

In addition to adding fiber to your diet, there are other steps you can take to reduce constipation in the long run. For example, limit foods in your diet that are high in fat and sugar and low in fiber, such as ice cream, cheese and processed foods. These foods can make constipation worse. Make sure you're drinking plenty of non-caffeinated liquids, particularly water, throughout the day.

Regular physical exercise, such as walking, swimming or biking, can help stimulate intestinal function and reduce constipation, too. Most doctors recommend at least 30 minutes of exercise most days.

Finally, don't ignore the urge to have a bowel movement. The longer you delay, the more water is absorbed from your stool and the harder it becomes.

Although there's no evidence of long-term side effects from taking fiber supplements, if constipation lasts, seek help. It can take some time for constipation to respond to treatment. But, if taking a fiber supplement, along with other diet and lifestyle changes, doesn't reduce constipation, talk to your doctor about additional treatment options.

-- Adil Bharucha, M.B.B.S., M.D., Gastroenterology, Mayo Clinic, Rochester, Minn.

Medical Edge from Mayo Clinic is an educational resource and doesn't replace regular medical care.

(c) 2009 Mayo Clinic