DEAR MAYO CLINIC: I experience constipation almost weekly, and eating bran flakes every day isn't helping. Are fiber supplements safe to use regularly and long term? Is there anything else I can do? I'm a 53-year-old woman and otherwise in excellent health.

ANSWER: When consumed at recommended levels, dietary fiber is widely recognized to have health benefits, including relief of constipation. Adult women 50 and younger should consume at least 25 grams of fiber a day. Women 51 and older should have at least 21 grams a day. Adult men need at least 38 grams of fiber a day if they are younger than 50 and at least 30 grams of fiber a day if they are 51 and older. Ninety percent of the U.S. population consumes far below those recommendations, averaging only 15 grams of daily fiber.

Fiber-rich foods include fruits, vegetables, whole grains and legumes. Many cereals, such as bran flakes, are good sources of fiber. Although fiber supplements can fill the daily fiber gap, they usually have only one type of fiber, rather than a variety of fibers and micronutrients, and they may not provide all the health benefits associated with fiber in food. Therefore, boost your fiber intake in your diet first by eating a wide variety of high-fiber foods.

If you still can't get enough fiber to meet the daily recommendation, consider using a supplement. Many fiber supplements can be used regularly long term. Fiber is classified as soluble or insoluble. Soluble fibers are more fermentable and may cause gas. Insoluble fibers move through the digestive system largely intact, and that can increase stool bulk.

Most fiber supplements are exclusively soluble or insoluble fiber. For example, FiberCon (calcium polycarbophil) and Benefiber (wheat dextrin) are mainly soluble fiber. They tend to cause more bloating and flatulence. Citrucel (methylcellulose) is mainly insoluble fibers that are nonfermentable, so it's less likely to contribute to bloating and gas. Psyllium husk (Metamucil and Konsyl) is rich in both soluble and insoluble fiber. Generally, fiber supplements with mainly insoluble fiber may be a better option for constipation.

Before taking a fiber supplement, ask your health care provider or pharmacist to review your medications. Fiber supplements can decrease the absorption of certain medications, including drugs that treat thyroid disorders, depression, diabetes, high cholesterol, seizures and various heart ailments. Even common medications such as aspirin, ibuprofen and penicillin can be affected by an increase in fiber. You may take your medications one hour before or two hours after eating fiber to minimize the interaction.

Some fiber supplements may not be appropriate for people with certain medical conditions. For example, if you have celiac disease, you may need to stay away from fiber products derived from wheat. If you have diabetes, you may need to use a flavorless formula to avoid extra sugar. Consult your health care provider for guidance about the appropriate fiber supplement.

Go slow as you begin fiber therapy. Fiber supplements may cause abdominal bloating, cramping and flatulence, especially if you start at a high dose. Begin with a low dose, gradually increasing the amount of fiber. Don't add more than 50 grams of fiber in a supplement per day, as that may affect how your body absorbs nutrients. Your health care provider can help determine what's right for you.

Drinking plenty of water and exercising regularly can help ease constipation, too. You also may want to consider nonfiber products, such as stool softeners, stimulant medications that cause your intestines to contract, enemas or suppositories.

If increasing fiber doesn't improve your symptoms, see your health care provider. Constipation can be a symptom of various underlying medical disorders, such as pelvic floor muscle dysfunction, slow gastrointestinal motility, anatomical abnormalities or endocrine dysfunction that may require different treatment. -- Yan Bi, M.D., Ph.D., Gastroenterology, Mayo Clinic, Jacksonville, Fla.

(Mayo Clinic Q & A is an educational resource and doesn't replace regular medical care. E-mail a question to MayoClinicQ&A@mayo.edu. For more information, visit www.mayoclinic.org.)

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