Dietary Fiber

Irritable bowel syndrome (IBS) is one of the most common and troublesome conditions for which individuals seek medical attention. Specific food practices may contribute to symptoms of constipation, diarrhea, bloating, gas, and abdominal pain. Adding fiber to your diet may help improve bowel function and decrease symptom severity.

Fiber is a double-edged sword for people with intestinal disorders. While fiber alleviates constipation, certain high fiber foods, such as bran, may increase gas production and bloating. However, it seems likely that most people with IBS will benefit from at least a moderate increase in dietary fiber intake.

While fiber may appear to be a simple solution, the typical Western diet for adults often fall below the current recommendation of 20–35gm per day. Adding too much fiber too fast can result in a worse condition than being on a low fiber diet. A gradual increase in dietary fiber can modify, improve and, in some people, eliminate the abnormal bowel habits and painful symptoms associated with IBS.

People who have difficulty obtaining the goal of 20–35gm per day through diet alone may find fiber supplementation helpful. With any dietary fiber, the guideline is to start low, go slow.

As an added benefit, consuming generous amounts of fiber in your everyday diet potentially can improve overall health. Fruits and vegetables appear to exert a strong healthy effect.

Gastrointestinal (GI) Health Benefits of Dietary Fiber

Dietary fiber has specific benefits for maintaining GI health. High fiber foods take longer to chew, which gives the brain a chance to register fullness, preventing overeating. High fiber foods also slow digestion, which prolongs this feeling of fullness.

Research in fiber and GI health took off in the 1970s when a link was first proposed between high fiber intake and low rates of some chronic diseases. While the use of dietary fiber in the treatment of certain GI disorders may be debatable, the evidence to at least consider fiber therapy is strong.

IBS patients who are prone to constipation appear to benefit the most from fiber treatment. Other people with various forms of GI disorders may benefit from a variety of treatments involving more than a little trial and error. Because these disorders have many components, the greatest challenge will be in identifying one or several strategies that prove effective.

Soluble and Insoluble Fiber

Dietary fiber can be classified as either soluble or insoluble. Soluble fiber (found in vegetables, fruits, and oat cereals for example) dissolves in water, becomes a soft gel, and is readily fermented. These include pectin, guar gum, and other gums.

Insoluble fiber does not dissolve or gel in water and is poorly fermented. Cellulose (found in legumes, seeds, root vegetables, and vegetables in the cabbage family), wheat bran, and corn bran are examples of insoluble fiber.

If you find that fiber seems to be a problem that causes you to feel bloating or pain, it is usually insoluble fiber that is the problem. Soluble fiber is less likely to be a problem. But the reaction is the opposite in some people, so trial and error may be the best option.

High fiber substances containing both soluble and insoluble fibers have the properties of both. They include oat bran, psyllium, and soy fiber. Methylcellulose is a semi-synthetic fiber. It is soluble and gel forming, but not fermentable.

Types of fiber differ in the speed and extent to which they are digested in the GI tract, and in the process of fermentation. There may be both good and bad aspects to fermentation, but there are certainly metabolic products produced by fermentation which contribute to colonic health. The solubility and fermentation of a particular fiber affects how it is handled in the GI tract.

Since the effect of identical fibers varies from person to person, individual response may vary. We encourage individuals try different types of fiber.

Specific Treatment Using Dietary Fiber

Despite some uncertainties about its use and effectiveness, fiber is a reasonable approach in treatment of GI disorders, particularly in IBS with constipation. Once a diagnosis of IBS is made, your physician may suggest the fibers listed below for treatment of various symptoms.

IBS Symptoms Fiber Treatment
Lower abdominal pain Methylcellulose or Psyllium
Upper abdominal pain Oatmeal, Oat bran, or Psyllium
Constipation Methylcellulose or Psyllium
Incomplete evacuation Methylcellulose or Psyllium
Diarrhea Psyllium or Oligofructose
Excessive gas Methylcellulose or Polycarbophil

Nutrition therapy, with an emphasis on dietary fiber modification, appears to be a safe and effective initial treatment of gastrointestinal disorders, particularly in constipation prone individuals. Fiber intake can be tailored to the symptoms most evident and can be fine-tuned in partnership with a medical care provider.

Tips for Adding Fiber to Your Diet

Making small, gradual changes can add up to a big difference in the nutritional value of your diet. Experiment with fresh foods and don’t be afraid to try new foods and recipes. Here are a few practical tips for adding fiber to your diet.


  • Cook in microwave to save time and nutrients
  • Cook only until tender-crisp to retain taste and nutrients


  • Replace the meat in salads and main dishes with presoaked dried beans and peas
  • Presoaking reduces the gas-producing potential of beans if you discard the soaking water and cook using fresh water
  • Use a slow cooker for bean soups and stews


  • Snack on fruit anytime, anywhere
  • Experiment with unusual fruits such as kiwi, pineapple, and mangos
  • Leave peelings on fruit whenever possible
  • Use fresh and dried fruit in muffins, pancakes, quick breads, and on top of frozen yogurt


  • Choose whole-grain varieties of breads, muffins, bagels, and English muffins
  • Try fresh pasta instead of dried
  • Mix barely cooked vegetables with pasta for a quick pasta salad


Adapted from IFFGD Publication #152 by James W. Anderson, MD, Professor of Medicine and Clinical Nutrition, University of Kentucky; Chief, Endocrine-Metabolic Section, VA Medical Center, Lexington, KY. Last modified on September 15, 2014 at 12:43:28 PM

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IFFGD is a nonprofit education and research organization. Our mission is to inform, assist, and support people affected by gastrointestinal disorders.

Our original content is authored specifically for IFFGD readers, in response to your questions and concerns.

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