Dietary fiber is the collective name for a group of indigestible carbohydrate-based compounds found in plants. They are the materials that give the plant rigidity and structure. The IBS diet is a high fiber/ low fat diet. The role of fiber is crucial in controlling the quality of stool in the colon, while reducing the consumption of fat is both healthful and avoids counteracting the actions of fiber. Fiber is also called roughage or bulk.

Two types of fiber are important to human health, insoluble fiber and soluble fiber. Insoluble fiber is fiber that moves through the digestive system essentially unchanged. It is not digested, and it does not provide energy (calories). What fiber does is provide bulk to stool that helps it move through the large intestine. It also traps water, which helps the stool remain soft and easy to eliminate. In people with diarrhea, it can help trap excess water.

Studies find that the average American eats only 5-14 grams of fiber daily, but the recommended amounts are much higher. The United States Institute of Medicine (IOM) of the National Academy of Sciences has issued the following daily Recommended Dietary Intakes (RDIs) for fiber.

•men age 50 and younger: 38 grams

•women age 50 and younger: 25 grams

•men age 51 and older: 30 grams

•women age 51 and older: 21 grams

•children: 5 grams plus at least one gram for every year of age


To follow the IBS diet, individuals should gradually increase their consumption of fiber to meet or exceed the RDI. Foods that are high in insoluble fiber include:

•whole grains and foods made of whole grains, such as whole wheat bread and whole wheat pasta, couscous, or bulgur

•bran and bran breakfast cereals

•brown rice




Soluble fiber dissolves in water to form a gel-like substance. This gel helps keep stool soft. Good sources of insoluble fiber include:

•oatmeal and foods made with oats

•foods such as chili or split pea soup that contain dried beans and peas




•citrus fruits


The total amount of fiber per serving must be listed on food labels in the United States. In 2007, regulations were under consideration that that would require soluble dietary fiber to be listed separately. A good list of high-fiber foods can be found at <http://www.gicare.pated/edtgs01.htm>. Most foods that are high in fiber are naturally low in fat.

People who have trouble consuming enough fiber and are still having difficulty with IBS symptoms can ask their doctor about bulk-forming or fiber supplement laxatives. These supplements are quite safe, although they should not be used for long periods unless directed by a doctor because the colon will become dependent on them to move stool. Some common brand names of fiber-supplement laxatives are Metamucil, Citrocel, Fiberall, Konsyl, and Serutan.

These must be taken with water. They provide extra fiber that absorbs intestinal water and helps keep the stool soft. The extra bulk also helps move materials through the colon.


Low residue/low fat IBS diet

For some people, the high fiber/low fat diet controls both constipation and diarrhea. For others, the high fiber foods trigger diarrhea. These individuals may have better control of diarrhea on the low fiber/ low residue diet. This diet substitutes cooked fruits and vegetables for raw ones and reduces the amount of whole-grain products. Along with these changes, the individual chooses a variety of low-fat foods.

Some foods that help control diarrhea on the low residue IBS diet include:


•low-fat mashed potatoes

•grated apples without the skin


•cream of rice

•smooth peanut butter



Other eating tips to control diarrhea are:

•Consume food and drink at room temperature rather than at hot temperatures

•Drink liquids between meals rather than with meals

•Limit dairy products

•Rest after meals. This slows down the digestive process


Because symptoms and triggers for IBS vary greatly, these diets are starting points for individuals to develop their own list of foods that control their individual symptoms. Keeping a food journal that records what was eaten and what caused symptoms can speed the development of a personalized IBS diet.