We created this section on Fiber, because we believe this is an important aspect of Irritable Bowel Syndrome. At the very bottom of this, you will find a list of foods with the grams of fiber they contain and a list of soluble and insoluble foods. You should be having 25g to 30g of fiber a day. Most people consume only 15g a day.

 There are different kinds of fiber. The more important one with those with IBS is soluble fiber. Most foods contain a mixture of soluble and insoluble fiber, so don't get confused when you see that one food is listed on both charts. A healthy diet should contain both soluble and insoluble fiber, meaning a variety of grains, vegetables and fruits.

Soluble substances are those that can be dissolved in water, whereas insoluble substances cannot. Soluble substances also tend to absorb water, which is where the principal benefit for IBS sufferers is derived. In comparison to insoluble fiber, the sugar molecules of soluble fiber are held together by chemical bonds that cannot be digested by the enzymes in the human gastrointestinal (GI) tract. As such, soluble fiber passes straight through your body intact meaning that more soluble fiber arrives in the colon and is available to absorb water. Water absorption from the colon by the fecal matter encourages the formation of stools that are gel-like, which helps to prevent diarrhea. But additional water absorption doesn’t mean that constipation-predominant sufferers will be adversely affected. In fact, the absorptive properties of soluble fiber mean that the passage of softer, gel-like waste will actually soften and encourage excretion of impacted fecal matter. Further, the gel-like consistency of waste containing soluble fiber means that the GI muscles are stretched around your full colon, which helps the muscles to grip during the waves of peristaltic contractions that act to force the waste through your gut. Violent and irregular muscle spasms are minimized, which means that abdominal cramping is also relieved.

Insoluble fiber does not dissolve in water but it attracts water into the small intestine. Insoluble fiber will decrease the time it takes for the intestinal content to pass through and be evacuated. It may also stimulate the production of mucus which coats the lining of the colon, and it is effective in promoting a normal bowel movement, and overcoming some abnormalities in colon motility. However, for IBS sufferers, insoluble fiber is a strong GI tract irritant. Transit time is speeded though the colon and some toxic substances may be excreted more rapidly with less possibility for injury to the body. The most common sources of insoluble fiber are bran, whole grains, some vegetables, and beans.

Fiber is also divided into two other categories: fermentable and nonfermentable. Fermentable fiber is fiber which may be acted on by the bacteria in the colon with the production of what are known as "volatile short chain fatty acids" as well as hydrogen, methane, and carbon dioxide. These are, of course, the elements of what we know commonly as "gas".

There are many dietary fiber supplements. Unprocessed wheat bran is also known as wheat bran or "Miller's bran". This is the husk of the wheat berry milled from flour. It contains no additives. It has very few calories and is not digested or absorbed normally, but it may be partially fermentable in the colon. Wheat bran is often mixed with other cereals, for example, All Bran. One tablespoon of wheat bran provides 4.5 grams of dietery fiber. Wheat bran may be added to other cereals, may be added to yogurt, cottage cheese, applesauce, and may be added to other foods in cooking such as bran mufins or even meat loaf. Psyllium seed, another common fiber supplement in many commercial preparations, is soluble and provides 6.0 grams of dietery fiber per tablespoon.

The following lists illustrate the foods with the highest fiber content in each grouping. We recommend that your diet contain 25 to 35 grams of fiber per minimum per day.