What role does fiber have in the treatment of IBS?

Lin Chang MD  

Fiber is indicated in the treatment of irritable bowel syndrome, but specifically it is more effective in patients who have predominantly constipation. In studies, it hasn't really been shown to be more effective than placebo in treating the overall symptoms of IBS, but it can certainly help constipation symptoms, such as easing stool passage, improving stool form. So I think it can be very useful in those patients. Anecdotally, it's been used in patients with IBS with diarrhea, but there haven't been any studies to support its efficacy over placebo in those situations.

There are different types of fiber that can be used. They typically will be subgrouped in two different types: psyllium products and the methylcellulose products. Also patients can increase fiber in their diet with fruits and vegetables. Usually, you're aiming for about 25 g of fiber per day to help constipation symptoms.

There are side-effects to fiber that the patients have to be educated about. Those include bloating, sometimes abdominal cramping, softening the stool and even diarrhea, if they're not used to taking fiber. Typically, I advise the patients to start with a smaller dose. For example, if the normal daily dose is one tablespoon per day of psyllium, I will tell them to start at one teaspoon and then work up to two teaspoons until they make it up to one tablespoon to see how they do with their symptoms.

I think fiber can be very useful, particularly in patients with mild constipation. Many of the patients whom I refer to tertiary care referral centers have more severe constipation. They'll have tried fiber and it usually doesn't help them. Or it may help them to a certain degree and they usually need other medications to help with their pain and their constipation.