Increase fiber or not?

Another way of treating the symptoms of IBS is increasing dietary fiber. Here's were it gets tricky for some people. Many foods high in fiber tend to bother people with IBS. Some of these foods are whole grains, fruits, vegetables and beans. Although fiber can help reduce constipation it can make gas and cramping worse.

A doctor may recommend taking fiber supplements such as psyllium (Metamucil) or methylcellulose (Citrucel). A supplement causes less gas and bloating. When taking these supplements it is important to introduce them gradually and drink plenty of water every day to minimize gas, bloating and constipation. A person who finds that taking fiber helps their IBS they should use it on a regular basis for best results.
Fiber may also be helpful for people with diarrhea predominant symptoms as it can improve the consistency of stool. For some people fiber will just make symptoms worse and are advised on other laxative treatments.
A person who is cutting out fruits and vegetables out of their diet may want to talk to a Dietitian because they are missing some essential nutrients

Mayo Clinic-Treatments
UpToDate-see link to laxative treatments (Patient information: Constipation in adults (Beyond the Basics)