Initially fibre supplements and fibreous foods can cause extra gas and bloating BUT, this is only temporary until your system adjusts then all the bloating goes away and gas is cut down to a very minimal amount, not to mention the many other benefits of taking enough fibre everyday...cut out my mucus, gave me formed stools and even cut back frequency...fibre is actually highly recommended for IBSers along with probiotics (friendly bacteria) as IBSers tend to have bacterial overgrowth which exacerbates symptoms.
Fibre also helps sweep the bowels clean of bacteria so it works very well in conjunction with probiotics.
Fibre should be started in a small amount and taken with plenty of water and only increased slowly if necessary....it's done wonders for my crohns and IBS.
That has not been my experience for the last 30 years dealing with IBS C. I understand that there is a seeminly universal rule of thumb regarding fiber supplements, but it does not always work for those of us with chronic C, regardless of the length of time one takes it. I took fiber supplements religiously for 15 years and always suffered with painful gas. In addition, I ended up with a full colon impaction as a result of fiber being poured into a slow moving colon.
It is possible to get the necessary soluble fiber through food, which is what I do now. It is also important to tailor fiber intake to each person's specific issues. I think we can all agree there is no one thing that works for everyone!