I came on this forum to read experiences about effects of dietary fiber and foods in general on gastrointestinal symptoms, since I'm writing an article about nutrients and I'm trying to get an impression about what can be good or bad "for many" and what only for some.
@Susan. You have a "pseudo" word in your sig, what made me think you consider your condition complicated, so I did not planned to come with some specific advice. I'm not trying to devaluate any condition. White bread constipates me, it may be annoying and I even don't have IBS.
I believe, a doctor can give a diagnosis of IBS based on symptoms (abdominal discomfort for at least three months, at least three days in a month...), but only after exclusion of organic disorders, including fructose malabsorption (FM). Diarrhea is a typical symptom in FM and insoluble fiber may worsen diarrhea in FM, since it absorbs water and makes stool bulky and thus acts as a laxative. I don't know why additionally include IBS principle here, but I'm sure Syl has some reason to sig with IBS rather than FM.
These search results show that *some* (not all) people on this forum believe psyllium may worsen their symptoms, despite its SF>IF ratio. It might simply be an *amount* of IF in psyllium that is problematic.
Fructooligosaccharides (FOS), a soluble fiber, may worsen symptoms in IBS, at least in first weeks after introduction.