I find that eating mild hot soup daily works.
Funny, soup was one of the things that made my IBS worse before I discovered activated carbon.
When doctors find themselves confronting something they don't know, they just call it a "syndrome." That's not a big deal, but then the temptation is to sweep other things that may or may not be related into the same "syndrome" basket.
Common sense would tell you that diarrhea-predominant IBS and constipation-predominant IBS might have very different causes and cures. But it's all IBS to the doctors.