There is no hard fast rule about fiber.It really makes a big difference for some people with diarrhea predominate IBS.It makes others worse.It makes sense to give it a couple of weeks to see if it overall reduces attacks or not.Even in it helps most of the time IBS is not constant so there may be times when it doesn't work. (and lots of things trigger diarrhea...caffiene, alcohol, fructose, sorbitol (in some fruits plus sugarless candies), manitol, lactose...)If it increases the # or severity of attacks while taking it for a couple of weeks then I would discontinue it.K