It depends on what kind of fiber you are talking about... There are two kinds.. soluable or insoluable... each works in a different way ..... If one has IBS C one would want to add the fiber that adds roughage.. leafy greens.. twigs and bark.... so to speak... adds lots of roughage.. to move things along.. drinking lots of water with this will help too..If one is IBS D they would want.. carrots.. apples.. oat bran...etc.. which form bulk.. but also absorb water.. Do a search to find out the foods that fall into each group.. You will be surprised by what you read and find..If you wait a few seconds too long before you drink your fiber supplement you are drinking a sludgey type drink.. well this is how these react in the bowel too... bulking things up..It works.... you just have to add the right one.. in the right amount..