Fiber absorbs water, so for some, depending on where they are on the diarrhea side and how fiber effects them, will find fiber helps.Others find it makes things worse.Some fibers are gassier than others, I can't predict ahead of time how much that may bother any given individual, or which fibers they may tolerate.Fiber is not a stimulatory or osmotic laxative. It absorbs water. It holds onto the water it absorbs. So it keeps the colon from removing as much water from stool keeping it wet enough to pass, but also it can absorb some excess water in the stool and provide a bit of bulk so there is something solid to make the stool from.