It's fiber. For those complaining about the size of the capsules, go get some kind of powder that you stir into your drink. I hate that powdery stuff. The capsules are the same size as BeneFiber pills, and most fiber supplements. I've found these to work better than most for keeping things regular, especially if you're on medication (such as pain killers) which might cause issues. Never tried them for dieting purposes or to "feel full" so I can't comment on such claims. I'm pretty sure the manufacturer doesn't make such claims either.Like I said - it's fiber. What else is there to say?