Any stimulant tends to do that ... for me caffeine seems to be the worst offender. I find by supplementing my diet with a bowl of Kellogg's All-Bran and some non-fat yoghurt (Astro brand), I can add 20g of fiber to my diet (the minimum amount of fiber you should be having is 25-30g) while only adding 250 kcals.
The alternative is chopped spinach, but that's not too pleasant, either.