There's not much evidence indicating fiber-fortified foods have the same effect on the body that naturally-occurring fibrous foods. The reality is that fiber-fortified foods tend to be not very nutritious in other ways (i.e., high sugar). Best recommendation: stick with naturally-occurring fibrous foods which have minimal, if any, processing involved (e.g., whole grains, legumes, vegetables, fruit).
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."