Different types of carbohydrates have different absorption rates. GU and others concentrate on giving you carbs that will absorb fast.
Bananas were my first attempt at fueling while cycling and they did reasonable for me. I cut them in thirds and put them in a plastic bag. Ate one section every 15 minutes. But when my rides got to be two or more hours....... well that just wouldn't work. So 60/40 or 40/60 (depending on ride type) water and fruit juice in the bottles became my norm. Currently I'm using Hammer's HEED in my bottles. But others are likely just as okay. So too are GU gels and other such if you prefer to eat your carbs.
Just remember it's fuel for the bike. If you are having issues off the bike, carbs alone probably won't fix that and actually will contribute to make it worse in the long run.