The starches in the banana have turned to sugar, but they should have the same amount of carbs. Bananas are fairly high on the glycemic index--high in simple sugars.

bananna sugar is fructose
thats a simple sugar but is low on the GI scale

some differnt GI ratings

Banana, slightly under-ripe (yellow with green sections) (USA) 42
Banana, over-ripe (yellow flecked with brown) (USA) 48

Porridge made from raw rolled oats 58
Porridge made from raw rolled oats (USA) 75
Raw rolled oats, uncooked: Lowan's Whole Foods,, Australia 59

from

http://www.glycemicindex.com/


But i wouldnt use them as my only source of carbs. not even close ide rather oats b.c of extra fiber and good fats.