Hey, everyone has pretty much said everything already but just a tip, try not eating within at least two hours before you exercise. Basically you burn what you eat first, so if you give it time to digest then you body will cross over to burning fats alot longer. Also if you are as fit you say you are then the cross over point will be faster too, fats are a better source of fuel for endurance. That said, dont be shy to do longer session that are less intense. So for instance, instead of going for a hour cycle at 80% of max HR, go for 1,5 hours, or 2hours at 60% max HR.. Goodluck.
