Your body burns 400 calories an hour even if you're just going easy, and you can burn over 1000 calories an hour going hard. Either way, you have to put back some of it, at least 180 - 250 calories an hour, or you'll start feeling lousy.
There are natural alternatives. Clif bars are pretty healthy and tasty. Even my step-mother, who refuses to eat anything that has more than six ingredients listed and was shocked when she saw I would give them to my kids, had to admit they are pretty non-threatening.
Bananas were popular with cyclists for decades and still work fine. Peanut M&M's, trail mix, rice cakes with honey or jam, Fig Newtons, have all gotten me through long rides at one time or another.
BL