Is eating a lot of junkfood bad for you if . . .?

Is eating a lot of junkfood bad for you if exercise almost daily, brush your teeth twice a day and eat just as much fruits, vegetables, etc as junkfood? I mean, I'm a very busy person and I find that if I don't eat food with sugar, I get really dizzy, and can't think straight sometimes. I mean, I'm six feet three inches and weigh 160 pounds which is a normal weight. So is it really that bad to eat junkfood a lot?