When I was in school I ate the fatty cheeseburgers, hot dogs, corn dogs, pizza, frito chili pie and so on... hell I still do. Guess what? I'm not fat! Do you know why? I got my lazy ass out of the house and exercised, played outside, ran around and so on. It's not so much as to what they're eating as to burning off the calories they're taking in. Back in the day there was no "opting" out of P.E. You went to class and did physical activity. In order to be in shape and not obese, you must exercise in some fashion. Eating well along side that definitely helps, but that alone doesn't solve the problem.