In the most recent Christmas lectures, they wired up an adult, and two groups of kids.
The adult rested throughout the programme, one group of kids just watched the lecture, and the other group exercised vigorously from time to time.
They all burned around about the same amount of calories! The differences were not great.
Exercising does make you fitter, and therefore more likely to have an otherwise non-sedentary life-style.
Perhaps that alone discourages one from eating so much, maybe because of the more content and fulfilled life. Certainly a healthier life-style.
But I would have thought that that alone seems to indicate, it is more about what goes in and the quality of what is going in!
Just to qualify my comment, I am not suggesting that a sedentary lifestyle burns as many calories as an active lifestyle. More of an "exercise routine" does not add much to an overall daily or weekly baseline of calories burnt.