As someone who yoyos from fit to land whale, I'd say there's a genetic component that drives one to overeat. It can be overcome, but it is persistent. You can contrast this with those who barely have an appetite at all. You can see it in animals, too. Friends and I have had some animals who would continuously eat if you allowed them to. Others can self regulate their food intake and seem to eat only when hungry. I have 2 cats and I just leave them a salad bowl filled with kibble. They're not fat by any means and self regulate their food. I've also owned cats that could not stop eating, and if left alone with food would eat until vomiting. LOL I've done the same. I can keep it under control but there will always be days in which I binge eat.