There's an actual, real, medically documented genetic condition called Prader Willis Syndrome. It causes people to feel hungry all the time, and if left unsupervised they can (and have) literally eaten themselves to death. Like stomach exploding kinda death. They also tend to have low IQs and learning disabilities, which makes the situation more difficult. There's some documentaries on Youtube about it. If you want to watch something about it that's not so depressing, search "Joe Blackburn"