@ Cornellian - how can you say obesity is genetic?! Sure, genetic disorders may result in slower / altered breakdown of various bits and bobs, but ultimately it comes down to taking in more than your body is using - that's down to choice, not your DNA. And we weren't talking about genetic or glandular disorders anyway.
Granted there is a very very small minority with such disorders, but the majority of fatties are the way they are because they eat too much, and exercise too little. Simple.