Disclaimer***I don't watch Dr. Phil, but sometimes when I'm flipping through channels it catches my attention and I stop for a few.***
Anyway, one episode was about an obese man whose wife and daugher were berating him for being heavy and the daughter herself was obese! Dr. Phil asked the daughter where she get's off calling her dad a fat slob when she is obese too and she answered, "It's genetic." Dr. Phil told her "Genetics only determines who has the potential to be fat."
I had never thought of it that way, but he's right.
While I'm sure there are some people who will never be skinny due to their genetics (talking about myself here :)), I would find it hard to believe you can maintain a 100, 200 or 300lb excess if you were eating healthy and taking care of yourself.