I have sort of come to the conclusion - after 30 years on this planet - that you are the weight you are destined to be.
You can change it by desperately manipulating certain factors.... changing your life radically.... if that's what makes you happy and content in your own skin, so be it. It made me happy for quite some while. It's a fucking blast to fit into size 8 jeans!
But now, my happiness comes from elsewhere.. eating a nice plate of spaghetti bolegnaise, enjoying a bottle of red wine, being with friends, having great sex (and by the way my sexuality hasn't changed one bit between sizes 8-12/14... and believe me I get picked up on more now I'm more voluptuous).
I don't know, I think priorities change. There is NO.. I repeat NO excuse, barring medical problems, to be obese... But I think our bodies do want to be a certain weight. Check out your parents for genetical clues. There comes a point where it doesn't matter anymore. At least not to the point of consuming your every thought. That's a waste of life, I believe.