You know this is a really interesting point you make. Nobody's inherently fat or thin. There are fat people who lose weight and become (and stay) thin. There are people who where once thin and spend the rest of their lives as fat. There are people who go through fat and thin "phases". There are people who do neither. What makes you a thin person, in both body and mind, is the attitude you just described. It's a kind of default. You just don't busy yourself with food and that's exactly why it's not a problem.