I was very thin and lanky as a child and a into my teens. I did obsess about my body image and weight. At 18 I had a very traumatic, life altering event and almost stopped eating. I alternated between not caring at all and then back to obsessing about body image. I dropped to nearly 100 lbs and it almost killed me. I have lasting GI issues to this day.
I'm glad to say that I'm relatively normal in diet now and do like certain rich foods again and am at a healthy 128 lbs. I think I've transferred the obsession to sports, working out and running and I do still have (less) obsessive thoughts about body image. I did get cranky and edgy once when I peaked 135 lbs.