You might like this one

http://mediaville.livejournal.com/57649.html

Lost and Found

Summary: Jensen Ackles is a shy, overweight songwriter whose body issues have prevented him from forming any real personal connections, and at thirty, he’s still unsure of his sexuality, and still a virgin. But when he signs up for an experimental obesity research program, he meets Jared Padalecki, a stunningly sexy fitness guru who slowly but surely changes Jensen’s life.

Not quite what your looking for but it's a good one

I totally disagree that the title says it all! I don't get it... Is "Chubby Chasin'" like people who like chubby people sexually and so they chase the chubby? Or is it like people who don't want to be chubby and so they have eating disorders to chase the chubby away? ... ... *Is confused*. Oh, or is chubby chasing liking chubby chasing but then you also want eating disorder fic as a seperate request that has nothing to do with the first? Hmmm...\

Well anyways! I've got a couple of fics saved here on my delicious: http://delicious.com/dirtydancer14/eatingdisorder
Just as a note not all the stories I have saved under the eatingdisorder tag are neccesarily dealing with Anorexia or Bulimia. All include eating issues that are related to that sort of thing but some instances are more situational (For example in one story, Jensen as a kid was fostered by a family who mistreated him by not feeding him enough and forcing him to eat cookies until he threw up as a punishment for taking one without permission and so as a result of that he doesn't eat cookies and will barely eat in times of stress. So eating issues but not neccesarily a "disorder".)