I have an ED too. It's very misleading to define an ED by how much weight a person loses or gains. It's not about pounds at all. It's also not about what other people think is acceptable for you - one person's idea of "slender" or "fat" could in fact be an very unhealthy ideal for another person. Once, I had an aunt tell me was fat when I was 12-13, and I only weighed 105 pounds at 5'4". In fact, at the time, I was a little underweight. But no surprise I spent the next 6 years trying to keep my weight under 110 pounds, despite growing taller, going through puberty and developing breasts.
All EDs hinge on unresolved psychological issues with anxiety, personal control and self-worth. Someone who is anorexic or bulminic may be doing these behaviors not necessarily to look a certain way, but to impose a sense of control and order, to alleviate anxiety or compensate overwheming emotional responses. I know a lot of anorexics who may not be dangerously thin but still have very serious psychological issues. So even if they aren't "concentration camp" thin, they're still unhealthy AND unhappy. For example, that's not uncommon is for the anorexic to deny her/himself food and then "prop" themselves up with rationalizations like "See, I can control what I eat unlike my fat mother/sibling/classmates/Britney Spears/etc" and that makes them feel OK for a little while - until the next thing that throws them emotionally off-balance. The problem of course is that it's irrational and the behavior is not an appropriate or effective response to the real problem, which is usually anxiety, feeling "chaotic emotions" or low self-worth.