@emeraldshamrock - I have also had one. No it wasn't peer pressure but it did begin as a fear of becoming fat and a desire to be thin. This was likely started through societal pressure and Tv shows like the ones I described.
Obviously it then develops into something worse. But often, as in my case, it starts with a fear of fatness.
Not every sufferer is the same - so please don't dismiss mine because it differs from yours.