There are so many ways in which eating disorders affect identity. Off the top of my head, talking to myself, my eating disorder (and some from other people) often sounds like "you are always the biggest/fattest person in the room", "you always eat too much/too little", "you're not sick enough to deserve treatment and care", "other people are sicker (often meaning "skinnier") than you and need treatment more", "you are worthless and you should be ashamed of that when you eat". Perhaps one of the hardest things to work on in recovery-based treatment (as opposed to harm reduction) is to separate that voice, learn to recognise it when it whispers to you, and neutralise it. This is a significant effort we make - or try to make - in our own personal journeys, and illustrates why weight restoration is only a part of the whole recovery process.
This challenge is even harder for those who developed their eating disorder while still a child, and for those who have been eating disordered for decades. We get asked in treatment, "Who were you before you developed and eating disorder" or "what did you weigh before you develop before you becamed eating disordered". Well, children and older adults just often don't remember a time before their eating disorders developed.
We don't know who we are without an eating disorder. We are terrified about who we might become. We look ahead and see only a void. "Fill your life up with meaningful activities and people", they tell us, but what if we think we've already done this and we don't want to be limited to just this if we let our eating disorder go. We want to end the misery of being eating disordered, but what if there is nothing left inside us but a huge empty hole? What then?
In the following article, the author gives a really good description of how it feels to believe that one has no identity except their eating disorder: How I'm Redefining Normal in Eating Disorder Recovery published by The Mighty.