My daughter has had an eating disorder since birth practically. She had a congenital heart condition that wasn't diagnosed where she threw up all the time, (every time she was fed).
As she reached 3 yrs old and should have been eating solid foods, she refused. Eventually I forced her to eat off a spoon, but she saw how much it affected, (hurt) me by her not eating, so she used it. I blamed myself.
Her father liked her older brother but did not like her, and she wanted her father to like her, so food became a way of showing her disapproval. I used every trick I could think of to get her to eat, hiding vitamins in drinks and foods, telling her they had no calories, threatening her, cajoling her, encouraging her, bribing her, teaching her to cook, having her friends over for parties, and anything I could think of, over and over again.
By the time she was 13 years old, she was 3 and a half stone, (around 48-49 lbs). I was at my wit's end, so I confronted her one day to bring it out in the open, and we "dealt" with a lot of stuff, and doing that did help, because she was willing to tell me then when she was having a bad day.
The only thing she was certain of at that stage was that I was not giving up on her, and it seemed to do the trick to get her to an acceptable level of weight for her age and build, even if it was the under side of that scale.
She tried using other shock tactics for getting attention in her teen years, like alcohol and cigarettes, which I dealt with as soon as I found out about them, but she never used food the same way again, although I knew it was a struggle for her and at times her weight was the underside of borderline anorexic again. She managed to talk about what was bothering her after that, and I supported and guided her as much as I could until she had control again, and did my best to teach her how to control her thinking herself, and how her weight affected her thinking.
People around her know not to ever mention weight issues, or make any reference to her size, good or bad, and to change the subject if she mentions it, so that if she is having problems, she will be more likely to talk about her issues, by subject matter and not by her coping mechanisms, and be more likely to deal with it in a healthy way.
Her relationship with her father is still not great, mainly because he is a selfish self-centred bastard who cares about no one but himself, but every so often I give out to him and he pulls his oars in, and she makes an effort to see him for a weekend, and they walk on eggshells around each other, because it is important to her to build even a tenuous relationship with him. As long as anything he says or does doesn't drive her back to that state I am ok with it.
I now have a niece who is having severe eating issues. She is 3 years old......... There might be something genetic in it too.