Anorexia nervosa starves the body to an unhealthily low weight
The number of young girls going to hospital because of anorexia has almost doubled in a decade.
New NHS figures for England show a rise in teenagers suffering from the eating disorder.
The number of girls under 16 who have been hospitalised with anorexia has increased by 80% in 10 years with close to 500 in 2006/2007.
Charities are saying more needs to be done, especially after the number of 12-year-olds seeking treatment tripled.
It wasn't until she found herself in hospital when she was a teenager that Heather Youel realised she was suffering from anorexia.
She said: "I was jogging one day, I came home and practically collapsed. My dad took me to hospital.
"When I got there they said, 'You've got days to live, you could die'."
Heather told Newsbeat her friends first noticed something wrong when she was 15.
She was working towards her GCSEs, but wasn't given the help she needed.
"I went to the GP and saw a nurse but she had no idea how to deal with it. She just said eat a bit more and you'll be fine," she said.
At 22, Heather has now fully recovered but says the effect it had will always stay with her.
Heather Youel is hopeful that the figures reflect greater awareness of the eating disorder she suffered with.
"I'm hoping it's because more people are aware of eating disorders, so they're getting admitted and getting treatment earlier," she said.
Beat, a charity dealing with eating disorders, says guidance on treating anorexics isn't clear enough.
It means too many teenagers are only getting the right treatment when they are so ill that hospital is the only solution.
Susan Ringwood from the charity said: "There's a lot of people being told wait and see and come back again and they get very, very ill before they get any treatment."
'Admit a problem'
The figures were revealed in Parliament after an MP questioned how the health service was doing at treating eating disorders.
Newsbeat asked the Prime Minister about the issue at his monthly news conference at Downing Street.
"We've got to do more to help those people who sometimes are not diagnosed properly. Sometimes it is late and sometimes things have gone too far," he said.
Heather Youel first noticed something was wrong aged 15
Gordon Brown admitted that treatment is not always good enough. "I think the more the health service can do to help, particularly teenage girls, the better."
And Heather agrees the care given in hospital is often not what patients need.
She said: "My treatment, through the whole time I was really ill, I found terrible."
But now she is keen to make sure others who may be suffering with anorexia know that there is help available.
She added: "The hardest thing to do is to admit you've got a problem, but that is the first step to getting help and recovery.
"So once you can admit it, speak to somebody and try and get help."