A Perth teenager has launched an online petition to help protect an eating disorder program which she credits with saving her life.

In less than two months, Grace Brandenburg went from a happy, healthy 13-year-old girl to one reliant on a tube to force-feed her.

"I would stand up and I would get so dizzy and faint, and I was just so cold all of the time, and all my muscles had wasted. Everything was effort," Ms Brandenburg, now 17, said.

"I remember one time just looking in the mirror and seeing how sick I'd gotten, and I just started crying because I didn't know how to fix it."

Ms Brandenburg was treated for Anorexia Nervosa at Princess Margaret Hospital (PMH), through an Eating Disorder Program which treats up to 160 similar patients a year.

Ms Brandenburg was treated at Princess Margaret Hospital when she was 14. ( Supplied: Grace Brandenburg )

"You forget how to listen to your body, because it gets to a point where you don't feel hunger anymore," she said.

"You just don't want to eat, you don't want to look at food, you don't want to smell it. There was a point for me where I thought I could inhale calories.

"Whilst I've been recovering, if I didn't have PMH to pull me back into line, then I don't know where I would be right now."

'I don't believe anybody will fall through the gaps', doctor says

While psychologists and patients say the hospital service is vital, part of the program, which treats patients during the day and allows them to return home at night, is now being put on hold for up to six months.

Ms Brandenburg said the decision would put young people at risk.

An online petition launched by the teenager calling for the program to continue running has already attracted more than 4,000 signatures.

Ms Brandenburg's online petition has more than 4,000 signatures. ( ABC News )

"Without it, I honestly don't know what would happen, because the amount of people who have been helped by this program, it's amazing," Ms Brandenburg said.

"I just don't see why they should stop it."

Phil Lucas, who runs the Eating Disorder Program at PMH, said the decision to temporarily close the day program would only affect a small number of patients.

He said there were other services available.

"I don't believe that anybody will fall through the gaps. I believe that our range of outpatient provisions is extensive enough and can be intensive enough to meet people's needs," he said.

"Only small numbers of our total number of patients are treated in the day program, and we have a suite of measures in place to support those people in other ways so they can remain as outpatients at home with their families and in their own schools."

Program on hold as hospital services reviewed

Dr Lucas said the program had been shut down so it could be assessed as part of a wider review of hospital services, ahead of the move from Princess Margaret Hospital to the new Perth Children's Hospital.

The program has been put on hold ahead of the move to the new Perth Children's Hospital. ( ABC News: Garrett Mundy )

"The service has been in existence for 20 years, and it's undergone numerous and repeated changes in that time ... so it can keep up with new evidence," he said.

"Evidence in the treatment of young people with eating disorders is a growth area and is changing all the time. We have to change the configuration of our services in order to keep up with that evidence."

Health Minister John Day said the decision was about improving and modernising care, not about saving money.

The day program is expected to be reinstated when the new Perth Children's Hospital opens later this year. The State Government has claimed that could be as early as October, but an official opening date is yet to be set.

Ms Brandenburg said the day program was helpful to patients transitioning back to "normal life".

"People who come out of in-patient, that's a good way to get them back into normal life, a nice transition, instead of just throwing them back out into the world and saying 'Go, just don't get sick again' because that's highly unlikely."