Leading mental health organisations have launched a campaign to educate Australians about the early signs of eating disorders and how to approach a difficult conversation with someone who is struggling.

Eating Disorders Queensland CEO Belinda Chelius says there is a strong link between a patient having a strong support network and a good outcome.

"The key to recovery is the more support you have around you," Ms Chelius told AAP.

"The more you have people asking questions in a way that is non judgemental, in a way that's loving and kind and supportive of that person."

An estimated one million people in Australia have an eating disorder but three-quarters will never seek help.

The Butterfly Foundation said patients who received early intervention were twice as likely to recover from their illness but just one in 10 people say they know what symptoms to look out for.

Butterfly Foundation spokeswoman Melissa Wilton said conversation about the issue could seem daunting but it was the most effective way to engage someone.

"The problem is that a lot of people do go undiagnosed for many years and eating disorders can be long lasting," Ms Wilton said.

"If you are worried about somebody, it's really critical that you have a conversation and just ask them if there's something that they're worried about."

The Eating Disorder Alliance of Australia said a change in behaviour could signal the beginning of a more serious health condition.

Signs can include bodychecking, a preoccupation with eating, eating in secret, overexercise or avoiding social situations involving food.

Physical changes include but are not limited to weight fluctuation, weakness, changes in mood, fainting, social withdrawal or poor concentration.

Ms Chelius said it's important to pay attention and not brush off new obsessions with diet, clean eating, restricting food or exercise.

"It's really, really important not to just write that off as a phase, or something that a teenager is going through," she said.

While the list of red flags is long, she said one of the most important things to remember was no one should think they were too well to seek help.

"The minute you feel uncomfortable or there's a warning sign please speak to somebody," she said.

"Never feel you have to be on that brink of hospitalisation before you reach out for support."