Australia is being accused of failing millions of obese people over its refusal to label obesity a disease.

The reclassification of obesity as a disease and its implications will be vigorously debated by medical experts at Obesity Australia's 5th Annual Summit in Sydney on Wednesday.

Obesity Australia has been calling for the reclassification for many years as a solution to the nation's growing obesity crisis.

Australia is currently the fifth most obese country in the OECD with 63 per cent of adults overweight or obese, and 28 per cent obese.

The World Health Organisation has recognised obesity as a disease for decades and The American Medical Association officially moved to class obesity as a disease in 2013.

But the Australian government has refused to follow suit, with the Australian Medical Association also having shied away from labelling it a disease.

The main roadblock to reclassifying obesity is the significant cost to the government.

The AMA estimated in 2014 that if obesity was labelled a chronic disease it would cost the government $700 million to cover the cost of GPs drawing up chronic health plans for obese patients.

But experts say the classification could help ensure patients receive proper management plans to help them shed weight and improve their health.

"If obesity is officially recognised and treated as a disease, it can be managed and prevented more effectively, and the future of Australia's health might look far more hopeful," says Stephen Simpson, executive director of Obesity Australia and director of the Charles Perkins Centre at Sydney University.

Prof Simpson says labelling obesity a disease would lead to better health-care strategies that aren't driven by the simplistic ideology that obesity is a failure of willpower.

"If that is the case it's the greatest failure of willpower that humanity has ever seen. Sixty three per cent of Australians are overweight or obese. It's the norm.

"We've built a society where everything mitigates against our being able to exert control over our weight and that is an enormous societal challenge."

It's also argued reclassification would attract more funding for treatment, but that's not necessarily the case, says Professor Stephen Colagiuri from The Boden Institute at the University of Sydney.

"There is no real pattern to indicate that a disease gets more funding than something that is classified as a risk factor like hypertension or smoking," he said.