A new study has discovered obesity has overtaken smoking as the leading cause of preventable diseases in Western Australia.

The figures are alarming and the obesity epidemic has now reached crisis point, health expert says.

Australia has one of the highest rates of obesity in the world, with more than 60 per cent of adults and one in four children overweight or obese.

The epidemic is on the rise, says the president of the Public Health Association of Australia, Professor Mike Daube.

We're aware of the problem (but) we're not doing enough about it, he said.

It's taken us 60 years since we knew about the dangers of smoking to get to this fairly encouraging decline. We need to move faster than that on obesity.

The federal government spends only 2 per cent of the country's health expenditure on prevention, which is not enough, Prof Daube says.

There should be more health and physical education in schools, as well as a halt on junk food advertising, he adds.

Australia has been slow to respond to the obesity problem, according to Tim Gill, the principal research fellow at the Boden Institute of Obesity Nutrition and Exercise at University of Sydney.

When we had the alarm bells ring 15 years ago very, very little was done and it's only really in recent times that we've started to take this problem seriously, said Associate Professor Gill.

As a consequence, we've now seen probably a generation of young adults go through a period of time where obesity wasn't seen as a serious issue ... and now they're the people who are starting to develop these chronic diseases, particularly type 2 diabetes, which is driving what we're seeing here in terms of the cost of illness.

The findings of the WA study on obesity have been published in the Australian New Zealand Journal of Public Health.