An obesity expert from the UK believes Australia has overtaken America as having one of the unhealthiest diets in the world.

Dr Tim Lobstein is the director of policy and programmes for the International Association for the Study of Obesity.

He is in Western Australia with Jane Landon from the National Heart Forum to host a number of public lectures on obesity for the Public Health Advocacy Institute.

They recently held a workshop in Geraldton, in WA's Mid West, to discuss growing concerns regarding obesity and the damaging effects on children.

Dr Lobstein says Australia's diet has changed dramatically over the last 20 years.

"We've found that your diets here in Australia are more fatty and oily than American diets, and we thought America was one of the worst in the world," he said.

"You've overtaken America. Your diets are now 40 per cent calories from fats and oils and that's a pretty shocking statistic - you should be down nearer 20.

"Your sugars are high, alcohol is about double what's the recommended level of intake and your fruit and veg are a bit under par."

He says the rate of obesity in WA is appalling.

"By the time you are middle-aged, the statistics in Western Australia are 82 per cent of men and 68 per cent of women are overweight or obese. That's pretty shocking. That means you've got a four out of five chance of being overweight,' he said.

Prevention the cure?

Both Dr Lobstein and Ms Landon are particularly concerned about the diets of Australia's children.

He estimates about 90,000 kids in WA are overweight or obese.

"It means each family practice in this state has probably about 2,000 overweight adults and 200 overweight kids to deal with, and they don't really know what to do because losing weight is a real battle," he said.

"The struggle we've got here is how we're going to implement policies to prevent the weight gain in the first place so at least the next generation will be healthier than this one."

The challenge, according to Dr Lobstein, is whether Australia can beat the trend.

"Can we have healthy fast foods? Can we have a cut in soft drinks? Can we have a cut in snacks? Can we improve the fruit and veg in this country?

"Australia can do it. It's got the will, it knows the policies that need to be implemented it just needs to get along and do it."