WESTERN Australia has the most overweight and obese young adults in the country.

New figures reveal half of all West Australians aged 18-24 are overweight, compared with a national average of 38 per cent.

A recent review of the health sector by the Productivity Commission reported that 25 per cent more young WA people are in the unhealthy weight range than four years ago.

In WA, 47 per cent of young women are overweight or obese, compared to only 35 per cent in NSW and 21 per cent in Victoria.

The proportion of young WA men with weight problems is 53 per cent, compared with 42 per cent in NSW and 37 per cent in Victoria.

Public health experts warn the generational glut of fat people will strain the health system as they get older and stack on more kilos.

Public Health Advocacy Institute of WA director Mike Daube said the figures should "jolt us out of our complacency".

"This means we are heading for catastrophic health outcomes," he said.

"We need a junk food tax to fund education and increase the price of junk food because obesity today means diabetes, heart disease and cancer tomorrow.

"How can we be expected to fight against junk food companies making millions in profit when we have pocket money budgets?"

Prof Daube said obesity was a bigger problem in WA partly because of our "drive everywhere" culture and so many young people being cashed up thanks to the mining boom.

"Everyone drives everywhere and junk food is readily accessible," Prof Daube said. "We have a youngish, more affluent population and governments that are not looking beyond next week."

Australian Medical Association president Richard Choong said the increase was disappointing, but young people were still able to change their lifestyles.

"We need to spend more time exercising and undertaking healthy living," Dr Choong said. "Hopefully, younger generations continue to have lower obesity rates, but we need to target young adults in light of this sudden percentage increase."

Cancer Council WA nutrition and physical activity manager Steve Pratt said anti-obesity campaigns started too late for the extra-large age group.

"The 2003 Child and Adolescent Physical Activity and Nutrition Survey gave us a massive wake-up call and in the next few years the government started injecting money into prevention programs," Mr Pratt said.

"That age group (18-24) would have been teenagers when all the obesity-prevention campaigns for children got into full swing.

"It's a surprise that there is a cohort with such high levels of obesity, but I think we've put a lid on that with all the campaigns, and the younger generation coming through has lower levels of obesity.

"It looks like the increase has stopped and plateaued, and though the rate is still too high, stopping the increase is a good step. We hope that would be the last of that cohort, before we managed to put the brakes on.

"Being overweight or obese means a greater risk of heart disease, diabetes and cancer, so this age group could potentially become quite a burden on the health system in the long term."

Heart Foundation chief executive Maurice Swanson said the figures should set alarm bells ringing for the government and community.

“Obesity is the leading cause of preventable death and disease in Western Australia and is a major driver of increasing costs in our public hospitals,” Mr Swanson said.

“There needs to be regulation to decrease the promotion, marketing and availability of junk food that is high in fat, sugar and salt.

“It is totally inappropriate for junk food companies to be major sponsors of sport in Australia.

“We should consider prohibiting the advertising of junk food on television before 9pm, and assess the impact of placing a tax on junk food and sugar sweetened beverages.”