THERE is nothing more certain than death and taxes, but now most Australians can add one more thing to that list: an ever-expanding waistline.
By 2025 the number of obese Australians will surpass those of healthy weight, say epidemiologists who have calculated the nation's future weight gain based on the rate we stacked on the kilograms between 2000 and 2005.
Only about 28 per cent of adults will be at a healthy weight in 2025 but nearly 34 per cent will be obese, said the study leader, Helen Walls, a research fellow at Monash University.
Dr Walls used data from nearly 6300 people collected as part of the landmark Australian Diabetes Obesity and Lifestyle (''AusDiab'') Study to predict the scale of the obesity epidemic.
While the percentage of people who were overweight was expected to remain steady - at about 38 per cent - over the 25-year period the numbers of obese would swell.
"That means a lot of people who are overweight will move into the obese category but they are being replaced by more people from the normal weight range," Dr Walls said.
Of the healthy-weight people aged 25-29 in 2000, fewer than 30 per cent would remain so 35 years later, according to the study, which was published in the journal Obesity this week.
Dr Wall said the surge in obesity could be prevented if the government implemented the recommendations of the National Preventative Health Taskforce, with a country-wide approach to tackling obesity.
"The evidence generally shows that individual-based strategies aren't going to work," she said.
"Educating people about good nutrition and the importance of physical activity isn't generally effective, and that is very intuitive for people who know how they can live more healthily but don't."
The director emeritus of the Baker IDI Heart and Diabetes Institute and a member of the Preventative Health Taskforce, Paul Zimmet, said Australia had only seen "the tip of the iceberg" in terms of weight-related health problems.
A plethora of obesity-related conditions, from arthritis to sleep apnoea to depression, would increase.
"People just haven't got their heads around what the impact of obesity through disease will be,'' Professor Zimmet said.
Professor Zimmet, who was the architect of the AusDiab study, said that between 1980 and 2000 there had been vast changes in the way people lived which had triggered obesity in genetically predisposed people.
These included loss of jobs involving more physical activity, and changes to transport.
"Just look at school kids," he said. "When I was a kid we walked three or four miles to school but now they get driven.''
