The report, Australia's Future 'Fat Bomb', from Melbourne's Baker IDI Heart and Diabetes Institute, will be presented at the Federal Government's inquiry into obesity, which comes to Melbourne today. A grim picture is painted of expanding waistlines fuelled by a boom in fast food and a decline in physical activity, turning us into a nation of sedentary couch potatoes. Those most at risk of premature death are the middle-aged, with 70% of men and 60% of women aged 45 to 64 now classed as obese. But some weight specialists have questioned the tool used to measure obesity, saying "entire rugby teams" would be classified as obese if their body mass index (BMI) was calculated. BMI is measured by dividing weight in kilograms by height in metres squared. A BMI of over 25 is considered overweight while more than 30 is obese.

But the tool does not distinguish between muscle and fat, prompting calls for the BMI overweight limit to be raised to 28. However, even leading nutritionist Jenny O'Dea from the University of Sydney  who recently claimed Australia's childhood obesity epidemic had been exaggerated  has backed the new figures, which suggest that the crisis for adults has been drastically underestimated. Professor O'Dea said that while being fat was not necessarily a health risk for everyone, there was no doubt obesity was taking its toll on the nation. It was previously thought that around 3 million adults were obese. But many past surveys were seen as unreliable as they often required participants to guess their own weight. The latest data was based on more than 14,000 people at 100 rural and metropolitan sites in every Australian state and territory. Each had their BMI recorded by having their weight, height and waist measured as part of a national blood pressure screening day last year.

The report's lead author, Simon Stewart, said that even allowing for the BMI's potential failings, the best case scenario was that 3.6 million adults were battling obesity. "We could fill the MCG 40 times over with the number of obese Australians now, then you can double that if you look at the people who are also overweight  those are amazing figures," Professor Stewart said. "And in terms of a public health crisis, there is nothing to rival this. If we ran a fat Olympics we'd be gold medal winners as the fattest people on earth at the moment," he said. "We've heard of AIDS orphans in Africa, we're looking at this time bomb going off where parents have to think about this carefully," Professor Steward said. "They're having children at an older age, if you're obese and you have a child do you really want to miss out on their wedding?

"Do you want to miss out on the key events in their life? Yes you will if you don't do something about your weight now." The obesity inquiry in Melbourne will be told that a national strategy encouraging overweight Australians to lose five kilograms in five months could reduce heart-related hospital admissions by 27% and cut deaths by 34% over the next 20 years. Among the radical solutions proposed in the report is a plan to make fat towns compete for "healthy" status in national weight loss contests tied to Federal Government funding. Towns that lost the most weight would be given cash to build sports centres and swimming pools. And like the "Tidy Towns" program, communities would have to meet targets to be eligible for a share of the funding pool.

Other suggestions from Professor Stewart's report include subsidised gym memberships, personal training sessions for heavier people and restricting weight loss surgery to those who show they can lose some weight on their own first. One of Australia's leading obesity experts, Boyd Swinburn, will tell the inquiry in his own submission that a crackdown on junk food marketing to children is paramount in the fight against the epidemic. With the fastest growing rate of childhood obesity in the world, Australia must make radical changes to the way unhealthy food is promoted if the rate is to be reduced, his submission reads. Professor Swinburn, director of the World Health Organisation Collaborating Centre for Obesity Prevention at Deakin University, will argue that better nutritional labelling and more funding for effective treatments such as weight-loss surgery are also necessary. "We've got a huge problem here and we can't bury our head in the sand any more," Professor Swinburn will tell the inquiry.

"The previous federal government blamed parents and individuals and told them to pull up their socks that's not going to achieve anything but make us fatter as a nation. "It's good to see the Rudd Government take obesity seriously with this parliamentary inquiry and the preventative health strategy but that has to be turned into proper policy, regulation and funding." Ian Caterson, director of the Institute of Obesity, Nutrition and Exercise at the University of Sydney, said innovative government "thinking outside the square" policies were necessary because, "as we get fatter and older as a nation things are just going to get worse." EXPANDING WAISTLINES About 4 million adult Australians are obese.

The "fat bomb" is ticking loudly, with 72% of middle-aged males and 58% of middle-aged females overweight or obese. About 1.5 million middle-aged Australians are obese and therefore at high risk of a heart attack or stroke in the longer term. Based on the best available evidence, our expanded middle-aged waistlines will result in an extra 700,000 cardiovascular-related hospital admissions in the next 20 years. These highly preventable admissions will cost Australia, conservatively, an extra $3 billion in health expenditure and $6 billion overall. Loading

An estimated 122,500 men and women will die, many prematurely, from heart problems related to their excess weight in the next 20 years. A simple strategy such as losing 5kg in five months could reduce heart-related hospital admissions by 27% and deaths by 34% over the next 20 years.