The ideal Antipodean, especially in the lead-up to an Olympic Games, may well be trim, taut and trouncing the opposition on the sporting field.

But in one field Australians are, unexpectedly, leading the way as the heavyweight champions of the world — with arguably a greater proportion of obese citizens than even the notoriously supersized Americans.

A study released yesterday shows that Australia’s obesity epidemic has been considerably underestimated, with almost 60 per cent of the adult population overweight.

Described as the most thorough study of the problem in Australia for a decade, it also shows that 26 per cent of adults, or four million people, are obese. Researchers say that the once mid-ranking nation, in terms of obesity, now weighs in at the top.

Simon Stewart, who led the research team, said that obesity was the big threat to Australia’s future health, with an estimated nine million people obese or overweight. “That is a million more obese adults than we had thought,” he said.

The study, which comes before a government inquiry into the epidemic, charted the height and weight of 14,000 adult Australians on a single day in 2005. It shows that the middle-aged are the fattest of all, with about seven in ten men and six in ten women aged 45 to 64 now registering a body mass index (BMI) of 25 or more — a definition of being overweight.

An over-abundance of food, particularly those high in fat and sugar, and reduced levels of physical activity, are blamed for the expansion in Australian waistlines.

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