The study reported Australians outweigh U.S. residents and 123,000 Aussies could experience premature deaths during the next 20 years, The Age reported.
Four million Australians -- 26 percent of the adult population -- are considered obese, compared to 25 percent of Americans, the report by Melbourne's Baker IDI Heart and Diabetes Institute said. An additional 5 million Australians are considered overweight.
If the crisis isn't averted, obesity experts said health costs could exceed $6 billion and hospitals would have to admit an additional 700,000 people heart attacks, strokes and blood clots caused by excess pounds.
Adults most at risk of premature death are in the 45-to-64 age group, with 70 percent of men and 60 percent of women classified as obese, the report said.
The data were based on more than 14,000 people at rural and metropolitan sites in all Australian states and territories, The Age said. Participants had their body mass index recorded by having their weight, height and waist measured as part of a national blood pressure screening day in 2007.