CANBERRA: Australia is on track to becoming the fattest nation, a study has showed, although experts questioned on Friday whether it had overtaken the United States and small Pacific countries for the unenviable title.

About 4 million Australian adults, or 26 percent of the population, were obese, eclipsing the 25 percent rate in the US, the study by the Baker Heart and Diabetes Institute released in Melbourne said.

"If we ran a fat Olympics we'd be gold medal winners as the fattest people on earth at the moment," the Institute's preventative cardiology head, Professor Simon Stewart, told The Age newspaper.