All the signs showed Australia was following the same trend as the United States where extreme obesity has been commonplace for a decade, Professor Dixon said.

Surgeon Harry Frydenberg said he saw up to 50 super obese patients a year who want to access bariatric surgery such as lapbanding. Ten years ago such patients were extremely rare, he said. Dr Frydenberg recently treated a man weighing 297kg. Many suffer from chronic conditions such as diabetes, sleep apnoea and depression. For some, going under the knife is too dangerous.

''We've had patients where their chance of dying is just too high, they've got serious cardiac or respiratory problems and anaesthetically they would just have no chance,'' Dr Frydenberg said. ''You don't see too many people with BMIs of 50 who are 70 years old because they just don't survive that long.''

Tim Gill, an associate professor at the Boden Institute of Obesity at Sydney University, said the trend had escalated of late. ''Like the rich get richer the fat get fatter and the more overweight you are the less easy it is for you to take those steps to prevent further weight gain.

''You've lost the ability to recognise when your body is telling you to stop eating, so you've been able to totally obliterate those types of controls,'' Dr Gill said.