According to a new medical report about four million Americans are categorised as obese.

Shocking statistics reveal that the numbers of Americans who are at least 100 pounds overweight soared from one in 200 to one in 50 between 1986 and 2000, according to the RAND Corporation in Santa Monica, California.

Previously, many doctors considered severe obesity to be an uncommon condition that largely represented a fixed percentage of people.

Flattening out

However, the study's author, Roland Sturm, senior economist with the Rand Corp., said as simple obesity increases, severe obesity grows even faster.

"We've reached Nirvana. Food is cheap and plentiful. You can stuff yourself on less than a half-hour of minimum wage"

Roland Sturm, senior economist

Overall obesity - generally those who are at least 30 pounds overweight - doubled during the study period.

"There is no evidence that it (the obesity rate) is flattening out," Sturm said. "It's full-speed ahead.

"The most dramatic part of the obesity epidemic has remained hidden."

Sturm's study, which appeared Monday in the Archives of Internal Medicine, is based on nationwide telephone surveys conducted by the US Centres for Disease Control and Prevention in which people are asked their height and weight.

Sturm said the trend largely is the result of the increasing affordability of calorie-dense food.

Just say no - chef preparing food

"We've reached Nirvana," he said. "Food is cheap and plentiful. You can stuff yourself on less than a half-hour of minimum wage."

So-called couch potatoes largely fall into the obesity category of people who pile on weight because they rarely exercise.

The trend also is fuelled by a substantial reduction in the amount of physical activity that Americans engage in, confirmed Linda Baumann, a nursing professor at the University of Wisconsin-Madison.

* America's best known 'crash dieter' - illusionist David Blaine - has now spent more than 20 days without food or water as he sits, suspended in a perspex box near London's Tower Bridge as part of a 44-day stunt.