The growth in American obesity has been concentrated on the section of the population that would already be fat, a dietary researcher from the USA's Rockefeller University has claimed.

Dr Jeffrey Friedman argued that popular opinion depicting Americans as becoming uniformly fatter is untrue. He told the New York Times that National Center for Health Statistics figures since 1991 show the weight of thinner people being stable.

However, the next heavier bloc of US citizens is around six or seven pounds heavier on average than in 1991. Meanwhile, the average girth of the clinically obese has ballooned by 25 to 30 pounds.