THE number of US residents who are severely obese shot up by 70pc in the past decade, but the increase has slowed in more recent years.
Between 2000 and 2010, the proportion of US residents who were severely obese -- at least 45kg overweight -- rose from 4pc to almost 7pc, said researchers whose findings appeared in the International Journal of Obesity.
The increase showed signs of slowing after 2005, they added. But the bad news is that the severely obese remain the fastest-growing segment of obese Americans, said study leader Roland Sturm, a senior economist at the non-profit research institute RAND Corporation.
"Everybody's talking about obesity levelling off," Sturm said. "But what tends to get lost in the discussion is the fact that severe obesity, with a body mass index (BMI) of 40 or higher, is still rising fast."
More than one-third of US adults are obese, having a BMI of 30 or higher. BMI is a measure of weight relative to height.
The findings for the current study were based on data from an annual government health survey of US adults. BMI estimates were made based on people's self-reported weight and height.
The rate of severe obesity was 50pc higher among women than men, and twice as high among black Americans as among white and Hispanic adults.
Severely obese people are at high risk of conditions like diabetes, severe arthritis and heart disease, and could also be candidates for obesity surgery.
Sturm said there are other costs besides the healthcare price tag, such as the human cost of living with obesity.
"There's the disability and inability to work. People may be basically forced into retirement because they can't work," he said.