Washington - Rising obesity is placing a major strain on the United States' already troubled heath care system, according to a study in the journal Health Affairs.

Obesity now accounts for 9.1 per cent of US medical spending. A decade ago, it accounted for 6.5 per cent. More than a quarter of Americans are now obese, up from 18.3 per cent in 1998.

The group of private and government researchers said obesity is driving up overall US medical spending, and taxpayers are feeling the burden.

Obesity costs could reach 147 billion dollars for 2008.

The estimated costs of obesity were as high as 78.5 billion dollars in 1998, nearly half of which was covered by Medicare or Medicaid, the government health programmes for the elderly and poor, the report said.

If not for obesity, the report said, current Medicare spending would decrease 8.5 per cent and Medicaid spending by 11.8 per cent.

"Although health reform may be necessary to address health inequities and rein in rising health spending," the report concludes. "Real savings are more likely to be achieved through reforms that reduce the prevalence of obesity and related risk factors, including poor diet and inactivity."(dpa)