Obesity now accounts for 9.1% of U.S. medical spending, up from 6.5% in 1998.

Researchers have presented that estimate in a study published today by Health Affairs, an academic journal that covers health care finance and health care delivery.

The percentage of U.S. residents who are obese has jumped to 25%, from about 18%, and that increase in the obesity rate accounts for about 89% of the increase in obesity-related spending, according to a team led by Eric Finkelstein of the Research Triangle Institute, Research Triangle Park, N.C.

Most of the money is going to pay for prescriptions related to conditions such as diabetes, and not to bariatric surgery or other treatments for obesity itself, the researchers report.

The researchers based their findings on analysis on data from the 1998 and 2006 Medical Expenditure Panel Surveys and data from the National Health Expenditure Accounts.

The researchers have defined obesity as having a body mass index greater than 30.

They found that annual, per capita medical spending for obese people is about $1,400 higher for obese people than for people of normal weight.