Obesity's not just dangerous, it's expensive. New research shows medical spending averages $1,400 more a year for an obese person than for someone who's normal weight.

Overall obesity-related health spending reaches $147 billion, double what it was nearly a decade ago, says the study published Monday by the journal Health Affairs.

The higher expense reflects the costs of treating diabetes, heart disease and other ailments far more common for the overweight, concluded the study by government scientists and the nonprofit research group RTI International.

RTI health economist Eric Finkelstein offers a blunt message for lawmakers trying to revamp the health care system: "Unless you address obesity, you're never going to address rising health care costs."

Obesity-related conditions now account for 9.1 percent of all medical spending, up from 6.5 percent in 1998, the study concluded.

Health economists have long warned that obesity is a driving force behind the rise in health spending. For example, diabetes costs the nation $190 billion a year to treat, and excess weight is the single biggest risk factor for developing diabetes. Moreover, obese diabetics are the hardest to treat, with higher rates of foot ulcers and amputations, among other things.

The new study's look at per-capita spending may offer a shock to the wallets of people who haven't yet heeded straight health warnings.

"Health care costs are dramatically higher for people who are obese and it doesn't have to be that way," said Jeff Levi of the nonprofit Trust for America's Health, who wasn't involved in the new research.

"We have ways of changing behavior and changing those health outcomes so that we don't have to deal with the medical consequences of obesity," added Levi, who advocates community-based programs that promote physical activity and better nutrition.

About a third of adult Americans are obese, and the obesity rate rose 37 percent between 1998 and 2006, the years covered by Monday's study.

Prescription drugs for obesity-related illnesses account for much of the rise in spending. Medicare spends about $600 more per year on prescriptions for an obese beneficiary than a normal-weight one, the study found.