Federal officials last week eliminated a line in Medicare's coverage manual that said "obesity itself cannot be considered an illness." That deletion could cost us billions. It opens the door to federal reimbursement for such weight-loss treatments as stomach surgery, diet drugs, counseling and exercise plans.

Federal officials need to insist the purveyors of such treatments prove their effectiveness so that we save tax dollars instead of bloating government costs for obesity.

Governors already bemoan rising Medicare and Medicaid costs. The surgeon general reports about 64 percent of U.S. adults are either overweight or obese. Health and Human Services Secretary Tommy Thompson sees the policy change as a way to save dollars through prevention. Up to now, Medicare's policy against obesity as a disease made it difficult for obese people to get coverage for stomach surgery, nutritional counseling, weight-loss drugs and other therapies unless it was to treat recognized diseases such as heart trouble or diabetes.

While Health and Human Services hasn't declared obesity a disease, this change amounts to the same thing - and private insurers take their cues from government. Thompson is banking that the policy change will help prevent costly fat-related diseases and screen out treatments that don't work. "With this new policy," he said, "Medicare will be able to review scientific evidence in order to determine which interventions improve health outcomes for seniors and disabled Americans who are obese and (have) many associated medical conditions."

Those are laudable goals, but they could backfire. Researchers already warn that the government will have a tough time defining success or what "effective" means. If it takes off weight, for how long?

Medicare officials expect to fund long-term, large-scale studies. That should help sort out legitimate treatments from scams. But meanwhile every group from Atkins Nutritionals to diet drug firms are lining up for a piece of the action.

This fall, HHS' Medicare Coverage Advisory Committee plans to evaluate evidence for whether gastric bypass surgery helps prevent heart disease and other obesity-linked illnesses. Blue Cross Blue Shield of Florida announced it will stop paying for stomach-stapling surgery next year, after the insurer found the surgery could cost it $200 million the next few years.

Health economists RTI International reported obesity cost the United States $75 billion in 2003 - more than $6 billion just in Ohio, Indiana and Kentucky. About 10 percent of Ohio's Medicaid budget is spent on obesity-related diseases.

All of us may feel the weight of obesity costs in higher health insurance premiums. Reason magazine's latest cover story asks: "Is the size of your butt the government's business?" It is, if government has to pay for your fat-related diseases. Federal officials need to keep responsibility on the backs of individual Americans, and make sure government pays only for health-enhancing, cost-saving treatments.