This month's decision by the Medicare program to begin paying for obesity treatments has prompted complaints that the government is forcing thin people to subsidize fat people. But the winners and losers from this policy shift are not as obvious as they might seem.

 To begin with, the government says two-thirds of us are overweight, so this is not so much the thin subsidizing the fat as the fat subsidizing the obese. And if all the taxpayer-financed surgeries, diet programs and counseling sessions actually work (a big if , the upshot could be lower taxpayer costs.

 A study published last year in the journal Health Affairs estimated that the health care costs associated with excessive weight amount to something like $93 billion a year, half of it covered by Medicare and Medicaid. On average, medical treatments cost $732 more per year for the obese and $247 more for the merely overweight.

 The increases in Medicare and Medicaid costs were statistically significant only for the obese -- a fact that widens the divide between the plump and the corpulent. If the big expenses don't kick in until you get really fat, I guess even the overweight have a right to object when their fellow Americans eat too much.

 So maybe it's not so strange to see George Washington University law professor John Banzhaf, a promoter of fast food lawsuits, complain that "obese patients are contributing to skyrocketing Medicare and Medicaid outlays and costing thin taxpayers tens of billions of dollars a year." Although Banzhaf is tubby, perhaps he's not fat enough to be a drain on the Treasury.

 For those who are, spending money on weight loss now could, in theory, avoid bigger costs down the road -- money that would be spent to treat diabetes, heart disease or other obesity-related illnesses. That's the fiscal justification for covering obesity treatments under taxpayer-financed health insurance (although it makes more sense with the younger population covered by Medicaid than with the retirees covered by Medicare).

 But there's a complication. We don't really know whether taxpayer costs are higher, on balance, than they would be if everyone were thin.

 In the case of smokers, economic analyses indicate that taxpayer savings from less health care in old age and fewer Social Security payments (because of shorter life expectancies) outweigh the costs of treating tobacco-related diseases. Something similar could be true of obesity.

 University of Chicago economist Tomas Philipson, whose work on weight trends is widely cited, says "it's not clear whether obese people are costing us more or costing us less." In all likelihood, however, we don't have to worry that subsidizing weight loss will inadvertently raise taxpayer costs by making people thinner and thereby extending their lives, because obesity treatments are notoriously ineffective. Continued...