Every government, it seems, is looking for a painless way to raise revenue. At the same time, government officials want to reduce obesity levels in America.

Is there some way to accomplish both objectives? Yes, say advocates of a tax on sugary soft drinks. Making calorie-laden soft drinks more expensive, they say, will discourage consumption, producing tax revenue from those who continue to drink them.

The problem, say researchers, is it might not work out that way. Eric Finkelstein, an economist at Duke-National University of Singapore, decided to construct an economic model to show the effect a soda tax might have on America's waistline.

Some states are currently considering a sugar tax on soda that would amount to anywhere from 20 percent to 40 percent. The prevailing assumption has been a 20 percent tax would reduce consumptions by as much as 16 percent.

Finkelstein says that might be overly optimistic. His model, he says, shows the tax wouldn't reduce consumption nearly that much.

Furthermore, in Finkelstein's model lower income consumers continued to buy sweetened beverages at about their present rate, regardless of the fact that the beverages cost more. They lost little weight in his model.

Beverage makers react

As one might expect, the American Beverage Association was quick to promote Finkelstein's findings.

"Making smart, educated decisions about diet and exercise does that," the association said in a statement. "This study is the latest in the compendium of science to reaffirm that new taxes will not have an impact on a complex issue like obesity and they will not teach children about healthy lifestyles or change their behavior."

However, Finkelstein's study does show that the tax has some effect on consumption, just not as large as its backers believed. He believes that a hefty tax on sodas would prompt many consumers - particularly lower income consumers, to switch to a sweetened beverage like fruit juice or energy drinks.

The take-away, he says, is that a soda tax might not have the result of helping consumers shed pounds. But expanding the tax to all sugary beverages might have a better chance.

 That's a position held by the Center for Science in the Public Interest, which has been an early champion of a beverage tax.

"Americans consume huge quantities of soft drinks, which promote obesity and other health problems,” the group says on its website. "Obesity alone costs $147 billion a year in medical expenditures, half of which are paid through Medicare and Medicaid. Taxing soft drinks is an effective approach for cash-strapped federal and state governments looking for ways to fund health care and disease-prevention programs.”