As a registered dietitian and avid exerciser, Kellie Glass understands better than most people the importance of healthy eating. So when she treats herself to ice cream, the last thing she wants is to be confronted by a “sin” tax.

“This is the most ridiculous idea I’ve heard,” Glass said of the mounting proposals to tax junk foods in an effort to slim down America. “Folks are just not going to give up all the foods they love, even if they are more expensive.”

Sin taxes on cigarettes have turned out to be the most effective weapon in the campaign to reduce smoking. Liquor, gambling and even gas-guzzling vehicles also are subjected to punitive assessments.

Why not Flamin’ Hot Cheetos, vanilla Coke and Twinkies?

With increasing vigor, public health experts and think tanks are calling for extra taxes on foods and drinks that are heavy in calories and light on nutrition. New York Gov. David Paterson proposed an 18 percent soda tax last year as part of a budget-balancing package, and lawmakers in other states have floated the idea behind closed doors.

Fat taxes are often mentioned as a way to help fund a restructuring of the health care system, although no one in Congress has yet endorsed them.

A report this summer from the Urban Institute said such taxes are needed to ensure that rising obesity rates don’t cause the average American life expectancy to fall for the first time in history.

“We are killing 100,000 people per year, so something needs to get done,” said Arthur Garson, a pediatric cardiologist at the University of Virginia, and one of the study’s authors. “This is not an off-the-wall set of ideas. These are ideas that have been tested and have worked in cigarettes.”

Tax gaining popularity

Although many citizens rail against the prospect of a paternalistic “nanny state” raising taxes on anything, the notion of a junk food tax is catching on with the general public. A Kaiser Family Foundation poll last month found that 55 percent of respondents favored a tax on unhealthy snack foods, up from 52 percent in April. Support for a soda tax rose to 53 percent from 46 percent.

And 63 percent of people who opposed the idea said they would change their minds if the revenue were used to fund health care reform and combat health problems related to obesity.

The logic of a junk food tax seems clear. Fattening foods tend to be cheap, while fresh fruits and vegetables and lean cuts of meat are often the most expensive. A tax could help offset that imbalance, nudging people to eat more of what they should and less of what they shouldn’t.

But research by epidemiologists, economists and other scientists suggests it’s hardly that simple.

To make a significant dent in escalating rates of obesity, taxes would have to be steep and widespread. Two-thirds of states now impose a modest soft-drink tax — the average rate is 5.2 percent — and although these tariffs statistically are linked to decreased body weight, the drop is extremely slight: about 3 ounces for a 5-foot, 10-inch person weighing 279 pounds.

Taxes on foods such as candy bars and microwave popcorn are even less effective, according to available data.

There’s even evidence that such taxes can have the perverse effect of increasing consumption of fatty or salty foods.

Cigarettes vs. junk food

There are reasons why taxes curb smoking but wouldn’t affect obesity.

Raise the cigarette tax and a smoker has two choices: Pay up or quit. Raise the tax on sugar-sweetened colas, however, and customers can switch to sports drinks or punch, which often contain even more calories.

Moreover, tobacco taxes apply to all products you can (legally) smoke. Junk food taxes are less logical. A 5.5 percent snack tax in Maine, for instance, covered blueberry muffins and fresh-baked apple pies, but not English muffins or frozen pies.

Tobacco taxes also are much higher than anything likely to be adopted for food and beverages. Slapping a 10 percent sin tax on a $1.50-bottle of Coke would raise the price a mere 15 cents, too little to persuade most shoppers to drink Diet Coke instead, experts said. Many calorie-laden foods are simply too inexpensive to be priced out of the market by any but the most draconian of taxes.

Taxes on snack foods are even less effective.

A team from the U.S. Department of Agriculture contemplated a tax on salty foods such as cheese puffs and pretzels. But unless the tax topped 10 percent, it would translate into much less than one pound of weight loss per year, the researchers reported in 2004.