ATLANTA - How much money would it take to get you to lose some serious weight? $100? $500?

Many employers are betting they can find your price. At least a third of U.S. companies offer financial incentives, or are planning to introduce them, to get their employees to lose weight or get healthier in other ways.

"There's been an explosion of interest in this," said Dr. Kevin Volpp, director of the University of Pennsylvania's Center for Health Incentives.

Take OhioHealth, a hospital chain whose workforce is mostly overweight. The company last year embarked on a program that paid employees to wear pedometers and get paid for walking. The more they walk, the more they win - up to $500 a year.

Half of the 9,000 employees at the chain's five main hospitals signed up, more than $377,000 in rewards have been paid, and many workers tell of weight loss and a sudden need for slimmer clothes.

But will this kind of effort really put a permanent dent in American's seemingly intractable obesity problem?

"It's probably a waste of time," said Kelly Brownell, director of Yale University's Rudd Center for Food Policy and Obesity. Brownell's assessment is harsher than most, but the limited science available seems to back him up.

Perhaps the largest effort to date was an observational study by Cornell University. It looked at seven employer programs, and the results were depressing: The average weight loss in most was little more than a pound.

Even so, there are grounds for optimism. Smaller experiments report some success. And other studies have shown promising results against tobacco.

One problem: "Food is more difficult than tobacco," said Steven Kelder, an epidemiology professor at the University of Texas School of Public Health.

The problem has a huge economic effect, with obese workers costing U.S. private employers an estimated $45 billion or more annually in health-care costs and lost labor, according to a report by the Conference Board, a research group.

In a campaign led by Michelle Obama, federal officials are emphasizing several approaches to slim the nation. Food companies, worried about potential anti-obesity rules and laws, have publicly endorsed the first lady's message and recently pledged to offer lower-calorie foods, change recipes, and cut portion sizes.

While watching to see if foodmakers follow through, some experts remain fascinated by the idea of using economics to get people to eat better and exercise. Sales taxes have been used to drive up the cost of cigarettes and drive down smoking rates, and Brownell and others are pushing for similar taxes on soda.

Many employers believe the wisest approach is to use financial incentives as just one facet of a broader effort to create a culture that makes it harder to be lazy and gluttonous.

Kevin Acocella illustrates their point.

Acocella, 35, an IBM marketing manager, was 5-foot-9 and a chunky 185 when he decided two years ago to enroll in the company's 12-week, web-based fitness program. He failed twice.

The problem, he said, was the culture he was in. "In New York City it was, 'What restaurant can we go to, or what bar can we go to?' "

Early this year, Acocella moved to the IBM office in San Jose, Calif. "Here it's, 'What activity can you do, and what can you go see, and how can we figure out a way to not take a car there?' " he said.

Acocella has lost nine pounds in the three months he's been there.