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.

Anecdotal success stories are everywhere. Half of the 9,000 employees at the chain’s five main hospitals signed up, more than $377,000 in rewards have already been paid out, and many workers tell of weight loss.

But does will this kind of effort really put a permanent dent in American’s seemingly intractable obesity problem? Not likely.

“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 science seems to back him up.

Only about 15 to 20 U.S. studies have tried to evaluate the effect of financial incentives on weight loss. Most of those studies were small and didn’t look at whether such measures worked beyond a few months. None could make conclusions about how much money it takes to make a lasting difference for most people.

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

There are grounds for optimism. Smaller experiments report some success. And other studies have shown promising results against tobacco.

A study reported in the New England Journal of Medicine found that cash rewards of a few hundred dollars nearly tripled quit-smoking rates.

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

While cigarettes can be addictive, people don’t need to smoke to live, and advertising and clean-air restrictions curb tobacco’s presence. People must eat, however, and sugary drinks and fatty snacks are everywhere.

Health officials lament that more than two-thirds of American adults are overweight and one-third obese, and lecture on fat’s role in deaths from diabetes to heart disease.

Some companies reward employees just for having a health evaluation or simply enrolling in a class — whether they complete it or not. Others require measurable weight loss or exercise achievement, sometimes structuring it in a contest like “The Biggest Loser” TV show.

The value of rewards can range from measly to thousands of dollars. Hunches and human resources budgets — not research — often drive decisions about financial incentive details, companies admit.

OhioHealth set the maximum reward for its step-counting program at $500. “It just sounded right to us. We thought that would be a big enough number to help people think twice,” said Lisa Meddock, OhioHealth’s benefits manager

IBM rewards employees for doing 12-week Web-based health programs. They offer $150 per program completed because there was a feeling that was the right amount to get people involved, said Dr. Joyce Young, the company’s wellbeing director.

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, a 35-year-old IBM marketing manager, was 5-foot-9 and a chunky 185 when he decided two years ago to enroll in the company’s web-based fitness program.

IBM’s worksite wellness program is often called a model, with roughly half of the workforce earning at least $150 a year for taking part. But Acocella failed twice.

The money got his attention. But 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 had lost 9 pounds in the three months he’s been there. He recently signed up for the IBM reward program again, but this time it’s incidental to his new active lifestyle.

“The real issue was getting myself in a program I could actually do and could keep up with. I don’t think those things swing on a dollar,” he said.