"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 and a sudden need for slimmer clothes.
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: The average weight loss in most was little more than a pound.
Sure, there are grounds for optimism. Smaller experiments report some success. And other studies have shown promising results against tobacco. One study published last year in the New England Journal of Medicine, co-authored by Volpp, 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, Kelder and others said.
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, heart disease and other conditions.
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.
Companies tend to be more interested in incentives than disincentives like taxes. But the perks they attach to wellness programs come in a variety of forms and sizes.
Some 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 along the lines of "The Biggest Loser" TV show.
Some companies offer money, some vacation trips. Some refund the cost of Weight Watchers classes. Others reduce health insurance premiums.
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 are quite frank about it.
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.
Companies "are making best their guesses about what might work and giving it a shot," said Robert Jeffery, a University of Minnesota professor. He's been experimenting with financial incentives and weight loss since the 1970s and is perhaps the most veteran researcher in the field.
If companies asked the experts, they might be counseled to make their incentives more dramatic -- more cash or a bigger penalty in premium costs.
Psychologists say people are more motivated by the risk of losing their own money than by a chance they'll win somebody else's. Applying that idea to weight loss, some studies have set up refundable bond systems: Volunteers sign a contract agreeing to lose a certain amount of weight by a certain date or they forfeit their deposited money.
One of the seven companies in the Cornell study offered a refundable bond option to employees. Its average weight loss was nearly 4 pounds. That doesn't sound like a lot but it's almost twice as much as the average weight loss at companies that paid quarterly rewards.
A 2008 University of Pennsylvania study found that after 16 weeks people who put their own money on the line lost about a pound more, on average, than people who got cash from others.
Besides employers, a few companies market refundable bond contracts to people trying to lose weight. Using a twist of black humor, a company called StickK.com, sends the forfeited money from those who fail to an organization the customer despises.
"The most popular is the George W. Bush Presidential Library," said Sam Espinosa, a company spokesman. "Last year, we sent $6,000 to them."
Such programs are voluntary. But critics say that while they may work for a few very motivated people, they may not be effective for most.
Some employers worry that if they go too far, it may seem coercive and even grounds for a lawsuit. "They're very nervous about doing anything that might seem invasive," said Helen Darling, president of the National Business Group on Health.
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-feet-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.
