Dieters Lose Weight When Reward Is Cash

When Cash Is the Carrot, Obese People Lose More Weight, Study Shows

From the WebMD Archives

Dec. 9, 2008 -- Cash diets help people achieve weight loss goals, a Wharton School/VA study shows.

The cabbage in these diets isn't a vegetable. It's cold cash, paid -- and sometimes lost -- on a daily basis.

Surprisingly, it's the immediacy of the payoff and not the dollar amount that matters, shows the study by Kevin G. Volpp, MD, PhD, director for health incentives at the University of Pennsylvania's Wharton School and the Philadelphia VA Medical Center, and colleagues.

"Behavior-change efforts are often futile because those changes might help you sometime in the future, but the average person has trouble making that future reward relevant today," Volpp tells WebMD. "Cash reward programs offer a chance to change behavior and get a reward right now."

Offering cash rewards for weight loss isn't a new idea, notes Martin Binks, PhD, director of behavioral health at the Duke Diet and Fitness Center in Durham, N.C. Binks was not involved in the Volpp study.

"Reward programs can be very effective in the short term," Binks tells WebMD. "But we see 750 new people a day at our center -- and 750 more who return for help losing weight. Those who lose weight in the long term really take this to a deeper personal level. They make the shift to connecting their everyday actions to broader personal goals."

Cash for Weight Loss

Most of us, Volpp says, "heavily discount the future." Human nature makes it hard for us to give up something today in hopes of a far-off reward. But we're easily motivated to act quickly by rewards dangled right in front of us.

To demonstrate the point, Volpp and colleagues designed two weight loss schemes and tested them on 57 obese, 30- to 40-year-old men and women who wanted to lose weight.

Their goal: Lose 16 pounds in 16 weeks. Every morning, they weighed themselves and called in the result to the researchers. At the end of each month, they went in for a weigh-in.

Participants randomly assigned to the first scheme got a lottery number. Every day, they had a 1-in-5 chance of winning $3 and a 1-in-100 chance of winning $100. They got a payout at the end of each month -- but only if they met their weight loss goal of losing a pound a week.


"They got fairly frequent positive rewards," Volpp says. "The particular design of this is important, because people win fairly often, so they know it is a real lottery. And then they have a chance of a bigger prize that serves as a carrot to move forward."

Those assigned to the "deposit contract" group had to put up their own money. They had to give the researchers a self-selected amount, from 1 cent to $3, for every day of the study. They got the money back -- sweetened by a matching amount from the researchers -- only if they met their monthly goal. At the end of the study, those who lost at least 20 pounds got to split the money forfeited by those who did not meet their goals.

"What a deposit contract does is create a way where people put their own money at risk," Volpp says. "But once they put the money down, loss aversion is a powerful motivator. Nobody likes to lose money. And we turbo charge this where we match what their deposits are, to make it even more powerful, to make it even more likely people will try really hard to lose weight."

In both incentive groups, those who did not meet their monthly goal got a "fresh start." That is, their overall weight loss goal remained the same, but their target rate of weight loss was adjusted so their cash diet didn't become a crash diet.

A third group, the control group, simply had to report for a monthly weigh-in, for which they got $20.

At the end of four months:

  • Members of the weigh-in group lost an average of 3.9 pounds.
  • Members of the lottery group lost an average of 13.1 pounds.
  • Members of the deposit contract group lost an average of 14.0 pounds.
  • About half the members of both cash-incentive groups met their goal of losing 16 pounds.

When the Money Stops ...

The story wasn't all rosy, however. When weighed again three months after the cash incentives stopped, it was clear that many of the cash dieters had begun to regain weight.


Does this mean cash diets can only work in the short term? Not necessarily, says Volpp.

"We don't think this has to run for a defined period of time and then be shut off," he says. "We could cycle people through different reward programs to keep things new and interesting. There is lots of potential for this to be done long term.

The problem, as Volpp sees it, is that people are constantly bombarded with temptations to eat fattening foods. That makes it even harder to adopt weight loss behaviors than to change other behaviors, such as smoking.

"The stimuli to eat low-cost, high-calorie food are all around you," Volpp says. "You can fly across the country, walk through an airport, and never be tempted to smoke. But if you're having trouble with dietary intake, the temptations are lurking at literally every corner, with neon sighs to draw you in."

But Volpp admits that cash rewards have never been tested in long-term programs. Binks agrees that sophisticated reward programs can get people on the right track. But he doesn't think they will result in permanent behavior change -- unless they can start seeing their new behaviors as part of a bigger picture.

"If we are going to achieve lasting change in health behavior, we need to help people to internalize a sense of responsibility to self and self-care," Binks says. "We need to help people value their own well-being if we are to truly engender lasting change."

Volpp and colleagues report their findings in the Dec. 10 issue of the Journal of the American Medical Association.

WebMD Health News Reviewed by Louise Chang, MD on December 09, 2008



Volpp, K.G. Journal of the American Medical Association, Dec. 10, 2008; vol 300: pp 2631-2637.

Kevin G. Volpp, MD, PhD, director of the center for health incentives, Leonard Davis Center for Health Economics, Wharton School, University of Pennsylvania, Philadelphia; and core faculty for health equity research and promotion, Philadelphia Veterans Affairs Medical Center.

Martin Binks, PhD, director of behavioral health and research director, Duke Diet and Fitness Center, Durham, N.C.

© 2008 WebMD, LLC. All rights reserved.


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