Weight-loss programs that give people a financial reward for their efforts to loose weight may be a powerful weapon in the fight against obesity, a new research from the University of Pennsylvania School of Medicine has shown.

In a study of 57 people trying to lose weight over four months, those who received a financial reward lost more than those who didn’t receive money. The idea of a financial gain may be seductive in the fight against obesity.

Dr. Kevin Volpp of the University of Pennsylvania School of Medicine and colleagues were looking for an effective way to treat obesity, a growing problem nowadays. The study, released yesterday in The Journal of the American Medical Association is based on the idea that reward programs can be very effective for those who want to achieve something.

Incentives can provide a “reinforcement mechanism” that helps people to act having in their mind the long-term consequences of their actions. The study authors explained that the reason for why many weight-loss programs fail to meet their goal is that they promise rewards in the future, instead of offering something tangible.

Study participants were split into three groups and they were allowed to receive their winning if they met their weight-loss target. In this lottery system, participants in the first group had the chance to win up to $100 a day for meeting daily weight loss goals. The participants in the second group were asked to bet their own money – between a penny and $3 per day – that they would meet their goals. If they failed to meet their goal, their money was forfeited and put into a pool to reward people who kept their promises. The control group received no money. Every morning, they weighed themselves and called in the result to the researchers.

At the end of the four-month study, investigators found people in the incentive groups lost far more weight than those who got no pay for their efforts, with about half of the participants in each group meeting their weight loss goals. Participants in the lottery program earned a total of $378.49 and lost about 13 pounds (5.9 kg), while people in the deposit group got $272.80 and lost 14 pounds (6.35 kg). Those in the control group lost about 4 pounds after four months.

Skeptics say that a long-term benefit of the approach is questionable. Participants in each group had gained back some of the weight after seven months. Dr. Kevin Volpp said the studies were highly effective at producing short-term weight loss, but when the money stopped flowing, the weight began to gain back the weight. Study authors say a longer study could produce more lasting results. More sophisticated reward programs can lure people to loose weight and to keep that weight off. People who have problems with their weight may be offered other types of rewards that are meaningful to them.

The study is published in the Dec.10 issue of the Journal of the American Medical Association. Investigators received funding to pay study participants from the U.S. Department of Agriculture, the Hewlett Foundation and the National Institute on Aging.