Doctors at the University of Pennsylvania found that people paid to lose weight lost about three times the pounds than those who did not.
Out of the study's 57 people, the control group lost 4 pounds, the rewarded group lost 13.
But after 7 months, participants regained 25 to 50 percent of the weight back.
Experts say rewards may spur weight loss, but willpower is still needed to keep it off.
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