Cash is a powerful motivator when it comes to shedding pounds, and the lure of money is even greater when dieters win or lose as a group.

Previous studies showed that earning money as a reward for losing weight is an effective motivator. Researchers at the Mayo Clinic recently found that participants with $20 a month on the line lost an average of nine pounds in a year, four times greater than the amount lost by those who didn't have a cash initiative. Now, a study published in the Annals of Internal Medicine finds that money motivates groups even more powerfully than it does individuals.

It's not a new idea — crass as it may seem, cash may be one of the easiest ways to inspire healthy behaviors. More employers are using financial incentives to help their employees get in shape, and office wellness programs offering cash rewards are likely to continue since the Patient Protection and Affordable Care Act will expand such health outcome–based incentives to up to 30% of total health insurance premiums beginning in 2014.

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