Cash and Weight Loss?
Researchers found money is an effective incentive when motivating people to lose weight. 62% of participants who received financial incentives ($20 if they met their monthly goal vs. paying $20 if they fell short of their goal) met their goal, compared with 26% of the non-incentive group. In the incentive group, the participants’ mean weight loss was 9.1 lbs (~4.1 kg), and for the non-incentive group it was 2.3 lbs (~1 kg).
Mayo Clinic, March 2013