Monetary rewards for healthy behavior can pay off both in the pocketbook and in positive psychological factors like internal motivation, according to a new University of Colorado Boulder study.

While programs involving monetary incentives to encourage healthy behavior have become more popular in recent years, the evidence has been mixed as to how they can be most effective and how participants fare once the incentives stop, said CU-Boulder doctoral student Casey Gardiner, who led the new study.

The study -- which encouraged daily consumption of fruits and vegetables in exchange for payment -- not only showed monetary incentives worked, but that participants increased their internal motivation to eat fruits and vegetables over time.

"Some psychological research and theories suggest that if individuals have external motivations like payment to perform tasks, their internal, or intrinsic motivation can be undermined," said Gardiner of the psychology and neuroscience department. "But in our study the subjects who had been assigned to receive payment for eating fruits and vegetables were still consuming more of them than usual two weeks after the study ended."

In the study, 60 adults were randomly assigned to three different groups. Individuals in one group received $1 for every serving of fruits and vegetables they reported consuming daily over a three-week period, with the money delivered daily by PayPal.

People in the second group accrued $1 for every serving of fruits and vegetables eaten, with the money delivered in a lump sum at the end of the study. Participants in the third group reported their fruit and vegetable consumption daily for three weeks with no incentives.

Participants who received daily monetary incentives had the greatest increase in their fruit and vegetable consumption, Gardiner said.

"This finding highlights the importance of incentive design in health programs," she said. "Differences in the timing or type of incentive can alter their effectiveness."

Gardiner will present the study results at the Society of Behavioral Medicine's 37th Annual Meeting & Scientific Sessions March 30 to April 2 in Washington, D.C. The presentation is tied to an upcoming paper on the subject by Gardiner and CU-Boulder Professor Angela Bryan of the psychology and neuroscience department.

"One of our goals in the study was to look at potential psychological mechanisms that underlie incentive-induced changes in behavior," said Gardiner. "We essentially showed that incentives may be able to help people to 'jumpstart' behavior changes, but that changes in key psychological factors help people maintain the behavior when the incentives end."

Increased fruit and vegetable consumption by participants was associated with more positive attitudes and self efficacy -- the confidence in one's own ability to succeed -- regarding the consumption of such produce, said Gardiner.

The CU-Boulder findings provide a new direction for incentive research in terms of psychological factors related to changing behavior, said Gardiner.