Association between monetary deposits and weight loss in online commitment contracts.

Purpose: To examine the characteristics of voluntary online commitment contracts that may be associated with greater weight loss.

Design: Retrospective analysis of weight loss commitment contracts derived from a company that provides web-based support for personal commitment contracts. Using regression, we analyzed whether percentage weight loss differed between participants who incentivized their contract using monetary deposits and those who did not.

Setting: Online.

Participants: Users (N = 3857) who voluntarily signed up online in 2013 for a weight loss contract.

Intervention: Participants specified their own weight loss goal, time period, and self-reported weekly weight. Deposits were available in the following 3 categories: charity, anticharity (a nonprofit one does not like), or donations made to a friend.

Measures: Percentage weight loss per week.

Analysis: Multivariable linear regressions.

Results: Controlling for several participant and contract characteristics, contracts with anticharity, charity, and friend deposits had greater reported weight loss than nonincentivized contracts. Weight change per week relative to those without deposits was −0.33%, −0.28%, and −0.25% for anti-charity, charity, and friend, respectively (P < 0.001). Contracts without a weight verification method claimed more weight loss than those with verification.

Conclusion: Voluntary use of commitment contracts may be an effective tool to assist weight loss. Those who choose to use monetary incentives report more weight loss. It is not clear whether this is due to the incentives or higher motivation.