Effect of commitments and contracts on outcomes among obese and overweight populations: a systematic review

Abstract

Background. Poor adherence to weight loss interventions can lead to poor outcomes, and including adherence strategies, such as formal commitments, has been identified as important. This review aims to identify the short and long-term effect of including a commitment BCT (commitment or behavioural contract) alongside lifestyle interventions on weight loss, and identify the most appropriate delivery mechanisms and target behaviours. Methods. We searched five databases and hand-searched reference lists for trials of interventions targeting diet and/or physical activity to achieve weight loss among obese or overweight adults (age≥18, BMI ≥25 or % overweight). Interventions including a verbal commitment and/or behavioural contract were included. Contracts including financial incentives were excluded. Findings. Of 2488 unique studies, nine met the inclusion criteria. Preliminary results suggest that contracts may improve short-term weight loss outcomes (4-6 months). Long-term evidence is limited, and suggests that contracts may improve attendance, but not weight loss maintenance. Commitments appear to be most successful when made publicly or witnessed by others. The most suitable target behaviours for commitments remains unclear, as all but one of the studies targeted both dietary and physical activity behaviours. Discussion. The findings suggests that using contracts as part of a weight loss intervention may be useful in improving short-term weight loss outcomes, but evidence is limited so results must be interpreted with caution. Poor reporting of individual behaviour change techniques may have limited the number of identified studies. More rigorous methodology and longer term follow ups are needed in the future to determine their effectiveness.