Background: The long-term impact and cost-effectiveness of weight management programmes depends on post-treatment weight maintenance. There is growing evidence that interventions based on third-wave cognitive behavioural therapy (3wCBT), specifically acceptance and commitment therapy (ACT), could improve long-term weight management however these interventions are typically delivered face-to-face by psychologists, which limits the scalability of this type of intervention.

Objective: To use an evidence-, theory- and person-based approach to develop an ACT-based intervention for weight-loss maintenance that uses digital technology and non-specialist guidance to minimise resources needed for delivery at scale.

Methods: Intervention development was guided by the Medical Research Council framework for the development of complex interventions in healthcare, Intervention Mapping Protocol, and the person-based approach for enhancing the acceptability and feasibility of interventions. Two phases of work were conducted: phase one consisted of collating and analysing existing and new primary evidence, and phase two consisted of theoretical modelling and intervention development. Phase one included a synthesis of existing evidence on weight-loss maintenance from previous research, a systematic review and network meta-analysis of 3wCBT interventions for weight management, a qualitative interview study of experiences of weight-loss maintenance, and the modelling of a justifiable cost for a weight-loss maintenance programme. Phase two included iterative development of guiding principles, a logic model and the intervention design and content. Target user and stakeholder panels were established to inform each phase of development and user-testing of successive iterations of the prototype intervention were conducted.

Results: This process resulted in a guided self-help ACT-based intervention called SWiM (Supporting Weight Management). SWiM is a 4-month programme, consisting of weekly web-based sessions for 13 consecutive weeks, followed by a 4-week break for participants to reflect and practice their new skills, and a final session at week 17. Each session consists of psychoeducational content, reflective exercises, and behavioural experiments. SWiM includes specific sessions on key determinants of weight-loss maintenance, including developing skills to manage high-risk situations for lapses, creating new helpful habits, breaking old unhelpful habits, and learning to manage interpersonal relationships and their impact on weight-management. A trained, non-specialist coach provides guidance for participants through the programme with four scheduled 30-minute telephone calls and three further optional calls.

Conclusions: This comprehensive approach facilitated the development of an intervention that is based on scientific theory and evidence of how to support people with weight-loss maintenance, and is grounded in the experiences of the target users and the context in which it is intended to be delivered. The intervention will be refined based on findings of a planned pilot randomised controlled trial.

Keywords: weight management; eHealth; acceptance and commitment therapy; third wave cognitive behavioural therapy; guided self-help