© 2020 The Authors. British Journal of Health Psychology published by John Wiley & Sons Ltd on behalf of British Psychological Society Objectives: To evaluate effectiveness and acceptability of a novel intervention, based on self-regulation theory, for weight loss. Design: A two-arm parallel group design was employed. Methods: Adult participants with a BMI ≥ 30 kg/m2 and the aim to lose weight were recruited and randomized to either a control or intervention group. Both groups were asked to weigh themselves daily for eight weeks. The intervention group was encouraged to use a weight tracking app, and complete daily and weekly questionnaires to prompt action planning, reflection, and evaluation of actions. Participants chose daily actions from a menu of 53 behaviours. The primary outcome was weight change after 8 weeks, assessed using linear mixed effects models. At follow-up, 20 intervention group participants were interviewed regarding their experiences in the trial. Results: 100 participants were recruited, and 98% were followed up at 8 weeks. Mean weight loss was −4.18 kg (SD = 3.84) in the intervention compared to −1.01 kg (SD = 2.67) in the control group; the adjusted difference was −3.20 kg (95% CI −4.49, −1.92). Participants rated the intervention’s usefulness as 8.25 (SD = 2.04) on a scale from 1 to 10. Adherence was a significant independent predictor of weight loss success (−1.54 kg per one SD, 95% CI −2.16, −0.93), but not a mediator of the intervention effect. Participants reported that the intervention enabled them to experiment with and identify effective weight loss actions. Conclusions: Guiding participants through the self-regulation process was feasible, acceptable to participants, and led to significantly greater short-term weight loss than unguided self-weighing.
British Journal of Health Psychology