Background

The superiority of an intervention combining two sets of theory-based behavior change techniques targeting planning and self-efficacy over an intervention targeting planning only or self-efficacy only has rarely been investigated.

Purpose

We compared the influence of self-efficacy, planning, and self-efficacy+planning interventions with an education-based control condition on adolescents' body fat, assuming mediating effects of respective social cognitive variables and moderate-to-vigorous physical activity (MVPA). The moderating role of the built environment was examined.

Methods

Participants (N = 1217, aged 14-18 years) were randomly assigned to four conditions: planning (n = 270), self-efficacy (n = 311), self-efficacy+planning (n = 351), and control (n = 285). The measurement was conducted at baseline (T1), two-month follow-up (T2), and fourteen-month follow-up (T3). Interventions/control group procedures were delivered at T1 and T2. Percent of body fat tissue (measured at T1 and T3) was the main outcome. Social cognitive mediators (self-efficacy and planning) were assessed at T1 and T2. The behavioral mediator (MVPA) and the presence of built MVPA facilities (the moderator) were evaluated at T1 and T3.

Results

Similar small increases of body fat were found across the three intervention groups, but the increment of body fat was significantly larger in the control group. On average, differences between control and intervention groups translated to approximately 1% of body fat. Effects of the interventions on body fat were mediated by relevant social cognitive variables and MVPA. A lower increase of body fat was found among intervention group participants who had access to newly-built MVPA facilities.

Conclusions

We found no superiority of an intervention targeting two social cognitive variables over the intervention targeting one cognition only.

Introduction

Digital behavioural weight loss interventions have the potential to improve public health; however, these interventions are often not adequately tailored to the needs of the participants. This is the protocol for a trial that aims to determine the effectiveness and cost-effectiveness of the Choosing Health programme as a means to promote weight loss and weight loss maintenance among overweight/obese adults.

Methods and analysis

The proposed study is a two-group randomised controlled trial with a nested interrupted time series (ITS) within-person design. Participants (n=285) will be randomly assigned to either the Choosing Health digital intervention or a control group. For intervention participants, ecological momentary assessment will be used to identify behavioural determinants for each individual in order to tailor evidence-based behaviour change techniques and intervention content.Control group participants will receive non-tailored weight loss advice via e-book and generic emails. The primary outcome is the mean difference in weight loss between groups at 6 months controlled for baseline. Secondary outcomes include blood pressure and percentage of body fat; self-reported measures of physical activity, sitting time, quality of life, cost and theory-derived correlates of weight loss. Secondary outcomes will be measured at baseline, 3, 6 and 12 months. The primary outcome for ITS will be daily weight loss plan adherence. Data will be analysed using regression and time series analyses.

Ethics and dissemination

Ethics approval was granted by Faculty of Psychology, SWPS University of Social Sciences and Humanities, Wroclaw, Poland, approval number 03/P/12/2019. The project results will be disseminated through structured strategy implemented in collaboration with the Ministry of Health.

Trial registration details

This trial was registered with www.clinicaltrials.gov; registration number NCT04291482.

The current article details a position statement and recommendations for future research and practice on planning and implementation intentions in health contexts endorsed by the Synergy Expert Group. The group comprised world-leading researchers in health and social psychology and behavioural medicine who convened to discuss priority issues in planning interventions in health contexts and develop a set of recommendations for future research and practice. The expert group adopted a nominal groups approach and voting system to elicit and structure priority issues in planning interventions and implementation intentions research. Forty-two priority issues identified in initial discussions were further condensed to 18 key issues, including definitions of planning and implementation intentions and 17 priority research areas. Each issue was subjected to voting for consensus among group members and formed the basis of the position statement and recommendations. Specifically, the expert group endorsed statements and recommendations in the following areas: generic definition of planning and specific definition of implementation intentions, recommendations for better testing of mechanisms, guidance on testing the effects of moderators of planning interventions, recommendations on the social aspects of planning interventions, identification of the preconditions that moderate effectiveness of planning interventions and recommendations for research on how people use plans.