A Theory-based Digital Intervention to Promote Weight Loss and Weight Loss Maintenance

Obesity can severely reduce quality and longevity of life and there is an urgent need to help people lose weight and maintain weight loss long term. Digital behaviour change interventions targeting diet and physical activity have the potential for public health gain; however, these interventions are often not adequately tailored to the participants. The aim of this study is to develop and test a digital intervention to help people make sustainable changes to diet and physical activity, and consequently their weight. This study is a hybrid trial that will evaluate the effectiveness, cost-effectiveness and implementation of the Choosing Health program among overweight/obese adults.

This study is a two-group randomised controlled trial (RCT) with within person assessment. Participants (N=285) will be randomly assigned to either the Choosing Health digital intervention or a control group. For intervention participants, Ecological Momentary Assessment (EMA) will be used to identify behavioural determinants for each individual in order to tailor evidence-based behaviour change techniques and intervention content. Control group will receive non-tailored factual weight loss advice. Primary outcome is mean difference in weight loss between groups at 6 months, in kilograms. Key outcomes will be measured at baseline, 3-, 6- and 12 months. Data will be analysed using multilevel modelling and time series analysis.

This is the first weight loss intervention applying individualised digital tailoring based on continuous assessment of individual's psychological determinants of behaviour measured over time. The Choosing Health will offer insight into factors associated with success in making sustained changes to weight, and secondary outcomes, such as diet and physical activity.

Behavioural science offers theory-driven and evidence-based behaviour change techniques that can support people in losing weight and maintaining it long term. These techniques have not yet been assessed in within-person studies that not only examine aggregated between-group effects (e.g., intervention versus control comparisons) but also determine personal trajectories of weight loss and maintenance and tailor accordingly to the strongest predictors of outcomes. The aim of the proposed study is to develop and test a digital intervention that uses Ecological Momentary Assessment (EMA) and tailors the evidence-based behaviour change techniques that are based on theory to the strongest predictors of outcomes (based on EMA responses collected over time).

This study will determine the effectiveness and cost-effectiveness of the proposed intervention through the Randomised Controlled Trial (EMA tailored intervention versus control), with within person component embedded in the trial. Study hypothesis is that participants in the EMA tailored intervention group will lose significantly more weight than participants in the control group from baseline to 6 months (post program comparison - primary outcome) and at 12 months (maintenance effects assessment - secondary outcome).

This is a two-group intervention trial adopting a randomised controlled design. It is a hybrid trial assessing intervention effectiveness, cost-effectiveness and implementation. This study has within person component embedded in the design and intervention group will answer EMA questions during the initial 3 months of the study and will receive tailored intervention at month 3 combined with additional EMA. There are two phases of the 6-month intervention (I) observational EMA phase and (II) active intervention phase.

The proposed intervention is delivered online through emails and text messages and based on the EMA responses in phase I, it is tailored in phase II. The intervention will have a non-automatic component, meaning trained facilitators will answer participants' queries and provide additional resources if and when needed to improve the engagement with the intervention. The study meets CONSORT criteria for RCTs and study ethical approval was obtained from SWPS University of Social Sciences and Humanities, Wroclaw, Poland (approval number 03/P/12/2019).

Eligibility Criteria:
Inclusion Criteria:

* Adults with overweight and obesity (18+);
* Individuals with a BMI 25 and higher at the baseline assessment.

Exclusion Criteria:

* Individuals who self-report a physical condition or impairment preventing them from being physically active or losing excess body weight;
* Individuals who have had a bariatric surgery or are planning to have one within the next 12 months;
* Individuals who are currently participating in another weight loss program (e.g., regular meetings with personal trainer);
* Individuals who report any contradictions to exercise as indicated by the PAR-Q or pregnant women who consulted their doctor to obtain approval to take part in the study and did not get the approval;
* Individuals who do not have a mobile phone with access to the internet;
* Individuals who are currently participating in another weight loss program (e.g., regular meetings with personal trainer);
* Pregnant women;
* Individuals who are planning to move outside of the study region and are not willing to travel for study measurement sessions;
* Individuals who are on medication that causes weight gain;
* Individuals with a pacemaker (the scale used in the study is not appropriate for use in these individuals).