Table 1

TIDiER checklist describing the intervention and control condition

Intervention: PREVAILControl: daily self-weighing without behavioural support
Brief namePREVAIL (People Regulating Themselves to Achieve Weight Loss)Self-weighing only
WhySelf-weighing: Monitoring weight on a daily basis will enable participants to take note of their weight loss progress.
Weighttracking: Our preceding study12 found that people can lose track of their weight loss progress when weighing every day because they struggle to remember measurements. We therefore ask participants to track their weight.
Action planning: In our preceding study, participants rarely made action plans to help them progress with their weight loss.12 If they did make action plans, they were rarely specific. Specificity of action plans is a significant predictor of the likelihood of implementation.33–35 We therefore guide participants through a specific action planning process.
Report email: Participants in our preceding study struggled to see trends in their weight data.12 Unfortunately, the app we are using for weight tracking does not provide users with trend information. We will therefore send out weekly emails, containing information on the trend of the weight measurements of the last week.
Reflection and action evaluation: Our preceding study revealed that daily fluctuations vary over time within people, making it difficult to interpret daily weight changes. We therefore want to encourage participants to reflect on their weight changes and the effectiveness of their weight loss actions on a weekly basis. Using the weekly weight trend information, participants will be able to evaluate whether they found the group of actions they performed effective and worth repeating.
A previous trial has found that self-monitoring of weight without further guidance is not effective for weight loss.11
WhatSelf-weighing: Participants will be instructed to weigh themselves daily using simple digital body scales (Etekcity Corporation, California). They will be asked to weigh themselves in a similar state every day, ideally first thing in the morning and without clothes.
Weight tracking: Participants will be asked to download the free app “Weight Loss Tracker, BMI” by aktiWir GmbH on their smartphone and use it on a daily basis to record their weight measurements. They will be asked to submit a backup of their data to the research team every week.
Actionplanning: Participants will receive a daily questionnaire helping them to plan a weight loss action. The questionnaire will start by asking participants to enter their morning weight. At the beginning of first week, they will then be asked to choose a category of actions, and they will be able to choose one of the actions within this category per day for the rest of the week. There are seven categories in total, five covering diet-related actions and two covering physical activity-related actions. Participants will be asked to specify for each action how, when and where they are going to perform it, and which cues they are going to use. They will also be prompted to think about how to overcome potential barriers. At the start of weeks 2 through 8, participants will be encouraged to try out a new category of actions. We will additionally ask participants on a weekly basis to commit to continuing some of the actions they tried out in previous weeks. In order to help participants to maintain an overview of the actions they performed so far, we will provide them with a non-digital action plan diary.
Report email: Once a week, participants will receive an email from the research team, informing them about their trend weight change for the last week. This trend weight change consists of the slope of a trend line fitted across all measurements of the week, multiplied by the number of days covered by the measurements. The weight measurements used to create these reports will be taken from the daily action planning questionnaires.
Reflection andactionevaluation: In the weekly report email, participants will receive a link to the reflection and action evaluation questionnaire. This questionnaire prompts participants to think about why their weight has changed as it has. They are further asked to evaluate the group of actions they performed across the week, including whether they found them useful and whether they would repeat them. On the basis of this evaluation, participants will be able to decide which actions they want to continue doing in the next weeks, and which ones to drop. Using this method of self-experimentation, participants will be able to try and test different weight-loss strategies and identify the ones that are effective and sustainable for them.
Self-weigh every morning in a similar state, using smart scales (BodyTrace, New York).
WhoThe chief investigator (KF) will deliver the intervention at the baseline session. She will also organise the mailing of all questionnaires and weekly report emails. She will be the primary contact for all participants. KF is a psychologist by background and has received Good Clinical Practice (GCP) training.The chief investigator (KF) will instruct participants in the control group to weigh themselves every day.
HowParticipants will measure their weight on provided body scales. They will use a free weight tracking app called ‘Weight Loss Tracker, BMI’ by aktiWir GmbH on their smartphone to track their weight loss progress. All questionnaires will be sent automatically to participants in the early morning by the survey platform Qualtrics (USA).Participants measure their weight on provided body scales.
WhereAt home.At home.
TailoredParticipants are able to tailor the intervention to themselves by choosing action plans relevant to them.N/A
How wellWe will request participants to send us a back-up of their data in the weight tracking app. This data will allow us to assess adherence to weight tracking. Completion of the daily action planning and weekly reflection questionnaires will allow us to assess adherence to action planning and reflection. Adherence to daily weighing will be assessed by combining weight records from the weight-tracking app and action planning questionnaires.The provided body scales contain a SIM card which automatically transfers the weight data to a secure research server. We will therefore be able to assess adherence.