Just-in-time Adaptive Intervention Messaging in a Digital Weight Loss Intervention for Young Adults

An estimated 1 in 2 US adults will have obesity by 2030, which is a major cause of morbidity and mortality. The highest risk of weight gain is among young adults ages 18-35 years. In-person behavioral interventions generally produce clinically significant weight losses, but cost and reduced reach limit their ability to impact obesity at a population level. Web-based interventions that mimic the structure of weekly face-to-face treatment have proven a viable alternative, though weight losses are generally smaller than in-person treatment. Mobile treatments have the potential for high reach, but have been less effective, producing 1-3 kgs over 6 months. Newer digital intervention approaches called "just-in-time adaptive interventions" (JITAIs) promise to improve upon mobile outcomes by offering adaptive, personalized feedback on behavior, which consists of providing the "right type of support" at "the right time" rather than on a fixed schedule. This "just-in- time," or JIT, approach is made possible by the emergence of low-cost and widely available digital health tools that allow for the collection of continually updated health data. However, to date, no JITAIs have successfully targeted multiple weight-related behaviors (weighing, activity, and diet), and there has been no systematic examination of what types of messaging interventions best promote adherence to these three weight loss behaviors, for whom they are effective, and under what conditions. To address this problem, a micro-randomized trial will be used to evaluate the effects of 7 types of intervention messages targeting specific behavior change techniques (i.e., BCT messages) delivered in JIT moments on daily achievement of behavioral goals among n=201 young adults with overweight and obesity. All participants will receive a 6-month behavioral weight loss intervention using our Nudge mobile app, which includes evidence-based weekly lessons, tailored feedback, self-monitoring, and daily BCT messages. Participants will receive a wireless scale, activity tracker, and track "red" foods (high-calorie foods) in the app and have 3 goals: weigh daily, a daily active minutes goal that gradually increases if met, and a daily red foods limit. At 3 decision points per day, participants will be micro-randomized to receive or not receive 1 of 7 types of BCT messages. Each intervention message has unique decision rules for availability. Candidate intervention message options have been carefully selected from empirical evidence, tested in our prior studies, or are from our pilot micro-randomized trial. Assessments will occur daily, and at 0, 3 and 6 months, to accomplish the following specific aims: 1) Evaluate the effects of each behavior change technique message (i.e., BCT message) on daily adherence to weight loss behaviors; 2) Determine whether the effects of BCT messages on proximal outcomes change over time; and 3) Assess whether the effects of BCT messages on proximal outcomes are moderated by participants' contextual factors. Findings will guide how adaptive, behaviorally- and contextually-dependent messages are incorporated into future JITAIs for weight loss.