Optimizing a mobile just-in-time adaptive intervention (JITAI) for weight loss in young adults: Rationale and design of the AGILE factorial randomized trial.

Background: Young adults (YAs) are underrepresented in behavioral health and weight loss interventions and express interest in flexible, highly tailored programs. Mobile interventions are a lower-burden, scalable approach to providing behavioral support. Just-in-time-adaptive interventions (JITAI) promise to deliver the "right" support at the "right" time using real-time data from smartphones and sensors. JITAIs hold promise for promoting behavior changes needed for weight loss (dietary intake, activity, and self-weighing); however, there is limited evidence for selecting treatment components and levels of adaptation that are needed for success.

Methods: The AGILE (Adaptive Goals and Interventions for Lifestyle Enhancement) trial utilizes the Multiphase Optimization Strategy (MOST) framework and a 2⁵ full factorial experimental trial to test the efficacy of 5 intervention components, each with two levels, on weight loss among 608 YAs recruited from around the United States. All participants will receive a core 6-month weight loss intervention that includes evidence-based lessons, behavioral skills training, and daily weighing. With the goal of determining if greater adaptation leads to greater weight loss, we will test standard versus adaptive options of 5 additional intervention components: 1) diet monitoring approach (standard vs. simplified), 2) adaptive physical activity goals (weekly vs. daily), 3) decision points for message timing (fixed vs. adaptive), 4) decision rules for message content (standard vs. adaptive), and 5) message choice (no vs. yes). Assessments will occur at baseline, 3 months, and 6 months.

Conclusions: Results of this trial will be used to create an optimized JITAI for weight loss in young adults.