Optimization of Dietary Adherence in a Mobile Weight Loss Intervention

SHIFT uses a highly efficient experimental design as part of the Multiphase Optimization Strategy (MOST) to optimize a 6-month behavioral weight loss intervention for improved dietary adherence among adults with overweight and obesity with initial nonresponse to the intervention. Investigators will test four unique treatment components added to a core mobile behavioral weight loss program.

All participants will receive the Core 6-month behavioral weight loss program, which is a comprehensive intervention that includes evidence-based behavior change strategies to promote self-monitoring and adherence to personalized dietary and activity goals. The program includes an individual kick-off session, native smartphone application, text messages, daily goals, self-monitoring of diet, weight, and physical activity, weekly lessons, tailored weekly feedback, and will start with 5-6 text messages per week. The intervention targets both dietary and physical activity changes, with a greater emphasis placed on improved dietary behaviors as the primary strategy for weight loss. Participants with lower than expected adherence to their dietary goals early in the program (weeks 3-8; "nonresponders") will be randomly assigned in a 2x2x2x2 factorial trial to the On or Off level of each of these 4 additional treatments added onto the core program: 1) switching dietary self-monitoring approach (Simplified Diet), 2) adding an autonomous goals and planning tool (Goal Autonomy + Planning), 3) adding just-in-time text messaging (JIT Messaging) 4) receiving 3 telehealth sessions with a health coach (Coach). Thus, each of these participants will receive 0-4 additional treatment components for the remainder of the 6-month program. Participants with recommended levels of dietary adherence in the first 8 weeks ("responders") remain in the Core program and are not randomized in the factorial trial.

All participants (those in the factorial trial and the responders who remain in the Core only) will complete assessments at baseline, 4 weeks (brief/online only), 8 weeks (brief/online only), 3 months, and 6 months. Primary and secondary research aims are limited to participants who are randomized into the factorial trial (estimated to be approximately 65% of the total sample). The primary aim is to determine the combination of additional intervention components that maximize dietary adherence from time of randomization to 6 months among participants with low early dietary adherence. A secondary outcome is percent of participants reaching 5% weight loss from baseline to 6 months.

Decision analysis for intervention value efficiency (DAIVE) will be the decision-making approach used to select the treatment components included in the final, optimized intervention. DAIVE uses a Bayesian factorial analysis of variance that maximizes the expected value of the outcome by evaluating the predicted value associated with all possible combinations of the components. DAIVE will be used maximize the expected value of both mean total weeks of dietary adherence from randomization to 6 months and proportion reaching 5% weight loss at 6 months.