Effect of Tailored Feedback on Physical Activity and Weight Loss Adherence in mHealth Trial

Introduction: Standard behavioral weight loss treatment entails self-monitoring (SM) of lifestyle behaviors (e.g., physical activity [PA]) and weight. However, adherence to PA guidelines and self-weighing often declines over time. Digital health devices can reduce the burden of SM and deliver timely tailored feedback (FB) to reinforce behavior change. Hypothesis: Positively worded tailored FB will result in greater adherence to PA goals and self-weighing than neutral or negatively worded FB. Aim: To examine the association between the sentiment of tailored FB received and adherence to weekly PA goals and self-weighing among SM+FB participants in a 12-month mHealth weight loss trial. Methods: Community-dwelling adults (N=502) with body mass index (BMI) from 27 to 43 kg/m 2 were randomized 1:1 to either SM+FB or SM alone. Participants tracked PA via digital activity trackers, weight with smart scales, and diet using logging apps up to 52 weeks. SM+FB participants received up to three FB messages daily, tailored based on their tracking data, using a study-developed app and a curated FB message library. PA-related and self-weighing FB messages were sentiment-coded as positive, neutral, or negative (inter-coder κ=.97). For analysis, a binary indicator denoted whether any positive behavior-specific FB was received in a given week. Weekly PA goal adherence was computed as the percentage of tracked minutes of moderate-to-vigorous PA relative to the study-prescribed PA goal, and weekly self-weighing adherence was computed as the percentage of days with self-weighing. Intensive longitudinal data modeling examined the association between receipt of positive behavior-specific FB and weekly PA goal and self-weighing adherence. Results: SM+FB participants (n=251) were 80% female and 84% white, with mean age of 45.0±14.3 years and BMI of 33.7±3.9 kg/m 2 . On average, participants received 2.3±1.1 PA-related and 0.8±0.4 self-weighing FB messages per week. Although PA goal and self-weighing adherence declined non-linearly over 12 months (p<.001), receipt of positive PA-related FB messages was associated with on average greater weekly PA goal adherence (b=6.50, 95%CI: 2.00,11.01; p=.005), while receipt of positive self-weighing FB messages was associated with a reduction in the linear decline in self-weighing adherence (b=0.20, 95%CI: 0.01,0.40; p=.040). Conclusion: Tailored FB, especially the positive sentiment of the messages, can enhance adherence to PA goals and self-weighing.