Journal of Medical Internet Research - International Scientific Journal for Medical Research, Information and Communication on the Internet #Preprint #PeerReviewMe: Warning: This is a unreviewed preprint. Readers are warned that the document has not been peer-reviewed by expert/patient reviewers or an academic editor, may contain misleading claims, and is likely to undergo changes before final publication, if accepted, or may have been rejected/withdrawn. Readers with interest and expertise are encouraged to sign up as peer-reviewer, if the paper is within an open peer-review period. Please cite this preprint only for review purposes or for grant applications and CVs (if you are the author). Background: Prevalent co-occurring poor diet and physical inactivity convey chronic disease risk to the population. Large magnitude behavior change could improve behaviors to recommended levels, but multiple behavior change interventions produce small, poorly maintained effects. Objective: The Make Better Choices 2 (MBC2) trial tested whether a multicomponent intervention integrating mHealth, modest incentives, and remote coaching could sustainably improve diet and activity. Methods: The 9-month RCT enrolled 212 Chicago area adults between 2012-2014 with low fruit and vegetable and high saturated fat intakes, low moderate vigorous physical activity (MVPA) and high sedentary leisure screen time. Participants were randomly assigned to either of two active interventions targeting MVPA Simultaneously with or Sequentially after other diet and activity targets or a stress and sleep contact control intervention. They used an app and accelerometer to track targeted behaviors and receive personalized remote coaching. Perfect behavioral adherence was incentivized $5/week for 12 weeks. Diet and activity behaviors were measured at baseline, 3, 6, and 9 months; primary outcome was 9-month diet and activity composite improvement. Results: Both Simultaneous and Sequential interventions produced large, sustained improvements exceeding Control (p<.001), and bringing all diet and activity behaviors to guideline levels. At 9 months, interventions increased fruit/vegetables by 6.5 servings/day, 95% CI [6.1, 6.8], increased MVPA by 24.7 min/day, 95% CI [20.0, 29.5], decreased sedentary leisure -170.5 min/day, 95% CI [-183.5,-157.5] and decreased saturated fat intake -3.6%, 95% CI [-4.1,-3.1]). Conclusions: Multicomponent mHealth diet and activity intervention involving connected coaching and modest initial performance incentives holds potential to scalably reduce chronic disease risk. Clinical Trial: URL: http://www.clinicaltrials.gov. Unique Identifier: NCT01249989