ABSTRACT
Weight is a dyadic health issue in married and cohabitating couples. Partners tend to enter this critical
interpersonal relationship with a similar weight status and gain weight together over time. Despite this shared
risk, standard behavioral interventions focus on individuals, not couples, largely ignoring the inherently dyadic
nature of weight management. Early tests of couples weight loss programs lacked a clear conceptualization
guiding spouse/partner involvement and results were mixed. Yet there are promising signals – theoretical and
empirical – to guide how couples’ relationships can be harnessed to improve weight loss outcomes. The
proposed study aims to build on this work and develop an efficacious couples-based mHealth approach to
weight loss using the multiphase optimization strategy (MOST) framework. In the preparation phase, we
developed a conceptual model drawing on Transactive Goal Dynamics Theory, our own pilot work, and the
published literature that includes four dyadic intervention components: dyadic action planning, joint feedback
on goal progress, autonomy support training, and home environment modifications. In the proposed
optimization phase, we plan to conduct an innovative and efficient factorial experiment to identify which
combination of the four dyadic intervention components – when added to the core components of a standard
behavioral weight loss program (BWL; e.g., weekly lessons, self-monitoring, feedback) – results in the greatest
weight loss at 6 months (primary outcome). The 6-month intervention will be delivered to married and
cohabitating couples (N=368 dyads) via a native smartphone app to enhance the reach of the intervention,
minimize burden, and attract couples with more demographic and relationship diversity. Assessments will
occur at 0, 3, and 6 months. Weight loss and theoretical mediators as framed by Transactive Goal Dynamics
Theory (e.g., goal coordination) will be assessed along with hypothesized moderators (relationship and
demographic variables). The set of novel dyadic intervention components that maximizes weight loss will be
selected for inclusion in an optimized intervention package to be evaluated in a future randomized controlled
trial. The proposed study is the first test of a fully mHealth weight loss intervention for married and cohabitating
couples. Using the MOST design, it will advance both intervention and theory development by isolating active
dyadic intervention components and their mechanisms of action.