1 Substantive-Methodological Synergy Research Laboratory, Department of Psychology, Concordia University, Montréal, Canada.
2 Substantive-Methodological Synergy Research Laboratory, Department of Psychology, Concordia University, Montréal, Canada; Optentia Research Unit, North-West University, Vanderbijlpark, South Africa. Electronic address: alexandre.morin@concordia.ca.
3 Department of Psychology, Concordia University.
4 Faculty of Land and Food Systems, University of British Columbia, Vancouver, Canada.
5 Department of Psychology, Université du Québec à Trois-Rivières, Trois-Rivières, Canada.
6 Department of Psychiatry, McGill University, Montréal, Canada.

Socioecological models of health view romantic relationships as micro-social systems in which spouses influence one another's health-related thoughts, feelings, and behaviors. Although prior work suggests spousal interdependence in eating behaviors, the degree of interdependence may vary as a function of the specific eating behaviors studied. In this longitudinal dyadic study, 204 cohabiting couples (N = 408 spouses) including a member living with overweight completed online questionnaires and provided BMI data at three separate time points spanning a total period of three months. Longitudinal cross-lagged actor-partner dyadic models were used to examine spousal interdependence in overeating, restrained eating, and body mass index (BMI) as well as potential moderators linked to a couple's relational context (i.e., gender, age, relationship length, and time spent in separate leisure activities). Results revealed participants' overeating scores were positively predicted by their spouse's overeating scores, particularly among those who reported spending more time in joint leisure activities and older participants (this effect emerged around 40 years of age and increased thereafter). Conversely, participants' overeating scores were negatively predicted by their spouse's BMIs. With respect to restrained eating, the significance and directionality of the partner effects depended on relational stage, where participants' scores were positively predicted by their spouse's scores in relationships of up to five years and negatively predicted by their spouse's scores in relationships of 35 years or more. No significant partner effects predicted BMI. These results reveal effects indicative of spousal interdependence related to different eating behaviors and BMI and highlight aspects of the relational context that modify such interdependence.