Examining a Ripple Effect: Do Spouses’ Behavior Changes Predict Each Other’s Weight Loss?

Background. Including spouses in obesity treatment has been found to promote weight loss. We assessed whether spouses’ diet and activity changes impacted each other’s weight loss when both members attended an active weight loss program (TOGETHER) or only the primary participant attended treatment (ALONE). Methods. Heterosexual couples ( ) enrolled in an 18-month randomized controlled weight loss trial were weighed and completed measures of dietary intake and physical activity at baseline and 6 months. We conducted dyadic data analyses using the Actor-Partner Interdependence Model. Results. Participants’ weight loss was not predicted by their partners’ behavior changes. However, partners’ weight loss was predicted by their participants’ changes in calorie and fat intake. When partners were coupled with a participant who did not reduce their own calorie and fat intake as much, these partners had higher weight loss when treated in the TOGETHER group but lower weight loss when they were untreated in the ALONE group. There were no reciprocal effects found with physical activity changes. Conclusions. Direct treatment had the greatest impact on participants and partners who were treated. Untreated partners’ weight losses were positively impacted by their spouses’ dietary changes, suggesting a ripple effect from treated spouses to their untreated partners. 1. Introduction Enhancing weight loss maintenance is an imperative in obesity treatment, and social networks are poised to be important facilitators of this process. A growing body of research suggests that romantic partnerships exert an influence on obesity and therefore may be an important network to intervene upon [1–4]. Married people are generally heavier, and weight gain, decreased physical activity, and poor diet changes after marriage are common [4–8]. Spouses tend to gain weight during the first few years of marriage [9, 10], and increased duration of cohabitation with romantic partners is associated with obesity [7]. Why married individuals tend to share an obesity risk is less understood. The mechanisms of assortative mating and shared home environment are potential explanations [11–13]. Assortative mating suggests that individuals select romantic partners with similar behaviors and body types. Thus, from the start of relationships, couples share an obesity status and behaviors that perpetuate this condition [12]. Similarly, the shared home environment mechanism suggests that spouses share an obesity risk, but instead the risk occurs as a result of their shared household, finances, and social