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The Couple Who Diets Together: How Your Partner Influences Your Weight Loss


Photo Credit: TVline.com“What should we do for dinner tonight, honey?”

Chances are you regularly factor your partner into many of your typical daily activities. The two of you have likely fallen into some lifestyle patterns together, for better or worse. One pattern likely focuses on choices around food consumption, mealtimes, snacking, physical activity level, and other lifestyle behaviors impacting weight. What happens when one partner in a relationship wants to change something in him or herself that could potentially disrupt established relationship patterns? For example, let’s say one partner decides to make changes in an effort to lose weight. How might one partner’s dietary changes affect related lifestyle behaviors in the other partner?

Across many studies, research suggests that weight changes in one partner are related to corresponding changes in weight in the other partner, or what is referred to as a “ripple effect” of weight change.Typically, the studies on this topic have relied on data from laboratory-based weight loss interventions or bariatric surgery candidates versus weight loss programs that anyone can access. Additionally, previous studies have typically have relied on self-report data on changes of weight in the non-dieting partner and have not directly weighed the partner. Additionally, few studies have explored the effect of the type of weight loss intervention in an experiment on both the individual trying to lose weight and the “not treated” partner. A recently-published study2 led by University of Connecticut psychologist Amy Gorin, Ph.D., however, has looked at the effectiveness of real-world, publicly available weight loss interventions. This work examines both the “treated” and “non-treated” partner in a couple, comparing weight loss interventions by randomizing participants to types of treatment.

In this study, researchers randomly assigned 130 cohabitating individuals with a BMI rendering them “overweight” or “obese” to one of two groups. Half (n=65) actively participated in a structured weight loss program consisting of both in-person and online support via Weight Watchers (i.e., the WW group) for six months while their “non treated” partner received no intervention. The other half of the sample (n=65) received a 4-page pamphlet about making healthy choices (e.g. portion control, exercise, nutrition) but no subsequent intervention. This group is the self-guided (SG) control group, and their partner similarly received no intervention. Researchers assessed weight loss progression of both members of all couples over 6 months (at baseline, at 3 months, and at 6 months). Both members of the couple were overweight or obese at study outset (based on BMI). Most (68.5%) of the “treated” partners were female.

The results of this study are insightful for many reasons.  First and foremost, weight loss efforts were successful. Throughout the study, treated partners in both groups lost weight, and there were similar percentages of weight loss between the two treated groups at 6 months, with slightly different weight loss trajectories over time. Secondly, weight loss occurred in the non-treated partner. That is to say, approximately one third of partners lost at least 3 percent of their baseline weight without receiving any

weight loss intervention themselves. Furthermore, there were no differences in the non-treated partners between those with partners in the SG and the WW groups. This latter finding suggests that the “ripple effect” happens whether weight loss efforts are structured (such as Weight Watchers) or unstructured (e.g. an educational handout).

Also notable among the findings was that couples lost weight (or struggled to lose weight) at a similar rate. So if one person tended to have success, their partner tended to have success at a similar rate. If one person struggled, their partner also tended to struggle with weight loss as well.

Interestingly, Weight Watchers funded this study, and all participants received compensation, so it is possible that receiving payment incentivized behavior change. Furthermore, this research was conducted on cohabitating partners, therefore it is unknown whether these patterns would exist in other types of relationships (e.g. platonic friendships, cohabitating family members)? Might there be something unique in a partnered relationship as it relates to the “ripple effect”, or might this effect be present in other types of close relationships? Despite what we don’t know, this study has many real world implications for successful weight loss. Healthcare providers may recommend including others in the home in making recommendations for weight-loss related behavior change. Additionally, structured weight loss programs could utilize this information in designing couples-based components.

Overall, this study provided support for the idea that when one person changes their behavior, the people around them also change. This provides food for thought when considering your own decisions and behaviors. What will you choose to do for dinner tonight? When you make positive lifestyle changes, you are likely to influence your partner on these behaviors as well.  

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1 Jackson S. E., Steptoe A., & Wardle J. (2015). The influence of partner’s behavior on health behavior change: The English Longitudinal Study of Ageing. JAMA Internal Medicine, 175, 385-392.

2 Gorin A.A., Lenz E.M., Cornelius T., Huedo-Medina, T., Wojtanowski, A.C., Foster G.D. (2018). Randomized controlled trial examining the ripple effect of a nationally available weight management program on untreated spouses. Obesity 26, 499-504. doi:10.1002/oby.2209 

Dr. Marni Amsellem

Marni Amsellem, Ph.D. (Clinical Psychology, Washington University in St. Louis) is a licensed clinical psychologist specializing in health psychology. She is a research consultant with hospitals, organizations, and corporations, as well as a practitioner. Her research interests include how physical health and health-related behaviors affect individuals and their relationships, and vice versa. You can reach her via twitter @smartpsychreads.

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