Partner Weight Loss and Diet Outcomes at 24 Months in a Randomized Controlled Trial of a Dyadic Versus Individual Weight Management Intervention.

BACKGROUND: Including romantic partners as supports in behavioral weight management programs targeting index participants could yield spillover effects, but few studies have explored the effects on partners. METHODS: Dyads included an index participant with BMI ≥ 27 kg/m2 and a cohabitating partner with BMI ≥ 18 kg/m2 randomized to a participant-only (N = 116) or partner-assisted (N = 115) intervention. All index participants received an evidence-based group weight management program. Partners in the partner-assisted group attended half of the sessions but were not required to make behavioral changes/lose weight. Linear mixed models compared changes in partner weight and self-reported caloric intake between groups at 24 months. RESULTS: Most partners identified as male (63%) and White (88%). Mean baseline weight and BMI were 98 kg (SD 28.1) and 32 kg/m2 (SD 7.8), respectively. At 24 months, partners in the partner-assisted versus participant-only group lost more weight (-2.5 kg vs. -0.4 kg; estimated mean difference: -2.0 kg [95% CI -3.5, -0.6]). There were no differences in caloric change (partner-assisted: -367 kcal, participant-only: -196 kcal; estimated mean difference: -171 kcal [95% CI -358, 17]). CONCLUSIONS: Involving romantic partners is an efficient weight management approach that generates meaningful long-term weight loss for cohabitating partners despite them not being the direct targets for weight loss. TRIAL REGISTRATION: Clinicaltrials.gov NCT03801174.