Dyadic Dynamics in a Randomized Weight Loss Intervention.

Background: Despite health and economic burdens associated with overweight and obesity, long-term weight loss intervention efforts have been largely unsuccessful. Observations that weight status tends to cluster in social groups, and findings showing "ripple" effects of weight change within social clusters, raise questions about the impact of social relationships on weight loss.

Purpose: Through a reanalysis of data from a randomized weight loss intervention, this study compared dyadic dynamics in intervention participants and in-home partners.

Methods: Over the course of 18 months, data was collected from 201 pairs enrolled in either behavioral weight loss treatment (BWL) or treatment including partners and providing items to facilitate healthy choices at home (BWL + H). Using a dyadic growth curve model, covariance between baseline BMI, BMI change trajectories, and starting BMI and BMI trajectory for both the self and the other were examined.

Results: There were strong indicators of dependence in the data. Baseline BMI was positively correlated for both treatment groups. In the BWL + H condition, BMI change trajectories were positively correlated. In the BWL condition, this reversed: Change trajectories were negatively correlated. Additionally, partner BMI and primary participant BMI change were positively correlated, indicating that a heavier partner at baseline related to less weight loss.

Conclusions: Social relationships exert a significant influence on weight loss outcomes. Depending on the intervention group, these influences may help (BWL + H) or hinder (BWL). It may be that home intervention changed social support and interaction in important ways and that these effects could be effectively harnessed to implement more effective interventions (NCT00200330).