Protocol for Partner2Lose: A randomized controlled trial to evaluate partner involvement on long-term weight loss

Behavioral interventions produce clinically significant weight reduction, with many participants regaining weight subsequently. Most interventions focus on an individual, but dietary and physical activity behaviors occur with, or are influenced by, domestic partners. According to interdependence theory, couples who approach behavior change as a problem to be tackled together versus independently are more likely to utilize communal coping processes to promote behavior change. We utilized interdependence theory to develop a partner-assisted intervention to increase long-term weight loss. Community-dwelling individuals (index participants) cohabitating with a partner with 1) overweight and at least one obesity-related comorbidity or 2) obesity are randomized to participate in a standard weight management program alone or with their partner. The weight management program involves biweekly, in-person, group sessions focusing on weight loss for six months, followed by three group sessions and nine telephone calls focusing on weight loss maintenance for twelve months. In the partner-assisted arm, partners participate in half of the group sessions and telephone calls. Couples receive training in principles of cognitive behavioral therapy for couples, including sharing thoughts and feelings and joint problem solving, to increase communal coping. The primary outcome is participant weight loss at 24 months, with caloric intake and moderate-intensity physical activity as secondary outcomes. Partner weight and caloric intake will also be analyzed. Mediation analyses will examine the role of interdependence variables and social support. This trial will provide knowledge about effective ways to promote long-term weight loss and the role of interdependence constructs in weight loss. Clinical trials identifier: NCT 03801174.