Optimizing an extended care intervention to promote weight loss maintenance: Protocol for the OPT-X multiphase optimization strategy factorial trial.

BACKGROUND: Weight loss maintenance (WLM) remains a limitation of behavioral obesity interventions, as long-term adherence is burdensome and diminishes over time. Simplified recommendations and/or alternative delivery methods that target evidence-based WLM strategies may reduce burden to improve long-term outcomes. METHODS: This protocol describes a multiphase optimization strategy (MOST) trial using a 2x2x2x2 factorial design to optimize a 12-month extended care program for weight loss maintenance. Adults with obesity who achieve at least 5% weight loss during an initial 4-month behavioral weight loss program are randomized to receive a core maintenance program plus zero to four "minimally disruptive" intervention components: reduced food variety, home-based resistance training, buddy training and support, and acceptance and commitment therapy workshops. RESULTS: The primary outcome is weight loss maintenance at 12 months following randomization. Secondary outcomes include treatment adherence, treatment burden, behavioral maintenance constructs, and hypothesized mediators and moderators of intervention effects. DISCUSSION: This study explores unconventional but evidence-based treatment strategies for WLM and applies a 'minimally disruptive medicine' paradigm to behavioral maintenance. These findings have the potential to inform best practices for the provision of WLM interventions, improve long-term outcomes for individuals accessing weight management services, and strengthen the overall public health impact of available interventions for disease prevention and management. TRIAL REGISTRATION: NCT, NCT06785064. Registered [01/15/2025], https://clinicaltrials.gov/study/NCT06785064?term=NCT06785064&rank=1.