RESUMO
Objective: Cross-sectional research has demonstrated that internalized weight stigma (IWS) is associated with less engagement in weight management behaviors, including physical activity. However, limited research has explored longitudinal relationships among IWS, physical activity, and weight loss. This study examined longitudinal associations of changes in IWS, physical activity, and weight and tested whether physical activity mediated the relationship between IWS and weight change. Methods: Individuals with obesity and high IWS (N = 105) participated in a 72-week behavioral weight loss intervention, with or without a weight stigma intervention. Measures of IWS (Weight Self-Stigma Questionnaire), physical activity (accelerometry and self-report), and weight were collected at baseline and weeks 20, 46 and 72. Correlations examined relationships among changes in variables from baseline to all timepoints, controlling for treatment condition. Mediation, controlling for treatment condition, tested whether IWS reductions during the first 20 weeks predicted greater weight loss at weeks 46 and 72 via increased physical activity between weeks 20 and 46 or 72. Results: Decreases in IWS at week 20 were associated with greater week-20 weight loss (r = 0.265, p = 0.012). Physical activity was not a significant mediator, but greater reductions in IWS at week 20 predicted greater week-46 weight loss with or without controlling for physical activity (WSSQ: b = 0.30, confidence interval: 0.12, 0.54). Significant associations were not found at week 72. Conclusion: Initial reductions in IWS were associated with greater week-46 weight loss. Further research should investigate whether reducing IWS early in obesity treatment enhances long-term outcomes. Clinical trial registration: ClinicalTrials.gov (NCT03704064).