Abstract
PURPOSE: To examine the effectiveness of ACT on weight (body mass index and body mass), eating behaviours (binge eating, emotional eating, external eating and restraint eating), and psychological outcomes (quality of life [QoL], depression, psychological flexibility, and weight stigma) among adults with overweight and obesity. METHODS: Seven electronic databases (CINAHL, EMBASE, PubMed, PsycInfo Scopus, The Cochrane Library, and Web of Science) were searched from inception through 17 June 2022. 13 studies and 48 unique effect sizes were analyzed using random-effects models. Pooled effect estimates were calculated using weighted mean differences (WMD) and standardized mean differences expressed in Hedges' g (g). Heterogeneity was assessed using Q-statistics and interpreted using I(2). RESULTS: ACT was found to be effective in improving weight loss in terms of BMI (k = 6, WMD = - .50, 95% CI = - .90; - .11, t = - 3.25, p = .20, I(2) = .0%), psychological flexibility and weight-related stigma. However, non-significant changes were found for body mass (k = 4, WMD = - 0.33 95% CI = - 1.53; 0.87, t = - .88, p = .44, I(2) = .0%), binge eating (k = 4, g = - .34, 95% CI = - 1.31; 0.62, t = - 1.13, p = .34, I(2) = 71.1%), emotional eating (k = 6, g = - .20, 95% CI = - 0.54; 0.15, t = - 1.47, p = .20, I(2) = 45.0%), external eating (k = 5, g = - .40, 95% CI = 0.96; 0.16, t = - 1.99, p = .12, I(2) = 81.8%), restraint eating (k = 3, g = .22 95% CI = - 0.57; 1.01, t = 1.19, p = .36, I(2) = 69.1%), QoL (k = 3, g = .01, 95% CI = - 1.51; 1.52, t = .02, p = .99, I(2) = 90.2%) and depression (k = 3, g = - .55, 95% CI = - 1.78; 0.67, t = - 1.94, p = .19, I(2) = 79.9%). CONCLUSION: ACT could be effective in improving weight loss but more studies are needed to ascertain its effectiveness and the underlying mechanism by which the various components influence weight-related outcomes. LEVEL OF EVIDENCE: Evidence obtained from a systematic review and meta-analysis of existing empirical studies.