The aim of this study was to evaluate the impact of mindfulness-based interventions on psychological and physical health outcomes in adults who are overweight or obese.We searched 14 electronic databases for randomized controlled trials and prospective cohort studies that met eligibility criteria. Comprehensive Meta-analysis software was used to compute the effect size estimate Hedge's g.Fifteen studies measuring post-treatment outcomes of mindfulness-based interventions in 560 individuals were identified. The average weight loss was 4.2 kg. Overall effects were large for improving eating behaviours (g = 1.08), medium for depression (g = 0.64), anxiety (g = 0.62) and eating attitudes (g = 0.57) and small for body mass index (BMI; g = 0.47) and metacognition (g = 0.38) outcomes. Therapeutic effects for BMI (g = 0.43), anxiety (g = 0.53), eating attitudes (g = 0.48) and eating behaviours (g = 0.53) remained significant when examining results from higher quality randomized control trials alone. There was no efficacy advantage for studies exceeding the median dose of 12 h of face-to-face intervention. Studies utilizing an Acceptance and Commitment Therapy approach provided the only significant effect for improving BMI (g = 0.66), while mindfulness approaches produced great variation from small to large (g = 0.30-1.68) effects across a range of psychological health and eating-related constructs. Finally, the limited longitudinal data suggested maintenance of BMI (g = 0.85) and eating attitudes (g = 0.75) gains at follow-up were only detectable in lower quality prospective cohort studies.Mindfulness-based interventions may be both physically and psychologically beneficial for adults who are overweight or obese, but further high-quality research examining the mechanisms of action are encouraged.