This systematic review and meta-analysis of intervention studies aims to evaluate the effect of preoperative and/or post-operative support for adults who elect bariatric surgery delivered by a multidisciplinary team (MDT) on post-operative body composition, mental health, co-morbidities, quality of life, and side effects. Six electronic databases were searched. Revman and GRADE were used to assess confidence in pooled effects. Included interventions (N = 1533 participants in total) focused on lifestyle counselling (n = 4 studies), psychology (n = 4 studies), or exercise (n = 10 studies); comparator groups were less intensive usual care. Intensive MDT interventions increased post-operative weight loss (SMD: −0.94; 95% CI: −1.27 to −0.61) if delivered post-operatively. Preoperative and post-operative intensive interventions improved symptoms of depression and anxiety, quality of life, diastolic blood pressure, and resting heart rate but not lipids or glycaemic measures. Whilst usual MDT care is important preoperatively, this review conditionally recommends intensive MDT interventions for enhanced post-operative weight loss if delivered in the post-operative period, led by any health professional, based on moderate evidence. This review also conditionally recommends preoperative and/or post-operative lifestyle, nutrition, or psychology counselling and/or physical activity for improved mental and physical health. Further randomized controlled trials are required, which aim to specifically evaluate the best use of MDT resources.