BACKGROUND: The effective treatment of postoperative anemia and nutritional deficiencies is critical for the successful management of bariatric patients. However, the evidence for nutritional risk or support of bariatric patients remains scarce. The aims of this study were to assess current evidence of the association between 2 methods of bariatric surgery, sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB), and postoperative anemia and nutritional deficiencies. METHODS: MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were searched for English-language studies using a list of keywords. Reference lists from relevant review articles were also searched. In the authors' meta-analysis, they included studies with a duration of>12 months, those comparing SG with RYGB, and those with available outcome data for postoperative anemia and iron and vitamin B12 deficiencies. Of 36 potentially relevant studies, 9 met the inclusion criteria. Data were combined by means of a fixed-effects model or random-effects model. RESULTS: Compared with the SG group, the odds ratio for postoperative vitamin B12 deficiency in the RYGB group was 3.55 (95% confidence interval, 1.26-10.01; P<.001). In the subgroup analysis, studies in which prophylactic iron or vitamin B12 was administered lost significance in the odds ratio for postoperative vitamin B12 deficiency. CONCLUSION: The authors' findings suggest that SG is more beneficial than RYGB with regard to postoperative vitamin B12 deficiency risk, whereas the 2 methods are comparable with regard to the risk of postoperative anemia and iron deficiency. Postoperative prophylactic iron and B12 supplementation, in addition to general multivitamin and mineral supplementation, is recommended based on the comparable deficiency risk of the 2 methods as indicated by subgroup analysis.