Several studies have recently conducted to investigate the link between anemia and bariatric surgery (BS). The results from these studies, however, were inconsistent. Therefore, a meta-analysis was conducted to determine whether BS for weight loss is a risk factor for anemia.

Studies were identified relevant papers published a cutoff date of May 2022 for meta-analysis by searching four electronic databases (PubMed, EMBASE, Web of Science and Cochrane Library). Pairs of authors conducted title and abstract, full-text assessment, data extraction and risk of bias assessment, and quality of articles. Random-effects models were used to estimate the pooled effect size and evaluated the overall quality of evidence. The sources of heterogeneity were assessed with I². The Newcastle-Ottawa scale (NOS) was used to assess the methodologic quality of selected studies. The publication bias was assessed using funnel plots and Egger's test statistics.

In all, eight studies comprising 3150 patients were finally included in the final study analysis. Of these, pooled analysis of eight studies detecting association between anemia and BS for weight loss yield a statistically significant correlation (SMD −1.12 (−1.46—−0.78, I²=93%). Subgroup analyses were performed according to postoperative follow-up time and operation method. Before 24 months postoperatively, no patient had a significant decrease in hemoglobin. More than 24 months after BS, patients show a significant reduction in hemoglobin. In addition, the hemoglobin level was not changed after sleeve gastrectomy (SG) and adjustable gastric banding (AGB) (SMD −0.19 (−1.04—0.67, I²=0% for SG; SMD −0.30 (−0.82—0.22 for AGB), but the hemoglobin level was significantly reduced after Roux-en-Y gastric bypass (RYGB) (SMD −1.19 (−1.52—−0.87, I²=94.2%).

This current meta-analysis found that at 24 months after RYGB, the patient's hemoglobin level was significantly reduced, increasing the risk of anemia. Therefore, attention should be paid to the occurrence of anemia after BS. A large, placebo-controlled, multi-center study is needed to clarify the role of BS for weight loss in this patient anemia.