After conducting systematic database and manual searches, a total of 1091 articles were retrieved. After excluding duplicate articles, there were 970 remaining. After reading the titles and abstracts to eliminate irrelevant articles, 37 articles were left for full-text screening. Finally, a total of 15 articles that met the criteria were included (Fig. 1).

Literature search process diagram

A total of 15 articles [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24] were included in this study (Table 1). All cases were sourced from hospitals or clinics where they were receiving medical treatment. A total of 2993 patients were included in the study, originating from different countries, including China, Spain, Switzerland, the UK, France, the Netherlands, the USA, Brazil, Iran, and Qatar, among others. The surgical approaches involved in the study included laparoscopic sleeve gastrectomy (LSG), RYGB, BPD/DS, and OAGB, among others. The primary surgical types constituted LSG, RYGB, and BPD/DS. The average age of the study population was 43.1 SD12.2 years, with an average preoperative BMI of 48.2 SD10.8 kg/m2.

The quality of the included studies was evaluated using the NOS tool, with scores ranging from 5 to 8. Among the included studies, three received a score of 8, four received a score of 7, seven received a score of 6, and one received a score of 5. No low-quality studies were included in this research. For a detailed assessment of the quality of the included studies, please refer to Table 2.

Analysis of 15 studies revealed that 9 studies reported zinc deficiency after 6 months post-surgery. The results indicated a significant increase in the risk of zinc deficiency at 6 months post-surgery compared to preoperative levels (RR = 2.45, 95% CI 1.62, 3.69; I2 = 80.0%; Fig. 2A). Furthermore, 11 studies reported zinc deficiency after 1 year post-surgery, and the risk of patients developing zinc deficiency remained high at 1 year post-surgery (RR = 3.08, 95% CI 2.09, 4.48; I2 = 77.8%; Fig. 2B). Additionally, six studies reported zinc deficiency after 2 years post-surgery, and it was observed that the risk of developing zinc deficiency significantly increased after 2 years of BS (RR = 3.28, 95% CI 2.24, 4.79; I2 = 58.1%; Fig. 2C). These findings suggest an increased risk of zinc deficiency in patients after BS.

The risk ratio of zinc deficiency after weight loss surgery. A Risk ratio of zinc deficiency at 6 months post-BS. B Risk ratio of zinc deficiency at 1 year post-BS. C Risk ratio of zinc deficiency at 2 years post-weight loss surgery. BS, bariatric surgery

A total of 10 studies reported the serum zinc levels of patients before BS, involving a total of 1792 individuals. The average serum zinc concentration was 87.8 SD23.4 μg/dL. Moreover, 7 studies reported the serum zinc levels of patients 6 months after BS, comprising a total of 1064 individuals. The average serum zinc concentration was 79.2 SD20.3 μg/dL. Additionally, 11 studies reported the serum zinc levels of patients 1 year after BS, involving a total of 1304 individuals. The average serum zinc concentration was 79.7 SD20.6 μg/dL.

Among the 15 included studies, 6 studies reported the serum zinc levels of patients before and 6 months after BS. It was found that the serum zinc levels of patients decreased by 6.29% (95% CI − 12.17%, − 0.41%) after 6 months of BS (Fig. 3A). Nine studies reported the serum zinc levels of patients before and 1 year after BS. Using a random-effects model analysis, it was found that the serum zinc levels of patients decreased by 8.97% (95% CI − 12.20%, − 5.74%) after 1 year of BS (Fig. 3B).

Changes in serum zinc levels after bariatric surgery. A Comparison of serum zinc changes at 6 months post-surgery compared to pre-surgery levels. B Comparison of serum zinc changes at 1 year post-surgery compared to pre-surgery levels. C Subgroup analysis of serum zinc changes at 6 months post-surgery compared to pre-surgery levels. D Subgroup analysis of serum zinc changes at 6 months post-surgery compared to pre-surgery levels

Based on the type of surgery, the analysis was further divided into three groups: LSG, RYGB/OAGB, and BPD/DS. After 6 months of surgery, the serum zinc levels of patients in the LSG group decreased by 7.58% (95% CI − 16.03%, 0.86%; Fig. 3C), the RYGB/OAGB group decreased by 6.91% (95% CI − 12.39%, − 1.43%; Fig. 3C), and the BPD/DS group decreased by 16.20% (95% CI − 21.80%, − 10.60%; Fig. 3C).

One year post-surgery, the serum zinc levels of patients in the LSG group decreased by 9.40% (95% CI − 16.44%, − 2.36%; Fig. 3D), the RYGB/OAGB group decreased by 9.33% (95% CI − 10.73%, − 7.92%; Fig. 3D), and the BPD/DS group decreased by 22.30% (95% CI − 30.14%, − 14.46%; Fig. 3D).

A total of 13 literatures reported the incidence of zinc deficiency 1 year after surgery, and I2 = 95.214%. Using random effects model analysis, the aggregate prevalence of zinc deficiency 1 year after surgery was 26.1% (95% CI 17.3%, 34.9%; Supplementary Fig. 2).

In order to assess publication bias, funnel plots and Egger’s test were used. All funnel plots showed good symmetry (Supplementary Fig. 1AB), and the corresponding p-values from Egger’s test were 0.772 and 0.686, all of which were greater than 0.05, indicating no significant publication bias in the results. Sensitivity analysis was conducted using the one-study-removed approach, and the results did not show significant changes. This suggests good overall stability of the results of this meta-analysis (Supplementary Fig. 1CD).