Objective  To systematically review the efficacy of oral probiotics on adults with type 2 diabetes.

Methods  PubMed, The Cochrane Library, EMbase, WanFang Data, CNKI and SinoMed databases were electronically searched to collect randomized controlled trials (RCTs) of oral probiotics in adult patients with type 2 diabetes from the inception to January 31st, 2022. Two reviewers independently screened the literature, extracted data, and assessed the risk of bias of the included studies. Meta-analysis, Egger's test, sensitivity analysis and meta-regression analysis were performed by RevMan 5.3 and Stata 16.0 softwares, respectively.

Results  A total of 30 RCTs involving 2 168 patients were included. The results of meta-analysis showed that the probiotic group was superior to the control group (placebo or blank control) in HbA1c difference (SMD=﹣0.58, 95%CI ﹣0.77 to ﹣0.39, P<0.00001), fasting blood glucose difference (SMD=﹣0.48, 95%CI ﹣0.66 to ﹣0.30, P<0.00001), HOMA-IR difference (SMD=-0.79, 95%CI ﹣1.20 to ﹣0.39, P<0.0001) before and after treatment. There was no statistically significant difference in BMI difference before and after treatment (MD=﹣0.27, 95%CI ﹣0.56 to 0.02, P=0.06). Meta-regression results showed that probiotics dose did not affect the differences of HbA1c, fasting blood glucose, BMI and HOMA-IR before and after treatment.

Conclusion  Oral probiotics contribute to controlling blood glucose and increasing insulin sensitivity in adult patients with type 2 diabetes. The effect of oral probiotics on BMI in adults with type 2 diabetes is still unclear and needs to be further explored by more high-quality studies.

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