Effect of Probiotic Supplementation on Glycemic Outcomes in Patients with Abnormal Glucose Metabolism: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Introduction: The effectiveness of probiotics in patients with abnormal glucose metabolism has not been clearly demonstrated. It is also unclear if outcomes are consistent across different probiotic formulations. Methods: A literature search was conducted using PubMed, EMBASE, and Cochrane CENTRAL database from inception through May 2020. Randomized controlled trials that evaluated the effect of probiotics on fasting blood glucose (FBG) or hemoglobin A1c (HbA1c) in patients with prediabetes, type 2 diabetes mellitus, or gestational diabetes were included. Outcomes of interest included FBG, HbA1c, fasting insulin, homeostatic model assessment of insulin resistance (HOMA-IR), homeostatic model assessment of beta-cell function (HOMA-B), and quantitative insulin sensitivity check index (QUICKI). Weighted mean difference (WMD) and 95% confidence intervals (CIs) were calculated using the DerSimonian and Laird random-effects model. Results: 31 studies involving 1,948 participants were included in this analysis. Compared to control, probiotics had a significant favorable effect on FBG (WMD -5.77 mg/dL, 95% CI -8.48 to -3.06), HbA1c (WMD -0.32%, 95% CI -0.47 to -0.18), fasting insulin (WMD -2.95 mu IU/mL, 95% CI -3.76 to -2.14), HOMA-IR (WMD -0.82, 95% CI -1.05 to -0.59), HOMA-B (WMD -14.86, 95% CI -24.57 to -5.16), and QUICKI (WMD 0.015, 95% CI 0.011-0.019). Further, probiotics were associated with favorable outcomes on all parameters at doses between 1 and 10 x 10(9) colony-forming unit per day (p < 0.004 for all) and formulations containing 2-4 strains (p < 0.05 for all). Discussion/Conclusion: Probiotics appear to have a modest effect on glycemic parameters in patients with abnormal glucose metabolism. Due to the limited number of trials conducted in patients with prediabetes, more studies are warranted in this population.