Effect of probiotic supplementation on the gut microbiota diversity in healthy populations: a systematic review and meta-analysis of randomised controlled trials

Abstract Background Probiotics are widely used dietary supplements promoted to positively influence gut health and microbiota diversity, making them popular among healthy individuals. One of the purported benefits of probiotics is their ability to enhance gut microbiota diversity, a feature associated with improved resilience and overall health. However, evidence supporting this claim remains inconclusive. We aimed to investigate whether probiotics significantly modify gut microbiota diversity in healthy populations through a systematic review and meta-analysis. Methods A systematic search of MEDLINE, Embase, and Cochrane databases was conducted on 12/04/2024, following the search strategy registered in PROSPERO (CRD42022286137). Out of 9217 identified articles, 47 met the inclusion criteria of the current review, and 22 studies with data from 1068 individual subjects were eligible for meta-analysis of changes in gut microbiota diversity assessed by diversity indices. A random-effects model was employed to estimate the means of median differences (MedD) with 95% confidence intervals (CI) due to the expected heterogeneity. Results The quantitative synthesis revealed no statistically significant effects of probiotics on Shannon diversity (MedD = − 0.08, 95% CI [− 0.16 to 0.01]), observed operational taxonomic units (MedD = 2.19, 95% CI [− 2.20 to 6.57]), Chao1 (MedD = − 3.19, 95% CI [− 27.28 to 20.89]), or Simpson’s index of diversity (MedD = − 0.01, 95% CI [− 0.02 to 0.00]) indices compared to unsupplemented controls. Subgroup and sensitivity analyses suggest that the probiotic taxonomic family, the risk of bias, or the duration of intervention did not change our findings. Insufficient data prevented us from meta-analysing other diversity indices; however, most of the included studies reported no difference in other reported α- and ß-diversity indices between the probiotic and control groups. Conclusions Our results indicate that probiotic supplementation does not produce statistically significant changes in gut microbiota diversity in healthy individuals. This study highlights the need for further research to determine whether specific probiotic strains or formulations may influence diversity in targeted subgroups or under specific conditions.