Background: Probiotics are often used to prevent antibiotic-induced low-diversity dysbiosis, however their effect is not yet sufficiently summarized in this regard. We aimed to investigate the effects of concurrent probiotic supplementation on gut microbiome composition during antibiotic therapy.Methods: We performed a systematic review and meta-analysis of randomized controlled trials reporting the differences in gut microbiome diversity between patients on antibiotic therapy with and without concomitant probiotic supplementation. The systematic search was performed in three databases (MEDLINE (via PubMed), Embase, and Cochrane Central Register of Controlled Trials (CENTRAL)) without filters on 15 October 2021. A random-effects model was used to estimate pooled mean differences (MD) with 95% confidence intervals (CI). This review was registered on PROSPERO (CRD42021282983).Results: Of 11,769 identified articles, 15 were eligible in the systematic review and 5 in the meta-analyses. Quantitative data synthesis for Shannon (MD = 0.23, 95% CI: [(−)0.06–0.51]), Chao1 (MD = 11.59 [(−)18.42–41.60]) and observed OTUs (operational taxonomic unit) (MD = 17.15 [(−)9.43–43.73]) diversity indices revealed no significant difference between probiotic supplemented and control groups. Lacking data prevented meta-analyzing other diversity indices; however, most of the included studies reported no difference in the other reported α- and ß-diversity indices between the groups. Changes in the taxonomic composition varied across the eligible studies but tended to be similar in both groups. However, they showed a potential tendency to restore baseline levels in both groups after 3–8 weeks.This is the first meta-analysis and the most comprehensive review of the topic to date using high quality methods. The limited number of studies and low sample sizes are the main limitations of our study. Moreover, there was high variability across the studies regarding the indication of antibiotic therapy and the type, dose, and duration of antimicrobials and probiotics.Conclusions: Our results showed that probiotic supplementation during antibiotic therapy was not found to be influential on gut microbiome diversity indices. Defining appropriate microbiome diversity indices, their standard ranges, and their clinical relevance would be crucial.

Background: Short-chain fatty acids produced by microorganisms living in the gastrointestinal tract are known to have numerous beneficial effects. Because certain probiotic strains may influence short-chain fatty acid production, probiotic supplementation has been proposed as a potential strategy to modify faecal short-chain fatty acid concentrations. Our aim was to investigate whether probiotics modify faecal short-chain fatty acid levels in healthy populations via systematic review and meta-analysis. Methods: We performed a systematic search of the MEDLINE, Embase, and Cochrane databases on 12/04/2024. We analysed exclusively randomized controlled trials meeting all the following criteria: population: healthy people; intervention: probiotic supplementation; control: no probiotic supplementation; outcome: faecal short-chain fatty acid concentrations. A total of 9217 articles were reviewed, 21 of which met the preset inclusion criteria. Twelve articles, including 541 subjects, were eligible for meta-analysis of changes in faecal short-chain fatty acid concentrations. The standardized mean difference (SMD, Hedges’ g) was chosen as the effect indicator due to the different measurement techniques used. A random-effects model was used to estimate SMD with 95% confidence interval (CI) due to the expected heterogeneity. Results: No statistically significant differences were detected in the faecal butyrate (SMD = 0.07, 95%CI:[(-)0.16 – 0.30]), acetate (SMD = 0.06, 95%CI:[(-)0.14 – 0.27]), and propionate (SMD = 0.09, 95%CI:[(-)0.07 – 0.25]) levels between individuals taking and not taking probiotics. Conclusions: Our results suggest that probiotic intake has a minor effect on faecal short-chain fatty acid concentrations, but this effect is not statistically detectable in healthy individuals. Thus, there is insufficient evidence of statistically significant effect of probiotic supplementation on stool short-chain fatty acid concentrations in healthy individuals. Trial registration: Research protocol was registered in PROSPERO (CRD42022286137).