Impact of probiotic supplementation on trimethylamine N-oxide (TMAO) in humans: A systematic review and meta-analysis of randomized controlled trials

Some clinical trial studies have shown the effect of probiotic supplementation on trimethylamine N-oxide (TMAO) levels through regulation of intestinal microbiota. However, the relevant findings in this area are still contradictory. The aim of this systematic study and meta-analysis was to investigate the effects of probiotic supplementation on TMAO levels using randomized controlled trials (RCTs).Available databases including PubMed/Medline, Web of Science, Scopus, Cochrane Library, and Embase were searched to find relevant RCTs up to August 2021. In this study, we examined the population over 18 years of age using probiotics as an intervention group compared to the control group to evaluate TMAO as a final outcome. Effect size was expressed as weighted mean difference (WMD) and 95% confidence interval (CI).8 RCT studies with 270 participants were included in this article. The results show that probiotic supplementation has no significant effect on TMAO levels compared to the control group (WMD - 0.08 μmol/L; 95% CI - 0.76 to 0.60, P = 0.813). Furthermore, the results of the analysis of the subgroups did not show a significant effect on this metabolite in both groups of healthy and unhealthy individuals following the intervention. However, probiotic supplementation further reduced TMAO in people less than 50 years of age compared to those over 50 years of age.This meta-analysis showed that probiotics did not have a significant effect on TMAO levels. However, further studies are needed to confirm the findings.