1 Concordia University, Montreal, QC, Canada, H4B 1R6, Department of Health, Kinesiology and Applied Physiology. Electronic address: antoinestamant@gmail.com.
2 Concordia University, Montreal, QC, Canada, H4B 1R6, Department of Health, Kinesiology and Applied Physiology. Electronic address: Andreas.Bergdahl@concordia.ca.

Background: The oxidative stress (OS) theory of disease stipulates that a chronic imbalance in the ratio of oxidants to antioxidants in the cellular environment leads to a variety of debilitating conditions, including type 2 diabetes, cardiovascular and liver diseases. Metabolites in the gut microbiome have been associated with increases in reactive oxygen species (ROS). Many randomized controlled trials (RCTs) have thus investigated the potential of probiotics as a nutraceutical intervention to improve parameters of OS.

Aim: The objective of this paper is to review relevant human RCTs exploring the potential of probiotic supplementation to prevent OS in metabolically healthy individuals.

Methods: This systematic review and meta-analysis was registered on PROSPERO (CRD42021297210). The PubMed database was searched using keywords related to probiotics and OS. In total, out of the 652 studies were screened, 9 respected the inclusion criteria.

Results: Total antioxidant capacity (TAC) (SMD: 0.83 mmol/L, 95% CI: 0.25-1.40, p = 0.005) and glutathione (GSH) (SMD: 0.45, 95% CI: 0.13-0.77, p = 0.006) are improved with probiotic ingestion, although there are no alterations in superoxide dismutase (SOD) (SMD: 0.33, 95% CI: -0.27-0.93, p = 0.28). Decreases in plasma concentrations of the OS biomarker malondialdehyde (MDA) (SMD: -0.55, 95% CI: -1.11-0.00, p = 0.05) are also detected.

Conclusion: Probiotics improve AS and OS in metabolically healthy individuals. However, more studies are needed to address the moderate to high degree of heterogeneity in methodology.