**2. Methods**

This meta-analysis was based on the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) criteria [36] (Figure 1). Medline®database was explored from its inception to March, 22th 2020 without language restriction. The research paradigm was: (depression OR schizophrenia) AND (gut microbiota). The references of each article were also checked. Medline is considered as the database of highest quality level. The associated articles were also explored. Scopus®and ScienceDirect®databases were explored with the same strategy (limited to research articles and research reviews and human studies). Two reviewers (GF and LB) decided on eligibility and extracted data from included studies. As this review involved data from published studies, an institutional review board approval was not required.
