*2.4. Data Screening*

Initially, the two authors (MR, AM) performed a first screening by titles and abstracts, following the selection criteria independently and in duplicate. Once a third author (CR) double-checked the screening and discussed any discrepancy, a full-text reading was performed for their quality appraisal by authors.

## *2.5. Quality Appraisal*

The quality of selected articles was assessed by two researchers independently (MR, AM). Any disagreements on quality ratings were discussed with a third author (CR) and a consensus was reached. The Jadad Scale of Clinical Trials was used to assess the methodological quality of experimental human studies included. This is a scale with five simple items and it has known reliability and external validity. A score below 3 points indicate low quality based on (i) the quality of randomization, (ii) double blinding, and (iii) drop-outs extracted from each study [24].

#### *2.6. Data Abstraction and Synthesis*

Consecutively, the relevant data from the included studies were extracted and tabulated according to (i) authors, (ii) country, (iii) population, (iv) probiotic strains, (v) variables, (vi) measures, and (vii) main findings.
