The objectives and inclusion criteria of the review were clear. Relevant sources were searched for trials. The restriction to English-language trials meant that one trial was excluded. The restriction to full text articles may have created potential for bias. As the authors noted, the potential for publication bias was unclear. The final search date was not reported. Steps were taken to minimise the risk of reviewer bias and error in trial selection and validity assessment, but it was unclear whether this applied to data extraction.
Relevant aspects of quality were assessed but no details were provided about the quality of individual trials (such as follow-up rates), which made it difficult to determine the reliability of the review findings. Adverse events were not reported and it was not entirely clear whether any data were available for this outcome. Appropriate statistical techniques were used to combine the trials and assess heterogeneity. Substantial statistical heterogeneity was found, which the authors attributed to use of a subtherapeutic dose of probiotics in one trial, but it was difficult to evaluate this explanation as the review provided insufficient detail about trial characteristics. As the authors noted, there were few trials, sample sizes were small and there were differences between the trials.
The review was generally well conducted but the authors’ conclusions require caution in interpretation because the evidence base was small in volume, diverse in character and of uncertain quality.