Currently, there is no scientific consensus on the efficacy of probiotics to treat irritable bowel syndrome (IBS). Authors of this paper attempted a meta-analysis of 56 studies on single-strain and multi-strain probiotics for the treatment of IBS, but trials were so heterogeneous when it came to probiotic concentration, duration of treatment, and methodology, that the meta-analysis was abandoned. Instead, they undertook a systematic review and found some evidence for the efficacy of single-strain probiotics (mostly bifidobacteria) in treating IBS.
The group summarized methodological issues that need to be addressed in future studies on probiotics, calling for more studies that follow strict trial guidelines (i.e. Food and Drug Administration & European Medicines Agency guidelines for clinical trials). Mazurak N, et al. (2015) Probiotic Therapy of the Irritable Bowel Syndrome: Why Is the Evidence Still Poor and What Can Be Done About It? J Neurogastroenterol Motil DOI: http://dx.doi.org/10.5056/jnm15071