Probiotics and irritable bowel syndrome: a rationale for their use and an assessment of the evidence to date

Probiotics, defined as live organisms that, when ingested in adequate amounts, exert a health benefit on the host, have been used for almost a cen- tury in the management of a variety of medical dis- orders, usually on the basis of little evidence. Advances in our understanding of the gut flora and of its relationship to the host, together with progress in microbiology, molecular biology and clinical research have identified important biological properties for probiotics and demonstrated efficacy in a number of gastrointestinal disorders. The clear delineation of a post-infective variety of irritable bowel syndrome (IBS), as well as the description, in a number of studies, of evidence of low-grade inflammation and immune activation in IBS, suggest a role for a dys- functional relationship between the indigenous flora and the host in IBS and, accordingly, provide a clear rationale for the use of probiotics in this disorder. Other modes of action, including bacterial displace- ment and alterations in luminal contents, are also plausible. While clinical evidence of efficacy is now beginning to emerge, a review of available trials emphasises the importance of clear definition of strain selection, dose and viability. This is evidently an area of great potential in IBS and deserves further study at all levels.