Background: The human gut harbours a complex community of bacteria whose relationship with their host is normally mutually beneficial. Recent studies suggest a disturbance of this relationship in irritable bowel syndrome (IBS) and the potential to correct this using prebiotics and probiotics.
Aim: To review the mechanisms of action of probiotics and prebiotics in IBS and to assess their performance in clinical trials.
Methods: Articles relating to modes of action and randomized control trials of treatment were reviewed by searching PubMed using terms 'probiotic', 'prebiotic' and 'irritable bowel'. Small uncontrolled studies in IBS were excluded.
Results: Probiotics can enhance gut barrier function, inhibit pathogen binding and modulate gut inflammatory response. They can also reduce visceral hypersensitivity associated with both inflammation and psychological stress. Probiotics can alter colonic fermentation and stabilize the colonic microbiota. Several large randomized, placebo-controlled trials of adequate design have shown an improvement in flatulence and abdominal distension with a reduction in composite IBS symptoms scores.
Conclusions: Each probiotic has unique features and IBS patients are heterogeneous. Future efforts should be directed to identifying biomarkers of responsiveness to facilitate better targeting of treatment and hence improved efficacy.