Probiotics in Irritable Bowel Syndrome: The Science and the Evidence.

Although probiotics have been used for many years by those who suffer from what would now be defined as irritable bowel syndrome (IBS), a scientific rationale for their use in this indication and clinical evidence to support their benefits have only emerged very recently. Evidence to support considering strategies, such as probiotics, that modulate the gut microbiome, in IBS, has been provided by laboratory studies implicating the microbiome and the host response to the enteric microenvironment in IBS, as well as in vitro and in vivo studies demonstrating the ability of various commensal bacteria to influence such relevant functions as motility, visceral sensation, gut barrier integrity, and brain-gut interactions. Clinical studies supporting a role for probiotics in the management of IBS predated such experimental data, and randomized controlled trials of probiotics in IBS continue to be reported. Their interpretation is hampered by the less than optimal quality of many studies; nevertheless, it is apparent that probiotics, as a category, do exert significant effects in IBS. Defining the optimal strain, dose, formulation, and duration of therapy is more challenging given the limitations of available data. There is also an urgent need for appropriately powered and rigorously designed clinical trials of appropriate duration of probiotics in IBS; such studies should also help to define those who are most likely to respond to probiotics. Future laboratory and translational research should attempt to define the mechanism(s) of action of probiotics in IBS and explore the response to bacterial components or products in this common and oftentimes troublesome disorder.