The mechanisms and effectiveness of probiotics in treatment of irritable bowel syndrome and inflammatory bowel disease are emerging.
In this review article from the UK and Ireland, the authors (who are international experts on functional bowel disorders and the role of the microbiota) summarize emerging evidence for the mechanisms and effectiveness of probiotics in the management of irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD).
Direct evidence exists for the role of GI microbiota in the pathogenesis of IBD, and there is some evidence that they play a similar role in IBS. Studies have demonstrated alterations in the luminal and mucosal microbiota and activation of the mucosal immune system, especially in IBD. Some probiotics have been shown to produce neurotransmitters or neuromodulators that can modify GI functions such as motility and sensation, and others have been shown to enhance mucosal barrier function and modulate inflammation. In the context of these potential benefits, the authors and the Agency for Healthcare Research and Quality note the lack of definitive data on safety, despite a substantial number of publications and decades-long use of probiotics.
The World Health Organization defines probiotics as “. . . a live organism that, when ingested in adequate amounts, exerts a health benefit to the host.” The authors note that few of the products now widely available satisfy this definition. Key limitations of current products include inadequate numbers of live organisms following commercial or home storage, and inadequate testing to ensure that they will survive transit through the GI tract. And many cannot claim to have a strong evidence base for a health claim (some have claimed health benefits that were shown for other bacterial strains). Future studies may determine whether dead bacteria, bacterial components, or substances secreted by bacteria contribute to any beneficial effects, which would make the delivery of live organisms less important.
Irritable bowel syndrome. Many studies report luminal dysbiosis in IBS, with decreased lactobacilli and bifidobacteria, and a single bout of infectious gastroenteritis has been shown to result in a 4-fold increase in the risk of developing IBS within 2 years. Increasing evidence points to chronic low-grade inflammation in IBS. Despite suggestive evidence, the research cannot easily tease out whether alterations in microbiota are primary events causing IBS or secondary effects of the syndrome. Most meta-analyses of probiotics in IBS report benefits in global symptoms, abdominal pain, and flatulence, but the impact on bloating is equivocal. Benefits are likely to be specific to the strain of bacteria in the probiotic under study, yet meta-analyses have lumped different strains together in their analysis, making strain-specific recommendations difficult.
Inflammatory bowel disease. The most convincing evidence for probiotic use in IBD is for pouchitis, in particular the VSL#3 bacterial mixture (a combination of 8 strains of live, freeze-dried lactic acid bacteria). A number of probiotic products have been shown to be effective in maintaining remission and in treating mild to moderately active ulcerative colitis. But the authors note that “. . . despite a convincing rationale and a deluge of convincing animal studies, clinical data on probiotics in IBD are rather scanty and far from convincing.” The data on ulcerative colitis are stronger than that for Crohn disease. Despite this lack of strong data to support widespread use, one study has reported that more than one-third of patients with IBD was using probiotics or had done so in the previous year.
Indeed, there are agents that will be widely used by our patients. So health professionals must question all patients with GI complaints about these products. Although the authors agree that probiotics have already been established as having limited but demonstrable value in the treatment of IBS and IBD, much more research is needed before they become a mainstay of that treatment.
Source: Whelan K, Quigley EM. Probiotics in the management of irritable bowel syndrome and inflammatory bowel disease. Curr Opin Gastroenterol. 2013;29:184-189.
The abstract is available here.