Probiotics

Probiotics are live microorganisms, most often Lactobacillus, Bifidobacterium, Escherichia, Bacillus, or Saccharomyces strains, taken to alter the gut’s bacterial community. The rationale in IBS is that disturbances in the gut microbiome may be involved in symptoms PMID 30294792. Products differ enormously in species, strain, dose, and formulation, which is the central problem in interpreting the research.

Pooled analyses have consistently found an average benefit while being unable to say which product delivers it. A 2014 meta-analysis of 43 trials reported a relative risk of symptoms persisting of 0.79 but noted that which species and strains are most beneficial remained unclear PMID 25070051. A 2018 update covering 53 trials (5,545 patients) concluded that particular combinations or strains appeared beneficial but that definitive conclusions were not possible PMID 30294792. The most recent analysis, 82 trials with 10,332 patients (2023), found only 24 trials at low risk of bias; it graded the evidence for a global-symptom benefit as moderate certainty for Escherichia strains, low for Lactobacillus strains and Lactobacillus plantarum 299V, and very low for most others, while adverse events were no more frequent than with placebo PMID 37541528.

The guideline split reflects different readings of the same literature: the ACG decided the very-low-quality evidence did not justify a recommendation for use PMID 33315591, whereas the BSG and NICE accept a time-limited trial for patients who want to try one PMID 33903147.

Points clinicians commonly raise: results from one strain do not transfer to another; trials typically run 4 to 12 weeks, so both NICE and BSG frame probiotics as a trial with a stopping rule; supplements are not regulated as drugs; and in a trial of the low FODMAP diet, a multistrain probiotic restored Bifidobacterium levels but did not itself change symptom scores PMID 28625832.

Talk to a clinician before starting or stopping anything.