Probiotics are widely consumed and the widespread advertising is often not really justified by the evidence. Many products were never studied as such and some companies use studies performed with other (and different) products for advertising.
In the March edition of GUT a systematic review on the randomised control trials (RCT) undertaken so far suggests that many are of good quality., they determine that meta-analysis is impossible due to the various strains, phenotypes and genome vary greatly. As a consequence and as stressed by the FAO/WHO joint report the benefits of one probiotic ‘cannot be extrapolated to other probiotic strains without experimentation. However there tend to be properties consistent with different groups, from which strain specific organisms may be extracted.
A probiotic contains thousands of genes which may potentially influence the clinical effects. Furthermore, interaction with the host, food components or endogenous substrates or the endogenous microbiota inside the gastrointestinal lumen may generate by-products or end-products with functional properties.
The intestine has between 1012 and 1014 organisms per millilitre, which is ~100-fold greater than the number of eukaryotic cells in the human body. Numerous mechanisms are involved in the action of probiotics. New discoveries which may have an impact on the understanding of the clinical effects in IBS include the demonstration of the presence of anti-inflammatory microorganisms in the endogenous microbiota (especially the phylum Firmicutes), and that of the action of probiotics on intestinal motility and visceral sensivity.
The use of probiotics in patients with IBS showed improvements in the following areas:
- Abdominal Pain (good improvement),
- Bloating (modest gains),
- Flatulence (good improvement),
- Urgency (modest)
Probiotics appear to be efficacious in IBS but the magnitude of benefit and the most effective species and strain are uncertain.
One of the issues with single therapy interventions, i.e the use of probiotics is that it may be inadequate to meet the individual needs of the patient. A clinical work up may allow for a greater degree of personalisation and in turn provide a degree of personalisation that would most like increase their benefits. In particular bloating as discussed by Michael Ash has a number of potential triggers and each of these would need to be addressed to ensure best outcome.
 Moayyedi P, Ford AC, Talley NJ, Cremonini F, Foxx-Orenstein A, Brandt L, Quigley The efficacy of probiotics in the therapy of irritable bowel syndrome: a systematic review. E.Gut. 2008 Dec 17. View Abstract
 Sokol H,Pigneur B, Watterlot L, et al. Faecalibacterium prausnitzii is an anti-inflammatory commensal bacterium identified by gut microbiota analysis of Crohn disease patients. Proc Natl Acad Sci U S A 2008;105:16731–6. View Abstract
 Bär F, Von Koschitzky H, Roblick U, et al. Cell-free supernatants of Escherichia coli Nissle 1917 modulate human colonic motility: evidence from an in vitro organ bath study. Neurogastroenterol Motil 2009;21:559–66. View Abstract