Yogurt with probiotics are one of the latest health fads, but no one is sure they are doing anything at all and, if they are, that it is helping. 

Probiotics are defined by marketing groups as "live micro-organisms which, when administered in adequate amounts, confer a health benefit on the host, beyond the common nutritional effects." Proponents believe they facilitate fiber digestion, might boost the immune system and prevent or treat diarrhea. Dozens of bifidobacteria and lactobacilli are marketed in foods like yogurts and fermented milk products.

We have been consuming fermented foods since the Neolithic Era 12,000 years ago, though obviously they did not know about bacteria and our understanding of any impact on the digestive tract remains just about as limited today. Until recently, technological barriers prevented studying the billions of bacteria living in our gut in detail. The European consortium MetaHIT, coordinated by INRA, and Danone Nutricia Research succeeded in analyzing the effects of consuming a fermented milk product containing probiotics such as Bifidobacterium lactis on gut bacteria. “In this study, we studied the effect of the product on individuals afflicted with Irritable Bowel Syndrome (IBS), a pathology affecting 20% of the population in industrialized countries” says Dusko Ehrlich who led the research at INRA.

In a small pilot study of 28 individuals they observed that, upon intake of this fermented milk product containing probiotics, the abundance of certain bacteria naturally producing butyrate increased, though the global composition of the flora remained unchanged. Butyrate is known for its beneficial effects on gut health. Some papers have found a decrease in butyrate producing bacteria in IBS individuals. Moreover, the scientists observed a decrease of Bilophila wadsworthia bacteria, which is thought to be involved in the development of intestinal diseases.

Though it was not a clinical trial and too small to be conclusive, the study shows the potential in using new tools to analyze existing interactions between gut microbiota and probiotics. “Up until now, it was impossible to study the impact of probiotics on gut microbiota at a bacterial species level; from now on we will have a much more detailed view of the dynamics of this ecosystem” says Ehrlich.

Citation: Patrick Veiga, Nicolas Pons, Anurag Agrawal, Raish Oozeer, Denis Guyonnet, Rémi Brazeilles, Jean-Michel Faurie, Johan E. T. van Hylckama Vlieg, Lesley A. Houghton, Peter J. Whorwell, S. Dusko Ehrlich&Sean P. Kennedy. Changes of the human gut microbiome induced by a fermented milk product. Scientific Reports, 11 September 2014. DOI: 10.1038/srep06328