Although not directly an IBD-related study, this paper from McNulty, Yatseuneko, Hsiao and colleagues attempts to answer an important question of direct relevance to IBD treatment: Do probiotic yoghurt drinks of the kind found in supermarkets have any effect on the bacterial communities of the gut? This study had two arms, both elegantly designed to answer this question. The first arm involved a set of seven healthy, identical adult twins who each consumed two servings of a fermented milk product containing 5 live bacterial strains (Bifidobacterium animalis, 2x Lactobacillus delbrueckii, Lactococcus lactis, and Streptococcus thermophilus) each day for 7 weeks. 7 faecal samples were collected at varying time points before and after the treatment course for detailed microbial analysis. Surprisingly, no significant difference was observed in the microbial communities after the introduction of the probiotic yoghurt drink. In order to confirm these findings, the second arm gave the same bacterial communities found in the yoghurt drink directly to mice who had their gut pre-colonised with a known mixture of 15 other bacteria. Again no significant impact was seen on the microbial community of the mice.
Interestingly the probiotic yoghurts were not entirely ineffectual and did influence the switching on of genes within the resident bacterial community, particularly with relevance to the breakdown of carbohydrates (sugars and starches). Why this occurred is not clear. Sufficed to say if probiotic yoghurts are effective in humans, it probably isn’t because their bacteria colonise the gut in large proportions or alter its overall composition, but by more subtle means. They may well have little to no practical effect in healthy people and their benefits in most variants of IBD remain to be proven.
It is noteworthy that this study was part-sponsored by Danone and published despite its potentially detrimental effect on their industry.
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