A group of scientists has claimed that probiotics, often called “good bacteria”, aren’t as great as we thought they were.
Two studies published in the journal Cell conducted a number of experiments looking inside the human gut. They found that the digestive tract in most people prevented probiotics from doing anything. They could even delay the return of normal gut bacteria after taking antiobiotics.
"People have thrown a lot of support to probiotics, even though the literature underlying our understanding of them is very controversial; we wanted to determine whether probiotics such as the ones you buy in the supermarket do colonize the gastrointestinal tract like they're supposed to, and then whether these probiotics are having any impact on the human host," senior author Eran Elinav from the Weizmann Institute of Science in Israel said in a statement.
"Contrary to the current dogma that probiotics are harmless and benefit everyone, these results reveal a new potential adverse side effect of probiotic use with antibiotics that might even bring long-term consequences."
Probiotic studies normally rely on stool samples, but in this research they analyzed the human gut directly. In the first study, 25 volunteers had their guts sampled via endoscopies and colonoscopies, with one subgroup taking probiotics, and another a placebo.
In the second study, 21 volunteers were given antibiotics and then split into three groups, to see if probiotics could counter the effects to repopulate gut bacteria. One group let the gut recover on its own, another used probiotics, and the third were given a transplant of their own bacteria via autologous fecal microbiome transplant (aFMT).
The results of the first study showed that some probiotics could colonize in some people’s guts, called “persisters,” but others labeled “resisters” got rid of them. So probiotics were only able to colonize some guts, but were found in all the stool samples, which is why previous studies may have been misleading. This basically means when you drink one of those probiotic yogurt drinks, it very likely goes in one end and out the other, without doing much in between
In the results of the second study, the team found that the microbiome and gut gene expression of the probiotics group was prevented from returning to normal for months. The aFMT group, on the other hand, returned to normal in days.
The researchers noted that probiotics were not completely useless. Moreover, it seems that different people respond to them in different ways – so treatments could be tailored more specifically to people.
As always with these sorts of things, more research will be needed, especially to work out the clinical effects of probiotics. But signs from this research seem to point towards good bacteria maybe not being as, well, good as we thought.