Beverages with probiotics that have become fashionable for a few years. In theory, the intake of these live microorganisms can boost the microbiome or restore the intestinal ecosystem of people after a dose of antibiotics. However, two investigations published in Cell show that not everything is clear.
To find out what really happens inside the intestine when people ingest probiotics, immunologist Eran Elinav of the Weizmann Institute of Science in Israel and his colleagues took samples from the microbiome of healthy volunteers.
The scientists used endoscopies and colonoscopies. Making a difference with most other research on microbiomes which are based on fecal samples as a substitute for intestinal microbes. They then fed 15 of the volunteers with a commercial probiotic supplement or a placebo.
Two unexpected results
The result was not what they expected. First, the microbes found in the feces were not representative of those that had colonized the intestine. “Relying on fecal samples as an indicator of what goes on inside the intestine is wrong,” says Elinav.
Second, the research also showed that while probiotics colonized the gastrointestinal tract of some people, the intestinal microbiome of others expelled them. There was no way to tell from his fecal sample what category people fell into. “Some people accept probiotics in the intestine, while others simply pass them from one end to the other,” says the immunologist.
Likewise, the researchers discovered that probiotic colonization patterns were highly dependent on the individual. Therefore, the concept that we can all benefit from a probiotic bought at the supermarket is empirically wrong, he explains.
“It’s potentially harmful”
In addition, the researchers measured what happens to the microbiome of people who take probiotics in the hope of restoring their microbiome after antibiotics. Twenty-one volunteers took an identical treatment with antibiotics and then they were separated into three groups.
The microbiome of the first group was allowed to recover by itself, while the second group received probiotics. The third group was treated with a dose of their own original pre-antibiotic microbiome by a fecal microbiota transplant.
The probiotic bacteria easily colonized everyone’s gut in the second group after the antibiotics had cleared the way. However, the researchers were surprised to discover that this prevented the return of the person’s normal microbiome for up to six months.
“Probiotics prevented very strongly and persistently that the original microbiome returned to its original situation,” says Elinav. “This was very surprising and alarming for us, this adverse effect has not been described to date,” he explains.
The opposite effect was observed in patients who were given a dose of their own pre-antibiotic microbiome through FMT. His native gut microbiome returned to normal in a matter of days.
Although the researchers did not measure the long-term clinical impact, previous studies have found a link between the disruption of intestinal microbes and obesity, allergies and depression. “It’s potentially harmful,” says Elinav. The conclusion is that probiotics do not always meet their harmless reputation, and to be effective, their formula must be adapted to each individual.