Probiotics are living micro-organisms that are taken by millions of people to boost their microbiome or to restore their gut ecosystem after a dose of antibiotics. Yet questions remain about whether they actually work.
To find out what really goes on in the gut when people ingest probiotics, immunologist Eran Elinav of the Weizmann Institute of Science in Israel, and colleagues, sampled the microbiome of healthy volunteers directly using endoscopies and colonoscopies. Most other microbiome research relies on faecal samples as a proxy for gut microbes.
They then fed 15 of the volunteers either a commercially available probiotic supplement or a placebo.
The outcome was striking. For a start, the microbes found in faeces were not representative of those that had colonised the gut. “Relying on faecal samples as an indicator of what goes on inside the gut is inaccurate and wrong” says Elinav.
The research also showed that while probiotics colonised the gastrointestinal tract of some people, the gut microbiome of others just expelled them. There was no way of telling from their stool sample which category people fell into. “Some people accept probiotics in their gut, while others just pass them from one end to the other,” says Elinav. They found that the probiotic colonisation patterns were highly dependent on the individual. That tells us that the concept that everyone can benefit from a universal probiotic bought from the supermarket is empirically wrong, he says.