Are Probiotics Good for You?

Millions of people worldwide consume probiotics for their apparent health benefits but there were mixed messages about them in the media last week as a result of two studies conducted by researchers at the Weizman Institute of Science in Israel. Whereas one media report concluded taking probiotics was “almost useless”, another stated the research found “some people’s digestive systems held on to the probiotics” while in others “the body expelled the good bacteria”. In fact, the researchers found probiotic bacteria were shed by all study participants consuming probiotics regardless of whether they were responsive to probiotics or not. More on the research findings in a moment.

Bottle and probiotics pills
Probiotics can be bought commercially and are found in some foods such as yoghurt.

Investigating the gut microbiome – the good and bad microbes you find in the human digestive system – is a rapidly growing and complex field. The gut microbiome plays an important role in good health as well as disease. Probiotics are foods and dietary supplements containing living bacteria that are thought to help the digestive system. The probiotics industry is booming.

So what’s the story with this latest research? Now the dust has settled let’s take a look…

Key points about the research results are:

1. People were different in how they responded to a commercial preparation of probiotics containing 11 types of bacteria. Some were “resistant” i.e. their digestive system showed no significant colonisation of probiotic species while other people were termed “permissive”, their gut showed colonisation of bacteria from the probiotics. Further investigation suggested that the types of bacteria already present in the digestive system before taking probiotics and local immune responses in the digestive system can affect colonisation by probiotic species.

2. When it comes to bacteria – what your poo says about you, is not much – i.e. the bacteria present in stool samples is not a good reflection of what’s going on in the gut. Therefore, only testing stool samples gives limited information about the gut microbiome. To date, most research on the impact of probiotics has been carried out using human and animal stool samples. Biopsies taken directly from inside the gut appear to be more informative.

3. Taking probiotics after a course of antibiotics delayed recovery of the digestive system back to the pre-existing bacterial flora. The gut/stool microbiome was still disrupted five months later. A personalised treatment, comprising an infusion made from a stool sample taken before antibiotic use, was very effective in restoring gut bacteria in just a few days.

The researchers acknowledged some limitations to their findings. The studies were detailed but involved a relatively small number of healthy adults, one commercial probiotics mixture and one type of antibiotic treatment. More investigation of other antibiotics and probiotics in larger numbers of people of various ages (including children and the elderly) is needed. Plus the effects of probiotics in the context of disease was not dealt with in their current research.

Despite these limitations, this new research casts significant doubt on a one-size-fits-all approach to taking probiotics routinely for general good health because people respond to them differently.

In addition, we cannot assume taking probiotics is safe in all situations. The research highlights an adverse effect associated with taking a commercial probiotic preparation to counteract the effects of a course of broad spectrum antibiotics. Previous advice has been to use probiotics to help replace good bacteria after taking antibiotics. It may not be that simple.

More high quality research is needed to understand probiotics and their impact on the gut microbiome to assess whether personalised probiotic approaches could be useful in the future.


Post-antibiotic gut mucosal microbiome reconstitution is impaired by probiotics and improved by autologous FMT. Cell (2018)

Personalized gut mucosal colonization resistance to empiric probiotics is associated with unique host and microbiome features. Cell (2018)

Probiotics – It’s complicated by Steven Novella. Neurologica Blog September 2018

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