I have a bad gut feeling about this


Recently, a good friend of mine told me about his – now ex – girlfriend and how she ended the relationship based on a “gut feeling”. I wonder if that girl was aware of the big excitement that is currently flooding media and scientific literature regarding this topic. Well, not the break-up but the influence of the gut on human life, health and even decision making. More precisely, the influence of the microbiome, the vast population of microorganisms living in the gut and other organs.

It’s been known for several years that microbial communities have a bigger impact on our general well-being than previously appreciated. Connections have been reported between microbiota and obesity, the function of the immune system but also severe diseases and disorders such as depression, anxiety, autism and cancer.

In love with your boyfriend’s bacteria?

The media has happily picked up the topic (you might have seen the Daily Mail article about a woman who reportedly suffered excessive weight gain after a fecal transplant) but in recent times the general enthusiasm has led to many rather far-fetched interpretations of scientific findings. In fact, in some worrying instances no correlation with published data exists at all and stories are simply made up.

It’s not always the media who are to blame. Some scientists have shown a remarkable affinity for the spotlight even if it is gained by presenting “findings” that are based on wishful thinking rather than proven facts.

If you’re in need of some entertainment I would suggest you check out Jonathan Eisen’s blog where he frequently presents researchers and journalists with the “Overselling the microbiome award” for notably hyped scientific claims in microbiology.

A particularly hilarious one was just posted a few days ago: Jason “The Germ Guy” Tetro was giving an interview on CBC about how similar microbiomes can initiate and maintain attraction between two people and how kissing – or rather the exchange of microbiota from the mouth’s ecosystem – can help with the search for an ideal mate. The sad thing is that Tetro is referring to an actual study where the exchange of microbiota during kissing was investigated – and confirmed. However, the conclusion drawn from the data had nothing to do with what Tetro is postulating but merely suggested that couples who frequently kiss share a salivary microbiota. Duh!

So what is true about the impact of our microbiome and what is exaggerated? Can bad bacteria really make you end a relationship? Or – even better – is the new love potion which will grant me my crush’s eternal devotion a drink of well-selected germs, as suggested on several commercial websites?

I have to say that despite the fun I have reading through all the hyped hogwash some websites are spreading, I’m a bit worried about the mess that has been made of a perfectly sound scientific finding.

Human microbiota during a life-span. Image source: Ottman N, Smidt H, de Vos WM and Belzer C (2012) The function of our microbiota: who is out there and what do they do? Front. Cell. Inf. Microbio. 2:104. doi: 10.3389/fcimb.2012.00104.
Human microbiota during a life-span. Image source: Ottman N, Smidt H, de Vos WM and Belzer C (2012) The function of our microbiota: who is out there and what do they do? Front. Cell. Inf. Microbio. 2:104. doi: 10.3389/fcimb.2012.00104.

Is there a problem with the data?

On a cellular level a human being contains more bacterial cells than human cells – with a striking ratio of 10:1. It has even been suggested to consider the microbiome as another organ. Regarding the complexity of its interactions with the cellular environment, that thought doesn’t seem too far-fetched.

By sequencing the DNA of fecal samples, scientists have discovered that more than 1,000 bacterial species can live in the human gut, help us digest food and communicate with the immune system. The average person is home to about 160 different species – but in cases of disease these species can vary substantially. And even among healthy individuals, microbial profiles differ – resulting in a microbial fingerprint that is unique for a person and tells a lot about individual genetic, environmental and lifestyle history. Without a doubt, the consequence is a strong link between our microbiota and our health – and one may influence the other. This has been proven and reproduced on many occasions and in many diseases. However, when such a powerful discovery is made – with the clear implication to change the way we treat diseases – it is tempting to interpret even more into it than there actually is. To use it as a theorem to explain everything.

When we talk about the microbiome hype the issue is not only that the media is making excessive claims that have never been backed up scientifically, as it happened with Tetro. But also research has increased massively in the last 5 years as scientists have started to acknowledge the importance of the gut microbiome in many processes.

But with so many studies being conducted in many different ways by researchers who might not even have contributed to the field of microbiology before, it is necessary to remain careful whenever a new claim is made. William Hanage has stated five helpful questions that should help when evaluating microbiome research and might put skeptics on the right path.
I can highly recommend his approach when being confronted with new studies that might raise doubts.

In any case more research will need to be done to back up findings that have already been made and to answer new questions. The field is still young – but it is an exciting time to follow its progress and I am sure there will be many more promising discoveries on the way.

Other sources

Microbiome: Cultural differences
The function of our microbiota: who is out there and what do they do?

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