Do Gut Microbes Affect Your Personality?

“We continue to shape our personality all our life.” —Albert Camus

The gut-brain axis is a mind-boggling concept. The idea that gut microbes could have something to do with our mood is humbling.

Yes, there are dozens of other non-microbial impacts on our mood: Genetics, upbringing, and life events like bereavement all play a role. But it’s too late to change our parents, and we can’t bring back the dearly departed. Microbes are cool because we can tune them to better harmonize our life. Upon reflection, the gut-brain axis may be more empowering than humbling.

That our moods may be affected by microbes is compelling and well supported. Our personality, on the other hand, seems untouchable. Unlike moods, our personality is (mostly) here for the duration. It defines us. It’s our proprietary essence. Surely, microbes can’t affect something so basic to our identity.

And yet, that’s exactly what a new study seems to suggest. In the study—currently a preprint that has not yet undergone peer review—researchers Anna Aatsinki, Siobhain O'Mahony, Gerard Clarke, John Cryan, and colleagues found that “the gut microbiota composition may be linked to certain temperament traits.”

A Disconcerting Study

The trait they concentrated on was exuberance. Amazingly, they discovered that they could transmit an exuberant personality via gut microbes. Not only that, but they could spread the cheerful attitude from one species to another, in this case from humans to rats. In essence, the researchers performed an interspecies personality transplant.

We may think of ourselves as nerdy introverts or garrulous party animals, but what if that is partly a consequence of our gut microbes? What if gut microbes aren’t simply content to slosh around as we trot through life, but are actually in the saddle and yanking the reins?

Personally, I imagine that this must be what it felt like when Copernicus pointed out that we weren’t the center of the universe. Now we learn we might not even be the center of our own personality. Are we mere bystanders in our own lives?

Studies comparing twins show that some 30 percent of our personality is genetic. That, presumably, is truly ours, but it still leaves 70 percent credited to the environment, which includes our gut microbes. In fact, what we call our personality may be more like a persistent proclivity or a mood that lingers, not a core aspect of our inner life.

Before we bemoan our personal devaluation, is there an upside? Could microbes give us a happier disposition?

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A Look at the Study

For the experiment, the researchers selected two-year-old toddlers as subjects. They had psychologists classify their temperaments as either exuberant or inhibited. They then took fecal samples from each group and transferred them to rats. These fecal microbial transplants are research gold, because they show strong evidence of causality, not just coincidence.

The rats that received the exuberant poop displayed more exploratory behavior and socializing—the rat version of exuberance—than those receiving the inhibited poop.

The rats receiving the inhibited poop were withdrawn and showed a decrease in dopamine pathways—the reward circuits—in their brains. Dopamine is a great motivator, but inhibitory gut microbes seem to squelch it.

The study was small, only looked at a few traits, and couldn't easily categorize any microbial “fingerprints” for exuberance. Some clostridial species, however, were enhanced. These clostridial microbes are butyrate producers known to have positive health effects.

The microbes in poop samples were sufficient to transmit temperament traits. If the findings hold up in further research, we may have to admit that at least some of our personality is being determined by our gut microbes.

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It sounds bad for our self-ownership, but ironically, it may actually be good news. That’s because we can control our microbes with diet, so we might be able to take advantage of this emerging research to build the personality we want. Imagine overcoming shyness and boosting exuberance by sculpting our microbiome appropriately.

Take Action

There is a simple way to push your microbes into the healthy zone: become a Sardinian. Or at least dine like one. Eat a Mediterranean diet with lots of different veggies and fruit, a little bit of fish, and plenty of grains and nuts. Variety is the key, as it will feed a diverse set of microbes. Ecosystems thrive on diversity because that is the best way to keep pathogens at bay while maintaining the multiple functions of a good microbiome.

Follow this high-fiber diet, get plenty of sleep and exercise, and your gut microbes will serve you well. They will create substances like the aforementioned butyrate that heal and nourish the lining of your gut. They will generate feel-good neurochemicals like dopamine and serotonin that can help keep your mind on an even keel. Your microbes can even create chemicals to encourage the growth of new brain cells, improving your cognition and memory.

While more peer-reviewed research is needed, the real take-home here could be that being painfully shy or a wallflower might not be a lasting character trait. It might be a sign of poor gut health.

And if this is the case, we might need to reconsider the way we see ourselves. Instead of being an anxious person, maybe we just have a little (curable) anxiety. The idea that microbes could affect our personality is sobering, but in my view, it’s also wonderful—it means we can take back the reins and choose our own path.

Every time science knocks us down a rung, it stings. Sure, maybe our gut microbes have something to say about our temperament. That’s discomfiting. But we still have some control over those microbes.

And that may hike us up a rung or two.