Microbes made me do it 🧠

Are our gut microbes controlling us, and who we are?

We know our microbes can influence sleep, appetite, and even mood.

But what about who we are as people?

In nature, parasites can have eerie effects on behaviour.

Mice infected with Toxoplasma gondii lose their fear of cats. Ants overtaken by a fungus climb high and clamp onto leaves, sacrificing themselves to help the fungus spread.

It’s the stuff of TV series The Last of Us, but could something similar be happening in us - could our own microbes be gently pulling our strings?

What we’ll cover today:

• Can your personality be seen in your poo?

• Extroverts vs. introverts for your gut microbes

• How often you poo? Could be your personality

• Are we “microbial zombies”?

• 5 ways to support your gut (and maybe your personality) (paid subscribers)

Can your personality be seen in your poo?

Sort of! In a study of over 600 adults, researchers found that people with certain personality traits had different gut bacteria.

People who were more neurotic had more of certain gut bacteria that carry compounds linked to inflammation.

Those who were more conscientious (organised, careful) had more of the bacteria that make butyrate, a short-chain fatty acid that supports gut health and overall well-being.

Another study in toddlers found that more outgoing kids tended to have more diverse gut microbes - especially boys.

And mice raised without any microbes, in totally sterile conditions, were more withdrawn from other mice.

Yet when researchers gave mice back gut microbes, some (but not all) of their social behaviours improved, like spending more time with other mice.

Extroverts vs. introverts

The more time you spend with other people, whether living in a busy household or regularly seeing friends, the more your gut microbes start to resemble theirs.

You don’t need to live together to share microbes (though those that do share about 12% of their gut microbial strains) - just eating meals together or greeting each other with a hug or kiss can increase how many you have in common.

In one study, people who saw each other almost daily and weren’t related shared more gut microbes than some family members. Your gut can even be influenced by your friends’ friends.

Many of the microbes we share this way are anaerobic (the ones that don’t like oxygen), meaning they don’t survive well outside the body - so they rely on close contact to spread.

Can your personality affect how often you poo?

Surprisingly, yes. In a study where everyone ate exactly the same high-fibre diet (down to the gram) people still varied in how often they went and how much they pooed.

And one of the best predictors? Their personality.

People who described themselves as more upbeat, outgoing and optimistic tended to go more often and had heavier poos. Those who were more socially withdrawn or anxious tended to go less.

Your brain and gut are tightly connected. How you feel, your stress levels, mood, even your personality traits, can influence the nerves and signals that control gut movement.

So even when we eat the same amount of fibre, what's going on in our heads might be just as important as what's going on in our bowls.

How could microbes shape our personality?

One way might be through oxytocin, the hormone that helps us feel bonded and connected.

In mice and rats, when oxytocin was blocked, they became more withdrawn. But when they were given oxytocin, they became more sociable again.

There’s some early research suggesting our gut microbes could affect how much oxytocin we make. So in theory, they might be nudging us towards being more social.

And since microbes can spread through touch or shared food, being sociable might help them too - so they may, in a way, encourage connection for both their benefit and ours.

Are our microbes controlling us?

Not really - but they can influence us in ways that come from how closely the gut and brain are connected.

Some microbes make molecules like neurotransmitters that can affect how we feel or behave. But these are probably by-products of how microbes live and grow, not something they make to control us.

True microbial mind-control is very unlikely. The gut is full of different microbes competing with each other, and any that tried to control us would likely be outcompeted by others that don’t.

So while microbes might affect our behaviour, it’s more likely a side-effect of how they live inside us, not because they’re trying to control us (phew!).

5 ways to support your gut’s personality