The mind and the gut microbiota

Today I’m bringing you a topic that has been booming in recent years and that I personally find fascinating: the relationship between the mind and the microbiota. So let’s start with…

Can our poo tell us something about the state of our mind?

Well, it seems it can.

For some years now, the microbiota and its relationship with the central nervous system, that is, our brain, have been getting special attention. It is now well established that the trillions of tiny bacteria in our gut, especially in the large intestine, have a major influence on the way we think, feel and behave. You might be wondering: how can the bacteria found in our poo (no giggling, studying it saves lives in many cases!) be related to how we think or behave? Well, they are. Don’t forget that the digestive system is now considered the second brain and contains hundreds of millions of neurons, as well as being directly connected to the brain in both directions. Just like the heart, considered the third brain.

Back to our little bugs… The most recent estimates put the number of bacteria in our body at around 38 trillion (Sender, Fuchs and Milo, 2016, PLOS Biology), roughly as many as our own cells, and most of them are concentrated in the gut, which is why, when people talk about the microbiota, they usually mean the gut microbiota. But we also have little bugs spread all over the rest of the body, and the relationship is symbiotic: they help our body work properly and our body gives them the right environment to survive. A good deal, you might say.

Several studies have linked an imbalance in the microbiota with problems of anxiety, stress, sociability and illness. In some experiments, rats with an altered microbiota developed dysfunctional behaviour and learning problems compared with their peers in the control group (those whose microbiota hadn’t been tampered with). A few other titbits you might find interesting: some of these bacteria have been found to synthesise tryptophan, the precursor of serotonin (the main neurotransmitter linked to mood, and the one many current antidepressants act on to produce their effect). It has also been observed that in stressed rats a particular group of bacteria grows significantly that doesn’t grow in the control group (non-stressed rats), which means there is a link between microbiota and stress. Harmful changes in the gut microbiota have also been seen to cause a reduction in brain-derived neurotrophic factor (BDNF) in brain areas related to memory, learning and mood. In other words, when the microbiota is disrupted, this seems to affect the growth and survival of neurons in these brain areas. And so on, with countless studies over recent years. In case you’re wondering, there are also studies in humans, and the results seem to point in the same direction.

That’s why, for several years now, many of the most prestigious universities and research centres have been devoting time and money to studying faeces: the type and amount of bacteria found in them can provide very valuable information.

How can I improve my microbiota?

A healthy diet, which is always advisable for everything, becomes even more important when it comes to the microbiota. For the same reason, it’s important that antibiotics are used as sparingly as possible and taken only when needed, since they are particularly harmful to the bacteria that live in our gut and quietly look after us. In addition, regular physical exercise has been shown to increase both the number and the diversity of beneficial bacteria. Once again, we see the countless benefits of moving our body, which is what it’s made for!

If this topic interests you, I recommend a couple of books for the general public that are also very enjoyable (both in Spanish): ¡Es la microbiota, idiota! (“It’s the microbiota, stupid!”) by Dr Sari Arponen, which covers the microbiota in full (not just the gut), and Neurociencia del cuerpo (“Neuroscience of the body”) by Nazareth Castellanos, which devotes a section to the topic, though the whole book is a gem if you’re interested in how the body as a whole influences our mind.