The gut–brain axis: how your gut and brain work together

The gut–brain axis is being mentioned more and more, but what does it actually mean and why is it getting so much attention? Your brain plays an important role in everything you think and feel, while your gut is also involved in many processes throughout the body. The interaction between your belly and your brain is complex and the subject of a growing body of scientific research. Increasingly, insights show that this connection is linked to both physical and mental processes. In this blog, you’ll learn more about how this connection works and the role that cortisol, serotonin and the nervous system, among other things, play in it.

What exactly is the gut–brain axis? 

The gut–brain axis is the communication channel between your gut and your brain. Through nerves, neurotransmitters and hormones – such as cortisol and serotonin – they ‘talk’ to each other all day long. This axis is very important: it influences how you deal with stress, your mood, and how well your digestion works. One of the key players is the vagus nerve (nervus vagus), a nerve that runs directly from your brain to your gut. That means your gut can influence your brain, and vice versa. 

Think of how, during stress, cortisol is released, which directly affects both your brain and your gut. You may recognise that feeling in your stomach when you’re about to do something exciting, like bungee jumping, or when you meet someone for the first time. Or the sudden urge to go to the toilet right before an important moment, such as a presentation or a job interview. But it also works the other way around: your gut health impacts your mood. It’s no wonder your gut is sometimes called your “second brain”! 

The vagus nerve and your nervous system 

Alongside your central nervous system (which includes your brain and spinal cord), you also have an enteric nervous system that plays a major role here. Your enteric nervous system is a kind of “gut brain” and is also known as the autonomous nervous system of your gut. It functions largely independently and communicates extensively with your brain via the gut–brain axis.  

The vagus nerve plays an important role here and acts like a motorway along which signals are sent. Those signals travel both from your brain to your gut and the other way round: from your gut to your brain. In this way, your brain and gut stay connected all day long, constantly sending each other updates. 

If your gut is out of balance, your brain receives a signal via the vagus nerve, which affects your central nervous system. You may feel restless or generally not quite yourself. Conversely, stress can affect your gut, making it more unsettled in turn. It’s important that your vagus nerve functions well, so these signals can reach each other properly.

The role of the microbiome 

Your gut is home to trillions of bacteria, fungi, yeasts and other organisms – together known as your microbiome. These micro-organisms help digest food, support your immune system and produce neurotransmitters such as serotonin, often referred to as the “happiness hormone”. Serotonin has a major influence on your mood and sleep, and as much as 90% of it is produced in your gut! 

A balanced microbiome contributes to a well-functioning digestive system. In addition, more and more research is being done into the relationship between the microbiome and various processes in the body, including mood and cognitive function. The microbiome also appears to be involved in processes linked to inflammatory responses. When the balance of the microbiome shifts — for example due to lifestyle factors such as diet or stress — this can influence how these processes unfold in the body.

In addition, your gut plays a leading role in your immune system, as a large proportion of your immune cells are located there.

The impact of stress on the gut–brain axis 

Stress is one of the biggest culprits when it comes to the gut–brain axis. When you experience stress, your body switches into “fight-or-flight” mode and produces a lot of cortisol to help you cope. Cortisol not only has a direct effect on your brain, but also on your gut. 

When your body is in stress mode too often and for too long, it can lead to an imbalance in your gut. High cortisol levels mean less blood is directed to digestion and fewer digestive juices (such as stomach acid) are produced. After all, when you need to fight or flee, digestion isn’t a priority. Your microbiome can be thrown off balance and you may experience inflammation. Because things in your gut are not working as smoothly, you might suffer from bloating, constipation or diarrhoea.  

Inflammation also affects your mental health and how well your nervous system functions. Persistently high cortisol can therefore impact your memory and concentration too. Your brain functions less effectively, and you may become more sensitive to stress again. This can quickly turn into a vicious circle.   

Stress can’t be completely avoided in modern life, but it is important to regulate it. Find ways that work for you to keep cortisol under control — think meditation, yoga, breathing exercises and moving regularly — to keep both your gut and your brain healthy.  

Serotonin: the connector 

Various substances involved in communication between the gut and the brain are produced in the gut, including serotonin. Gut bacteria play a role in supporting processes related to the production and regulation of this substance. Although serotonin produced in the gut does not enter the brain directly, it is part of a complex communication system between the gut and the brain, also known as the gut–brain axis.
In the gut, serotonin is involved in several processes, such as: