What is the gut–brain axis?

Have you ever felt butterflies before a big moment, or lost your appetite when worried? That is your gut and your brain talking to each other. Scientists call this two-way link the gut–brain axis, and research over the past two decades has shown how closely the two are connected.

A two-way conversation

The gut–brain axis is a complex communication system that runs in both directions. Signals from the brain shape how the gut moves and works. Signals from the gut travel back to the brain, where they can influence emotions and even decision-making [1].

How the gut and the brain talk

Messages travel along four main channels [1, 2]:

1. Nerves. The nervous system connects the brain directly to the gut wall.
2. Gut hormones. Specialised cells lining the gut release chemical messengers that the brain can sense.
3. The immune system. Immune cells in the gut wall pass on information about what is happening there.
4. Gut microbes. The bacteria living in your gut produce substances that nerves can detect and relay to the brain.

The vagus nerve: the main line

The most important nerve link is the vagus nerve. It is the main nerve of the parasympathetic nervous system, which supports the body’s “rest and digest” state. Around 80% of its fibres carry information from the body up to the brain, so it acts largely as a listening line from the gut [2].

Why stress can upset your stomach

When you are stressed, the nerves that control the gut respond. This can change how the gut moves and what it secretes, which is why emotions so often show up as stomach symptoms [1]. NHS guidance notes that stress and anxiety can trigger or worsen gut symptoms such as diarrhoea, constipation and nausea in some people [3].

Looking after your gut–brain connection

You cannot remove stress from life, but NHS guidance suggests ways to manage how much you face and how you respond to it [3]:

• Identify the stresses you can control and tackle those first.
• Try relaxation techniques such as slow breathing exercises.
• Stay active with walking, swimming, yoga or other exercise you enjoy.
• Make time for people and activities that you find rewarding.

If gut symptoms are ongoing, changing or affecting your daily life, speak to your GP.

A growing field

Scientists are still uncovering how the gut and brain influence each other, and new findings appear every year. At CortiAura, we follow this research closely as we develop new technology built around the gut–brain connection. Join our Founding Community for updates.

References

1. Mayer EA. Gut feelings: the emerging biology of gut–brain communication. Nature Reviews Neuroscience 2011;12:453–466.
2. Bonaz B, Bazin T, Pellissier S. The vagus nerve at the interface of the microbiota–gut–brain axis. Frontiers in Neuroscience 2018;12:49.
3. NHS inform. IBS and your mental health.