Older couple eating healthy lunch together


What is the gut-brain connection?

7 February 2024

We all know that our mood can be affected by what we eat. But the connection between the gut and the brain goes a lot deeper than a short-term energy boost or a blood-sugar crash.

The gut and the brain are linked, both physically and chemically, and they communicate with one another in a number of ways. Commonly referred to as the gut-brain axis, this connection means that the gut influences how we feel, and vice versa.

So, if you’ve ever wondered about those butterflies in your stomach during times of excitement, or you want to understand why you get bloated when you feel stressed, the gut-brain axis may hold the answers.

What is the gut-brain axis?

The gut-brain axis is the two-way communication system that exists between the gut and the brain. It’s made up of both physical and chemical connections, including:

The vagus nerve – one of the longest nerves in the body, the vagus nerve creates a direct physical link between the gut and the brain. Signals and messages are sent in either direction, so not only is the brain communicating with the gut, but the gut sends signals the other way.

The ‘second brain’ – or, to give it its scientific name, the enteric nervous system (ENS). This is a complex network of more than 100 million nerve cells1 (neurons) that line the gastrointestinal tract, including the oesophagus, stomach and both the small and large intestines. This ‘second brain’ primarily controls digestion, but it also communicates with the main brain, which is why poor gut health and digestive issues can trigger an emotional reaction.

Neurotransmitters – these are biochemicals that are responsible for allowing neurons throughout the body to communicate with one another. Neurotransmitters transmit messages within the brain and many of them are created within the gut.

The gut microbiota – there are trillions of bacteria and other microbes that live in the gut. Collectively, these are called the gut microbiota. These microbes are responsible for creating various chemicals and compounds that interact with the brain or aid digestive processes which, in turn, can impact our emotions and mood.

An important connection

While this may all sound very scientific, the bottom line is that the gut-brain axis is a two-way communication system.

For many years, medical professionals and scientists understood that anxiety, depression and stress could cause or affect digestive issues, such as irritable bowel syndrome (IBS). But more recent studies and an improved understanding of the gut-brain connection show that this can also work the other way around.2

For example, the gut produces around 95% of the body’s serotonin,3 a neurotransmitter that regulates sleep, appetite and mood. So, issues or imbalances with the gut’s microbiota can have a significant impact on your mood and overall mental health if they disrupt the production of serotonin.

Studies also show that there’s a strong connection between the health of the gut microbiota and serious mental health issues like depression.4 So, maintaining a healthy gut can be very important in preventing or even treating low mood and mental health conditions.

Brain food

With the gut playing such an important role in our mental health, diet is integral to maintaining balance and looking after our emotional wellbeing.

While certain foods give us energy, alter blood-sugar levels or impact hormone production – all of which can affect the way we feel on a day-to-day basis – some types of food are specifically beneficial to the microbiota of the gut and the gut-brain axis. These include:

Omega-3 fatty acids – Aside from having anti-inflammatory properties and aiding digestion, omega-3s can help promote the diversity and health of the gut’s good bacteria. They can also prevent or slow cognitive decline, so they’re essential to any diet.

Omega-3s can be found in oily fish like salmon, sardines and mackerel, as well as flaxseeds, walnuts and soy.

Fermented foods – Preserved in a way that boosts both the nutritional value and the shelf-life of certain produce, fermented foods like yogurt, sauerkraut and kefir contain healthy bacteria These are live healthy microbes that can be highly beneficial to healthy digestion.

Foods that are high in fibre – Fibre is vital to aiding digestion and maintaining a healthy gut. And prebiotic fibres are good for gut bacteria and stress reduction. These prebiotics can be found in nuts, seeds, whole grains (oats, barley, quinoa, brown rice), as well as fruits and vegetables.

Polyphenols – Polyphenols are a group of compounds or chemicals found in plants. They boost digestion and promote the growth of healthy gut bacteria. They’re found in all kinds of plant-based food and drink, including cocoa, green tea, berries, olive oil and coffee.

Amino acids – There are around 20 amino acids that the body needs to function. Some of these must be obtained via food as the body can’t produce them on its own. These include tryptophan, which helps make serotonin, and histidine, which helps create a neurotransmitter called histamine, which is important for digestion, immune function and sleep.

Foods that are high in these amino acids include lean meats, soy, fish, eggs and cheese.

We’ve examined more examples of the foods and eating habits that can affect our mood in our article, Food to fuel your feelgood.

And, while diet is key, it’s not the only thing we need to think about when managing out gut health. Sleep, exercise, lifestyle choices, habits and stress all play an important role. Our article, The truth about gut health takes a wider look at how we can maintain gut health, while debunking some common myths.


  1. The Brain-Gut Connection - Hopkins Medicine 
  2. Gut feelings: the emerging biology of gut-brain communication - NIH
  3. The Gut-Brain Axis  - NIH
  4. The Microbiota–Gut–Brain Axis in Depression - NIH
  5. Omega-3 fatty acid report - Nature Science Journal