Do you ever get butterflies in your stomach when you’re nervous or excited? Or, find that what you eat impacts your mood? These behaviours and sensations are the result of the gut-brain connection, which explains how our digestive and mental health are so intricately connected.
Here, we’ll look closer at how the gut and brain are connected and how this can influence health.
What is the gut-brain connection?
The gut-brain connection, or gut-brain axis, is a two-way communication system made up of a network of chemicals, nerve cells, and microbes that connect the gut and brain.
Scientifically speaking, it connects the central nervous system (the brain and spinal cord) with the enteric nervous system, which is found in the gut.
This connection means that the gut and brain are in constant communication and, therefore, heavily influence one another. For this reason, many experts refer to the gut as the ‘second brain’.
How are the gut and brain connected?
The gut and brain are connected through various pathways. This includes…
The vagus nerve
Neurons are cells which send and receive messages to and from the brain and the rest of the body. According to research, there are around 100 billion neurons in the human brain, and 500 million more in the gut. They send and receive messages via nerves, which are bundles of fibres made from neurons.
One of the largest and most significant of these nerves is the vagus, which runs from the brain to the colon – physically connecting the gut to the brain. Both animal and human studies have recognised the role of the vagus nerve in carrying signals between the gut and brain, and explored how and why they influence each other.
In this study, stress was found to impact signals sent through the vagus nerve, which resulted in gastrointestinal issues. Another study revealed that people with irritable bowel syndrome (IBS) or Crohn’s disease showed signs of reduced vagus nerve function compared to people without the condition.
This study also found that when mice were fed a probiotic (live bacteria that are beneficial for gut health), stress hormones in their blood reduced. Interestingly, when the mice’s vagus nerve was cut, the probiotic no longer had an effect.
Neurotransmitters
Neurotransmitters are the chemical messengers needed for numerous body functions. They’re produced in the brain and gut, and form another key part of the gut-brain connection.
Research shows that the health of our gut microbiome influences the production of several neurotransmitters. This includes serotonin and gamma-aminobutyric acid (GABA), which both play a role in mental and emotional wellbeing.
A large proportion of the body’s serotonin is produced in the gut, and studies have revealed that the gut microbiome is essential for regulating its function – both in the gut and brain. In the gut, serotonin is important for healthy digestion, and in the brain it’s heavily tied to sleep and mood regulation.
Similarly, gut bacteria also produce GABA, which we know from research helps to reduce stress, fear, and anxiety. In this study, taking probiotics to improve gut health increased the GABA production and resulted in reduced anxiety and depression-related behaviours.
The immune system
The immune system is the body’s defence against illness and disease. It’s made up of a network of cells, organs, and chemicals that work together to fight harmful viruses and bacteria.
As much as 70-80% of the immune system is found in the gut, so it’s heavily involved in the gut-brain connection. For example, studies have found that gut bacteria can influence the production of proteins called cytokines, which play an essential role in the body’s inflammatory response and can impact brain function.
However, further research is needed to learn about the relationship between gut microbes, brain health, and the immune system.
Gut health and mental health – how do they influence each other?
Connected physically and chemically, our gut health and mental health are closely tied.
For example, mental health conditions such as anxiety are often associated with gut conditions like IBS. In fact, some studies have linked specific gut microbes with an increased risk of anxiety and depression.
This study found that people with depression had lower levels of two types of gut bacteria (Dialister and Coprococcus). Meanwhile, participants of the same study who had more of these bacteria in their gut scored higher when asked about their quality of life.
There’s also been research into fecal microbiota transplants (FMT) as a potential treatment for mental health conditions. FMT involves taking gut bacteria from a person’s stool and transplanting it into another person’s gut.
Various studies have revealed that FMT from donors without mental health conditions reduced symptoms in people with anxiety and depression.
These findings suggest that, as a result of the gut-brain connection, eating a gut-friendly diet may improve your mental health. We’ll cover this in greater depth below.
Improving your diet for mental health and brain function
Overall, eating a balanced diet full of essential vitamins and minerals is one of the best things you can do for your overall health. However, there are several food groups worth focusing on when looking to improve mental health and brain function.
On the other hand, diets high in inflammatory foods, such as ultra-processed foods, have been linked to a greater risk of mental health conditions, including depression.
Some of the most beneficial food groups for gut health – and therefore mental health and brain function – include…
Fermented foods
Fermented foods, such as kefir, sauerkraut, and yoghurt, are good for gut health because they contain live bacteria called probiotics. Probiotics help to increase the number and diversity of bacteria in the gut microbiome.
By improving gut health, studies show that fermented foods may boost brain activity – particularly areas of the brain that process emotion and sensation. For example, in this study of people who were prone to anxiety, eating fermented foods containing probiotics was linked to reduced social anxiety.
To find out more, have a read of our articles; 8 fermented foods for gut health and How to make your own fermented foods at home.
Omega-3 fatty acids
Various studies suggest that omega-3 fatty acids can increase good bacteria in the gut and reduce the risk of brain disorders, including depression.
Sources of omega-3 fatty acids include fatty fish like salmon and mackerel, nuts, seeds, and soya beans. You can read more in our article; Omega-3 – what is it and why do we need it?
Prebiotics
Fibre is another key player in gut health. Prebiotics are a type of fibre that’s particularly important because it provides food for the good bacteria in your gut.
Studies have found that diets containing plenty of prebiotics can reduce cortisol (the stress hormone) levels and improve mood.
Examples of prebiotics include garlic, flaxseed, asparagus, and barley. Find out more in our articles; 13 prebiotics foods to add to your diet and What’s the difference between probiotics and prebiotics?
Foods rich in polyphenols
Polyphenols are a type of compound that occur naturally in plant foods. Among other health benefits, research has found that polyphenols can increase healthy gut bacteria and may improve brain function.
Other studies have noted the beneficial effects of polyphenols on brain ageing, mainly due to their antioxidant and anti-inflammatory properties. For example, this study suggested that the antioxidant effects of polyphenols may help to protect against neurological conditions like Alzheimer’s disease.
Examples of polyphenol-containing foods include apples, berries, onions, whole grains, and dark chocolate. Check out this list of foods highest in polyphenols from Zoe for more information.
Foods containing tryptophan
Tryptophan is an amino acid found in various protein-containing foods. Among other things, tryptophan is used to make serotonin. Serotonin affects several organs, including the brain and gut, and impacts everything from sleep and mood to brain function.
As a result, low levels of tryptophan have been linked with reduced brain function and an increased risk of mental health issues, including low mood and impaired memory.
Foods high in tryptophan include eggs, cheese, legumes, seafood, and turkey. Find out more on the Web MD website.
Final thoughts…
The gut-brain axis refers to the communication system between the gut and the brain. Experts are increasingly understanding how our gut and brain influence each other, and what this could mean for overall health.
For further reading, head over to the general health section of our website. Here, you’ll find information on everything from heart and bone health to important health checks for over 50s.
What aspects of the gut-brain connection interest you the most? Has anything in this article surprised you? We’d be interested to hear from you in the comments below.
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