The gut-brain axis: Are the gut & brain really connected?

Reviewed by Ro Huntriss, Registered Dietitian

That fluttering butterflies feeling you get when you’re nervous is more than just a feeling in the pit of your stomach.

They’re a sign of the fact that our brain – all the way up in our head – and our gut – all the way down in our tummies – are actually inextricably intertwined.

Studies have found that an entire communication system between the brain and gut exists, which is commonly referred to as the gut-brain axis.

In this article, we will cover

• What is the gut-brain axis and why is it important?
• Does it really exist?
• What does it do? And can we influence how it works?

What is the gut-brain axis?

The gut-brain axis is a two-way communication pathway that exists between the gut and the brain.

Not only does the brain know what is happening in the gut, the gut has access to the emotional and cognitive centres in the brain too.

This means that conditions in the gut have an impact on what the brain does and how we feel, and conversely, how we feel emotionally can impact on how the gut functions.¹

Summary

• The gut-brain axis is a two-way communication channel that runs from your brain to your gut and back again
• Our gut has the ability to influence what our brain does and how we feel
• At the same time, our emotions can also impact how our gut functions

Why is the gut-brain axis important and what does it do?

A good illustration of the gut-brain axis in action is when we get ‘knots’ in our stomach because we feel nervous.

Stress or anxiety can often cause digestive issues, such as constipation or diarrhoea, which is a result of the close relationship between the brain and gut.

When something stressful happens, our bodies produce a hormone called cortisol. This hormone has quite a few jobs, including reducing inflammation and – key in this context – diverting energy to the ‘fight or flight’ response.²

This involves energy being funnelled to the muscles and away from the digestive system.

As a result, food ends up staying in the intestines rather than being digested.

In turn, this can cause inflammation in the gut, which may alter the intestinal environment and disrupt the microbiome.³

And this disruption means that all of the really important jobs that gut bacteria perform, may not be happening as efficiently or effectively as they used to.

Because of the two-way feedback, unfortunately, this inflammation and reduced functioning in the gut leads to altered communication with the brain, which can generate more stress, and so on.

What’s taking place here is a stress-digestion cycle. In fact, people who suffer from Irritable Bowel Syndrome (IBS) are reportedly more likely to suffer from anxiety and depression.⁴

However, the good news is there are numerous ways we can improve our gut health that centre around general healthy living (e.g. eating a healthy, balanced diet and exercising regularly).

If you do happen to suffer from any digestive issues, or depression, anxiety or stress, speak to your GP.

They will be able to provide you with an accurate diagnosis and advise you on the best treatment based on your symptoms.

Summary

• Feeling stressed or anxious can lead to digestive issues, such as constipation or diarrhoea, which are caused by the close relationship between the brain and gut
• When we feel stressed, our bodies produce cortisol, which helps divert energy into the ‘fight or flight’ response, with energy being channelled away from the digestive system
• This can lead to gut inflammation, which alters the intestinal environment and causes microbiome disruption

How can we influence how it works?

Due to the link between the enteric nervous system (the part of the nervous system that controls our gut) and the central nervous system (the part of the nervous system that controls our brain) now being established, some medical professionals are choosing to offer treatments that communicate with both ‘brains’, so to speak.

For instance, gastroenterologists may prescribe certain antidepressants for IBS —not because they think the problem is all in a patient’s head, but because these medications calm symptoms by acting on nerve cells in the gut.⁵

At the same time, improved gut health has been recognised as having a positive effect on the gut-brain axis.

There are several ways you can enhance your gut health. They include:

1. Supporting your gut bacteria

The microbiome is an essential part of the gut - without actually being part of it. It is made up of bacteria that we have a symbiotic relationship with.

They perform functions for us, such as making neurotransmitters, training the immune system and digesting food and, in return, we provide them with food in the form of fibre (also known as prebiotics) from our diet.⁶

In order to keep the microbiome thriving, you need to feed it well.⁷

Vegetables, beans and whole grains all have good amounts of fibre in them and can help to feed the friendly bacteria in our gut, acting as prebiotics.

2. Taking probiotics

As well as prebiotics, we can also take probiotics either as ready-made products or from fermented foods.

Fermentation produces lactic acid bacteria in foods, like yoghurt and kefir, which populates the gut when eaten and may have a positive effect on metabolism.⁸

A study by UCLA in 2013 examined 36 women split into three groups: those who ate two bacteria-containing yoghurts every day for a month, those who ate a dairy product without any bacteria, and a control group.⁹

Results showed that those in the bacteria yoghurt group experienced changes in the part of the brain that processes emotions linked to visual stimuli, with some decrease in activity, suggesting a reduction in anxiety.

It’s believed that the research could one day lead to so-called psychobiotics – medicines based on bacteria – being used as treatments for mood disorders, including depression.¹⁰

3. Spending time outdoors

To get a broad range of bacteria populating your gut, you need to come into contact with a lot of different environments.

There’s a big difference between the bacteria that live in cities compared to those that live in farms with livestock, for instance.

Taking a trip to the countryside – as well as being a nice day out- can actually improve our risk of allergies because exposure to this kind of bacteria helps to train our immune systems to tolerate non-harmful bacteria and substances.¹¹

4. Being physically active

Physical activity can improve conditions in the gut so that anti-inflammatory bacteria can thrive.¹²

Exercise could even affect the types of bacteria that thrive in your intestine.

Especially if you can combine it with getting into a different environment – running in a woods versus running on a treadmill, for example.¹³

It can also prevent constipation by making sure the muscles in the gut keep contracting and moving food through.¹⁴

5. Minimising stress levels

Early research on animals has found that stress can impact the composition of the gut microbiota and that this can have an effect on the host, (i.e the person experiencing stress).¹⁵

A number of studies using germ-free mice (mice who have no microorganisms living in them) have shown a link between microbiota and anxiety-like behaviours.Further research has shown that particular microbiota transfers can improve anxiety-like behaviours and increased production of dopamine and serotonin, demonstrating the role of microbiota in mood and behaviour.¹⁶

Summary

• We can fundamentally influence how our gut-brain axis operates
• This includes prescribing treatments that communicate with both ‘brains’
• Improving gut health can also be beneficial for boosting the gut-brain axis

A final few words about the gut-brain axis

Believe it or not, our brain and gut are connected, even if they happen to be at completely different ends of our body.

Research has found, and continues to find, that the brain does directly affect our stomach and intestines.

More specifically, the brain and gastrointestinal system are intimately linked, with both signalling to each other via a connection that can go both ways.

Managing your stress levels and taking good care of your gut, particularly your gut bacteria, has been proven to play an instrumental role in improving the gut-brain axis.

What’s more, it can be easily achieved by implementing everyday measures that are easy to embrace and follow, such as taking probiotics, eating a healthy, balanced diet, spending time outdoors, taking part in regular exercise and managing stress.

The gut-brain axis is a silent force to be reckoned with.

If you feel you are experiencing symptoms caused by the relationship between your brain and gut, speak to your GP about it in the first instance.

The advice in this article is for information only and should not replace medical care. Please check with your GP or healthcare professional before trying any supplements, treatments or remedies. Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.

Last updated: 8 February 2023