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

For a lot of people, the idea that the brain and gut share a connection makes instant sense. We often turn to ‘gut feelings’ to get through some of life’s biggest decisions and you might even have seen the gut being referred to on your social feeds as the ‘second brain'.

Of course, your gut doesn’t think or make decisions like your brain – but it does have its own nervous system.¹ So what really is the gut-brain axis and what could it mean for health? We asked Jasmine Bliss, a registered nutritionist and gut health specialist, to share her insight.

The gut-brain axis is a two-way communication line between the gut and brain. Their 'conversations' happen through nerves, hormones, immune signals and ‘messengers’ produced by gut microbes.² Ever had a dodgy stomach when you're nervous? That could be an example of the gut-brain axis. “What happens in your gut could potentially influence your mood and stress response, while your brain can directly affect digestion and sensitivity to pain,” says Jasmine.²

The vagus nerve plays an important role in maintaining the conversations between the mind and the digestive system. “This long nerve runs all the way from our brain to our gut and is part of our parasympathetic nervous system, which dictates our stress response," says Jasmine.³ So, there's not only a metaphorical link, but a physical one too. The vagus nerve helps your body relax and digest food, supporting things like stomach acid and movement in your gut.³ In contrast, the ‘fight or flight’ system takes over when you’re stressed and slows down digestion. This is actually an ancient survival response – breaking down food uses up a lot of internal energy. In a threatening situation, your brain decides to put that energy towards running or fighting instead.⁴

Research is still emerging, but it's thought that our gut microbiome (the community of trillions of microbes in the gut) may play a role in the gut-brain connection too. Around 70% of your immune system lives in the gut – “this means our gut health could be linked to whether we catch a cold and even how well we respond to vaccines,” says Jasmine.⁵

“Our gut microbiome also helps regulate inflammation, metabolic health and nutrient absorption, meaning two people can eat identical diets but absorb different levels of nutrients from them.” That’s because gut microbes can influence the bioavailability and absorption of nutrients, including minerals such as iron, calcium and magnesium, meaning the amount we absorb from food can vary between individuals.⁶

However, some of the hype around gut health has jumped ahead of the science, so it's worth approaching any gut health 'fixes' with caution. While commercial microbiome tests are available, there currently isn’t a validated test that can simply tell you whether your gut microbiome is ‘healthy’.

There's more to the gut-brain axis than getting butterflies when you're nervous. Early research suggests it could potentially affect a huge amount of body functions, from mood and appetite to immune function.⁷ Emerging evidence also suggests it might also affect what we crave and choose to eat, though many factors are involved,’ says Jasmine.⁷

However, none of this is a perfect science and researchers are only just scratching the surface of these potential links. “Research is also still ongoing into links between the gut and neurodegenerative conditions (like Parkinson’s and Alzheimer’s), as early evidence suggests that gut changes may be an early symptom of these diseases. Other studies are also investigating whether certain probiotic strains can impact mental health conditions like anxiety or depression, but at the moment the research is still in its infancy."^8,9

Yes, and vice versa. If you live with chronic stress or anxiety you might experience gut symptoms, and having a digestive disorder like IBS or Crohn's may indirectly take a toll on your mental health too.¹⁰

“Gut microbes also produce dopamine and GABA, which are neurotransmitters that regulate mood and motivation,” says Jasmine.^11,12,13 About 90% of serotonin (our ‘happy’ hormone) is made in the gut.¹⁴ Certain gut bacteria have been linked to depression, as suggested in some research where transferring gut bacteria from people with depression to mice made the mice act depressed.¹⁵ This suggests the gut can affect the brain, although scientists are still studying how this works in humans.

As we mentioned, stressful moments can cause temporary changes to your digestion. The 'fight or flight' response may change the speed your gut processes food (motility) and contribute to symptoms such as constipation or diarrhoea.⁴ But if you're living with chronic stress, these changes may last longer. Long-term stress may increase your risk of gastrointestinal disorders and infection and may negatively shift the balance of the gut microbiome.^16,17

You can't support the 'connection' itself, but looking after both your brain and your gut will help them function normally – both together and on their own. You can help look after your gut by:

• eating a diverse range of nutritious foods – you might find a Mediterranean diet useful for this ⁷

• getting plenty of fibre in your diet – the UK government recommends 30g per day ¹⁸

• including fermented foods in your diet, like sauerkraut, kombucha and kefir ⁷

• drinking around six to eight cups of water per day ¹⁹

• limiting foods high in saturated fat, salt and sugar, including some ultra-processed foods ⁷

And you can support your brain by:

• getting seven to nine hours’ sleep each night ²⁰

• maintaining hobbies to keep your brain active – this could be anything from cooking to reading or playing board games with friends ²¹

• regularly getting out in nature ²²

• exercising for roughly 150 minutes each week ^23,24

• managing stress where you can ²⁵

Many of these habits are good for both your brain and gut – for example, some foods in the Mediterranean diet also contain brain-supporting nutrients like omega-3 fatty acids.²⁶

Better digestion isn’t the only reason to support your gut health. Emerging research suggests the gut-brain connection may be linked with mood and stress, while researchers are also exploring its potential role in long-term brain health. Getting on top of any stress may also support our gut health, so remember to take extra care of your digestive health during unavoidable anxious times. But if you have continuous gut issues, it’s important to speak to your GP as well.

Want to learn more about how the gut impacts your body? Discover our guide to the gut-skin connection or learn more about the vagus nerve...

Disclaimer – This article provides informational advice and is not a substitute for medical care. Working with experts for accuracy, we take great care to ensure the information is up-to-date and relevant. However, you should always consult your GP or healthcare professional before using supplements or alternative products, particularly if you have medical conditions or are under supervision.