The gut has the obvious role of digesting food, but it also has many less obvious functions. It has a role in immunity, allergies, the production of neurotransmitters and we now know that there is a direct connection between the gut and our brain.
The Gut-Brain Axis
The gut-brain axis is a two-way communication pathway 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
A good illustration of this is the “butterflies” feeling when you are nervous. Stress or anxiety can often cause digestive issues like constipation of diarrhea, which is a result of the close relationship between 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 sees energy funneled to the muscles and away from the digestive system. This means that food stays in the intestines rather than being digested. This can cause inflammation in the gut which alters the intestinal environment and disrupts the microbiome.3
In turn, this disruption means that all of the really important jobs that gut bacteria perform, are no longer happening as efficiently. Because of the two-way feedback, unfortunately this inflammation and reduced functioning in the gut leads to altered communication with the brain, which can mean more stress and so on. This is a kind of stress-digestion cycle. In fact, people who suffer from irritable bowel syndrome (IBS) are more likely to experience anxiety and depression.4
The good news is that we have lots of ways to help our gut health from generally healthy living, to medication. If you do experience any digestive issues, or depression, anxiety or stress, go and see your GP who can give you an accurate diagnosis and advise you on treatment.
How to improve your gut health
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 like making neurotransmitters, training the immune system and digesting food5, and in return we provide them with food in the form of fibre (also known as prebiotics) from our diet. And to keep the microbiome thriving, you need to feed it well.6 Vegetables, beans and whole grains all have good amounts of fibre in them.
As well as prebiotics, we can also take probiotics either as a ready-made preparation, or from fermented foods. Fermentation produces lactic acid bacteria in foods like yogurt and kefir, which populates the gut when eaten and may have a positive effect on metabolism.7
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.8
Physical activity can improve conditions in the gut so that anti-inflammatory bacteria can thrive.9 Exercise can even effect 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.10 It can also prevent constipation by keeping the muscles in the gut moving food through.11
Written by: Jo Travers, Nutritionist, Registered Dietitian with a First Class BSc (Hons) in Human Nutrition & Dietetics
Last updated: 31 January 2023
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6. Diet rapidly and reproducibly alters the human gut microbiome Lawrence A. David et al Nature volume 505, pages 559–563 (23 January 2014) doi:10.1038/nature12820
7. Fermented kimchi reduces body weight and improves metabolic parameters in overweight and obese patients. Nutr Res. 2011 Jun;31(6):436-43. doi: 10.1016/j.nutres.2011.05.011. https://www.ncbi.nlm.nih.gov/pubmed/21745625
8. Microbial ‘Old Friends’, immunoregulation and stress resilience. Graham A. W. Rook*1, Christopher A. Lowry2 and Charles L. Raison3 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3868387/pdf/eot004.pdf
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10.1155/2017/3831972. 10. Zhou D., Zhang H., Bai Z., Zhang A., Bai F., Luo X., et al. (2015). Exposure to soil, house dust, and decaying plants increases gut microbial diversity and decreases serum IgE levels in BALB/c mice. Environ. Microbiol.
11. Lawrence Leung, MBBChir, FRACGP, FRCGP, Taylor Riutta, MD, Jyoti Kotecha, MPA, MRSC and Walter Rosser, MD, MRCGP, FCFP Chronic Constipation: An Evidence-Based Review. J Am Board Fam Med July-August 2011 vol. 24 no. 4 436-451