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

24 Jan 2024 • 8 min read

The gut-brain axis has gained a lot of popularity lately, from its apparent effects on our mood to our thought patterns and processes. But what is it, and how does it work?

That flutter you get when you’re nervous is more than just a feeling in the pit of your stomach. It's a sign of the fact that our brain and gut are actually inextricably intertwined in ways we still don’t fully understand. Studies have found that an entire communication system exists between the brain and gut, which is commonly referred to as the gut-brain axis.2

In this article, we’re going to look at the gut and brain connection, how it works from our current understanding, why it’s important, and what you can do to influence it.

What is the gut-brain axis?

The gut-brain axis is a two-way communication pathway that exists between the gut and the brain.2 Not only does the brain have a connection to the gut, but the gut has access to the emotional and cognitive centres in the brain too.2

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

What does the gut-brain axis do?

The gut-brain axis is a two-way feedback loop in the body that plays an important role in several digestive, psychiatric, and neurological disorders.2

Responsible for overseeing and bringing together the functions of the gut, gut and brain connection also serves to connect the emotional and cognitive regions of the brain with other intestinal activities. This encompasses mechanisms such as immune activation, intestinal permeability, enteric reflex, and entero-endocrine signalling.3

The effects of the gut microbiome on the brain are complicated and not very well understood. What we do know is that changes in the gut microbiome can change all sorts of things, from feeding habits to our inflammation response, irritable bowel syndrome (IBS) and even anxiety and depression.2

Why is the gut-brain axis important?

Emerging research suggests that the gut-brain axis has so many effects on our health, both mental and physical, so it is really important to take good care of your gut health.

Here are just some of the ways that the gut and brain connection is important: 
  • anxiety and depression – Studies have found that there is a link between our gut health and mental health. Although research into the link between gut health and mood disorders like anxiety and depression is still very early, the results are promising.4
  • IBS – People with IBS are more likely to report being anxious or depressed, and they may also find that stress can cause their symptoms to be more severe.5,6
  • inflammation – Your inflammatory response can also be affected by your gut health.7 We’ve got more information on the link between gut health and inflammation here.

How can we influence how the gut-brain axis 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 (SSRIs) 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. 

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

1. Supporting your gut bacteria

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

Bacteria 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.9

In order to keep the microbiome thriving, you need to feed it well.10

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. We’ve got a full round-up of the best foods for your gut health here.

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 populate the gut when eaten and may have a positive effect on metabolism.11

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.12

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.12

Some scientists believe that the research could one day lead to so-called psychobiotics – medicines based on bacteria – being used as treatments for mood disorders, including depression.13

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 on farms with livestock, for instance.14

Taking a trip to the countryside – as well as having 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.15

4. Being physically active

Physical activity can improve conditions in the gut so that anti-inflammatory bacteria can thrive.16

Exercise could even affect the types of bacteria that thrive in your intestines. Especially if you can combine it with getting into a different environment – running in the woods versus running on a treadmill, for example.17

It can also prevent constipation by making sure the muscles in the gut keep contracting and moving food through.18

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).2

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 some microbiota can improve anxiety-like behaviours and increase the production of dopamine and serotonin, demonstrating the potential role of gut microbiota in mood and behaviour.19 More research is needed in clinical human studies to understand the role of the gut microbiota on mood.

The final say

Research has found, and continues to find, that the brain directly affects 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, eating healthily, and taking good care of your gut, particularly your gut bacteria, has been proven to play an instrumental role in improving overall gut and brain health. If you’re looking to change up your diet, we’re on hand to help.

If you are experiencing uncomfortable symptoms related to your gut health, it is best to speak to your GP. They will be able to offer you tailored advice and support based on your symptoms.

Want to know more about gut health? We’ve got a full guide to the gut microbiome, as well as more information on digestion and a guide to having a happy gut.

Dr Megan Rossi: Eat more for good gut health

Dr Megan Rossi, known as the Gut Health Doctor, is one of the leading experts in the world when it comes to gut health. In this information-packed episode, Megan discusses: 
  • why we should all be eating more plant-based foods for better gut health. 
  • why restrictive diets can be bad for our gut health.
  • recipe inspiration for sneaking and squeezing more plants into our diets.

Disclaimer

 

Sources

1. Konturek PC, Brzozowski T, Konturek SJ. Stress and the gut: pathophysiology, clinical consequences, diagnostic approach and treatment options. J Physiol Pharmacol. 2011. Available at: https://www.jpp.krakow.pl/journal/archive/12_11/pdf/591_12_11_article.pdf?utm_medium=wo&%20utm_source=link&%20utm_campaign=healthy-body/leaky-gut-healing-tips/
2. Bercik P, Collins SM, Verdu EF. Microbes and the gut‐brain axis. Neurogastroenterology & Motility. 2012. Available at: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2982.2012.01906.x
3. Carabotti M, Scirocco A, Maselli MA, Severi C. The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Ann Gastroenterol. 2015. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4367209/
4. Järbrink-Sehgal E, Andreasson A. The gut microbiota and mental health in adults. Current opinion in neurobiology. 2020. Available at: https://www.sciencedirect.com/science/article/pii/S0959438820300362
5. Lee C, Doo E, Choi JM, Jang SH, Ryu HS, Lee JY, Oh JH, Park JH, Kim YS. The increased level of depression and anxiety in irritable bowel syndrome patients compared with healthy controls: systematic review and meta-analysis. Journal of neurogastroenterology and motility. 2017. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5503284/
6. Qin HY, Cheng CW, Tang XD, Bian ZX. Impact of psychological stress on irritable bowel syndrome. World J Gastroenterol. 2014. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4202343/
7. Al Bander Z, Nitert MD, Mousa A, Naderpoor N. The gut microbiota and inflammation: an overview. International journal of environmental research and public health. 2020. Available at: https://www.mdpi.com/1660-4601/17/20/7618
8. Bundeff AW, Woodis CB. Selective Serotonin Reuptake Inhibitors for the Treatment of Irritable Bowel Syndrome. Annals of Pharmacotherapy. 2014. Available at: https://journals.sagepub.com/doi/abs/10.1177/1060028014528151
9. Jandhyala SM, Talukdar R, Subramanyam C, Vuyyuru H, Sasikala M, Reddy DN. Role of the normal gut microbiota. World journal of gastroenterology: WJG. 2015. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4528021/
10. David LA, Maurice CF, Carmody RN, Gootenberg DB, Button JE, Wolfe BE, Ling AV, Devlin AS, Varma Y, Fischbach MA, Biddinger SB. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014. Available at: https://www.nature.com/articles/nature12820
11. Kim EK, An SY, Lee MS, Kim TH, Lee HK, Hwang WS, Choe SJ, Kim TY, Han SJ, Kim HJ, Kim DJ. Fermented kimchi reduces body weight and improves metabolic parameters in overweight and obese patients. Nutrition Research. 2011. Available at: https://www.sciencedirect.com/science/article/abs/pii/S027153171100114X
12. Tillisch K, Labus J, Kilpatrick L, Jiang Z, Stains J, Ebrat B, Guyonnet D, Legrain–Raspaud S, Trotin B, Naliboff B, Mayer EA. Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology. 2013. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0016508513002928
13. Del Toro-Barbosa M, Hurtado-Romero A, Garcia-Amezquita LE, García-Cayuela T. Psychobiotics: mechanisms of action, evaluation methods and effectiveness in applications with food products. Nutrients. 2020. Available at: https://www.mdpi.com/2072-6643/12/12/3896
14. Ruiz-Calderon JF, Cavallin H, Song SJ, Novoselac A, Pericchi LR, Hernandez JN, Rios R, Branch OH, Pereira H, Paulino LC, Blaser MJ. Walls talk: microbial biogeography of homes spanning urbanization. Science advances. 2016. Available at: https://www.science.org/doi/10.1126/sciadv.1501061
15. Rook GA, Lowry CA, Raison CL. Microbial ‘Old Friends’, immunoregulation and stress resilience. Evolution, medicine, and public health. 2013. Available at: https://academic.oup.com/emph/article/2013/1/46/1858882
16. Monda V, Villano I, Messina A, Valenzano A, Esposito T, Moscatelli F, Viggiano A, Cibelli G, Chieffi S, Monda M, Messina G. Exercise modifies the gut microbiota with positive health effects. Oxidative medicine and cellular longevity. 2017. Available at: https://www.hindawi.com/journals/omcl/2017/3831972/
17. Zhou D, Zhang H, Bai Z, Zhang A, Bai F, Luo X, Hou Y, Ding X, Sun B, Sun X, Ma N. Exposure to soil, house dust and decaying plants increases gut microbial diversity and decreases serum immunoglobulin E levels in BALB/c mice. Environmental microbiology. 2016. Available at: https://ami-journals.onlinelibrary.wiley.com/doi/abs/10.1111/1462-2920.12895
18. Leung L, Riutta T, Kotecha J, Rosser W. Chronic constipation: an evidence-based review. The Journal of the American Board of Family Medicine. 2011. Available at: https://www.jabfm.org/content/24/4/436.short
19. Foster JA, Rinaman L, Cryan JF. Stress & the gut-brain axis: regulation by the microbiome. Neurobiology of stress. 2017. Available at: https://www.sciencedirect.com/science/article/pii/S2352289516300509
 
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