What is the Gut-Brain Connection?
Liv Salter
Have you ever experienced ‘butterflies’ in your stomach before a big event, lost your appetite when stressed, or had an intuitive ‘hunch’ about someone? These intriguing sensations are all down to a highly sophisticated network called the gut-brain connection.
The gut-brain connection, or gut-brain axis, is a stunningly complex communication highway between your gut and brain. Until recently, scientists believed that only the brain could influence the gut. However, research now suggests the inverse is also true. In other words, your brain can affect your gut just as much as your gut can affect your brain.
In this article, we delve deeper into the gut-brain connection, exploring its effects on mental health and outlining the best dietary changes to support this all-important network.
Understanding the Gut-Brain Connection
The gut-brain axis bridges the central nervous system, encompassing the brain, with the enteric nervous system in the gut – often dubbed the ‘second brain’.
The enteric nervous system contains over 100 million nerve cells, which are divided into the parasympathetic (‘rest and digest’) or sympathetic (‘fight-or-flight’) nervous systems.
The parasympathetic nervous system is active during moments of rest, supporting contractions in the gastrointestinal tract. When stress arises, however, the sympathetic nervous system takes over, suppressing digestion to prioritise survival.
For a happy, balanced gut and brain, we want to be in a predominantly parasympathetic state. This paves the way for a harmonious coexistence between the gut and the brain.
Unfortunately, chronic stress can disrupt this delicate relationship, throwing the gut-brain connection off-kilter and compromising both digestion and mental wellbeing.
How are the Brain and Gut Connected?
The brain and the gut are biochemically and physically tied through the vagus nerve, neurotransmitter production, and the gut microbiome.
The Vagus Nerve
The gut and brain connect via the vagus nerve, a large nerve running from the colon to the amygdala – the region of the brain responsible for processing primal emotions, such as fear and stress (1).
This connection highlights how mind-body practices like diaphragmatic breathing can reduce stress so quickly. Consciously breathing from your diaphragm (stomach) massages the vagus nerve and activates a parasympathetic response, helping the body relax and rebalance.
Neurotransmitters
The gut and brain are also closely intertwined through neurotransmitters, chemical messengers regulating emotions, mood, and digestion.
Studies suggest that gut bacteria are responsible for producing around 95 per cent of serotonin, an important neurotransmitter that influences mood, sleep, and gastrointestinal activity (2).
The Gut Microbiome
The gut microbiome, consisting of trillions of microbes in the digestive tract, shares a significant relationship with the brain (3). When these gut microbes digest fibre, they produce short-chain fatty acids (SCFAs) such as butyrate, propionate, and acetate, which impact brain function (4).
Moreover, the gut microbiome plays a crucial role in regulating inflammation by closely interacting with the immune system. About 70% of the immune system, including the white blood cells responsible for fighting pathogens, is located in the large intestine, where it engages in continuous interaction with gut microbes.
A well-balanced gut microbiome with ‘good’ strains of bacteria can help reduce chronic inflammation, characterised by the overactivity of the immune system (5). However, an imbalance favouring ‘bad’ communities of bacteria could lead to inflammation associated with mood changes and neurodegenerative diseases (6).
How Does the Gut-Brain Connection Affect Mental Health?
Digestive issues, such as bloating, constipation, nausea and abdominal pain, have long been associated with stress and depression (7).
Traditionally, scientists believed mood disturbances contributed to digestive problems, with studies highlighting how mental health conditions like anxiety are associated with increased chronic gut disorders (8).
However, research now suggests poor gut health may also drive psychological changes. Indeed, a recent observational study found people with depression often have depleted levels of Coprococcus and Dialiste, compared with those who reported better emotional health (9).
What is clear is that gastrointestinal stress can be the cause or the result of anxiety, stress, and low mood. And that’s because the gut-brain axis goes both ways.
Improving Gut Health for Better Mental Wellbeing
According to the emerging field of nutritional psychiatry, food can significantly impact the gut-brain axis.
A healthy digestive system should be able to digest food, absorb nutrients, and effectively excrete waste from the body. By maintaining these functions, you can support a happy gut and, consequently, a happy brain.
Here are some basic dietary principles to support and nurture the gut-brain connection.
Eat More Plants
It can be helpful to think of the gut microbiome as your pet. And if you feed and sustain this 'pet', it will feed and sustain you.
Research suggests people who eat a typical Western diet, often laden with ultra-processed foods, refined sugar, and unhealthy fats, have more ‘bad’ bugs in their gut than those who avoid these foods (10).
On the other hand, the Mediterranean diet, which celebrates plants, is often associated with positive health outcomes. Some scientists believe this might be down to positive changes in the gut microbiome (11).
The Smiles Trial is one of the best demonstrations of the power of plant foods, highlighting how a healthy, balanced gut can set the stage for good emotional wellbeing (12).
Researchers recruited participants with low moods and randomly assigned them to either social support or nutritional support for 12 weeks. Those in the nutritional support group were given a predominantly plant-based diet, while the other group received therapeutic support.
Remarkably, more than 30 per cent of those in the nutritional support group experienced positive changes to their wellbeing, compared to 8 per cent of those in the social support group.
This landmark study demonstrated that a plant-focused, whole-food diet can be an effective and accessible way to manage low mood, with the gut-brain axis playing a significant role.
To support the gut-brain connection, the take-home message is choosing plant foods over processed foods.
Diversify Your Diet
And don’t just think plants, think diversity, too. ‘Eating the rainbow’ means getting a range of fibre and polyphenols, which appeal to the varying tastebuds of your gut microbes. Therefore, mixing and matching different plant foods is key.
According to the American Gut Project, individuals who consumed 30 different types of plant foods every week had more diverse gut bacteria, an indicator of better gut health, compared to those who ate ten or fewer plants weekly (13).
While aiming for 30 plant foods may sound challenging, it becomes easier with practice. You can supercharge salads with mixed seeds, spice up dishes with plenty of herbs, and bring yoghurt to life with berries and nuts.
Eat More Fermented Foods
Health experts now believe that incorporating a small amount of fermented foods weekly may further support the gut microbiome and, subsequently, the gut-brain connection.
Historically used for preservation, the fermentation process also enhances the natural, live bacteria found in food, increasing the number and diversity of bacteria in the gut.
A study conducted by researchers at Stanford School of Medicine found that participants who followed a ten-week diet rich in fermented foods experienced improvements in microbiome diversity (14).
Fermented foods include:
Kimchi (fermented cabbage Korean-style)
Kefir (fermented milk)
Sauerkraut (fermented cabbage)
Miso (fermented soybean paste)
Tempeh (fermented soybeans)
Kombucha (fermented tea)
Yoghurt (fermented milk)
Lassi (soured milk)
Sourdough bread (fermented dough)
Some cheeses (aged cheddar, parmesan, and Swiss cheeses)
Feed Your Gut Microbes
Although it’s important to populate your gut with live bacteria, it’s equally important to think about what you feed them. Like us, these bacteria need plenty of nourishment to help them grow big and strong. And this is where special prebiotic plant fibres come in.
Your hungry gut microbes particularly enjoy feasting on the following foods, so try to include more of them in your diet.
Fructooligosaccharides (FOS): asparagus, onions, leeks, garlic, bananas, Jerusalem artichokes, chicory root
Galactooligosaccharides (GOS): legumes like chickpeas and lentils
Inulin: asparagus, onions, leeks, garlic, bananas, Jerusalem artichokes, chicory root
Beta-glucan: some mushrooms, barley, oats, rye, and other whole grains
Consider Fasting
Your dietary choices aren’t the only factors that can shape and improve gut health; when you eat is also a consideration.
Similar to humans, the gut microbiome operates on a circadian rhythm and requires time to rest, especially since a portion of your stomach lining repairs and replaces every night.
However, approximately half of adults in Western countries consume food over a period of 15 hours or longer each day, depriving the gut of essential recuperation.
Recent research suggests that short periods of fasting, also known as time-restricted feeding, could significantly alter the composition of your gut microbiome, improving overall health and, crucially, supporting the gut-brain connection (15).
One of the easiest ways to get started is by having an 8-10 hour eating window that's flexible around your personal and professional commitments. For example, this could involve eating between 9 am and 5 pm or between 12 pm and 8 pm.
Nevertheless, there are some caveats to keep in mind. Firstly, menstruating women should only fast from days 1-19 of their cycle to support progesterone production. Pregnant women, those with a history of disordered eating, or people engaged in intensive training should also avoid fasting.
If you have any questions about fasting, always consult your GP. Our expert Nutrition Advisors may also be able to help.
Add Specific Nutrients
Additionally, incorporating the nutrients below can provide targeted support for gut health, aiding digestion and nurturing the gut-brain connection.
Live cultures
Live cultures are made up of good bacteria that play a vital role in gut health. Aside from increasing fermented foods, taking a live bacteria supplement can support the bustling ecosystem in your gut.
Omega-3 fatty acids
Research suggests the omega-3s found may support the production of short-chain fatty acids, which are beneficial for gut health (16). You can find omega-3 fatty acids in oily fish like salmon, mackerel, and anchovies, as well as plant foods, such as walnuts, chia seeds, and Brussels sprouts. Alternatively, you could take a high-strength supplement or vegan alternative derived from plant-based microalgae.
Peppermint has long been used to support gut health, with research continuing to highlight its soothing and calmative action on the digestive system (17).
A protein found in the stem of fresh pineapples, bromelain is a digestive enzyme known to support digestion and overall gut health.
Stress can impair your body's ability to produce digestive enzymes, leading to nutrient absorption issues. Many people find relief by supplementing with a natural blend of enzymes to support gut health and digestion.
Poor emotional health can also affect hydrochloric acid (HCl) production in the stomach, which may lead to digestive issues and gut dysregulation. HCl creates an acidic environment necessary for the activation of pepsin, an enzyme that aids in protein digestion. It also supports the bacteria in the gut microbiome.
Want to Find Out More?
We’re only beginning to understand the incredible complexity of the gut-brain connection. What is abundantly clear, however, is that making simple tweaks to your diet can improve your gut health, nurture the gut-brain axis, and support your mood.
For more information on gut health, please contact our team of expert Nutrition Advisors, who are on hand to provide free, confidential advice, or head over to Nutrition Buzz.
References
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Yano JM, Yu K, Donaldson GP, Shastri GG, Ann P, Ma L, Nagler CR, Ismagilov RF, Mazmanian SK, Hsiao EY. (2015) Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell. 161(2):264-76.
Clarke G, Stilling RM, Kennedy PJ, Stanton C, Cryan JF, Dinan TG. (2014) Minireview: Gut microbiota: the neglected endocrine organ. Mol Endocrinol. 28(8):1221-38.
Ríos-Covián D, Ruas-Madiedo P, Margolles A, Gueimonde M, de Los Reyes-Gavilán CG, Salazar N. (2016) Intestinal Short Chain Fatty Acids and their Link with Diet and Human Health. Front Microbiol. 7:185.
Lucas SM, Rothwell NJ, Gibson RM. (2006) The role of inflammation in CNS injury and disease. Br J Pharmacol. 147 Suppl 1(Suppl 1):S232-40.
Song, Z., Song, R., Liu, Y., Wu, Z. and Zhang, X. (2023). Effects of ultra-processed foods on the microbiota-gut-brain axis: The bread-and-butter issue. Food Research International. 167, 112730.
Haug TT, Mykletun A, Dahl AA. (2002) Are anxiety and depression related to gastrointestinal symptoms in the general population? Scand J Gastroenterol. 37(3):294-8.
Popa SL, Dumitrascu DL. (2015) Anxiety and IBS revisited: ten years later. Clujul Med. 88(3):253-7.
Valles-Colomer, M., Falony, G., Darzi, Y. et al. (2019) The neuroactive potential of the human gut microbiota in quality of life and depression. Nat Microbiol. 4, 623–632.
Bolte, L., Vich Vila, A., Imhann, F., Collij, V., Peters, V., Fu, J., Kurilshikov, A., Campmans-Kuijpers, M., Dijkstra, G., Wijmenga, C., Zhernakova, A. and Weersma, R. (2021). OP29 Long-term dietary patterns are associated with pro-inflammatory and anti-inflammatory features of the gut microbiome. Journal of Crohn’s and Colitis. 15(Supplement_1), S028-S029.
Wang, D.D., Nguyen, L.H., Li, Y. et al. (2021) The gut microbiome modulates the protective association between a Mediterranean diet and cardiometabolic disease risk. Nat Med. 27, 333–343.
Jacka, F.N., O’Neil, A., Opie, R. et al. (2017) A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Med. 15, 23.
American Gut Project - The Microsetta Initiative. (2021). https://microsetta.ucsd.edu/ about/american-gut-project
A fermented-food diet increases microbiome diversity and lowers inflammation, Stanford study finds. (2021). https://med.stanford.edu/news/all-news/2021/07/fermented-food- diet-increases-microbiome-diversity-lowers-inflammation
Zeb F, Wu X, Chen L, et al. (2020) Effect of time-restricted feeding on metabolic risk and circadian rhythm associated with gut microbiome in healthy males. British Journal of Nutrition. 123(11):1216-1226.
Vijay, A., Astbury, S., Le Roy, C., Spector, T., & Valdes, A. (2020). The prebiotic effects of omega-3 fatty acid supplementation: A six-week randomised intervention trial. Gut Microbes. 13(1), 1863133.
Alammar, N., Wang, L., Saberi, B., Nanavati, J., Holtmann, G., Shinohara, R. T., & Mullin, G. E. (2019). The impact of peppermint oil on the irritable bowel syndrome: a meta-analysis of the pooled clinical data. BMC complementary and alternative medicine. 19(1), 2.
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Posted May 14, 2024
Explore the fascinating connection between gut health and mental health, and learn how your microbiome influences your wellbeing.
