Discover how your gut microbiome shapes your mood, immunity and overall health

We’ve always known the gut handles digestion. But science is revealing that your digestive system is far more than a biological food processor – it is the mission control centre for your entire body.

In fact, scientists have begun calling it our “second brain” due to profound influence this internal ecosystem, known as the gut microbiome, wields over our bodily functions.

Deep within you lies a vast internal ecosystem teeming with trillions of microscopic organisms. These microscopic inhabitants in our gut also manufacture vitamins, train our immune system, and send chemical messages that regulate mood.

This universe of bacteria doesn’t just process nutrients; it orchestrates a range of biological processes that impact every facet of your life:

• Energy & Vitality:How refreshed you feel when you wake up.
• Mental Wellbeing:The “gut-brain axis” that regulates your mood and contentment.
• Immune Resilience:Your primary defence for sailing through flu season unscathed.

Our gut also houses nerve cells and produces the same neurotransmitters that regulate happiness and anxiety.

Understanding your gut health is no longer just about avoiding bloating; it’s about mastering your performance, longevity, and health from the inside out.

Mood Regulator

A healthy gut contributes to improved focus, cognitive function and a good mood through its connection with the brain.

This gut-brain axis involves the intricate communication between the digestive system and the central nervous system, which is regulated by hormones like serotonin – about 90% of all our serotonin is produced in our gut (by specialised cells called enterochromaffin cells).

This neurotransmitter acts as a chemical messenger between the gut and the brain, influencing digestion, mood, sleep, and immune function.

As research delves deeper into understanding our guts, we are also discovering direct links between our gut and our mood. What we know now is that a poor diet and an unbalanced microbiome can impact our mood by contributing to conditions like depression and anxiety.

One study¹ showed that poor nutrition may cause us to experience “low mood”, and that improving our diet may help protect mental health.

Healthy eating patterns, like the Mediterranean diet, are associated with better mental health compared to unhealthy ways of eating, such as the modern Western diet. Eating this type of diet was linked to a reduced risk of depression in a major meta-analysis².

The research also affirmed that “western-style” eating – a diet that includes “refined grains, sweets, high-fat dairy products, butter, potatoes and high-fat gravy, and low intakes of fruits and vegetables”, may increase the risk of depression.

Another way the food we eat impacts our mood is its effect on the probiotic bacteria that live in our guts.

Research³ has established a possible link between microbiome diversity and the composition of bacteria in our gut to depression and pinpointed specific probiotic strains that are associated with depressive symptoms.

The researchers explained that these bacteria “are known to be involved in the synthesis of glutamate, butyrate, serotonin and gamma-aminobutyric acid (GABA), which are key neurotransmitters for depression.”

Studies also increasingly link gut inflammation and depression, with a 2020 study⁴ confirming that depression is “a pro-inflammatory state”. Evidence⁵ also links gut barrier leakiness to “negative emotional symptoms reported in mood disorders, possibly through stress‐induced inflammation”.

Stronger Immunity

A healthy gut can bolster our immunity because 70-80% of your immune cells live in your gut⁶, making it a powerful frontline defence against infections.

This powerful connection between gut health and immunity is known as the gut-immune axis and includes physical barriers in the gut lining and chemical signals that regulate immune responses.

For example, the inner lining of the gut acts as a physical barrier, preventing potentially harmful substances, like viruses, bad bacteria, toxins, and undigested food particles from entering the bloodstream.

Specialised immune cells in this lining constantly monitor for threats and help coordinate our body’s immune response through chemical signals.

The probiotics that live in our gut also play a key role in regulating immune responses⁷ as they are involved in the production of white blood cells and cytokines⁸.

These are cell signalling molecules in the immune system that help to reduce inflammation and protect against foreign invaders like viruses and bacteria.

Some probiotic strains, such as Lactobacillus rhamnosus GG (LGG), Lactobacillus reuteri, Bifidobacterium bifidum, and Saccharomyces boulardii, even strengthen the intestinal lining by repairing damage and tightening junctions between cells⁹, which creates a more robust physical barrier.

Better Overall Health

A healthy gut that contains the right balance of probiotic bacteria enhances digestion, helping our bodies break down and absorb the nutrients needed to fuel the natural processes that support our health and various bodily functions.

By facilitating nutrient absorption, a healthy gut helps balance our hormones and ensures we give our skin and hair the nutrients they need.

Studies also show that probiotics can improve insulin sensitivity¹⁰, which makes your body more sensitive to circulating glucose from the carbohydrates we eat. This can boost our energy levels, limit fat storage, and help reduce the risk of developing lifestyle diseases.

The International Society of Sports Nutrition (ISSN) position stand¹¹ on probiotics highlights additional research-backed health benefits, which include normalising age-related declines in testosterone levels and reducing cortisol levels, which can improve our responses to physical or mental stress.

Support Your Gut

The best way to maintain a healthy gut and a balanced microbiome is through a wholesome diet that includes natural sources of probiotics, with support from probiotic supplements, and a lifestyle that supports overall health.

Mediterranean-style eating is generally promoted as the ideal diet for gut health. The diet is rich in natural and minimally processed foods, including vegetables, fruits, whole grains, natural oils, nuts, and fish and seafood, with only modest amounts of meat and dairy.

You can also boost gut health by adding probiotics from natural food sources, especially fibre, plants, and fermented foods. Ideal options include:

• Yoghurt: Look for plain yoghurts that contain live or active cultures.
• Kefir: A drink made by fermenting milk with kefir grains, which are a combination of various strains of beneficial bacteria and yeasts.
• Sauerkraut: Cabbage that undergoes a natural fermentation process. It is rich in lactic acid bacteria.
• Kimchi: A traditional Korean side dish made by fermenting cabbage and radishes that contains beneficial bacteria.
• Miso: A traditional Japanese seasoning made from fermented soybeans, rice, or barley that contains probiotic bacteria.
• Tempeh: An Indonesian fermented soybean product made using a fungus called Rhizopus oligosporus.
• Kombucha: A fermented tea beverage made by fermenting sweetened black or green tea with a symbiotic culture of bacteria and yeast (SCOBY).

Probiotic supplements  are an effective and convenient way to populate your gut with a range of different combinations of bacteria and varying colony-forming unit (CFU) counts to meet your individual gut health needs.

Lifestyle factors like stress and regular exercise also have a profound impact on your gut health and the balance of your microbiome.

For instance, stress can disrupt the balance of gut bacteria (called dysbiosis), reducing the number of beneficial microbes and allowing harmful ones to thrive.

With regard to exercise, moderate, consistent physical activity has been shown to increase microbial diversity, which is a key marker of a healthy gut.

References:

1. Joseph Firth, James E Gangwisch, et al. Food and mood: how do diet and nutrition affect mental wellbeing? BMJ. 2020; 369: m2382. Published online 2020 Jun 29. doi: 10.1136/bmj.m2382.
2. Ye Li, Mei-Rong Lv, et al. Dietary patterns and depression risk: A meta-analysis. Psychiatry Res. 2017 Jul;253:373-382. doi: 10.1016/j.psychres.2017.04.020. Epub 2017 Apr 11.
3. Radjabzadeh, D., Bosch, J.A., Uitterlinden, A.G. et al. Gut microbiome-wide association study of depressive symptoms. Nat Commun 13, 7128 (2022). https://doi.org/10.1038/s41467-022-34502-3
4. Emanuele F Osimo, Toby Pillinger, et al. Inflammatory markers in depression: A meta-analysis of mean differences and variability in 5,166 patients and 5,083 controls. Brain Behav Immun. 2020 Jul;87:901-909. doi: 10.1016/j.bbi.2020.02.010. Epub 2020 Feb 27.
5. Ellen Doney, Alice Cadoret, et al. Inflammation‐driven brain and gut barrier dysfunction in stress and mood disorders. Eur J Neurosci. 2022 May; 55(9-10): 2851–2894. Published online 2021 May 17. doi: 10.1111/ejn.15239.
6. Wiertsema SP, van Bergenhenegouwen J, Garssen J, Knippels LMJ. The Interplay between the Gut Microbiome and the Immune System in the Context of Infectious Diseases throughout Life and the Role of Nutrition in Optimizing Treatment Strategies. Nutrients. 2021 Mar 9;13(3):886. doi: 10.3390/nu13030886. PMID: 33803407; PMCID: PMC8001875.
7. Carolina Maldonado Galdeano; Silvia Inés Cazorla; et al. Beneficial Effects of Probiotic Consumption on the Immune System. Ann Nutr Metab (2019) 74 (2): 115–124.. https://doi.org/10.1159/000496426.
8. Djaldetti M, Bessler H. Probiotic strains modulate cytokine production and the immune interplay between human peripheral blood mononucear cells and colon cancer cells. FEMS Microbiol Lett. 2017 Feb 1;364(3). doi: 10.1093/femsle/fnx014. PMID: 28104778.
9. Xie Z, Zhang G, Liu R, Wang Y, Tsapieva AN, Zhang L, Han J. Heat-Killed Lacticaseibacillus paracasei Repairs Lipopolysaccharide-Induced Intestinal Epithelial Barrier Damage via MLCK/MLC Pathway Activation. Nutrients. 2023 Apr 4;15(7):1758. doi: 10.3390/nu15071758. PMID: 37049598; PMCID: PMC10097264.
10. Salles BIM, Cioffi D, Ferreira SRG. Probiotics supplementation and insulin resistance: a systematic review. Diabetol Metab Syndr. 2020 Nov 11;12(1):98. doi: 10.1186/s13098-020-00603-6. PMID: 33292434; PMCID: PMC7656736.
11. Jäger, R., Mohr, A.E., Carpenter, K.C. et al. International Society of Sports Nutrition Position Stand: Probiotics. J Int Soc Sports Nutr 16, 62 (2019). https://doi.org/10.1186/s12970-019-0329-0.

Author: Pedro van Gaalen

When he’s not writing about sport or health and fitness, Pedro is probably out training for his next marathon or ultra-marathon. He’s worked as a fitness professional and as a marketing and comms expert. He now combines his passions in his role as managing editor at Fitness magazine.