This article is the second in a three-part series about your brain and will spotlight the powerful connection between your brain, your gut and your mental health.(If you missed it, go here to read the first post.)

Two brains are better than one

Did you know that you have two brain systems?  Together, your brain and spinal cord is your central nervous system (CNS). You’re likely aware of how it works: Your brain is headquarters. Information passes by nerve signals to and from your brain via your spinal cord. The cord is a column of nerve tissue that runs from the base of your skull down the centre of your back. This cord is protected by three thin membranes and is surrounded by the vertebrae (bones) that make up your spinal column. Spinal cord nerve signals help you move and feel physical sensations. [1]

Your second brain system may be less familiar to you. This information highway travels from your brain to your gut and is known as the enteric nervous system (ENS). The ENS also plays a role in what you’re feeling, but in the case of this brain system, it’s more about your mood.

What is the ENS?

The ENS is part of the autonomic nervous system, which means that it operates mostly without your conscious control. Also known as the “second brain,” the ENS connects the brain and the digestive system through nerves that pass between it and your CNS. The ENS is responsible for digestion of your food from first bite all the way to bathroom, as well as and modulating immune and endocrine (hormone) functions.

Messages travel along the gut-brain axis through your vagus nerve, which is the longest cranial nerve in the body and has been nicknamed the “great wandering protector.” This nerve is crucial for helping to balance body systems including your digestive tract, as well as your cardiovascular, respiratory, immune, and hormone systems.[2]

As much as 80-90% of communication between your brain and your gut starts in your gut rather than the other way around.[3] As you can imagine, this is where things get interesting because a variety of factors influence the messages your gut sends to your brain. For example, naturally occurring bacteria in your gut (collectively known as your microbiome) influence the information that travels along the gut-brain axis.

The microbiome impacts neurons, which regulate both the movement of food through the digestive tract and brain signaling.[4] Studies show that changes in the microbiome impact the signals sent to the brain about hunger and fullness, and could play a role in over-eating.[5] Other research has shown a two-way relationship between weight and mood.[6] This likely isn’t a surprise if you like to turn to comfort foods when you’re stressed.

ENS, hormones and mental health

Your microbiome also produces hundreds of neurochemicals that regulate basic physiological and mental processes including learning, memory and mood. For instance, gut bacteria manufacture about 95% of the body's supply of the “feel good” hormone serotonin. Serotonin influences gastrointestinal tract activity as well as memory, emotion and psychological mood states. In the pineal gland, serotonin is also converted to the “sleep hormone” melatonin.[7] Inadequate serotonin, then, could keep you up at night.

ENS, stress, anxiety and depression

You likely don’t need much convincing that there’s a link between stress and how your gut functions. You might experience insatiable hunger or lose your appetite entirely when you’re stressed. Maybe you get very loose bowels, or very sluggish ones. Digestive disorders like irritable bowel syndrome often have a stress component.

But the gut-mood connection goes beyond digestion. Research has linked instability of the microbiome with increased risk of anxiety or depression,[8] and the relationship is circular.[9] Part of the explanation for this might be that microbe imbalances have a negative impact on levels of brain-derived neurotrophic (BDNF) factor levels.[10] BDNF is critical for your healthy brain function.

Instability in the microbiome can result from a single use of antibiotic medication,[11] drinking chlorinated water,[12] diet composition[13] and factors like carrying excess weight.[14] For many reasons, you want to support a diverse and robust microbiome by eating a variety of foods daily that promote the “good” bacteria in your gut.

You can do this by consuming the bacteria directly in the form of fermented foods or a probiotic supplement, and by providing your existing gut bacteria with the nutrients they prefer so they remain strong and reproduce well.

Feed your microbiome

Dietary fibres are the residuals from carbohydrates in plant foods and fungi that you eat but can’t completely digest. The leftovers that become food for beneficial bacteria are known as prebiotics. Your beneficial gut bacteria convert the dietary fibres to health promoting short-chain fatty acids (SCFA). Be sure to eat a variety of veggies daily to produce a variety of SCFA. If you’re experiencing low mood, however, you might choose to amplify your microbiome strategy.

Fungi factor 

Therapeutic mushrooms including chaga, cordyceps and turkey tail provide an abundance of prebiotic fibres that stimulate SCFA production. Some research suggests that individual mushrooms promote the proliferation of different strains of beneficial bacteria, so a variety may be helpful to build a robust microbiome.[15] Along with nourishing the good bacteria, other functional mushrooms may directly improve mood, too. For example, components in reishi have neurotropic properties, including promoting BDNF to keep your brain vibrant.[16]  

Perhaps the most well-known functional mushroom for mood is lion’s mane. Lion’s mane not only helps to promote recovery of the gut microbiota, but it may help protect the brain from aging. Compounds in lion’s mane mushroom called hericenones and erinacines can easily cross the blood-brain barrier, where they stimulate the creation of nerve growth factors that maintain and organize neurons.¹⁵ Studies also indicate that lion’s mane may support cognition and improvement of anxiety and depression.²⁵

If your mood matters, turn to functional mushrooms for support.

Next time, we’ll explore how the gut-brain axis interacts with the immune system.

REFERENCES

[1] Queensland Brain Institute. University of Queensland. https://qbi.uq.edu.au/brain/brain-anatomy/central-nervous-system-brain-and-spinal-cord

[2] Browning, K., Verheijden, S., & Boeckxstaens, G. (2017). The Vagus Nerve in Appetite Regulation, Mood, and Intestinal Inflammation. Gastroenterology, 152(4), 730–744. https://doi.org/10.1053/j.gastro.2016.10.046

[3] Breit S, Kupferberg A, Rogler G, Hasler G. Vagus Nerve as Modulator of the Brain-Gut Axis in Psychiatric and Inflammatory Disorders. Front Psychiatry. 2018;9:44. Published 2018 Mar 13. doi:10.3389/fpsyt.2018.00044 9

[4] Bastiaanssen, T., Cowan, C., Claesson, M., Dinan, T., & Cryan, J. (2019). Making Sense of … the Microbiome in Psychiatry. The International Journal of Neuropsychopharmacology, 22(1), 37–52. https://doi.org/10.1093/ijnp/pyy067

[5] Sáez-Lara, M. J., Robles-Sanchez, C., Ruiz-Ojeda, F. J., Plaza-Diaz, J., & Gil, A. (2016). Effects of Probiotics and Synbiotics on Obesity, Insulin Resistance Syndrome, Type 2 Diabetes and Non-Alcoholic Fatty Liver Disease: A Review of Human Clinical Trials. International journal of molecular sciences, 17(6), 928. https://doi.org/10.3390/ijms17060928

[6] Talbott, S., Talbott, J., Stephens, B., & Oddou, M. (2020). Modulation of Gut-Brain Axis Improves Microbiome, Metabolism, and Mood. Functional Foods in Health and Disease, 10(1), 37–. https://doi.org/10.31989/ffhd.v10i1.685

[7] Jonnakuty, C., & Gragnoli, C. (2008). What do we know about serotonin? Journal of Cellular Physiology, 217(2), 301–306. https://doi.org/10.1002/jcp.21533

[8] Madison, A., & Kiecolt-Glaser, J. K. (2019). Stress, depression, diet, and the gut microbiota: human–bacteria interactions at the core of psychoneuroimmunology and nutrition. Current Opinion in Behavioral Sciences, 28, 105–110. https://doi.org/10.1016/j.cobeha.2019.01.011

[9] Vigna, L., Morelli, F., Agnelli, G. M., Napolitano, F., Ratto, D., Occhinegro, A., … Rossi, P. (2019). Hericium erinaceus Improves Mood and Sleep Disorders in Patients Affected by Overweight or Obesity: Could Circulating Pro-BDNF and BDNF Be Potential Biomarkers? Evidence-Based Complementary and Alternative Medicine, 2019, 7861297–12. https://doi.org/10.1155/2019/7861297

[10] Maqsood, R., & Stone, T. W. (2016). The Gut-Brain Axis, BDNF, NMDA and CNS Disorders. Neurochemical Research, 41(11), 2819–2835. https://doi.org/10.1007/s11064-016-2039-1

[11] Lurie, I., Yang, Y.-X., Haynes, K., Mamtani, R., & Boursi, B. (2015). Antibiotic exposure and the risk for depression, anxiety, or psychosis: a nested case-control study. The Journal of Clinical Psychiatry, 76(11), 1522–1528. https://doi.org/10.4088/JCP.15m09961

[12] Martino D. The Effects of Chlorinated Drinking Water on the Assembly of the Intestinal Microbiome. Challenges. 2019; 10(1):10. https://doi.org/10.3390/challe10010010

[13] Tidjani Alou, M., Lagier, J.-C., & Raoult, D. (2016). Diet influence on the gut microbiota and dysbiosis related to nutritional disorders. Human Microbiome Journal, 1, 3–11. https://doi.org/10.1016/j.humic.2016.09.001

[14] Vigna, L., Morelli, F., Agnelli, G. M., Napolitano, F., Ratto, D., Occhinegro, A., … Rossi, P. (2019). Hericium erinaceus Improves Mood and Sleep Disorders in Patients Affected by Overweight or Obesity: Could Circulating Pro-BDNF and BDNF Be Potential Biomarkers? Evidence-Based Complementary and Alternative Medicine, 2019, 7861297–12. https://doi.org/10.1155/2019/7861297 

[15] Li, M., Yu, L., Zhao, J., Zhang, H., Chen, W., Zhai, Q., & Tian, F. (2021). Role of dietary edible mushrooms in the modulation of gut microbiota. Journal of Functional Foods, 83, 104538–. https://doi.org/10.1016/j.jff.2021.104538

[16] Ryu, S. H., Hong, S. M., Khan, Z., Lee, S. K., Vishwanath, M., Turk, A., Yeon, S. W., Jo, Y. H., Lee, D. H., Lee, J. K., Hwang, B. Y., Jung, J.-K., Kim, S. Y., & Lee, M. K. (2021). Neurotrophic isoindolinones from the fruiting bodies of Hericium erinaceus. Bioorganic & Medicinal Chemistry Letters, 31, 127714–127714. https://doi.org/10.1016/j.bmcl.2020.127714