Gut-Brain Axis

Did you know that your digestion impacts your mental health?

I know, it sounds wild, but it’s true. In fact, there are many ways in which the gut and brain are connected. It’s a broad and complex topic which is hard to fully encompass, so I’ve chosen a few topics to dive into.

To start off, here’s a few definitions of terms I will be using:

The Gut- Brain Axis

The gut-brain axis (named this to simplify a complex system) describes the ways that the gut communicates with the brain, and conversely, the brain communicates with the gut. This communication occurs through the nervous, endocrine, immune and hormonal systems.

Gut Microbiome

The gut microbiome refers to the collection of microbacteria within the digestive system- a flourishing system of different bacteria that balance our digestive tract. Research shows that our gut microbiome have an impact on almost all aspects of health including our immune system, metabolism, physiology and of course, mental health.

Neurotransmitters

Neurotransmitters are chemicals that provide information to neurons (nervous system cells). They are often referred to as the body’s chemical messengers. They are imperative in regulating our nervous systems. There are three types of neurotransmitters: excitatory, inhibitory, and modulating. Excitatory means that they are actively ‘exciting’ the nerve to transmit a message. Inhibitory neurotransmitters block messages from being passed along. Modulatory neurotransmitters influence the effect of other chemical messengers.

Now that we’ve defined these terms, here’s a few ways in which the gut and brain communicate:

Neurotransmitters- Made in the gut?!

Yes, you read that right. Neurotransmitters are made in the gut- not exclusively, but certainly enough to be significant. For example, over 90% of serotonin is produced by the enterochromaffin cells in the intestine, then transported to the brain for use. Other neurotransmitters are produced in a similar way. This means that the health of the gut microbiome directly affects brain health and mood. Research has linked gut microbiome to anxiety, depression, Alzheimer’s, Parkinson’s, autism, schizophrenia, and more. Specific microbacteria strain imbalances have been linked to different mood disorders as well. GABA, a neurotransmitter which decreases anxiety, is produced by Bacteroides fragilis, Parabacteroides, Eubacterium, and Bifidobacterium. A lack of these bacteria can lead to increased anxiety.

So, how does this affect treatment for mood disorders? Inflammation of the gut through dysbiosis, food sensitivities, celiac disease, frequent antibiotic use and more can all affect the quality of the microbiome. Treating these imbalances can restore a healthy microbiome in order to encourage optimal production of neurotransmitters.

The Vagus Nerve

The vagus nerve is an example of how the brain can directly impact digestion, and therefore the gut. There are entire books about the vagus nerve, so a paragraph will only describe so much- I will do my best to encapsulate the various functions of the vagus nerve.

The vagus nerve is one of the twelve cranial nerves- meaning it runs from the brain to elsewhere in the body. The vagus nerve controls digestion, heart rate, breathing, and more.

When we are about to eat, the vagus nerve stimulates secretion of enzymes throughout our digestive tract to help break down food. The vagus nerve works parasympathetically, meaning it is more active when we are relaxed and at rest. If we are eating while ‘stressed’- eating lunch at our work desk, trying to eat while watching a scary movie, eating as fast as possible to get somewhere else- the vagus nerve won’t be as active. This can lead to digestive upset, indigestion and even chronic digestive problems. Inflammatory bowel disease has been shown to be linked to vagus nerve malfunction. Stimulation of the vagus nerve has been shown to be an effective treatment in inflammatory bowel disease.

Beyond digestive concerns, vagus nerve stimulation has also been shown to be beneficial in treating depression and PTSD.

One of the easiest ways to self-stimulate the vagus nerve is to take a few long, deep breaths before eating. This allows the body to relax, reset and get ready to digest. Meditation and gentle yoga, singing and laughing are also excellent ways to stimulate the vagus nerve.

Probiotics

Probiotics have been studied to be alternative treatments for depression and anxiety. Studies show that a probiotic reduced depressive symptoms as well as common anti-depressants such as Citalopram and Diazepam. Another study looked at anxiety, and showed that probiotics reduced anxiety symptoms as much as Escitalopram, without any weight gain which would be a typical medication side effect. Symptoms of chronic stress have also been alleviated through probiotic supplementation.

Probiotics come up a lot in the media- they are made to seem like the only solution for digestion. While they can be extremely helpful (as discussed above), they are not a solution for every type of digestive difficulty. As well, quality and specific type of probiotic varies between brands, so please consult a naturopathic doctor if you think you want to try a probiotic.

Disclaimer

When discussing mental health, it’s important to remember how many aspects impact mental health: lifestyle, genetics, neurotransmitters, nutrition status, exercise, hydration, and the list goes on. Treating the gut is one option in treating mental health, but all aspects should be addressed. Medication is a great option for many, and treating the gut should not be substituted for medication that is managing mental health effectively. I can and do prescribe medications for mental health, and also offer my patients many other ways in which to support their mental health.

Conclusion

The gut-brain axis is a complex topic. New research is coming out all the time to add to what we already know, and to give new perspectives. I’ve only scratched the surface here, but overall wanted to give a quick glimpse into the world of the gut-brain axis. If you have questions or are interested in learning more about the subject, please contact me. I’ve also listed my references below.

References

Bonaz, B., Bazin, T., & Pellissier, S. (2018). The vagus nerve at the interface of the microbiota-gut-brain axis. Frontiers in neuroscience, 12, 49.

Breit, S., Kupferberg, A., Rogler, G., & Hasler, G. (2018). Vagus nerve as modulator of the brain–gut axis in psychiatric and inflammatory disorders. Frontiers in psychiatry, 44.

Chen, Y., Xu, J., & Chen, Y. (2021). Regulation of neurotransmitters by the gut microbiota and effects on cognition in neurological disorders. Nutrients, 13(6), 2099.

Clapp, M., Aurora, N., Herrera, L., Bhatia, M., Wilen, E., & Wakefield, S. (2017). Gut microbiota’s effect on mental health: The gut-brain axis. Clinics and practice, 7(4), 987.

Cryan, J. F., O'Riordan, K. J., Cowan, C. S., Sandhu, K. V., Bastiaanssen, T. F., Boehme, M., ... & Dinan, T. G. (2019). The microbiota-gut-brain axis. Physiological reviews.

Foster, J. A., & Neufeld, K. A. M. (2013). Gut–brain axis: how the microbiome influences anxiety and depression. Trends in neurosciences, 36(5), 305-312.

Liang, S., Wu, X., & Jin, F. (2018). Gut-brain psychology: rethinking psychology from the microbiota–gut–brain axis. Frontiers in integrative neuroscience, 12, 33.