The gut is one of the most exciting new frontiers in mental health. Increasingly, scientific evidence shows the importance of a healthy gut, not only for our immune system, but also for our mental health.
The association between gut health and mental health was first described in 1999 by Dr. Michael Gershon, Professor of Pathology and Cell Biology at Columbia University, who called the gut “the second brain”.
Unfortunately, the link between our gut and our mental health is still highly undervalued by the majority of mainstream medical practitioners. Despite over 50,000 scientific papers written on the link between the gut and the brain, when you see your doctor for anxiety, depression or other mood issues, rarely will he or she prescribe a stool test or probiotics.
We believe that any good psychiatric assessment and diagnosis should include gut testing and repair.
We tend to assume that our brain mostly impacts our gut. While our brain does impact our gut, our gut also has a significant effect on our brain. Indeed, issues with our gut can cause serious disturbances in our brain such as mood swings, depression, anxiety, insomnia, irritability, poor memory and poor concentration and attention.
Most of us are intuitively aware of this gut-brain link. Often, when we are nervous, we may experience butterflies in our stomach, or in times of stress we may suffer from diarrhea or irritable bowel syndrome (IBS).
The link between our gut and our brain, also called the ‘gut-brain axis’ can be described as the connection between our gastrointestinal tract and our nervous system:
- The gut-brain axis controls and monitors gut functions and links the brain’s emotional and cognitive centres (mood, motivation, anxiety, memory, attention, focus) Carabotti, M., Scirocco, A., Maselli, M. A. and Severi C. (2015). The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. [online] Annals of Gastroenterology, 28 (2), pp. 203-9. Available at: https://www.ncbi.nlm.nih.gov/pubmed/25830558 [accessed 14 Dec. 2017].
- Physically, our gut and brain are intricately connected by nerves such as the vagus nerve
- The nervous system in our gut, known as the enteric nervous system (ENS), has its own reflexes and senses, allowing it to control functions independently of our brain
- The ENS contains between 200-600 million neurons, while the brain contains 100 billion neurons Hall, J. (2016). Guyton and Hall Textbook of Medical Physiology. 13th ed. Philadelphia, PA: Elsevier.
- The ENS is part of the stress response of the body through its direct link to the brain
- Most of the neural functions of the gut are focused on digesting food – breaking it down, absorbing nutrients and expelling waste products Hadhazy, A. (2010). Think Twice: How the Gut’s “Second Brain” Influences Mood and Well-Being. [online] Scientific American. Available at: https://www.scientificamerican.com/article/gut-second-brain/ [accessed 14 Dec. 2017].
- The gut is responsible for manufacturing a number of key neurotransmitters such as dopamine and serotonin
- Many neurotransmitters which are present in the brain, for example dopamine and serotonin, are also manufactured in the gut, and bidirectional communication takes place between the two
- 80% of key neurotransmitters for mental health are manufactured in the enteric nervous system (ENS) Amen, D. (2013). Unleash the Power of The Female Brain. New York: Harmony Books, p. 83.
- Serotonin and dopamine present in the ENS help to regulate gut and bowel motility and function
- The microbes in our gut play an important role in the production of serotonin and dopamine in the gut, and a healthy gut biome is crucial to regulating serotonin and dopamine levels Yano, J. M., Yu, K., Donaldson, G. P., Shastri, G. G., Ann, P., Ma, L., Nagler, C. R., Ismagilov, R. F., Mazmanian, S. K. and Hsiao, E. Y. (2015). Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. [online] Cell, 161 (2), pp. 264-76. Available at: https://www.ncbi.nlm.nih.gov/pubmed/25860609 [accessed 14 Dec. 2017].
- Altered levels of serotonin and dopamine in the gut can contribute to diarrhea, constipation and IBS Thijssen, A. Y., Mujagic, Z., Jonkers, D. M., Ludidi, S., Keszthelyi, D., Hesselink, M. A., Clemens, C. H., Conchillo, J. M., Kruimel, J. W. and Masclee, A. A. Alterations in serotonin metabolism in the irritable bowel syndrome. [online] Alimentary Pharmacology & Therapeutics, 43 (2), pp. 272-82. Available at: https://www.ncbi.nlm.nih.gov/m/pubmed/26538292/ [accessed 14 Dec. 2017].
- Medication which affects serotonin levels such as Selective Serotonin Reuptake Inhibitors (SSRIs) may have gastrointestinal upset as a side effect
- Medications which affect dopamine levels such as morphine and antipsychotic drugs can impact motility of the gut and colon
Gut issues which can negatively impact mental health
Causes of gut issues
- Antibiotics are extremely detrimental to healthy gut flora, as they kill not only the bad bacteria, but also the good bacteria, and can cause gut dysbiosis
- The loss of healthy bacteria after a course of antibiotics can have an impact on your brain chemistry, causing mental health issues such as mood swings, depression, anxiety, insomnia, etc. Kharrazian, D. (2013). Why Isn’t My Brain Working? Carlsbad, CA: Elephant Press, p. 173.
- What we eat and how we eat it is essential to our gut health
- A diet high in refined carbohydrates, salts, additives, bad fats can wreak havoc on the gut by causing bacterial dysbiosis and inflammation
- Undiagnosed food intolerances can cause low grade inflammation in the gut, which can then inhibit proper digestion and absorption of key brain nutrients and can be a contributing factor to the development of leaky gut
- Full blown food allergies such as coeliac disease and IgE mediated food allergies can cause inflammation in the gut, as well as affect brain function
- During times of stress, blood is diverted from its “rest and digest” functions, to serve its “fight or flight” purpose, and therefore blood is diverted from the stomach and intestines to the extremities, slowing or even stopping digestion and absorption of nutrients
- Chronic stress can also cause leaky gut and gut dysbiosis
- From our mid-30s onwards, the natural production of stomach acid, essential for digestion and absorption of food and maintaining a healthy microbiome and an optimal PH in the digestive system, starts to diminish
- By the time we are in our late 40s or early 50s, most women and men produce less than half the stomach acid they did in their 20s
- This means an increased risk of bacterial, fungal or parasitical infections and a reduced ability to digest food and absorb nutrients
- While there is some controversy over this hypothesis, the hygiene hypothesis suggests that due to increased hygiene, use of antibiotics and sterile food preparation and reduced exposure to a variety of microorganisms there is reduced gut microbial diversity
- This may contribute to autoimmune diseases and other immune-mediated inflammatory diseases such as depression, Parkinsons, Alzheimer’s, autism
- It is thought that early-life exposure to microorganisms such as bacteria (both harmful and beneficial), fungi and parasites can aid in strengthening our overall immunity to any pathogens later in life and reduces our susceptibility to chronic inflammatory diseases