Updated: Aug 7
Also check out our blog “Trust Your Gut” which is an introduction to the human microbiome!
Western society has a long history of brushing off mental health issues as “all in your head” - that is both simplistic and offensive. Today, scientists are showing how microbes in our digestive system may have a major influence on our mood, behavior, and emotions - ie. how gut health affects mental health.
GUT HEALTH AND BABIES
Our microbial and neurological development coincide with one another, and scientific evidence suggests that the bacteria in our gut plays a critical role in the development of our Central Nervous System (CNS) (ie. the development of our brain) from the time we are first born!
Bifidobacterium and Lactobacillus bacteria are reported to have a strong influence on the brain-gut axis. They are the most dominant species in the digestive systems of breast-fed infants and absent in that of formula-fed infants. This shows a clear link between gut health and babies.
Interestingly, there have been a few studies that have found breastfeeding to promote healthy brain development. Although these studies are only connected through correlation, it is likely that the beneficial bacteria transferred during breastfeeding plays a role in healthy brain development. - showing that gut health can affect our mental health as young as new-born infants.
Early colonization of the digestive system is also important for the development of our immune system and neuroendocrine systems. Our neuroendocrine system connects our nervous system and our endocrine (aka “hormone”) system.
There is a critical period in which the microbiota (bacteria in our gut) needs to establish themselves for normal development to occur. Factors such as maternal stress, early infection and antibiotics can disrupt the microbiota during this critical juvenile period resulting in irreversible harm to our brain and mind.
To summarize, the bacteria that develops in our gut from the time we are born impacts the development of our immune system, brain development, central nervous system and neuroendocrine system - and that’s just the beginning.
OUR SECOND BRAIN & OUR BRAIN-GUT AXIS
The Enteric Nervous System (ENS) is composed of hundreds of millions of neurons embedded into the lining of the human digestive system. It is known as the “Second Brain” because the ENS can function without direction from the Central Nervous System (CNS) (which is comprised of the brain and spinal cord) - in other words, the ENS can operate independent of the brain.
Between our two brains is a line of communication known as the brain-gut axis:
The gut appears to do most of the talking; 90% of vagal fibres that link the gut and the brain are carrying a message FROM the gut TO the brain.
Serotonin is the key neurotransmitter for facilitating communication along this axis.
The gut is responsible for the production of 90% of the body’s serotonin, and it is believed gut microbiota is highly involved.
WHY IS SEROTONIN IMPORTANT?
Serotonin is known as the "happy chemical". It regulates a huge range of functions including our emotions, mood, social behaviour and sexual desire - just to name a few. People who struggle with depression typically have low levels of serotonin.
Serotonin is important for sleep as well. It impacts our sleep because serotonin is the precursor to melatonin - the hormone which is responsible for your sleep cycle.
Since serotonin is related to so many mental functions, and the gut produces the majority of serotonin in the body - it makes sense that gut health affects mental health! Don't forget, gut health affects sleep too!
OTHER WAYS GUT HEALTH AFFECTS MENTAL HEALTH
There is a strong correlation between the diversity of one’s gut microbiota and an individual's level of conscientiousness or neuroticism.
Antibiotics and stress can disturb the gut microbiota and cause anxious and depressive behavior.
Consuming fermented foods benefits the gut microbiota and has been shown to promote a calm demeanor during emotional tasks.
Our gut microbiota plays an important role in regulating pain perception and influencing pain response:
Following antibiotic treatment or infection (which kills both bad and good bacteria in the body) pain sensitivity increases.
Dysbiosis (ie. an imbalance) of the gut has been linked to stomach aches, migraines, and chronic back pain.
Individuals suffering from chronic fatigue syndrome tend to have an irregular gut microbiota.
Human cognitive abilities, such as learning and memory, have also been linked to the microorganisms in our gut:
Disruptions of the gut microbiota have been shown to damage memory, whereas probiotic consumption has the ability to improve memory.
Certain probiotics have been found to improve some of the above-mentioned symptoms.
Below is a list of microorganisms found in our gut, which metabolite they impact and the effect they have on our body.
MENTAL HEALTH ISSUES AFFECTED BY GUT HEALTH
Many studies today are finding dysbiosis in the gut to be connected to specific neuropsychiatric disorders. The following is a list of mental health issues believed to be affected by gut health.
Obsessive compulsive disorder (OCD)
Post-traumatic stress disorder (PTSD)
Autism spectrum disorder
Attention deficit hyperactivity disorder (ADHD)
Scientists have found many of the symptoms of these conditions to be alleviated by probiotic intervention. The probiotics capable of producing these therapeutic effects are known psychobiotics.
Timothy Dinan and colleagues define psychobiotics as “a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness”
Lactobacillus and Bifidobacterium species are two examples of psychobiotics currently being studied for their potential in mental healthcare. They have been shown to:
Reduce anxiety and depression-like behavior
Improve cognitive function
Restore the abnormalities of the gut microbiota causing symptoms.
As researchers dive further into the study of psychobiotics, the illusion of separation between our mental- and physical-selves has grown ever fainter. Our ever-expanding knowledge of the connection between our gut microbiota and mental health give hope for a world where analysis of our gut microbiome could be harnessed to offer personalized mental health care!
Disclaimer: This article does not provide medical advice around mental health, pre- or postnatal care. If interested in bringing probiotics into your health care regime for specific purposes, speak to your health care provider about what is best for you.
WE WANT TO HEAR FROM YOU!
If you’ve experienced any of the above mental disorders and you found a change in diet - or the addition of probiotics - helped; share your story below! There are so many people out there struggling and searching for answers but not knowing where to begin.
Catharine Paddock, Ph.D. Gut microbes important for serotonin production.(2015). Medical News Today.
Cerdó, T., Ruíz, A., Suárez, A., & Campoy, C. (2017). Probiotic, Prebiotic, and Brain Development. Nutrients, 9(11), 1247. https://doi.org/10.3390/nu9111247
Dinan, T. G., Stanton, C., & Cryan, J. F. (2013). Psychobiotics: A Novel Class of Psychotropic. Biological Psychiatry, 74(10), 720–726. doi: 10.1016/j.biopsych.2013.05.001
Evrensel, A., & Ceylan, M. E. (2015). The Gut-Brain Axis: The Missing Link in Depression. Clinical psychopharmacology and neuroscience : the official scientific journal of the Korean College of Neuropsychopharmacology, 13(3), 239–244. https://doi.org/10.9758/cpn.2015.13.3.239
Frazer A, Hensler JG. Serotonin Involvement in Physiological Function and Behavior. In: Siegel GJ, Agranoff BW, Albers RW, et al., editors. Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition. Philadelphia: Lippincott-Raven; 1999. Available from: https://www.ncbi.nlm.nih.gov/books/NBK27940/
Furness JB, Callaghan BP, Rivera LR, Cho HJ. The enteric nervous system and gastrointestinal innervation: integrated local and central control. Adv Exp Med Biol. 2014;817:39‐71. doi:10.1007/978-1-4939-0897-4_3
Huttenhower, C., Gevers, D., Knight, R. et al. Structure, function and diversity of the healthy human microbiome. Nature 486, 207–214 (2012). https://doi.org/10.1038/nature11234
Huang, T. T., Lai, J. B., Du, Y. L., Xu, Y., Ruan, L. M., & Hu, S. H. (2019). Current Understanding of Gut Microbiota in Mood Disorders: An Update of Human Studies. Frontiers in genetics, 10, 98. https://doi.org/10.3389/fgene.2019.00098
Liang, S., Wu, X., & Jin, F. (2018). Gut-Brain Psychology: Rethinking Psychology From the Microbiota–Gut–Brain Axis. Frontiers in Integrative Neuroscience, 12. doi: 10.3389/fnint.2018.00033
Mishra, A., Singh, S., & Shukla, S. (2018). Physiological and Functional Basis of Dopamine Receptors and Their Role in Neurogenesis: Possible Implication for Parkinson's disease. Journal of experimental neuroscience, 12,, 1179069518779829. https://doi.org/10.1177/1179069518779829
Mittal, R., Debs, L. H., Patel, A. P., Nguyen, D., Patel, K., O'Connor, G., Grati, M., Mittal, J., Yan, D., Eshraghi, A. A., Deo, S. K., Daunert, S., & Liu, X. Z. (2017). Neurotransmitters: The Critical Modulators Regulating Gut-Brain Axis. Journal of cellular physiology, 232(9), 2359–2372. https://doi.org/10.1002/jcp.25518
O'Donnel, J., Zeppenfeld, D., McConnell, E., Pena, S., & Nedergaard, M. (2012). Norepinephrine: a neuromodulator that boosts the function of multiple cell types to optimize CNS performance. Neurochemical research, 37(11), 2496–2512. https://doi.org/10.1007/s11064-012-0818-x
O'Mahony SM, Clarke G, Borre YE, Dinan TG, Cryan JF. Serotonin, tryptophan metabolism and the brain-gut-microbiome axis. Behav Brain Res. 2015;277:32‐48. doi:10.1016/j.bbr.2014.07.027
Rao, M., & Gershon, M. D. (2016). The bowel and beyond: the enteric nervous system in neurological disorders. Nature reviews. Gastroenterology & hepatology, 13(9), 517–528. https://doi.org/10.1038/nrgastro.2016.107
Weintraub, P., Guthrie, C., Hyman, M., & Ohlson, K. (2020, February 21). Your Microbiome: The Ecosystem Inside. Retrieved from
Yano, J. M., Yu, K., Donaldson, G. P., Shastri, G. G., Ann, P., Ma, L., Nagler, C. R., Ismagilov, R. F., Mazmanian, S. K., & Hsiao, E. Y. (2015). Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell, 161(2), 264–276. https://doi.org/10.1016/j.cell.2015.02.047