The Gut-Brain Axis – What’s The Connection?

NeuronThe gut is an area of specialty in my naturopathic practice. Strangely enough (or not), so is the brain & nervous system. Over and over again I see the connection, underlined and in italics so to speak. But what is this connection & how does it work?

It operates on several levels

Have you heard of the enteric nervous system? Lots of people haven’t. It’s part of the autonomic nervous system, receiving information from both sympathetic (fight or flight) & parasympathetic (rest & digest) divisions. It regulates the function of the digestive organs, and it is huge. It operates mainly on it’s own with little intervention from the central nervous system. The gut & enteric nervous system function as a sensory organ which digest & absorb nutrients, but in doing so, they gain information from the food we eat. This information is then used by the body to regulate genetic expression. Research has discovered that about 90% of the fibres in the vagal nerve carry information to the brain, not vice versa (1). For this reason, the gut has earned the title of “the second brain”.

The Microbiome

It’s easy to take our gut bacteria for granted. After all, we can’t see them and what they do for human health can easily go unnoticed – but the bacteria that exist in the digestive tract are an organism unto themselves. There are more than 400 species that live in the gut (weighing up to 1kg),  mainly located in the large intestine (2).They perform various actions that support and assist human survival, including the synthesis of certain nutrients and enzymes that the human body is unable to make for itself.

Gut bacteria assist in the production of neurotransmitters like serotonin and GABA. In fact, somewhere between 80-90% of serotonin produced in the body is made in the gut. (3) In terms of those suffering from depression, anxiety and other mood disorders, the ramifications of a poorly functioning gut are substantial. Co-morbidity for depression and IBS, Crohn’s disease or ulcerative colitis are common, therfore the link between gut and brain health cannot be dismissed.

The multiple bidirectional routes of communication between the brain and the gut ...

(Source: Dinan., G. T et al, 2015.)

Because of their interaction with the nervous system, gut flora have a significant impact on human behaviour and cognitive processes. There is a large body of research which now points to brain & immune development of children being partially dependent on the make-up of their gut bacteria. A newborn’s gut flora is largely determined during birth and early childhood. Researchers theorise that this may provide evidence as to why more Caesarean-born children suffer from allergies, as opposed to those who experience vaginal brith –  they are not exposed to the mother’s flora.(6) By the same token, the development of a healthy microbial population is equally important in supporting behavioural & cognitive development.

Modifying the Microbiome

Clinical studies have proven that probiotic treatment can assist sufferers of gut conditions and mood disorders alike. Microbiome modification is showing huge promise in areas such as treatment-resistant depression, autism, even schizophrenia (4). However, for long-term management of a sustainable microbiome, diet must be addressed. A diet high in processed foods, saturated fats & sugar is more likely to promote imbalances and dysbiosis. A diet high in vegetables, fruit, good quality protein and essential fatty acids promotes a healthy, self-sustaining microbial population.

It is very clear that gut microbiota influence the human body more than ever thought possible. Not only is the brain aware of our internal flora, but these microorganisms have the ability to alter our brain function, mood and behaviour.



(2) Medical Microbiology. 4th edition.  Chapter 95. Microbiology of the Gastrointestinal Tract. Sherwood L. Gorbach.


(4) Tomasik., J et al. (2015). Immunomodulatory Effects of Probiotic Supplementation in Schizophrenia Patients: A Randomized, Placebo-Controlled Trial. Biomark Insights. Jun 1;10:47-54.

(5) Dinan, .T.G et al. (2015) Collective unconscious: How gut microbes shape human behavior. Journal of Psychiatric Research. Volume 63, Pages 1–9

(6)Biasucci., G et al. (2008) Cesarean Delivery May Affect the Early Biodiversity of Intestinal Bacteria. The Journal of Nutrition. vol. 138 no. 9 1796S-1800S


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