Gut Brain Axis – How is the gut connected to the brain in the first place?
The gut-brain axis is used to describe the system of connection between the gut and brain. This connection is made through several different and complex ways, both physically and chemically.
1. The Vagus Nerve
The 100 billion of neuron cells in the brain are connected to the 500 million neurons in the gut, via nerves in the nervous system. The Vagus Nerve is the longest nerve in the body’s autonomic nervous system that runs from the brain stems, branching out and reaching to the gut. It allows signals to be sent in both directions, therefore, the Vagus Nerve is the main and physical communication pathway for these two organs.
To break it down even further, Neurotransmitters shows a way of chemical connection between the gut and the brain. These neurotransmitters are chemical substances that send signals between neurons to transmit information throughout the brain and body. Our body rely heavily on the communication of neurotransmitters to function, they are responsible for the proper functioning of your heart, lungs, and stomach. Also, affecting things such as sleep, moods, and feelings. Serotonin is one of the many and most important type of neurotransmitters, regulating appetite, sleep, anxiety, sexuality, temperature, muscle contraction and function (The Chalkboard, 2020). It’s even considered as a natural mood stabilizer, according to the Healthline Media by Robertson (2020). Most importantly, up to ninety percent of these serotonin is entirely produced in the gut! Suggesting how connected your gut health is to the health of your brain.
However, all these different pathways of connection and overall gut-health have been shown to be influenced by the gut microbiomes.
Microbes are essentially bacteria, fungi, viruses and archaea. The gut microbiome is the collective community of these microbes, found in your gastrointestinal track. Good bacteria help to extract nutrients from food intakes, improve immune function of the body and protect intestinal walls. Studies of the gut-brain-microbiome axis have been only recent, many questions regarding the relationship between gut bacteria and brain function are still left uncovered. This recent research does maintain that gut bacteria are indeed extremely important to our health. They found correlations between imbalances in the microbiome with certain diseases (diabetes, heart disease and obesity) and to mental health conditions like depression and anxiety.
Furthermore, microbiomes can be shown to influence the above gut-brain connection of the Vagus Nerve and Neurotransmitters. Despite not being in direct contact with the gut microbes, terminals of the Vagus Nerve do sense the microbial compounds that interact with cells of the intestinal walls where these terminals are scattered (Adães, 2019). Adães also specified that the microbial compounds that interact with the walls convey information to and from the microbiomes. Similarly, microbes affect neurotransmitters as they maintain our gut health and help cells to produce many of these chemical messengers – as previously mentioned, the large proportion of serotonin. Individually, microbes also produce a neurotransmitter called gamma-aminobutyric acid (GABA) which helps to control feelings of fear and anxiety (Robertson, 2020). This is why eating probiotic rich foods like yoghurt, kombucha and kimchi is considered to be good for you. These foods naturally contain good levels of probiotics which is the good bacteria we have been talking about.
An example on gut-bacteria impacting mental health is the UCLA study that investigated whether the consumption of fermented milk products with probiotics (FMPP) would alter any function of the brain. The study randomly assigned a fermented milk product (yoghurt), a non-fermented milk product, or a no intervention category, to each of the three groups of healthy women with no gastrointestinal or psychiatric symptoms. The two groups assigned with an intervention consumed the products twice daily for 4 weeks. All participants’ brain images were collected before the 4 weeks so researchers can compare them to the images taken after the intervention, where these participants were tested in response to an emotional task. This is further explained in an article of Psychology Today by professor Azab (n.d). She describes that the group of women who consumed fermented milk had calmer brains during the emotional task, whereas, the no-intervention (no yogurt or milk product) group showed the opposite trend and had more brain hyperactivity during the emotional task. Note that this is just one in many other experiments that justify and strengthens the link of gut-bacteria to mental health. Azab also added that as the knowledge of the exact nature behind this brain-gut interaction unfolds, specifically in relation to mental health, treatments for psychiatric disorders may include probiotic instead of Prozac.
What are your thoughts on gut-bacteria affecting mental health? And if there’s any important information you’ve learnt from this article, it’s to tend to your gut-bacteria and keep your gut health in check!
Adães Sara (2019). What is the gut-brain axis? An Explanation of The Communication Pathways Between the Brain, The Gut, And The Microbiota. Neurohacker Collective. [Accessed 24 Jan 2021]. Available at:
Authors of The Chalkboard (n.d.). Here’s How Your Gut Microbiome Actually Affects Your Brain. The Chalkboard. [Accessed 24 Jan 2021]. Available at:
Authors of The University of Queensland (n.d.). What are neurotransmitters?. The University of Queensland. [ Accessed 24 Jan 2021]. Availlable at:
Azab Marwa (2019). Gut Bacteria Can Influence Your Mood, Thoughts, and Brain. Psychology Today. [Accessed 24 Jan 2021] Available at:
Oord V. Geraldine (2019). The Gut-Brain Axis Explained in Plain English. Diet v.s. Disease. [Accessed 24 Jan 2021]. Available at:
Robertson Ruairi (2020). The Gut-Brain Connection: How it Works and The Role of Nutrition. Healthline Media. [Accessed 24 Jan 2021] Available at:
Scaccia Annamarya (2020). Serotonin: What You Need to Know. Healthline Media. [Accessed 24 Jan 2021]. Available at:
Tillisch K., Labus J., Kilpatrick L., Jiang Z., Stains J., Ebrat B., Guyonnet D., Legrain-Raspaud S., Trotin B., Naliboff B., Mayer A E., (2013). Consumption of fermented milk product with probiotic modulates brain activity. National Library of Medicine. [Accessed 24 Jan 2021]. Available at:
Features image retrieved from:
Protecting Probiotic Bacteria From The Stomach | Asian Scientist Magazine