What is the gut and brain connection?
Most people have had firsthand experience with how the brain communicates with the gut - think butterflies in your tummy when you’re nervous. But the brain-gut connection actually goes both ways. This complex communication system is known as the gut-brain axis and there is increasing evidence that this partnership may have an impact on emotional well-being. Perhaps most interesting of all is that the trillions of inhabitants in the gut, collectively known as the microbiome, appear to play a very important role in brain health and function.
How does the gut-brain axis work?
The gut and brain are connected in several ways, allowing the brain to influence digestive activities and the gut to influence the brain and mental well-being. Physically, the gut and brain are connected through millions of nerves. The biggest and most significant being the vagus nerve. The vagus nerve begins in the brain stem, travels through the neck and the thorax and into the abdomen. It is responsible for carrying signals from the digestive system and other organs to the brain and vice versa. 80% of the nerve signals of the vagus nerve travel from the gut to the brain and only 20% from the brain to the gut.1
Another significant component of the gut-brain relationship is the microbiome. The bacteria in the gut communicate with the brain and affect brain function in a number of ways:
- Via the vagus nerve – Research suggests that gut bacteria can modify the activity of the vagus nerve, which communicates directly with the brain.1
- Through the production of neurotransmitters – Many of the neurotransmitters (chemical messengers) produced in the brain can also be made by the microbes in the gut including serotonin, GABA and dopamine.2 All of which play a vital role in how we think and feel. Interestingly, 90% of the body’s serotonin is made in the gut not the brain,3 a neurotransmitter that affects our mood, sleep, hunger, learning and memory.
- By modifying the stress response – Through the communication with the vagus nerve and neurotransmitter release, gut bacteria can reduce cortisol levels and alter the body’s stress response.4
- Via other indirect mechanisms - Gut microbes play a role in the body’s immune system and inflammatory responses and make other compounds such as short-chain fatty acids, which can impact brain health in various ways.5
What impact does an unhealthy gut microbiome have on the brain and what symptoms could it cause?
When the microbiome is challenged by poor diet, the use of antibiotics or a high stress lifestyle it can lead to imbalance or ‘dysbiosis’. Evidence suggests that gut dysbiosis and a low diversity of bacteria strains can change the stress response and may influence mood.4
On the flipside, taking specific probiotic strains has been shown to improve stress symptoms. For example, lactobacillus plantarum 299v has been shown to alter the body’s stress response by decreasing cortisol levels6 and a multispecies probiotic was shown to buffer against the negative effects stress has on memory and brain function.7 Probiotics show great potential in relieving stress and reducing the risk of stress-related health problems.8
Importance of keeping a healthy gut to support the mind
Considering how closely the gut and brain interact and the influence the gut microbiome has on brain function, it makes sense that supporting a healthy microbiome can help support a healthy mind. The best ways to strengthen your microbiome and improve gut diversity is to eat a varied diet with plenty of fresh fruits and vegetables, consume high fibre prebiotic sources and probiotic-rich fermented foods and take a good quality probiotic supplement with strains that have been tested and researched to support mental well-being and a healthy stress response.
- Bonaz B 2018, ‘The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis’, Front Neurosci, vol 7, no 12, p49, doi:10.3389/fnins.2018.00049
- Strandwitz P 2018, ‘Neurotransmitter modulation by the gut microbiota’. Brain research, 1693, Pt B, pp 128-133, doi:10.1016/j.brainres.2018.03.015
- Yano JM at al 2015, ‘Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis,’ Cell. Vol 161, no 2, pp 264-276, doi:10.1016/j.cell.2015.02.047
- Madison A et al 2019, ‘Stress, depression, diet and the gut microbiota: human-bacteria interactions at the core of psychoneuroimmunology and nutrition’, Curr Opin Behav Sci, vol 28, pp 105–110, doi: 1016/j.cobeha.2019.01.011
- Wang H et al 2016, ‘Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic Review’. J Neurogastroenterol Motil, vol 22, pp589-605, https://doi.org/10.5056/jnm16018?
- Andersson H at al 2016, ‘Oral Administration of Lactobacillus plantarum 299v Reduces Cortisol Levels in Human Saliva during Examination Induced Stress: A Randomized, Double-Blind Controlled Trial’, Int J Microbiol, doi: 10.1155/2016/8469018
- Papalini S et al 2019, ‘Stress matters: Randomized controlled trial on the effect of probiotics on neurocognition’, Neurobiology of stress, vol 10
- Zhang N 2019, ‘Probiotic supplements for relieving stress in healthy participants’, Medicine (Baltimore), vol 98, no 20, e15416, doi: 1097/MD.0000000000015416