If you’ve ever had a “gut feeling” about something or symptoms in your stomach when you’re feeling nervous, you’re likely getting messages from your body’s second brain, the gut. Your gut and the brain in your head are inextricably linked, via a sophisticated communication system known as the gut-brain axis. And just like your brain, the well-being of your gut can significantly impact your mood and the way you think.
What is the gut-brain axis?
The gut-brain axis refers to the bidirectional communication system that connects your gut and brain. These organs talk to one another in different ways:
How does the gut influence mental and emotional well-being?
Given how closely the brain and gut interact, it is no wonder the health of the gut has a ripple effect on our state of mind. There are several mechanisms by which the gut influences mental and emotional well-being, mostly thanks to gut microbes:
Neurotransmitter production – as discussed above, many of the neurotransmitters produced in the brain can also be produced by gut microbes, which may have a direct effect on mental and emotional wellbeing. In fact, 90% of serotonin (the mood stabiliser) is produced in the gut, not the brain3.
Altering the body’s stress response – Certain gut microbes, including Lactobacillus plantarum 299v, have been shown to alter the body’s stress response by decreasing cortisol levels, which can have a positive effect on our mental well-being and emotions4.
- Other mechanisms – Gut microbes make other chemicals that can affect how the brain works including short-chain fatty acids. They also influence the immune system and inflammation, which can have an indirect effect on mental well-being and brain function5.
Why is our mental focus, recall and clarity affected in times of stress and how can we support it?
When we’re under stress, the body goes into ‘fight or flight survival mode. The body’s stress response involves a coordinated cascade of hormones, like cortisol and adrenaline, and physiological changes designed to make the body alert and ready to face what it deems a “threat”. This could be everyday hassles like a looming deadline or being attacked by a dog. The body treats them the same.
Your heartbeat quickens and blood rushes to your muscles and other vital organs that it needs in an emergency. Less important body processes like digestion slow down and the brain changes how it processes information. Parts of the brain that govern memory and higher-order tasks are given less energy to get their jobs done. When you experience a lot of stress or it becomes chronic, the effects of cortisol and other stress hormones continue long after the stressor has gone. This is why you might feel more forgetful and frazzled when you’re stressed out. Interestingly, specific probiotic strains have been shown to buffer against the detrimental effects of stress on memory and cognition6.
1 Bonaz B, Bazin T, Pellissier S. The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis. Front Neurosci. 2018 Feb 7;12:49. doi:10.3389/fnins.2018.00049. eCollection 2018. Review. PubMed PMID: 29467611; PubMedCentral PMCID: PMC5808284.
2 Strandwitz, Philip. “Neurotransmitter modulation by the gut microbiota.” Brain research vol. 1693,Pt B (2018): 128-133. doi:10.1016/j.brainres.2018.03.015
3 Yano JM, Yu K, Donaldson GP, et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis [published correction appears in Cell. 2015 Sep 24;163:258]. Cell. 2015;161(2):264-276. doi:10.1016/j.cell.2015.02.047
4 Andersson H, Tullberg C, Ahrné S, Hamberg K, Lazou Ahrén I, Molin G, Sonesson M, Håkansson Å. 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. 2016;2016:8469018. doi: 10.1155/2016/8469018. Epub 2016 Dec 22. PMID: 28101105; PMCID: PMC5217173
5 Wang H, Lee I, Braun C, Enck P. Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic Review. J Neurogastroenterol Motil 2016;22:589-605. https://doi.org/10.5056/jnm16018
6 Papalini S et al. “Stress matters: Randomized controlled trial on the effect of probiotics on neurocognition.” Neurobiol Stress. 2018;10:100141.