How your gut brain connection works, and how to improve it
Did you know your brain affects your gut health, and vice versa?
And that the microbes in your gut can impact on both your stress levels and brain health?
Our enteric nervous system (ENS) is our guts very own nervous system that wraps around our intestinal walls - it has more nerve cells than any other organ in our body apart from our brain!
And our gut brain axis is the missing link that connects our mind and digestive system, it consists of:
✔️the vagus nerve ( nerve connecting our ENS and our brain)
✔️neurotransmitters (chemicals that are sent along our vagus nerve from brain to gut and vice versa)
✔️the bacteria that live in our gut and affect both our vagus nerve and neurotransmitters, as well as the general health of our gut
Our brain affects our gut by sending signals to it through the vagus nerve, which control digestive function
This includes gut muscle activity (peristalsis), and digestive enzyme secretion - having a huge impact on how well we can digest food, and how well our bowels work. It's not the only factor (as food, activity, medication, illness, and even lack of sleep also play a role), but it's hugely important
What many people don't realise however, is that stress signals can also go through vagus nerve and alter our gut function.
When we are stressed, our gut literally stops- causing poor digestion, slowed gut muscle contractions, reduced digestive enzymes and even altering our gut microbiome and increased intestinal permeability (leaky gut). This can cause symptoms such as reflux, bloating, cramps, diarrhoea or constipation. It can also alter the immune function of our gut, contributing to food allergies, eczema, asthma, autoimmune disease, and even inflammatory bowel disease (IBD)
Our sympathetic nervous system (fight or flight) is designed to help us escape threats - and digestion isn't a priority!!
In people with Irritable Bowel Syndrome and Crohns disease, reduced vagal nerve tone is thought to play a central part in the symptoms associated with these, and research shows there is very strong link between stress levels and gut symptoms. Even food allergies, stomach ulcers, and reflux can be caused or exacerbated by stress!
✔️In one interesting study, gut wall permeability (leaky gut) was studied before and after people had to give a public speech. People who had higher stress hormone levels (cortisol), had significantly higher levels of gut wall permeability, just from one bout of public speaking!
✔️The vagus nerve may also send signals from the gut back to the brain as well - in mouse studies, a probiotic supplement given to the mice reduced how many stress hormones they produced in response to stressful situations, however when their vagus nerve was cut, this effect disappeared 😳
Vagus nerve stimulation may help improve symptoms of gut diseases such as IBS and IBD, and strategies to improve vagal tone (diaphragmatic breathing, meditation, yoga) can help gut issues such as indigestion, bloating, diarrhoea, constipation, IBD, and IBS. Diaphragmatic breathing may even help reflux, although this thought to be more due to improving muscle tone in the diaphragm
Our brain also sends neurotransmitters to our gut, which have an impact on gut function
Serotonin (happy hormone) is one of the main ones - 95% of the body's serotonin is released in our gut, through intestinal cells! These cells are immune cells, nerve cells or neurons, and enterochromaffin (EC) cells.
This is influenced by our gut microbiome as well as diet and other factors.
✔️One mouse study even showed that our gut bacteria could influence up to 60% of the serotonin production by EC cells! And other research shows our gut bacteria may even produce their own serotonin….
✔️In other mouse studies, altering the gut microbiome changed the levels of happy hormones (serotonin) and stress hormones (cortisol) in the bloodstream, indicating that our gut microbiome plays a key role in regulating this.
Gut produced serotonin affects gut muscle function, digestion, and pain, and many of the symptoms of IBS are thought to be due to altered serotonin levels - helping explain the connection between IBS and depression /anxiety/stress. Low serotonin is linked to mood disorders, and commonly used anti-depressants (SSRI drugs) work by increasing serotonin levels in our body.
Although the serotonin produced in our gut can't get into the brain (due to a barrier called the blood brain barrier that protects our brain), it's thought that it may travel back up the vagus nerve to impact on mental health - there are many studies currently looking at psychobiotics - whether specific probiotics can improve mental health symptoms - it's an exciting space to watch!
Alongside higher rates of anxiety and depression, people with IBS can also have an elevated response to stress - in one study cortisol levels were far higher in IBS patients than in people without IBS when the same stress occurred in both groups - suggesting people with IBS may have a greater reaction to stressful events (for various reasons, including genetics, environment, past experiences, and other health issues), which then impacts on gut symptoms.
People with IBS are also known to have increased sensitivity to gut stimuli, meaning they experience more bloating, discomfort, and altered bowel habits (diarrhoea/constipation), than people without IBS.
It is important to note that this response is not under our conscious control - ie we are not being ‘overly sensitive’, and its not ‘all in our heads’ - it is a very real physiological process that occurs without us often even being aware of it.
But given these studies, it also makes complete sense that trials looking specifically at stress reduction practices show marked improvement in IBS symptoms, as MBSR helps to ‘down-regulate’ our stress response ie the amount of stress we experience in a certain situation.
✔️In one study, 8 weeks of mindfulness based stress reduction training (MBSR) resulted in a 70% improvement in IBS symptoms.
✔️And another randomised controlled trial (RCT) compared MBSR to an emotional support group, and found 8 weeks of MBSR was 4x more effective at helping IBS symptoms, and this improvement actually increased at 3 month followup (ie it continued to improve even after the MBSR training and support finished)
✔️One further study looked at the effect of gut directed hypnotherapy on IBS, and compared this to a low FODMAP diet (a specific diet often used for IBS that excludes foods that commonly cause bloating). It found that both treatments had a found a 70% improvement in symptoms, but that the hypnotherapy group had this WITHOUT having to have any dietary restrictions! Symptoms were still improved 6 months later, and people in the hypnotherapy group also scored better in anxiety and depression symptoms
As low FODMAP diets are highly restrictive, and hard to maintain longterm, this study was super exciting to see
So while we're still learning more about how the gut brain connection works all the time, starting to use some of these strategies in your life if you're struggling with gut issues is a great idea - as they have the potential to make a massive difference 💙
https://pubmed.ncbi.nlm.nih.gov/32266762/
https://pubmed.ncbi.nlm.nih.gov/21691341/
https://pubmed.ncbi.nlm.nih.gov/27397586/
https://www.sciencedirect.com/science/article/pii/S0092867415002482