Could Your Vagus Nerve Be The Missing Link For Your Gut Health?
By Dr Marissa Kelaher
Ever wondered why you feel nauseous when you're anxious, or get an upset tummy when stressed?
Are you struggling to figure out what’s triggering off your bloating or reflux, but can’t quite put your finger on the cause?
It could be something that’s never even crossed your mind, but is absolutely key to good gut health: the gut-brain connection, and your vagus nerve.
This complex two-way system plays a vital role in many parts of our wellbeing. It’s involved in digestive function, mental wellbeing, and even immunity. Yet it’s so often overlooked in our journey towards better health.
When it goes wrong, we’ll notice. It’s responsible for many common symptoms people can struggle with, like abdominal pain; feeling like it’s hard to swallow; bloating; indigestion; diarrhoea; and constipation.
It even plays a role in conditions like anxiety, depression, allergies and autoimmune diseases!
So if this sounds like you, read on, as in this blog we’ll take a deep dive into our gut brain connection and the vagus nerve.
— Jump straight to the recommendations
What is the gut-brain connection anyway?
Our gut-brain connection is the intimate and complex link between our digestive system and our nervous system.
It’s is made up of several main parts:
our enteric nervous system or ENS (a dense network of nerve cells that line our gastrointestinal tract).
neurotransmitters produced in our gut (signalling molecules such as serotonin that are sent from our brain to our gut and vice versa)
our gut microbiome (the bacteria that live in our gut and affect our vagus nerve, the general health of our gut, and neurotransmitter production)
our gut immune cells (these line our digestive system and send signals to our brain and the rest of our body, playing an important role in “training” our immune system to work well)
This connection is SO important that it even has a whole medical specialty dedicated to it: neurogastroenterology. This is the science of how our nervous system affects the gut and vice versa.
Why a whole specialty? Our enteric nervous system (ENS) is huge, containing 200 million to 600 million neurons (nerve cells). That’s as many as our spinal cord, and more than any other organ outside our brain!
This is why the scientists will often refer to our ENS as the “second brain”.
Our amazing enteric nervous system
Our ENS is incredibly important for good health, as it’s directly responsible for controlling all the functions of our entire digestive system. It controls
breaking down and absorbing food
secreting digestive enzymes
blood flow and hormone release within our gut
moving food through our digestive tract from one end to the other
It also does this independently, meaning it doesn’t need much input from our central nervous system (brain) to function.
Our ENS isn’t just in charge of our gut health either. It plays a role in other parts of our health too, such as our immune health, mental health and brain health, and is implicated in disorders such as anxiety, depression, and neurodegenerative diseases like Alzheimer’s and Parkinson’s.
This huge intricate nervous system really is an unsung hero in our wellbeing!
Our ENS is one of three key branches of our autonomic nervous system, which controls many vital functions in our body such as breathing, blood pressure, digestion, blood sugar levels, and heart rate. These branches are:
the enteric nervous system (gut nervous system)
the parasympathetic nervous system (PNS) aka our rest, digest and breed system
the sympathetic nervous system (SNS), commonly known as our fight-or-flight response
These branches of our autonomic nervous system constantly communicate with each other. Our ENS receives signals from our brain and other parts of our autonomic nervous system (such as our breathing and heart), as well as from inside our gut (including from our gut bacteria!).
It then sends messages to our gut cells, to tell them to manage the complex process of digestion, as well as sending messages back to our brain keeping it up to date on what’s happening inside our gut.
And as there’s such a close intertwined relationship between our ENS, our PNS and our SNS systems, it’s no wonder our mood, emotions, stress levels, and even past experiences and trauma can have a huge impact on our gut health and gut symptoms.
Why our vagus nerve is at the core of gut health
At the root of all these connections is our vagus nerve - a long nerve that connects our brain to our gut, as well as to our lungs, heart and other organs. It’s the longest single nerve in our body. Its name comes from the Latin word for “wandering”, due to the convoluted path it takes linking so many different areas.
Our vagus nerve is super important. It’s like like a super highway, constantly sending signals back and forth between our digestive system and our brain. It tells your body whether to switch on and digest food, or to switch off and take a break. Our SNS and PNS impact these signals along the way too.
Our ENS is also super smart. It adapts its function constantly depending on our diet; our mood; our stress levels; our emotions; our energy levels; our activity levels; and even our body clock (circadian rhythm)!
It also responds to things like infections, and is responsible for the all-too-familiar symptoms of tummy bugs (vomiting and diarrhoea).
Yet most of this happens outside of our conscious control, so our thoughts, feelings, and even memories, can directly affect our gut without us even being aware of it.
This means stress and an overactive fight-or-flight (sympathetic) nervous system have the potential to play havoc with our gut health too 😯.
Plus it doesn’t stop there!
To make things even more complicated, our ENS makes its own neurotransmitters and hormones. These hormones are serotonin (happy hormones), dopamine (feel-good hormones) and opioids (pain relief). Almost 95% of our body’s serotonin is actually made by our gut!!
These neurotransmitters can travel up our vagus nerve from our gut back to our brain, so the health of our gut (and our gut microbiome) can impact on our mental health and brain health, even affecting our stress levels and mood.
It’s literally got it’s own little ecosystem going on.
How does our gut-brain connection affect our gut health?
So now we’ve explored what the gut-brain connection is, let’s dive deeper into the finer details of how it actually works
Our ENS is responsible for controlling SO MANY functions in our gut, including:
✔️ the integrity (health) of our gut wall (stopping leaky gut)
✔️ secreting digestive enzymes (to help digest and break down food)
✔️ motility of our gut muscles (to move food through our digestive system)
✔️ blood flow and fluid absorption in our gut (keeping our gut tissues healthy and functioning)
✔️ neuroendocrine production (production of compounds like serotonin, opioids, dopamine etc.)
✔️ immune defence (fighting off bugs, and helping to “train” our nervous system to avoid autoimmune diseases and allergies)
✔️ monitoring and regulating acidity levels in the gut (impacting on symptoms like reflux)
✔️ altering the composition and health of our gut microbiome (the bacteria that live in our gut – more on this here)
This means our ENS also plays a key role in many common gut issues such as irritable bowel syndrome (IBS); inflammatory bowel disease (IBD); reflux; indigestion; and even coeliac disease and inflammatory bowel disease (via it’s connection with our immune system).
And it’s why things like vagal tone (how well our vagus nerve is working), and HRV (heart rate variability) are closely linked to our gut health. More on this later.
When we are relaxed, our rest and digest (parasympathetic or PNS) nervous system kicks into gear. It sends signals to our gut via our vagus nerve telling it that it’s safe, and can start digesting food and doing it’s thing. Our digestive system starts to work in a smooth, synchronised manner all the way from our mouth to our anus.
When this is working well it’s like a complex dance. Saliva, enzymes and stomach acid are produced to break down food. Our gut muscles contract to move food through our digestive system. The lining of our intestines is healthy and intact and can absorb just the right amount of nutrients we need (while keeping out bugs and harmful substances). Beneficial neurotransmitters are produced helping us feel happy and content. And our gut microbiome thrives, boosting our gut health and overall wellbeing.
In contrast, when we are stressed, rushing, or feeling unsafe, the opposite occurs. Our sympathetic nervous system (SNS) activates, telling our gut to shut down digestion while our body starts to get ready to flee from a threat (real or perceived).
This means when we eat food in this state, things just don’t work the way they’re meant to. We can still digest it, but this complex dance gets jerky and disjointed, and just doesn’t go so smoothly.
Short term, this is fine. It’s what our body is designed to do, to keep us safe.
But if we’re chronically stressed or busy, or suffering from unresolved trauma and emotions, these stress signals keep on getting sent to our gut. Our SNS stays switched on, and can completely disrupt the normal function of our gut, setting off a damaging chain of events.
Our gut function literally halts in it’s tracks, resulting in reduced digestive enzymes and acid production, and slowed (or sped up) gut muscle contractions. An over-activated SNS can also impact our gut microbiome and gut immune system, increasing the risk of autoimmune diseases and allergies. It sometimes even leads to a condition called “increased intestinal permeabaility” (leaky gut).
Which is not good news for our health...
It’s estimated that 3 in 20 people struggle with symptoms caused by gut-brain interactions. It’s more common in women, as well as in those who experience anxiety or depression.
One of the most common manifestations of an altered gut-brain axis is irritable bowel syndrome (IBS).
In people with IBS, an altered gut-brain response is thought to play a central part in the symptoms people commonly experience, such as bloating and diarrhoea. This explains why stress can be such a common trigger of flare-ups, and also why flareups will often impact on mood symptoms at the same time.
There is also a strong link between IBS and other pain-related disorders (chronic overlapping pain conditions), such as migraines, chronic pain, fibromyalgia/CFS, tension headaches, temporomandibular disorder (TMD), interstitial cystitis, and vulvodynia. Many people experience several of these. Although we don’t fully understand why, an altered gut-brain axis is thought to potentially play a role, along with genetics, environment, and other factors.
Interestingly, research shows that people with IBS tend to have far higher stress hormone levels in response to stressful situations than those without IBS, and these are thought to impact directly on gut symptoms.
Rates of anxiety and depression are also almost twice as high in people with IBS than people without. Alterations in the gut-brain axis are thought to be one underlying mechanism, as well as changes in the gut microbiome.
And it doesn’t just stop at IBS. In another 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 had significantly higher levels of gut wall permeability, just from one bout of public speaking!
Finally, did you know our vagus nerve also sends signals from our gut back to our brain? In animal studies, altering the gut microbiome of mice consistently alters the mice’s mood and mental wellbeing, as well as their stress response (how much cortisol they produce in response to stressful situations). When their vagus nerve is cut, these effects disappear 😳
It is important to note that this response is not under our conscious control. We are not being “overly sensitive”, and its not “all in our heads”. It is a very real, hardwired physiological process, that occurs without us often even being aware of it.
So what can we do to help?
How mind-body practices can heal our body and mind
If you’ve been reading this and wondering what steps you can take to help improve your gut health, this section is for you!
While our gut brain connection is super complex, it responds really well to therapies that aim to “rewire” it when it’s not working so well.
Our vagus nerve is the main player here, because it controls so much of how our gut works, as well as the rest of our body.
When it’s not firing properly and sending the right signals to our gut and body (this is called low vagal tone), it can play havoc with our health - causing not just gut issues, but also symptoms like brain fog, low mood, fatigue, chronic pain and headaches.
Low vagal tone is linked with poorer health in general, including a higher risk of heart disease, cardiac arrythmias, type 2 diabetes, autoimmune disease, and mental illness. In contrast, healthy vagal tone means better emotional regulation, a greater sense of connection and happiness, and better physical health and resilience.
This means improving our vagal tone is a vital part of not just gut health, but overall health and wellbeing!
If you’re interested in finding out what your vagal tone is, you can measure it by measuring your heart rate variability (HRV) with a smart watch or similar device. For more info, check out our article on heart rate variability.
Practices to rewire your vagal nerve, and your gut-brain connection
The coolest thing about our vagus nerve is that even though it’s not something we can consciously control, it’s actually possible to “exercise” it to help it function better, and improve our vagal tone.
This not only improves gut symptoms such as indigestion, bloating, diarrhoea, constipation and reflux; but also improves overall gut health in conditions like inflammatory bowel disease (IBD).
And as an added bonus, improving vagal nerve function helps our mental wellbeing and overall physical health too.
In general, any mind-body strategy that helps to switch on our “rest and digest” nervous system will improve vagal nerve function. This includes practices like yoga, mindfulness, meditation, exercise, diaphragmatic breathing, cold water immersion, physical touch and more.
If you’d like to learn about mind body-strategies in more depth (and how to use them), we explore these in our Take Control of Your Stress course.
Interestingly eating a high-fibre whole food diet rich in plants may improve our vagal tone too, by boosting the health of our gut microbiome!
Here’s a few other examples of just how powerful mind body strategies can be in improving gut health:
Mindfulness: In one study, eight weeks of mindfulness-based stress reduction training (MBSR) resulted in a 70% improvement in IBS symptoms.
Mindfulness based stress reduction: Another randomised controlled trial compared MBSR to an emotional support group, and found eight weeks of MBSR was four times more effective at helping IBS symptoms. This improvement actually increased at the three-month follow-up (it continued to improve even after the MBSR training and support finished).
Gut-directed hypnotherapy: 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 six months later, and people in the hypnotherapy group also scored better in anxiety and depression symptoms. The gut-directed hypnosis program can be accessed via an on-demand app called Nerva.
Cognitive behavioural therapy: Therapies such as cognitive behavioural therapy can also be effective for IBS, consistently reducing symptoms and improving quality of life.
Moderate exercise: Low-to-moderate-intensity exercise can significantly improve constipation-predominant IBS.
Yoga: Yoga has been shown to improve mood and pain in people with IBS, and improve reflux.
Diaphragmatic breathing: This can improve symptoms in many gut disorders, including reflux, pain, bloating and more.
So if you’re struggling to get to the bottom of your gut issues, or just want to improve your overall health, don’t forget your gut-brain axis, and consider trialling some of these strategies today. There’s nothing to lose and you might just have everything to gain!
Dr Marissa Kelaher is an integrative GP, who specialises in taking an evidence-based whole-person approach to health.
She runs virtual clinics New Zealand-wide, as well as workshops; online health courses; and corporate wellbeing packages. Please check out the rest of this website to find out more, and take the first steps towards improving your health today!