THE GUT BRAIN CONNECTION AND THE VAGUS NERVE
Edited September 13th, 2020 by Caroline Sabbah
How Are the Gut and Brain Connected Exactly?
You’ve probably heard of the gut and brain connection by now and might be wondering how they are connected.
First, the gut-brain axis is the term used for the communication network that connects your gut and brain (1, 2, 3).
These two organs are connected both physically and biochemically in a number of different ways but here we will look at the vagus nerve and nervous system. (4)
What Is The Vagus Nerve?
Neurons are cells found in your brain and central nervous system that tell your body how to behave. There are approximately 100 billion neurons in the human brain (5). Interestingly, your gut contains 500 million neurons, which are connected to your brain through nerves in your nervous system (6). The vagus nerve is the only nerve that originates from the brain stem and runs through the entire body, connecting your gut and brain and sends signals in both directions (7,8).
You’re probably already familiar with the branches of the Autonomous Nervous System the Sympathetic and Para-Sympathetic Systems commonly referred to as the Fight or Flight and Rest and Digest response. Now here’s interesting part, the vast majority of the rest and digest system runs through the vagus nerve.
It’s also responsible for regulating the heart, lungs, muscles of the throat and airways, liver, stomach, gallbladder, spleen, kidney, small intestine and part of the large intestine.
It is the most important communication pathway regarding digestion, nutrient status and with your microbiota and yet we know so little. But this is starting to change after a 2018 study on the benefits on your health was published in the Journal of Clinical Medicine (9).
What is even more interesting is that chronic inflammation may very well be the most common and obvious sign of an ineffective signaling from the vagus nerve. That’s where vagus nerve activation can become so beneficial in managing inflammation (10).
While it’s not the “root cause” of the inflammation, it’s an important factor to take into consideration to help reduce the inflammatory signals. Managing the inflammatory system is one of its most important functions. We will look into the role of the gut microbiota with respect to inflammation a little later on.
The vagus nerve is responsible for digestive sequencing and signalling to your digestive organs to release the digestive juices and the dysfunctional digestive rhythm is directly correlated to vagus nerve dysfunction. Another reason why I think we should start looking into the vagus nerve more closely. For example, in animal studies, stress inhibits the signals sent through the vagus nerve and also causes gastrointestinal problems (11). Similarly, one study in humans found that people with irritable bowel syndrome (IBS) or Crohn’s disease had reduced vagal tone, indicating a reduced function of the vagus nerve (12). An interesting study in mice found that feeding them a probiotic reduced the amount of stress hormone in their blood. However, when their vagus nerve was cut, the probiotic had no effect (13).
What Is The Microbiome/ Gut Microbiota?
This is where I tell you that you have more bacteria than human cells in our entire body. That you are more bacteria than you are you. That we are sharing our body with 100 trillion bacteria (possibly more) and well over 500 bacterial species compared with the 40 to 60 trillion human cells that make up our body. There are even some estimates that state there are 10 times more bacterial cells living in and on us than there are human cells in our bodies. Interestingly, there are 150 times as many genes in our microbiomes than there are in the human genome.
We are barely starting to understand the pivotal role of the microbiome on our gastro intestinal function, our metabolism, our brain function, our nervous system and our immune system.
They work much like an organ and act as a major part of our immune system. In fact, our microbiome represents more than 75% of our immune function. They play an important role in inflammation.
We live in symbiosis with theses bacterial communities (microbiota) and when they become out of balance between the good and the bad (they’re talking about a ratio of 85-15), disease results. This community of bacteria, this microbiome, works in synergie with our human selves, they live in your digestive tract but also on your skin, in your nose, eyes, breast, lungs, blood and mouth.
Although we are still unclear about how the vagus nerve communicates with the microbiome, there is much research to show that many of the effects of the gut microbiota on brain function are highly dependent on vagus nerve activation and its signaling (9, 10).
It is clear that the makeup of your gut microbiome has very specific effects on not simply gut function but also on the nerves that signal within the enteric nervous system and along the vagus nerve itself. Balancing the microbial population in your gut is one of the major steps you can take to ensure that the gut is functioning optimally and that vagus nerve signaling is working as it should be.
Are you starting to see how the gut microbiota together with the vagus nerve play an important role in inflammation, gut and brain health?
Neurotransmitters In the Gut
Your gut and brain are also connected through neurotransmitters. Neurotransmitters produced in the brain control feelings and emotions. For example, the neurotransmitter serotonin contributes to feelings of happiness and also helps control your body clock (14). Interestingly, many of these neurotransmitters are also produced by your gut cells and microbiota. A large proportion of serotonin estimated as up to 90% is produced in the gut (15).
They also produce a neurotransmitter called gamma-aminobutyric acid (GABA), which helps control feelings of fear and anxiety (16). Studies in laboratory mice have shown that certain probiotics (lactobacillus rhamnosus) can increase the production of GABA and reduce anxiety and depression-like behavior (17).
How Gut Microbiota Make Other Chemicals That Impact the Brain
The trillions of microbes that live in your gut also make other chemicals that can impact how your brain works (18). The byproducts of bacterial metabolism include very important and nourishing molecules called short-chain fatty acids (SCFAs), such as butyrate, propionate and acetate, which are important in reducing the amount of inflammation in the gut and throughout the body (19, 20).
Butyrate is the most-researched SCFA that has shown to be lacking in those with high levels of inflammation. Butyrate, and the microbes that produce it are also important for forming the barrier between the brain and the blood, which is called the blood-brain barrier (18).
How Your Gut Microbiota Affect Inflammation
Your gut-brain axis is also connected through the immune system. The gut and gut microbiota play an important role in your immune system and inflammation by controlling what is passed into the body and what is excreted (21,22). It is your first line of defence and contact to the exterior world.
If your immune system is switched on for too long, it can lead to inflammation, which is associated with a number of brain disorders like depression and Alzheimer’s disease (23).
Lipopolysaccharide (LPS) is an inflammatory toxin made by certain bacteria. It can cause inflammation if too much of it passes from the gut into the blood. This can happen when the gut barrier becomes permeable, which allows bacteria and LPS to cross over into the blood. Inflammation and high LPS in the blood have been associated with a number of brain disorders including severe depression, dementia and schizophrenia (24).
What Foods Help the Gut-Brain Axis?
Gut bacteria affect brain health, so changing your gut bacteria may improve your brain health. Here are a few groups of foods are specifically beneficial for the gut-brain axis.
Here are some of the most important ones:
Omega-3 fats: These healthy fats are found in oily fish and also in high quantities in the human brain. Studies in humans and animals show that Omega 3’s can increase good bacteria in the gut and reduce risk of brain disorders (25,26)
Fermented foods: Yogurt, kefir and sauerkraut all contain healthy microbes such as lactic acid bacteria. Fermented foods have been shown to alter brain activity (27, 28).
High-fiber foods: Whole grains, nuts, seeds, fruits and vegetables all contain prebiotic fibers that are good for your gut bacteria. Prebiotics can reduce stress hormone in humans (28,29).
Polyphenol-rich foods: Cocoa, green tea, olive oil and coffee all contain polyphenols, which are plant chemicals that are digested by your gut bacteria. Polyphenols increase healthy gut bacteria and may improve cognition (30,31,32).
Choline rich foods: when looking to increase specifically vagus nerve function- food that contain nutrients to the production of Ach (antinflammatory messenger) are essential. Acetylcholine is a major neurotransmitter used by the vagus nerve– egg yolks are a great source of choline or high quality organ meats.
In summary, Omega-3 fatty acids, fermented foods, probiotics and other polyphenol-rich foods may improve your gut health, which may benefit the gut-brain axis. Now, you’ve surely connected the importance of diet to a healthy microbiome and are probably wondering how can you improve your vagal tone to further support the gut-brain axis and manage inflammation.
How Can You Activate Your Vagus Nerve?
You can enjoy the benefits of vagus nerve stimulation naturally by following these steps (33).
1. Cold Exposure
Acute cold exposure has been shown to activate the vagus nerve and activate cholinergic neurons through vagus nerve pathways (34). Researchers have also found that exposing yourself to cold on a regular basis can lower your sympathetic “fight or flight” response and increase parasympathetic activity through the vagus nerve (35).
Try finishing your next shower with at least 30 seconds of cold water and see how you feel. Then work your way up to longer periods of time or splash some cold water on your face to ease into it.
2. Deep and Slow Breathing
Deep and slow diaphragmatic breathing is another way to stimulate your vagus nerve. It’s been shown to reduce anxiety and increase the parasympathetic system by activating the vagus nerve (36, 37). You should breathe in deeply from your nose into your diaphragm. Begin by trying with a count of 5 to 7. When you do this, your belly should expand outward. Then hold you breath for a count of 2 to 3. Then exhale through the mouth for a count of 6 to 8, it should be long and slow, allowing your belly to fall. Then you can hold for a count of 1 or 2. Repeat 4 or 6 times. This is key to stimulating the vagus nerve and reaching a state of relaxation.
3. Singing, Humming, Chanting and Gargling
The vagus nerve is connected to your vocal cords and the muscles at the back of your throat. Singing, humming, chanting and gargling can activate the larynx and pharynx and stimulate your vagus nerve. And this has been shown to increase heart-rate variability and vagal tone (38). Gargling is another way discussed more in Dr. Datis Kharrazian’s book, Why Isn’t My Brain Working?
4. Yoga
Yoga is a “mind-body” activity that works by stimulating the vagus nerve and increasing the activity of your parasympathetic “rest and digest” nervous system (39,40, 41). Studies have shown that yoga increases GABA, a calming neurotransmitter. The “OM” chanting, which is often done during yoga and meditation, has also been shown to stimulate the vagus nerve (42).
5. Meditation
Meditation is a wonderful relaxation technique and it can stimulate the vagus nerve and increase vagal tone. Research shows that meditation increases vagal tone and positive emotions (43,44). Another study found that meditation reduces sympathetic “fight or flight” activity and increases vagal modulation (45).
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