The gut-brain connection

Gut Health
gut-brain connection

The gut-brain connection

Have you ever noticed how many emotions are felt in your gut? This is because of something called the gut-brain connection.

How gut health effects your mood via the gut-brain connection

I am sure you have heard phrases like “trust your gut” and “it’s just a gut feeling”. Have you also noticed that many emotions can be felt in your gut as well? Nerves are often felt as knots in the stomach. Test and performance anxiety can easily send a person running to the restroom. A broken heart often leads to a loss in appetite, and a traumatic experience can result in the need to throw up. 

What all of this means is that there is a very real connection between our emotions and our digestive system. However, it wasn’t until recently that science decided to take a deeper look into this connection, which is now being termed the gut-brain axis or the gut-brain connection.

In this article, I am going to explore the gut-brain connection and how we can use it to improve many factors in our life including our mental health. But to truly understand this interconnectivity we must first understand some of the key players in this connection.

The Microbiome

The microbiome is like a village of trillions of microorganisms that live within our body as well as on our skin. This village of microbes is first introduced while a baby develops in the womb, and then again while leaving the womb and traveling through the vaginal canal. 

So much research is unfolding surrounding the microbiome these days and the role that it plays in overall health. Scientists have discovered “good” bacteria and “bad” bacteria, and that each strain of bacteria communicates with the body in a unique way.

These microbes can either help or hinder your health depending on the abundance and types of microbes you possess. But how does the gut microbiome have so much power over your health? And how does the brain send messages to this tiny village of microbes that live in your gut? Keep reading to find out.

The Enteric Nervous System (Second Brain)

parasympathetic vs sympathetic nervous system

You may have heard of the gut being referred to as the second brain. This is due to the fact that the gut actually has its own nervous system called the enteric nervous system (ENS). The ENS is a very complex system. It contains 200-600 million neurons, which is the same amount contained in the entire spinal cord. It communicates with our central nervous system (brain and spinal cord), but is also capable of functioning entirely on its own (1). This extensive nervous system is a key player in making the gut-brain connection possible.

The ENS has many important roles in our digestive tract. It regulates movements such as peristalsis, the process of moving food through the digestive tract. It is also responsible for regulating blood flow and fluid exchange. The fluid exchange that occurs primarily in the small intestine helps to maintain proper electrolyte balance throughout the entire body. Some secretions from the stomach and pancreas are also controlled by the ENS, along with defensive actions such as diarrhea and vomiting (1).

While the function of the ENS is very important, what we are most interested in is how this second brain is connected to our primary brain. This is where the vagus nerve comes in.

The Vagus Nerve

vagus nerve

The nervous system is a very complex system that gets broken down into different subcategories based on the actions of the nerves involved. One of the subcategories of the nervous system is the parasympathetic nervous system (PNS). 

The PNS is involved in mood regulation, digestion, immune function and heart rate. The main nerve associated with the PNS is the vagus nerve. The vagus nerve is one of the 12 cranial nerves that originate in the brainstem. It is the longest nerve in the entire body and runs down the neck, through the chest, and into the abdomen. The vagus nerve is one of the most important components of the gut-brain connection. It is responsible for monitoring the emotional and cognitive areas of the brain with intestinal functions such as immune activation, intestinal permeability, digestion and motility, and hormonal signaling (2).  

If the vagus nerve is functioning optimally this is termed good vagal tone. If a person has good vagal tone, this helps to decrease inflammation, reduce the risk of a stroke or heart disease, lower blood pressure, improve digestion and absorption, and balance blood sugar levels. On the other hand, poor vagal tone is associated with heart disease, stroke, chronic fatigue, depression and anxiety, diabetes, cognitive impairment, and higher rates of systemic inflammation. Increased inflammation then leads to an increased risk for autoimmune conditions (3).

chronic diseases

Have you ever noticed that after eating certain foods or a really large meal, that your heart rate increases and you start to feel warm or a little anxious? This response means that you either ate too much food or your digestive system didn’t like something you ate. As a result it communicates through the vagus nerve, and the vagus nerve responds by increasing your heart rate. 

The vagus nerve is actually the main pathway of communication between the microbiome and the brain. Scientists discovered this by performing various studies on mice. They compared the differing results of probiotic therapies on mice that possessed a vagus nerve to a group of mice whose vagus nerve had been removed. The mice with no vagus nerve showed no changes in brain chemistry with probiotic therapy. The mice that still possessed a vagus nerve showed improvements in anxiety and depression after probiotic therapy (4). This suggests that the increase in good bacteria in the gut through probiotic therapy was able to impart a mental health benefit on the host by communication to the brain through the vagus nerve.

Now that you know how important the vagus nerve is, you can see why good vagal tone is important for overall health. Here are some techniques that can be performed to help you tone your vagus nerve and improve digestion and mood.

meditation and relaxation

  • Singing, Humming, & Gargling: Because the vagus nerve runs down your neck, it is involved with your vocal cords. This means the act of singing, humming, and gargling helps to vibrate the vagus nerve and stimulate it. I try and make a point to sing in the shower or the car where nobody has to hear me. I also gargle water at the end of brushing my teeth every day.
  • Cold Exposure: Cold exposure has been shown to stimulate the vagus nerve. If done often enough, it can decrease the body’s “fight or flight” stress response and improve the “rest and digest” relaxation response. Try spending a couple of minutes outside when it is cold without being bundled up. Or finish your morning shower with 30 sec of turning the dial all the way to cold. It might not be easy, but it is well worth it. 
  • Deep Breathing: Deep breathing helps to reduce stress and therefore increase parasympathetic activity. Try counting to 4 while you breathe in and then count to 4 again while you exhale. Repeat this multiple times until you are feeling more relaxed. Doing this anytime you feel tension in your body will greatly improve overall stress and in turn vagal tone.
  • Yoga: Studies have demonstrated that yoga improves relaxation by increasing levels of GABA (the calming neurotransmitter) and decreasing stress. This is accomplished through breathing techniques and fluid motions that stimulate the vagus nerve.
  • Acupuncture: If you haven’t experienced acupuncture yet in your life, I highly recommend that you give it a try. The benefits are significant. Acupuncture is excellent at decreasing stress and improving digestion. It can also provide direct stimulation to the vagus nerve.
  • Meditation: By now you must be seeing a trend towards relaxing activities resulting in stimulation to the vagus nerve, and meditation can’t be forgotten. Meditation is excellent at improving parasympathetic activity through stimulation of the vagus nerve. You don’t have to be an expert at meditation either. There are so many wonderful guided meditation recordings you can use to show you how it’s done. Even 15 mins a day can make a big difference.



Research tells us that the microbiome, vagus nerve, brain, and ENS all play an important role in the development of neurotransmitters. There are many different neurotransmitters and each one of them has a different role in the body. The following is a list of some of the neurotransmitters important for this topic.

  • GABA: Gamma aminobutyric acid (GABA) is an inhibitory neurotransmitter involved in motor function, vision, and feelings of calmness and relaxation. If you are feeling stressed, agitated, restless, or anxious, then you are likely experiencing lower levels of GABA.
  • Dopamine: Dopamine is an excitatory neurotransmitter involved with movement, posture, and feelings of pleasure and reward. Part of the reason various addictions are common in America comes from the fact that many addictive substances increase dopamine levels and therefore sensations of pleasure.
  • Serotonin: Serotonin is another inhibitory neurotransmitter responsible for regulating body temperature, sleep, appetite, and pain. It also plays a role in overall mood, and with adequate levels it creates a sensation of happiness and contentment. One interesting fact about serotonin is that over 90% of it is made in the gut through bacterial communication with the ENS.
  • Norepinephrine: An excitatory neurotransmitter responsible for attentiveness, alertness, dreaming, learning, and heart rate. It should be noted that too much norepinephrine and too little GABA and serotonin can contribute to depression and anxiety.

The Gut-Brain Connection & Depression & Anxiety

One way we know the microbiome affects our mood is from research on the use of antibiotics and depression. While antibiotics are good at eliminating bad bacterial infections in the body, the unfortunate side effect is that they also kill off good bacteria as well. This means that even one round of antibiotics can greatly reduce the abundance and diversity of the microbiome, and as a result that one round of antibiotics creates a 20%-25% greater likelihood for experiencing depression. In addition to this, scientists have also looked at the effects of antibiotic use during the first year of life. Kids who received antibiotics were more likely to display behavioral problems, and show signs of depression or anxiety. These behavioral problems lasted as long as 10 yrs in some cases. And this is all due to the bacterial changes that occur in the gut as a result of antibiotics. This alone proves that certain gut bacteria play an important role in maintaining healthy brain chemistry.

Another medication that alters the gut microbiome are proton pump inhibitors (Prilosec), used to treat heartburn. Because they are designed to stop the stomach from producing acid, it results in a change in the pH of the digestive tract. This leads to an increase in bad bacteria vs good bacteria. One study showed that the likelihood of experiencing depression increased the longer proton pump inhibitors were used. What is even more shocking is that once this medication was used for at least one year, people experienced depression 100% of the time!!

So what does all of this tell us? It tells us that altering the bacteria in the gut leads to a change in mood. In situations where people are unable to restore the healthy bacteria in their microbiome, it would make sense why long term emotional effects might be experienced.


Part of the reason we see such mental emotional changes from altering the gut bacteria is due to the fact that certain species of bacteria interact with cells in the digestive tract called enteroendocrine cells. Once these cells are triggered, serotonin gets released. This is a good thing, because serotonin is a neurotransmitter that plays a role in regulating mood and social behavior, appetite and digestion, sleep, memory, and sexual function. Low levels of serotonin are associated with an increase in depression and anxiety.

In addition to serotonin, other species of bacteria play a role in increasing GABA and dopamine. GABA is responsible for decreasing sensations of fear and anxiety, and increasing a sensation of calmness. Only the good bacteria in our gut contribute to these awesome neurotransmitters, so when their quantities get depleted, so do all of your happy feelings. 

The Gut-Brain Connection & Stress

fight or flight response

So if you have been wondering how exactly stress affects the gut, here is the answer. When we feel stressed, it triggers the release of noradrenaline into the intestines. The problem with this is that too much noradrenaline kills the good bacteria in the gut. Therefore long-term stress can really wreak havoc on this delicate ecosystem. When we have fewer good gut bacteria, then we have less stimulation of all of the happy neurotransmitters such as serotonin, GABA, and dopamine. When there is less of these happy hormones, then there is a greater likelihood of feeling more stress. This means more noradrenaline gets released, and you can probably see how this further perpetuates the vicious cycle.

So often people underestimate the importance of stress management when they are wanting to heal. I always tell my patients that it has to be a top priority, because eating a healthy diet and exercising regularly can only do so much. If there is still a high stress life, it will feel like fighting an uphill battle.

For me personally, the way that I deal with stress is through learning how to change my perception of various experiences. There are many things in life that are out of our control, but what we do have control over is how we choose to view each circumstance. It is a daily practice learning how to not sweat the little things, and to find more appreciation and gratitude for everything good in this moment. But it is a practice that holds the key to true happiness.

stress management


Although I have mentioned good bacteria and bad bacteria multiple times in this article, it really isn’t accurate to discriminate in that way. For the most part all bacteria in the gut plays an important role, so it is more about balance. Even too much of a good thing can become bad, and trying to eliminate bad bacteria entirely can also cause problems.

That being said, we often refer to gram negative bacteria as being the bad guys in our gut. This is because they have a structure on their surface called lipopolysaccharide aka endotoxin. When these bacteria die, they release these endotoxins into your gut. If you have leaky gut, which most people do, then these endotoxins can get into your bloodstream and then into your brain. When this happens it causes systemic inflammation. Just a few of the symptoms that come from chronic inflammation include depression, anxiety, headaches, fatigue, brain fog, joint pains, and weight gain.

There is no such thing as having no gram negative bacteria in the gut. The problem comes when there are too many of them. Things that cause you to have more gram negative bacteria rather than gram positive bacteria are high stress, a diet rich in sugar and low fiber, persistent use of ibuprofen, and binge drinking. If you can minimize these things in your life, then you can greatly improve the types of bacteria you have in your gut, and in turn your overall mental and emotional well-being.

Conclusion & Recommendations

healthy food

So the takeaway message here is that gut health is very important to mental emotional health and vice versa. The single most important thing you can do for your gut health is finding ways to create more relaxation in your life. This can be done with any of the techniques mentioned above for toning the vagus nerve, and through any other techniques you find personally calming. 

In additional to finding peace in your life, there are other efforts that can be made to improve gut health. Decreasing processed foods and focusing on a more vegetable-forward diet is a great way to protect your gut health. You can also take advantage of probiotics and prebiotics. Add some exercise into your daily routine, and find techniques and activities that allow you to destress after your long day. Also make sure you are getting plenty of sleep, and drinking lots of clean water.

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Affiliate Disclosure: In the spirit of full disclosure, there are affiliate links in this article, which means that I may get a commission if you decide to purchase any such product. I only recommend products and services that I use and love myself.