The Gut Brain Axis
The Second Brain
“I thought of my whole body as an ear.”
In 1822, a young Canadian voyageur named Alexis St. Martin was accidentally shot in the abdomen at close range. The wound was so severe that he was not expected to survive. He did, but his body healed in an extraordinary way. An opening remained in his abdomen through which the inside of his stomach could be observed.
The physician who treated him, William Beaumont, realized that he had an opportunity no doctor had ever had before. Over the following years, he studied human digestion by observing what was happening inside St. Martin’s stomach.
Among his observations was something fascinating.
When St. Martin’s emotional state changed, his stomach changed too.
Anger and agitation were accompanied by visible changes in digestive activity. Nearly two hundred years ago, a physician could literally look inside a living person and see something we have all experienced in our own bodies: what happens in our emotional lives can be felt in our gut.
We have known this without knowing the science.
We get butterflies in our stomach before something important. Anxiety can make us nauseated. Stress can change our appetite and digestion. Terrible news can make eating impossible and excitement can do the same.
Our language has been recording the connection for generations.
We have a gut feeling.
Something is gut wrenching.
It takes guts to do something courageous.
Our bodies knew the connection long before most of us knew there was a name for it.
Science now calls it the gut brain axis.
A Conversation Inside Us
The gut and the brain are in continuous communication.
Signals travel between them through several pathways, including nerves, hormones, the immune system, and substances produced during digestion and by microorganisms living in the gastrointestinal tract.
One of the important communication routes is the vagus nerve, which travels from the brainstem through the body and connects with organs including the heart, lungs, and digestive tract.
Inside the walls of our gastrointestinal system is another remarkable structure: the enteric nervous system, an extensive network of neurons that helps regulate digestion.
It is often called our second brain.
The name is captivating, but it can also be misleading.
Our gut is not sitting inside us thinking.
It is not deciding whom we should marry, whether we should leave our job, or where we should live. It does not have thoughts in the way our brain does.
What makes the enteric nervous system remarkable is its ability to coordinate much of the complicated work of digestion with considerable independence while remaining in communication with the brain.
The important idea for our lives is simpler.
The conversation goes both ways.
Most of us already understand one direction.
Brain to gut.
We become nervous and our stomach tightens. We are frightened and suddenly need the bathroom. We are under enormous pressure and lose our appetite.
What is less obvious is that signals also travel in the other direction.
Gut to brain.
The gastrointestinal system is continuously sending information upward about what is happening inside the body. The nervous system, immune system, hormones, metabolism, and the enormous community of microorganisms living in our gut all participate, directly or indirectly, in this conversation.
The brain is listening to the body while the body is responding to the brain.
The World Living Inside Us
Our digestive tract contains an extraordinary ecosystem of microorganisms collectively known as the gut microbiome.
Trillions of microorganisms live there. They help break down components of food, interact with our immune system, produce biologically active substances, and participate in many processes scientists are still working to understand.
During the past several decades, researchers have become increasingly interested in how this microbial world participates in communication along the gut brain axis.
The findings are fascinating.
They have also created an enormous amount of hype.
You can now find claims suggesting that a particular probiotic, food, supplement, or bacterial strain can transform your mood, eliminate anxiety, cure depression, or somehow give you a better brain.
The science is nowhere near that simple.
Some of the most dramatic discoveries in microbiome research have come from animal studies. Human research is growing rapidly, and there is compelling evidence that the microbiome participates in systems that communicate with the brain, but we are still learning how these enormously complex interactions work.
That is worth remembering.
Science can be exciting without being exaggerated.
We do not need to turn an emerging field into a miracle in order to appreciate how remarkable it already is.
Why Stress Can Reach the Stomach
Think about what happens during a period of intense stress.
Your brain recognizes that something requires attention. The nervous system and hormonal systems respond. Heart rate can change, muscles tense, energy is redirected. Digestion can speed up, slow down, or simply feel different.
The stomachache before an important presentation is not imaginary.
Neither is the loss of appetite during grief or the sudden digestive urgency that can accompany anxiety.
The experience is physical because emotion itself is not something happening in an isolated compartment called the mind.
We divide ourselves into systems because it helps us study an enormously complicated organism. We have a nervous system, digestive system, endocrine system, immune system, cardiovascular system, and many others.
The body itself does not experience life as separate departments.
The systems interact.
That may be one of the most useful things the gut brain axis can teach us.
We are integrated.
Should We Trust Our Gut?
Once we understand that the gut and brain communicate, an obvious question appears.
What about a gut feeling?
Most of us have experienced one. We meet someone and something feels wrong. We walk into a situation and feel uneasy without knowing why. We are presented with an opportunity and something inside us seems to say yes before we have consciously worked through the reasons.
There is science that helps us understand part of this experience.
Our brains continuously receive information from inside our bodies. Heartbeat, breathing, tension, hunger, fullness, and signals from internal organs all contribute to our internal sense of what is happening.
Experience matters too.
The brain is constantly recognizing patterns. Years of experience can allow us to notice something before we can consciously explain what we noticed. A highly experienced person can sometimes sense that something is wrong because the present situation differs subtly from patterns encountered hundreds of times before.
That can feel like intuition.
It can also be wrong.
Anxiety can feel like intuition.
Fear can feel like a warning.
An old experience can make a new situation feel dangerous even when the circumstances are different.
Bias can feel like certainty.
Our bodies give us information. They do not give us infallible instructions.
I think there is a beautiful practical lesson here:
Listen to your gut. Do not automatically obey it.
Notice the signal, become curious about it, and then bring the rest of yourself into the decision.
Listening to the Whole Body
Maya Angelou’s words begin to mean something different here.
“I thought of my whole body as an ear.”
She was describing her own childhood experience, not explaining neuroscience still, the image is extraordinary.
Our whole body is receiving, responding, adapting, and communicating all the time.
Most of us notice only when the volume becomes loud enough. We notice the stomach after weeks of stress, exhaustion when we can no longer push through it, tension when it becomes pain. We notice that we are not sleeping well after we have spent days feeling depleted.
Awareness gives us an opportunity to notice sooner. We can begin paying attention to how our bodies respond to the way we live.
We can become curious.
What happens when I sleep well for several nights? How does my body respond during periods of sustained stress? How do I feel when I move regularly, eat differently, spend time outside, slow down, or live for weeks without enough recovery?
We do not need to turn every sensation into a message requiring interpretation, we can simply become more aware of the patterns.
Caring for the Conversation
Understanding the gut brain connection also gives additional meaning to some very ordinary things we already know matter.
Food matters.
A varied diet rich in plant foods and fiber supports digestive health and provides nourishment for many beneficial gut microorganisms.
Movement matters.
Regular physical activity affects the brain, metabolism, immune function, stress regulation, and the gastrointestinal system.
Sleep matters.
Chronic stress matters.
How we care for our bodies matters.
None of this means that eating vegetables or sleeping eight hours will create the perfect microbiome or prevent every psychological or physical problem.
It means that caring for our mental life and caring for our physical life are not entirely separate projects.
We are caring for one human being.
Designing a Life for the Whole Human Being
When we think about designing our lives, it is easy to do it almost entirely from the neck up.
We make plans, we set goals, we decide what we want to accomplish.
We think about our careers, finances, relationships, homes, travel, purpose, and what we want the next chapter to look like.
Then our bodies have to live the life we designed.
Our bodies carry the schedule, experience the stress, need the sleep, eat the food, live inside the relationships.
They inhabit the environments.
They carry us through every ordinary Tuesday between the goals we put on paper.
A life that looks beautiful from the outside can feel very different from inside the body living it.
This is why awareness matters.
In the essay titled “Metacognition,” we explored the remarkable ability of the mind to observe its own thinking.
Here, the invitation becomes wider.
Notice the body too.
Notice what gives you energy and what repeatedly depletes it. Notice what happens when stress becomes your normal state. Notice how your body responds to the rhythms of the life you are creating.
Listening does not mean allowing every sensation to make our decisions for us.
It means including the body in the conversation.
There is something profoundly humbling about realizing how interconnected we are inside ourselves.
The brain influences the gut.
The gut communicates with the brain.
The nervous system speaks with the immune system. Hormones carry messages. Microorganisms participate in an ecosystem we are only beginning to understand.
Meanwhile, we experience all of it simply as being alive.
Nearly two hundred years ago, William Beaumont looked through an opening into Alexis St. Martin’s stomach and saw that emotion and digestion were somehow connected.
Today we understand vastly more about the pathways carrying that conversation, and there is still much we do not know.
Perhaps the most useful lesson does not require us to understand every pathway.
It requires us to remember that we are whole.
Maya Angelou once imagined her entire body as an ear.
Maybe there is wisdom in becoming a little better at listening.
What is your body telling you about the life you are living?
Live by Design, Not by Default.
Until the next horizon,
Coach • Traveler • Believer in Intentional Living
