⏱ 6-minute read

I spent many years in nursing school, and many more working at the bedside. Years reading, studying, and caring for patients across some pretty complex health situations. Somehow — through it all — I never heard about the ‘second brain’ within my gut microbiome.

I find that extraordinary — because once I finally learned what it was, I could not stop thinking about how much it explained. It was one of those ‘ah ha’ moments. It made sense now, those gut feelings that turned out to be right. The way stress goes straight to the pit of the stomach. The ‘feeling sick to your stomach’ before something frightening.

It was not imagination. It was not coincidence. It was biology — specifically, it was the enteric nervous system. And it changes everything about how we understand the gut, the brain, and the connection between the two.

I cannot accept "that's just how it is" as a satisfying answer to a health question. I need to understand the mechanism. It’s important to understand the why. It provides the insight needed to make the best approach to our health.

When I first heard someone refer to the gut as "the second brain," I did what I always do — I went looking for the science.

What I found genuinely surprised me. And I believe it will surprise you too — in the best possible way, because understanding this changes how you approach your gut health, your mental health, managing stress, and your overall health and wellbeing in a way that nothing else quite does.

Your brain and spinal cord make up what is called the central nervous system — the command center most of us learned about in school. But there is a second, largely independent nervous system embedded in the walls of your gastrointestinal tract — from your esophagus all the way through your stomach, small intestine, and large intestine — called the enteric nervous system (ENS).

The ENS contains somewhere between 100 and 500 million neurons — nerve cells. To put that in perspective, that is more neurons than your spinal cord contains. It is woven into the lining of your digestive tract in two thin layers of neural tissue that stretch the entire length of your gut, spanning approximately nine meters.

It regulates every aspect of digestion independently — the muscular contractions that move food through your intestines (called peristalsis), the release of digestive enzymes and stomach acid, blood flow to the gut, immune responses in the intestinal lining, and the communication between gut cells and the bloodstream. It does all of this largely without needing instructions from the brain (your primary one).

This is why it earned the name "the second brain." Not because it thinks, feels, or reasons the way your brain does — but because it operates with a degree of autonomy and complexity.

The enteric nervous system and the brain communicate constantly through the vagus nerve — the primary communication highway of the gut-brain axis that we have discussed extensively in previous issues. But the direction of that communication is not what most people would assume.

Approximately 80 to 90 percent of the signals traveling through the vagus nerve travel upward — from the gut to the brain — rather than downward from the brain to the gut.

Your gut is sending far more information to your brain than your brain is sending to your gut.

This means that the state of your gut — the health of your microbiome, the integrity of your gut lining, the activity of your enteric nervous system — is actively shaping what happens in your brain. Your mood. Your cognitive clarity. Your stress resilience. Your anxiety levels. Your body’s ability to shift from stress mode to calm mode.

The gut is not passively responding to what the brain tells it. It is actively informing, shaping, and influencing the brain in real time.

The enteric nervous system is directly involved in some of the most significant health outcomes most people are dealing with right now.

Serotonin production. Approximately 90% of your body's serotonin — your primary mood-regulating neurotransmitter — is produced in the gut, manufactured by specialized cells in the intestinal lining in a process that depends heavily on ENS function and microbiome health. When the ENS is dysregulated, serotonin production is impaired. The downstream effects impact mood, sleep, and stress resilience.

Stress response. The ENS is exquisitely sensitive to stress hormones. When cortisol and adrenaline flood the system during a stress response, the ENS detects them immediately and alters gut function in response — slowing digestion, changing gut motility, increasing gut permeability, and sending distress signals back up the vagus nerve to the brain. This is the biological basis of every gut sensation you have ever had in a stressful moment. It is not "all in your head." It is the ENS responding to the same hormones your brain is responding to — simultaneously.

Immune regulation. The ENS communicates constantly with the gut-associated lymphoid tissue (GALT) — the 70% of your immune system that lives in your gut. This communication helps calibrate immune responses, regulate inflammation, and distinguish between harmless substances and genuine threats. A dysregulated ENS contributes directly to immune dysregulation — including the chronic low-grade inflammation that underlies so many modern chronic diseases.

The gut feelings that turn out to be right. The ENS processes information, integrates signals from the gut environment, and communicates patterns to the brain that the conscious mind cannot always articulate. This is the biological basis of intuition — the "gut feeling" that something is wrong, or right, before you can explain why. It is not mystical. It is your second brain doing its job.

The enteric nervous system is profoundly sensitive to the inputs it receives.

Chronic stress is one of the most potent ENS disruptors — directly altering gut motility, increasing intestinal permeability, disrupting the microbiome, and impairing the serotonin production pathway. Chronic stress and chronic gut dysfunction are not coincidentally correlated. They are causally connected through the ENS.

Ultra-processed foods, refined sugar, and seed oils disrupt the microbial environment that the ENS depends on for healthy signaling. Poor sleep impairs ENS repair and regeneration. Chronic antibiotic use depletes the microbiome that ENS neurons communicate with. And the chronic low-grade inflammation that results from all of the above physically damages enteric neurons over time.

This is why addressing gut health is not just about digestion. It’s about mental health, immune function, metabolic health, stress resilience, and neurological wellbeing — because all of those systems are directly connected to the health of your second brain.

1. Feed the microbiome your ENS depends on. The enteric nervous system communicates constantly with your gut bacteria — and the quality of that communication depends on the diversity and health of the microbial ecosystem. Daily fermented foods (plain yogurt, kefir, sauerkraut, kimchi), adequate dietary fiber, and a quality gut-brain axis probiotic like Zenith — which is specifically formulated to support the ENS-microbiome connection — directly nourish the environment your second brain functions within. A depleted microbiome is a depleted ENS. Learn more about Zenith here:

2. Activate the vagus nerve daily. The vagus nerve is the primary communication channel between your ENS and your brain — and its tone directly determines the quality of that communication. Extended exhale breathing (inhale 4, exhale 6–8), humming or singing, cold water on the face, and intentional prayer and stillness all activate the vagus nerve and improve the bidirectional signaling between your two brains. As we have covered in previous issues, vagal tone is one of the most important — and most accessible — levers in your entire nervous system.

3. Drink organic bone broth daily. The enteric nervous system is embedded in the gut lining — which means the structural integrity of that lining directly determines the environment in which ENS neurons operate. Organic grass-fed bone broth provides glycine, glutamine, and collagen — the primary building materials for tight junction proteins that maintain gut lining integrity. A leaky gut lining is a stressed ENS. Daily bone broth is one of the most direct structural supports for your second brain's operating environment.

4. Manage stress as a non-negotiable. Because the ENS is so directly and immediately responsive to stress hormones, every practice that reduces cortisol and activates the parasympathetic nervous system — prayer, breathwork, time in nature, movement — directly reduces the stress hormone burden that the ENS is receiving and allows it to return to its natural regulatory function. You cannot fully heal your gut while your stress response is chronically active. The ENS makes this biological fact unavoidable.

We are told in Scripture that we are fearfully and wonderfully made. I believe that. Understanding the enteric nervous system gives that truth new depth and meaning. The complexity and the intelligence of what is happening in the human body — in systems we are only beginning to truly understand — points unmistakably toward a design that did not happen by accident.

"I praise you because I am fearfully and wonderfully made; your works are wonderful, I know that full well." — Psalm 139:14

You have a second brain. It has been there your whole life, quietly running your digestion, producing your serotonin, communicating with your immune system, shaping your mood, and sending 80–90% of the information traveling through your vagus nerve directly to the primary brain.

It is real and extraordinary, and its health is directly connected to how you feel — mentally, physically, emotionally, and immunologically — every single day.

It’s important to feed it and protect it. To activate the vagus nerve that connects it to your brain, and to give it the environment it needs to do what it was designed to do.

With faith, science, and wellness,
Liz, The Wellness Nurse

Registered Nurse | Certified Mental Wellness Coach

P.S. Hit reply and tell me — did you know about the enteric nervous system before reading this? I genuinely want to know how many people have heard of it.

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