There are expressions we use without thinking much about them:
“I have butterflies in my stomach.”
“My stomach is in knots.”
“Something is eating me up inside.”
For a long time, we thought these were just metaphors.
Poetic ways of describing emotions.
But biologically speaking, they’re not metaphors at all.
Inside our abdomen exists a nervous system so complex that scientists call it — without exaggeration — the second brain.
It’s not a figure of speech.
It’s real.
It’s called the enteric nervous system, and it contains hundreds of millions of neurons spread throughout the digestive tract. A network so vast that it can function on its own, constantly communicating with the brain in our head through the vagus nerve, hormones, and chemical signals.
It doesn’t “think” in words.
It doesn’t make conscious decisions.
But it senses, reacts, and influences our emotional state far more than we realize.
About 90% of the body’s serotonin — the neurotransmitter associated with well-being — is produced in the gut, not in the brain. That doesn’t mean happiness “comes from the belly,” but it does mean that gut health and mental health are far more connected than we were taught.
In recent years, research on the gut–brain axis has become one of the most fascinating areas in neuroscience. Studies published in Nature Reviews Neuroscience, as well as research from Harvard Medical School and UCLA, show that the gut microbiome — the trillions of bacteria living inside us — can influence stress response, anxiety levels, and even how the brain processes emotions.
Not as magic.
Not as a simple explanation for everything.
But as part of an ongoing dialogue between body and mind.
When we’re stressed, the brain sends signals to the gut. Digestion shifts. Cramps, nausea, that familiar “knot” appear. When we’re calm, the parasympathetic nervous system — the “rest and digest” mode — activates, and the gut functions more smoothly.
That’s why emotions feel so physical.
They’re not just “in your head.”
Children feel this most clearly.
An anxious child before an exam often says their stomach hurts. Not because they’re exaggerating, but because their digestive system is genuinely reacting to emotion. Teenagers, moving through intense hormonal and emotional changes, frequently experience digestive discomfort without a clear medical cause. Their bodies are processing stress in real time.
In adults, the connection becomes more subtle.
Chronic stress, rushed meals, fragmented sleep, and lack of real pauses affect the microbiome and gut motility. We may not notice the link right away, but over time a vague sense of discomfort can appear: bloating, abdominal tension, fatigue, irritability.
The body isn’t divided into chapters.
Everything communicates.
There are also differences between women and men. Research shows that women generally have a more sensitive gut–brain axis. Irritable bowel syndrome, for example, is diagnosed more often in women and is strongly influenced by stress and hormonal fluctuations. Not because women “stress more,” but because their neuro-hormonal and digestive systems are more interconnected.
In men, the connection is just as real but often less consciously acknowledged. Digestive discomfort is less frequently linked to stress or emotions, even though the body responds in similar ways. Sometimes it shows up as internal tension, fatigue, or irritability rather than obvious digestive symptoms.
Mental health and digestive health are far more connected than we once believed. Recent studies suggest that imbalances in the microbiome may be associated with a higher risk of anxiety and depression — not as a single cause, but as part of a complex system where inflammation, stress, and lifestyle continuously influence one another.
Lack of sleep can alter gut bacteria.
Chronic stress can disrupt digestion.
Social isolation can influence inflammation and the microbiome.
In turn, the gut sends signals back to the brain, influencing mood and energy levels. It’s a continuous loop — quiet, invisible, but constant.
We live, however, in a rhythm where silence has become rare. I recently wrote about the habit of taking our phones everywhere, even into the bathroom — not to judge, but to notice how difficult it has become to sit with ourselves for a few minutes without stimulation. There are very few moments in a day when the body naturally enters deep relaxation mode. Digestion, slow breathing, real pauses are among them.
The gut — this second brain — responds strongly to our internal rhythm. To rushing. To tension. To the absence of pause. But it also responds to safety, routine, calm meals, and slow breathing.
It doesn’t ask for perfection.
It doesn’t ask for perfect diets.
Just a minimum of human rhythm.
We don’t need to obsess over bacteria or neurotransmitters.
We don’t need to turn every sensation into a medical analysis.
We just need to understand that emotions aren’t separate from the body.
That mental health doesn’t live only in the brain.
And that sometimes, when we say “I feel it in my gut,” the body is describing something real.
We have a brain in our head that analyzes the world.
And a brain in our abdomen that responds to it.
Between them, there is a constant conversation — even when we can’t hear it.
And the way we live — how fast, how tense, how connected or disconnected we are from ourselves — is often written there first.
In silence.
In depth.
In that place in the body we simply call the gut.