BIORYA Observatory · Science · 7 min read

The gut, that "second brain" quietly shaping your mood

"Butterflies in the stomach", "gut feeling", "knotted stomach"… Language guessed it long before science proved it: your belly and your brain talk to each other all day long. Here is what that conversation changes for your mood.

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Your digestive tract houses its own nervous system — around 200 million neurons, more than a cat's brain. Researchers call it the enteric nervous system, and the public calls it the "second brain". It works closely with the trillions of bacteria of your gut microbiota, and together they send the brain a constant stream of messages that influence stress, mood and even sleep. The conversation is real, measurable — and it goes both ways.

Colourful balanced plate with vegetables, egg and avocado on a wooden table
Feeding your gut well is one of the most concrete things you can do for your mood.

1. A real nervous system in your belly

Neurons in the gut~200 million — a nervous system of its own
The hotlineThe vagus nerve links gut and brain non-stop
Serotonin~95 % of the body's serotonin is produced in the gut
The tenantsTrillions of bacteria, hundreds of species: the microbiota
Direction of traffic~80–90 % of vagus nerve fibres go from belly to brain
The fieldResearchers now speak of the "gut-brain axis"

2. How the belly talks to the brain

The vagus nerve, the trunk line

This long nerve runs from the brainstem to the abdomen. Most of its traffic flows upward: the belly reports, the brain listens — and adjusts alertness and mood accordingly.

Chemical messengers

Gut bacteria help produce or regulate serotonin, dopamine and GABA precursors — the same messengers involved in calm and mood balance.

Stress goes down too

The conversation is two-way: acute stress slows digestion, knots the stomach, alters the microbiota. That's why tense weeks so often come with digestive complaints.

The inflammation route

An unbalanced microbiota can promote low-grade inflammation, which research increasingly links to low mood. Balance in the belly supports balance upstairs.

3. A few numbers

200 Mneurons in the enteric nervous system — the body's "second brain"
~95 %of the body's serotonin is made in the gut, not in the head
x10research on the gut-brain axis has roughly multiplied tenfold in fifteen years
30+different plant foods per week is the diversity target researchers associate with a richer microbiota

4. What feeds the duo

Fibre, the microbiota's fuel

Vegetables, fruit, pulses, whole grains: fibre is what your good bacteria actually eat. Variety matters as much as quantity.

Fermented foods

Yogurt, kefir, sauerkraut, miso… Studies associate regular fermented foods with a more diverse microbiota and lower inflammation markers.

Regular meals, calm meals

Digestion works best in "rest" mode. Eating at steady times, sitting down, without a screen shouting at you, is already gut care.

Managing stress — really

Slow breathing directly stimulates the vagus nerve, the gut-brain hotline. A few slow breaths before a meal is the simplest "gut-brain" exercise there is.

Educational content, not medical advice. Persistent digestive issues or a lasting low mood deserve a healthcare professional's attention.

5. And day to day?

You don't need to become a microbiologist. The gut-brain duo mostly asks for regularity: varied plants, calmer meals, slow breathing, steady sleep. That's exactly the philosophy of the BIORYA ritual — a fixed morning minute with a large glass of water, slow breaths that wake up the vagus nerve, and a journal that helps you notice, over the weeks, how your mood and your body respond.

6. Sources

  • Mayer E. A. (2011). Gut feelings: the emerging biology of gut–brain communication. Nature Reviews Neuroscience.
  • Cryan J. F., Dinan T. G. (2012). Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nature Reviews Neuroscience.
  • Foster J. A., McVey Neufeld K.-A. (2013). Gut–brain axis: how the microbiome influences anxiety and depression. Trends in Neurosciences.
  • Gershon M. D. (1998). The Second Brain. HarperCollins.
  • Wastyk H. C. et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell.
  • Breit S. et al. (2018). Vagus nerve as modulator of the brain–gut axis. Frontiers in Psychiatry.

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