GUT–BRAIN AXIS

The Gut–Brain Axis: How Your Gut Talks to Your Brain

By The Scora Science Team · June 26, 2026 · Updated June 26, 2026

TL;DR

The gut–brain axis is a constant two-way conversation between your gut and brain — carried by the vagus nerve, hormones, the immune system, and microbe-made chemicals. Most of your serotonin is made in the gut, which is why gut health and mood are deeply linked.

The gut–brain axis is the two-way communication network that connects your digestive system with your brain. It runs along nerves, hormones, immune messengers, and the chemical output of your gut microbiome. The headline idea is simple: your gut and your brain are in constant conversation, and each can shape the other.

Your “second brain”

Lining your gut is the enteric nervous system — roughly 500 million neurons that can run digestion largely on their own. This semi-autonomous network is why scientists call the gut a “second brain.” When people say “trust your gut,” they are describing a real organ doing real information processing.

The chemistry of mood

Around 90–95% of your body’s serotonin — a chemical central to mood, sleep, and digestion — is produced in the gut. Gut microbes also generate short-chain fatty acids and other compounds that influence inflammation and the stress response. The balance of your microbiome, then, is not just a digestive matter; it is part of how you feel.

The main communication lines

  • The vagus nerve — the fast, direct cable between gut and brain. Read more →
  • Hormones — including stress hormones like cortisol.
  • The immune system — much of which lives in the gut wall.
  • Microbial metabolites — chemicals made by your gut bacteria.

Why this matters for you

The gut–brain axis reframes gut health as whole-body health. Stress can upset digestion; an imbalanced gut can cloud mood and focus. Supporting one tends to support the other — which is why diet, sleep, and stress all show up in the gut-health conversation.

Scora is building a way to listen to the gut’s side of that conversation — the chemical signals it sends every day. Join the waitlist or explore the research.

Educational content, not medical advice. For mental-health or digestive concerns, please consult a qualified professional.

FAQ

Frequently asked questions

What is the gut–brain axis?+

The gut–brain axis is the two-way communication network linking your digestive system and your brain. It connects them through nerves (especially the vagus nerve), hormones, immune signals, and chemicals made by gut microbes — so the state of your gut can influence your mood, and your mental state can influence your gut.

How does the gut affect mood and mental health?+

Gut microbes help produce and regulate neurotransmitters, and roughly 90–95% of the body’s serotonin is made in the gut. Microbes also produce short-chain fatty acids and influence inflammation and the stress response. Through the vagus nerve and these chemical signals, gut activity can affect mood, stress, and cognition.

Is the gut really a "second brain"?+

Yes, in a real sense. The gut has its own nervous system — the enteric nervous system — with around 500 million neurons that can operate independently of the brain to control digestion. It is genuinely a second, semi-autonomous neural network, which is why scientists call it the “second brain.”

Can improving gut health improve mental wellbeing?+

Emerging research suggests that supporting a diverse, balanced microbiome — through fiber, fermented foods, sleep, and stress management — may benefit mood and stress resilience via the gut–brain axis. It is a promising and active research area, not a cure, and serious mental-health concerns need professional care.