What Happens in Vagus

They say what happens in Vegas stays in Vegas. But when it comes to the Vagus nerve, the opposite is true. Everything happening in your gut is being broadcast directly to your brain, and it is fundamentally changing how we understand mental health, addiction, and even our personalities.

I recently returned from a microbiome conference in Serbia where the atmosphere was electric. My colleagues and I were discussing a wave of new research that is turning our traditional view of the “mind-body connection” completely on its head.

For decades, we viewed the brain as the master commander and the gut as a mere subordinate—receiving orders to speed up or slow down digestion. We now know that the reality is far more “bottom-up” than we ever dared to imagine.

The Vagus nerve is the longest cranial nerve we have. It is the only one that travels outside of the head, stretching roughly 50 centimeters down through the neck, past the heart and lungs, and weaving itself into every corner of the gut.

The real bombshell? 80% of the traffic on this highway is one-way, from the gut back to the brain.

Rather than the brain telling the gut how to feel, the gut is constantly “reporting” to the brain on the state of our internal world. It is the primary way the brain keeps up with our physiology, and the “reporters” filing those reports are your gut microbes.

Recent studies published in journals like Nature have mapped out exactly how our microbes “talk” to the endpoints of the Vagus nerve. They do this through a variety of chemical signals called metabolites:

• The Good Guys (SCFAs): Microbes ferment fiber to produce Short-Chain Fatty Acids. These send beneficial, anti-inflammatory signals up to the brain.

• The Disruptors (MCFAs): We’re now learning about Medium-Chain Fatty Acids produced by certain bacteria. Unlike their short-chain cousins, these can actually inhibit Vagal signals and trigger general inflammation.

• Direct Stimulation: Microbes can even trigger immune cells to release signals or use their own cell wall components (like lipopolysaccharides) to “poke” the nerve directly.

Perhaps the most ground-breaking research, including a study in Science Advances by Onimus et al., shows that this gut-brain axis actually governs the reward mechanisms in our brainstem and hypothalamus.

This explains a phenomenon we are seeing globally with GLP-1 drugs like Ozempic. These drugs mimic gut hormones to signal the brain, but patients often find that their addictions—to alcohol, smoking, or shopping—simply vanish. This isn’t a coincidence. By modulating the signals traveling up the Vagus nerve, we are directly tapping into the brain’s “addiction centers.”

It turns out that your “willpower” might actually be a reflection of the chemical signals being sent by your microbiome. My colleague Dr Federica Amati’s new book ‘The Appetite Reset’ covers this in fascinating detail.

Pre-order The Appetite Reset

Every year, the science moves further away from the idea that we are “thinking” beings who happen to have a digestive system. Instead, we are starting to see that our gut microbiomes are really the ones in charge.

If we want to fix our mental health, our cravings, and our moods, we have to stop looking only at the “top floor.” We have to look at the “engine room”—the trillions of microbes that are currently dictating what your brain should do next.

• Feed the “Good” Signals: To increase those beneficial Short-Chain Fatty Acids, you must eat a diverse range of fiber. Aim for 30 plants a week to ensure your microbes have the fuel they need to send “happy” signals to your brain.

• The Fermentation Effect: Traditional fermented foods (like kefir, kimchi, and kombucha) provide the “live” signals that help prime the Vagus nerve and support immune regulation.

• Listen to Your “Gut Feeling”: That phrase exists for a reason. Often, feelings of anxiety or “butterflies” are literal signals from your Vagus nerve. Before reaching for a pill, consider if you’ve been reaching for too much ultra-processed food.

The Bottom Line: You are not just what you eat; you are what your microbes tell your brain you are. Look after them, and they will look after your mind.