Your Brain:
The Gut-Brain Axis

Over 90% of your body's serotonin is made in your gut. Here's why fixing your digestion often fixes your brain fog, anxiety, and mood — and what to do about it.

By Brehan Crawford, MAcOM, LAc

Your second brain lives in your belly

Our gut and brain are closely connected through what researchers call the gut-brain axis. This isn't a metaphor — it's a physical communication network involving the vagus nerve, the enteric nervous system (a complex neural network embedded in your gut wall), your immune system, and an array of chemical messengers produced by your gut bacteria.

What happens in your gut directly affects your brain, and vice versa. This is why so many patients come to me with both digestive issues and cognitive symptoms — brain fog, anxiety, low mood, poor concentration. They're not separate problems. They're the same problem, expressing through different systems.

The good news: once you're digesting well (Part 1) and sleeping well (Part 2), there's a good chance your mental clarity will really start to improve on its own. But there are additional practices that can accelerate that process significantly.

Simple practices that support your gut-brain connection

Get outside first thing in the morning. Even if it's still a little dark or cloudy, natural light and fresh air first thing in the morning sets your circadian rhythm for the entire day. This isn't just about mood — morning light exposure helps calibrate cortisol timing, melatonin production, and the bacterial rhythms in your gut that depend on both.

While you're out there, move gently. Take some deep breaths and do some light exercises — shaking, stretching, anything that gets your blood moving early in the day. You don't need to train hard. You need to wake up your body's communication systems.

Practice mindful reflection regularly. This can be meditation, a gratitude journaling practice, or even just a heart-to-heart conversation with a close friend. The vagus nerve — the primary communication highway between your gut and brain — responds to calm, social engagement, and parasympathetic activation. Anything that genuinely relaxes your nervous system is gut medicine.

Break up long sitting periods. If you sit at a desk all day, set an alarm to get up once an hour. Do a little shaking, stretching, and deep breathing. Or a 5-minute dance party — it's up to you. Movement stimulates vagal tone, peristalsis, and lymphatic flow. All of these support the gut-brain connection.

Part 4: Next Steps

You have the foundations — diet, sleep, and brain. In the final post, we'll pull it all together and show you how to take the next step.

1. Hwang YK, Oh JS. (2025). Interaction of the vagus nerve and serotonin in the gut-brain axis. International Journal of Molecular Sciences, 26(3), 1160. doi:10.3390/ijms26031160
2. Zheng P, Zeng B, Zhou C, et al. (2024). Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases. Signal Transduction and Targeted Therapy, 9(1), 37. doi:10.1038/s41392-024-01743-1
3. Spencer NJ, Kyloh MA, Travis L, Hibberd TJ. (2024). Identification of vagal afferent nerve endings in the mouse colon and their spatial relationship with enterochromaffin cells. Cell and Tissue Research. doi:10.1007/s00441-024-03879-6