Over the last 20 years or so, we’ve begun to learn more and more about an unexpected connection in all our bodies—the gut-brain axis.
We now know that our stomachs and our brains are far more deeply connected than we ever imagined—so much so that we now understand how crucial a role the gut-brain axis plays in your overall health.
Scientists have even discovered that this connection extends to some of the most important chemicals in our bodies: our hormones.
In this post, you’ll learn what the gut-brain axis is, what role it plays in our health, and how it affects our hormones.
What Is the Gut-Brain Axis?
The gut-brain axis is essentially a two-way communication highway between your digestive tract and your central nervous system.
While we once thought brain function drove everything in your body, we now understand that your gut and brain are in constant communication, each influencing the other in important ways.
Your digestive system houses what scientists call the "enteric nervous system" or your "second brain,” which is a complex network of more than 100 million nerve cells lining your gastrointestinal tract.
This system doesn't act literally like your brain—instead, it exchanges crucial information about your body's status and needs with your brain constantly.
What makes this connection even more fascinating is the role of your gut microbiome—the trillions of bacteria, fungi, and other microorganisms living in your digestive tract.
These creatures aren't just passive hitchhikers—they're active participants in the gut-brain connection, producing compounds that influence both brain function and hormone production.
How Do Your Gut and Brain Communicate?
This biological communication system operates through several pathways. The vagus nerve serves as the primary communication channel between your gut and brain.
This cranial nerve—the longest in your body—sends signals in both directions, allowing your brain to influence digestive processes and your gut to send feedback to your brain.
Shockingly, your gut microbes produce neurotransmitters—the same chemicals your brain uses to regulate mood and cognition. Surprisingly, about 95% of your body's serotonin (the "happiness" neurotransmitter) is produced in your gut, not your brain.
Your gut also houses approximately 70 to 80% of your immune system cells. The immune signals generated in response to gut conditions travel throughout your body, affecting brain function and hormone production.
Your digestive system also produces various hormones that can travel through your bloodstream to affect brain function, while your brain releases hormones that influence digestive processes.
Finally, the beneficial bacteria in your gut produce short-chain fatty acids and other compounds that can influence brain function, inflammation levels, and hormone signaling throughout your body.
Why Is the Gut-Brain Axis So Important?
The importance of this bidirectional relationship extends far beyond occasional stomach butterflies. Research increasingly shows that gut health impacts virtually every aspect of your well-being.
Some studies have linked gut microbiome imbalances to anxiety, depression, and stress responses, which has lead researchers to investigate gut-targeted approaches for supporting mental health.
There also seems to be a connection between gut health and cognitive abilities, including memory and concentration. It also appears that your gut microbiome regulates your immune system, which in turn affects inflammation levels throughout your body—including your brain.
Finally, gut dysfunction has been associated with numerous conditions beyond digestive disorders, including autoimmune diseases, metabolic disorders, and even neurodegenerative conditions.
The Gut-Brain-Hormone Connection
Perhaps one of the most unexpected aspects of the gut-brain axis is its influence on your hormonal systems. Your endocrine (hormone) system doesn't operate in isolation—it's intimately connected to both your digestive health and brain function.
For example, when you're stressed, your brain triggers the release of cortisol and other stress hormones. These hormones can alter gut function, changing motility (how quickly food moves through your system), increasing permeability (potentially leading to leaky gut syndrome), and disrupting the microbial balance.
On the other end of the gut-brain axis, an unhealthy gut can send signals that trigger stress responses, creating a potentially vicious cycle.
Your gut microbiome also influences the metabolism of estrogen and other sex hormones. Certain gut bacteria contain an enzyme called beta-glucuronidase that affects how estrogen is processed and recirculated in your body.
Imbalances in gut bacteria can lead to either excess or insufficient estrogen activity, potentially contributing to conditions like PCOS, endometriosis, and hormone-related cancers.
Additionally, your gut plays a critical role in converting inactive thyroid hormone (T4) to its active form (T3). Digestive issues can impair this conversion, contributing to symptoms of hypothyroidism even when thyroid hormone blood tests appear normal.
On top of that, your gut microbiome influences how your body processes carbohydrates and regulates insulin sensitivity. This affects not only diabetes risk but also other hormonal systems, as insulin interacts with sex hormones and adrenal function.
Finally, your gut produces hormones that signal hunger (ghrelin) and fullness (peptide YY, cholecystokinin). Disruptions in gut health can alter these hormonal signals, potentially contributing to overeating or irregular eating patterns.
How Gut Health Directly Impacts Hormone Production
The relationship between your gut and hormones goes beyond simple influence—your digestive system is actually a hormone-producing organ itself.
As mentioned earlier, most of your body's serotonin is produced in your gut. This neurotransmitter (which is also a hormone) affects not only mood but also digestive function, sleep cycles, and pain perception.
Your gut also produces melatonin, the hormone that regulates your sleep-wake cycles, which can have a major effect on your overall hormonal balance.
Finally, when your beneficial gut bacteria ferment fiber, they produce compounds that influence hormone signaling throughout your body, affecting everything from hunger signals to inflammatory responses.
If You Think You Might Be Suffering from Leaky Gut Syndrome, We Can Help
If you think your gut health isn’t where it needs to be, we can help. Learn more about leaky gut syndrome (and what we can do about it) here.
You can also schedule an appointment with a specialist today to discuss your gut health and what we can do to potentially improve it.