Gut-Brain Connection

Amber Belt, ND 

Have your ever heard the saying, ‘the gut is the second brain’? Have you ever wondered what it means when people say that? I’d like to answer those questions and more today! First, the second brain is your enteric nervous system (ENS) and it consists of hundreds of millions of neurons, or nerve cells, that line your gastrointestinal tract from the esophagus to the rectum. The connection between the gut and the brain is becoming more and more recognized when it comes to our moods, such as anxiety and depression.

This brings up the question, how does the enteric nervous (ENS) system play into our moods? Isn’t the brain in the head in charge of how we feel? Of course, the enteric nervous system plays a primary role in our digestive function. This alone makes the ENS crucial to our survival and ability to thrive. But there is crosstalk between the central nervous system, which consists of our brain and spinal cord, and the gut. The communication between the brain and the gut, of course, helps to regulate our digestive function but it’s interesting to note that signals from the gut to the brain can trigger mood changes. People experiencing irritable bowel syndrome, diarrhea, constipation, heartburn, or other gastrointestinal dysfunction may also experience anxiety, depression, or other mood changes due to this connection between the gut and the brain.

The connection between the brain and the gut is one way that the enteric nervous system regulates our mood. But there’s also communication between the gut and autonomic nervous system, which governs our fight or flight reactions. And, of course, this connection can play a role in mood too. When we perceive stress our immune system, which is largely housed in our gut, undergoes changes and releases inflammatory chemicals. From an evolutionary standpoint, these inflammatory changes hopefully help us survive the attack from the lion or the bear. However, since we tend to perceive almost everything in the world today as stressful, those inflammatory components are up and running for much longer than they should be. These chronic inflammatory elements can cross the blood brain barrier to cause neuroinflammation that result in short-term or longstanding mood changes.

The chronic stress that we experience also dysregulates the hypothalamic-pituitary-adrenal (HPA) axis. The enteric nervous system interacts with our hypothalamic-pituitary-adrenal axis, which plays a critical role in regulating our stress response. The HPA axis, when dysregulated, can cause us to produce inappropriate amounts of a hormone called cortisol. If cortisol levels are chronically too high or too low, mood changes such as anxiety and/or depression can be seen. Dysregulation of the HPA axis can also cause fatigue and insomnia, both of which play a huge role in mood disorders. The levels of cortisol a person is producing is easily measured with salivary or urine testing.

There’s yet another way that our second brain influences our mood and that is via our gut microbiome. Our gut microbiome consists of the organisms that live in our gut, which can be helpful or harmful to our health. In fact, the bugs in our gut can release their own neurotransmitters, impacting our mood! If bad bugs are allowed to grow out of control, they release inflammatory mediators that spark the release of cortisol and adrenaline. This can result in a stress response without you perceiving any stress! This sounds a lot like unprovoked anxiety, right? Helpful organisms keep the bad bug count low, limiting the effect they can have on inflammation and mood. Our good intestinal bugs also interact with our hormones, such as adrenaline and cortisol, to modulate and turn down our stress response. Dysbiosis, the imbalance between good and bad bugs, in our gut has been highly associated with mood disorders and linked to the dysregulation of serotonin, GABA, and other mood-impacting neurotransmitters.

One of the most common conditions that I treat where I can clearly see the gut-brain connection is Small Intestinal Bacterial Overgrowth, otherwise known as SIBO. SIBO is quite common and results from the overgrowth of bacteria in the small intestine. This bacterial overgrowth has huge implications for mood. When I work with a patient to treat their SIBO, I most often see a sharp decrease in anxiety as we reestablish proper bacterial balance in the gut. The most accessible way to test for SIBO is with a simple breath test that can be done in the home.

I hope you’ve found this article helpful understanding the gut-brain connection. We can help our gut health and, therefore, our moods by eating real food rather than processed foods. Some of us may find probiotics (the good bugs) in foods or supplements helpful. And, sometimes, testing for imbalances in the gut microbiome is crucial for restoring the health of the enteric nervous system which can, in turn, help us to our best mental health.