The Second Brain

The Second Brain and Mood


Ever hear the phrase “trust your gut instinct” or “what does your gut say”? What about feeling butterflies right before a first date or feeling sick to your stomach with nerves before an exam? The mind-gut connection is not just metaphorical. Our brain and gut are connected by a large network of neurons and a highway of chemicals and hormones that constantly provide feedback about how hungry we are, whether or not we feel stress, or if we’ve ingested a disease-causing microbe. That is why our gut -and maintaining a healthy microbiome- is so important and has a large impact on our mental health and general well-being.


The enteric nervous system (found in the gut) is typically referred to as the body’s second brain. There are millions of neurons that connect the brain to our enteric nervous system AKA the part of the nervous system that controls the gastrointestinal tract all the way from our esophagus to our anus.  The enteric nervous system or “ENS” is so complex and intricate that it can operate and control our GI tract without any input from our central nervous system! The network of neurons in the gut is just as vast and complex as the network of neurons in our spinal cord. This is to show that our digestive tract is a pretty complex system that is controlled mainly by our second brain. Our second brain will constantly collect information from our GI tract and send this information to the brain to respond accordingly.


This constant communication between the brain and digestive system is opening up new ways to think about mental health and diseases. Not only do the gut and brain communicate through the nervous system, but also through hormones and the immune system. The microbials in our gut help regulate the body’s immune response. This has led to a lot of research around depressive symptoms, pain, anxiety and other neuro conditions and how our microbiome affects these conditions.


It is becoming clear that the influence of our microbiota reaches beyond the gut to affect our mind. For example, gut microbiota influences the body’s level of serotonin – a neurotransmitter responsible for regulating feelings of happiness. This means that our microbiota can send signals to our brain to alter the amount of serotonin produced in-turn changing our mood. Stress-induced changes to the microbiome may affect the brain and behaviors. A few studies suggest that cytokines (molecules that help protect our gut during infection) disrupt brain neurochemistry and make people more vulnerable to anxiety and depression. This could potentially be why so many people who are diagnosed with chronic GI disorders such as Crohn’s, ulcerative colitis and irritable bowel syndrome struggle with anxiety and depression.


The gut-brain axis is a bidirectional powerhouse that plays a strong role in our mood, cognition and mental health. There is still plenty of research coming out on this fascinating subject. It is important to keep our microbiome happy by trying to eat of variety of foods and nutrients. Also remember that when we take antibiotics, we lose all of our gut bacteria- good and bad- which is why it might be a good idea to consult with your doctor about taking a probiotic. If you would like to learn more on this subject, I highly recommend reading The Mind-Gut Connection by Dr. Emeran Mayer. Next time you are having a flutter in your stomach- remember that our gut might be trying to tell us something.





  1. Clapp M, Aurora N, Herrera L, Bhatia M, Wilen E, Wakefield S. Gut microbiota’s effect on mental health: The gut-brain axis. Clin Pract. 2017;7(4):987. Published 2017 Sep 15. doi:10.4081/cp.2017.987
  2. Mayer E. The mind-gut connection: How the hidden conversation within our bodies impacts our mood, our choices, and our overall health. New York: HarperCollins Publisher; 2016.
  3. Sonnenburg J, Sonnenburg E, Weil A. The good gut: taking control of your weight, your mood, and your long-term health. London: Penguin Press; 2015
  4. Bastiaanssen TFS, Cussotto S, Claesson MJ, Clarke G, Dinan TG, Cryan JF. Gutted! Unraveling the Role of the Microbiome in Major Depressive Disorder. Harv Rev Psychiatry. 2020;28(1):26-39. doi:10.1097/HRP.0000000000000243





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