The Second Brain In Your Gut


Some people call it the hangries. Others call it food fury. In my house it’s called the Shan Monster and my husband generally gets a fifteen-minute warning before she starts spitting venom. The only way to fend her off is to feed her. Fast.


I know I’m not alone when I confess to being grumpy when I’m underfed and this week I’ve found myself looking into the science of how being nutritionally deprived can set off mood changes in my brain. It’s an amazing example of the mind body connection and it’s fascinating.


If you’ve seen my feature documentary The Connection, you may recall the animated graphic which explains the brain-body connection and how scientists are starting to understand that the communication between the two is far more complex than they’d once realized. If you haven’t seen it yet, then here it is.




One major break through came with the discovery of the enteric nervous system. But before I continue about the marvel of this discovery, lets brush up on a little biology.


You may have heard of your skeletal nervous system – your brain’s connections to your muscles. This is a conscious system that allows you to pick something up, or feel if something is hot. You may also have heard of autonomic nervous system. This is your unconscious, automatic function in your body, like your heart beating, breathing, or sweating. You may even have heard that the autonomic nervous system is generally thought to have two divisions – the sympathetic nervous system, often considered the ‘fight or flight’ system and the parasympathetic nervous system, often considered the ‘rest and digest’ or ‘feed and breed’ system.


But a major revelation came when scientists confirmed the existence of the enteric nervous system; a third unconscious system in your body. And it’s found in your gut. They’re calling it the second brain because while it talks to the brain, it also has the ability to act independently and influence behavior.


It’s estimated that there are between 400 and 600 million neurons in your gut – that’s up to three times as many neurons than in the brain of a rat. You’re not conscious of your gut thinking, but the system produces about 95% of the serotonin and 50% of the dopamine found in your body.


So lets look at the biology of having a bad case of the hangries. Researchers at Monash University have looked at the appetite hormone ghrelin, which is produced in the second brain in your gut and plays a role regulating eating behavior, weight gain and metabolism. It also helps with building muscle mass, reduces anxiety and enhances memory. Receptors for the hormone are found throughout the body, including in the brain in your head. Ghrelin can produce an anxiety response that goes away when you eat. I spoke with a leading researcher in the field, Professor John Furness from the University of Melbourne, who explained that when we think about it from an evolutionary perspective, the role of ghrelin makes sense. If we didn’t have such a strong response, we could easily ignore hunger signals and therefore starve. Ghrelin makes us stronger so we can go and find the food; makes us less anxious so we can face any dangers needed to hunt and gather; and the enhanced memory helps us remember where the food is.


Research from the University of Cambridge has also identified that serotonin may further strengthen the link between your emotional response and hunger. In one study, low levels of serotonin were induced in people by changing their diet and giving them a chemical mixture that lacked the building block for serotonin. When they studied their brains they noticed that the communication between the part of the brain that sets off feelings of anger (called the amygdala) and the part of the brain that calms down the emotional response (called the prefrontal cortex), was much weaker. The more prone people were to aggression, the more sensitive they were to serotonin depletion.


The message I’m taking away from all this is rather obvious. What we feed our stomach, also feeds our mind. And this leads me to the microbiome, which you may have noticed is quite the buzz in nutrition circles.


The microbiome is the term being used to describe the existence of a complex community of bacteria living in your gut. You may not realize this, but it’s estimated that as many as 90% of the cells in your body are bacterial. In fact, bacterial genes outnumber your own human genes at a ratio of a hundred to one. In his TED Talk, one of the researchers at the forefront of studying the microbiome, Professor Robert Knight stated, “The three pounds of microbes that you carry around with you might be more important than every single gene you carry around in your genome.”


So far researchers know these bacteria harvest energy from the diet, protect against infections, provide nutrition to cells in the gut and can influence our mood and behaviour.  Scientists are still trying to work out the complex interaction between bacteria and the brain, but it seems that bacteria may be able to affect the immune system and produce their own versions of neurotransmitters.  I intend to write more about the microbiome in this blog in the future because in the last few years there has been an explosion of fascinating research indicating that this gut bacteria is linked to heart disease, colon cancer, obesity and irritable bowel syndrome in humans, as well as linked to illnesses like multiple sclerosis, depression and autism in mice. But for now, let me tell you about some remarkable studies done in mice.


In a study published in the journal Gastroenterology in 2011, researchers from McMaster University gave typically timid mice a mixture of antibiotics, which changed the composition of their gut bacteria. The researchers recorded a striking change in the mice behavior. They became bold and adventurous. In a follow up experiment, the same researchers took bacteria from the guts of the shy mice and swapped it with bacteria from the guts of mice known for their brave, exploratory behavior. They also placed the gut bacteria from the shy mice into the guts of the brave mice. The result was remarkable. The normally nervous mice became more fearless explorers, while the typically venturesome mice grew more timid and shy. The influence of the gut bacteria overcame the genetic predisposition of the mice.


Findings like this have raised audacious questions about the importance of the second brain and how it may be harnessed to enhance our emotional and physical well being. The day where a patient’s gut bacteria is being analyzed in order to treat their chronic illness may not be far off (I’ll write about experiments being done with ‘Transpoosions’ another time) and while a host of companies have been quick to jump on the bandwagon producing prebiotics and probiotics in various forms in the name of well being, it’s important to note that the research on how gut bacteria may affect our mental and physical well being is still in its infancy.


If you’d like to read more about the enteric nervous system, I highly recommend the book The Second Brain by Dr. Michael Gershon. He’s one of the scientists who identified the second brain and the book is a blend of journey-style story telling of how his discoveries were made as well as covering the fascinating science behind the nerve cells in your gut that act like a brain. His work has lead to a new understanding of gastrointestinal problems like irritable bowel syndrome.


If you’d like to Learn more about the mind-body connection and how the health of your gut can affect your brain, you can watch my film The Connection. Check out the trailer below.


  • Chris

    hi Sharron.
    Just a comment about the gut article.
    1. I plan to read the book and learn more.
    2. I'm recovering from a knee replacement. Normally considered very painful.
    The CODIENE based analgesics gave me Severe Constipation within days.
    With persistence I convinced them to reduce the CODIENE and an emnema fixed it.
    The pain was about 3 x worse than the knee, yet they kept saying "how is your knee pain?"
    My gut was trying to tell me something and I'm thinking more holistically today.

    The medical profession needs to incorporate this new science into practice, thank you for helping that happen

  • Shannon

    Hi Chris,

    Thanks for your comment. I can only imagine what kind of pain is associated with a knee replacement and hope you are now on the fast road to recovery.

    Knowing what I now know about the latest science in mind body medicine, it really surprises me that some doctors are still focusing on just one specialist part of the body rather than viewing it as a whole and while I understand that it would be asking them to be super human to be across everything, it raises a bigger question about the system. When you have something as major as knee replacement surgery, in an ideal world, the best care would involve a team of people working together. I'm glad to hear that you're finding your own holistic approach.

    Wishing you wellness on your journey and hope you're up and about very soon,

  • Armando Ribeiro

    The advancement of psychoneuroimmunology studies allowed the understanding of what was once just a disease of "mind" turn into a deep area of research on the close relationship between body and mind. Who will say in the future that we find throughout the body there is "little brains"? Perhaps, the closer we are the ancient medical traditions who saw the body as having a natural wisdom or healing power of nature. Congratulations on "The Connection"!

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  • Travis

    This is fascinating, I recently came across an article where researchers found that microRNA molecules in food travel intact directly into your bloodstream where it can generate epigenetic changes. This brings a whole new meaning to the phrase "you are what you eat"- the gut, like all other parts of the body, cannot be overlooked.

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  • Shannon

    Hi Travis, I just noticed your comment here as I'm following up another post about the gut-brain axis. Any chance you have the link to the piece you've mentioned?

  • katrina
  • katrina this links to how gut health and auto immune go together very interesting

  • Shannon

    Thanks Katrina, although I read things like this with a skeptical eye. For instance there is no evidence to support the sentence that 'for many people a gut bacteria imbalance can begin at birth because of a C-section or because the mother didn’t have a healthy gut herself.' So far the evidence shows that babies born the old fashion way all have a similar looking bacteria population because the mother's vaginal population changes during pregnancy. As far as I can see there is not evidence to say that she passes on her own gut bacterial population to her baby. You might be interested to read the researcher who is at the forefront of this work looking at the gut bacteria populations of babies. His name is Professor Rob Knight and his book is called Follow Your Gut.

  • anneta

    This is a fascinating eye opener. I was previously aware of heart neurons but not gut neurons. Thank you.

  • Shannon Harvey

    Thanks for reading Aneeta

  • Shannon

    Thanks for reading Anneta.

  • tortuga63

    Actually there is ongoing research (an ivy league school and university of puerto rico) supporting just the opposite

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  • Mike Koehler

    I'm so baffled that science is finally making a gut/brain connection; Edgar Cayce was aware of such relationship and he left us in 1945. Even more concerning is the off label use of miralax; we're eradicating the bacteria from developing children's intestines which is more than likely why we're seeing the increase in childhood illnesses like autism, epilepsy, adhd and the list goes on.

  • Shannon

    Thanks for your comment Mike. I've recently been reading about the research that you mention on disappearing microbiota diversity and the link the illness. Fascinating stuff. It's a very exciting time for gut bacteria research.

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  • Graham

    There has also been testing done where poop from a healthy person is implanted into the intestine of an unhealthy person where the unhealthy person regains health from certain medical conditions. My memory of the details are sketchy at best, but there was something involved tying the two together.

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  • Moses Herve Johnson II

    That's absolutely amazing

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  • Kathleen Sisco

    FEB 2018 Herbal and spring water user experiences broken tooth exposing rot, developed itchy rash on forehead next month. Treating at home for months with herbals no change. Non stop vomiting required hospital ER visit. Given lidocaine by mouth to quell stomach pain. Sent home. The following day still stomach pain but see in mirror face appears 'refreshed." From 70 to 50. Only for the day. Spatial awareness also seems altered.
    My guess is that the lidocaine 'disconnected' the stomach so that it was not able to get 'current' readings on state of inflammation and gave a 'false' reading until it could restore connections. Just a guess.

About the author: Shannon Harvey

Shannon Harvey is a journalist and producer who was diagnosed with an autoimmune disease when she was 24 years old. Although doctors meant well, none could offer her a cause or a cure. Since then Shannon has been researching the latest scientific research linking her mind and body to health outcomes. Nearly 10 years have passed since her diagnosis and today Shannon is well and not taking medication. Shannon has worked as a television, radio and online journalist and producer and has a Master’s degree in Communications. She worked for the ABC and Fairfax before starting her own production company, Elemental Media. Shannon is the director of the feature film The Connection.



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The Connection is a feature documentary and blog about integrating the latest science in mind body medicine into our everyday lives.


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