What Is The Gut-Brain Connection?

The gut-brain connection is the system within your body that facilitates a two way communication between the GI tract and the brain. The gut or GI tract has its own nervous system called the enteric nervous system (ENS) which means there is a complex signaling system from the gut to the other parts of the body. Primarily, this signaling goes to from the gut to the brain. This is why many people with neurological disorders have underlying gut issues that may not even be symptomatic. For example, one study in children with autism found that 43% of those with autism had intestinal permeability (leaky gut) even without any gastrointestinal (GI) symptoms. This means they had neurological symptoms as a result of the gut issues.  

The vagus nerve is the primary nerve for this information superhighway because it runs from the base of the brain down the whole length of the back. The vagus nerve is actually able to sense information from the gut (primarily the gut bacteria) and transfer that information to the brain. Because of this, the vagus nerve is sometimes called the 6th sense. The gut-brain connection integrates bacterial colonies with the nervous system and the brain where the bacteria actually sense and send information through the nerve signaling. It may sound like a sci-fi movie, but it is part of the brilliance of the human body. With the advances in science and technology, we are now better able to understand just how phenomenal our bodies are!  

The gut-brain connection is connected to the concept of “leaky gut” or intestinal permeability because leaky gut affects the brain, causing what is now called “leaky brain.”  The GI tract is the gateway to the rest of the body. Everything you consume goes through the GI tract where it is broken down into the sizes of molecules that are carried into the bloodstream. Granted, this comes with complex signalling from the nervous system and tons of enzymatic reactions, but at the end of the day, when all goes well, what should be in the gut stays there and continues on to become bowel movements, and what is designed to get into the bloodstream for nutrients to the rest of the body, does so.

Leaky gut occurs when this system is disrupted by either faulty signaling from the nervous system, lack of enzymes for adequate digestion, or poor digestion resulting in molecules not being broken down correctly (and all of those combined). At the same time, damage to the gut lining occurs from the issues listed above, and various other sources of inflammation. When the lining of the GI tract is not what it should be, molecules that are too large are able to escape. When the wrong types move into the bloodstream, the immune system is alerted that there are foreign invaders and this creates an immune system flare and more inflammation in the body.

Because of the vagus nerve signaling processes, the leaky gut inflammation can, and does, send the faulty signaling to the brain. This is the root-cause of most neurological disorders, including spectrum disorders like ADD/ADHD and Autism. The research and medical literature proving these connections is so clear and foundational to the current trends of mental health issues that anxiety, depression, bipolar, schizophrenia, ADD/ADHD, Autism, etc are no longer considered only mental health disorders. They are whole system biochemical imbalances that find their root, and most of often their resolution/improvement  in improving gut health.

The large amount of research currently happening around the gut microbiome now considers the quantity, quality, and diversity of gut bacteria to play a key role in gut and neurological functions. The gut-brain connection, is now the gut, brain, bacteria connection. A recent article titled “I Am I And My Bacterial Circumstances,” links the gut microbiome to depression and neurodevelopment suggesting that gut bacteria directly link to incidence of and risk of neuropsychiatric disorders. This is just one of many in the medical literature confirming this connection.

More On Microbiome And The Brain

Because of the ability to map the DNA sequences of bacteria in the GI tract, so much has been learned the past decades about the impact of bacteria on our bodies. In fact, it is the life’s work of many researchers, biologist, and doctors. The study of the human microbiome is likely impacting medicine more directly and profoundly with more implications for the future of medicine than many other areas of medical research. All this information points directly to the need for a functional medicine approach to health issues, including mental health. The level of information available about the effects of the gut microbiome on humans is vast and wide, but point here is to recognize that there is no disease, condition, or imbalanced system that will not be affected by the GI tract and vice versa. The ways in which we do or don’t care for the GI tract will affect the future of your health.

Your GI tract has trillions-literally, of bacteria. The majority of these bacteria are friendly. They are a benefit for you, the human host.  These microorganisms aid in digesting food and providing nutrients for your body. Your friendly bacteria actually produce vitamins your body needs, specifically B vitamins and vitamin K and the gut bacteria impact the way your body uses fats, proteins and carbohydrates. Your gut bacteria also helps you breakdown and get rid of endocrine disrupting chemicals and supports your immunity.

Gut bacteria impact every part of the human body.













The gut microbiome is a human interaction story of diversity and adaptability. The bacteria in your gut are always adapting to do their best to serve you well, and work best for you when you support them. There is exciting research work being done on specific microorganisms that affects specific functions in the body and even produce certain human traits. For example, it has been found that there are specific microorganisms that most elite athletes have, that others do not. There are similar findings in people who are overweight, and those who have Autism. The map of bacterial diversity is now telling the story of people and perhaps even shaping the story of people’s lives. How you support your gut microbiome affects your future more than we’ve ever known. In fact, the diversity of bacteria developed within the first 36 months of life can contribute to risk of depression later in life. Having enough good bacteria and good diversity of bacteria is what is most consistent with good overall health, so this is the best place to start.  

Ways to support your gut microbiome include:

  • Increasing Probiotic foods and supplements (provide new good bacteria)
  • Increasing Prebiotic foods and supplements (support existing good bacteria)
  • Limiting sugar (decrease good bacteria)
  • Limiting chronic stress (decreases good bacteria)
  • Avoiding toxic chemicals from body products, cleaning products, and home products

A Way Forward to Correct and Protect Your Gut-Brain Connection

At the end of the day we can spend a whole life studying and understanding the implications of the gut-brain connection and the influences of our gut bacteria on these connections, but what we do with the information is what is most important. This is where food, environment, and lifestyle play a massive role in your health. Although our genetic factors can predetermine your resilience or vulnerability towards a particular health issues, the food, environment, and lifestyle determine how your genetics will be switched on or off.

If the digestive tract is the gateway for all consumed substances passing into the body, then what you eat impacts your whole health. Most people agree with this in theory, but in practicality of daily food choices, this can break down a bit. Finding the best way to eat for your health, is highly individualized and what may be causing inflammation for one person may be actually a key to lowering inflamation for another person. This is why working with a functional medicine team to determine what foods are causing inflammation in your body and what probiotic and prebiotic strains will be best for your specific needs is the best.

However, there are a few food principles that will be beneficial for everyone that anyone can begin doing. We call it 3-3-3. Three things to increase, three things to decrease, and three things to avoid.


  • Increase organic vegetable intake
  • Increase purified water intake
  • Increase quality fat intake (olive oil, coconut oil, avocado, MCT oil, nuts, grass-fed butter)
  • Decreased processed/refined carbohydrates
  • Decrease natural/organic sugars like: honey, maple syrup, coconut sugar, agave nectar
  • Decrease or eliminate foods with  added chemicals, preservatives, and food dye
  • Eliminate gluten containing foods
  • Eliminate GMO, refined sugar sources
  • Eliminate drinks containing sugar including fruit juice

A full functional medicine assessment is the best way to ensure you have the information, tools and resources you need to correct and protect your gut-brain connection. This assessment includes a discussion with the functional medicine doctor about your medical and health history, laboratory data that give accurate data of where your support needs to be and ongoing support to help you understand and implement your healing plan. Both children and adults benefit from this process.  If you or someone you love suffers from mental health disorders, including anxiety, depression, autism, ADD/ADHD, or OCD, supporting the gut-brain connection is fundamental for them. and the team at in2GREAT Integrative Health is passionate and committed to supporting the mental health aspects of your biochemistry that are so profoundly affected by the gut-brain connection.


  1. I Am I and My Bacterial Circumstances”: Linking Gut Microbiome, Neurodevelopment, and Depression
  2. Role of the normal gut microbiota
  3. Host microbiota interactions in the intestines
  4. Rapidly expanding knowledge on the role of the gut microbiome in health and disease
  5. Influence of the gut microbiome on autoimmunity in the central nervous system
Dr Corey Priest, DC - Functional medicine practitioner

About the author

Dr. Corey Priest has been practicing functional medicine since 2001. in2GREAT was founded in 2014 by Dr Priest after 13 years of experience with his other practices. Over his career, Dr. Priest has worked with and helped well over 10,000 patients under a functional medicine model.

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