Chapter 3 | Review & Discussion | The Mind Gut Connection by Emeran Mayer, MD
The Canary in the Coal Mine
Did you know that coal miners used to place canaries in cages and take them deep down into the mine shafts with them as a companion? You might ask, “Why in the world would they do that?” Well as it turns out, the canaries were more than just a companion to lonely miners – instead, they acted as an alert system to toxic carbon monoxide gas that was sometimes present in the mine shafts. Canaries are more sensitive to carbon monoxide than humans and would pass out long before the people did, giving the miners a sure reason and adequate warning to get out of the area, fast!
“Hey miner, need a canary? Cause I can paint this bird yellow…”
The miners learned and quickly adapted to find ways to protect themselves from a dangerous situation. Dr. Mayer states that some people in the world act like our canaries, physically reacting to shifts in food additives or changes in the food supply before the rest of us have ever noticed. Therefore, we should be paying closer attention to their symptoms as our own warning signals. Chapter 3 of The Mind-Gut Connection explores how our gut communicates with our brain, and Dr. Mayer gives his explanation of why some people are more sensitive to their gastrointestinal (GI) tract than others.
What is Our Gut Telling Us?
If the gut-brain axis is a superhighway of information, most of the traffic runs north from the gut to the brain, according to Dr. Mayer. The brain relies so heavily on the data that it constantly receives from the gut that scientists now believe many more aspects of our health are controlled by what the gut is telling our bodies than we ever thought before. Let’s dive right in to explore how the gut communicates with the brain.
Listen to Your Gut
Have you ever REALLY tried to “listen” to your gut? Dr. Mayer begins by offering a case study of a young woman who spent a day paying attention to the signals that her stomach was sending to her throughout her normal routine. We do not normally notice what our gut is doing because we have no real reason to, with the exception of the major signals that are sent to our brains telling us that we’re hungry, full, worried, or sick. It’s almost a survival instinct that we do not have to care what’s going on down in our gut unless a response is needed – and this fact keeps us from being in a constant state of distress by being worried about how our bodies are reacting to the food we eat.
“File:A woman shouting into a man’s ear-trumpet. Wood engraving. Wellcome V0011264.jpg” is licensed under CC BY 4.0
However, there are some people in the world who CAN feel every small movement in their digestive system. They have been shown on medical tests to be super sensitive to all signals in their bodies, including signals stemming from the gut. Can you imagine being able to feel food move through your intestines? Or, maybe even worse, being one of the 10% of the population whose signals are jumbled and corrupted between the gut and the brain? Until recently, scientists dismissed hypersensitivity symptoms as being purely psychological. However, they’ve started realizing the importance of the gut brain connection, and doctors have begun to think that the real culprit might lie in the fact that the receptors in the digestive tract are overly sensitive to stress and change.
Stress can Change Gut Brain Communication
What did you think when you read ‘menthol’?
Take Frank, for example, a 75 year old retired schoolteacher whose wife had passed away five years earlier, and who went to see Dr. Mayer with GI problems that developed after his wife died. While he exhibited classic IBS symptoms, he also complained of strange sensations like discomfort behind his sternum that sometimes tasted like menthol. What? No, Frank hadn’t started smoking menthol cigarettes, but that right there is enough to make you stop and wonder.
Dr. Mayer determined that something had shifted in Frank’s eating habits that potentially correlated to the death of his wife – he had begun eating fattier foods like chocolate cake, pizza, french fries, and rich cheeses. Disturbances like these changes in the diet are enough to cause major communication breakdowns between your gut and your brain, sending jumbled sensations and signals coursing through your body. In Frank’s case, this resulted in the menthol taste he experienced. Like the canary in the coal mine, Frank’s sensitivity to change in his food supply should be a warning sign to the rest of us that we need to pay closer attention to what we eat and how changes relate to our overall wellness.
Enteric Nervous System & Receptors
Most of the information that the gut reports to the brain is motor sensory data, like how much food you’ve eaten, how fast or slow to move it through the digestive tract, and how much bile acid to produce to properly break everything down. The GI tract even reports on the state of the microbiota in your gut, including if there are parasites that you’ve ingested and how to expel them. The enteric nervous system is the system of neurons in your GI tract that regulate digestive function and communicate with the brain. We now know that this system is lined with some of the same receptors that are in your tongue that send taste signals to your brain. Why in the world would the inside of your body be lined with “taste” receptors?
They have so far found 25 different bitter taste receptors in the human gut, and scientists are still trying to figure out why. They think that the gut’s phytochemical receptors, the receptors that respond to chemicals found in plants, are sensitive to herbs and chemicals in the plants that we eat for functional health reasons that go farther than just making our food taste good to us. Perhaps culturally we’ve adapted to liking certain spices or herbs in our diets because they help the people in that region of the world properly digest the available food; OR, does our gut tell us to eat certain spices and herbs because the microbes crave them as food with the end result of making the body feel better and healthier?
The Microbiome & Obesity
Also, when your diet shifts it changes the way your microbiota produce bi-products, like metabolites (the end product of bacterial metabolism). Your gut receptors are sensitive to the metabolites that your trillions of microbiota produce, and if the metabolites change, your reaction to them will change as well. It makes sense that if your diet shifts to being more high fat, your microbiota metabolites will also shift, and the gut receptors’ reaction to them will shift as well, and scientists now think this could be more related to obesity than we ever thought before. There is a scientific hypothesis that the metabolites produced from your microbiota could play a crucial role in obesity, and scientists are now studying the microbiome as a potential cause and solution to the obesity epidemic.
But what do the receptors and nerves in your gut actually do with the data they collect? They communicate with the endocrine and immune systems, which send signals to either the enteric nerve system running through your digestive tract or to your brain via the vagus nerve (the axis). Your endocrine system releases hormones depending on the signals received from your gut, and your immune system controls the release of inflammatory molecules called cytokines (bad) depending on whether the gut tells the immune system that something is wrong with the food you just ate. This may mean that if you eat fatty foods or gluten, your receptors can send signals to your immune system to release harmful cytokines into your bloodstream that can travel to your brain, causing anxiety, depression, and other negative brain disorders.
Cutting the Vagus Nerve
The vast amount of neurons located in your gut’s sensory network relay chemical, nutritional, and physical information to your small brain, the enteric nervous system in your gut, and to your large brain in your head through your vagus nerve. The vagus nerve is so important and misunderstood that doctors in the 1980’s used to cut the nerve in patients that had ulcers in order to stop the symptoms. They understood that there is a connection between the gut and brain, but did not realize that by cutting the vagus nerve they would cause a wide range of new problems to evolve. These procedures, called vagotomies, are rarely done anymore now that we understand a bit more about the importance of the vagus nerve in gut brain communication. However, a silver lining is that the patients who received vagotomies gave doctors and scientists case studies as to what happens when your vagus nerve is cut, so stay tuned for more about this in a future blog post! We did discover, though, that vagal nerve stimulation can be used as a novel therapy to treat a range of disorders such as depression, epilepsy, chronic pain, obesity, and chronic inflammatory diseases such as arthritis. Exciting!
The Role of Serotonin
When we talk about the gut-brain connection, the conversation always leads back to serotonin, the hormone that helps stabilize our mood. However, did you know that when you get food poisoning, it’s the rush of serotonin that is released in your gut that tells your brain to get rid of what’s in your stomach by whatever means possible – meaning both ends of your body? Normally, a slow release of serotonin helps regulate peristalsis (movement) in the digestive process, but when you ingest toxins after eating contaminated food, the concentrated release of serotonin suddenly increases peristalsis, making you vomit and have diarrhea.
According to Dr. Mayer, serotonin is the “ultimate gut-brain signaling molecule”, playing a role in almost every signal between our “little brain” and our “big brain”. If serotonin signals are constantly being sent from our gut to our big brain, and serotonin is made by the amino acid tryptophan that we consume in our diet, then if we do not consume enough tryptophan we will not produce enough serotonin to send regular signals to our brain, resulting in depression. Yet again, another connection between what we eat, how we digest it, and how our gut signals affect how we feel and our overall mood.
The Mind Gut Connection via the Gut-Brain Axis
All of this leads us to ask why the gut would contain such complex information data receptors anyway? The immense amount of information that the gut transmits to the brain from both our digestive processes and the 100 trillion microbes living in our intestinal tract tell us that we need to realize NOW that gut function is more than just about nutrients and metabolism. Our gut system, with its huge nervous system and population of microbial residents, surpasses our brains in the number of cells it has and needs to be studied as closely as our first brains for ultimate mental health and wellness.
When we think about the food entering our gut, now maybe we will also stop to think about what is in the soil when the food is grown and the chemicals added to our packaged food before we eat it. We should learn from the human canaries in the coal mine who are sensitive to food allergies, gluten, and dietary shifts, because ultimately foods and chemicals result in signals being sent from our gut to our brain. After all, every signal our gut receptors transmit has an effect on our overall health, so shouldn’t we be paying a lot closer attention to nurturing them?
Our bodies and minds are extremely complex, yet highly organized. We must better understand the relationship between the mind and the gut to become masters of these connections, and to help ourselves control both our physical and mental well-being.
Join us on this journey and check out the book for yourself! Read along with us if you like. You can then comment and share your views on this book and the subject of the gut and mind connection.
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