The Mind-Gut Connection
June 5, 2023
When I read a book I have the habit of highlighting certain passages I find interesting or useful. After I finish the book I’ll type up those passages and put them into a note on my phone. I’ll keep them to comb through every so often so that I remember what that certain book was about. That’s what these are. So if I ever end up lending you a book, these are the sections that I’ve highlighted in that book. Enjoy!
A dite that is high in plant-based complex carbohydrates (from a large variety of different plants), plant-derived fat, grains, naturally fermented foods, and fish, and low in red meat, animal-derived fat, refined sugars, and processed food is the blueprint for most healthy diets around the world. If you add the benefits of polyphenols (molecules with health-promoting effects that are largely processed by the git microbiota) contained in olive oil and red wine, certain plant products with anti-inflammatory effects such as turmeric, curcumin, and ginger, and a large number of fermented foods teeming with microorganisms, you have a simple road map for a diet that is good for your microbes (increases the diversity, abundance, and populations of health-promoting microbes), good for your gut (reduces intestinal permeability, e.g., improves a leaky gut), and good for your brain (prevents low-grade immune activation in your brain).
Traditional Asian diets, for example, including the Japanese, Korean, and Chinese diets, share a high consumption of fish, varied plant-based foods rich in polyphenols and anti-oxidants, grains, and naturally fermented foods, and limited meat and dairy products.
Food has a strong communal element, especially the sharing of several small dishes during a meal.
Infancy is a period that is particularly critical for the formation of a healthy microbiome and the brain-gut axis.
Eating a Japanese meall fully engages one’s attention, appealing to all the senses, including visual appeal, texture, and taste.
The gut microbiota is basically the microbes living in the gut. The signaling molecules that the microbes produce from the their vast number of genes is call the microbiome.
The gut can influence our basic emotions, our pain sensitivity, and our social interactions, and even guide many of our decisions.
The gut-based immune defense system is capable of identifying and destroying a single species of dangerous bacterial invaders that makes it into our digestive system when we accidentally ingest contaminated food or water. What is even more remarkable, it accomplishes this task by recognizing the small number of potentially lethal bacteria in an ocean of a trillion other benevolent microbes living in your gut, the gut microbiota.
95% of the body’s serotonin is stored in the gut.
Gut feelings are stored in vast databases in the brain, which can later be accessed when making decisions.
If you put all your gut microbes together and shaped them into an organ, it would weigh between 2 and 6 pounds–on par with the brain, which weighs in a 2.6 pounds. Based on this comparison, some people have referred to the gut microbiota as a “forgotten organ”.
No two people’s gut microbiota are exactly alike in terms of the many strains and species of microbes they contain. The microbes present in your gut depend on many factors, including your genes, your mother’s microbiota, which all of us take on to some extent, the microbes that other members of your household carry, your diet, and your brain’s activity and state of mind.
Are our human bodies just a vehicle for the microbes living in it? Do the microbes manipulate our brains to make us seek out foods that are best for them?
A particularly important role of such microbe-produced molecules is their ability to induce a state of low-grade inflammation in their target organs.
When you are fuming in traffic, your brain sends out a characteristic pattern of signals to your digestive system, just as it does to your facial muscles; the digestive system also responds dramatically. As you sat fuming about the driver who cut you off, your stomach went into vigorous contractions, which increased its production of acid and slowed the emptying of the scrambled eggs you ate fro breakfast.
Every time your stomach was tied up in knots, you had a gut-wrenching experience, or you felt butterflies in your stomach, it was the emotion-generating circuits of your brain that were responsible.
Here’s what happens when you sit down for a meal and put the first bite of food in your mouth:
Even before you chew and swallow your food, your stomach fills with concentrated hydrochloric acid that can be as acidic as battery acid. When the partially chewed bites of steak get there, your stomach exerts grinding forces so intense that they break up the steak into tiny particles. Meanwhile, your gallbladder and pancreas are preparing the small intestine to do its job, by injecting bile to help digest fat, and a variety of digestive enzymes. When your stomach passes the tiny steak particles to the small intestine, the enzymes and bile break them down into nutrients that the gut can absorb and transfer to the rest of the body. As digestion proceeds, the muscles in your intestinal walls execute a distinct pattern of muscular contractions called peri-stalsis, which moves food down and through your digestive tract. The strength, length, and direction of peristalsis depend on the type of food you have ingested, ensuring, for example, that the gut has more time to absorb fat and complex carbohydrates, and less for a sugary drink. At the same time, parts of your intestinal walls contract to steer the food being digested to the lining of the small intestine, where nutrients are absorbed. In your large intestine, powerful waves of contraction move contents back and forth to enable the organ to extract and absorb go percent of the water in intestinal contents. Another powerful wave of contraction then moves contents toward the rectum, typically triggering an urge to have a bowel movement. Between meals, a different pressure wave–the migrating motor complex–serves as your gut’s housekeeper, sweeping out anything else your stomach couldn’t dissolve or break down into small enough pieces such as undissolved medications and unchewed peanuts. This wave slowly travels from the esophagus to your rectum every ninety minutes, generating enough pressure to crack a Brazil nut and sweeping undesirable microbes from your small intestine into the colon. Unike the peristaltic reflex, this housekeeping wave operates only when there’s no food left to digest in your GI tract–when you’re sleeping for example–and it switches off as soon as you take your first bite of breakfast
If your dinner conversation takes a wrong turn and you get into an argument with your friend, your stomach’s wonderful meat-grinding activity is quickly turned off and instead goes into spactic contractions that no longer allow it to empty properly. Long after you have left the restaurant, your stomach will still be in spasms as you lie awake. Becuase there is still food in your stomach, the nocturnal migrating contractions won’t happen, preventing the usual overnight cleasning of your gut. This is how stress can be unhealthy for you, and also why you shouldn’t eat right before bed.
The Second Brain likes to show a video clip that demonstrates the enteric nervous system’s ability to operate independently. In it, a section of guinea pig intenstine sits in a bath of fluid, and on its own propels a plastic pellet from one side of the intestine to the other–all without any connection to the brain.
When we face life-threatening situations the emotion-related brain circuits send signals to the stomach and intestine to rid themselves of contents that might otherwise drain energy required for action, which is why you might need to head to the bathroom before your big presentation. Our cardiovascular system reroutes oxygen-rich blood from the gut to the muscles, slowing digestion and preparing us to fight (or flee).If you also experienced emotional trauma as a child, your body added chemical tags to these key stress-response genes. As an adult, you will most likely experience exaggerated gut reactions to stress. This explains the common observation that two individuals exposed to the same stressful situation may show very different reactions to it.
If you can return to the restaurant where you argued with your spouse over dinner (Say an Italian place) even the mere thought of risotto di mare may trigger the anger program. Explore whether it’s the food in fact a recollection of an earlier event that’s responsible for the symptoms.
Think about all the horrendous-tasting bitter herbal medicines employed in traditional Chinese medicine. It seems much more likely that their therapeutic effects have little to do with the bitter taste experience they give you, but are related in some way to the activation of one or more of the gut’s twenty-five bitter receptors, thereby sending healing messages to your brain and body.
Today we know about the complexity of gut sensations and the crucial role the vagus nerve plays in transmitting these signals to the brain regions liek the hypothalamus and limbic brain regions, which in turn influence a wide range of vital functions such as pain, appetite, mood, and even cognitive function.
The new symbiosis between the tiny marine creatures and their resident microbes led to many benefits for both of them. The animals gained the ability to digest certain foods, obtain vitamins that they couldn’t synthesize themselves, and evade or expel toxins and other dangers in their environment.
Microbes are kind like parasites, but mostly helpful ones. That’s how they started out in the beginning of time and this symbiotic relationship between git microbes and their hosts turned out to be so beneficial for both partners that it has been conserved in virtually every living multicelluar animal on earth today.
Microbes are just trying to live good lives. If we eat bad and provide them with bad food, they signal our brain to feel bad, in hopes of making us eat better next time so that they have better food next time.
Microbes gain by being able to live a privileged life in our intestines, which comes with a constant supply of food, moderate temperatures, and unlimited free travel. In exchange, the microbes provide us with essential vitamins, metabolize digestive compounds, called bile acids, that are produced by the liver, and detoxify foreign chemicals that our bodies have never experienced–so-called xenobiotics. Most important, they digest dietary fiber and complex sugar molecules that our digestive system can’t break down or absorb on its own, and thus provide us with a substantial number of additional calories that we would otherwise lose in our stool. In prehistoric times, when people were more concerned with hunting and gathering enough food to eat than fitting into their skinny jeans, the extra calories that gut microbiota extracted from food helped them survive. But today, as we’re awash in excess food and obesity is epidemic, the extra calories that gut microbes provide have become a liability.
Your gut microbes can listen in on your brain’s ongoing conversation and vice versa, and information flow through the biological channels that your gut microbes use to communicate with your brain is highly dynamic. The amount of information that is allowed to travel through this system depends in large part on the thickness and integrity of the thin mucus layer lining the gut surface, the permeability of your gut wall (its leakiness), and the blood-brain barrier. Normally, these Barries are relatively tight, and the flow of information from gut microbes to the brain is restricted. But stress, inflammation, a high-fat diet, and certain food additives can make these natural barriers leakier.
People eating a high animal fat diet have an increase in the relative abundance of such gram-negative bacteria in their gut, of Firmicutes anbd Proteobacteria, and are therefore more likely to chronically engage his immune activation mechanism. A diet low in plant-based fiber reduces the abundance of a particular microorganism called Akkermansia muciniphilia inside of our gut. Under normal conditions, this thickness of the mucus layer that is part of the barrier separating the inside of our gut from our immune system.
The thinner the mucus layer, the closer th intestinal microbes get to the cells lining the gut, the leakier the gut becomes and the easier it is for the gut microbes to activate the gut’s immune system.
During birth, a baby born naturally is exposed to the mother’s vaginal microbiota, including this lactobacillus species, providing the key source of microbes to colonize the infant’s gut. In this wa, your mother’s distinct set of vaginal microbes formed the basis for your own distinct pattern of gut microbes, and will for the rest of your life.
It is important to remember that ther are several factors that contribute to Jonathan’s gastrointestinal symptoms. Firstm he chooses food based on its texture rather than its tast, resulting in a highly restricted diet avoiding many plant-based foods. Second, he consumes a lot of processed food. Third, his high anxiety levels and stress sensitivity alter his gastrointestinal contractions and secretions and increase the leakiness of his gut.
The cycling experience in infancy of feeling full of hungry–good or bad–maa lay the foundation for the moral judgements of good and bad that emerge into gut feeling later in life. In other words, your gut registered how well your needs were met or not met in infancy. A hungry babe left in its crib to cry for an hour perceives the world very differently form the baby who is quickly picked up, cradled, and fed. Thus your earliest git feeling serve as a model fro “what the world is like and what I must do to survivie in it.”
It’s clear that those first two and a half to three years shape our gut microbiome for a lifetime.
We know today that it’s the infant’s food supply, in particular breast milk, which helps her gut fill with the initial healthy mix of microbes. Keep in mind that the composition of breast milk is crucially dependent on the diet the mother consumes.
When you are born into Western civilization, you acquire a Western microbiome as well. Even if you go vegan today, your gut microbiota will remain that of a typical omnivore, and even if you eat a paleo diet for the rest of your life, your gut microbiota won’t turn into that of a hunter-gatherer. However, the pattern of microbial metabolites you produce depends on which diet you consume. Even if you and a neighbor eat a very sinmilar diet, you will have different species of microbes in your gut than she does.
Studies in animals and humans have demonstrated that a key link between the overconsumption of animal fats and the onset of disease.
The North American diet–high in animal fat, low in plants, and enriched with chemicals and preservatives–is reprogramming our gut-brain microbiome axis, and not for the better.
Our livestock often live out their lives in small pens, eating feed (liek corn) that their digestive systems are not built to handle. They ingest antibiotics and other chemicals, which reduce the diversity of their gut microbes and make them more vulnerable to serious gut infections. For all these reasons, the meat, eggs, and milk in today’s processed food–are dramatically different from only fifty years ago.
There are several factors that have been implicatyed as the major culprit in the dysregulation of gut microbiome brain affecting our health, including the excessive consumption of sugar and the insufficient intake of dietary fiber.
There is a detrimental role of high consumption of fat from animal sources.
Today, there’s far more animal fat hidden in all the things we love to eat, and while we are craving and enjoying the consumption of these tasty meals, they secretly manipulate our gut microbiota, their metabolites, and our eating behavior.
The language that signals your brain to stop eating when you’ve eaten enough and feel hungry again when your stomach is empty includes hormones that can stimulate or turn off your appetite, the latter being called satiety hormones. Thesegut hormones target a brain regionm called the hypothalamus, which is the msater regulator of our eating behavior. When the system is working properly, the hypothalamus can precisely compute how many calories your body needs on any given day, based on your level of physical activity, the temperature, and other factors that influence your metabolism.
A large portion of this information comes from the gut, sent in the form of various gut hormones and vagal nerve signals. When you’re hungry, enteroendocrine cells interspersed within the calles lining your stomach release a hormone, called ghrelin, also known as the hunger hormone, which either travels through the bloodstream to the brain or stimulates the tips of the vagus nerve in the gut to signal the brain directly. On the other hand, when you’ve had enough to eat, a different group of appetite-supressing hormones (including cholecystokinin and glucagon-like peptide) are released from enteroendocrine cells in your small intestine, and these hormones turn the system off and suppress appetite.
A regular high-fat diet can numb the satiety response both at the gut and the brain level, reducing your ability to tell when you’ve eaten enough. It does this in both locations by causing low-grade inflammation. In the gut, that inflammation reduces sensitivity to satiety signals by sensors on the vagus nerve, which normally tell your hypothalamus that you’re full. In your hypothalamus, it reduces sensitivity to satiety signal arriving from the gut.
When you ingest a high-fat meal, blood levels of inflammatory molecules increase throughout your body.
When a gut microbes approaches the cells that line the inner gut, these cellse recognize LPS on the microbe’s surface and use a receptor to bind it. LPS stimulates these cells to produce other inflammatory molecules (cytokines), makes the gut leakier, and activates the immunes cells in the gut.
Several barriers prevent LPS and other microbial inflammatory signals from initiating this sequence of events. As LPS levels increase (as they do in response to a high-animal-fat diet), the molecule starts to breach these barriers and activate the git’s immune system to produce cytokines and reach distant sites within our bodies, including our brain. Once these molecules reach the brain, they get access to its immune system, the glial cells, which start producing inflammatory molecules themselves, targeting nearby nerve cells in the brain.
Women who regularly eat comfort doos when stressed dampen their physiological response to stress.
High fat intake can have an emotionally comforting effect.
Artifical sweeteners not only fail to help you lose weight in the short term, They can also be a mjor cause of the inflammatory changes in your gut-brain axis.
Several mechanisms have been proposed to explain the extensive health benefits of the Mediterranean diet. Besides the high levels of protective antioxidants and polyphenols contained in olve oil and red wine, which have benefical effects on cellular health, the anti-inflammatory effect of the Mediterranean diet on the body is most often cited. Polyphenols are plant-based compounds found in a variety of foods and beverages. Besides red grapes and olives, many other fruit and vegetables are rich sources of polyphenols, as are coffee, tea, chocolate, and some nuts.
All the efforts of the harvest ritual–the age of the trees, picking of the mostly green olives, preserves the maximum amount of polyphenol content. Based on scientific analyses, that Marco performs on the fresh-pressed olive oil every year, it is obvious that the polyphenol content in oil made from these ancient olive trees is severalfold higher than that from younger trees, where most of the commercially available oil comes from.
We now know that, in addition to the high levels of complex carbohydrates in thei largely plant-based diet, it is the high levels of polyphenols that exert a benficial effect on the gut microbiota. The polyphenols not only come from the daily consumption of extra virgin olive oil; these health-promoting compounds are also contained in notes, berries, and red wine, all of which are essential elements of the Mediterranean diet.
There are other traditional dietary habits aroudn the world which have demonstrated similar positive effects on health. They include the traditional Japanese diet, including the Okinawan diet, and the traditional Chinese and Korean diets.
Not surprisingly, all these health promoting diets share the high ratio of plant-to-animal-derived food items associated with high dietary fiber consumption, and the high intake of products with anti-inflammatory and disease fighting molecules.
Only a small percentage of people in the Uited States live in a state of optimal health, a condition that has been defined as complete physcial, mental, emotional, spirtual, and social well-being, with peakl vitality, optimal personal performance, and high productivity. In other words, it’s a person who not only has nbo bothersome physical symptoms but is also happy, optimistic, has lots of friends, and enjoys his or her work.
If there is one characteristic that stands out among all of them, it is their curiosity and excitement about all things in life, their positive view of the world, and their unwillingness to be bogged down by negative people or events. Their gut-based decisions seem to have a consistenly positive bias, assuming that no matter what, they will be okay.
Our gut-microbiota-brain interactions are shaped early in life, from before birth to age eighteen, through our interactions with the world–our psychosocial influences, diet, and chemicals in our food (including antibiotics, food additives, artifical sweeteners, and more). Eearly life–from before birth to age three–is a particularly crucial period for the shaping of the gut microbial architecture.
How & what to feed your gut microbes
Diversity – One of the generally agreed-upon criteria for a healthy gut microbiome has been its diversity and the abundance of microbial species present in it. As in the natural ecosystems around us, high diversity of the microbiome means resilience and low diversity mean vulnerability to perturbations.
Stability & Resilience – Although you may carry different microbial species than your coworker or cousin, you tend to carry the same key set of species for long periods. This stability is critical for your health and well-being. It ensures that friendly git microbes can return quickly to an equilibrium state following a stress-related perturbation, which allows them to keep up their beneficial activites over time. This makes a microbiome resilient.
Practice natural and organic farming of your gut microbiome – Consider your gut microbiome as a farm and your microbiota as your own personal farm animals, then decide what to feed them to optimize their diversity, stability, and health, and optimize production of beneficial signaling molecules that affect our brains.
Cut down on animal fat in your diet – Since our brain-gut axis has not evolved to cope with a daily avalanche of fat and corn syrup, a high-fat diet sets up a vicious cycle of dysregulated eating behavior that harms your brain health.
Maximize your gut microbial diversity – In addition to eating moderate quantities of meats low in fat, mainly from fish and poultry, increase your intake of food items that contain multiple prebiotics in the form of different plant fibers.
Avoid mass-produced and processed foods and maximize organically grown food – Bascially only buy things in the market that look like food.
Eat fermented foods and probiotics – Regular intake of probiotics may help to maintain gut microbial diversity during times of trouble, and it can normalize that pattern of metabolites produced by your gut microbes.
Fast to starve your gut microbes – A popular explanation for the benefits of fasting is based on the idea that it cleanses the gut and the body by getting rid of harmful and toxic substances. Even though people have believed this throughout history, there is little scientific evidence for this hypothesis. However, fasting may have a profound effect on the composition and function of your gut microbiome and possibly on your brain. When your stomach is empty, it activates periodic high-amplitude contractions that slowly but forcefully sweep from the esophagus to the end of the colon. At the same time, the pancreas and the gallbladder secretion release a synchronized burst of digestive juices. The combined effect of this reflex, called the migrating motor complex, in analogous to a weekly neighborhood street sweeping. It removes microbes from the small intestine, where most gut microbes live. In people with an inactive migrating motor complex, microbes grow more abundantly in the interior of the small intestine, a condition called small intestinal bacterial overgrowth. This causes abdominal discomfort, bloating, and altered bowel habits.
Don’t eat when you are stressed, angry, or sad – A negative emotional state will throw the gut-microbiota-brain axis out of balance in several ways It makes your gut leakier, it activates your gut-based immune system, and it triggers endocrine cells in the gut wall to release signaling molecules such as the stress hormone norepinephrine and serotonin. It can also reduce important members of your gut microbial communities, in particular lactobacilli and bifidobacteria. Scan you body and mind and tune in to your emotions before you sit down to eat something.
Enjoy meals together – If you eat when you’re happy, your brain send signals to your gut that you can think of as special ingredients that spice up your meal and please your microbes. Try to switch to a positive emotional state and experience the difference this shift has on your overall well-being.
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