Mindblowing Facts about Your Gut-Brain Connection

I recently read Emeran Mayer’s book, The Mind-Gut Connection: How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices, and Our Overall Health.

In it, Mayer argues that while the dialogue between the gut and the brain has been recognized by ancient healing traditions, including Ayurvedic and Chinese medicine, Western medicine has by and large failed to appreciate the complexity of how the brain, gut, and more recently, the gut microbiota — the microorganisms that live inside our digestive tract — communicate with one another.

If your curiosity about what is being dubbed ‘our second brain’ has been piqued, Dr. Emeran Mayer, a professor of medicine and executive director of the UCLA Center for Neurobiology of Stress, offers a provocative look at this developing science, teaching us how to harness the power of the mind-gut connection to take charge of our health and listen to the innate wisdom of our bodies.

My main gripe about the book (and it’s a big one) is Mayer’s tendency to conflate and/or lump sugar and fat into the same bucket, despite their very different effects on the body, and despite conventional wisdom in this space touting the value of fat and ketogenic diets. Time and time again, he also fails to distinguish between different types of fat. Apart from that, the writing was a little too academic for my liking, but the content made the read compelling enough to not put this down until it was read.

The book offered up lots of golden nuggets about how our gut affects our brain, and perhaps more importantly, what you can do to develop a healthier gut, so that you can not only feel better, physically and emotionally, but make better decisions, and thus lead a better life.

I’ve captured these golden nuggets in my book notes, condensed for your benefit, below.

Note: The following does not constitute medical advice, and should you be suffering from any related symptoms, please consult a trusted medical professional.

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Your gut has capabilities that surpass that of all your other organs and even your brain.

It has its own nervous system known in scientific literature as the enteric nervous system, or ENS, and it is often referred to in the media as the ‘second brain’. This second brain is made up of 50 to 100 million nerve cells, as many as are contained in your spinal cord.

The guy is connected to the brain through thick nerve cables they can transfer information in both directions and through communication channels that use the bloodstream.

The gut is the largest storage facility for serotonin in our body

95% of the body serotonin is stored in the gut. Serotonin is a signaling molecule that plays a crucial role within the gut-brain axis, and it plays a crucial role in functions such as sleep, appetite, pain sensitivity, mood, and overall well-being.

When spread out the gut has the size of a basketball court

If you put all your gut microbes together and shape them into an organ they would weigh between 2 and 6 pounds, on par with the brain, which weighs in at 2.6 pounds. Based on this comparison, some people refer to the gut microbiota as a forgotten organ.

Gut decisions

What we feel in our gut will ultimately affect not only the decisions we make about what to eat and drink, but also the people we choose to spend time with and the way we assess critical information such as workers, jury members, and leaders.

Yin Yang

We can view our gut feelings as the Yin, and gut reactions as the Yang.

There are 100,000 times more microbes in your gut as there are people on Earth

Bacteria, archaea, fungi, and viruses live inside the gut, which are collectively called the gut microbiota. Only about 10% of the cells in or on a human being actually human.

Our human bodies might just be a vehicle for the microbes living in it.

However, we are inseparable and dependent on each other for survival.


What starts as a stimulus in the brain influences your gut and your microbes, and these signals intern communicate back to the brain, reinforcing and sometimes even prolonging the emotional state.

Gut and neurodegenerative diseases

The modern diet is suspected to alter gut diversity and pre-empt neurodegenerative disease.

Autism spectrum disorders have become at least twice as prevalent in the last decade alone.

As many as 5 million Americans were living with Alzheimer’s disease in 2013 and by 2050 this number is projected to rise nearly 14 million. The number of people with the disease doubles every 5 years beyond age 65.

Gut microbiota has also been linked to depression which is the second leading cause of disability in the United States.
“ Tell me what you eat and I will tell you who you are” — Jean Anthelme Brillat-Savarin

Fecal transplants 💩

Transferring fecal pellets containing gut microbiota from an extrovert mouse can change the behavior of a timid mouse, making it behave more like the gregarious donor mouse.

Transplanting a stool and its microbes from an obese mouse with a voracious appetite can make a lean mouse prone to voracious overeating.

Your gut mirrors every emotion that arises in your brain

When you’re stressed, your heartbeat speeds and your neck and shoulder muscles tighten, and the reverse happens when you’re relaxed. The gut is, in fact, a theatre in which the drama of emotion plays out and mirrors how you feel.

Nearly 15% of the US population suffers from a range of aberrant gut reactions, including irritable bowel syndrome (IBS), chronic constipation, indigestion, and functional heartburn, which all fall into the category of brain-gut disorders.

In the brain, spiking corticotropin-releasing factor, or CRF, levels rise anxiety and make people more sensitive to a range of sensations, including signals from the gut, which are experienced as severe belly pain.

The gut can work independently of the brain

A video by Michael Gershon shows that guinea pig intestine sitting in a bath of fluid on its home proposal plastic pallet from one side of the intestine to the other without any connection to the brain, demonstrating the independence of the enteric nervous system (ENS).

Emotions and our genes

How emotional operating programs are in part is inherited from our parents and it is also influenced by events we experience early in life.

Evolutionary programming of gut and brain

Evolutionary programming for trouble may be a good thing for surviving in a dangerous world, but it is a liability if you live in the safety of a protected environment.

Avoid carby lunches

The next time you’re in the midst of a particularly stressful day, just remember that you might not want to eat a large lunch.

The vagus nerve

The vagus nerve is an essential bundle of nerve fibers that connects the brain and the gut. 90% of the signal is conveyed through the vagus nerve travel from the gut to the brain, while just 10% of the traffic runs in the opposite direction from the brain to the gut.

In the majority of rodent studies on the effects of gut microbiota changes and emotional behaviors, the effects for no longer seen after the vagus nerve was cut.

Ghrelin is also known as ‘the hunger hormone’.

Satiety hormones are released to tell you that you are full. Absence or a deficiency in this hormone makes you prone to over-eating.

Serotonin is the ultimate gut-brain signaling molecule


While all Toxoplasma can reproduce in one place only, the gastrointestinal tract of infected cats, the parasite can actually infiltrate the brain of any mammal including humans. Thus gynecologists recommend that pregnant women keep cats and the little boxes out of the house, and refrain from Gardening in areas with cats may bury their feces in the ground. Toxoplasma-infected rodents not only lose their instinctive fear of cats, but he also begin to prefer areas that smell like cat urine.

If only Tom knew about toxoplasma!

Plant power

Diets low in plant-based fiber reduces the abundance of a particular microorganism called akkermansia muciniphila inside of our gut. Under normal conditions, this organism plays an important role in regulating the quality and thickness of the mucus layer that is part of the barrier separating the inside of the gut from the immune system.

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There are 360 microbial genes in the gut for every human gene

Childhood experiences and adult gut symptoms

Children or teenagers who experience adverse events have a higher likelihood of suffering from poor health heart attack stroke asthma and diabetes as adults. They have of 4 to 12 fold increase in the risk for alcoholism depression and substance abuse and a 2 to 4 fold reduction in self-rated health.

Case Study: When Jennifer was still in the womb, her maternal grandmother was diagnosed with breast cancer and the crisis distressed her pregnant mother. She witnessed her parents arguing to fight for years when she was a girl and they split up in a bitter divorce when she was eight. Jennifer’s history tipped Emeran off to possible causes of both her brain and GI symptoms.

Repressed emotion is buried in the body, causing physical symptoms.

Nurtured pups become adults that are more laid back and less reactive to stress, and less prone to addictive behavior such as overdoing it when given a free supply of alcohol or cocaine.

Nurtured rats have lower levels of corticosteroid, the rat stress hormone.

Stressed rat mothers trample their pups and don’t give them enough time to nurse. Their neglected offspring have a greater production of the stress molecule CRF, and less efficient systems that can regulate the stress response.

Adverse childhood events predispose adults to anxiety, panic attacks, and depression.

Babies born to highly stressed mothers develop more slowly, weigh less at birth, and are more vulnerable to infections.

There are at least two major pathways by which early adversity can affect the brain-gut axis:

  • Epigenetic modification of the stress response system
  • Stress-induced changes in the gut microbiota and their products

The dangerous gut microbes clostridium difficile is more likely to overgrow in the gut and harm C-section babies. C-section babies are more likely to become obese as they get older. Scientist suspect that C-section birth may also make a child more vulnerable to serious brain disorders including autism.

The salience system

The salience system plays an important role in predicting positive or negative outcomes of situations and is an integral part of our capturing based decision making.


The good news is that humans have a very unique part of the brain, the prefrontal cortex, which gives us the ability to override the function of altered brain circuits and learn new behaviors, otherwise known as neuroplasticity.

Therapies such as cognitive behavioral therapy or CBT, hypnosis, or other mind-body intervention, such as mindfulness-based stress reduction can also help.

Food and your mood

Beneficial microbes such as lactobacilli on bifidobacteria, delivered by fermented foods, yogurts, or in probiotic capsules, may improve the diversity of the gut microbiome ecosystem.

Fermented foods include yoga, sauerkraut, and kimchi.

Broad-spectrum antibiotics reduce the populations of GABA producing bacteria, leading to lower GABA levels in the brain and improve brain function.

Studies suggest that adding an extra supply of these microbes to our diets can make us more relaxed.

Mediators of our stress systems such as the stress hormone, norepinephrine, can profoundly alter gut microbial behavior making them or aggressive and dangerous.

Flow, happiness and why not all stress is bad for us

In contrast to chronic or recurrent stress, acute stress and it’s associated emotional arousal improve our performance and difficult tasks, such as taking a test or giving a talk.

It also benefits gut health by strengthening our defenses to get infections this works in multiple ways. Acute stress increases acid production by the stomach in response to stress-related brain signals which makes it more likely that invading microbes will be killed before they reach our intestines. It also signals to the intestines to increase fluid secretion and excrete contents, including the pathogen. Finally, it increases the secretion of antimicrobial peptides. All these responses defend the integrity of the gastrointestinal tract against potentially dangerous invaders and infection.

Signals associated with happiness may prove to increase gut microbiome diversity, improve gut health, and protect us from the infections and other diseases.

Pain as your guide

Events related to gut sensations are usually accompanied by an emotional feeling of discomfort and sometimes pain, letting us know that something important is going on the requires attention and a behavioral response.

Breast milk

Human breast milk contains complex sugars that are not only essential for the babies to develop but also contribute to microbial diversity, and may also contribute to a baby sense of wellbeing when it is fed.

Intuition cells

Studies suggest that you probably had 28,000 intuition cells at birth, 184,000 by the time you were 4 years old, and 193,000 as an adult. These are also referred to as Von Economo neurons or VENs.

Why your intuition can actually cripple you

Our ability to make gut-feelings based predictions and decisions is a byproduct of evolution in a dangerous world, filled with life-threatening situations, systemic bias assumed a high likelihood of bad outcomes, and optimized for behaviors that can provide a significant survival advantage. Today however, such a system has become maladaptive in most parts of the developed world, and life-threatening physical threats have largely been replaced by daily psychological stressors, the result being that negative gut-based decisions may result primarily in unhappiness and negative health outcomes.


Write down your dreams every morning and then reflect on them without a therapist to gradually bring you to a point where you’re able to connect with your internal database of emotional memories and begin trusting your internal wisdom. This can help you to make important decisions rather than just rely on the advice of friends and colleagues.

Can we even change our gut?

While we all want to optimize our health, findings of the Yatsunenko study show that some of the most consequential influences of food on the gut microbiome start long before we can make our own decisions about what we eat and which probiotics we choose.

The first two and a half to 3 years shape our gut microbiome for a lifetime.

Your microbes might generate an appetite for particular types of food that give them an advantage over competitive microbial species

They may also create negative mood states causing us to feel depressed and that feeling won’t go away until we eat certain food components that benefit these gut microbes.

Food safety and the FDA

Safety tests used by the FDA have largely relied on short-term animal models that were designed to detect additives that had a fast-acting toxic effect. None of these short-term tests are able to inform us about the possible detrimental effects of such additives on long-term brain health.

Beware of artificial sweeteners

Artificial sweeteners such as saccharin, sucralose, and aspartame can induce glucose intolerance and signs of metabolic syndrome in mice.

Beware of additives and food emulsifiers

Sorbitan tristearate in chocolate, polysorbates in ice cream, and citric acid esters in processed meat can all have a negative effect on your gut microbiome diversity. So too can two commonly used food emulsifiers such as polysorbate 80 and carboxymethylcellulose.

Why all olive oil is not created equal

Polyphenol content in oil made from ancient olive trees is several folds higher than that of younger trees where most of the commercially available oil comes from today.

Social connectedness and gut feelings

While it is likely to have a positive effect on the gut, feeling of social connectedness when sharing a delicious meal and the attitude and outlook of those enjoying can’t be empirically assessed.

How to improve your gut health

  • Reduce the inflammatory potential of your gut microbiota by making better nutritional choices. For example, cut down on animal fat in your diet and avoid, whenever possible, processed food.
  • Eat organic
  • Eat smaller servings at meals.
  • Be mindful of prenatal nutrition
  • Engage in intermittent fasting
  • Reduce stress and practice mindfulness
  • Avoid eating when you are stressed angry or sad
  • Enjoy the secret pleasures and social aspects of food
  • Meditteranean diets
  • Become an expert and listening to your gut feelings
May 27, 2019




Steve Glaveski


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