The Mind-Gut Connection by Emeran Mayer

Book Reviews, July 31, 2023

This book explains how our health and wellbeing has in large part to do with the microbes that live within us. Our mind and gut are intrinsically linked.

In "The Mind-Gut Connection," Emeran Mayer, a renowned gastroenterologist and neuroscientist with over 30 years of experience in the field, shines a light on the dynamic interaction between our brain and gut, and how this relationship impacts not just our physical health but also our thoughts and emotions.

Mayer begins the book with a comprehensive yet accessible introduction to the basic science underlying the brain-gut connection. We humans are supra-organisms, comprised of closely interconnected human and microbial components, which are inseparable and totally dependent on one another. He deftly explains how trillions of microbes that reside in our gut communicate with the emotional and cognitive centers of our brain, and how this communication is a two-way street. The brain, gut, and the microbiome are parts of a single system with plenty of cross talk and feedback from one part to another. Mayer refers to this system as the brain-gut-microbiome axis.  The author uses understandable language to break down complex scientific concepts, making it a valuable read for anyone wanting to improve their holistic health.  Our gut has it's own nervous system (enteric nervous system ENS) and is often referred as the second brain. It's made up of 50-100 million nerve cells, as many as in our spinal cord!. Our gut is the largest storage facility for serotonin (95%). The immune cells in our gut make up the largest component of our bodies immune defense.

Our gut microbes are a collection of around one thousand different species. One thousand times more cells than in our brain and spinal cord, and ten times more than the number of human cells in our entire bodies.  Together the microbes weigh more than our liver. We humans differ very little from each other genetically, sharing more than 90% of our genes, but the assortment of microbial genes in our guts differs dramatically, and only 5% of them are shared between any two individuals.  There are 360 microbial genes in the gut for every human gene.  Changes in diet, antibiotic treatment or severe stress can shake up the population of our biome transforming former symbionts (beneficial for wellbeing) into pathobionts (potentially harmful microbes). 

In contrast to recurrent or chronic stress, acute stress and it's associated emotional arousal improve our performance on difficult tasks, and also benefits gut health by strengthening our defenses to gut infections.  This works in multiple ways - 1) Increasing acid production in the stomach in response to brain related stress signals; this increases the chances that invading microbes from our food will be destroyed before they reach the intestine. 2) It also increases the secretion of antimicrobial peptides called defensins. These responses aim to defend the integrity of the GI tract against potentially dangerous invaders and shortening the duration of the infection.

The best diet for our gut-brain axis? - We need to look at the science and also understand that we are all individuals. Over millions of years our digestive systems, gut microbes, and brains evolved together improving our ability to seek out and prepare food that is good for us and to avoid unhealthy food. For most of our history this was done by hunting and gathering. Humans from different environments were able to thrive on a diverse array of diets. From the tubers, berries, and fruits of the Tanzania's hunter gatherers to the seals, whales of the meat loving Intuits. There are two remaining primitive hunter gatherer tribes that we can learn from. These people's diets haven't changed much from the way our bodies have evolved over ten's of thousands of years.

Yanomami (Venezuelan Jungle, Amazon rain forest)

Despite the abundance of wild animals in the forest animal products account for only a small percentage of the Yanomami's food supply. They also never eat their domestic animals which they keep as pets. They grew sweet potatoes, and foraged from the forest grubs, termites, frogs, honey, and seedlings. They also caught fish from the pristine waters. Gathering food was always associated with extensive physical activity. The families depend on the large diversity of the forest, and that diversity is reflected in their gut biome. In addition to their staple of fruit and vegetables the Yanomamis also employ fermentation in food preparation. Overall their diet was rich in plant foods supplemented with occasional bits of meat - unlike the Western meat the meat the Yanomamis ate came from animals that were wild, lean, and healthy. Their diet  - rich in vegetables, fruit, and occasional fish and lean meat, with no additives or preservatives is in line with Michael Pollan's well known advice from The Omnivore's Dilemma : "Eat food, not too much mostly plants."

Malawians (Arid Savanna)

Even thou the Malawians live in a very different environment to the Yanomami it turned out both traditional societies had a similar diet consisting of a large variety of plant based foods with occasional lean meat from hunted animals.  Both of these cultures had a similar pattern of microbes in their gut which is a tell tale signature for humans adhering to a diet high in plant and low in animal products. Our Western diets have lost up to third of the microbial diversity compared to individuals living a hunter gatherer lifestyle - this is directly comparable to the estimated 30 % loss of biodiversity that the planet has experienced since 1970 - much of which has happened in the Amazon Rain Forest.

Just as greater diversity in natural systems provides resilience against diseases, greater diversity and richness in a hosts microbial species and their metabolites is associated with greater resilience in the face of infections, carcinogenic chemicals, and chronic stress. Fat cells in our body, particularly fat stores in our belly are a primary source of inflammatory molecules called cytokines or adipokines. These circulate in the blood reaching the heart, liver, and brain. These contribute to low grade inflammation which increases the chance of cardiovascular disease and cancer.  One high fat meal can switch our guts immune system into the low grade inflammation mode and regular consumption of a diet high in animal fat can trigger persistent low grade inflammation long before a person becomes obese. Mayer states on pg 99 "People eating a high animal fat diet have an increase in the relative abundance of gram -ve bacteria in their gut, or Firmicutes and Proteobacteria, and are therefore chronically engage an immune activation mechanism."  Butyrate is an excellent example of the many health promoting effects of plant based diets on the health of the gut-brain axis. It plays a crucial role in providing food for the cells lining the colon, but also has many other health promoting effects for the enteric  nervous system (anti-inflammatory properties, neuroprotective effects, modulation of gut motility, regulation of neurotransmitters)

One aspect where Mayer's book truly shines is in its exploration of the practical applications of this science. He discusses how the mind-gut connection can influence various aspects of our lives, ranging from mood and mental health to dietary choices and obesity. His insights into how the gut can affect conditions like anxiety and depression are especially intriguing. One of his case studies discussed how his patient with autism spectrum disorder with OCD, and chronic anxiety had massive symptom improvements with a shift to a more plant based diet with fermented items. The patient was also taught breathing techniques to aid self relaxation and Cognitive behavioural therapy (CBT).

Twenty four hours a day, seven days a week our GI tract, enteric nervous system, and brain are in constant communication. Our guts sensory network is distributed over the guts entire surface area, which is 200 times larger than the surface of the skin - the size of a basketball court!  The connection from the gut to the brain is the superhighway of neural activity the vagus nerve. It allows traffic in both directions; but 90% of the traffic flows from the gut to the brain. It links the brain not just to the GI tract but to all other organs as well.

The book also provides practical advice on how to 'listen to your gut' and make lifestyle changes that can help enhance your overall health. Mayer emphasizes the importance of a healthy diet, stress management, and regular exercise in maintaining a healthy mind-gut balance. The many phyto-chemicals derived from a diet rich in diverse plants, combined with the array of perfectly matching sensory mechanisms in our gut, synchronises our internal ecosystem (gut microbiome) with the world around us. This is another reason we need to keep the diversity of our crops, and the health of our soil and waterways. If these are degraded then our internal health will be negatively affected.

There are specific studies that show how our emotions can affect our gut. Alexis St. Martin, was a fur trapper who in 1822 was accidently shot. The army surgeon William Beaumont couldn't close the wound completely and St. Martin was left with an open gastric fistula. Beaumont was able to observe directly the digestion and noticed that when St. martin was angry his digestion speed was slowed. He was the first physician in history to show that emotions influence the activity of the stomach.  It has also been shown that if you experience trauma as a child it can ramp up emotional operating programs in our genes with the net result is an exaggerated gut reaction to stress.  While some readers may feel overwhelmed by the amount of information provided, Mayer's step-by-step approach to implementing these changes is helpful and encouraging.

However, the book is not without its drawbacks. Some may find the scientific details to be too dense or complex. Additionally, while Mayer does an excellent job of explaining the mind-gut connection and its implications, some readers might wish for more simple guidance on how to leverage this connection for better health. One such practical bit of advice was to increase the amount of plant variety eaten in our diets, and looking at fermented food such as sauerkraut, and kimche. Changes in our diet can have incredible potential to change our brain. Our gut biome has the potential to produce 500,000 distinct metabolites, known collectively as the metabolome, many of these are neuroactive, meaning they can influence our nervous system. These metabolites are produced by 7 million genes, far more than the 20,000 in the human genome.

In the last chapter Mayer gives his top tips for improving health by targeting the gut biome.
  • Practice natural and organic 'farming' of your guy microbiome
  • Cut down on animal fat in your diet
  • Maximise your gut microbial diversity
  • Avoid mass produced and highly processed foods and maximise organically grown food.
  • Eat fermented foods and probiotics
  • Eat smaller portions
  • Fast to starve your gut microbes
  • Don't eat when you are stressed, angry, or sad
  • Enjoy meals together
  • Practice mindfulness meditation
  • Work on aerobic fitness and strength

Despite some minor criticisms, "The Mind-Gut Connection" is a fascinating, thought-provoking exploration of a field of medicine that is still relatively under-explored. Mayer's expertise and passion for the subject matter are evident in every page, and his ability to communicate complex ideas in an accessible way makes this book a highly engaging and informative read for most people.

"The Mind-Gut Connection" is a must-read for those who are interested in understanding the profound interplay between our gut health and mental well-being. It provides valuable insights and practical advice that can be applied to improve both physical and mental health. Whether you're a healthcare professional or someone simply interested in enhancing your well-being, this book is a valuable addition to your reading list. As the author states on pg 27 "The time has come to empower ourselves to become the engineers of our own internal ecosystem, and our bodies and minds." 


For Physiotherapy, Coaching, my book 'Holistic Human', Training Plans, YouTube, FREE recipes, 

Connect below