The Mind-Gut Connection by Emeran Mayer, Book Review

Emeran Mayer is a Medical Doctor specialised in gastroenterology and neuroscientist, lecturer and executive director of the Oppenheimer Family Center for Neurobiology of Stress. He is recognized as a true expert of the gut-brain axis by his peers.

The Mind-Gut Connection was written to the attention of the general public so I mostly recommend it to people still discovering the existence of the gut-brain axis. Psychology professionals or gastroenterologists that don’t know about the gut-brain axis and don’t include it in their practice, or people who suffer from chronic intestinal disorders like IBS or chronic constipation can benefit from connecting the dots between early life adversity, emotions, stress and gastrointestinal symptoms. If you are knowledgeable around the microbiome, if you are looking for the data and the facts, this book may be too general for you. Sometimes inaccurate with reference to the nomenclature and microbiology, and failing to report precisely the probiotic strains in evoked studies, the author seldom links the affirmations to the corresponding bibliography, making it difficult to retrieve the correct and full information. For more precise traceability of the facts and studies behind, I would rather recommend Dr. Perlmutter’s Brain Maker, on the same subject.

Physiology lessons

The first part of the book is about physiology and general information on how the brain and the gut are connected. The Second Brain by Gershon is the reference handbook to deepen that topic. Taste and olfactory receptors are located throughout the gastrointestinal tract, harnessing a massive amount of information on what goes on where, signaling to endocrine cells that transmit the information to nerves that send signals to the enteric nervous system or to the brain. Amazingly, over 90% of the sensory information collected by the gut never reaches our awareness. We perceive consciously the digestive sensations only when these require an active reaction. If you need to have a bowel movement, you need to find a toilet. If you are hungry, you need to get food.

Integrative psychology

Brain rewiring in response to adverse early life events (during the first 20 years of life) can persist for all the lifetime, and makes individuals that suffered such events more at risk to be anxious and more risk-adverse than other individuals, whether they encounter or not gastrointestinal symptoms. IBS patients have brain networks alterations playing an important role in their hyperresponsiveness to psychological stress.

Stress effects can be transmitted from one generation to the next (demonstrated by mice data) mostly through epigenetics. A hyperreactive stress system was probably an advantage when born in a dangerous world, so these effects of maternal stress (including in the womb) can be interpreted as a preparation of the next generation for the challenges of the world.

Patient stories and Doctor’s advice

To his patients suffering from cyclical vomiting syndrome, IBS, chronic constipation (potentially an early sign of Parkinson disease), autism, anxiety, depression or chronic pain, Dr. Mayer’s approach is usually a combined treatment against anxiety and gut symptoms, which can comprise low-dose antidepressants, mind-based therapies including cognitive behavioral therapy, hypnosis and meditation, as well as and increased intake of probiotics (especially those proven beneficial in clinical trials).

The languages behind gut feelings

Emotional stress is mirrored in the gut by physiological stress, expressed with hormones, contractions, and physiological responses adapted for the fight-or-flight response or for evacuation of infectious agents. The communication involves specialized immune cells that can detect pathogens and trigger a cascade of inflammatory reactions. People eating a high animal fat diet have an increase in Gram- bacteria which express inflammatory lipopolysaccharides on their membranes and are therefore more likely to engage in this immune activation. The inflammation process can spread throughout the body, a phenomenon referred to as metabolic toxemia. The digestive, immune and nervous tissues are communicating with each other with molecules that include gut peptides, cytokines and neurotransmitters. Crucially, all of these substances are elements of a biochemical language that, thanks to our long, shared evolutionary history, are the same language that microbes use. It is estimated that 40% of the metabolites circulating in our bodies are produced not by our own cells and tissues but by gut microbes. The brain, the gut and the microbiome are parts of a single integrated system with plenty of cross-talk and feedback from one part to another. Its role is major not only in digestion but also in appetite-control systems and emotional operating systems, making a difference in how we feel, how we make our gut-based decisions and how our brain develops and ages.

A new understanding of emotions, a role for bacteria

Broad-spectrum antibiotics decrease the population of GABA-producing bacteria, which may lead to the side effect of increased anxiety disorders in overstressed people. Certain probiotics (such as L. rhamnosus and B. longum) decrease anxiety-like behaviors in mice, and clinical evidence suggests such psychobiotic effects can be achieved in patients. For example, Tillisch et al. in 2013 showed probiotics B. lactis, St. thermophilus, L. bulgaricus and Lactococcus lactis to be able to measurably dampen emotional brain reactions to negative contexts.

Microbiota health and resilience

People living on the typical North American diet have lost up to one third of their microbial diversity compared to Malawaians and Amerindians. “This dramatic change in our gut-based ecosystem is directly comparable to the estimated 30% loss of biodiversity that our planet has experienced since 1970.” This is worrisome because it also implies a loss in resilience. Our microbiota may be less efficient in fermenting complex plant-based carbohydrates due to the absence of certain species that are essential for initiating the degradation of hard-to-breakdown substances. Ruminococcus bromii for instance starts the degradation of resistant starch, which can benefit down the line to a number of other species.

Obesity, food addiction and the North American diet

It is estimated that at least 20% of obese individuals suffer from food addiction. The dominance of hedonic food seeking may be caused by the inactivation of the hypothalamic control system by metabolic toxemia. Joe Alock hypothesises that gut microbes manipulate human eating behaviors to benefit them (aren't we just a vessel for bacteria?) though the idea yet needs to be tested scientifically.

Mayer points at some flaws of the North American diet. The use of chemicals in agronomy including glyphosate (RoundUp) can question whether the chemical insult on the ecosystems is contributing to the current dramatic increase in certain brain diseases. This is a bright intuition, as this year Caroline Amiel from the French university of Caen demonstrated that Roundup in mice’s drinking water at the levels authorized by the authorities (0,1 ppm) showed a dramatic shift on the females gut microbiota towards a dysbiotic signature, substantially overlapping with liver dysfunction.

Artificial sweeteners can induce glucose intolerance and signs of metabolic syndrome in mice. Transplanting stools from mice or from saccharin human consumers into germ-free (GF) mice causes the colonized mice to develop glucose intolerance and signs of metabolic syndrome, pointing towards a microbiota-mediated effect. Common food emulsifiers induce low grade intestinal inflammation, obesity and features of metabolic syndrome in mice – but not when the mice receive antibiotics. Similarly, fecal transplant to GF mice confirmed this data and the responsibility of the microbiota. Regarding gluten, Mayer considers the possibility of a non-celiac gluten sensitivity, which could be much more common than celiac disease, but poorly understood to date. Are patients with sensitivities to these substances canaries in the coal mine, announcing the devastating effects of the transformations undergone in our diet and lifestyle?

The Mediterranean diet

An extensive medical literature based on large epidemiological studies and clinical trials documents the beneficial role of the Mediterranean diet with regard to mortality from all causes, especially metabolic syndrome, cardiovascular disease, cancer, cognitive impairment and depression. The Mediterranean diet even correlates with brain volume, and the integrity of nerve brain tissue. These benefits are probably due to high antioxidants, polyphenols, and anti-inflammatory effect, but very likely also linked to social connectedness, attitude and mindfulness about the food, and the control of stress, anger and anxiety – a wholistic point of view that I fully share.

So how to become “ecosystem engineers” and nurture our gut-brain axis?

-         Practice natural and organic farming of your gut microbiome, avoid additives

-         Cut down on animal fat

-         Maximize your gut microbial diversity, by increasing intake of prebiotic foods and a variety of plants naturally-grown

-         Avoid mass-produced and processed foods and maximize organically grown food

-         Eat fermented foods and probiotics

-         Be mindful of prenatal nutrition and stress

-         Eat smaller portions (by the way, that will also help you live longer)

-         Fast to starve your gut microbes (or rather to support the ones that grow on mucus and favour its growth, like Akkermansia muciniphila)

-         Don’t eat when you are stressed, angry or sad (actually this is the tradition in Okinawa, the place with the most healthy centenarians on Earth)

-         Enjoy meals together

-         Listen to your gut feelings (you can use mindfulness meditation)

-         Exercise regularly

(strangely Mayer fails to mention to avoid unnecessary antibiotics)

Conclusion

“This new awareness will shift our focus from treating disease toward achieving optimal health. It will shift us away from spending billions on treating cancer with warlike, scroched-earth therapies, on treating obesity with crippling surgeries of the gastrointestinal tract, and on dealing with the fallouts from cognitive decline with expensive long-term support measures. It will shift us away from being passive recipients of an ever-increasing number of medications to taking responsibility for the optimal functioning of our brain-gut axis by becoming ecological systems engineers with the knowledge, power, and motivation to get our gut-microbiota-brain interactions functioning at peak effectiveness, with the goal of optimal health.”

I fully embrace these last words and hope the Western world will recognize what was already known in Hippocrates' time, that food can be your medicine, and your medicine can be your food. This would require a paradigm shift of the food and drug regulations, but would support individual responsibility and empowerment to be actors of our own health and focus on prevention rather than just treatment.