‘All prejudices can be traced back to the intestine’. Friedrich Nietzsche
Man has long acknowledged the close connection that exists between the mind and the gut. Our ‘gut feelings’ and ‘gut reactions’ are part of our emotional language, ‘I can’t swallow that’, ‘You make me sick’, ‘It’s a pain in the gut’ and ‘It gives me the shits’. The nineteenth century physicians, William James and James Lange, writing at the same time as Nietzsche, believed that emotion originally came from the body. My experience with patients with unexplained abdominal symptoms would accord with that, suggesting that it is only when the gut reactions can be brought to mind, contextualized and converted to an emotion that it can be dealt with and resolved. But it was not until the fur trapper, Alexis St Martin, accidentally shot himself in the stomach, that US Cavalry physician, William Beaumont first observed and documented the effect that emotion had on gut physiology. His observations were confirmed and extended by Dr Thomas Almy, whose patient Tom had, as a boy, inadvertently scalded his oesophagus by swallowing a gulp of boiling hot clam chowder, cooling in a pitcher on the kitchen table, thinking it was cold beer, and needed to have a hole fashioned between the skin and the stomach wall so he could feed. Both noted how anger could make the lining of the stomach turn a livid red and secrete copious amounts of acid and how fear could cause a blanching and inhibit motility and acid secretion. These observations were followed by similar observations in the colon. In one study, Almy observed the colon though a sigmoidoscope and pretended he could see a cancer. The lining of the colon immediately turned white and listless, but when he subsequently admitted the hoax, it turned a livid red and contracted violently.
Emeran Mayer is the kind of scientist driven by curiosity rather than politics and not afraid to express opinions that are not held by the majority of his peers. I got to know him on the conference circuit in the nineteen eighties and he invited me to contribute to the conference on The Mind and the Body, he organised in Sedona, Arizona in 2000. SInce then our trajectories have diverged. I became fascinated in the psychological and narrative underpinnings of physical disease, culminating in the publication of Sick and Tired in 2005. He sought to explain the connections between the mind and the gut by an extensive series of carefully designed experimental observations published in the leading scientific journals over the next 25 years. Since then, along with many of his peers, he has become fascinated by the microbiome as an essential modulator. He has now brought his research and clinical experience together in a remarkable new book, published in June last year: ‘The Mind-Gut Connection; How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices and Our Overall Health.
Two and half thousand years ago, Hippocrates of Cos claimed that ‘All disease begins in the gut’, but it only now that scientists are beginning to discover how. In his book, Dr Mayer describes how the gut communicates with the brain and the rest of the body via hormones, neurotransmitters, inflammatory mediators and products of digestion. The colonic microbiome is a key mediator in this dialogue. Who would have believed that simply transferring faecal pellets containing gut microbiota from an extrovert mouse could make a timid mouse become more gregarious or that transplanting stool from an obese mouse could give a lean mouse a voracious appetite?
Microbial products affect our emotions by functioning as chemical switches that turn on and off behaviours involved in hunger, anger, fear and anxiety. They can even influence the decisions we make. Our intuition or gut feelings, Dr Mayer explains, develop from our experience. What happens early in life can influence the way a person is and the illnesses they get. I had always assumed this was related either to the formation of a somatic memory that recruited bodily reactions to trauma or the coexistence of trauma with an acute injury or illness – something akin to Antonio Damasio’s somatic markers, but Mayer suggests there may be more to it. Stress can influence the physiology of the gut, altering secretion, transit of contents, the absorption of nutrients and all of these can change the composition of bacteria to more harmful gram negative species. Alcohol and a high fat, high sugar diet can have similar effects. All of these influences make the gut more leaky, exciting the immune system and releasing inflammatory transmitters, which are capable of causing a continuous long-lasting low-grade inflammation in organs throughout the body, but in particular the liver, the pancreas, the heart, the joints and even the brain and even affect the systems that control appetite. This may be how diseases begin in the gut.
There is growing evidence that on-going visceral inflammation caused by the effects of a stressful life situation, poor diet, chronic alcohol intake, frequent antibiotics – all the features of our contemporary life style – are major factors in the development of obesity, diabetes, coronary artery disease, Parkinson’s disease, dementia, myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), depression, dementia and many other ailments. Although I have always sought to reassure my patients that that IBS does not lead to life threatening disease, I do wonder whether it might be a marker for a chronic state of dysbiosis and immune hyper-reactivity, brought on by factors such as stress, infection and antibiotics. If so, should we take it as an alarm signal; a call to action to sort our life style and life situation out? We and others have shown that catching a gut infection when you are in severe stress can lead to longstanding post infectious IBS. Mayer has suggested that the combination of stress and the infection lead to a more harmful population of microbes, that can modify the stress hormone, noradrenaline, intensifying its deleterious effect on the microbiome and the gut. Antibiotics can make animals nervous, but probiotics help to ameliorate that and may ameliorate depression in humans.
There is evidence to suggest that effects on the microbiome may be programmed very early in life. In utero, the foetus is exposed to its mothers bacteria and products in the placenta. During birth, the baby is coated with vaginal lactobacilli, which quickly colonise the infant gut. More maternal bacteria is ingested in breast milk, which also includes human maternal oligosaccharides, providing the prebiotic nutrients to sustain the infant’s gut microbiome. Vaginal delivery and breast feeding also releases the bonding hormone, oxytocin, from the hypothalamus and posterior pituitary gland. This has a calming effect on the gut.
Stress exposes her foetus to harmful bacteria, can reduce beneficial lactobacilli in vaginal secretions and can alter the amount and composition of breast milk. Antibiotics, Caesarian section and bottle feeding can also have a deleterious effect on the baby’s microbiome and make the gut leaky and the infant and subsequent adult more susceptible to illness. The later adoption of a less stressful life style and a better diet can reduce the harmful effects of a disadvantageous microbiome and prevent illness, but it does not necessarily alter the basic features of a microbiome that has been programmed early in life, but it .
This intestinal microbiological perspective underpins holistic advice for wellness and optimal health. A balanced life style, stress reduction, regular exercise, mindfulness, a diet low in animal fat and artificial sweeteners and high in poorly absorbed carbohydrate, can all reduce intestinal dysbiosis and permeability and help to prevent the chronic inflammation, which imposes a constant wear and tear on bodily systems. But, Mayer emphasizes, there is not one perfect microbial composition, just several healthy ecosystems, and some that are vulnerable to an unhealthy lifestyle.
The Mind Gut Connection is a fascinating amalgam of research, clinical experience, anecdote and a healthy dose of informed speculation. It is, as Professor Michael Gershon, author of The Second Brain, states, both scholarly and fun to read. Dr Mayer does not make extravagant claims; he readily acknowledges that a lot of research would need to be done before some of the ideas expressed in this book become converted to clinical interventions, but his book is a masterly and useful description of the state of the art and science as it exists in 2017.
While making a convincing case for the importance of the gut micro-biome in our emotional functioning and in the gamut of human and animal disease, this volume is perhaps as important for what it leaves out. Perhaps surprisingly for a gastroenterologist and research scientist working in Los Angeles, there is cursory discussion of small intestinal bacterial overgrowth, no mention of the Rome Diagnostic Criteria for IBS and no mention of FODMAPs. Does Dr Mayer disagree with them? I can picture his smiling response: ‘you might think so but I could not possibly comment’.