Humans have long known about the connection between our guts and our emotions. We have gut feelings, butterflies in our stomachs, and feel queasy about strange situations. To this ancient knowledge modern science has added much detail: for example that sometimes a majority of the sensory data reaching your brain is coming from your gut, and that 90 percent of the serotonin in your body actually resides in your intestines. And now, over the past 30 years, the news that much of what happens in your gut is actually controlled by the trillions of microorganisms that reside there. This microbiome is essential for digestion and probably much else; some studies suggest that a majority of the bioactive molecules circulating in your blood (hormones, neurotransmitters, etc.) are produced by bacteria. One of my favorite facts about our physiology is that mother's milk contains proteins that can't be digested by the baby but instead serve to encourage the growth of favorable bacteria species in the baby's gut.
My readers know that I have long been fascinated by this science, so when I saw Emeran Mayer's new book in my library I snapped it up. Mayer is a practicing gastroenterologist who also leads research studies about the connections between the mind and the gut. He knows a lot about the science and also about the troubles of his patients. Unfortunately he is a lousy writer whose idea of crafting a popular book is to give everything a cutesy name, viz, the vagus nerve is the "gut-brain information superhighway," and the nexus of nerves and bacteria in the gut is a "supercomputer." But he still managed to fit a lot of information into this book.
Sadly, there is very little magic here. We are learning about mind-gut-microbiome connections at a remarkable rate, thanks in part to new DNA-based technologies that allow scientists to put whole communities of bacteria into a blender and identify the species present. But this knowledge is not leading to any breakthroughs in treatment, or to clear knowledge about how a surplus of this sort of bacteria causes that psychological or GI symptom. As with so much about our brains and bodies, the systems are so complex, and vary so much from one person to another, that clear statements of any sort are all but impossible. One simple claim Mayer does make is that the basic makeup of our gut microbiomes is determined very early in life and remains very hard to change thereafter, and this makes him dubious of claims that fecal transplants can have a big impact.
To judge from his anecdotes, Mayer's typical patient is suffering from some combination of anxiety and GI symptoms. He treats them with combination therapies aimed at both the mind and the gut: anti-anxiety drugs, anti-depressants, meditation techniques, antacids, probiotics. (He is big on probiotics and seems to recommend them to everybody, although in this book he never says which ones he recommends.) His overall lesson seems to be that if we are worried about our mental health, we should look to our diets. He says all the usual things about avoiding too much fat or sugar, eating more plants instead of processed food, etc. In particular he recommends the "Mediterranean diet."
I have found that my diet and moods seem to track each other pretty well, although I am not sure about the causality. That is, when I am down I tend to binge on cookies, and when I am up I make more salads, so that I am definitely eating better when I am happy. But as with almost everything about the mind, the driving forces remains obscure.