When Michael Gershon called the digestive system “the second brain” in his 1999 book, it was because scientists were beginning to realize that the gut and the brain in humans were engaged in constant conversation. Emeran Mayer, a leading researcher in the field of the gut-brain axis, affirms that this connection has been known for years. “Gut-brain communication is firmly established. There’s no question,” Mayer says in an interview with GMFH editors. “There’s extensive animal data and clinical observations: if you feel stressed you will feel the effects in your gut, if you feel anxious you notice the butterflies in your stomach, if you’re depressed, you may develop constipation.”

Mayer, a gastroenterologist who encountered many patients in his career with curious constellations of gut-brain symptoms, became preoccupied with finding out the how this back-and-forth messaging occurs.  He had more questions than answers in his clinical practice, but a breakthrough came when more data began to emerge on the microbiome.

“I’ve spent my entire career studying brain-gut interactions,” says Mayer. “Only in the last five years I’ve included the microbiome in our studies.” He notes that this new angle is starting to advance scientists’ understanding of how gut-brain communication occurs—both from the bottom up and from the top down—and the consequences of disruptions in this communication.

Mayer has authored a new book, The Mind-Gut Connection, aimed at covering gut-brain communication for a lay audience. In it, he emphasizes the role of the gut microbes and the many aspects that require more investigation in human populations. He says that, remarkably, the gut microbiota during certain periods in life may set the framework for subsequent patterns of gut-brain communication.

“Almost certainly the most important effects happen early in life, starting prenatally and in the first three years when the microbes, as well as the basic brain circuit[s], are being assembled and become adult-like,” Mayer says.

Mayer says knowing that microbes play a part in gut-brain communication—and indeed, in many other aspects of brain health and function—necessitates a new approach in medicine. “The book makes the case for a new ecological view of health and disease,” he says. “Such a new view is essential if we want to strive for optimal health and not just prevention or treatment of disease.” At the end of his book, Mayer provides suggestions on how to improve health by targeting the gut microbiome, like limiting animal fat and consuming more fermented foods and probiotics.

In Mayer’s gastroenterology practice, he sees many who could benefit from new microbiome-based therapeutic approaches to both gastrointestinal and brain disorders, yet he currently advises caution. He says, “We’re really just beginning to understand what a healthy microbiome is, and how it is altered in different diseases. I think in five years we’ll know a lot more, and may be able to use our knowledge about the gut microbiome for diagnosis, prediction of treatment outcomes and for the development of new therapies.”


Mayer E. The Mind-gut connection: How the hidden conversation within our bodies impacts our mood, our choices, and our overall health. New York, NY: Harper Wave; 2016.