“Being healthy starts in the gut,” Emeran Mayer, MD, explained during his presentation at the 2022 ACG Annual Scientific Meeting in Charlotte, North Carolina, on October 26.

Dr Mayer is a gastroenterologist and neuroscientist, and a professor in the departments of medicine, physiology, and psychiatry at the David Geffen School of Medicine at University of California, Los Angeles.

“Microbes have an ancient history of mediating between the environment and the gut’s immune system in a bidirectional way,” Dr Mayer explained. “The great majority of diseases of the current noncommunicable disease epidemic can be related to the interaction of the chronic inflammation with genetic vulnerabilities.”

The body is made up of 20,000 human genes, which is only 1% of the system. “We neglect 99% of the system,” he said of the roughly 2 to 20 million microbial genes. The brain affects the gut and vice versa; add to that psychosocial stress and dietary stress, and the interconnection becomes even more complicated, Dr Mayer said.

He classified autism, Alzheimer’s, depression, Parkinson’s disease, obesity, cardiovascular disease, colon cancer, nonalcoholic fatty liver disease, metabolic syndrome and inflammatory bowel disease as part of the chronic noncommunicable disease (CNCD) network. All of these share pathophysiological factors with each other, are comorbid, and linked to the gut, he said.

To elaborate on the core problem underlying the chronic immune activation in the gut, he differentiated between a healthy gut and a ‘leaky’ gut. A healthy gut, predominated by a healthy diet, would have increased mucus thickness and an intact gut barrier, contrary to a ‘leaky’ gut, which, due to chronic dietary and psychological stress would suffer from a reduced mucus lining resulting in increased genetic risk of developing depression, colon cancer, Parkinson’s disease, and cognitive decline, among others.

Providing scientific evidence to the gastroenterological and gut microbiome connection, Dr Mayer cited a cross-sectional study authored by Judith Aron-Wisnewsky and colleagues that established a connection between gut microbiota and human NAFLD. Mentioning “The gut microbiome and metabolic syndrome” in the Journal of Clinical Investigation, he said, “Events that start in the gut, often in response to external cues such as diet and circadian disruption, have far-reaching effects beyond the gut.” To support his theory about colon cancer, Dr Mayer spoke of “Gut microbiota, inflammation, and colorectal cancer” by Caitlin Brennan and Wendy Garrett that highlighted the gut microbiome immune interactions in cancer pathophysiology. Gut microbiota composition can also be helpful in determining disease severity and dysfunctional immune responses in patients with COVID-19, he said.

Why have gut-microbiome-related diseases increased so rapidly in the past few years and among younger age groups? “Combined psychological and dietary load,” he said in simple words. Increasing allostatic load associated with gut microbiome alterations, structural and functional brain changes and alteration s in the body’s metabolism may lead to increased risk for chronic non-infectious diseases.

The solution to improving the gut microbiome is extremely simple, Dr Mayer said. “Healthy food. Healthy food makes healthy microbes makes healthy humans.”

In conclusion, Dr Mayer said, “Communication between the gut microbiome and the gut based immune system is an ancient, evolutionary conserved system that modulates the function of every organ in the body, including brain structure and function.”

—Priyam Vora

Reference:
Mayer E. Why do all diseases start in the gut? (David Y Graham Lecture) Presented at: ACG 2022 Annual scientific meeting and Postgraduate course. Charlotte, North Carolina. October 26, 2022.