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  • Joan Rothchild Hardin

How the Gut Microbiome Influences the Brain – and Vice Versa

Maybe you’re used to thinking of the brain in your head as your only brain – but your body actually has TWO BRAINS: In fact, the ‘brain’ in your gut does a lot more than digest your food. While this brain doesn’t produce thoughts, it contains its own independent nervous system along with more neurotransmitters and serotonin than the brain in your head. Sheaths of neurons are embedded in the walls of the entire alimentary canal. Technically known as the enteric nervous system, this gut brain measures about 9 meters (29.5 feet) from esophagus to anus and contains about 100 million neurons, more neurons than exist in either the spinal cord or the entire peripheral nervous system. Equipped with its own reflexes and senses, this second brain can control gut behavior independently of the brain. Here’s a single example to  give you an idea of the importance of the gut brain for the entire body:  About 90% of the fibers in the vagus nerve, the largest of the visceral nerves, carry information FROM the gut TO the brain – but not the other way around. (Hadhazy, 2010) Living inside the intestines of the gut brain is a huge population of microbes – our gut microbiome, which contains 10’s of trillions of microorganisms and weighs up to 5 pounds. The gut microbiome  consists of at least 1,000 different species of known bacteria and other microscopic life forms comprised of more than 3 million genes.  To put it another way: The number of NON-human genes living in your gut is vastly greater than the genes in your human genome.

One third of the micro-organisms living in your particular gut microbiome is also found in most other people’s gut microbiomes – but two thirds of the micro-organisms in your gut are specific just to you. In other words, the microbiome in your intestines is like an individual identity card.

With that gut microbiome information under your belt, I hope you’re ready to watch a delightful TEDMED talk given by the illustrious John Cryan. John F. Cryan is Professor and Chair of the Department of Anatomy and Neuroscience at University College Cork (Ireland) and a Principal Investigator at the Alimentary Pharmabiotic Centre there. His research focuses on the neurobiological basis of stress-related neuro-psychiatric disorders – including depression, anxiety and drug dependence. His group is also looking into the interaction between the brain and gut microbiome as it affects stress and immune-related disorders, including irritable bowel syndrome, obesity, and neuro-developmental disorders such as autism.

Professor Cryan, on right, receiving a Researcher of the Year award

Cryan’s research has far-reaching public health implications: How we view C sections versus vaginal births, how the gut microbiome influences brain development, the impact of probiotics on mood, how to prevent and repair IBS, and much more. It also suggests that the term gut feeling makes neuro-biological sense. In this 2014 TEDMED talk, Dr Cryan shares some intriguing facts and insights on how our thoughts and emotions are connected to our guts. TEDMED Video – Food for thought: How gut microbes change your mind

If you want to read, watch or listen to more fascinating information on the topic of the gut microbiome’s two-way relationship with the brain, here are some other resources. I’m particularly fond of Cryan’s Radiolab interview: More than a gut feeling Q&A with John Cryan on the TEDMED blog Gut Feelings Radiolab, Robert Krulwich, WNYC, Season 10, Episode 7. Can the bacteria in your gut send message to your brain? Science Friday, Ira Flatow, WNYC, Aug. 27, 2014. Probiotic Material Chill Out Anxious Mice Science Friday, Ira Flatow, WNYC, Sept. 02, 2011. Cesarean birth alters immune system, social behavior in mice Hughes, V. Simons Foundation Autism Research Initiative. Nov 18 2014. Mental Health May Depend on Creatures in the Gut Schmidt, C. Scientific American. February 2015. When Yogurt Affects the Brain Khazan, O. The Atlantic. Sept 23 2014. Our Microbiome May Be Looking Out For Itself Zimmer, C. New York Times. Aug 14 2014. Understanding psychobiotics Lawson, C. WIRED Health. Mar. 9 2015. Body bacteria: Can your gut bugs make you smarter? Swain, F. BBC. Feb. 21, 2014. Mental Health: Thinking from the gut Schmidt, C. Nature. Feb. 26, 2015. Gut-brain link grabs neuroscientists Reardon, S. Nature. Nov. 12, 2014. Friends with social benefits: host-microbe interactions as a driver of brain evolution and development? Stilling, R, SR Bordenstein, et al. Front Cell Infect Microbiol. Oct 2014. Mind-altering microorganisms: the impact of the gut microbiota on brain and behavior Cryan JF, TG Dinan. Nat Rev Neurosci. Oct 2012. 13, 701–12.

Study of the gut microbiome and its influence on the body is in its infancy now and John Cryan is one of its pioneers. Stay tuned … we’re going to find that probiotics and prebiotics (nutrients necessary for probiotics) become central to the practice of psychiatry, gastroenterology, obstetrics, gynecology, neonatology and pediatrics, allergy and immunology, cardiology, dermatology, endocrinology, infectious disease, neurology, pulmonology, urology, surgery and likely across all medical fields. And then there are the body’s OTHER microbiomes, which I didn’t even talk about in this piece! My thanks to Matt Keschner, DC, for bringing this video to my attention.


REFERENCES Cryan, J.F. (2014). TEDMED Video – Food for thought: How gut microbes change your mind. See: http://www.modernhcp.com/tedmed-video-food-for-thought-how-gut-microbes-change-your-mind/?utm_source=ModernHCP&utm_campaign=e1513feace-04-08-15+-+MHCP&utm_medium=email&utm_term=0_c7098f57a2-e1513feace-235695269 Hadhazy, A. (2010). Think Twice: How the Gut’s “Second Brain” Influences Mood and Well-Being: The emerging and surprising view of how the enteric nervous system in our bellies goes far beyond just processing the food we eat. Scientific American. See: http://www.scientificamerican.com/article/gut-second-brain/ © Copyright 2015 Joan Rothchild Hardin. All Rights Reserved.


DISCLAIMER:  Nothing on this site or blog is intended to provide medical advice, diagnosis or treatment.



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