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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.