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  • Writer's pictureJoan Rothchild Hardin

Intriguing Facts About the Gut and Brain

(Boron & Boulpaep, 2005)

On average, the human brain, the seat of all our thinking, contains 86 billion neurons (the building blocks of the nervous system) engaged in transmitting information to and from the body. (Randerson, 2012) The human enteric nervous system (the gut) contains 100 million neurons – about 1000th the number in the human brain and about equal to the number in the human spinal cord.

The digestive system is a complex chemical processing machine, breaking down food, absorbing nutrients and moving waste via muscular contraction down towards the anus for expulsion. The autonomous nervous system of the gut allows it to work independently of the brain. When the vagus nerve connecting the brain and the gut is surgically interrupted, the gut runs the bowels all on its own. (Gershon, 1998)

In fact, our guts make more independent decisions for us than any other part of the body. The gut’s endocrine signaling to the entire body is quite elaborate. Communication from our gut-dwelling microbes to the anterior cingulate, orbitofrontal cortex and amygdala up in the brain affects our emotions, motivation, cognition, memory and behavior. (Lieff, 2012).

Just like our primary brain, our gut brain is also able to learn and remember. (Gershon, 1998)

Human intestines measure about ten times the length of the body they reside in.

In the lowest, most primitive part of our brains, a neural network called the basal ganglia is constantly evaluating the outcomes of our every behavior, extracting decision rules: When I said that, it worked out well. When I did this, bad things happened. And so on, like a tireless experimental scientist tasked with guiding us wisely through our lives. The basal ganglia store our accumulated life wisdom. But when we are faced with a decision, it is our verbal cortex that delivers our thoughts about it, often drowning out the wisdom accumulated inside the basal ganglia’s storehouse. (Goleman, 2011)

The most interesting part: The basal ganglia area is so primitive it has no connection to the verbal cortex so it can’t share its knowledge in words – but its connections to the gut are plentiful. The basal ganglia area tells us what is right or wrong for us as a gut feeling. So trust your gut, your felt sense, your intuition – not what comes to you in words from your brain! (Goleman, 2011)

Nearly every brain-regulating chemical found in our skull brains has also been found in our gut brains. This includes major neurotransmitters (serotonin, dopamine, glutamate, norepinephrine and nitric oxide), brain proteins called neuropeptides, major immune system cells, a class of the body’s natural opiates (enkephalins), and even benzodiazepines (the family of psychoactive chemicals found in drugs such as Valium and Xanax). (Gershon, 1998)

The gut has opiate receptors much like the brain. Drugs like morphine and heroin attach to opiate receptors in the brain and also in the gut, causing constipation. Both brains can be addicted to opiates. (Loes, 2003)

Our emotions are greatly influenced by chemicals and nerves inside the gut. Most of us know Prozac as a best-selling anti-depressant pharmaceutical. In 1971, when Eli Lilly was developing the drug, they expected it would become a treatment for high blood pressure or obesity. Prozac (fluoxetine hydrochloride) works by increasing brain levels of serotonin, a neurotransmitter that produces feelings of well-being. Serotonin also affects sleep, appetite and aggression (Bellis, 2013)

Known side effects of Prozac, one of the antidepressants in the selective serotonin reuptake inhibitor (SSRI) class, include nausea, diarrhea, insomnia, and a lowered sex drive – clear evidence of a gut-brain interaction. (Bellis, 2013)

90 percent of the body’s serotonin is located in the gut, where it regulates intestinal movements. Only 10 percent is synthesized in the central nervous system, where it serves many functions – including mood regulation, appetite, sleep, and the cognitive functions of memory and learning. (Berger, Gray & Roth, 2009) (King, 1996-2013)

People with bowel problems also tend to have disturbances in their REM (dream cycle) sleep causing fatigue in the morning even after what felt like a sound sleep. (Alternative Medicine Angel, 2013)

Alzheimer’s and Parkinson’s disease patients often report being constipated. We think of these diseases as central nervous system problems yet our guts also play an important role. (Alternative Medicine Angel, 2013)

A genetically engineered (GE) food is a plant or meat product that has had its DNA artificially altered in a laboratory with genes from other plants, animals, viruses or bacteria in order to produce foreign compounds in that food. An example is sweet corn that has been engineered to produce a pesticide (Bt toxin) in its own tissue and be herbicide resistant (to Monsanto’s weed killer, Roundup). Genetically Modified (GMO) corn is regulated by the Environmental Protection Agency (EPA) as an insecticide but is sold in the US unlabeled. If you eat products containing high fructose corn syrup and many other corn-containing substances, you are consuming this pesticide. There have been no long-term studies to determine the safety of GE and GMO foods. Many countries, containing over 40 percent of the world’s population, already label GE & GMO foods, nevertheless, the US Food and Drug Administration (FDA) does not. Even China labels GE foods as do all the European Union countries. (Label, 2013)

The Standard American diet (aptly abbreviated as SAD) is common in developed countries like the US. It is characterized by high intake of sweets, animal products, cooking oils, high-fat and processed foods. People living on SAD have a higher incidence of heart disease and cancers. (Fuhrman, 2011)

It is well known that factory farmed and processed foods are more likely to cause illness than organically grown, unprocessed foods. Yet 90 percent of the American food budget is spent on processed and fast foods. (Schlosser, 2001)

Since we now know that broad spectrum antibiotics kill the beneficial bacteria in our guts along with the infection-causing ones, here’s an alarming piece of information: Children in the US and other developed countries have received 10-20 courses of antibiotics by the age of 18. (Blaser, 2011)

The existence of the enteric nervous system was first detected by a scientist named Auerbach, working in Germany with a primitive optical microscope in the mid 1800’s, while America was embroiled in our Civil War. (Gershon, 1998)

The traditions of Chinese medicine, Ayurvedic medicine and Hatha Yoga have been aware of this communicating dual-brain system for centuries. The colon cleansing process of Ayurveda and Nauli, a digestive cleaning exercise practiced in classical Hatha Yoga, help cleanse the gut and increase feelings of wellness. In Mayur Asana (Peacock Pose) the body is balanced on the navel. The pressure stimulates the vagus nerve, helping improve the brain-gut connection. (Rajvanshi, 2011)

The belly has been seen as a center of energy and consciousness throughout the world’s healing and mystical traditions. The huge paunches depicted on many of India’s deities indicate that these gods are full of prana (life force or qi). (Alternative Medicine Angel, 2013)

The gentle art of tai chi emphasizes the lower abdomen as a reservoir for energy. It teaches strengthening of the abdominals by learning how to compact prana into the belly. From the Chinese viewpoint, the belly is considered the dan tian, the body’s energy center. The dan tian is an important focal point for meditation and exercise techniques such as qigong and martial arts – and also in traditional Chinese medicine. (Cohen, 1997)

I’ve noticed as a psychotherapist that people’s voices relax and become lower pitched when they’re speaking their gut truths and get tenser and higher pitched when they’re saying what they think.


Alternative Medicine Angel. (2013). See

Bellis, M. (2013). Prozac: The making of a miracle cure? – The history of Prozac. See

Berger, M., Gray, J.A., Roth, B.L. (2009). The expanded biology of serotonin. Annual Review of Medicine. 60, 355–66.

Blaser, M. (2011). Stop the killing of beneficial bacteria: Concerns about antibiotics focus on bacterial resistance — but permanent changes to our protective flora could have more serious consequences. Nature, 476, 393-4.

Boron, W. F. & Boulpaep, E. L. (2005). Medical Physiology, 883.

Cohen, K. S. (1999). The Way of Qigong: The Art and Science of Chinese Energy Healing.

Fuhrman, J. (2011). Super Immunity: The essential nutrition guide for boosting your body’s defenses to live longer, stronger, and disease free.

Gershon, M.D. (1998). The Second Brain: A groundbreaking new understanding of nervous disorders of the stomach and intestine.

Goleman, D. (2011). The Brain and Emotional Intelligence: New Insights (Kindle eBook).

King, M. W. (1996-2013). Serotonin, The Medical Biochemistry Page. Indiana University School of Medicine. See

Lieff, J. (2012). Searching for the Mind with Jon Lieff, M.D. Blog post 11/19/2012. Gut Feelings: The Brain-Gut-Microbe Axis. See

Loes, M.W. (2003). The Healing Response.

Rajvanshi, A. K. (2011). The Times of India, Brain, heart and gut minds, July 10. See

Randerson, J. (2012). The, How many neurons make a human brain? Billions fewer than we thought, February 28. See

Schlosser, E. (2001). Fast Food Nation: The dark side of the all-American meal

A version of this page content will appear in my forthcoming 2014 Oriental Medicine Journal article THE MICROBIOTA-GUT-BRAIN AXIS: The constant two-way communication between our guts and our brains.

© Copyright 2013-2014 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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