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Essential Gut Health—The Second Brain

China Scenary
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A growing body of research in recent years has demonstrated an intimate two-way connection between brain and the digestive system[1,2,31]. Without all this communication back and forth, it would be impossible to control our eating behavior and digestion.

In this article, you will also find out that improving the relationship between our brain and our gut can improve our overall health and sense of wellness.

The Second Brain

It is quite remarkable—so stunningly complex is that the relationship that the gut can be considered the largest sensory organ in the body. Michael Gershon, author of the book The Second Brain[2], calls our gut the second brain.  It is the hub of intelligence, which is equivalent to a pet's brain.  It has the powers that go far beyond making sure that things keep moving through and out of our colon.  

Why the second brain?  "Rather than Mother Nature's trying to pack 100 million neurons someplace in the brain or spinal cord and then sending long connections to the GI tract, the circuitry is right next to the systems that require control[10]," explains Dr. Jackie D. Wood. Therefore, two brains make literal and evolutionary sense.

Gut-to-Brain Connection

The gut sends information to the brain via the vagus nerve and so-called spinal afferent nerves.  The purpose of this gut-to-brain signaling is to provide input to a hierarchy of reflex loops at different levels of the central nervous system.  Through this signaling, the brain receives information about what's going on in the gut.  For example,

  • Two pathways— nerve signals and hormonal signals
    • Our bodies relay signals of health in their intricate networks of hormones and neurotransmitters.
      • The gut can emit hormonal signals that reach the brain directly or through stimulation of the sensory nerves.
      • Via this intricate networks, gut hormones can transmit sensations of fullness and hunger.
  • Inflammation in the gut can trigger a feeling of being sick.
    • If you suffer from a disease, illness, or infection that affects your gut,  it can have an impact on 
      • How you think (sick vs well)
      • How much pain you experience (see IBS below)
      • How well you sleep
      • What your energy levels are (fatigue vs energized)

Because the gut sends an enormous amount of information to an area of the brain responsible for our feelings of self-awareness and well-being, the health of our gut can be a much bigger factor in your perception of health than we might imagine.

Brain-to-Gut Connection

Likewise, the central nervous system sends information back to the gut to ensure optimal functioning during sleep, fasting, and digestion. For example, 

  • The very thought of eating can release the stomach’s juices before food gets there
  • A surge of stress hormones released by the body in a "fight or flight" situation can cause butterflies in the stomach
  • Stress can overstimulate nerves in the esophagus, causing a feeling of choking.
The gut actually has its own little network that allows it to respond to the brain and signal when something isn't right. For example, anger, anxiety, sadness, elation — all of these feelings (and others) can trigger symptoms in the gut. 


IBS (Irritable bowel syndrome)

We already know that our emotions can influence our gut.  Now we also know that our gut can influence our emotions.  Under normal conditions, the exchanges between brain and gut take place without our knowing it.   Unfortunately, sometimes the communication problem crops up in the brain-gut couple, one of them is IBS or Irritable Bowel Syndrome.  IBS is a common disease affecting around ten to 15 percent of people in industrialized countries, which is normally characterized by a sever abdominal pain.

What could be the main cause(s) of  this communication problems? 

There are no clear answers to the answer yet. However, biopsies of patients with irritable bowel syndrome have shown that the nerves in their gut wall respond poorly to a cocktail of inflammatory substances.[33] This refutes the previous theory that patients with irritable bowel syndrome may have an overly sensitive gut.  Notice that

Researchers, however, have not ruled out the possibility of the gut's sensitization to other substances in other cases.  In addition, as its name suggests, IBS is a syndrome and it could have many causes.

Even without knowing the exact causes of IBS, doctors in China have been routinely practiced abdominal acupuncture on patients with abdominal pain, depression, etc.  And, it seems to be effective in relieving at least some of the patient's pain and/or anxieties.[31]


By maintaining a healthy gut, you can also achieve the overall health and sense of wellness.  In [3], it describes how stress (or depression or other psychological factors) can affect movement and contractions of the GI tract, cause inflammation, or make you more susceptible to infection. So, it's essential for you to reduce stress and/or treat depression for better gut health and overall wellness.[4,9]

Finally, to maintain a healthy gut, do

  • Eating a healthy diet that is:[13,14]
    • Low in fat and refined sugars[5]
    • High in natural fibers[6-7]
    • Low in calories[8]
    • More with traditional fermented foods[12]
      • Probiotics can help optimize gut flora
  • Avoid western diets (see details here)
  • Taking in several small portions during the day[8] 


  1. The California Cure—Dr. Emeran Mayer: Second Brain
  2. Second Brain: A Groundbreaking New Understanding of Nervous Disorders of the Stomach and Intestine by Michael Gershon.
  3. The gut-brain connection (Harvard Health Publications)
  4. Breathe Deeply to Activate Vagus Nerve
  5. The Sweet Relished and the Bitter Loathed
  6. Eating Organic, Local, and Seasonal Foods
  7. Plant-based vs. Animal-based Diets
  8. Eat Less Live Longer
  9. Stress and How to Diffuse It
  10. The Other Brain Also Deals With Many Woes (The New York Times)
  11. The Emotional Life of Your Brain by Richard J. Davidson, Ph.D. with Sharon Begley
  12. The Root Cause of Anxiety and Depression That Few Suspect (Dr. Mercola)
  13. The End of Illness by David B. Agus, MD
  14. In Defense of Food by Michael Pollan
  15. Fat and cholesterol aren’t only heart dangers of red meat (The Washington Post)
    • As bacteria in the gut breaks carnitine down, it turns into a compound known to harden arteries.
  16. How Our Guts – and What We Eat – Contribute to Heart Disease, Stroke and the National Debt
    • TMAO helps fatty substances in the blood to accumulate in the walls of the coronary arteries. 
    • TMAO is created when bacteria in the gut interact with two specific dietary nutrients – carnitine (found in red meat and dairy products) and lecithin (found in egg yolks, liver, beef, pork and wheat germ)
  17. The Ins and Outs of Gut Bacteria
    • The Human Microbiome Project has identified roughly 10,000 species of gut bacteria, but each of us carries around about 1,000
    • Healthy adults carry up to five pounds of bacteria in their digestive tracts alone – roughly the weight of a brain
  18. What You See in the Toilet Can Give You Valuable Insights into Your Health
    • Your stool is about 75 percent water. The rest is a fetid combination of fiber, live and dead bacteria, miscellaneous cells and mucus.
  19. 'Weight loss gut bacterium' found (BBC News)
  20. Some of My Best Friends Are Germs (New York Times)
  21. Fecal Transplants
    • Which involve installing a healthy person’s microbiota into a sick person’s gut, have been shown to effectively treat an antibiotic-resistant intestinal pathogen named C. difficile, which kills 14,000 Americans each year.
  22. Can you coordinate the dance of your body's 100 trillion microorganisms? (TedMed)
  23. Can Parasites Heal the Gut? (Travel and Health)
  24. Gut Microbes for Life
  25. Gut Bacteria May Be Implicated in Rheumatoid Arthritis
  26. Missing link found between brain, immune system -- with major disease implications
  27. Early Studies Linking Gut Bacteria to Atherosclerosis, Offer Tantalizing Glimpse at New Drug Target
  28. Immune homeostasis, dysbiosis and therapeutic modulation of the gut microbiota
  29. Imbalance Of Gut Bacteria Linked To Elevated Risk For Diabetes
  30. Could Parkinson's disease start in the gut?
  31. The Gut: Our Second Brain (Amazon Prime)
    • 95% of our body's serotonin is produced in our gut
  32. How Gut Bacteria Tell Their Hosts What to Eat
  33. Insensitive irritable bowel syndrome
  34. Health Benefits of Eating Fermented Foods (Travel to Health)
  35. Leaky Gut Syndrome and Autoimmune Disease (Travel to Health)
  36. Western Diets and Western Diseases (Travel and Health)
  37. Tweaking the gut microbiome may hold promise for fighting stress, anxiety
  38. TMAO-Producing Enzyme Shown to Regulate Obesity in Humans
  39. Brain-Gut Connection, Linda Nguyen, MDStanford Health Care