Stress and Digestion: Part I The Science

I have always said, half jokingly, that stress was responsible for all my digestive problems because I didn’t know of any other cause.  I finally decided to do some research into stress and digestion to see if there actually is a credible link. The wealth of information I found has nearly overwhelmed me, but it has answered many of my questions, and has offered me hope.  It is with thankfulness that I want to share with you what I’ve found.

This will be a two part article.  In the first part we’ll look at the problem and delve into the science which links the mind and digestive system.  The second part will focus on how to help both the body and the mind.

Your Gut and Your Nerves

Have you ever said, “I had butterflies in my stomach,” “It was a gut-wrenching decision,” or “I choked under stress”?  If so, then you intuitively know that there is a connection between your emotions and various parts of your digestive system.  Well, your intuition is correct! There is a very good reason why we say such things.

First, some definitions for the purposes of this article:

  • “gut” includes stomach, and small and large intestines
  • “digestive system,” “gastrointestinal tract” or “GI tract” include everything from the mouth to the annus
  • “central nervous system” or “CNS” is the brain and spinal cord
  • “enteric nervous system” or “ENS” is the system of nerves and ganglia (nerve centers) which surround and control the digestive system, especially the gut
  • “neurotransmitters” (including acetylcholine, serotonin, dopamine and histamine) are chemical messengers that allow nerve and muscle cells to talk to each other.

The enteric nervous system is the key link between your brain and your gut.  When your brain perceives a stressor, it sends out messages via the central nervous system to put the entire body into a fight or flight mode.  When these messages reach your digestive system they enter the enteric nervous system.

The ENS is called “the brain of the gut” or “the second brain.” It is made up of two layers of over 100 million nerve cells (more nerves than are in your spine), and it lines your GI tract from esophagus to rectum. The ENS produces some of the same neurotransmitters that are in your brain.  In fact, about 95% of your serotonin is in your gut, not your brain (Nutritional Psychiatry, ).  Serotonin governs your sleep, appetite, mood, and sense of pain.  The ENS also produces dopamine (the “feel good” chemical) and acetylcholine (the chemical by which a nerve tells a muscle to move).

The ENS not only receives messages, it sends them, too.  Research at Johns Hopkins Center for Neurogastroenterology has found evidence that the ENS sends mood messages to the brain, through the CNS, and in the brain these messages trigger mood changes.  This explains why people with irritable bowel syndrome have a higher than normal rate of depression and anxiety. It also explains why eating makes us feel good. All that serotonin in the gut is released when food is present to help the food move along through the GI tract.  Conversely, no food means low serotonin, which often makes you grumpy (as the Snickers commercials tell us).

So the nerve pathway between the brain and the gut is a two way street.  This is why we feel our emotions in our gut.  Interestingly, over 40 million people in the U.S. suffer from some sort of psychiatric illness, while 70 million are diagnosed with a digestive disorder, but doctors rarely connect the two problems.  So you must consider a connection if you want to find a solution to either problem.

Enter Stress

Stress comes in many different forms and is relative to each individual.  Obvious stressors are easier to recognize and confront, such as, if your house is on fire.  When you smell the smoke, see and hear the flames, your brain begins a cascade of reactions in the body which enable you to fight or flee. While you run out of the house and make sure your family gets out, call 911 and turn on the garden hose, your body is restricting blood flow to non-essential parts and redirecting it to your heart and the muscles in your limbs. It also releases neurotransmitters and the stress hormone  cortisol, which elevates blood glucose and blood pressure.

Stress holds your digestive system hostage by slowing the whole process to a crawl because digestion is not essential to fight or flight.  Blood flow is redirected away from the gut, and digestive secretions are stopped. So, if you had just finished dinner when you realized your house was on fire, the food in your system would be left undigested, or is deposited as fat to be digested later when you are calm.

Now suppose you have lost your job and your mortgage payment is due.  Running out of the house and turning on the garden hose would be ridiculous, and calling 911 would be futile.  Yet your body reacts to this stress with the same fight or flight response, and it has the same effect on your digestion.

Or imagine that you have a good job and a secure house, but whenever you go home your spouse and children fight with you, and you feel trapped by your responsibilities. Day after day your body remains in that fight or flight mode of restricted blood flow, continual release of stress chemicals, and minimal digestion (not to mention effects to other parts of the body).

Effects of Stress

There are four major effects of continuing stress on the digestive system.

  1. Disrupted Peristalsis.  Food should move through the GI tract at a certain rate for optimal break-down, metabolism and absorption (this is called peristalsis).  But stress can slow or shut down the muscles that do this moving. The result is constipation and fermentation of food in the gut. Or the result is moving undigested food along so quickly that nutrients can not to be absorbed, and this leads to diarrhea and malnutrition.
  2. Heartburn.  The muscle that closes the stomach off from the esophagus does not function properly when you are under stress.  This results in stomach acid leaking back up into the esophagus where it burns the more delicate lining and leaves it open for diseases (such as hiatal hernia and cancer).  Over-the-counter medications for heartburn are the best selling of all OTC medicines, but they do not fix the underlying cause, which is stress.
  3. Gut Immunity.  About 70% of your body’s fight against harmful invaders takes place in the gut.  You can have literally pounds of bacteria in your gut! Some bacteria help in digestion, some produce chemicals your body needs to be healthy, others are bad–even toxic.  The body’s chemical reactions under stress kill large amounts of the good bacteria, so the bad bacteria flourish, weaken your immune system, and cause inflammation.
  4. “Leaky Gut.”  A healthy gut works like a fine sieve.  It allows small particles of digested nutrients to be absorbed, and it sends everything else on down the line toward elimination.  When this gut sieve breaks, you have “leaky gut.” Things that should never be absorbed, get in and create havoc for your whole body.  Under stress, the mast cells of your gut (which normally produce serotonin) are triggered to produce histamines instead. This causes a massive allergic response in your gut. The resulting inflammation  makes it more porous, or “leaky”. On one hand, this makes sense because combating a stressor requires energy, and a leaky gut allows more glucose to get into your system faster to help you fight or flee.  But, undesirable things also flow into your bloodstream, along with the glucose, and invade your whole body. Research indicates that it may take several days of zero stress before the inflammation subsides, the gut stops “leaking” and returns to normal.  In the short term your white blood cells, liver, and kidneys can cope with these invaders, but when stress is chronic, inflammation and leaky gut also become chronic, and the invaders just keep pouring in, overwhelming your whole body.

When you combine these four factors, you can see how stress harms the digestive system, and chronic stress wreaks havoc on the entire body through the gut.


Stress literally makes your stomach hurt!  It injures the gut and this causes the ENS to send pain messages back to the brain.  This in turn causes more stress, which creates more injury and then more pain.

To break this toxic cycle you must treat the cause of your stress, your emotional health, and your gut health all at the same time. Because of the way the ENS operates as a two-way street in sending pain messages, it may not be obvious which pain is the cause of your stress and which is the effect–the brain or the gut.  Also, one may not heal if you are not treating the other as well. For example, if you discover you have a parasite in your gut, and you seek treatment to get rid of it, you may not be successful as long as your gut is full of bad bacteria and remains leaky due to chronic emotional stress in your life.

In Part II of this blog, we will look at ways to help you cope with both mind and gut stress.  Please feel free to share your thoughts or your story in the comments below. I look forward to hearing from you.

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