Issue 42 Traumatic Stress

By Stanley Coren

Stress is indigestible

Stress is indigestible


Excerpt from Stress is indigestible: the mind and stomach link, by Stanley Coren, PhD, FRSC, original article in WellnessOptions #25, 2006.

We owe our first confirmation of the fact that stress and emotions affect our digestive processes to the bad temper of a French-Canadian trapper.

In June 1822, William Beaumont, a U.S. army surgeon serving at Fort Mackinac (now in Michigan), was summoned to nearby Michilimackinac to treat Alexis St. Martin, a 19-year-old trapper.

The patient’s temper had gotten him into an argument, which ended when he was wounded at close range by a shotgun blast. The shot removed a portion of his abdominal wall and left a hole in the front wall of his stomach.

During the year it took for the wound to heal, the hole in his abdominal wall never sealed correctly. Instead, it was held closed by the odd growth of a sort of a flap, leaving a passage (called a gastric fistula). When Beaumont pressed his finger against the flap, the passage opened and he could see the activities going on within St. Martin’s stomach.

The first scientific report

Beaumont used the trapper’s unique condition to benefit medical science, and his studies ultimately led to a few discoveries about digestion. What surprised him the most was how anger, fear, or any strong emotion seemed to affect the stomach, causing the normal flow of fluids to diminish to such a degree that the stomach wall would lose its healthy appearance.

Since the 1833 publication of Beaumont’s results, there has been a large amount of research that establishes a definite connection between activities in the brain and in the gastrointestinal system.

Functional disorders

The three common functional diseases affecting digestion that often bring people to seek medical help are excessive gas, functional dyspepsia, and irritable bowel syndrome.

The term functional disease refers to a disorder in which the only observable change is in the way the systems in the body work, rather than an observable inflammatory condition, infection, or structural abnormality that can be confirmed by common examination procedures, x-rays, or laboratory tests.

It is now apparent that these three functional problems are associated with a mind-body link and are, to some degree, consequences of psychological stress and intense emotions.

Excessive gas

Excessive gas is the simplest and least threatening of the three, although it can sometimes accompany other problems. A common source of upper intestinal gas is air that is swallowed.

Each time we swallow, a small amount of air enters the stomach and is usually passed into the small intestine. Any remaining gas travels into the colon (large intestine) and is passed out through the rectum. In some people, part of the gas is belched out instead of being passed from the stomach into the intestine.

There is a simple relationship between gas and emotion. People under a lot of stress tend to breathe more with their mouths and tend to swallow large amounts of air—much more than the intestines can absorb. Too much gas is annoying and uncomfortable, and its release can be embarrassing.

Dyspepsia and irritable bowel syndrome

The other two functional problems associated with digestion are more serious.

The symptoms of functional dyspepsia include upper abdominal pain (above the navel), belching, nausea (with or without vomiting), and a sensation that the stomach is uncomfortably full (often coming after eating only a very small amount of food). There may also be abdominal distention (swelling). These symptoms are most often triggered by eating.

Irritable bowel syndrome is a disorder most commonly characterized by cramping, abdominal pain, bloating, constipation, and diarrhea. It occurs more often in women than in men and begins before the age of 35 in about half of the cases.

Psychological stress

Both functional dyspepsia and irritable bowel syndrome are connected to psychological stress and intense emotions. Together, these problems affect more than one out of four people in North America to some extent.

There are numerous studies, which show that individuals whose lives are undergoing major upsets (divorce, death of a spouse or child, loss of a job, and so forth) are much more likely to develop symptoms.

Individuals with a history of childhood abuse, sexual abuse, or spousal violence are at higher risk as well. It is also clear that personality factors play a role. Individuals who are emotionally reactive, score high on neuroticism tests, have sleep difficulties, or have tendencies toward depression are all more likely to have both of these digestive difficulties.

Many people often experience cramps or “butterflies” when they are nervous or upset. In people with irritable bowel syndrome, the colon can be overly responsive to even slight conflict or stress. For such people, the stress makes them more aware of the sensations that arise in the colon, which in turn adds to the unpleasantness of the episodes.

How stress affects digestion

We have a pretty good idea as to how stress affects digestion. The body has four different major nervous systems. The somatic nervous system controls muscles. The central nervous system includes the brain and spinal cord.

There is also the autonomic nervous system, which consists of two competing nervous systems—the sympathetic nervous system and the parasympathetic nervous system.

The parasympathetic nervous system handles many basic life maintaining functions, including digestion. Under parasympathetic control, digestive fluids are generated in the stomach, the stomach contracts to move food along, and other contractions assist movement, further digest food in the intestines, and finally remove waste material by passing it through the colon.

In times of stress, the sympathetic nervous system takes over. It is concerned with immediate survival from threats, so it speeds the heart, increases oxygen consumption, and generates stress related hormones like cortisol.

You get much the same stress response from the sympathetic nervous system whether the stressor is a tiger that you must run from, or a hostile comment from your professor, boss or lover.

When the sympathetic nervous system goes into high gear, it commands all of the resources that it can. This requires shutting down much of the parasympathetic activities. In effect, digestion stops. Digestive fluids stop flowing. Movement of materials through the gastrointestinal system stalls.

If this response continues for any significant period of time, irritation develops in the stomach walls. When this occurs frequently, stomach upset and even ulcers may result.

The mucous membranes that line the intestines can also become damaged. Partially digested materials at a stand still in the gastrointestinal system upset the normal intestinal bacteria flora.

The parasympathetic nervous system seems to recognize that this is not a good state of affairs, so it tries to restore normal digestion as soon as possible.

However, if the sympathetic nervous system is still responding to stress, conflicting messages may be sent to the gut that can exaggerate the irritability of the digestive system.


Bhatia, V. and Tandon, R.K. (2005). Stress and the gastrointestinal

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Mawdsley, J.E. and Rampton, D.S. (2005). Psychological stress in

IBD: new insights into pathogenic and therapeutic implications.

Gut, 54; 1481-1491.

Smith M. L. (2005). Functional dyspepsia pathogenesis and

therapeutic options—Implications for management. Digestive and

Liver Disease, 37, 547–558.

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