Broadly, there are two types of gastrointestinal disorders. In the first, you feel terrible, something isn’t working right, and the doctors find something wrong. These are “organic” GI disorders.
A gaping hole in the wall of your stomach, in other words, a peptic ulcer, counts as there being something demonstrably wrong. We’ll consider ulcers shortly. Out-of-control inflammation of tissue throughout your GI tract, which is what inflammatory bowel disease is, also counts as demonstrably wrong.
But suppose you feel terrible, something isn’t working right, and the docs can’t find anything wrong. Congratulations, you now have a “functional” GI disorder.
These are immensely sensitive to stress. And this is not just the touchy-feely psychologists saying this. Papers about stress and functional GI disorders are even published in tough-guy meat-and-potato scientific journals with names like Gut.
The most common functional GI disorder, which will be considered here, is irritable bowel syndrome (IBS), which involves abdominal pain (particularly just after a meal) that is relieved by defecating and symptoms such as diarrhea or constipation, passage of mucus, bloating, and abdominal distention.
Despite physicians checking you from every which end, they can’t find anything wrong, which qualifies IBS as a functional disorder.
IBS is among the most common of stress-sensitive disorders. Personally, all the major rites of passage in my life have been marked by pretty impressive cases of the runs a few days before.
Carefully conducted studies show that major chronic stressors increase the risk of the first symptoms of IBS appearing, and worsen preexisting cases.
This makes sense. As we saw, what stress does is increase the contractions in the colon, getting rid of that dead weight. And IBS, also known as “spastic colon”, involves the colon being too contractile, an excellent way of producing diarrhea. It is not clear why lots of stress-induced contractions of the colon can lead to constipation.
As a possible explanation, the stress-induced contractions in the colon are directional, which is to say, they push the contents of the colon from the small intestinal end to the anus. And if they do that a lot, things get accelerated, resulting in diarrhea.
However, in one plausible scenario, with long enough periods of stress, the contractions begin to get disorganized, lose their directionality, so that not much of anything moves toward the anus.
So people with IBS are disproportionately likely to be experiencing a lot of stressors. But in addition, IBS can be a disorder of too much gastrointestinal sensitivity to stress.