Why does anxiety cause diarrhea or constipation?

[Ganesh Ujwal]

Anxiety sometimes cause diarrhea, sometimes constipation, and sometimes both. It's interesting because it seems their underlying neurophysiology is somehow different. What are underlying physiological processes that lead to these two symptoms in anxious people? Particularly in terms of the activity of sympathetic and parasympathetic nervous system?

 

[berkeman]

Both?

 

[Danger]

I've never heard of the constipation aspect, but the other might be due to the fight-or-flight instinct to evacuate in order to make one unappetizing to predators.

 

[Pythagorean]

Fight or flight responses are normal, healthy responses in which your brain allocates resources to handling an immediate threat. During this allocation, processes like digestion are given less priority. And this would be fine, since the state is usually short lived and normal functioning can resume.

Anxiety is a persistent fight-or-flight state that isn't short lived, so the reduction in normal digestive processing becomes problematic.

 

[Danger]

Anxiety is a persistent fight-or-flight state that isn't short lived, so the reduction in normal digestive processing becomes problematic.

Gotcha.

 

[Suraj M]

anxiety is stimulant for the production of adrenaline... a particular effect it has is ..that it stops the contraction of the GI tract muscles
correct me if i am wrong but this would greatly effect the process of digestion and absorption and hence resulting in loose stools...diarrhea ..

 

[Amaterasu21]

I've never heard of the constipation aspect, but the other might be due to the fight-or-flight instinct to evacuate in order to make one unappetizing to predators.

anxiety is stimulant for the production of adrenaline... a particular effect it has is ..that it stops the contraction of the GI tract muscles
correct me if i am wrong but this would greatly effect the process of digestion and absorption and hence resulting in loose stools...diarrhea ..

I don't have anything to contribute regarding why anxiety causes diarrhoea or constipation, but I think these two different answers are interesting because they highlight the fact that "why does (biological process) happen?" is actually two different questions:

1. How did (biological process) evolve? What is its selective advantage? What's the "reason" this process occurs? (The "reason" being in terms of selective advantage and adaptational value, of course, within a framework of random variation acted upon by natural selection - we must be careful not to let teleology seep into our biological explanation!) An example would be asking "Why do plants contain chlorophyll?" and answering that question by talking about the circumstances under which chlorophyll evolved and the selective advantage that pigment has when it comes to efficient photosynthesis. Danger's answer is an answer of this type - talking about why this particular biological process would have been a selective advantage.
2. How does (biological process) work? What is its function? What's the physiology behind it? For the same "Why do plants contain chlorophyll?" question, an answer in these terms would talk about the role chlorophyll plays in absorbing photons in the light-dependent reactions, and explain the physiology and biochemistry of how photosynthesis works. Suraj M's answer is an answer of this type - talking about how this biological process works at the level of physiology and hormones.

Both types of answers are essential to understand any biological process fully, but I think it's important to understand that any "Why?" question in biology will have at least two different answers.