Post-Exercise Bloody Stool
If you are reading this, you either are experiencing some worrying toilet issues, or you are a curious individual. In this brief article, we will understand why we poop blood from exercise.
What causes bloody feces?
The cause of your bloody diarrhea is due to a process called splanchnic hypoperfusion .
How common is it?
Luckily, if you have suffer from it, you are not even close to alone – up to 70% of people are thought to suffer from it at one time or another .
Understanding the Physiology
When we exercise, blood flow is quickly diverted toward our musculature – especially that which is in use (if running, your legs) to flood the cells with a constant stream of nutrients for energy generation, but also to remove heat. Fulfilling this process is a matter of taking blood away from other areas of the body, and that means the intestinal system . So, vasoconstriction occurs to the celiac artery (also known as the celiac trunk), as well as the superior and inferior and superior mesenteric arteries, which all extend off the inferior aorta (originating from the heart) . This substantial reduction in blood flow to the intestinal tract means more is available for the muscles, but the intestinal tract suffers. This process is mediated by norepinephrine release through the sympathetic nervous system binding a-adrenergic receptors leading to the vasoconstriction of the aforementioned arteries and the removal of what little blood still passes through the portal vein .
The lumen of the intestine is lined by intestinal villi, finger-like projections that allow the intestine to maximize its surface area, and these villi are lightly perfused by tiny venules and arterioles that supply what limited oxygen can reach them . So, reducing the blood flow is manageable by the epithelial cells, endocrine cells, and stem cells making up the base of the villus, but not so for the tips of the villus, where blood flow and oxygen delivery is scarcest (as well as being more prone, in particular context, to programmed cell death) . The lack of blood flow is a form of ischemia and leads these cells to die; however, upon reperfusion (return of blood flow) of these particular cells after exercise could also be an issue as inflammatory cells release tumor necrosis factors, interleukins, and other cytokines, recruiting more and more immune cells to further eliminate damaged cells . It is also thought that reperfusion can lead to unwanted oxidative stress as the sudden reintroduction of abundant oxygen could overcome an already struggling enterocyte/epithelial cell of the villus, leading to further damage, opening of the tight junctions between cells, and death .
How to Prevent it?
Consume carbohydrates during exercise – while the absorption will certainly be impaired, the stimulus of quickly absorbable carbohydrates may lead to slightly more blood flow allowed to the intestinal tract .
In short, bloody stools are a consequence of splanchnic hypoperfusion. When we exercise intensely, more and more blood is diverted from the intestines to the muscles, leading to less oxygen and nutrients reaching the tips of the villi involved in food absorption; consequently, this can cause cell death, which is observed in our bathroom habits. Now, you may be able to mitigate this a bit by simply consuming a little carbohydrate before an exercise event, as this will encourage the intestinal tract to assume more blood flow.
Author: Nicolas Verhoeven
 Van Wijck, K. (2012). Physiology and pathophysiology of splanchnic hypoperfusion and intestinal injury during exercise: strategies for evaluation and prevention. American Journal of Physiol Gastrointest Liver Physiology, 303(2), G155-168. doi:10.1152/ajpgi.00066.2012
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 Costa, R. J., Snipe, R. M., Kitic, C. M., & Gibson, P. R. (2017). Systematic review: exercise-induced gastrointestinal syndrome-implications for health and intestinal disease. Alimentary Pharmacology & Therapeutics, 46(3), 246-265. doi:10.1111/apt.14157