ZocdocAnswersWhat could cause very black stools in athletes?

Question

What could cause very black stools in athletes?

I run about 15 miles a day and have had very black stools of late. Why is this? I am a 24 year old guy and have never had this problem before.

Answer

Black stools can be caused by a few different things. Sometimes our stools our effected by our diet. I you have altered your diet lately, especially if you are eating a lot more meat, then this could explain this problem. Another cause of dark stools is iron. If you take iron supplements, or if you take multivitamins with high levels of iron, then this would also result in the change in your stool color. The last reason is the most concerning. A bleeding stomach ulcer or other gastrointestinal (GI) bleed can cause dark stools. As blood passes through the GI tract, some of it gets digested. The left over material from the blood is not longer red but a very dark and somewhat sticky texture. It is for this reason that I always spend time working up patients with a report of dark stools to make sure that this does not represent a GI bleed. I don't think this has anything to do with your running. I suggest that you schedule an appointment with your primary care physician. Her or she can take a close look at you and order blood tests including your blood counts. Your doctor will likely need to do a rectal exam to gather a sample of stool to test it for blood. If it is positive, you will need referral to a gastroenterologist.

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