Foods That Cause Dark Stools and When to Be Concerned GoodRx Black, Green or Bloody: What's Up With My Poop? Diet vs Disease Melena Wikipedia Melanosis Coli Gastroenterology & Hepatology of CNY Dark stool vs black stool the difference can be serious. Dark brown stool is often food or iron related. Black, tarry stool may indicate internal bleeding and needs urgent medical attention.