Too much iron can darken stools, which is common for people taking iron supplements. Although iron-rich foods don't typically cause the same effect as iron pills, some deeply hued fare can turn your stool a different color, making you look twice after using the restroom. If your stool is sticky like tar in addition to appearing black or having red streaks, this could be a sign of bleeding and requires medical attention.
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Food and Stool Color
Along with iron supplements, dark foods such as chocolate cookies and licorice can make stool appear black. If you haven't eaten black foods or taken iron supplements, your stool should not appear black -- even if you've eaten iron-rich foods such as eggs or shrimp. Spinach and other leafy greens may turn your stool dark green, which may appear black in dim lighting. Beets and tomato products may turn stool red, which can be difficult to distinguish from blood. Unexplainable black or red stool could signify a medical issue.