Why is My Poop Green?

4. Black Stools and the Foods That Cause Them

A popular misconception is that black stools always indicate a serious condition, such as internal bleeding. That isn't usually true. Certain foods, such as black licorice, blueberries, dark chocolate sandwich cookies, blood sausage, and iron-rich foods can cause a color change. Just about any dark-colored food can turn the stool to a blackish-blue or very dark, blackish-green color. If the individual is taking an iron supplement, their stools could be black for as long as they continue taking the supplement. Bismuth, a common ingredient in Pepto-Bismol can cause black stools as well.