There is no clear relationship between eating dragon fruit and black stools. Black stools may be normal, or they may be caused by diseases such as peptic ulcers leading to upper gastrointestinal bleeding, which is not normal. Eating dragon fruit does not usually cause black stools, but if you eat red dragon fruit may appear feces, urine purple-red situation. Black stools may be caused by eating iron-rich foods such as animal blood or taking iron or bismuth medications, in which case black stools are normal. However, if peptic ulcer, esophagogastric varices, gastric cancer and other diseases induced upper gastrointestinal bleeding can also appear after the black stool, such cases are not normal, need to be treated immediately. If you suspect that a disease is the cause of black stool when eating dragon fruit, you need to go to the hospital and ask the doctor to make a judgment.