Eating blueberries may cause black stools. Blueberries are a common fruit, rich in vitamin C, dietary fiber, carotene, potassium, folic acid and other nutrients, proper consumption of blueberries can replenish nutrients and promote health. If you eat blueberries after the stool becomes black, it may be because blueberries contain blue-violet pigment, if the pigment can not be digested and absorbed will appear in the stool becomes black. In addition, the cause of black stools may also have taken iron, bismuth and other drugs, the adverse effects of drugs, including black stools or eating iron-rich foods, such as animal blood or green vegetables, as well as peptic ulcer, gastric cancer, esophagogastric fundal varicose veins and other diseases can be triggered by upper gastrointestinal bleeding, will also cause black stools. Eating blueberries after the stool becomes black when suspected of pathological factors can go to the hospital for medical treatment.