A person's diet and the amount of bile in his stool cause his stool to have different colors, according to Mayo Clinic. Certain medications, supplements and diseases also cause stool to change color.
A healthy bowel movement comes in different shades of brown, according to WebMD. If food takes a short time in the digestive tract, the resulting stool may be green. Possible dietary causes of green stool include green leafy vegetables, iron supplements and green food coloring, notes Mayo Clinic.
White, clay-colored or light-colored stool may indicate a lack of bile in the stool, explains Mayo Clinic. This may be a symptom of bile duct obstruction. However, there are certain medications, such as bismuth subsalicylate and other anti-diarrheal drugs, that may cause light-colored stool.
If the stool is yellow and greasy, it may mean that there is excess fat in the stool, states Mayo Clinic. This is a sign of pancreatic insufficiency or a malabsorption disorder, which can be caused by celiac disease, pancreatitis or cystic fibrosis, notes MedicineNet. A dietary cause of yellow stool is gluten, which is found in cereals and bread.
Black stool may indicate bleeding in the upper gastrointestinal tract, according to Mayo Clinic. This may be due to tumors or ulcers, explains MedicineNet. Dietary causes of black stool include black licorice and iron supplements. Bright red stool can signify bleeding in the middle and lower intestine or proximal colon due to tumors, ulcers, hemorrhoids or Crohn's disease. However, dietary causes include red food coloring, beetroot and cranberries.