What should you know about black stool after fasting?

After fasting, the first bowel movement may look different because less food and fluid have passed through the gut. Dark foods eaten before the fast, iron supplements, and bismuth medicines can also make stool appear black. These changes generally do not make stool sticky and tar-like. Melaena, by contrast, can signal bleeding in the stomach or upper intestine. Possible sources include gastritis, a peptic ulcer, or Helicobacter pylori-related irritation. Fasting does not rule out these causes, and colour should be judged alongside texture and symptoms.

Review what you ate and which medicines or supplements you used before fasting. Drink fluids gradually when the fast ends, unless a clinician has given you a fluid restriction. Observe the next bowel movement without delaying care if it remains black, sticky, or unusually foul-smelling. Arrange prompt medical advice and mention any abdominal discomfort, nausea, dizziness, or unusual tiredness.

Go to emergency care if black stool is repeated or accompanied by fainting, severe weakness, breathlessness, a racing heartbeat, severe abdominal pain, or vomiting blood or coffee-ground material. These symptoms may indicate active bleeding. Seek advice sooner if you take blood-thinning medicine or have a known ulcer.

Ask whether your medicines or supplements explain the colour, whether stool testing or blood tests are appropriate, and which changes should prompt emergency assessment. Tell the clinician how long the fast lasted and whether the stool was sticky or loose.