Medical Q&As

Stools - dark colour significant?

Is it possible that Guinness and chocolate can colour the faeces in a way that looks like melaena?

Melaena is the technical term for black, tarry and foul smelling stools. This indicates that bleeding has taken place somewhere along the gastrointestinal tract. Usually the bleeding arises from the upper tract and the black tarry nature of the stool indicates that the blood has been partly digested. In contrast bleeding from the lower gastrointestinal tract has not been digested and therefore will usually look like fresh red blood in the stool. It is estimated that it is necessary to lose at least 200 millilitres of blood in order to produce melaena. If it is suspected that a person has suffered a gastrointestinal bleed it is possible to confirm the presence of blood by analysing the stools. There are several innocent causes of dark coloured stools but I stress that these stools will not have the classic tarry consistency of melaena nor are they as foul smelling. Stout can result in dark coloured stools, as can liquorice and blueberries. Iron tablets are a well-known cause of dark coloured stools and many expectant mothers notice this change when they take iron supplements during pregnancy. If a person were to eat a lot of black pudding or red meat this could also cause dark stools because of the rich iron content in those foods. I am not aware if chocolate can cause dark stools but have never had a patient bring that observation to my attention in clinical practice. The various causes of dark stools that I have mentioned do not have any health consequences but if there were a suspicion that a person might be bleeding in the gut that matter should be medically assessed.