It’s happened to many of us at some point in our lives: we finish our bowel movement, look down in the bowl and have a moment of panic when we see an unusual colour. Poo can be found in many colours other than brown, with green poo often eliciting concern. But it’s surprisingly common and is usually no reason to be alarmed.
Why poo is usually brown
The brown colour of poo initially comes from the red of blood. Haemoglobin is the red protein in blood that transports oxygen around the body. It’s eventually broken down into a substance called bilirubin.
In the liver, bilirubin is used to form bile and is released into the small bowel to help digest food. Bile then passes into the colon and the bilirubin is broken down by bacteria.
The final stage in the process is the addition of a substance called stercobilin, which gives poo its brown colour.
All shades of brown are considered normal.
Green poo in adults
Stool colour is very heavily influenced by the substances in the gut that digest food and what you eat.
Green stools contain significantly more bile acids than brown stools. If food is moving through the bowel very quickly – if you have diarrhoea, for instance – there isn’t enough time for the green bile to break down completely, giving stools a green colour.
Green leafy vegetables such as spinach and lettuce contain large amounts of chlorophyll (green pigment) bound to magnesium. This can lead to stools turning green.