You have noticed that your stools are green and you are worried. At this point you need to think carefully, review what you have been eating recently and analyse what may be causing the unusual coloured faeces. Most likely it’s nothing to worry about but let’s start with asking why poo is brown in the first place?
The brown colour of poo is mostly caused by the bacteria working on the food you’ve eaten. Also mixed in will be the bile, which is essential for digestion and is a yellowish green colour. There will also be some dead red blood cells, and together this results in a mix which is characteristically brown.
If you have diarrhoea this process does not work fully, because what you’ve eaten goes through your body too quickly, so there is not enough time for the bacteria to properly digest the food. There may also not have been enough bile released into the digestive tract. As a result if you have diarrhoea and you have eaten green vegetables such as broccoli, kale, or spinach your stools may be dark green. Other foods which could contribute would be green food colouring or blueberries (which are green inside!). So most commonly green stools will be the result of diarrhoea or lack of bile, but there are some other possibilities…
Sometimes antibiotics can interfere with the digestive process and lead to dark green poo, or a bacterial infection can interfere with digestion. A recent medical procedure might lead to green stools such as a bone marrow transplant, or possibly an underlying medical condition. But you should only worry about this if the problem persists. Generally if you have had diarrhoea for more than three days you should consult a doctor. You certainly should not jump to the conclusion that you have cancer – if anything cancer is more likely to be associated with brown or tarry coloured faeces. If you have blood in your poo that is more likely to be of concern to your doctor.