Having green faeces may be the result of any one of many conditions. Ultimately the colour of the faeces determines how your digestive tract is working and metabolising food and hormones. Green-hued stool may be the result of illness, diet or stress. While there is little concern if your stool is periodically green, you should consult a doctor if the condition becomes regular or chronic.
The liver produces a hormone called bile which is used to digest fats. It is comprised of cholesterol, lecithin, pigments and salts. Bile is stored in the gallbladder and has a green pigment. If your digestion is sped up, your body may not have the time to metabolise the bile therefore your stool may be green. This can occur through stress or illness. Essentially the faster the faeces travels through the system, the more green it will be.
When you get the flu or food poisoning, you may experience a bout with diarrhoea. When this happens, it is not uncommon to have green faeces. This is particularly true of children with infectious diarrhoea. With diarrhoea the digestive process is sped up so dramatically that your the bile has no time to be broken down with the bile salts being absorbed. Your doctor may prescribe antibiotics depending on whether or not your illness is bacterial. Your stool should return to a normal colour when you are feeling better.
What you eat determines the colour of your stool. You can have green stool if you eat a lot of green vegetables. These include spinach, lettuce, broccoli, peas and green peppers. Other foods that contain green food colouring can also lead to green stool. While this is often not of great concern and will alleviate itself if you cut back on the vegetables or reduce processed foods, you do want to monitor food that is high in iron. The body needs iron but also has great difficulty in absorbing too much iron. When it is faced with this dilemma it produces more bile iron salts making your stool green. Consult your doctor about any risks this poses to your health.
Certain diseases prevent proper absorption in the intestines. This prevents the bile salts from being absorbed and they are then excreted in the stool giving it a green pigment. Diseases that may create chronic green faeces are Crohn's disease, colitis, coeliac disease and irritable bowel syndrome. It is best to discuss your condition with your doctor about how to improve your body salt absorption. Poor digestive health resulting from these conditions can lead to serious nutritional deficiencies.
Stress can indeed affect your digestive function and may speed it up. While this may not be an instantaneous effect, stress can lead to having to move your bowels sooner than normal, with the faeces' colours sometimes also being abnormal. Children starting school are often afflicted with this but are not alone. Adults experiencing stress may also find the urge to go to the bathroom more often than normal. When you adjust to the stress, your body should return to its normal digestive function.