You’re not alone. In surveys, 30 to 60 per cent of people report that they need a poo after drinking a coffee. Like any food or drink, coffee stimulates the ‘gastrocolic reflex’, where the colon contracts in response to stretching of the stomach or digestive activity in the small intestine, which gives the sensation of needing a poo.
In a 1998 study at the University of Iowa, researchers found that caffeinated coffee causes more colon contractions than decaffeinated coffee or hot water. However, decaffeinated coffee still had more of an effect than water, so caffeine can’t be entirely to blame. Other chemicals in coffee that could be stimulating the colon include chlorogenic acid and the snappily named N-alkanoyl-5-hydroxytryptamide.