Why does coffee make you poop?

Coffee stimulates the colon directly, and studies measuring gut activity found contractions beginning within about four minutes of drinking, far too fast for caffeine to have been absorbed and gone to work. Decaf produces much of the same effect, so caffeine is an accomplice, not the mastermind.

The leading explanations: coffee prompts the release of gastrin and cholecystokinin, hormones that fire up the digestive tract, and it amplifies the gastrocolic reflex, the wake-up call your colon gets whenever the stomach fills. Morning timing helps too, since the colon is naturally most active after waking.

Roughly a third of people report the effect, it skews slightly more common in women, and it is entirely normal. If anything, gastroenterologists regard coffee's gut-moving reputation fondly.