Why does coffee make you poop?
Because coffee wakes up your colon. In a 1990 study, 29% of young adults said coffee made them need to go. When researchers measured, the lower colon of those people started moving more within 4 minutes of a cup, and it happened with decaf too. Caffeine adds a little on top, but something else in coffee does most of it.
It’s one of the things lots of people notice and few can explain. People often assume it’s the caffeine, or the heat, or that something’s wrong with their gut. The studies point somewhere else, and it’s normal.
What the studies found
In 1990 researchers asked 99 healthy volunteers aged 17 to 27 about their bowel habits. 29% said coffee brought on the urge to go, and 63% of those were women. Then they put pressure sensors in the lower colon of 14 people and gave them black, unsweetened coffee. In the 8 people who’d said coffee affected them, the colon got more active within 4 minutes of regular or decaf coffee, and it stayed that way for at least 30 minutes. Hot water did nothing.
In 1998 another team measured most of the way up the colon in 12 healthy people. Caffeinated coffee got the colon working about as hard as a 1,000-calorie meal. That was 60% more than water, and 23% more than decaf.
| Drink | How hard it got the colon working |
|---|---|
| Caffeinated coffee | about like a 1,000-calorie meal |
| Decaf coffee | between water and caffeinated coffee |
| Hot water | the least, and nothing in the 1990 study |
Hot water didn’t do it, so the warmth isn’t the reason. Decaf did much of it, so caffeine isn’t the main reason either. Coffee works your colon about as hard as a meal does.
Is it a problem?
No. For most people it’s a normal response, like your mouth watering when you smell food. It only affects some people, about three in ten in the 1990 survey, and it comes on within minutes. If coffee gives you diarrhea or stomach pain, or it’s a change from how you used to be, talk to a doctor.
If you’d rather it didn’t happen at work, decaf softens it a little. Is it bad to drink coffee on an empty stomach? has more on morning coffee, and is coffee healthy? has the bigger picture.
