Why does coffee makes you poop?

morning coffee

I used to drink a cup of Joe while smoking a cigarette in the morning. I would start by making the coffee, drink a few sips, turn my computer on, check the emails then go for a smoke. A few puffs and in the urge for a bathroom would kick. Fast forward a few years, and I have quit smoking. But haven’t quit drinking coffee (especially from my Delonghi Magnifica S). Yet, not long after a morning coffee, bowel movement. Cigarette wasn’t the only culprit it seems.

Despite being of interest to a large part of the population who enjoys indeed its morning cup, no large scale study has been made. Experts however link the phenomenon to some bowel-stimulating substances in the coffee. Caffeine, the stimulant alkaloid present in coffee (and tea), provokes colon contractions. It isn’t clear how much caffeine itself is responsible though. A number of factors are to be examined.


“But, but, I only drink decaffeinated!”

Rachel, decaffeinated coffee drinker, morning bowel movement victim

Despite having an effect, caffeine is not the sole culprit. Regular meals provoke the production of acidic juices, themselves activating the colon and peristaltis. A 1998 study found that all types of coffee, or a large meal (1,000 kcal), can provoke the same contractions. The study wasn’t large enough to provide any definitive answer on the question, but it is a step towards understanding our morning puzzlement.

Other factors

  • Acidity: coffee is quite acidic, and this acidity tends to activate peristaltis. This works similarly to digestive juices released by digestion activity. As coffee is drunk by many on an empty stomach, first thing is the morning, the effect can be even more noticeable.
  • Additives: while regular black coffee doesn’t (or shouldn’t) contain additives, most people don’t drink plain black coffee, but add sugar, cream, Starbucks flavor (for a Starbucks like experience without the hefty price tag)
  • Habit: when I was a kid, my grandmother had me go to the bathroom within 20 minutes of waking up, even if I didn’t feel like it. The end goal was to discipline my body to learn to poop early morning, so for the rest of the day to be free of intempestive bowel disruptions. I didn’t care and never persevered, and nothing more annoying than having to poop on school’s not-so-clean toilets. Fast forward 20 years, it’s actually amazing to go on your day without worrying about yesterday’s chili disrupting your important meeting. Hormones in your body, linked to the circadian cycle, can be taught and regulated through habit. Going to the bathroom every morning for years is likely to cause your next morning’s bowel movement even if you don’t have coffee that day.
  • Irritable Bowel Syndrom (IBS) : Irritable Bowel Syndrome can also be a factor, as coffee and caffeine irritate your colon. If you have IBS you are indeed more likely to feel the effect of coffee.
  • Lactose intolerance: a non negligible share of people are lactose intolerant, especially people of Asian descent. For a number of people, depending where you live, a latte may be your only source of lactose, so you wouldn’t pay that much attention to it. The only perceived effect would be the urge for a bathroom not long after your drink. What you think is a coffee effect can instead be a milk effect.

More studies

More studies have been conducted over the past decades, but none with a large enough panel of participants. In 2005 this study showed that coffee or water didn’t affect the force of bowel contractions after 45 minutes. Only 16 participants were tested though.

Last year a study was made about the influence of coffee on food travelling in the intestines. The more cups a week the longer food average travel time.

Different studies, different results: some that coffee doesn’t influence bowel movements, one that coffee influences them over longer periods of time.

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