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It's common knowledge: you drink a lot of coffee, you're definitely going to poop. What isn't common knowledge is why your body reacts that way...

Hosted by: Michael Aranda
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Picture this: It's Monday morning in the office, and you've got to start the day off right with a little caffeine. So, you pour yourself a nice, hot cup of coffee, settling in at your desk and get to work. But soon, your guts start to rumble, things start moving, and you got to poop. The phenomenon is so well known that it's even plastered on mugs, "Coffee makes me poop."

Around 3 in 10 people find themselves on their way to the bathroom after their morning cup of joe. And a small study done in 1990 found that it wasn't just that people felt the urge to go, within few minutes of drinking coffee, people who needed to poop also had an increase in motor activity in their colons. So their guts were physically responding to the drink. Which brings us to the questions, why?

Some scientists think that it might not be the coffee at all. It could just be that coffee is the first thing you put in your stomach in the morning, and as your stomach stretches, it triggers the gastrocolic reflex. Basically, your guts wake-up and things get moving. On the other hand drinking a glass of water when you wake up, doesn't necessarily send you to the bathroom. So there's probably more to it then that. 

Strangely enough, there's never been a large-scale study investigating the mechanism of the post-coffee poop. But researchers have done smaller studies to test different possibilities. Caffeine could be part of what's causing the effect, since caffeine is a stimulant, it could be stimulating some things at the other end as well. Except that studies have found that even decaf coffee can make you have to go, which means it can't just be the caffeine's fault. 

Coffee is pretty acidic, and acid in the stomach might be another part of the problem. When there's a lot of acid in your stomach, you produce more bile, which can in turn cause diarrhea. But that takes a while, and the urge to use the restroom happens just a few minutes of after drinking coffee. Research from the 1980s showed that drinkin regular and decaf coffee increases the release of a hormone called gastrin, which helps the stomach produce acid and encourages movement in the intestines. But gastrin wasn't released when the subjects drank hot water, or a simulated coffee beverage that contained caffeine and sugar. 

So there's something about coffee specifically that leads to the production of this hormone encouraging your guts to move thing along a little faster than normal, and interrupting morning meetings everywhere. We just don't know what that is.

Thanks for asking and thanks especially to all of our patrons on Patreon, who keep these answers coming. If you'd like to submit some questions to be answered just go to Patreon.com/SciShow. And don't forget to go to YouTube.com/SciShow and subscribe.