Perhaps the greatest coffee question of our time is this: did you really have that first cup of coffee in the morning if it didn’t make you poop? We’ve reported previously that, when it comes to coffee, not everybody poops; in fact, only about 29% do. The other 71% of the coffee consuming public have found a way to somehow defy physics—my guess is a wormhole in space-time—and go straight to the second, poopless cup of the day.

But for we lucky few, coffee makes us poop. Science has proven it to be true. But what they aren’t entirely sure of, though, is why.

As reported by Insider, traditional wisdom on the fecal phenomena—that caffeine is what makes you get up and go—has been shown to not be the case, or isn’t the entire story at least. While caffeine is a stimulant that can that help reverberate nature’s call all up in your guts, studies have found decaffeinated coffee to have a similar effect. Similarly, there has been no research to show other caffeinated beverages—sodas, tea, kombucha, energy drinks, etc.—have the same sort of laxative effect some people experience with coffee.

“The short answer is that we aren't quite sure! It seems just to be the overall formulation of coffee that helps us poop,” says [director of the Yale Functional Gastrointestinal Disorders Program Jill] Deutsch, MD.

One potential explanation is gastrin, a hormone that increases colon activity and thus have a laxative effect. Both caffeinated and decaffeinated coffee can increase gastrin levels. Combine that with the timing of when folks generally consume coffee—after waking up in the morning, when colon activity is already rising naturally—and the poo poo choo choo may be pulling into station.

But again, because not everyone experiences the coffee poops, scientists can’t quite be sure what factor(s) are at play. Whatever the reason, I would like to thank the coffee poop gods sitting atop their porcelain throne for allowing me to be one of the Chosen Ones Twos.

Zac Cadwalader is the managing editor at Sprudge Media Network and a staff writer based in Dallas. Read more Zac Cadwalader on Sprudge.