Curious Why Coffee Gives You the Runs? (You Know You Are)

So this is why you’ve always gotta go when you drink up.

We’re constantly talking about how we can’t live without our morning Starbucks. But can we get real for a second? The thing we’re not talking about is how that cup of Joe is giving our intestines a wake-up call as well.

Niket Sonpal, M.D., a gastroenterologist and assistant clinical professor of medicine in New York City, teaches 8 a.m. classes at Touro College of Medicine and is always amused by his students guzzling coffee. “By 8:45, everyone looks a bit uncomfortable,” he laughs.

But what is it about java that has us making a beeline for the ladies' room in the middle of a morning meeting?

RELATED: Your Definitive Guide to Pooping

There’s a general consensus that, directly or indirectly, coffee stimulates the digestive system. But research on why and how isn’t conclusive. Some studies claim that it’s caffeine—not coffee—that gives us the urge to go, while others find that it might be something more intrinsic to coffee itself.

“There is an association between caffeine and having a bowel movement,” says Sonpal. “It’s not completely understood, but the thinking is caffeine is a pro-motility agent.” Motility is the contraction of the muscles that move food through the digestive tract. Sonpal explains that caffeine can act as a catalyst to your body’s natural response to ingestion, which is called the gastrocolic reflex.

“Anytime you or I eat, your stomach stretches and sends a signal to your colon saying, ‘Hey, something is coming in, something has to go out,’” he says. “The question becomes: Is [the urge to go] an effect of the stomach stretch and gastrocolic reflex or a combination of that and caffeine?”

Here's what we know for sure: There are actually tons of neurons surrounding the digestive tract (the only place with more neurons in the body is your central nervous system), says Murray Orbuch, M.D., assistant professor of medicine at Mount Sinai School of Medicine.

This means that our digestive systems aren’t just sensitive to physical stimuli, they’re also hyper-sensitive to chemicals that cause an emotional response (and ever notice how caffeine can lead to excitement or heighted anxiety?).

RELATED: 5 Ways Your Period Messes with Your Pooping Habits

“It’s not actually the substance you take but a cascade of events that it triggers,” says Orbuch. “It’s an electro-muscular response to either caffeine or some mechanism the caffeine stimulates.”

Aside from the caffeine, the acidic nature of the brewed beverage causes the body to produce more bile (the kind of bitter, alkaline substance that makes your stomach churn), which can build up in your gut and cause a case of the runs.

So how can we keep ourselves moving in the morning without—ahem—getting things moving below the belt? First, choose your coffee wisely.

“Richer coffees like espresso and French roast actually have less caffeine because they’re roasted longer,” says Orbuch.

Less caffeine means less laxative effect. This is also the reason we don’t always experience the same gotta-go effect with soda or tea, which tend to have lower caffeine levels.

And beware the cheaper coffees served at diners or by your favorite street vendor. They carry a lot more caffeine (100 milligrams per cup, versus only 40 milligrams in a shot of espresso). Sounds like a perfect excuse to #treatyoself to a more expensive slow-roasted reserve blend.

Secondly, skip the sugars and lactose-laden creamers. Artificial sweeteners can cause bloating and diarrhea and lactose can cause digestive troubles even for those who aren’t strictly intolerant.

RELATED: How to Poop Politely at Work, on Planes, and at a Guy’s Place

Ultimately, it all comes down to the individual and how sensitive your system is. People with preexisting digestive issues like Irritable Bowel Syndrome (which is more common in women) are more sensitive to this and might want to consider cutting out the coffee altogether.