For some, as sure as the sun will rise, a cup of joe will make you go. If you’ve ever wondered why, sadly there are no definitive answers—taking the kids to the pool after a cuppa isn’t exactly a scientific priority—but there are a few ideas that might hold the answer.
It’s coffee’s fault
One study published in Gut in 1990 found that coffee causes 29% of healthy young adults to sink submarines after consumption, regardless of caffeine. Authors Brown, Cann, and Read (their real names; we cannot make this up) hypothesized that coffee effects the tissues lining the stomach and small intestine, triggering the release of gastrin. Gastrin is a hormone that causes the colon to increase its contractions that push excrement along.
A later study verified that coffee leads to faster contractions, with effects similar to eating a meal. Besides having the effect of speeding things up, your colon is responsible for reabsorbing water from fecal matter as it traverses through your body. If contractions are faster, your body has less time to absorb water, causing looser stools. Looser stools move more quickly—because excess liquid in the colon increases motor contraction and because they are easier to push.
And, according to the IBS Network, coffee also causes your gall bladder to release bile acids. Bile acids normally help you digest fat, but without food, they can cause you to, ehem, download a brownload. Like gastrin, bile acids stimulate contractions, but the acids go beyond to actively decrease water reabsorption if bile acid levels are high—causing looser stools again.
So in short, coffee causes things to move fast and to be softer, leading to your becoming a porcelain assassin.
…It might not be coffee’s fault
If you’ve looked at any reviews on Amazon of sugar-free gummy bears, you know non-nutritive sweeteners can also cause digestive struggles. Because the body doesn’t absorb them, non-nutritive sweeteners draw water into the colon, triggering diarrhea.
You also might be lactose-intolerant without knowing it. Dairy products can cause diarrhea in those sensitive to lactose, and as humans age, then tend to have more and more problems handling it.
Beyond what you consume, it could just be the time of day—your body might just be on a schedule. Or, if you drink coffee as soon as you wake up, it could just be coincidental timing—colonic motor activity increases sharply upon waking up.
Finally, people suffering from Irritable Bowel Syndrome can be especially triggered by coffee. Symptoms of IBS include bloating, stomach pain, and changes in bowel movements.
Coffee makes some people poop, but we’re not exactly sure why. There are answers, but none are definitive, and since everyone is different, different answers can apply. Some people are probably relieved to find out they’re not alone in coffee-induced caca, but if you’re concerned, we urge you to talk to a doctor.