(CNN)For some people, coffee jump-starts their bowel movements in addition to their energy.
Despite the drink's popularity, there isn't a lot of research on why coffee sends many people running to the bathroom within minutes of consuming it.
"In some cases, as with coffee and bowel movements, there likely just hasn't been the medical demand to merit serious investigation," Dr. Kyle Staller, director of the Gastrointestinal Motility Laboratory at Massachusetts General Hospital, said via email.
"It may also be a case of obviousness, meaning it doesn't take multiple studies to know that coffee induces bowel movements when it's such a part of many people's daily lives."
There just might be something special about coffee, and the research that exists proves "that patients are right," said Staller, also an assistant professor of medicine at Harvard Medical School. Some small studies have shown that drinking coffee was more effective than warm water at inducing bowel movements -- that's saying something since "water is an integral part of normal digestion with large amounts being released and reabsorbed by your digestive tract every day," he said.
This of course doesn't mean that adequate water intake isn't essential for your overall health. "About 60% of your body is made of water," Jerlyn Jones, a registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics, said via email.
And whether the coffee's caffeinated or decaffeinated doesn't seem to matter in all studies, according to other research -- suggesting that, in some cases, coffee compounds besides caffeine might be responsible for sudden bowel movements.
The identities of these compounds and how they might interact with the digestive tract are still largely unknown, but here's what researchers have discovered so far.
Coffee might cause colon contractions
The colon experiences three types of contractions that work together to mix, knead and ultimately eject poop. The occurrence, timing and frequency of these contractions are influenced by muscular, neural and chemical factors.
Coffee might stimulate this colonic motor activity within minutes of consuming it, based on the limited available research, Staller said. Twelve healthy people experienced this activity during a 1998 study when they agreed to have a sensor probe inserted into their colons. Over a 10-hour period the next day, the participants consumed warm coffee, decaf coffee, water or a meal in random order. Both types of coffee and a meal caused more colon contractions and pressure, compared with water. Caffeinated coffee was 60% more effective than water at stimulating colonic motor activity and 23% more impactful than decaf.