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A simple cup of coffee a day may do more than just wake you up in the morning. A new study suggests that drinking coffee regularly may be linked to differences in how the digestive system works.
Researchers at the University of Copenhagen examined 61 healthy adults to investigate how coffee consumption affected the gut. Beyond confirming that people who drank coffee frequently had a greater diversity of microorganisms in their gut compared with occasional drinkers, the findings also revealed that regular coffee consumption appeared to affect the physiology of the gut itself.
The research team monitored participants over nine consecutive days. Volunteers recorded everything they ate and drank over eight days, while researchers assessed their coffee consumption using both dietary records and caffeine-related substances found in urine.
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Fifty participants also swallowed a wireless capsule known as SmartPill, which as it moved through the digestive system, recorded information about transit time, temperature, acidity (pH), pressure, and intestinal contractions.
This allowed scientists to examine how the digestive tract was functioning.
Participants were divided according to their coffee habits. Frequent drinkers were defined as those consuming between one and five cups a day on more than three of the eight recorded days. The remaining participants were classified as less frequent coffee drinkers.
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The findings, published in Gut Microbiology, revealed that frequent coffee drinkers had significantly lower pH levels in their small intestine. They also showed an association between greater coffee consumption and more frequent contractions in the colon.
These contractions, according to its first author Francesca Bucci, a PhD student at the Department of Nutrition, Exercise and Sports at the University of Copenhagen, can support healthy digestion, help prevent constipation and keep the intestinal muscles in good condition.
"Frequent coffee consumption appears to affect the physiology of the gut itself, in other words how the gut functions," she said.
The significance of the lower small intestinal pH remains uncertain. Researchers have not established whether it's beneficial or harmful, although acidity is known to influence digestive enzymes and the breakdown of food.
Despite the differences observed, the researchers caution that their findings cannot prove coffee directly causes the changes. However, senior author Henrik Munch Roager, the Associate Professor and Research Group Leader at the Department of Nutrition, Exercise and Sports, believes there is good reason to think coffee plays a key role.
"We already know from other studies that coffee can influence a range of processes in the digestive system, including acid secretion in the stomach. So, there are good reasons to believe that what we are seeing is not merely coincidence. Anecdotally, many people also report that coffee affects their digestion," he said.
What exactly is behind the increased colon contractions is also unresolved. "It could either be due to signalling from the stomach to the colon via the nervous system or via coffee molecules interacting locally with colonic cells thereby stimulating contractions. Caffeine could be involved, but coffee contains hundreds of bioactive molecules, which may be involved as well – this remains unresolved," Roager told Newsweek.
Dr. Dan Carter, the director of neurogastroenterology at Sheba Medical Center, told Newsweek that coffee's effects on the gut extend beyond caffeine.
"Coffee is much more than just caffeine. It contains hundreds of biologically active compounds, including polyphenols, which may influence the bacteria in our intestines, collectively known as the gut microbiome.
"Studies show that coffee can stimulate colon contractions, sometimes within just a few minutes. Interestingly, decaffeinated coffee can produce a similar effect, although regular coffee may be slightly stronger," Carter said.
While the exact mechanism is not completely understood, one potential explanation is the gastrocolic reflex, the natural increase in bowel activity that can occur after eating or drinking.
"Coffee appears to stimulate communication between the stomach, the nervous system, and the colon, possibly through digestive hormones and what we call the gastrocolic reflex—the natural increase in bowel activity after eating or drinking."
But whether these physiological and microbial changes ultimately mean better digestive health remains unclear, according to Carter.
Roager said that further investigation should involve controlled experiments comparing gut activity during periods when participants consume coffee and periods when they don't.
The researchers hope a better understanding of coffee's effects on intestinal movement could eventually contribute to new approaches to digestive problems.
"A great many people struggle with constipation and irregular bowel movements. If we can understand how coffee affects digestion and intestinal contractions, it may be possible to use that knowledge to stimulate gut motility in a natural way. That would be extremely valuable," Roager said.
According to Carter, while there is reasonably good evidence that coffee can stimulate bowel contractions, the evidence that it effectively treats chronic constipation is far less convincing.
He said that while trials involving patients recovering from abdominal surgery have found that coffee can help bowel function return sooner, this does not establish that daily coffee consumption treats chronic constipation.
"We still lack large, well-designed clinical trials demonstrating a consistent, long-term benefit for patients with constipation."
He also stressed that while he doesn't discourage consumption of coffee in patients who benefit from it, he wouldn't recommend it as a substitute for established treatments, particularly for patients with persistent or severe constipation.
"My general advice is simple," he said, "if you enjoy coffee, tolerate it well, and it helps you maintain a regular bowel habit, there is usually no need to stop. But if it causes urgency, discomfort, or diarrhea, reducing your intake or switching to decaf may be worthwhile. As with many aspects of digestive health, individual responses matter more than any universal rule."
Roager said the findings could help focus research on which specific components of coffee may be responsible.
"I hope that our findings will stimulate more interest and research to figure out which bioactive molecules of coffee that may be able to interact with gut motility, since such knowledge could inform new solutions targeting constipation."
Reference:
Bucci et al. Habitual coffee consumption is linked to differences in gut microbiota and gut physiology. Gut Microbiology. DOI: 10.1016/j.gutmic.2026.100018
Contact Newsweek editors on this story: Kara Dolman and Paul Donnelley.
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