Regular coffee consumption appears to affect not only the composition of gut bacteria but also the physiology of the gut itself. This was the conclusion of a team of researchers from the University of Copenhagen; their findings were published in the scientific journal Gut Microbiology.

The participants — 61 healthy Danish adults — swallowed a small electronic capsule that measured gastrointestinal transit time, temperature, pH levels, and intestinal contractions as it passed through the digestive tract. Coffee drinkers were defined as those who drank one to five cups a day on more than three of the eight study days; the remaining participants were classified as less frequent coffee drinkers.

First and foremost, the results confirmed that coffee affects the composition of gut bacteria: frequent coffee drinkers had greater microbial diversity in their gut than those who drank it less often.

“But perhaps more importantly, frequent coffee consumption appears to affect the physiology of the gut itself — in other words, how it functions,” said the study's first author, Francesca Bucci, a PhD student at the University of Copenhagen.

The researchers found that frequent coffee drinkers had significantly lower pH levels in the small intestine, while higher coffee consumption was associated with more contractions in the colon. “Intestinal contractions can support healthy digestion, help prevent constipation, and keep the intestinal muscles in good shape,” Bucci noted.

The scientists cannot yet determine whether a lower pH is beneficial or harmful, but pH levels in the small intestine play an important role in digestive enzyme activity and the breakdown of food.

The authors emphasize that the study cannot establish whether the differences were caused solely by coffee. Nevertheless, senior author Henrik Munch Roager believes there are grounds for considering coffee a key factor: other studies have already shown that coffee affects a range of processes in the digestive system, including gastric acid secretion. “Many people also report that coffee affects their digestion,” he added.

According to Roager, the next step should be an intervention study in which researchers control how much coffee participants drink and compare gut physiology during periods of high coffee consumption and periods without coffee. The researchers hope these and future findings will help address a common problem.

“A great many people suffer from constipation and irregular bowel movements. If we understand how coffee affects digestion and intestinal contractions, that knowledge could be used to stimulate gut motility naturally. That would be extremely valuable,” the scientist said.