Regular coffee consumption is linked to measurable physical changes inside the human digestive tract, according to new research from the University of Copenhagen. The study, published in November 2026 in the journal Gut Microbiology, found two key physical effects in frequent coffee drinkers: more frequent colon contractions and a more acidic small intestine.
Study method and findings
The research tracked 61 healthy Danish adults over nine days to examine how regular coffee consumption affects the gut. Instead of relying only on stool samples, the Copenhagen researchers asked participants to swallow a tiny wireless sensor capsule that measured internal acidity, pressure, transit time, and muscle movements in real time as it travelled through the digestive tract.
The main discovery was that regular coffee consumption is linked to measurable physical changes inside the gut, alongside a wider variety of gut bacteria. Participants with higher levels of caffeine breakdown products in their urine experienced more active muscle contractions in their colon, which helps keep intestinal muscles working and moves waste along.
Acidity and colon effects
Frequent coffee drinkers, defined as those having one to five cups a day on more than three days a week, had a lower pH, meaning higher acidity, in their small intestine compared to rare drinkers. Scientists noted that while acidity in the small intestine plays a key role in breaking down food, it is not yet clear whether this shift is helpful or harmful.
"Frequent coffee consumption appears to affect the physiology of the gut itself, in other words, how the gut functions," first author Francesca Bucci, a PhD student at the Department of Nutrition, Exercise and Sports at the University of Copenhagen, said.
Implications for digestion
The findings help explain why a single cup of coffee might not relieve constipation on demand. Despite the extra colon contractions, overall transit time through the digestive tract did not change dramatically between frequent and rare drinkers.
Because the study observed everyday habits in a small group rather than running a controlled trial, it cannot prove coffee alone caused these effects. For reliable daily regularity, experts still recommend drinking plenty of water and eating fibre-rich foods.
