Why coffee sends you running to the toilet, according to researchers

For many people, it's a familiar morning routine. You pour your first cup of coffee, enjoy a few sips, and before long, you feel the need to visit the bathroom. It's something regular coffee drinkers often joke about, but researchers have now taken a closer look at what's actually happening inside the digestive system. The answers are fascinating, and reveal a lot more about our digestive system and gut health.

Researchers used a capsule to study the gut

The study, published in Gut Microbiology in September 2026 and highlighted by the university in November, followed 61 healthy Danish adults over nine consecutive days.

Participants recorded everything they ate and drank for eight days. Researchers also examined urine samples for caffeine-related substances and analyzed stool samples to identify gut bacteria.

Fifty participants swallowed a small electronic capsule that traveled through their digestive systems. Unlike a regular camera capsule, this device measured temperature, acidity, transit time, and intestinal contractions.

People who drank between one and five cups of coffee a day on more than three of the eight recorded days were classified as frequent coffee drinkers.

Three differences stood out

The researchers identified three interesting patterns among regular coffee drinkers.

First, they had a greater variety of gut bacteria. Certain bacterial groups, including Lawsonibacter and Slackia, were also more common.

Second, their small intestines had a lower pH, meaning the environment was more acidic. Researchers don't yet know whether this difference is beneficial or harmful.

Third, higher levels of caffeine-related substances were associated with more contractions in the colon. These muscular movements help push waste through the digestive system.

Francesca Bucci, the study's first author, explained that the findings suggest regular coffee consumption may be linked not just to changes in gut bacteria, but also to how the intestines function.

Could coffee help with constipation?

That possibility particularly interests the researchers.

Constipation becomes more common as people get older, and sluggish bowel movements can cause bloating, discomfort, and difficulty passing stool.

Senior researcher Henrik Munch Roager believes understanding coffee's relationship with intestinal movement could eventually help researchers develop ways to support digestion naturally.

However, there's an important limitation. The study observed people's existing coffee habits rather than assigning them to drink coffee or avoid it. That means other differences in lifestyle or diet could have influenced the results.

It also doesn't explain exactly why some people need the bathroom shortly after their first morning cup.

And what about decaffeinated or filtered coffee? The study wasn't designed to establish whether either produces the same effects.

What actually helps when your bowels are sluggish?

For now, drinking more coffee isn't an established treatment for constipation.

Instead, health services including the NHS and Thuisarts recommend several everyday measures:

• Eat more fiber. Choose whole-grain bread, vegetables, fruit, beans, and lentils. Increase your intake gradually.
• Drink enough fluids. Water and other drinks help keep stools easier to pass.
• Move every day. Even a regular walk can support bowel movements.
• Don't ignore the urge. Give yourself unhurried bathroom time, perhaps after breakfast when it fits your routine.

If constipation doesn't improve, keeps returning, or comes with blood in your stool, unexplained weight loss, or a sudden change in bowel habits, contact your doctor.

Your morning coffee may be associated with more intestinal activity than you realized. But until further studies establish cause and effect, the best approach to tackle constipation remains a combination of healthy habits and appropriate medical advice.