Coffee changes gut bacteria and mood, study finds

Coffee affects the bacteria in our gut as well as our brains, and decaffeinated coffee has benefits of its own, according to new research from University College Cork in Ireland.

The study, published in Nature Communications, was carried out at APC Microbiome Ireland and led by Professor John Cryan.

How the study worked

The team recruited 31 regular coffee drinkers, who drank three to five cups a day, and 31 people who did not drink coffee. The coffee drinkers gave up coffee for two weeks and were then given either caffeinated or decaffeinated coffee. Throughout, the researchers carried out psychological assessments and collected stool and urine samples.

What they found

When coffee was reintroduced, participants reported lower levels of perceived stress, depression and impulsivity, whether the coffee contained caffeine or not. Both kinds of coffee were linked to increases in particular gut bacteria, including Eggerthella and Cryptobacterium curtum, and to higher levels of bacteria in the group known as Firmicutes.

There were differences, too. Decaffeinated coffee was associated with improved learning and memory. Caffeinated coffee was linked to reduced feelings of anxiety, better vigilance and attention, and a lower risk of inflammation.

More than caffeine

"Coffee is more than just caffeine -- it's a complex dietary factor," Professor Cryan said, explaining that it interacts with gut microbes, metabolism and emotional wellbeing.

The results add to a growing body of research on the gut-brain axis, the two-way communication between the digestive system and the brain. Scientists are increasingly finding that the trillions of microbes living in the gut can influence mood, stress and even thinking.

A note of caution

The study was small, and the researchers say more work is needed to understand exactly how coffee produces these effects. But it suggests that for many people the daily cup offers benefits beyond the familiar lift of caffeine, and that decaf drinkers may be getting some of those benefits too.