For years, coffee has been discussed primarily in terms of caffeine: how much is too much and when to stop drinking it. An Irish team looked elsewhere, at the bacteria living in our intestines. Their results suggest that even a cup of decaf does more than people think.
In brief
- Researchers from University College Cork studied 31 regular coffee drinkers and 31 non-drinkers.
- Giving up coffee for two weeks was linked to changes in gut microbiome metabolites.
- After coffee was re-introduced, both the caffeinated and decaffeinated groups reported lower stress and depression scores.
- Some effects were specific: improved memory with decaf, attention with caffeinated coffee.
The study
The research was led by Professor John Cryan, Principal Investigator at APC Microbiome Ireland, University College Cork, and published in Natural communicationsthe university announced in April 2026. Its findings were then widely disseminated, including in National Geographic Spain.
The team recruited 31 people who regularly drink 3 to 5 cups of coffee per day and 31 people who do not. The coffee drinkers first stopped for two weeks, giving psychological assessments and stool and urine samples along the way. Then coffee was reintroduced without them knowing what kind they were getting: half decaffeinated, half caffeinated.
What happened in the intestine
Going without coffee was linked to significant changes in gut microbiome metabolic profiles compared to non-drinkers. Coffee drinkers also had higher levels of certain bacteria, and Firmicutes bacteria increased; the university notes that these have been associated with positive emotions in women.
“Coffee is so much more than caffeine,” Cryan said, describing it as a complex dietary factor that interacts with our gut microbes. “Coffee can change what microbes collectively do and the metabolites they use,” he explained.
))>
Caffeinated or decaffeinated: different effects
After the coffee returned, both groups reported lower perceptions of stress, depression, and impulsivity, regardless of whether their coffee contained caffeine. But other effects are divided. Learning and memory only improved in the decaffeinated group, suggesting that other compounds, such as polyphenols, may play a role. Only caffeinated coffee was associated with reduced anxiety and better alertness and attention, and caffeine was also associated with a lower risk of inflammation.
This is the meaning of Cryan’s conclusion: “coffee, whether caffeinated or decaffeinated, can influence health in distinct but complementary ways. » The everyday foods we take for granted can surprise researchers, as a CDC ranking did with the vegetable that beats kale and spinach.
Why it matters
For many people who have switched to decaf for sleep or blood pressure reasons, this is reassuring: the cup can still provide something beyond taste. Hot drinks have many fans at home, from coffee to boiled lemon zest with ginger.
The limit
The study involved 62 people, which is small, and measured short-term associations and changes. It was sponsored by the Coffee Scientific Information Institute, an organization linked to the coffee industry. That’s not to say that more coffee is always better: People sensitive to caffeine, pregnant women, and people with heart problems should talk to their doctor.
That’s the thing.
Gn Health
