Researchers at APC Microbiome Ireland, based at University College Cork, conducted a double-blind, randomized study that, for the first time, thoroughly investigated the underlying processes responsible for coffee’s beneficial effects on the “gut-brain” axis.
Their findings have been reported in the journal Nature Communications. These results suggest that consistent consumption of both regular and decaffeinated coffee has the potential to impact the gut microbiome, which consequently affects mood and stress levels.
Thirty-one habitual coffee drinkers—defined by European standards as individuals who regularly consume three to five cups daily—participated in the trial. An additional thirty people who abstained from coffee entirely served as the control group.
For a two-week period, the regular coffee drinkers had to stop drinking it. Subsequently, the stimulating beverage was reintroduced: some participants received caffeinated coffee, while others received the decaffeinated version. To ensure experimental rigor, participants were unaware of which type of coffee they were consuming. Throughout the entire study, the participants’ psychological states were assessed, and they provided stool and urine samples for analysis.
The devotees of coffee were found to be more emotional and impulsive, and discontinuing their preferred drink mitigated these traits—though it also caused a decline in memory. However, resuming coffee consumption—irrespective of whether it contained caffeine or not—restored memory function to its prior levels.
A noticeable enhancement in learning ability and memory was observed only in those who consumed decaffeinated coffee; this suggests that other constituents, such as polyphenols, are likely responsible for these cognitive advantages, rather than caffeine itself. Concurrently, only caffeine was linked in the study to a reduction in anxiety, improved alertness and focus, and a decreased risk of inflammation.
Regarding the impact on the microbiome, coffee enthusiasts exhibited significantly higher levels of certain bacteria, such as Eggerthella sp. or Cryptobacterium curtum—both species are actively involved in the secretion of digestive juices. An increase in Firmicutes was also observed, which in women has been associated with positive emotions.
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