A study published in April 2026 in Nature Communications suggests that the benefits of coffee on memory are not solely due to caffeine. Researchers from University College Cork found that decaffeinated coffee significantly improved memory scores in a trial involving 62 adults aged 30 to 50, while caffeinated coffee mainly affected attention and stress. The participants, who were regular coffee drinkers consuming three to five cups per day, were asked to abstain from coffee for two weeks before resuming consumption for three weeks, randomly divided between regular coffee and decaffeinated coffee. At the end of the trial, the caffeinated group improved on two memory tests, the learning of word lists and a spatial recognition test, where errors became less frequent. In contrast, the drinkers of decaffeinated coffee showed no comparable memory improvement. However, the volunteers who drank caffeinated coffee reported feeling less anxious and less stressed, with vigilance and concentration improving over the weeks. Both groups, caffeinated and decaffeinated, also reported less perceived stress and fewer depressive symptoms. Blood tests confirmed this dual effect. After three weeks, caffeine drinkers also showed lower levels of certain inflammatory proteins, indicating a slightly calmer bodily environment. Memory, however, only improved with decaf, proof that other compounds in the bean are involved. Researchers point to polyphenols, antioxidant compounds abundant in the bean, and the way coffee reshapes the intestinal microbiota. Among coffee drinkers, certain bacteria such as Eggerthella and Cryptobacterium multiplied, while brain chemical messengers, including GABA, a calming compound, became less frequent. Nine metabolites, including caffeine, theophylline, and phenolic acids, linked the cup to these bacteria and cognitive performance. These changes were also found to be reversible, disappearing upon stopping coffee and quickly returning upon resuming. The study remains small and preliminary, and its authors are careful not to conclude that daily decaffeinated coffee enhances everyone's memory. It mainly outlines a path, that of a permanent dialogue between coffee, intestinal bacteria, and the brain. Future trials, conducted on more volunteers, will need to determine which of the hundreds of compounds in the bean truly pull these strings.