In 62 adults, stopping then restarting coffee shifted gut metabolites; decaf lined up with learning scores

What the research found

Study (observational, small). Serena Boscaini, John F. Cryan, and colleagues at APC Microbiome Ireland, University College Cork, report in Nature Communications (2026; 17(1); doi 10.1038/s41467-026-71264-8; ScienceDaily 28 September 2026). They compared 31 people who usually drank 3 to 5 cups of coffee a day with 31 people who did not. Regular drinkers stopped coffee for two weeks, then restarted without knowing whether they received caffeinated or decaffeinated coffee. Stopping coffee shifted stool and urine metabolite profiles. After coffee returned, both groups reported lower perceived stress, depression, and impulsivity scores. Eggertella and Cryptobacterium curtum were more abundant in coffee drinkers. Improved learning and memory scores appeared only in the decaf arm; caffeinated coffee lined up with lower anxiety scores and better vigilance. The study was sponsored by the Institute for Scientific Information on Coffee. Sixty-two people cannot prove that coffee changes mood. Educational notes.

Evidence level: Human study. A study in people, but an association isn't proof of cause.

Read the original at University College Cork / Nature Communications