Study Links Coffee Polyphenols to Gut Bacteria and Mood Changes

A study of 62 healthy adults examined how caffeinated and decaffeinated coffee affect mood, cognition, and the gut microbiome. Researchers at University College Cork and the University of Parma collected blood, saliva, urine, and stool samples before, during, and after controlled coffee consumption periods.

Regular coffee drinkers abstained from coffee for 14 days, then consumed either caffeinated or decaffeinated coffee for 21 days. Both types of coffee were associated with lower stress and depression ratings. Caffeinated coffee correlated with reduced anxiety and better attention, while decaffeinated coffee linked to improved memory scores and sleep quality.

Microbiome composition changed within days of removing or reintroducing coffee. Both caffeinated and decaffeinated versions increased levels of beneficial gut bacteria. Cognitive improvements correlated with polyphenol metabolites measured in urine rather than caffeine levels.

John Cryan at University College Cork said the system responded rapidly. Daniele Del Rio at the University of Parma noted that roasting degree alters coffee's chemical profile and called for further tests on different coffee types. Nicola Segata at the University of Trento said the sample size limits broad application of the results.

Telmo Pievani at the University of Padua said the findings suggest the gut ecosystem may help humans adapt to new diets without genetic change. 1038/s41467-026-71264-8.