Gut bacteria help process components of our diet and produce substances that may influence inflammation, stress responses, mood, and cognition. What the Study DidResearchers at University College Cork compared 31 habitual coffee drinkers with 31 people who did not regularly drink coffee. The habitual coffee drinkers then stopped drinking coffee for two weeks. At the initial comparison, habitual coffee drinkers showed greater impulsivity and emotional reactivity, while non-coffee drinkers performed better on certain memory measures. Decaffeinated coffee may provide some coffee compounds without the same stimulant burden, but it is not entirely caffeine-free and may still cause digestive symptoms in susceptible people.