A new study suggests that coffee’s effects on mood, memory, and stress may not come from caffeine alone. The research, a randomized crossover trial, indicates that the drink also works through the gut, influencing brain function via the gut-brain axis.
Researchers tested healthy adults in three phases: a period of regular coffee consumption, a washout phase with no coffee, and a reintroduction phase with either caffeinated or decaffeinated coffee. They measured cognitive tasks, mood, stress, and emotional reactivity. They also analyzed the gut microbiome and tracked metabolites, small molecules produced during digestion that can affect brain function.
Both caffeinated and decaffeinated coffee led to improvements in mood after the washout period. Participants reported lower stress, fewer symptoms of depression, and less impulsivity. This suggests caffeine is not the only factor at work.
Caffeinated coffee was more strongly linked to reduced anxiety and better attention and vigilance, matching known stimulant effects. Decaf was associated with better sleep, improved memory and learning, and higher levels of physical activity. The study shows coffee has multiple effects depending on its composition and how the body responds.
Coffee intake changed the composition of the gut microbiome, increasing certain bacterial species and shifting the production of metabolites linked to brain health and inflammation. Some of these compounds help regulate mood and cognitive function, which may explain why benefits appeared even without caffeine. This occurs through the gut-brain axis, where gut microbes help produce neurotransmitters and immune signals that the brain uses.
According to the study, coffee is a complex mix of compounds, including polyphenols, which can act as fuel for beneficial gut bacteria. These downstream effects may be part of why coffee has been linked to better long-term brain and metabolic health. For people sensitive to caffeine or trying to cut back, decaf still provides many of the same gut and mood-related benefits without the stimulant effect.
