Could Coffee Change the Gut–Brain Connection?

Coffee is one of the most widely consumed drinks in the world, but its relationship with the gut microbiome is still being studied. A recent human study published in Nature Communications examined whether regular coffee intake is linked with changes in gut bacteria, microbial metabolites, and measures of mood and cognition.

The study included 62 healthy adults in Ireland, ages 30 to 50. Thirty-one participants were regular moderate coffee drinkers, reporting about three to five cups a day, while 31 did not drink coffee. Researchers compared the groups and then followed the coffee drinkers through a two-week coffee-free period. After that, they were randomly assigned to receive either caffeinated or decaffeinated coffee for 21 days.

The researchers used shotgun metagenomic sequencing to examine the gut microbiome and measured microbial and coffee-related metabolites. They found differences in gut microbial composition between regular coffee drinkers and non-drinkers. Some bacterial species, including Cryptobacterium and Eggerthella, were more abundant among coffee drinkers.

The study also found differences in several gut-related metabolites. Levels of indole-3-propionic acid, indole-3-carboxyaldehyde, and GABA were different between groups. Some metabolic changes shifted during the coffee-free period and changed again after coffee was reintroduced, suggesting that at least some microbiome and metabolite patterns were responsive to coffee intake.

Researchers also examined cognition, mood, stress, and behavior. Some measures changed during coffee withdrawal and after coffee was reintroduced. However, the study found associations between coffee intake, microbial features, metabolites, and cognitive measures rather than proving that gut bacteria directly caused changes in brain function.

The study has several limitations. The sample was relatively small and included healthy adults from a limited population. Participants were also classified partly by habitual coffee intake, and not every outcome was designed to establish long-term health effects. The researchers also noted that stool transit time was not directly measured.