Your Morning Coffee Is Reshaping Your Gut and Brain
A new study shows regular coffee consumption changes specific gut bacteria and is linked to higher impulsivity, lower inflammation, and shifts in brain chemistry.
Researchers at University College Cork have found that drinking coffee regularly changes the gut microbiome in specific, measurable ways, and those changes are linked to how you think, feel, and behave. The study, published in Nature Communications, also found that coffee drinkers score higher on impulsivity and emotional reactivity than non-drinkers, and that taking a break from coffee can actually improve memory and reduce those behavioural traits. Not only that, decaffeinated coffee produced its own distinct set of effects, suggesting the hundreds of other compounds in coffee also play a real role.
Aim
The study set out to examine how coffee consumption affects the gut-brain axis — the two-way communication network between the gut microbiome and the brain. Researchers wanted to understand what happens to the microbiome, metabolism, cognition, and mood when people drink coffee, stop drinking it, and then start again. Importantly, they wanted to separate the effects of caffeine from those of coffee as a whole.
Methods
62 healthy adults aged 30 to 50 living in Ireland were recruited. 31 were moderate coffee drinkers (3 to 5 cups per day) and 31 were non-coffee drinkers. The study ran in three phases. First, both groups were compared at baseline. Then coffee drinkers stopped drinking coffee for two weeks. After that, they were randomly assigned to drink either caffeinated or decaffeinated instant coffee for three weeks.
Horrible conditions.
Researchers collected stool, urine, blood, and saliva samples at each stage. They used shotgun metagenomics to analyse the gut microbiome in detail, alongside both targeted and untargeted metabolomics to map the chemical changes happening in the gut and body. Participants also completed a battery of cognitive tests and questionnaires covering stress, anxiety, depression, sleep, impulsivity, and emotional reactivity throughout.
Results
Behaviour and cognition
Coffee drinkers scored higher on impulsivity and emotional reactivity compared to non-coffee drinkers at baseline. After two weeks without coffee, those scores dropped significantly. When coffee was reintroduced, both caffeinated and decaffeinated versions reduced impulsivity and perceived stress. Only caffeinated coffee reduced anxiety and psychological distress. Decaffeinated coffee improved memory performance, sleep quality, and physical activity levels. Caffeinated coffee improved attention and cognitive performance on the PASAT test.
During the two-week washout, withdrawal symptoms were elevated in the first few days but dropped by day four. Fatigue decreased, and energy levels rose across the withdrawal period.
Gut microbiome
Coffee drinkers had higher levels of Cryptobacterium curtum and Eggertheilla species in their gut compared to non-drinkers. These species dropped when coffee was removed and responded again when coffee was reintroduced, regardless of whether it contained caffeine. Overall gut microbial diversity differed between coffee drinkers and non-drinkers, but abstaining from coffee did not significantly change diversity levels. The effects were strain-specific rather than broad.
Metabolites
Coffee drinkers had higher faecal levels of theophylline, caffeine, and hippuric acid, and lower levels of indole-3-propionic acid (IPA), indole-3-carboxyaldehyde (ICA), and GABA. IPA has been linked to improved cognition, and ICA plays a role in gut barrier integrity, so their reduction in coffee drinkers is worth noting. After the washout period, most of those metabolite levels shifted toward levels seen in non-coffee drinkers. Reintroducing caffeine restored caffeine-related metabolites, while (poly)phenol-related metabolites increased with both caffeinated and decaffeinated coffee.
Inflammation and immune response
Coffee drinkers had lower levels of the inflammatory marker CRP and higher levels of the anti-inflammatory cytokine IL-10 compared to non-drinkers. After two weeks without coffee, CRP and TNF-alpha increased, suggesting coffee may have a protective anti-inflammatory role. Both caffeinated and decaffeinated coffee reduced LPS-stimulated IL-6 secretion upon reintroduction.
Blood pressure
Coffee drinkers showed a significant decrease in systolic and diastolic blood pressure during the two-week abstinence period. When caffeine was reintroduced, systolic blood pressure was lower compared to the decaffeinated group.