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A study of 62 people found that stopping and then resuming coffee was associated with changes in gut metabolites, mood and some cognitive measures. Some findings differed between caffeinated and decaffeinated coffee, but the small study does not show that coffee caused the changes.
Researchers at APC Microbiome Ireland reported that both caffeinated and decaffeinated coffee were associated with changes in gut microbes and measures of mood and stress in a study of 62 people. The findings offer evidence about possible links between coffee and the gut-brain communication system, but the study was small and does not establish that coffee caused the reported effects.
The researchers recruited 31 regular coffee drinkers and 31 people who did not normally drink coffee. Regular drinkers were defined as people who consumed three to five cups a day. Participants completed psychological assessments and kept records of their diet and caffeine intake; researchers also analyzed stool and urine samples for microbial and metabolic changes.
Regular coffee drinkers first stopped drinking coffee for two weeks. During that period, researchers observed shifts in their gut metabolite profiles compared with the non-coffee-drinking group. Coffee was then added back without participants knowing whether they were receiving caffeinated or decaffeinated coffee. Both groups reported lower perceived stress, depression and impulsivity scores after coffee was reintroduced.
The study also found differences in the abundance of several bacteria between coffee drinkers and non-drinkers, including Eggertella and Cryptobacterium curtum. Learning and memory improvements were observed only in the decaffeinated group. The caffeinated group showed reduced anxiety and improved vigilance and attention. These are study findings, not proof that coffee produces the same changes in other people.
Coffee’s Effects Beyond Caffeine
The results add to research on the microbiota-gut-brain axis, the two-way communication between gut microorganisms and the brain. Researchers describe several possible routes for these signals, including nerves, immune activity, hormones and chemicals produced by microbes. The study suggests that coffee’s effects may involve more than caffeine alone, since some reported changes appeared in both coffee groups and the memory finding appeared in the decaf group.
Coffee contains many compounds, including polyphenols, which can interact with gut microbes. The findings may help researchers investigate how dietary compounds relate to digestion and mental processes. They do not show that coffee is a treatment for stress, depression or memory problems, or that people should change their coffee intake based on this study.
How Researchers Tested Coffee
Earlier research has examined coffee in relation to digestion, mood and health, while the biological pathways behind reported associations have remained an open research question. This study focused on whether changes in coffee consumption coincided with changes in gut microbes, metabolites and psychological measures.
The research was conducted by scientists at University College Cork’s APC Microbiome Ireland and published in Nature Communications. The report states that the study was sponsored by the Institute for Scientific Information on Coffee. The researchers used a withdrawal period followed by a blinded reintroduction of caffeinated or decaffeinated coffee for regular drinkers, alongside a comparison group that did not normally drink coffee.
“Coffee is more than just caffeine — it’s a complex dietary factor that interacts with our gut microbes, our metabolism, and even our emotional well-being.”
— Professor John Cryan, corresponding author and principal investigator at APC Microbiome Ireland
Limits of the Findings
The study included just 62 participants, and the reported associations do not establish cause and effect. It is not clear from the source material how long any changes lasted after coffee was reintroduced, or whether the results apply to people with different diets, coffee habits or health backgrounds.
The study also reported several outcomes across microbes, metabolites and psychological assessments. The available report does not provide effect sizes or enough detail to judge how large or practically meaningful each change was. The authors’ discussion of possible long-term microbiome benefits remains a possibility, rather than a demonstrated outcome.
Questions for Follow-Up Studies
Further research would need to examine larger and more varied groups and track participants for longer to determine whether the reported changes persist. Studies could also investigate which coffee compounds are linked to particular microbial or cognitive findings and whether the results hold under different diets and consumption patterns.
For now, this report provides early evidence of associations between coffee, gut measures and selected psychological outcomes. No next study or follow-up milestone is specified in the source material.
Key Questions
Did the study prove coffee improves gut health?
No. Researchers observed differences in gut microbes and metabolites, but the small study does not establish that coffee caused them or show that they amount to improved health.
Did decaf and caffeinated coffee have the same reported effects?
No. Both groups reported lower perceived stress, depression and impulsivity after coffee was reintroduced. Learning and memory improvements were observed only in the decaffeinated group, while the caffeinated group showed reduced anxiety and improved vigilance and attention.
How many people took part?
The study included 62 people: 31 regular coffee drinkers and 31 people who did not normally drink coffee. Regular coffee drinkers were defined as consuming three to five cups a day.
Does the research mean people should drink more coffee?
The study does not provide a recommendation to increase coffee consumption. It reports associations in a small group and does not establish coffee as a treatment for mood, stress or cognitive concerns.
Source: rss
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