The Coffee-Microbiome-Gut-Brain Axis Study: How coffee can increase impulsivity and impact memory

Published Study: Habitual coffee intake shapes the gut microbiome and modifies host physiology and cognition

Reason Behind the Study:

Coffee is the world's most widely consumed psychoactive beverage, with a rich body of epidemiological evidence linking moderate intake to reduced risks of type 2 diabetes, cardiovascular disease, Parkinson's disease, depression, and even all-cause mortality . Despite this, the mechanisms through which coffee exerts its systemic effects have remained poorly understood. Prior research had established that coffee intake strongly correlates with gut microbiome composition, indeed, a 2024 metagenomics study of over 22,000 participants found that coffee was, among more than 150 food items, the single best predictor of microbiome structure . What remained unknown was whether these microbiome changes functionally connect to host physiology and cognition through the microbiota-gut-brain axis, and whether caffeine alone or the broader complex of coffee compounds drives the effects.

Goals

The 2026 study by Boscaini and colleagues, published in Nature Communications, aimed to fill these gaps . The primary objective was to characterize how habitual coffee intake shapes the gut microbiome and whether those microbial changes are linked to alterations in cognition, mood, and behavior through the microbiota-gut-brain axis . A secondary, and critical, goal was to determine which effects are attributable to caffeine and which are driven by other coffee constituents. The study employed a three-phase prospective interventional design in healthy adults comparing non-coffee drinkers with habitual coffee drinkers at baseline, then following the coffee drinkers through a 14-day abstinence period, and finally randomizing them to 21 days of either caffeinated or decaffeinated coffee reintroduction .

Key Eye-Opening Findings

The study produced several paradigm-shifting results. First, coffee drinkers and non-drinkers harbour fundamentally distinct gut microbiomes, with coffee drinkers showing increased relative abundance of Cryptobacterium and Eggerthella species . Second, these microbial differences are accompanied by changes in neuroactive metabolites: coffee drinkers had reduced fecal levels of the neurotransmitter γ-aminobutyric acid (GABA), indole-3-propionic acid, and indole-3-carboxyaldehyde . Third, and most provocatively, behavioral profiles diverged substantially between the groups. Coffee drinkers scored significantly higher on measures of impulsivity and emotional reactivity, while non-coffee drinkers demonstrated better memory performance . Fourth, the reintroduction phase revealed that some coffee-driven microbiome changes occur independently of caffeine, as both regular and decaffeinated coffee triggered acute microbial shifts upon reintroduction . Finally, an integrated multi-omics model identified nine key metabolites, including theophylline, caffeine, and specific phenolic acids, that link specific microbial species to cognitive and behavioural measures, mapping a comprehensive gut-brain axis network for coffee .

2. Study in Detail

Design and Participants

The study was a three-phase prospective intervention trial with two registered clinical protocols, NCT05927038 and NCT05927103, approved by the Clinical Research Ethics Committee of the Cork Teaching Hospitals . Sixty-two healthy adults were enrolled and divided into two groups at baseline: 31 habitual coffee drinkers (CD) who consumed coffee regularly, and 31 non-coffee drinkers (NCD) who did not. The CD group was predominantly female, and most participants were born per vaginum . At baseline, coffee drinkers consumed more daily caffeine than non-drinkers, though the NCD group had given up some caffeine before baseline; this amount was described by the authors as substantially lower than what would be considered addictive . Groups were well matched on alcohol consumption, education, childhood trauma scores, and predicted IQ .

The Three-Phase Protocol

The study proceeded through three sequential phases :

· Phase 1, Baseline Comparison: The CD and NCD groups were compared on all measures simultaneously.

· Phase 2, Abstinence Washout: All coffee drinkers abstained from all coffee for 14 days. Measurements were taken post-washout.

· Phase 3, Reintroduction Intervention: Coffee drinkers were randomized to reintroduce either caffeinated coffee (n = 16) or decaffeinated coffee (n = 15) for 21 days. The NCD group did not participate in this phase.

Methodology

Data collection was unusually comprehensive, integrating multiple cutting-edge platforms :

· Shotgun metagenomics: Faecal samples were profiled using whole-genome sequencing to identify microbial species and functional gene pathways at high resolution.

· Targeted and untargeted metabolomics: Faecal metabolites, including neurotransmitters, phenolic acids, and alkaloids, were quantified using mass spectrometry platforms.

· Cognitive and behavioural assessment: Validated self-report questionnaires measured impulsivity using the UPPS-P scale, emotional reactivity using the Emotion Reactivity Scale, and memory using standardized instruments.

· Physiological and immune measures: Blood pressure, BMI, and markers of inflammation including C-reactive protein (CRP), tumour necrosis factor alpha (TNFα), and interleukin-10 (IL-10) were serially assessed.

· Dietary monitoring: Participants completed 7-day weighed food diaries prior to each study visit to control for dietary confounds.

· Genetic characterization: Participants were genotyped for the caffeine-sensitivity-related SNPs rs2298383 and rs5751876 in the ADORA2A gene .

3. Key Findings

Distinct Gut Microbiome Composition Between Coffee Drinkers and Non-Drinkers

At baseline, shotgun metagenomic profiling revealed significant differences in faecal microbiome composition between CD and NCD groups . Coffee drinkers showed increased relative abundance of Cryptobacterium curtum and Eggerthella species. These differences were substantial enough that microbiome profiles could, in principle, predict coffee consumption status. When participants abstained from coffee for 14 days, some of these microbial alterations partially reversed, indicating that the coffee-microbiome relationship is dynamic and causally influenced by ongoing consumption .

Microbiome Changes Occur Independently of Caffeine

A critical finding from the reintroduction phase was that both caffeinated and decaffeinated coffee triggered acute changes in the gut microbiome . This demonstrates that coffee compounds beyond caffeine, likely its rich repertoire of polyphenols including chlorogenic acids, are bioactive microbial modulators. This is consistent with earlier work showing that Lawsonibacter asaccharolyticus, the bacterial species most strongly associated with coffee intake across large populations, grows better when coffee is added to culture media regardless of whether the coffee contains caffeine .

Neuroactive Metabolites Are Altered in Coffee Drinkers

Coffee drinkers exhibited reduced faecal concentrations of the inhibitory neurotransmitter γ-aminobutyric acid (GABA), along with reductions in the microbial metabolites indole-3-propionic acid and indole-3-carboxyaldehyde . GABA is a major inhibitory neurotransmitter that also functions as a signalling molecule within the gut-brain axis. The reduction in these neuroactive compounds suggests that coffee consumption shifts microbial metabolic output in ways that may influence central nervous system function through the gut-brain communication pathway.

Divergent Behavioural Profiles: Impulsivity and Reactivity vs. Memory

The behavioural findings revealed a striking double dissociation. Coffee drinkers scored significantly higher on impulsivity, particularly on the Sensation Seeking subscale of the UPPS-P, which measures motivation for novelty and excitement . They also exhibited higher emotional reactivity scores. In contrast, non-coffee drinkers demonstrated better performance on memory measures . These behavioural differences were linked to the microbial and metabolomic data through an integrated model, suggesting that the divergent cognitive profiles between habitual coffee consumers and non-consumers may be partly mediated by microbial metabolism.

Immune Markers Shift with Consumption and Abstinence

Coffee drinking was associated with a lower baseline C-reactive protein (CRP) and higher interleukin-10 (IL-10), a broadly anti-inflammatory cytokine profile . When coffee drinkers underwent the 14-day abstinence washout, CRP and the pro-inflammatory cytokine tumour necrosis factor alpha (TNFα) rose, and the reduction in blood pressure that had accompanied coffee cessation during the abstinence phase suggests complex cardiovascular and immune dynamics with consumption and withdrawal .

An Integrated Multi-Omics Model Links Coffee Metabolites to Microbes and Cognition

The integrated analysis identified nine key metabolites, including theophylline, caffeine, and several phenolic acids, that served as hubs linking specific microbial species to cognitive and behavioural outcomes . These metabolites were associated with measures of perceived stress and sleep quality, providing a molecular map of the coffee-microbiome-gut-brain axis. The model demonstrates that coffee's effects on the brain are not simply a matter of caffeine pharmacology but involve a complex network of microbial transformation, metabolite production, and host-microbe signalling.

4. Lessons Learnt

Coffee is a complex biological intervention, not just a caffeine delivery system.

The finding that decaffeinated coffee triggers microbiome changes comparable to caffeinated coffee dismantles the assumption that coffee's biological effects reduce to the pharmacology of caffeine. Coffee contains hundreds of bioactive compounds, including chlorogenic acids, melanoidins, and diterpenes, many of which reach the colon where they interact with the gut microbiota . Understanding coffee's health effects requires studying coffee, not just caffeine.

The gut microbiome mediates dietary effects on the brain.

This study provides one of the most comprehensive demonstrations in humans that a habitually consumed food or beverage can shape cognition, behaviour, and mood through the microbiota-gut-brain axis. The integration of metagenomics, metabolomics, and behavioural phenotyping across a prospective interventional design represents a methodological template for nutritional psychiatry and precision nutrition.

Habitual consumption patterns create stable biological states.

The baseline differences between habitual coffee drinkers and non-drinkers, and the partial reversibility during abstinence, suggest that repeated dietary choices create a stable, albeit modifiable, biological state that encompasses the microbiome, the metabolome, the immune system, and brain function. The implications are profound: what we eat and drink every day shapes not just our metabolism but our cognitive and emotional phenotype.

Coffee's cognitive profile is nuanced, not universally positive.

While coffee is widely associated with increased alertness, this study revealed a more complex picture. The finding that habitual coffee drinkers exhibit higher impulsivity and emotional reactivity while non-drinkers demonstrate better memory challenges the simple narrative that coffee is uniformly beneficial for brain function. Different dimensions of cognition and behaviour may be divergently influenced by long-term coffee consumption.

Nine metabolites may serve as biomarkers and future intervention targets.

The identification of a small set of key metabolites that bridge microbes and brain function provides candidate biomarkers for future research and potential targets for nutritional or pharmacological interventions aimed at modulating the microbiota-gut-brain axis.

5. How This Research Can Help Humanity

Informing Personalised Nutrition and Dietary Guidance

The demonstration that habitual coffee consumption shapes stable biological states opens the door to microbiome-informed dietary recommendations. Individuals considering changes to their coffee habits can be counselled that altering intake is likely to produce temporally dynamic shifts in gut microbial composition and potentially in cognition and mood . For those for whom high impulsivity or emotional reactivity is a clinical concern, a trial of coffee reduction may be a low-risk dietary intervention worth exploring.

Reframing Coffee's Health Narrative with Nuance

The behavioural findings add necessary complexity to public understanding of coffee's health effects. Coffee is not simply "good" or "bad" for the brain. Different dimensions of cognitive function, impulsivity, emotional reactivity, and memory, appear to be divergently associated with habitual consumption. An informed decision about coffee intake should consider this full profile, particularly for individuals with conditions characterized by impulsivity or emotional dysregulation.

Clarifying the Role of Caffeine vs. Other Coffee Compounds

The demonstration that decaffeinated coffee produces acute microbiome changes independently of caffeine has immediate practical implications . Individuals seeking the microbial and metabolic benefits of coffee without the stimulant effects of caffeine can be reassured that decaffeinated coffee retains bioactive compounds that influence the gut ecosystem. The health effects of coffee cannot be reduced to caffeine alone.

Providing a Template for Microbiota-Gut-Brain Axis Research

Methodologically, this study establishes a gold-standard framework for investigating how dietary components influence brain function through the gut. The three-phase design capturing baseline comparison, withdrawal, and reintroduction, combined with multi-omics integration and behavioural phenotyping, is replicable and can be applied to other foods, beverages, and dietary patterns. This template can accelerate the translation of nutritional epidemiology into mechanistic understanding and actionable dietary recommendations.

Identifying Metabolite Targets for Future Therapeutics

The nine key metabolites linking microbes to brain function represent potential targets for novel interventions aimed at the microbiota-gut-brain axis . If specific microbial metabolites are causally responsible for aspects of coffee's cognitive and emotional effects, modulating those metabolites directly, through diet, probiotics, or postbiotic supplements, could provide targeted mental health benefits.

6. Final Summary

Most Important Takeaways

1. Coffee fundamentally shapes the gut microbiome in both caffeine-dependent and caffeine-independent ways.

Habitual coffee drinkers and non-drinkers harbour distinct gut microbial communities. While some of these differences are attributable to caffeine, the reintroduction phase demonstrated that decaffeinated coffee also drives acute microbiome changes, revealing the independent bioactivity of coffee's polyphenolic compounds .

2. Coffee consumption is linked to divergent cognitive and behavioural profiles.

Habitual coffee drinkers exhibited higher impulsivity and emotional reactivity, while non-coffee drinkers demonstrated better memory performance. These findings challenge unidimensional narratives about coffee and brain function, revealing a nuanced profile of cognitive trade-offs associated with long-term consumption .

3. Key neuroactive metabolites are altered by coffee consumption.

Coffee drinkers had reduced faecal levels of GABA, the brain's primary inhibitory neurotransmitter, as well as indole-3-propionic acid and indole-3-carboxyaldehyde . These metabolites are known to participate in gut-brain axis signalling, providing a plausible mechanistic pathway for coffee's cognitive and behavioural associations.

4. Coffee's effects on the brain are mediated by a multi-omic network, not a single compound.

An integrated model identified nine key metabolites, including theophylline, caffeine, and phenolic acids, that connect microbial species to cognitive and behavioural outcomes . This network-level understanding challenges the reductionist focus on caffeine and supports a systems-biology view of coffee's health effects.

5. Withdrawal and reintroduction reveal dynamic, reversible biology.

The prospective interventional design showed that some coffee-associated microbiome and metabolite changes are reversible upon abstinence and re-emerge upon reintroduction, establishing a causal, dynamic relationship between coffee consumption and gut microbial ecology .

Action Points

For Individuals:

· Consider the full cognitive profile when making coffee decisions: If you experience challenges with impulsivity or emotional reactivity, a trial period of coffee reduction may be informative. Conversely, if memory concerns are more salient, the study's finding that non-drinkers performed better on memory tasks may be relevant.

· Expect a transition period when changing coffee habits: The withdrawal and reintroduction phases of this study demonstrated that the gut microbiome shifts dynamically with changes in coffee intake. Gastrointestinal or mood changes during the first two weeks of altering your coffee routine may reflect real biological adaptation, not merely psychological expectation.

· Decaffeinated coffee retains gut-active compounds: If you wish to reduce caffeine intake while preserving the microbial effects of coffee, decaffeinated coffee remains a source of bioactive polyphenols that influence the gut ecosystem.

For Clinicians and Mental Health Practitioners:

· Assess coffee intake when evaluating impulsivity and emotional reactivity: The study's finding that habitual coffee drinkers exhibit higher scores on these dimensions suggests that coffee consumption should be part of a comprehensive clinical assessment for conditions where these features are prominent.

· Counsel patients on the biological reality of coffee withdrawal: The rise in inflammatory markers during the abstinence phase provides objective evidence that coffee withdrawal is a physiological process, not merely psychological discomfort, and should be managed with appropriate expectations and support.

· Consider coffee as a modifiable dietary factor in gut-brain conditions: For conditions involving the gut-brain axis, including functional gastrointestinal disorders and mood disorders, coffee intake may be a relevant variable to modify in a structured manner.

For Researchers:

· Extend the multi-omics approach to other dietary factors: The integrated metagenomics-metabolomics-behavioural framework used in this study should be applied to other foods, beverages, and dietary patterns to map their effects on the microbiota-gut-brain axis.

· Conduct long-term longitudinal studies: This study captured acute and short-term dynamics over weeks. Studies tracking individuals over years are needed to determine whether the microbial and cognitive profiles associated with coffee consumption reflect stable trait-like states or continuously dynamic adaptations.

· Investigate causality through intervention trials: While the prospective interventional design is strong, longer-term randomized trials assigning individuals to different coffee consumption conditions and measuring cognitive, behavioural, and neuroimaging outcomes would strengthen causal inference.

· Identify the specific non-caffeine compounds driving microbiome shifts: The finding that decaffeinated coffee is bioactive invites research to isolate which specific coffee polyphenols or other compounds are responsible for the microbial changes.

For the Food and Beverage Industry:

· Develop coffee products that optimize gut-brain benefits: Understanding which coffee compounds drive beneficial microbiome changes could inform the development of coffee varieties, roasting methods, or brewing techniques that maximize bioactive polyphenol delivery.

· Support transparency in caffeine content: Given the independent effects of caffeine and non-caffeine compounds identified in this study, accurate and accessible labelling of caffeine content in coffee products supports informed consumer decision-making.

-x-x-

Recommended Follow-Up Study

The Coffee-Microbiome-Brain Randomised Controlled Trial with Neuroimaging Outcomes

The Boscaini study established associations between coffee consumption, the gut microbiome, and cognitive-behavioural measures using self-report instruments. The critical next step is a randomized controlled trial that assigns non-coffee drinkers to sustained consumption of caffeinated coffee, decaffeinated coffee, or a placebo beverage for six months, with pre- and post-intervention neuroimaging using functional magnetic resonance imaging (fMRI) and cognitive testing using standardized computerized batteries. Outcomes would include resting-state functional connectivity, structural brain measures, performance on objective memory, attention, and impulsivity tasks, and comprehensive faecal and plasma metabolomics. A parallel amendment tracking sleep-deprived participants would extend the recent animal findings on coffee's ability to mitigate sleep-deprivation-induced cognitive impairment and gut dysbiosis through the gut-brain axis . This design would provide the strongest evidence to date on whether coffee causally modulates brain function and behaviour through the gut microbiome in humans.

List of Other Related / Connected Studies and Research

The Manghi-Segata Lawsonibacter asaccharolyticus Study (2024)

This landmark multi-cohort investigation of over 22,000 participants demonstrated that coffee consumption is the single strongest dietary predictor of gut microbiome composition among more than 150 food items, an association largely driven by the bacterium Lawsonibacter asaccharolyticus, which is 4.5 to 8 times more abundant in high coffee drinkers . In vitro experiments confirmed that coffee stimulates L. asaccharolyticus growth independently of caffeine. This study provided the population-scale foundation for the Boscaini findings examined in the current monograph.

The ZOE PREDICT Programme (Multiple Cohorts)

The PREDICT studies constitute a large-scale research programme linking dietary intake, gut microbiome composition, postprandial metabolic responses, and cardiometabolic health. Coffee was identified as the food item most strongly correlated with microbiome composition across these cohorts, and the standardized dietary assessment tools used in PREDICT informed the dietary monitoring protocols in the Boscaini study .

The Coffee-Mitigated Cognitive Impairment in Sleep-Deprived Mice Study (2025)

A 2025 mouse study published in Clinical Nutrition Open Science demonstrated that moderate coffee consumption improved cognitive performance and ameliorated synaptic structural abnormalities in chronically sleep-deprived mice . The study found that coffee upregulated circadian rhythm genes, enhanced antioxidant defences, strengthened gut barrier integrity through tight junction protein expression, suppressed pro-inflammatory cytokines, and restored beneficial gut microbiota. This study provides complementary evidence from a controlled animal model for coffee's gut-brain axis effects, extending the human findings into the specific context of sleep-deprivation-induced cognitive impairment.

The Epithelial Barrier Hypothesis Studies (Akdis Lab) and Gut Permeability Research

Connecting to the broader theme explored throughout this monograph series, the finding that coffee upregulated gut tight junction proteins ZO-1, Claudin-1, and Occludin in the sleep-deprived mouse study supports the importance of barrier integrity in the microbiota-gut-brain axis. This concept echoes the epithelial barrier hypothesis's framework that a compromised gut barrier is a common pathway through which modern environmental exposures drive chronic inflammatory and neuropsychiatric disease .

The DIABIMMUNE Study and Karelia Allergy Study

The coffee-microbiome link connects conceptually to the earlier monographs in this series on the DIABIMMUNE Study and Karelia Allergy Study. Just as reduced microbial diversity in modern environments is implicated in immune dysregulation, specific dietary components such as coffee appear capable of actively reshaping the gut ecosystem toward a potentially more beneficial configuration, suggesting that dietary choices can partially compensate for the microbial losses of modern sanitized environments. Both frameworks demonstrate that food and environmental exposures provide the signals that calibrate host-microbiome interaction.

The Glucose-Willpower and Willpower Dynamics Studies

The finding that coffee drinkers exhibit higher impulsivity and emotional reactivity connects to the monographs on glucose and willpower dynamics. A high degree of sensation seeking and emotional reactivity may place greater demands on self-control resources, creating an intriguing potential relationship between the metabolic-fuel model of willpower and the behavioural phenotype associated with habitual coffee consumption. If habitual coffee intake is associated with higher impulsivity, the interaction between coffee's effects on the microbiome and its effects on self-control regulation warrants further investigation.

Caffeine, Adenosine, and Brain Aging Research

Extensive epidemiological evidence, cited in the introduction of the Boscaini study, has demonstrated that coffee consumption reduces the risk of Parkinson's disease in a dose-dependent manner, is associated with a 27 percent reduction in Alzheimer's disease incidence in meta-analyses, and reduces depression risk . These neuroprotective associations, initially attributed to caffeine's antagonism of adenosine receptors, may now be partially understood through the microbial pathways characterized in the current study, representing a paradigm expansion from a purely pharmacological model to one that incorporates the gut-brain axis.