Frequent Coffee Drinkers Carry More Diverse Gut Bacteria, New Study Finds

If you start your day with coffee and have ever wondered whether it's helping or hurting your gut, a new human study offers some of the most detailed evidence yet. Researchers tracked 61 healthy adults' real-world coffee intake alongside urine chemistry, stool samples, and a swallowable sensor that measures gut function in real time — and found that habitual coffee drinkers carry a different, somewhat more diverse population of gut bacteria, plus measurably different gut chemistry, than people who rarely drink it. The findings don't prove coffee itself is reshaping anyone's gut, but they add real physiological detail to a question a lot of people troubleshooting bloating, irregularity, or a finicky digestive system end up asking: does a daily coffee habit actually matter down there?

Key takeaways

• In a 61-person study, people who drank coffee on 4 or more of 8 tracked days had significantly higher gut microbial richness, and higher levels of specific bacteria (Lawsonibacter, Slackia, unclassified Eggerthellaceae), than people who rarely drank coffee.
• Using a swallowable sensor capsule, the same frequent coffee drinkers showed a measurably more acidic small intestine and more coffee-linked colonic contractions than rare drinkers.
• This is a correlational snapshot, not a trial: the individual bacterial differences didn't survive statistical correction for testing many microbes at once, and nothing here proves coffee causes these changes or treats any digestive condition.

Frequent Coffee Drinkers Have More Diverse, Distinct Gut Bacteria

People who drink coffee most days carry a richer mix of gut bacteria than people who rarely drink it, according to a study published in Gut Microbiology. Researchers classified 61 healthy Danish adults as "frequent" coffee drinkers (48 people who drank coffee on 4 or more of 8 tracked days, averaging 343.5 mL a day) or "rare" drinkers (13 people averaging just 17.7 mL a day), based on detailed 8-day food diaries. The frequent group had significantly higher observed richness — the raw count of distinct bacterial types detected in a stool sample (p = 0.038) — and a similar, non-significant trend in the Shannon index, a common measure that combines richness with how evenly those bacteria are represented.

Three specific bacteria stood out: Lawsonibacter spp., Slackia spp., and an unclassified member of the family Eggerthellaceae (a group of gut bacteria known for breaking down plant compounds called polyphenols) were all more abundant in frequent drinkers. Lawsonibacter and Eggerthellaceae also rose in step with how much coffee someone drank on a continuous scale — Lawsonibacter (ρ = 0.39, p = 0.002; confirmed with a mixed model, β = 0.14, p = 0.009) and Eggerthellaceae (ρ = 0.45, p < 0.001) — echoing a 2024 multi-cohort study that found coffee consumption tracks Lawsonibacter asaccharolyticus abundance across multiple independent populations. It also fits an earlier, smaller study of 147 healthy volunteers that linked long-term coffee consumption to a distinct fecal bacterial profile, though the specific bacteria highlighted differed somewhat between the two studies.

Why Gut Microbial Diversity Matters to People Managing Digestion

Lower gut microbial diversity has repeatedly shown up as a feature of conditions many readers already research for themselves, including IBS, IBD, and metabolic disease, which is why any diet factor linked to higher diversity draws attention. This study did not enroll anyone with a diagnosed digestive condition and did not test whether coffee changes symptoms, so it cannot say coffee helps or worsens IBS or IBD. What it does show is that an extremely common daily habit correlates with a measurably different gut ecosystem in healthy people, which is the kind of groundwork that eventually gets tested in people who do have gut conditions.

How Researchers Measured Coffee Habits With Urine Chemistry and a Gut Sensor Pill

Researchers verified people's coffee habits objectively rather than relying on memory alone. Alongside 8-day dietary records, they measured urinary caffeine and its breakdown products (including paraxanthine, the main metabolite caffeine turns into in the liver), and found these biomarkers correlated with self-reported coffee intake (ρ up to 0.55), confirming the exposure data was reliable. A subset of 50 participants also swallowed the SmartPill, a wireless capsule that records pH, pressure (contractions), and transit time as it travels through the gut — allowing the team to measure gut physiology directly instead of relying on symptom questionnaires. This same physiological-measurement approach was established by the same research group in an earlier study of gut environment and microbiome variation in this cohort, giving the coffee analysis a validated methodological foundation to build on.

Coffee Intake Tracks With More Gut Contractions and a More Acidic Small Intestine

Caffeine's breakdown products were positively linked to increased colonic contractions (ρ = 0.31–0.38 across four metabolites), and habitual coffee intake was linked to a more acidic small intestine, with small intestinal pH significantly lower in frequent than rare coffee drinkers (p = 0.022). Notably, none of this showed up as faster colonic transit time, meaning the gut appeared to squeeze more without necessarily moving stool through any quicker — a distinction the authors say fits coffee stimulating mixing rather than pure propulsion. Frequent coffee drinkers also had higher fecal energy density and lower stool moisture, hinting the gut may be absorbing slightly more when coffee stimulates this extra mixing, though the study stops short of confirming why.

What This Means if You're Paying Attention to Your Own Gut Health

If coffee already seems to "move things along" for you, these findings offer a plausible physiological reason: caffeine's metabolites correlate with more colonic contractions, which lines up with a common personal experience many coffee drinkers already report. That is not the same as coffee being an established treatment for constipation, IBS, or any other digestive issue, and the study makes no such claim. There's also nothing here suggesting people should start or increase coffee intake for gut health, or that a supplement mimicking one of these compounds would recreate the effect. Anyone managing a diagnosed digestive condition should treat this as background context for a conversation with a doctor, not a reason to change their coffee habits on their own.

Why the Bacterial Differences Don't Prove Coffee Caused Them

This is an observational comparison between two groups of existing coffee drinkers, not a trial where people were randomly assigned to drink more or less coffee, so it cannot establish cause and effect. Just as importantly, the specific taxon-level differences in Lawsonibacter, Slackia, and Eggerthellaceae did not remain statistically significant once the researchers corrected for testing many different bacteria at once — a standard safeguard against false positives. The study was also a secondary analysis of a cohort originally recruited for a broader gut-physiology project, drew from a single Danish population, did not track the type or brewing method of coffee people drank, and could not fully separate caffeine from tea or other sources in the seven people who reported drinking no coffee at all.

Where This Research Heads Next

The authors say the clear next step is testing coffee's acute effects — what happens in the hours right after a cup, rather than comparing habitual drinkers versus non-drinkers — and comparing caffeinated against decaffeinated coffee to separate caffeine's role from other bioactive coffee compounds like chlorogenic acids. Larger, sex-balanced studies are also on the list, since coffee consumption patterns and caffeine metabolism can differ by sex. Separately, a 2026 study in Nature Communications has already begun extending this line of research into the gut-brain axis, linking habitual coffee intake to both microbiome shifts and measurable changes in mood and cognition.

Common Questions

Does this study prove coffee changes your gut bacteria? No. It's an observational comparison between existing frequent and rare coffee drinkers, not an experiment where coffee intake was controlled, so it can show a correlation but not prove coffee causes the differences.

Does this mean coffee helps with IBS or constipation? The study didn't test people with any diagnosed digestive condition, so it can't answer that directly. It did find that coffee-linked compounds correlated with more colonic contractions, which fits reports that coffee affects bowel habits, but that's not the same as a proven treatment.

What are Lawsonibacter and Eggerthellaceae? They're gut bacteria groups; Eggerthellaceae is a bacterial family known for breaking down plant compounds called polyphenols, and Lawsonibacter is a genus that a separate 2024 multi-cohort study has already tied specifically to coffee intake across multiple independent populations.

Should I drink more coffee for gut health based on this? No. The study doesn't establish an ideal amount of coffee or claim coffee is a proven intervention for any gut outcome; it simply found a correlation in healthy adults that needs to be tested further.

References

1. Francesca Bucci, Marie-Luise Puhlmann, Paula Rodriguez-Garcia, et al. (2026). Habitual coffee consumption is linked to differences in gut microbiota and gut physiology. Gut Microbiology. https://doi.org/10.1016/j.gutmic.2026.100018
2. Paolo Manghi, Amrisha Bhosle, Kai Wang, et al. (2024). Coffee consumption is associated with intestinal Lawsonibacter asaccharolyticus abundance and prevalence across multiple cohorts. Nature Microbiology. https://doi.org/10.1038/s41564-024-01858-9
3. Nicola Procházková, Martin F. Laursen, Giorgia La Barbera, et al. (2024). Gut physiology and environment explain variations in human gut microbiome composition and metabolism. Nature Microbiology. https://doi.org/10.1038/s41564-024-01856-x
4. Serena Boscaini, Thomaz F. S. Bastiaanssen, Gerard M. Moloney, et al. (2026). Habitual coffee intake shapes the gut microbiome and modifies host physiology and cognition. Nature Communications. https://doi.org/10.1038/s41467-026-71264-8