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You have trillions of bacteria in your gut, and not all of them pull equal weight. One species, F. prausnitzii (Faecalibacterium prausnitzii), stands out as an anti-inflammatory workhorse that can make up 2 to 20 percent of the bacteria in a healthy adult's large intestine.
This stool test counts how much of that specific bacterium is living in your gut. Low readings keep showing up in people with inflammatory bowel conditions, certain skin diseases, type 2 diabetes, and some cancers, which makes this one of the most-studied beneficial microbes in human health.
F. prausnitzii produces a short chain fatty acid called butyrate. Butyrate is the preferred fuel for the cells lining your colon, and it helps teach your immune system to tolerate food and friendly microbes rather than attack them. When this species is abundant, your gut barrier is better nourished and your body produces more regulatory T cells, the calming branch of the immune system that dampens inflammation.
When F. prausnitzii drops, the protection drops with it. Lower counts are associated with a weaker gut lining, higher inflammatory signaling, and a shift in the rest of the microbiome toward more pro-inflammatory species.
The strongest signal in the research links low F. prausnitzii to inflammatory bowel disease (IBD), the umbrella term covering Crohn's disease and ulcerative colitis. A meta-analysis pulling together multiple studies found consistently lower abundance in both conditions versus healthy people, with levels dropping further during active flares. In ulcerative colitis, low counts during remission were linked to shorter remission periods and more frequent relapses.
The ratio of F. prausnitzii to E. coli tracks with response to anti-TNF (a class of biologic drugs that block a key inflammatory signal) therapy in Crohn's disease. Higher baseline Faecalibacterium has also been linked to better response to infliximab, ustekinumab, and vedolizumab across multiple studies. First-degree relatives of people with ulcerative colitis tend to show reduced levels too, even before developing symptoms.
What this means for you: if you have IBD or a close family history, a low reading is consistent with the pattern seen in active and relapse-prone disease, while a higher reading aligns with the pattern seen in stable remission.
Research has linked low F. prausnitzii, including shifts toward lower-butyrate subspecies, to atopic dermatitis (the most common form of eczema). The pattern fits a gut-to-skin connection where reduced gut barrier function feeds systemic immune reactivity.
A similar reduction shows up in psoriasis, closely mirroring the pattern seen in IBD. Another inflammatory skin condition, hidradenitis suppurativa, did not show the same shift, suggesting this is not a generic finding across every skin disease but a specific immune signature.
People with type 2 diabetes tend to have lower F. prausnitzii counts, and this species has been inversely linked to HbA1c (your three-month average blood sugar) and several markers of inflammation. Research tracking the gut microbiome after bariatric surgery found that F. prausnitzii abundance was associated with lower low-grade inflammation in people with obesity and diabetes, independent of how many calories they were eating.
In a hypertension cohort, F. prausnitzii was enriched in people with healthy blood pressure and negatively correlated with both systolic and diastolic numbers, even after adjusting for age, BMI (body mass index), body fat, LDL cholesterol, waist circumference, and fiber intake.
In elderly adults, F. prausnitzii was lower than in younger adults and lower still in elderly people with heart failure compared to healthy elderly controls, with a diagnostic accuracy score (AUC, where 1.0 is perfect and 0.5 is a coin flip) of 0.703 for predicting heart failure. In a study of 90 people hospitalized with ischemic stroke, lower F. prausnitzii was linked to worse stroke severity, worse prognosis, and higher pro-inflammatory markers.
Reduced abundance has also been reported in chronic fatigue syndrome (ME/CFS) and in colorectal cancer cohorts, where it is studied as one supporting signal in microbiome-based cancer prediction rather than a standalone test.
You may notice this bacterium shows up as "low" across many different conditions, from Crohn's to diabetes to heart failure. That is not a contradiction. F. prausnitzii is best understood as a general indicator of gut ecosystem health, not a specific marker of any one disease. A low number signals that the protective, anti-inflammatory environment in your gut has been disrupted, but it does not tell you which downstream condition is most relevant for you. That interpretation requires pairing this result with your symptoms, history, and companion tests.
F. prausnitzii is a research-grade microbiome marker without clinical cutoffs set by any guideline body. Results depend heavily on the lab method (PCR versus 16S ribosomal RNA sequencing versus shotgun metagenomics) and on how the lab reports the number. The ranges below come from published research on what is typical in healthy adults compared to disease states, not from a consensus clinical guideline.
| Pattern | Typical Finding | What It Suggests |
|---|---|---|
| Healthy adult range | Around 2 to 20 percent of total gut bacteria | A protective, anti-inflammatory gut ecosystem |
| Reduced | Noticeably below your lab's healthy reference | Pattern seen in IBD, ongoing inflammation, and metabolic disease |
| Severely depleted | Near-absent or undetectable | Pattern seen in active IBD flares, recent broad antibiotic exposure, or severe gut imbalance |
These ranges are illustrative orientation, not targets. Compare your results within the same lab over time for the most meaningful trend, because different labs will report different absolute numbers for the same sample.
One reading of F. prausnitzii tells you less than a trend. Gut microbiome composition shifts with diet, travel, medications, illness, and stress, and a single snapshot can be misleading. A year-long longitudinal study in Swedish adults found that about 23 percent of the variation in the gut microbiome over time came from within-person shifts, not differences between people.
Treat your first reading as a baseline. If you are changing your diet, starting prebiotics, recovering from antibiotics, or working on an inflammatory condition, retest in 3 to 6 months. After that, an annual check is a reasonable cadence if you are tracking this as a longevity marker. Direction of change over time tells you far more than any single result.
If your F. prausnitzii comes back low, the first question is context. Recent antibiotics, a strict low-FODMAP diet, an acute illness, or a recent chemotherapy cycle can all suppress levels temporarily. If none of those apply and the number stays low on a retest a few months later, the broader picture deserves a look.
Companion tests worth pairing with this one include fecal calprotectin (a marker of gut inflammation), secretory IgA (a measure of gut immune activity), short chain fatty acids like butyrate (the end product this bacterium makes), and Akkermansia muciniphila (another beneficial gut species that tracks similarly). If you have ongoing GI symptoms or blood in the stool, work with a gastroenterologist on an IBD workup. If your concern is metabolic, pairing this with HbA1c, fasting insulin, and hs-CRP (high-sensitivity C-reactive protein, a marker of low-grade inflammation) gives a more complete picture.
Evidence-backed interventions that affect your Faecalibacterium Prausnitzii level
Faecalibacterium Prausnitzii is best interpreted alongside these tests.