Eubacterium Rectale

Your colon lining does not run on the food you eat. It runs on a fatty acid called butyrate that certain gut bacteria make when they ferment fiber you cannot digest yourself. This test measures how much of one of the biggest butyrate makers you are carrying.

When that population drops, it drops alongside a long list of conditions: ulcerative colitis, Crohn's, psoriasis, ME/CFS, colorectal cancer. Whether the drop causes any of them is a separate and mostly unanswered question. What a low result tells you reliably is that one of your gut's main fuel-production lines is running thin.

What This Test Actually Measures

The assay uses PCR, a lab method that copies a specific stretch of DNA until there is enough to count. It targets a gene sequence from this species and reports how much of it is in your stool sample. So you are counting bacterial DNA, not bacterial activity, and not butyrate itself.

That distinction matters more than it sounds. DNA counts can include dead cells. And a stool sample reflects what is being shed into stool, not what is attached to the mucus layer against your colon wall. Studies that sampled both found the two do not always match.

This species belongs to a group of oxygen-sensitive gut bacteria that break down resistant starch and other fiber that survives your small intestine. In a healthy adult eating enough fermentable carbohydrate, it can be one of the most abundant species in the colon. In one controlled feeding study, a single strain of E. rectale rose to about 8% of the gut bacteria sequenced on a high resistant starch diet, while a broader E. rectale/Roseburia count reached about 10%.

Where the Evidence Is Strongest: Inflammatory Bowel Disease

The clearest repeated finding is depletion in inflammatory bowel disease. A Crohn's disease stool microarray found E. rectale roughly five to ten times more abundant in healthy volunteers than in people with Crohn's. In ulcerative colitis, mucosal PCR studies measured the E. rectale group in colon tissue and found lower counts tracking with worse disease activity and more mucosal damage.

The depletion does not always lift when the disease quiets down. A study of ulcerative colitis in remission found a stable deficit in the broader E. rectale-related group over time and across patients from different countries. That is one of the more useful things to know about this marker. It looks like a persistent feature of the gut ecosystem in these diseases, not just a temporary consequence of a flare.

Alone, though, this one species is not a diagnostic test for inflammatory bowel disease. Newer multi-bacteria panels show why. A 2024 digital PCR study found E. rectale depleted in Crohn's disease, but the final selected diagnostic panels did not use this exact species. The ulcerative colitis digital PCR model reached 85.0% sensitivity and 81.8% specificity in the discovery cohort. In a separate IBD-vs-IBS comparison, the multi-bacteria panel reached 79% sensitivity and 92% specificity, while fecal calprotectin reached 68% and 89%. The point is simple: the pattern is stronger than the single organism.

Colorectal Cancer, and Why the Evidence Points Both Ways

One small stool PCR study found levels about four times lower in people with colorectal cancer than in healthy controls. A larger pooled analysis of stool bacterial DNA later found strain-level patterns involving this species in colorectal cancer, but it did not turn a low stool result into a standalone cancer screen.

Then the picture flips. Tissue-level profiling found this species enriched near some colon tumor sites, where a bacterial surface extract switched on NF-kB in colon lining cells. NF-kB is a gene switch cells use to turn on inflammation. Mouse work went further and suggested this organism can worsen colitis in a setting that precedes tumor formation. Other animal work found its butyrate suppressed lymphoma growth.

Both things can be true, and the way to reconcile them is location. In the stool stream, this bacterium can be a fuel factory feeding your colon cells. Pressed against inflamed tissue in a specific niche, the same organism may become a source of bacterial signals your immune system reacts to. This is not a good-number, bad-number marker for cancer. A stool test cannot tell you which situation you are in, and no one should read a high or low result here as a cancer signal in either direction. For cancer screening, the fecal immunochemical test and multi-target stool DNA tests are the validated tools.

Conditions Outside the Gut

The least intuitive associations are outside the digestive tract. Butyrate does more than feed colon cells. It also helps immune cells stand down, which is the likely reason a colon bacterium keeps showing up in diseases of the skin and joints.

• Psoriasis and psoriatic arthritis: stool levels are substantially depleted in both, and on their own separate psoriatic disease from healthy controls only moderately well (area under the curve 0.74 to 0.77). That is real but well short of diagnostic.
• ME/CFS: in a 197-person study, reduced levels tracked with reduced butyrate-making capacity across the whole microbiome and with fatigue severity.
• Rheumatoid arthritis: human genetic analysis plus mouse work point toward a protective role. Giving the bacterium to mice with arthritis raised regulatory T cells, the immune cells that hold inflammation in check, reduced joint inflammation and improved bone density. That is animal evidence; it has not been tested as a treatment in people.
• COVID-19: across stool samples from 2,871 adults in 16 countries, populations with lower average levels had higher standardized COVID mortality. Hospitalized severe cases showed the same depletion alongside higher inflammatory markers. Depletion persisted up to 30 days after the virus cleared.

An ecological correlation between country-level bacterial abundance and country-level death rates is weak evidence about any individual. Read it as a hint that butyrate capacity and immune resilience travel together, not as a claim that your own number predicts how a virus will treat you.

What the Mortality Data Does and Does Not Show

Current cohort data do not support using this species by itself to estimate death, heart attack or cancer risk. Where it appears in survival analyses, it appears as one contributor inside a broader dysbiosis score.

One study of organ transplant recipients linked a microbial component containing this species with lower cancer mortality, while a broader dysbiosis score predicted higher all-cause mortality. That is useful for understanding the gut ecosystem. It is not support for treating one stool species as a personal survival marker.

Why a Single Reading Can Fool You

This number moves fast. In a controlled feeding study, switching people onto high resistant starch or off it shifted the E. rectale/Roseburia group within three to four days, and the shift reversed just as quickly when the diet stopped. A result collected during a week of low-carb eating is not measuring your baseline gut. It is measuring last week's dinners.

Beyond diet, three things distort a single sample. Stool water content and how fast things move through your colon change what gets shed into a sample. Acute diarrhea drives levels down sharply and they recover once the illness passes, so testing during or just after a stomach bug will read low for reasons that have nothing to do with your baseline. And labs differ: DNA extraction protocols and analysis pipelines produce meaningfully different numbers for the same stool, so a result from one lab is not comparable to a result from another.

There is no validated reference range for this species. Healthy adults vary enormously in baseline abundance, and what counts as low depends partly on what you eat. Treat any commercial out-of-range flag as a rough orientation, not a threshold you have crossed.

Tracking Your Trend

Given all that, your own trajectory is worth more than any single number. Individual gut profiles are personal and reasonably stable over months, which is exactly what makes repeat testing informative. A genuine move against your own baseline means something. One reading against a population range mostly does not.

Use the same lab every time. Switching labs mid-trend makes the comparison weak, because the method can change as much as the biology.

What to Do With an Unexpected Result

A low result in isolation is a prompt to look wider, not a finding to act on. The useful move is to see what else in your gut panel is moving in the same direction. If other butyrate producers are down too, particularly Faecalibacterium prausnitzii, you are looking at a real loss of fermentation capacity rather than one species fluctuating.

Pair it with a host inflammation marker. Fecal calprotectin measures neutrophils leaking into your gut. Neutrophils are white blood cells that show up when the lining is inflamed. Low bacteria plus normal calprotectin suggests thin fermentation capacity without active gut inflammation. Low bacteria plus elevated calprotectin, especially with diarrhea, blood in the stool, weight loss or ongoing abdominal pain, is a gastroenterology conversation and a likely colonoscopy, not something to manage with fiber.

Two other pairings are worth knowing. If diarrhea is the reason you tested, a multiplex pathogen panel rules out infection first, since commensal levels drop during any acute gut infection and will mislead you. And if you have psoriasis, psoriatic arthritis or rheumatoid arthritis, a low result is consistent with what is seen in those conditions but does not change treatment. No trial has shown that raising this bacterium improves any of them in people.