Anaerotruncus Colihominis/Massiliensis Test · Stool

Your gut is home to trillions of bacteria, and research keeps pointing to a small group of them as quiet signals of bigger things happening in your body. Anaerotruncus colihominis and Anaerotruncus massiliensis are two closely related species whose levels in stool have been linked to colon cancer risk, gestational diabetes, age-related eye disease, and mood-related gut inflammation.

This is a research-stage marker without standardized clinical cutpoints. That does not mean the result is useless. It means the best use is to establish a baseline, track how your levels move with lifestyle and medication changes, and interpret any shifts in the context of your broader gut microbiome and inflammatory markers.

What These Bacteria Do

Anaerotruncus species are strict anaerobes, meaning they live in parts of your large intestine where there is almost no oxygen. They are normal residents of a healthy gut, typically present at low abundance. Most published research looks at the whole genus Anaerotruncus rather than separating the two species, so findings usually apply to both together.

Because the genus shows up across many different disease associations, researchers now view these bacteria less as a single cause of anything and more as a sensitive indicator of broader shifts in the gut community, including changes tied to inflammation, bile acid metabolism, and short chain fatty acid production.

Colorectal Cancer Risk

A genetics-based analysis found that people with naturally higher gut levels of Anaerotruncus had roughly 16% greater risk of colorectal cancer than those with lower levels. The effect is modest, and the statistical power was limited, but the method used (Mendelian randomization, which uses inherited genetic variants as natural experiments to test whether a trait causes a disease) makes this closer to a causal signal than a simple correlation. Evidence was measured at the genus level, not at the specific species level.

If you have a family history of colorectal cancer or are approaching screening age, an elevated Anaerotruncus reading is one of many data points that can inform how urgently you should pursue colonoscopy. It is not a replacement for direct colon screening.

Metabolic and Pregnancy-Related Conditions

In a study of 207 pregnant women, those with gestational diabetes showed higher Anaerotruncus levels in late pregnancy than those without the condition, even after adjusting for pre-pregnancy weight. This pattern lines up with broader evidence that the gut microbiomes of people with gestational diabetes share features with those seen in type 2 diabetes.

In a species-level analysis of 48 adults, Anaerotruncus colihominis specifically was more abundant in people with slow-transit constipation than in matched controls. The shift was part of a broader pattern involving bile acid and cholesterol metabolism, suggesting these bacteria may sit at the intersection of slow gut movement and changes in how the body processes fats.

Depression, Fatigue, and Mood

In 62 people with active inflammatory bowel disease, Anaerotruncus appeared within bacterial networks tied to worse depression and fatigue. Most of the surrounding signal came from reductions in butyrate-producing bacteria (a type of short chain fatty acid your gut cells use for fuel). A separate 2025 study tied Anaerotruncus colihominis to obesity-related depression through the amino acid glutamate, which plays a role in brain signaling.

In a population study of 1,784 ten-year-old children, higher Anaerotruncus levels showed a weak, borderline association with more internalizing behaviors and physical complaints. The link did not survive statistical correction, so it should be treated as preliminary rather than confirmed.

Age-Related Eye Disease

In a case-control study using deep DNA sequencing, Anaerotruncus species were enriched in people with neovascular age-related macular degeneration, a leading cause of vision loss in older adults. A later genetic causality analysis supported a causal link between higher Anaerotruncus levels and age-related macular degeneration, though the effect was measured at the genus level.

Lung Cancer Signal

In a 302-person study comparing people with and without non-small-cell lung cancer, higher Anaerotruncus abundance was one of the dysbiotic patterns linked to cancer risk. As with most of the evidence in this article, this is associative, not proven causal.

How to Read the Broader Pattern

Across studies, Anaerotruncus tends to be enriched in people with inflammatory, metabolic, and certain cancer-related conditions, yet these bacteria are also normal residents of healthy guts at low levels. The most honest framing is not that they are good or bad but that they are a sensitive indicator. When your Anaerotruncus is elevated alongside low butyrate producers, low diversity, or elevated inflammatory markers, the pattern as a whole is what carries the signal, not any one species.

Reference Ranges

No major clinical guideline has set standardized cutoffs for Anaerotruncus colihominis or A. massiliensis. Ranges vary by the lab and sequencing method used. The most useful approach is to compare your results within the same lab over time, rather than against a universal target.

Because absolute numbers depend heavily on sequencing depth and reporting methods, your lab's own reference range (usually shown on your result) is the most appropriate comparison point for a single reading. Treat any population-based number as orientation, not a target.

Why One Reading Is Not Enough

Gut bacteria shift daily with diet, stress, sleep, travel, and medications. A single stool test gives you a snapshot at one moment. What actually carries information is the trend over months. A baseline result, followed by a retest in 3 to 6 months after changes to diet, supplements, or medications, tells you whether your microbiome is moving in the direction you want.

For general tracking, at least annual retesting is reasonable. If you are recovering from antibiotics, treating an inflammatory condition, or trying a specific dietary intervention, 3 to 6 months is a more useful interval for seeing meaningful change.

What to Do With an Abnormal Result

An elevated or depressed Anaerotruncus reading on its own should not drive a major clinical decision. What it should drive is a wider look. Order or review companion markers: calprotectin (a gut inflammation marker), pancreatic elastase (a marker of pancreatic digestive function), short chain fatty acids, and a fecal occult blood test if you are at colon cancer screening age.

If your Anaerotruncus is elevated alongside other signs of inflammation or dysbiosis, or you have gut symptoms or a family history of colorectal cancer, work with a gastroenterologist to decide whether colonoscopy, further imaging, or targeted treatment makes sense. If the pattern is isolated and you have no symptoms, retesting in a few months to see whether the shift persists is often the right next step.

When Results Can Be Misleading

Several factors can distort a single stool reading and lead you to the wrong conclusion:

• Recent antibiotics: broad-spectrum antibiotics reduce gut anaerobes within days, with recovery taking weeks to months. Test at least 1 to 2 months after finishing a course.
• Acute illness or diarrhea: a recent stomach bug, food poisoning, or bout of diarrhea can reshape your stool microbiome for days to weeks. Wait until your bowel habits have normalized before testing.
• Medications that reshape gut communities: proton pump inhibitors (acid reducers, or PPIs), metformin, antipsychotics, and opioids can shift gut bacteria without causing any of the conditions this marker is associated with. Your reading may reflect the drug, not your underlying biology.
• Bowel prep or contrast: any recent colonoscopy preparation or imaging contrast can transiently alter gut bacterial composition. Wait at least 2 to 4 weeks after these procedures before collecting a sample.