The Same Gut Bacteria Vanish Across 6 Autoimmune Diseases, Preprint Finds

If you manage rheumatoid arthritis, lupus, multiple sclerosis, type 1 diabetes, inflammatory bowel disease or ankylosing spondylitis, you have probably already heard that "gut health" is somehow tangled up in your condition. A new preprint meta-analysis puts a number on that idea: pooling 47 previously published studies, researchers found the same handful of gut bacteria missing across all six diseases, most consistently a butyrate-producing (short-chain fatty acid making) species called Faecalibacterium prausnitzii. The paper has not yet been peer-reviewed, and its authors are explicit that the pattern is an association, not proof of cause.

Key takeaways

• A meta-analysis of 47 studies (3,847 autoimmune disease patients, 2,956 healthy controls) found Faecalibacterium prausnitzii, a butyrate-producing gut bacterium, significantly depleted in all six autoimmune diseases studied: RA, lupus, MS, T1D, IBD and ankylosing spondylitis.
• Two other bacteria linked to gut health, Roseburia species and Akkermansia muciniphila, were also reduced in most of the pooled studies, alongside a broader drop in gut bacterial diversity.
• Each disease also carried its own distinct signature, such as Prevotella copri expansion in rheumatoid arthritis and Ruminococcus gnavus enrichment in lupus.
• This is an unreviewed preprint built mostly from cross-sectional (single-timepoint) data, so it cannot say whether the bacterial changes cause disease, result from it, or both, and heterogeneity across the pooled studies was moderate to high.

Faecalibacterium Prausnitzii Depletion Spans Six Autoimmune Diseases

The core finding is that one gut bacterium, Faecalibacterium prausnitzii, was significantly depleted in every one of the six autoimmune diseases the researchers examined, turning up reduced in 89% of the 47 pooled studies (42 of 47). F. prausnitzii is one of the gut's main producers of butyrate, a short-chain fatty acid (a small molecule bacteria make by fermenting fiber) that feeds the cells lining the colon and helps calm immune activity there. Two other bacteria known for supporting gut health followed a similar downward trend without reaching all six diseases: Roseburia species were reduced in 76% of studies (across five of six diseases) and Akkermansia muciniphila, a bacterium that maintains the gut's protective mucus layer, was reduced in 71% of studies (also five of six diseases). The preprint, posted on Research Square, also reports that functional analysis of the pooled data showed reduced butyrate synthesis pathways across all six conditions, with the steepest drops in inflammatory bowel disease (down 68%) and multiple sclerosis (down 54%).

Rheumatoid Arthritis, Lupus, MS, T1D, IBD and AS All Carry the Signature

This matters directly if you have one of the six conditions studied: rheumatoid arthritis, systemic lupus erythematosus (SLE), multiple sclerosis, type 1 diabetes, inflammatory bowel disease, or ankylosing spondylitis, because the meta-analysis found the shared bacterial depletion in every one of them rather than in just one or two. Alongside the shared signature, the researchers found disease-specific patterns worth knowing about. Rheumatoid arthritis patients showed expansion of Prevotella copri in 67% of RA studies, particularly pronounced in new, untreated cases. Lupus patients showed enrichment of Ruminococcus gnavus in 82% of SLE studies, correlating with disease activity scores. Ankylosing spondylitis patients showed more Klebsiella pneumoniae, a bacterium researchers have proposed, but not proven, may trigger immune cross-reactivity with the HLA-B27 gene variant common in AS. If this cross-disease pattern holds up under peer review, it would support the idea that a family of related mechanisms, rather than six unrelated diseases, may be at work in the gut.

How Researchers Pooled 47 Studies From 23 Countries

The researchers did not run a new clinical study; they combined existing ones. They systematically searched PubMed, Web of Science, and public repositories like NCBI's Gene Expression Omnibus, following the PRISMA 2020 reporting guidelines for systematic reviews, and ended up with 47 studies covering 3,847 autoimmune disease patients and 2,956 healthy controls from 23 countries. They graded the quality of each underlying study using the Newcastle-Ottawa Scale and rated 60% of the 47 studies as high quality. Using random-effects statistical models designed to account for differences between studies, they then pooled the results for each disease and flagged bacteria that came up depleted or enriched across multiple conditions rather than just one.

What the Findings Mean for Managing Your Own Condition

Nothing in this preprint shows that restoring F. prausnitzii or any other bacterium would change the course of RA, lupus, MS, T1D, IBD or AS, and the authors do not claim otherwise. What it means practically, for now, is that a "leaky gut" or dysbiosis (imbalanced gut microbiome) narrative some readers hear anecdotally has some pooled observational support behind the specific bacteria involved, which may be worth mentioning to a doctor or rheumatologist if you are already discussing diet or gut health as part of your care. It is not, however, a green light to try a specific probiotic or supplement expecting it to treat the underlying disease; the paper itself frames butyrate supplementation and probiotic strains as ideas for future clinical trials, not established treatments.

Preprint Status, Heterogeneity and an Unproven Causal Link

Three caveats matter here. First, this is a Research Square preprint that has not been peer-reviewed, so the findings could still change during review. Second, statistical heterogeneity across the pooled studies was moderate to high (I-squared values of 52 to 78%), meaning the underlying studies did not agree closely with each other, something the authors themselves list as a limitation tied to differing sequencing platforms and bioinformatics pipelines. Third, almost all of the underlying studies were cross-sectional, comparing patients and controls at a single point in time. That design cannot distinguish whether depleted bacteria contribute to autoimmune disease or whether having the disease, and its medications, simply changes the gut microbiome afterward. One of the two authors, El-kalam Busair, is affiliated with a company called Autgenix rather than an academic institution; the paper does not describe any product tied to this specific finding, and the authors state they have no competing interests.

What Comes Next: Trials and Longitudinal Studies

The authors call for longitudinal studies that track the same patients over time, along with randomized controlled trials of butyrate or butyrate-producing probiotics such as Faecalibacterium prausnitzii itself, to test whether restoring these bacteria changes disease outcomes rather than just tracking alongside them. They also point to Mendelian randomization, a genetic method for testing causality without a clinical trial, as a way future work could help separate cause from effect using this kind of pooled data.

Common Questions

Does this mean gut bacteria cause autoimmune disease?

No. The studies pooled here are almost all cross-sectional, comparing microbiomes at a single point in time, so they can show association but not whether bacterial changes come before or after disease onset.

Which bacteria were most consistently missing?

Faecalibacterium prausnitzii was the most consistent finding, depleted in 89% of the 47 studies and in all six autoimmune diseases examined, followed by Roseburia species and Akkermansia muciniphila.

Is this preprint peer-reviewed?

No. It was posted on Research Square in August 2026 and, as of this writing, has not gone through peer review at a journal.

Should I take a probiotic based on this?

The study does not test any probiotic or supplement. The authors describe such interventions as directions for future randomized trials, not proven treatments, so talk to your doctor before changing your regimen for an autoimmune condition.

References

1. Abdullah Ahmad, El-kalam Busair (2026). Cross-Disease Microbiome Signatures Associated with Autoimmune Disorders: A Comparative Meta-Analysis of Public Sequencing Datasets. https://doi.org/10.21203/rs.3.rs-10630518/v1
2. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. NIH. https://pubmed.ncbi.nlm.nih.gov/33782057/