Autoimmune Disease

A shared gut pattern across very different diseases

Autoimmune diseases happen when the immune system mistakenly attacks the body's own tissue, and despite affecting very different organs, from joints to nerves to the pancreas, several of these conditions share a common gut feature: increased intestinal permeability, often called a leaky gut. A specific test measuring how much of two sugar molecules, lactulose and mannitol, pass into urine after being swallowed is used to assess this. A higher-than-normal ratio, indicating a leakier gut barrier, has been found in people with multiple sclerosis, rheumatoid arthritis, type 1 diabetes, and coeliac disease.

Source: Gut Microbiota and Autoimmune Diseases: Mechanisms, Treatment, Challenges, and Future Recommendations

A specific, testable mechanism, not just a correlation

One proposed route is called molecular mimicry, where a bacterial protein resembles a protein made by the body closely enough that antibodies trained to fight the bacteria mistakenly attack the body's own tissue instead. A more specific version of this has been demonstrated for rheumatoid arthritis directly: certain gut bacteria, including Prevotella copri, produce enzymes that convert the amino acid arginine into citrulline on host proteins, and antibodies against these citrullinated proteins are a genuine, standard diagnostic marker doctors already test for in rheumatoid arthritis.

A leaky gut lets more than nutrients through

When the gut barrier is compromised, bacterial fragments called lipopolysaccharides can cross into the bloodstream, triggering the kind of widespread immune activation that's been linked to autoimmune flares. As with any probiotic-based approach to this, introducing helpful bacteria without also feeding them and the rest of the gut with fibre gives them far less chance of genuinely repairing that barrier, rather than just passing through a gut that stays leaky regardless.

What this means for you

Autoimmune diseases need proper diagnosis and disease-specific treatment from the right specialist, since this general gut-immune connection doesn't replace condition-specific care, and several conditions mentioned here, including rheumatoid arthritis, have their own dedicated page on this site with more detailed evidence. Persistent, unexplained joint pain, fatigue, or other symptoms suggestive of autoimmune disease are worth a proper medical work-up rather than assuming a gut-health explanation on their own. A varied, plant-rich, fibre-rich diet supports the same gut barrier this research ties to calmer, less permeable gut function across multiple autoimmune conditions. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.