By Adrian Stone, BHSc (Nutritional Medicine), BHSc (Naturopathy), Living Holistic Health — Gut health and autoimmune disease: what the research shows for rheumatoid arthritis, thyroid disease, lupus and type 1 diabetes, and the one pattern they share.
Your Gut Is Not Like Las Vegas · Part 5 of 5 · Part 1 · Part 2 · Part 3 · Part 4
We started this series with multiple sclerosis, an autoimmune disease that happens to attack the brain. We finish with the rest of the family: rheumatoid arthritis, autoimmune thyroid disease, lupus, type 1 diabetes. Four conditions, four different organs, four different specialists — and, when you look at the gut, a pattern that repeats.
That pattern — gut health and autoimmune disease moving together — is the point of this final part. It is not that the gut causes autoimmunity. Nobody has shown that, and the rule from Part 1 holds to the end: association is not cause. It is that across conditions with nothing else in common, the gut of people with autoimmune disease tends to look the same way. Fewer of the bacteria that make short-chain fatty acids. More of the ones that inflame. A gut wall that lets more through than it should.
If you have one of these diagnoses, you have almost certainly been told gut health and autoimmune disease are one problem with one answer. It isn’t. It is one of the places the work happens.
What Does the Gut Have to Do with Rheumatoid Arthritis?
More than almost any other autoimmune disease outside the gut itself. In 2013, a New York team found that people with new, untreated rheumatoid arthritis carried far more of one gut bacterium, Prevotella copri, than healthy controls, with a loss of protective organisms alongside it. The pattern has held up in later cohorts.
The 2013 study is a good example of what a careful gut study looks like. It sequenced stool from 114 people. It separated those with new-onset disease from those already on treatment, because the treatment changes the gut. Then it went back to the lab to ask what the organism actually does. In mice, Prevotella copri colonised the gut and made chemically induced colitis worse. That is a biological effect, not just a correlation — though colitis in a mouse is not arthritis in a person. It still isn’t proof that the bacterium causes arthritis in people. The arrow may run from an inflamed immune system to a gut that favours Prevotella. But it is the strongest single-organism story in autoimmunity.
Does diet change it? The honest answer from a 2026 randomised trial in Ireland is: partly. Forty people with rheumatoid arthritis were randomised to a Mediterranean diet or standard healthy-eating guidelines for twelve weeks. Both groups’ diets became measurably less inflammatory. Neither group’s patient-reported symptoms changed significantly in that time. Diet quality moved; how people felt, over twelve weeks, did not. I include that because it is exactly the kind of result the marketing skips, and because twelve weeks is short for a disease that runs for decades.
Is Gut Health Linked to Autoimmune Thyroid Disease?
Yes — the gut is different in both Hashimoto’s thyroiditis and Graves’ disease, and the differences track with thyroid antibodies. Two meta-analyses, in 2021 and 2023, found altered diversity and composition in autoimmune thyroid disease. One detail stands out: the strongest correlations were between thyroid peroxidase antibodies and bacterial abundance.
This is the condition I see most often in clinic among the four, so I want to be precise. The 2023 meta-analysis of 16 studies found that diversity actually ran higher in Hashimoto’s and lower in Graves’. So “more diversity is good” fails here, as it did in Part 1. What held across studies was a shift in which organisms were present. More Prevotella and Bifidobacterium in Hashimoto’s, and a relationship between the bacterial load and the antibody level. The earlier 2021 meta-analysis pooled eight studies and 196 patients and found the same broad shift. Fewer of the organisms usually counted as protective; more of the ones usually counted as harmful.
What none of this tells you is direction. Thyroid hormone itself changes gut motility — an underactive thyroid slows the bowel — and a slow bowel grows a different microbiome. The antibodies and the bacteria may both be downstream of the same immune shift. What it does tell you is that in Hashimoto’s, digestive symptoms are not a separate problem to be filed elsewhere. They are part of the same picture, and the same unglamorous work applies. If you have a thyroid diagnosis, our thyroid conditions page sets out how we approach that alongside your doctor.
What About Lupus and Type 1 Diabetes?
Both show the same shape of evidence: a gut that looks different, something that tracks with disease activity, and no proof of cause. In lupus, one gut commensal, Ruminococcus gnavus, was five times more abundant and tracked with kidney involvement. In type 1 diabetes, the largest infant study to date found the protective signal was a function, not a bacterium.
Lupus
The 2019 study looked at 61 women with lupus. Ruminococcus gnavus was expanded five-fold, and most in those with the most active disease. More striking, the patients had antibodies against that specific organism, and those antibodies tracked with their lupus antibodies and with kidney inflammation. Immunity to a gut commensal and immunity to the self were moving together. It was validated in two more cohorts. It remains an association.
Type 1 diabetes
The TEDDY study followed 783 children from three months of age with monthly stool samples, nearly 11,000 metagenomes in all. It followed them until they developed islet autoimmunity, type 1 diabetes, or didn’t. No single bacterium predicted the disease. What the children who did not develop the disease had more of was the machinery for fermentation and short-chain fatty acid production, regardless of which species carried it. “Taxonomically diffuse but functionally coherent” is how the authors put it. That is the sentence I would want anyone who has been sold a specific “good bacteria” product to read.
Why Do Gut Health and Autoimmune Disease Share One Pattern?
Because the immune system is trained in the gut, and the gut wall is where tolerance is taught. By most estimates the largest share of the body’s immune tissue sits along the intestine, learning what to attack and what to leave alone. When the short-chain fatty acid producers run low and the barrier loosens, the lessons change.
The mechanism runs through a few well-described routes. Short-chain fatty acids, butyrate above all, are the main fuel for the cells lining the colon. They are also one of the main signals that expands regulatory T cells, the immune cells whose job is to say “stand down”. Lose the bacteria that make them and both the barrier and the brake weaken. A looser barrier lets more bacterial fragments into the circulation, which keeps the immune system on alert. And a few organisms carry proteins that resemble our own, which is called molecular mimicry. An immune response trained on the bacterium can then cross-react with the thyroid, the joint, or the kidney. Every one of these is real. None of them is the whole story, and in any individual patient we usually can’t say which is operating.
A 2025 comprehensive synthesis of gut microbiota across autoimmune diseases reaches the same conclusion I reached over five articles. In rheumatoid arthritis, MS and type 1 diabetes — thyroid disease, as above, runs the other way on diversity — there is a consistent loss of specific protective taxa. And there is a clear need for larger, longer, better-controlled trials before anyone claims to have a treatment.
Can Improving Gut Health Change Autoimmune Disease?
Partly, on inflammation markers; not yet, on the disease. A 2026 meta-analysis pooled 28 randomised trials of probiotics, prebiotics, synbiotics and faecal transplant: 2,002 patients across eleven countries. It found lower CRP and TNF-α on average, strongest in rheumatoid arthritis, MS and inflammatory bowel disease. Heterogeneity was 80 to 98 per cent, which the authors call exploratory.
That review is worth reading for its limits as much as its findings. The trials disagreed with each other on strain, dose, duration and patient group so thoroughly that the pooled numbers cannot be turned into a recommendation. Lower CRP on average is not the same as fewer flares, less joint damage, or a lower thyroid antibody. Those outcomes were mostly not measured. If a practitioner tells you a capsule will “calm your immune system”, ask which trial, in which condition, measuring what.
The stronger, quieter evidence is the same as in every part of this series. Fibre feeds the short-chain fatty acid producers that run low in autoimmunity. A Mediterranean-style pattern lowers the dietary inflammatory load; the Irish trial showed that much, even without a symptom change in twelve weeks. And a gut that moves and is fed is a better place for the immune system to be trained. None of that is a cure. All of it is yours to do, and we plan all of it around the treatment your specialist has prescribed — including when it is taken.
Where Does a Naturopath Fit Alongside a Rheumatologist or Endocrinologist?
Alongside them. We don’t diagnose or treat autoimmune disease; that stays with your specialist and your doctor. Our part is the nutritional, herbal and lifestyle work that sits alongside their care. That means the diet quality, the digestive symptoms, the nutrient status, the sleep and the stress load that a specialist review isn’t designed to cover.
Nothing in this article is a reason to change an immune medication or a thyroid hormone dose. Those conversations belong with the prescriber, and we work around them, never against them. What we add is a long first appointment: the timeline, a system-by-system history, your diet and stress load, and a read of every report you bring. Then the terrain work. Our autoimmune conditions page sets out how that runs.
What the Whole Series Adds Up to
Five conditions. Five specialists. One gut, and one pattern: the fibre-fermenting bacteria run low, inflammation runs high, and the thing that helps is the same unglamorous plate every time. Your gut is not like Las Vegas — what happens there goes everywhere — and that is precisely why it is worth doing the boring work well.
We want the body to do most of the work. Our job is to create the conditions.
If you’re in Geelong or on the Bellarine, living with an autoimmune diagnosis and a gut nobody has looked at properly, the first appointment is where we start. Alongside your specialist, never instead.
Your Gut Is Not Like Las Vegas — a series on why what happens in the gut doesn’t stay there.
Part 1: The gut microbiome and multiple sclerosis
Part 2: ADHD and gut problems
Part 3: Parkinson’s and constipation
Part 4: Depression, anxiety and the gut-brain axis
Part 5: Autoimmunity beyond MS (this article)
Part 1: The gut microbiome and multiple sclerosis
Part 2: ADHD and gut problems
Part 3: Parkinson’s and constipation
Part 4: Depression, anxiety and the gut-brain axis
Part 5: Autoimmunity beyond MS (this article)
Frequently Asked Questions
Can gut bacteria cause autoimmune disease?
Not on current evidence. Specific organisms track with rheumatoid arthritis, lupus and thyroid disease, and in mice some of them worsen inflammation. In humans the evidence is association, and the immune disease itself reshapes the gut. The gut is one contributor alongside genetics, infections and other environmental factors.
Is the gut different in Hashimoto’s thyroiditis?
Yes. Meta-analyses find altered composition in autoimmune thyroid disease, with the strongest correlations between thyroid antibody levels and bacterial abundance. Diversity runs higher, not lower, in Hashimoto’s — so “more diversity is better” does not apply. Direction of cause is not established.
Will a probiotic calm my immune system?
Pooled trials across autoimmune conditions show lower inflammatory markers on average, but the studies disagree so widely that the result is exploratory, and flares, damage and antibody levels were mostly not measured. Diet has the steadier evidence. Discuss any supplement with your specialist.
What can I do about my gut if I have an autoimmune disease?
Eat for the short-chain fatty acid producers — fibre from vegetables, legumes and whole grains — in a Mediterranean-style pattern; take digestive symptoms seriously rather than filing them elsewhere; protect sleep and manage stress load. Keep all of it alongside your specialist’s treatment.
References
Research located via PubMed. All links go to the original papers.
- Scher JU, Sczesnak A, Longman RS, et al. Expansion of intestinal Prevotella copri correlates with enhanced susceptibility to arthritis. Elife. 2013;2:e01202. https://doi.org/10.7554/eLife.01202
- Curran M, Canning N, Wrenne A, et al. Comparison of Mediterranean and healthy eating guideline interventions on the dietary inflammatory index in rheumatoid arthritis: results from a dietary randomised controlled intervention trial. Eur J Nutr. 2026;65(4). https://doi.org/10.1007/s00394-026-03987-9
- Alkader DAA, Asadi N, Solangi U, et al. Exploring the role of gut microbiota in autoimmune thyroid disorders: a systematic review and meta-analysis. Front Endocrinol. 2023;14:1238146. https://doi.org/10.3389/fendo.2023.1238146
- Gong B, Wang C, Meng F, et al. Association between gut microbiota and autoimmune thyroid disease: a systematic review and meta-analysis. Front Endocrinol. 2021;12:774362. https://doi.org/10.3389/fendo.2021.774362
- Azzouz D, Omarbekova A, Heguy A, et al. Lupus nephritis is linked to disease-activity associated expansions and immunity to a gut commensal. Ann Rheum Dis. 2019;78(7):947-956. https://doi.org/10.1136/annrheumdis-2018-214856
- Vatanen T, Franzosa EA, Schwager R, et al. The human gut microbiome in early-onset type 1 diabetes from the TEDDY study. Nature. 2018;562(7728):589-594. https://doi.org/10.1038/s41586-018-0620-2
- Adawi M. The role of gut microbiota in autoimmune disease progression and therapy: a comprehensive synthesis. Front Microbiomes. 2025;4:1553243. https://doi.org/10.3389/frmbi.2025.1553243
- Ashkanani G, Rob M, Yousef M, et al. The effects of microbiome modulating therapies on inflammatory markers in autoimmune disease: a systematic review and meta-analysis. Nutrients. 2026;18(4):560. https://doi.org/10.3390/nu18040560
This article is general information only and is not a substitute for individual medical advice. If you have an autoimmune condition, please discuss any change to your diet, supplements or lifestyle with your specialist or GP. For private health consultation claiming, please enquire with your health fund to assess coverage. Nutrition consultations are covered by some private health funds — please check with yours first.
