In this article
Fibromyalgia is linked to measurable changes in the gut microbiome: a 2019 McGill University study in the journal Pain found that the gut bacteria of 77 women with fibromyalgia differed from those of 79 controls, and the size of the difference tracked symptom severity. In 2025 the same research group reported in Neuron that gut bacteria transferred from fibromyalgia patients into germ-free mice produced pain, which suggests the microbiome can contribute to symptoms rather than simply reflect them.
Gut-focused care, such as testing for small intestinal bacterial overgrowth (SIBO), dietary change and probiotics, is a reasonable add-on for many people with fibromyalgia, especially those with bloating or irritable bowel symptoms. The evidence is early, the trials are small, and none of these approaches replaces exercise, sleep care and the medications already approved for fibromyalgia.
At a Glance
- The connection: Minerbi and colleagues (Pain, 2019) found that the gut microbiome of women with fibromyalgia differs from that of controls, and that microbiome data alone could separate the two groups with machine learning.
- Key pathways: Researchers propose that gut dysbiosis, intestinal permeability (“leaky gut”), systemic inflammation and altered neurotransmitter and short-chain fatty acid production link the gut to fibromyalgia pain, fatigue and fibro fog.
- SIBO link: Pimentel and colleagues (Annals of the Rheumatic Diseases, 2004) found an abnormal lactulose breath test in all 42 fibromyalgia patients tested, and the degree of pain tracked the hydrogen level on the test.
- Interventions studied: Small trials of probiotics, low-FODMAP and anti-inflammatory diets, SIBO treatment and fecal microbiota transplant (FMT) show mixed results; probiotics have helped attention and decision making more consistently than pain.
- Status: Gut-targeted therapy is not part of the EULAR fibromyalgia recommendations (Macfarlane et al., 2017), so it is best treated as an add-on to standard care that rheumatologists, gastroenterologists and integrative physicians coordinate.
Fibromyalgia: A Condition Without Clear Answers
Fibromyalgia affects an estimated 2-4% of the global population, causing widespread pain, fatigue, cognitive difficulties (“fibro fog”), sleep disturbances, and heightened sensitivity to stimuli. Despite decades of research, the underlying cause remains unclear. The diagnosis is clinical, meaning there is no blood test, imaging study, or biopsy that confirms it.
Clinicians usually diagnose fibromyalgia with the American College of Rheumatology (ACR) criteria, which score how widespread the pain is and how severe the fatigue, unrefreshing sleep and cognitive symptoms are. Researchers now describe fibromyalgia as a disorder of central sensitization, sometimes called nociplastic pain, in which the nervous system amplifies pain signals.
This diagnostic frustration has pushed researchers to look beyond the central nervous system for contributing factors. One of the most compelling threads in recent fibromyalgia research points directly to the gut. For a broader overview of the condition, see our fibromyalgia guide.
Gut symptoms are common in fibromyalgia. Irritable bowel syndrome (IBS) overlaps heavily with it, and many patients report bloating, abdominal pain and irregular bowel habits alongside their widespread pain. The fibromyalgia condition overview covers the full symptom picture and the treatments clinics offer for it.
The Microbiome Is Different in Fibromyalgia Patients
In 2019, a landmark study published in the journal Pain by Minerbi et al. made headlines. The McGill University team analyzed the gut microbiome of 77 women with fibromyalgia and 79 controls using 16S ribosomal RNA sequencing and whole-genome sequencing. Their findings were striking:
- Fibromyalgia patients had significantly different microbiome compositions compared to controls
- Certain bacterial species were either elevated or depleted in fibromyalgia patients
- The degree of microbiome alteration correlated with symptom severity; patients with the most abnormal microbiomes had the worst pain, fatigue, and cognitive symptoms
- Serum levels of butyrate and propionate, two short-chain fatty acids made by gut bacteria, also differed in the fibromyalgia group
- Machine learning algorithms could distinguish fibromyalgia patients from healthy controls based on microbiome data alone with approximately 87% accuracy
The authors described it as the first demonstration of gut microbiome alteration in a pain condition that does not start in the gut. FM-related variables explained more of the variation between microbiomes than any other innate or environmental variable they measured.
Follow-up studies have confirmed and expanded on these findings. Specific bacterial groups implicated include reduced Faecalibacterium prausnitzii (a key anti-inflammatory species), altered Bacteroidetes-to-Firmicutes ratios, and changes in butyrate-producing bacteria that are essential for gut barrier integrity.
An altered microbiome in fibromyalgia patients does not automatically mean the gut is causing the disease. It is possible that fibromyalgia itself (through stress, medications, altered diet, reduced activity) changes the microbiome. It is also possible that microbiome changes contribute to or amplify symptoms. The relationship may be bidirectional. Current evidence is suggestive but not definitive about the direction of causality, although the 2025 mouse transfer study described below is the strongest sign so far that the microbiome can drive pain.
The SIBO-Fibromyalgia Connection
Small intestinal bacterial overgrowth (SIBO) occurs when bacteria that normally reside in the large intestine colonize the small intestine. This causes bloating, gas, abdominal pain, diarrhea or constipation, and nutrient malabsorption. For more on this condition, see our SIBO guide.
Research linking SIBO and fibromyalgia dates back to a 2004 study by Pimentel et al. in the Annals of the Rheumatic Diseases. They found that 100% of their fibromyalgia cohort tested positive for SIBO using lactulose breath testing, compared to a much lower rate in controls: 42 of 42 fibromyalgia patients had an abnormal test, against 3 of 15 controls. The degree of somatic pain in the fibromyalgia group correlated with the amount of hydrogen on the breath test. While subsequent studies have not replicated the 100% figure, they consistently show elevated SIBO rates in fibromyalgia patients, typically ranging from 30-60%.
Even more compelling: some studies have shown that treating SIBO with antibiotics (rifaximin) or herbal antimicrobials led to improvement in fibromyalgia pain scores, not just GI symptoms. This suggests that bacterial overgrowth in the small intestine may be contributing to systemic symptoms through inflammatory pathways. These studies are small and mostly uncontrolled, and rifaximin is prescribed off label for SIBO, so the result is a reason to test rather than a reason to treat everyone.
The lactulose test used in 2004 is now known to overcall SIBO in some people, because fast gut transit lets lactulose reach the colon early. Gastroenterologists interpret results with that in mind, and the article comparing IBS vs SIBO explains how the two overlap. The SIBO treatment guide covers antibiotic, herbal and dietary approaches in more detail.
How SIBO May Amplify Fibromyalgia Symptoms
- Endotoxin production: Overgrown bacteria produce lipopolysaccharide (LPS), an endotoxin that triggers systemic inflammation when it crosses the gut barrier
- Nutrient malabsorption: SIBO impairs absorption of B12, iron, and fat-soluble vitamins; deficiencies in these nutrients can worsen fatigue and neurological symptoms
- D-lactic acid production: Certain bacteria produce D-lactic acid, which can cause neurological symptoms including brain fog, fatigue, and impaired cognition
- Bile acid deconjugation: Bacterial overgrowth disrupts bile acid metabolism, affecting fat absorption and liver function
Leaky Gut: The Bridge Between Gut and Systemic Symptoms
Intestinal permeability, commonly called “leaky gut,” is the mechanism that most plausibly connects gut dysbiosis to the widespread pain and inflammation seen in fibromyalgia. For a deeper exploration, see our leaky gut guide.
The intestinal lining is a selectively permeable barrier. Tight junction proteins between epithelial cells allow nutrients to pass while blocking bacteria, toxins, and large undigested food particles. When these tight junctions become compromised, the barrier “leaks.”
Several studies have documented increased intestinal permeability in fibromyalgia patients:
- Elevated serum zonulin (a protein that regulates tight junction permeability) in fibromyalgia cohorts
- Increased circulating LPS (bacterial endotoxin) levels, suggesting bacterial products are crossing the gut barrier
- Higher levels of antibodies against LPS and intestinal proteins, indicating immune activation from gut-derived antigens
Increased intestinal permeability is a measurable research finding, while “leaky gut syndrome” is not a recognized diagnosis in mainstream gastroenterology. Gastroenterologists accept that the barrier can weaken; what remains unsettled is how much that weakening explains symptoms outside the gut.
The Inflammation Cascade
Here is the proposed pathway from gut dysfunction to fibromyalgia symptoms:
1. Dysbiosis and/or SIBO alter the gut environment, reducing protective species and increasing endotoxin-producing bacteria.
2. Tight junction breakdown occurs as the gut lining is damaged by bacterial toxins, nutritional deficiencies (especially zinc, vitamin D, and glutamine), and local inflammation.
3. Bacterial products (LPS) enter the bloodstream, triggering an immune response. Toll-like receptor 4 (TLR4) on immune cells recognizes LPS and activates inflammatory signaling.
4. Systemic inflammation follows, with elevated pro-inflammatory cytokines (IL-6, TNF-α, IL-8) that have been consistently documented in fibromyalgia patients.
5. Central sensitization is amplified. Inflammatory cytokines cross the blood-brain barrier, activate microglia (the brain’s immune cells), and increase central nervous system pain processing. This is the hallmark of fibromyalgia: the brain’s pain volume is turned up.
6. Symptoms intensify: Widespread pain, fatigue, cognitive impairment, and sleep disruption.
| Pathway | What Goes Wrong | Fibromyalgia Symptom |
|---|---|---|
| Microbiome dysbiosis | Loss of anti-inflammatory species, reduced butyrate | GI symptoms, systemic inflammation |
| SIBO | Bacterial overgrowth producing endotoxins, D-lactic acid | Bloating, brain fog, fatigue |
| Intestinal permeability | Tight junction breakdown allows LPS translocation | Immune activation, widespread pain |
| Neuroinflammation | Cytokines cross blood-brain barrier, microglial activation | Central sensitization, heightened pain |
| Serotonin/tryptophan | Altered gut serotonin production, tryptophan steal via IDO pathway | Mood disturbance, sleep disruption, pain sensitivity |
How Does the Gut-Brain Axis Affect Fibromyalgia Pain?
The gut-brain axis is the two-way signaling network between the digestive tract and the central nervous system. It runs through the vagus nerve, the immune system, hormones such as cortisol, and chemical messengers made or modified by gut bacteria. In fibromyalgia, researchers suspect this network helps set how strongly the brain amplifies pain.
Short-chain fatty acids are one channel. Gut bacteria ferment fiber into butyrate, propionate and acetate, which feed the cells of the gut lining and calm immune activity; the 2019 Pain study found altered blood levels of butyrate and propionate in fibromyalgia. Tryptophan is another: gut microbes influence how much of it becomes serotonin and how much is diverted into the kynurenine pathway during inflammation.
Stress closes the loop. Chronic pain and poor sleep raise stress hormones, which slow gut transit and change the microbiome, which in turn feeds inflammation and pain sensitivity. That cycle is one reason gut symptoms, brain fog and widespread pain so often travel together in fibromyalgia.
Can a Fecal Microbiota Transplant Help Fibromyalgia?
Fecal microbiota transplantation (FMT) moves stool bacteria from a screened healthy donor into a patient's gut. It is the most direct test of whether the microbiome drives fibromyalgia symptoms, and the first results point in that direction. They come from small, early studies, though.
Cai and colleagues, a team including Minerbi and Khoutorsky at McGill, reported in Neuron in 2025 that bacteria from fibromyalgia patients transplanted into germ-free mice caused pain and immune changes. Bacteria from healthy controls did not. Replacing the fibromyalgia microbiota with a healthy one eased the pain in mice, and a small open-label trial in women with fibromyalgia linked healthy-donor FMT with less pain and better quality of life.
A separate open-label randomized study in The Journal of Pain (2024) followed 45 patients and found lower pain, sleep and anxiety scores after FMT. Neither human study had a placebo arm. In the United States, the FDA regulates FMT as a biologic and allows it outside clinical trials mainly for recurrent Clostridioides difficile infection, so FMT for fibromyalgia remains a research procedure. The article on fecal transplants and gut health covers how FMT works.
Probiotics for Fibromyalgia: What the Research Shows
If the gut microbiome is altered in fibromyalgia, can fixing it improve symptoms? Several clinical trials have tested this hypothesis with probiotics.
A 2018 systematic review by Roman and colleagues in Beneficial Microbes found that the probiotic evidence in fibromyalgia and chronic fatigue syndrome was still limited. The best data at the time came from chronic fatigue syndrome: Lactobacillus casei Shirota taken for 8 weeks reduced anxiety scores.
The same Spanish group ran a pilot randomized controlled trial in Scientific Reports (2018) using a multispecies probiotic for 8 weeks. Impulsivity and decision making improved in the probiotic group, but pain, fibromyalgia impact, anxiety and depression did not improve more than with placebo.
A 2021 follow-up pilot trial by Cardona and colleagues in 31 patients found that a multispecies probiotic reduced errors on an attention task after 8 weeks. A larger 2021 randomized trial by Calandre and colleagues tested the multi-strain probiotic VSL#3 for 12 weeks in 110 fibromyalgia patients with gut symptoms and found no benefit over placebo for abdominal pain, bloating or fibromyalgia severity.
The pattern across studies is consistent: probiotics tend to improve cognitive symptoms and some measures of mood more reliably than they reduce pain intensity. This makes biological sense. Probiotics primarily affect gut-brain signaling and inflammation, which would impact cognitive and emotional symptoms before modifying deeply entrenched central pain sensitization.
Based on current evidence, the following strains have the most data in fibromyalgia or related chronic pain conditions:
- Lactobacillus casei Shirota: Anxiety, studied mainly in chronic fatigue syndrome
- Bifidobacterium longum: Gut-brain signaling and mood, studied mainly outside fibromyalgia
- Lactobacillus rhamnosus GG: Gut barrier integrity, anti-inflammatory effects
- Multi-strain formulations: Attention and decision making in small fibromyalgia trials
Give any probiotic at least 8-12 weeks before evaluating its effect on fibromyalgia symptoms. The microbiome takes time to shift.
Dietary Interventions for the Fibromyalgia-Gut Connection
Beyond probiotics, several dietary strategies target the gut-fibromyalgia link:
Low-FODMAP diet: Reduces fermentable carbohydrates that feed bacterial overgrowth. Particularly useful if IBS-like symptoms coexist with fibromyalgia (which they do in 30-70% of patients). Marum and colleagues (Scandinavian Journal of Pain, 2016) reported less pain and better daily function in fibromyalgia patients who followed it, in a small study without a control group. The low-FODMAP diet guide explains the elimination and reintroduction phases.
Anti-inflammatory diet: Emphasizes omega-3 fatty acids, colorful vegetables, berries, turmeric, and ginger while reducing processed foods, refined sugar, and industrial seed oils. Several small studies show symptom improvement in fibromyalgia patients following Mediterranean-style diets.
Gluten-free diet: Some fibromyalgia patients (particularly those with elevated anti-gliadin antibodies) report improvement on a gluten-free diet. A 2014 study in Rheumatology International found that a subgroup of fibromyalgia patients with gluten sensitivity showed significant symptom improvement after gluten elimination. That study, by Isasi and colleagues, was a case series of 20 patients. A later randomized trial by Slim and colleagues (Nutrients, 2017) found a gluten-free diet worked no better than a calorie-reduced diet, so testing for celiac disease comes before cutting gluten long term.
Bone broth and glutamine: L-glutamine is the primary fuel source for enterocytes (intestinal lining cells) and supports gut barrier repair. While large clinical trials in fibromyalgia are lacking, the biological rationale for gut-barrier support is sound.
A registered dietitian who works with IBS can run these diets without leaving gaps in fiber, calcium or protein. The fibromyalgia diet article lists foods by category.
Testing and Assessment
If you suspect your gut is contributing to fibromyalgia symptoms, several tests can provide useful information:
- SIBO breath test: Lactulose or glucose breath test to check for small intestinal bacterial overgrowth; current tests measure both hydrogen and methane
- Celiac blood test: Tissue transglutaminase IgA (tTG-IgA), taken while you still eat gluten, rules celiac disease in or out before any gluten-free trial
- Detailed stool analysis: Evaluates microbiome diversity, inflammatory markers, digestive function, and pathogenic organisms
- Zonulin/intestinal permeability testing: Blood test measuring zonulin levels as a proxy for gut barrier integrity; researchers have questioned whether commercial zonulin kits measure zonulin accurately
- Food sensitivity testing: IgG panels are controversial, but elimination diets remain the gold standard for identifying food triggers
Breath tests and celiac blood tests are standard medical tests that insurance often covers. Stool microbiome panels and zonulin tests are usually cash pay, and no guideline yet tells clinicians how to act on their results in fibromyalgia.
A Practical Approach: Where to Start
Given the current evidence, here is a reasonable, stepwise approach for fibromyalgia patients who want to address the gut connection:
Step 1: Clean up the diet. Remove processed foods, excess sugar, and common triggers (gluten, dairy) for a 4-week trial. Follow a Mediterranean-style or anti-inflammatory eating pattern. Get a celiac blood test first if you plan to drop gluten.
Step 2: Get tested for SIBO, especially if you have significant bloating, gas, or IBS-type symptoms.
Step 3: Start a well-researched probiotic. Multi-strain formulations or specific strains listed above. Commit to at least 8-12 weeks.
Step 4: Support gut barrier function with L-glutamine (5-10 g/day), zinc carnosine, and vitamin D optimization.
Step 5: Reassess symptoms at 3 months. Track pain levels, fatigue, cognitive function, and GI symptoms. If improvements are noted, continue and consider in-depth stool testing for more targeted interventions.
Keep the core fibromyalgia plan running alongside these steps. EULAR recommends graded exercise as the first-line treatment, and the FDA has approved pregabalin, duloxetine and milnacipran for fibromyalgia. The fibromyalgia treatment guide compares those options with integrative ones.
Who Treats the Gut Side of Fibromyalgia?
No single specialty owns the gut and fibromyalgia connection. Rheumatologists usually make the fibromyalgia diagnosis, gastroenterologists run breath tests, celiac workups and colonoscopies, and functional or integrative medicine physicians often coordinate diet, probiotic and SIBO plans. Registered dietitians handle low-FODMAP and elimination diets.
Gut symptoms that look like irritable bowel syndrome deserve a standard medical workup first, especially with weight loss, blood in the stool or symptoms that start after age 50. The IBS treatment guide and the chronic pain treatment guide describe what clinics offer for each.
Some people with fibromyalgia also look at off-label options such as low-dose naltrexone for fibromyalgia or hyperbaric oxygen therapy, which a 2015 trial by Efrati and colleagues in PLOS ONE studied in fibromyalgia. Hyperbaric oxygen is cash pay for this use and not FDA cleared for it; the hyperbaric oxygen therapy guide explains the evidence, and the directory of hyperbaric oxygen clinics lists providers. Listing order in the directory is not paid ranking, Featured slots are labeled and capped, Verified means a clinic passed credential checks rather than paid for the label, and the directory is free for patients. Inclusion is not an endorsement; the guide to Featured, Verified and organic listings explains each label.
Frequently Asked Questions
Does fixing your gut make fibromyalgia go away?
Fixing gut problems does not make fibromyalgia go away, but it can ease symptoms for some patients. Research by Minerbi and colleagues (2019) and Cai and colleagues (2025) suggests the microbiome contributes to fibromyalgia pain, and small trials show gains in gut symptoms, attention and quality of life. Gut-focused care works best as one part of a plan that also includes graded exercise, sleep care, stress management and, where appropriate, medications such as duloxetine, pregabalin or milnacipran.
How long does it take for gut-focused interventions to improve fibromyalgia symptoms?
Gut symptoms such as bloating and irregular bowel habits often improve within 2-4 weeks of a diet change or SIBO treatment. Pain, fatigue and fibro fog usually take longer, often 8-12 weeks or more, which matches the 8 to 12 week length of most probiotic trials in fibromyalgia. Microbiome change and gut barrier repair are gradual, so track symptoms for about three months before judging whether an approach is working.
Should I get tested for SIBO if I have fibromyalgia?
SIBO testing is reasonable for anyone with fibromyalgia who has bloating, gas, abdominal pain or irregular bowels. Pimentel and colleagues (2004) found abnormal lactulose breath tests in all 42 fibromyalgia patients they tested, and later studies still show higher SIBO rates than in the general population. If your fibromyalgia shows up mainly as pain and fatigue without gut symptoms, testing is less pressing but still worth discussing with a gastroenterologist.
Can antibiotics for SIBO help fibromyalgia pain?
Antibiotics for SIBO help fibromyalgia pain in some patients, but not in all. Small studies report lower pain scores after rifaximin or herbal antimicrobials, and the 2004 Pimentel study found that pain tracked breath test hydrogen levels. The trials are small and mostly uncontrolled, rifaximin is off label for SIBO, and treating SIBO alone rarely resolves every fibromyalgia symptom. For patients who test positive, treatment addresses a real contributing factor.
Are there specific foods that make fibromyalgia worse through the gut?
High-FODMAP foods such as garlic, onion, wheat, dairy and beans are the most common gut triggers, followed by processed sugar, alcohol, excess caffeine and, for some people, gluten even without celiac disease. Individual triggers vary widely. A structured elimination diet, ideally run with a registered dietitian, is more reliable than a generic foods to avoid list, because it reintroduces foods one at a time and shows which ones actually matter for you.
Is the gut-fibromyalgia connection accepted by mainstream medicine?
Mainstream research increasingly recognizes the gut and fibromyalgia connection, with studies in Pain, Neuron, Rheumatology International and the Annals of the Rheumatic Diseases. Gut-targeted therapy is not yet part of the ACR criteria or the 2017 EULAR fibromyalgia recommendations, and larger placebo-controlled trials are still needed. Many rheumatologists, gastroenterologists and integrative physicians already ask about gut symptoms as part of a fibromyalgia workup and treat SIBO, IBS or celiac disease when tests confirm them.
