SIBO and Systemic Sclerosis: Could Small Intestinal Bacterial Overgrowth Affect Lung Health?
Why Is SIBO So Common in Systemic Sclerosis?
Systemic sclerosis, also known as scleroderma, can affect far more than the skin.
The gastrointestinal tract is one of the most commonly involved organ systems.
Patients may experience:
reflux
difficulty swallowing
early satiety
bloating
abdominal distension
diarrhea
constipation
weight loss
malabsorption
One particularly important gastrointestinal complication is small intestinal bacterial overgrowth, or SIBO.
SIBO occurs when the number or composition of microorganisms in the small intestine becomes abnormal.
This is especially relevant in systemic sclerosis because the disease can impair normal intestinal movement.
When intestinal contents move too slowly, bacteria have greater opportunity to accumulate and proliferate.
The result can be a cycle of:
intestinal dysmotility → bacterial overgrowth → fermentation → gastrointestinal symptoms → malabsorption and nutritional problems
But there is another reason SIBO has become interesting in systemic sclerosis.
Systemic sclerosis is also an important cause of interstitial lung disease (SSc-ILD).
And recent human research suggests that patients with SSc-ILD may have distinct gut microbial patterns.
This raises a fascinating question:
Could SIBO and intestinal dysbiosis have any relationship with lung disease in systemic sclerosis?
The answer requires careful interpretation.
SIBO is clinically important in systemic sclerosis.
The gut microbiome is increasingly associated with SSc-ILD.
But we do not currently have evidence proving that SIBO causes lung fibrosis—or that treating SIBO slows SSc-ILD.
Understanding this distinction is essential.
What Is SIBO?
The small intestine normally contains microorganisms, but its microbial population and density differ from those of the colon.
Several protective mechanisms help regulate this environment.
These include:
gastric acid
pancreatic and biliary secretions
intestinal immune defenses
normal anatomy
coordinated intestinal motility
the migrating motor complex
When these protective mechanisms are disrupted, microorganisms may accumulate excessively in the small intestine.
This is known as small intestinal bacterial overgrowth.
SIBO can interfere with digestion and nutrient absorption.
Depending on its severity and underlying cause, it may produce symptoms ranging from mild bloating to significant malnutrition.
Why Does Systemic Sclerosis Cause SIBO?
The major connection is gastrointestinal dysmotility.
Systemic sclerosis can affect the smooth muscle, nerves, connective tissue and blood vessels involved in gastrointestinal function.
As the disease progresses, intestinal contractions may become weaker or less coordinated.
Food and intestinal contents then move more slowly.
This creates an environment in which bacteria can accumulate.
A simplified pathway is:
systemic sclerosis ↓ intestinal neuromuscular dysfunction and fibrosis ↓ slower intestinal transit ↓ microbial stasis ↓ SIBO
This is why simply treating bacteria without addressing motility may result in recurrence.
How Common Is SIBO in Systemic Sclerosis?
SIBO is substantially more common in systemic sclerosis than in the general population.
Published estimates vary according to:
diagnostic technique
patient population
disease severity
definition of SIBO
Systematic reviews have estimated that approximately one-third to two-fifths of patients with systemic sclerosis may have SIBO, although individual studies report a broad range.
A recent 2025 review continues to identify SIBO as an important gastrointestinal manifestation of systemic sclerosis, closely linked with intestinal dysmotility and altered microbial ecology.
This makes SIBO one of the gastrointestinal conditions clinicians should actively consider when compatible symptoms are present.
What Are the Symptoms of SIBO in Systemic Sclerosis?
Symptoms may include:
bloating
abdominal distension
excessive gas
abdominal discomfort
diarrhea
constipation
altered bowel habits
nausea
early satiety
More significant disease may contribute to:
malabsorption
weight loss
vitamin deficiencies
nutritional deterioration
However, symptoms are not specific.
Bloating does not automatically mean SIBO.
Systemic sclerosis itself can cause dysmotility and gastrointestinal symptoms even without bacterial overgrowth.
Other disorders may also produce similar symptoms.
Therefore, diagnosis should be based on the overall clinical picture rather than symptoms alone.
Why Does SIBO Matter in Someone With Lung Disease?
Even if SIBO does not directly cause pulmonary fibrosis, it can still be clinically relevant to a patient with SSc-ILD.
A patient with significant lung disease needs adequate:
calories
protein
micronutrients
muscle mass
physical reserve
Chronic gastrointestinal symptoms can make this difficult.
If SIBO contributes to poor intake, diarrhea, malabsorption or weight loss, it may indirectly reduce the patient’s physiological reserve.
This becomes particularly important in advanced ILD, where maintaining muscle and nutritional status can affect:
exercise capacity
rehabilitation
frailty
quality of life
transplantation candidacy
Therefore, gastrointestinal health should not be dismissed simply because we cannot yet prove a direct antifibrotic benefit.
Is SIBO the Same as Gut Dysbiosis?
No.
These terms are often used interchangeably online, but they describe different concepts.
SIBO refers specifically to abnormal microbial overgrowth or composition in the small intestine.
Gut dysbiosis is a broader term describing disruption of the intestinal microbial ecosystem.
A patient can have gut dysbiosis without SIBO.
A patient with SIBO will have abnormal microbial ecology in the small intestine, but this does not necessarily tell us what is happening in the colon.
This distinction becomes important when interpreting microbiome studies.
Most research microbiome studies analyze stool, which predominantly reflects distal intestinal microbial communities.
A stool microbiome analysis is therefore not equivalent to a SIBO breath test.
What Does SIBO Have to Do With the Gut–Lung Axis?
The gut–lung axis describes communication between intestinal and respiratory systems through immune and metabolic pathways.
Intestinal microorganisms produce compounds capable of influencing the host.
These include:
short-chain fatty acids
tryptophan metabolites
bile-acid metabolites
microbial peptides
bacterial cell-wall components
If SIBO substantially changes intestinal microbial activity, it could theoretically alter the profile of these signals.
However, whether this has a clinically meaningful effect on SSc-ILD remains unknown.
What Does the New SSc-ILD Microbiome Evidence Show?
This is where the field has become particularly interesting.
An international study investigated 285 patients with systemic sclerosis from seven centers across five continents.
Approximately 62.5% had ILD.
Researchers used shotgun metagenomic sequencing to characterize intestinal microbial communities.
Patients with SSc-ILD demonstrated a distinct microbial signature compared with systemic sclerosis patients without ILD.
In addition, particular microbial species and microbial functional pathways were associated with the radiological extent of lung disease.
This provides important human evidence supporting a relationship between intestinal microbial biology and SSc-ILD.
But it is crucial to understand what the study did not demonstrate.
It did not show that SIBO causes SSc-ILD.
It did not show that treating SIBO improves pulmonary fibrosis.
And it did not establish a microbiome treatment for SSc-ILD.
SIBO and Gut Dysbiosis May Overlap
Although SIBO and colonic dysbiosis are different concepts, they can coexist.
Systemic sclerosis creates several factors capable of disrupting microbial ecology simultaneously:
reduced intestinal motility
altered transit time
proton-pump inhibitor exposure
antibiotics
dietary restriction
malabsorption
autoimmune inflammation
disease severity
This makes it difficult to determine which microbial changes are primary and which are secondary.
Could SIBO Increase Systemic Inflammation?
Potentially.
Excessive or abnormal microbial activity may alter exposure to bacterial products and microbial metabolites.
One molecule frequently discussed is lipopolysaccharide, or LPS.
LPS can activate innate immune pathways such as:
TLR4 → NF-κB
which may increase inflammatory cytokines.
Intestinal-barrier dysfunction could theoretically increase systemic exposure to such microbial molecules.
However, direct evidence connecting SIBO-induced endotoxemia with progression of human SSc-ILD remains insufficient.
This is currently a mechanistic hypothesis.
SIBO, SCFAs and Microbial Metabolism
Another potential pathway involves short-chain fatty acids.
SCFAs include:
acetate
propionate
butyrate
These compounds are produced through microbial fermentation.
They can influence:
intestinal-barrier integrity
immune regulation
Treg activity
inflammatory pathways
SIBO can alter where and how fermentation occurs.
But it would be overly simplistic to say that SIBO merely causes “low butyrate.”
Different microbial communities may produce different metabolic profiles.
The important issue may ultimately be microbial function rather than bacterial quantity alone.
SIBO and Tryptophan Metabolism
Gut microorganisms also metabolize tryptophan into compounds capable of influencing immune signaling.
Some microbial indoles interact with the aryl hydrocarbon receptor, or AhR.
AhR signaling can affect:
epithelial integrity
immune tolerance
Treg/Th17 balance
Abnormal microbial ecology could therefore theoretically alter tryptophan-derived signaling.
This represents another possible gut–immune–lung pathway, but its role specifically in SIBO-associated SSc-ILD has not been established.
The Immune System May Be the Missing Link
Systemic sclerosis involves dysregulated immunity.
The microbiome also regulates immunity.
This overlap makes the gut–lung hypothesis particularly attractive.
Gut microorganisms can interact with:
regulatory T cells
Th17 cells
macrophages
dendritic cells
B-cell responses
If dysbiosis or SIBO modifies these pathways, it could potentially influence systemic autoimmune activity.
Whether that translates into measurable changes in pulmonary fibrosis remains an unanswered question.
Reflux May Be More Directly Relevant to the Lung
There is another gastrointestinal issue in systemic sclerosis with a more direct anatomical connection to the lung:
gastroesophageal reflux and microaspiration.
Systemic sclerosis commonly impairs esophageal function.
The lower esophageal sphincter may become weak, and esophageal clearance may become poor.
This can cause severe reflux.
Small amounts of gastric or esophageal contents may then enter the respiratory tract.
This is called microaspiration.
Microaspiration Versus the Gut–Lung Axis
These mechanisms should not be confused.
The gut–lung axis generally refers to:
microbiome → metabolites/immune signals → systemic circulation → lung
Microaspiration involves:
esophagus/stomach → refluxed material → direct entry into the respiratory tract
A patient with systemic sclerosis may potentially have both.
This is why gastrointestinal evaluation in SSc-ILD can be relevant for more than one reason.
Could Reflux Worsen SSc-ILD?
Several studies have found associations between esophageal dysfunction, reflux severity and pulmonary involvement in systemic sclerosis.
Microaspiration provides a biologically plausible mechanism for repetitive epithelial injury.
However, association does not establish that reflux is responsible for all progression of SSc-ILD.
Treating clinically significant reflux remains important for appropriate gastrointestinal indications.
Whether aggressive reflux treatment specifically alters ILD progression remains more complex.
Does Treating SIBO Improve Lung Fibrosis?
At present, there is no convincing evidence that treating SIBO:
improves FVC
improves DLCO
reduces HRCT fibrosis
prevents progressive pulmonary fibrosis
reduces the need for antifibrotic therapy
improves survival from SSc-ILD
Therefore, SIBO treatment should not be presented as treatment for lung fibrosis.
This is an important evidence boundary.
Why Treat SIBO Then?
Because SIBO itself can be clinically significant.
Treatment may be appropriate to address:
bloating
diarrhea
abdominal discomfort
malabsorption
nutritional deficiency
weight loss
Improving gastrointestinal function may also make it easier for patients to maintain adequate nutrition and participate in rehabilitation.
These are meaningful clinical outcomes even without proving an antifibrotic effect.
How Is SIBO Diagnosed?
Breath testing is commonly used.
Patients consume a substrate such as:
glucose
lactulose
and breath samples are collected over time.
The test measures gases generated by microbial metabolism, particularly:
hydrogen
methane
Interpretation should follow accepted clinical criteria.
No test is perfect.
Breath testing has limitations related to intestinal transit, substrate choice and test methodology.
Hydrogen and Methane Are Not the Same
Patients may have different gas patterns.
Hydrogen-predominant overgrowth is often associated with diarrhea or loose stools.
Methane production is frequently associated with slower transit and constipation.
Strictly speaking, methane overproduction is increasingly referred to as:
intestinal methanogen overgrowth — IMO
because methane is produced by archaea rather than bacteria.
This distinction can matter clinically.
What About Hydrogen Sulfide?
Hydrogen sulfide represents another microbial gas pathway.
It is increasingly recognized in SIBO-related research and may be associated with particular gastrointestinal symptom patterns.
Testing remains less universally available and standardized than conventional hydrogen and methane testing.
Importantly, none of these breath-gas patterns has been validated as a pulmonary-fibrosis biomarker.
How Is SIBO Treated in Systemic Sclerosis?
Treatment is individualized and may involve several components.
Antibiotics are commonly used when clinically indicated.
Depending on the situation, clinicians may also consider:
improving intestinal motility
addressing constipation
correcting nutritional deficiencies
dietary modification
treating underlying gastrointestinal dysfunction
Because impaired motility often persists in systemic sclerosis, recurrence is common.
This means SIBO management may require more than a single course of treatment.
Why Motility Matters So Much
If bacterial overgrowth occurs because intestinal contents are not moving properly, eliminating bacteria without improving motility may provide only temporary benefit.
This creates the classic cycle:
dysmotility → bacterial overgrowth → treatment → temporary improvement → persistent dysmotility → recurrence
Therefore, management should consider the underlying physiology.
What About Prokinetics?
Prokinetic medications may be considered in selected systemic sclerosis patients with documented or clinically significant dysmotility.
The appropriate medication depends on the affected part of the gastrointestinal tract and the patient’s clinical situation.
This should be managed medically rather than through a universal SIBO protocol.
What About Diet?
Diet can help control symptoms in some patients.
However, systemic sclerosis requires particular caution with restrictive diets.
A patient may already be at risk of:
low body weight
muscle loss
malnutrition
micronutrient deficiencies
Long-term highly restrictive diets can worsen these problems.
A temporary dietary strategy aimed at reducing fermentation may help selected patients with severe symptoms, but nutritional adequacy should remain a priority.
Should Everyone With SSc-ILD Avoid Fermentable Foods?
No.
The presence of ILD does not itself justify a low-FODMAP or other restrictive diet.
Dietary intervention should be driven by:
gastrointestinal symptoms
nutritional status
confirmed or suspected GI pathology
individual tolerance
The goal should be improving health—not simply feeding or starving particular bacteria.
What About Probiotics?
Probiotics are sometimes suggested for SIBO or systemic sclerosis.
However, the evidence is heterogeneous.
Different strains have different effects, and some patients with severe fermentation symptoms may experience increased bloating.
There is currently no probiotic shown to treat SSc-ILD.
Probiotics should therefore be considered according to the patient’s gastrointestinal indication rather than prescribed as antifibrotic therapy.
Could SIBO Treatment Improve the Microbiome?
Potentially, but the relationship is complicated.
Antibiotics can reduce microbial overgrowth while simultaneously altering microbial diversity.
Diet can change substrate availability.
Prokinetics can change the intestinal environment by improving transit.
Therefore, the goal should not simply be to maximize or minimize bacteria.
The goal is to restore appropriate gastrointestinal physiology and improve symptoms and nutritional health.
Functional and Integrative Medicine Perspective
SIBO provides an excellent example of where functional and conventional medicine can overlap productively.
A comprehensive assessment can ask:
Does the patient actually have symptoms compatible with SIBO?
Is intestinal dysmotility present?
Is reflux significant?
Is constipation contributing?
Is the patient losing weight?
Are there nutritional deficiencies?
Are medications influencing gut function?
Is there evidence of malabsorption?
Is the dietary plan sustainable?
For a patient with SSc-ILD, these questions should sit alongside:
pulmonary function
HRCT findings
oxygenation
disease progression
autoimmune activity
pulmonary hypertension assessment
appropriate immunomodulatory or antifibrotic treatment
This is what genuinely integrated care looks like.
What We Know
We know that:
SIBO is common in systemic sclerosis
gastrointestinal dysmotility is an important driver
SIBO can cause clinically significant gastrointestinal symptoms and nutritional problems
systemic sclerosis is associated with intestinal dysbiosis
recent multinational human research demonstrates distinct gut microbial signatures in SSc-ILD
some microbial features correlate with radiological ILD extent
What We Do Not Know
We do not know whether:
SIBO causes SSc-ILD
SIBO accelerates lung fibrosis
treating SIBO slows FVC decline
SIBO eradication alters pulmonary prognosis
probiotics prevent SSc-ILD
specific SIBO gas patterns predict lung progression
These remain research questions.
What Should Patients Take Away From This?
If you have systemic sclerosis and significant gastrointestinal symptoms, those symptoms deserve proper assessment.
They should not automatically be dismissed as “just part of scleroderma.”
SIBO, reflux, esophageal dysfunction, dysmotility and nutritional problems may all require attention.
But treating these conditions should not be confused with treating the underlying interstitial lung disease.
Both aspects of health matter.
And they may eventually prove to be more interconnected than we currently understand.
Conclusion
SIBO is common in systemic sclerosis because the disease can profoundly disrupt gastrointestinal motility.
At the same time, emerging human evidence demonstrates that the intestinal microbiome differs in patients with systemic sclerosis-associated ILD.
This creates a compelling gut–lung hypothesis.
SIBO and intestinal dysbiosis could theoretically influence systemic immunity, microbial metabolites, intestinal-barrier function and inflammation.
However, there is currently no evidence that SIBO itself causes SSc-ILD or that treating SIBO slows pulmonary fibrosis.
The clinical message is therefore more nuanced.
SIBO should be identified and treated when clinically appropriate because it can substantially affect gastrointestinal symptoms, nutrition and quality of life.
Meanwhile, SSc-ILD should continue to receive appropriate specialist pulmonary and rheumatological treatment.
Future research must determine whether these two areas eventually intersect therapeutically.
If treating intestinal microbial dysfunction can one day be shown to change pulmonary outcomes, it could add an entirely new dimension to the management of systemic sclerosis.
For now, the gut–lung connection remains an important emerging field—promising enough to investigate seriously, but not yet strong enough to replace established treatment.
About Dr. Samar Shadly
Dr. Samar Shadly is a Consultant Pulmonologist and Certified Functional Medicine Practitioner, with advanced subspecialty training in interstitial lung disease, pulmonary fibrosis, pulmonary hypertension and lung transplantation at the University of Toronto.
Her clinical approach combines evidence-based pulmonary medicine with functional and integrative medicine, with particular interest in autoimmune-associated ILD, the gut–lung axis, gastrointestinal health, nutrition and metabolic factors that may influence overall health in people with chronic lung disease.
Living With Systemic Sclerosis and Interstitial Lung Disease?
If you have systemic sclerosis-associated ILD and are also experiencing gastrointestinal problems such as persistent bloating, reflux, altered bowel habits or suspected SIBO, a comprehensive assessment can consider these issues alongside your pulmonary disease rather than treating them as completely separate problems.
To learn more about online consultation options, contact us through the consultation page or WhatsApp.
Functional and integrative care is intended to complement—not replace—appropriate pulmonary, rheumatological, immunomodulatory or antifibrotic treatment.
Medical Disclaimer: This article is for educational purposes and is not a substitute for individualized medical advice. SIBO testing and treatment should be selected according to the patient’s clinical presentation, and patients with SSc-ILD require appropriate specialist follow-up.