SIBO vs IBS: What Is the Difference?
- Ola Krawczyk, Clinical Nutritionist
- 10 minutes ago
- 11 min read
ATMS Accredited Member | SIBO-Certified Nutritionist | Microba Certified Nutritionist
Published: 28 August 2026 | Last reviewed: 28 August 2026
Bloating, excessive gas, abdominal discomfort, diarrhoea and constipation can occur with both small intestinal bacterial overgrowth (SIBO) and irritable bowel syndrome (IBS).
Because the symptoms overlap, people are sometimes told they have IBS when SIBO has not been considered—or assume that every episode of bloating must be SIBO.
However, SIBO and IBS are not the same condition.
IBS is a disorder of gut–brain interaction diagnosed from a characteristic pattern of abdominal pain and altered bowel habits. SIBO refers to an excessive number or altered balance of microorganisms in the small intestine that may contribute to digestive symptoms and, in some cases, nutrient malabsorption.
It is possible to have IBS without SIBO, SIBO without IBS, or features of both. This is why symptoms should be assessed in the context of your medical history, medications, bowel patterns, risk factors and relevant investigations.
Clinical Nutritionist’s Perspective from Ola Krawczyk: “SIBO and IBS can produce very similar symptoms, but they are not interchangeable diagnoses. Persistent bloating does not automatically mean SIBO, and an IBS diagnosis should not prevent further investigation when the symptoms, history or risk factors suggest that something else may be contributing.” — Ola Krawczyk, Clinical Nutritionist, ATMS Member, SIBO-Certified Practitioner and Microba Certified Practitioner
SIBO vs IBS: quick comparison
SIBO | IBS | |
Full name | Small intestinal bacterial overgrowth | Irritable bowel syndrome |
What it is | Excessive numbers or an altered population of microorganisms in the small intestine | A disorder of gut–brain interaction involving abdominal pain and altered bowel habits |
Main location | Small intestine | Involves communication between the gut and brain; symptoms often relate to bowel function |
Common symptoms | Bloating, distension, gas, abdominal discomfort, diarrhoea or constipation | Abdominal pain, bloating and constipation, diarrhoea or mixed bowel habits |
How it is assessed | Clinical history, risk factors and usually hydrogen-methane breath testing; small-bowel aspirate is used in selected settings | Symptom-based diagnostic criteria, medical history and appropriate exclusion of other conditions |
Does a colonoscopy diagnose it? | No | No—but investigations may be required to exclude other conditions |
Can both occur together? | Yes | Yes |
Is there one treatment for everyone? | No | No |
Are restrictive diets a cure? | No | No |
What is IBS?
Irritable bowel syndrome is a chronic disorder of gut–brain interaction. This means it involves changes in how the digestive tract and nervous system communicate, rather than being simply a problem “in your head.”
People with IBS may experience altered intestinal movement, increased sensitivity to normal digestive sensations, changes in gut–brain signalling and differences in the way the body responds to food, stress or a previous gastrointestinal infection.
Common symptoms include:
Recurrent abdominal pain or cramping
Bloating or visible distension
Constipation
Diarrhoea
Alternating constipation and diarrhoea
Changes in stool form or frequency
Urgency or a feeling of incomplete emptying
Symptoms that fluctuate over time
IBS does not ordinarily cause visible structural damage to the bowel. However, the symptoms are real and may significantly affect eating, work, exercise, sleep, travel and quality of life.
The American College of Gastroenterology classifies IBS as a disorder of gut–brain interaction and recognises abdominal pain and altered bowel habits as central features.
How common is IBS?
The reported prevalence depends considerably on the diagnostic criteria and the population studied.
A large Rome Foundation study collected data from 73,076 adults across 33 countries.
In countries assessed by internet survey, approximately 4.1% met the Rome IV criteria for IBS, compared with 10.1% under the broader Rome III criteria.
The study also found that disorders of gut–brain interaction were associated with reduced quality of life and greater healthcare use. Rome Foundation global epidemiology study
These results demonstrate why prevalence estimates differ and why IBS should be identified using recognised diagnostic criteria rather than bloating alone.
What are the different types of IBS?
IBS is classified according to the predominant stool pattern:
IBS-C
IBS with predominant constipation. Stools may be hard, difficult to pass or less frequent, and a person may experience straining or incomplete emptying.
IBS-D
IBS with predominant diarrhoea. Loose stools, frequency and urgency may be prominent.
IBS-M
IBS with mixed bowel habits. Both hard and loose stools occur.
IBS-U
Unclassified IBS. The person meets the overall criteria for IBS, but the bowel pattern does not fit clearly into the other categories.
The subtype can change over time. This is one reason an individualised assessment is more helpful than applying the same diet or supplement protocol to everyone with IBS.
How is IBS diagnosed?
There is no single blood, stool or imaging test that confirms IBS.
Doctors may use the Rome IV diagnostic criteria, which describe IBS as recurrent abdominal pain, on average, at least one day per week during the previous three months, associated with at least two of the following:
The pain is related to bowel movements
There has been a change in stool frequency
There has been a change in stool form or appearance
The symptoms should have begun at least six months before diagnosis.
Depending on the person’s symptoms and history, a doctor may also consider blood tests, coeliac screening, stool testing, inflammatory markers, colonoscopy or other investigations.
An IBS diagnosis should not be based on symptoms alone when warning signs or an alternative medical explanation may be present.
What is SIBO?
SIBO stands for small intestinal bacterial overgrowth.
The small intestine normally contains microorganisms, but generally in smaller numbers and a different balance from the large intestine. SIBO describes an excessive number or altered population of microorganisms within the small intestine.
These microorganisms can ferment carbohydrates and produce gases, potentially contributing to:
Bloating or visible abdominal distension
Excessive gas
Belching
Abdominal discomfort
Diarrhoea
Constipation
Nausea
Food-related digestive symptoms
Fatigue
Nutrient deficiencies or weight loss in more significant cases
These symptoms are not specific to SIBO. They can also occur in IBS, coeliac disease, inflammatory bowel disease, constipation, lactose or fructose malabsorption, pelvic-floor dysfunction and other gastrointestinal conditions.
What is intestinal methanogen overgrowth?
Methane is produced by microorganisms called archaea, not bacteria. Therefore, a methane-positive breath test is more accurately described as intestinal methanogen overgrowth, or IMO, rather than “methane SIBO.”
Methanogens may be found in the small or large intestine. Higher methane production is commonly associated with constipation and slower intestinal transit.
This distinction matters because someone with constipation, bloating and a methane-positive test may require a different clinical approach from someone with a hydrogen-predominant pattern and diarrhoea.
What causes SIBO?
SIBO is often a consequence of another factor that has disrupted the small intestine’s protective mechanisms.
Potential contributors or risk factors may include:
Impaired intestinal motility
Chronic constipation
Previous gastrointestinal surgery
Structural changes in the small intestine
Small-intestinal diverticula
Certain neurological or muscular conditions
Diabetes-related motility changes
Reduced digestive function in particular clinical circumstances
Some medications
Conditions affecting the pancreas or bile flow
Previous gastrointestinal infection
Finding a positive breath test does not automatically explain why SIBO developed. Identifying and addressing possible contributing factors may be important, particularly when symptoms keep returning.
How is SIBO assessed?
A glucose or lactulose hydrogen-methane breath test is commonly used to support a SIBO or IMO assessment.
During the test, the person drinks a measured carbohydrate solution. Breath samples are collected at regular intervals to measure gases produced when microorganisms ferment the test substrate.
The American College of Gastroenterology notes that breath testing is commonly used as an indirect method of assessing suspected SIBO. Preparation—including instructions about food, fasting and certain medications—is important for obtaining a meaningful result. American College of Gastroenterology: SIBO
Breath testing has limitations. The substrate used, intestinal transit time, preparation quality and interpretation criteria can all affect the result.
A test should therefore be interpreted alongside:
Symptoms and their timing
Constipation or diarrhoea patterns
Medical and surgical history
Medications and supplements
Previous gastrointestinal infections
Relevant pathology
Other possible digestive conditions
Whether the test preparation was completed correctly
Is IBS caused by SIBO?
Not in every case.
Research suggests an association between SIBO and IBS, but it has not established that SIBO explains all cases of IBS.
A systematic review and meta-analysis involving 25 studies, 3,192 people with IBS and 3,320 controls found that positive SIBO tests were more common among people with IBS. However, the researchers rated the overall quality of evidence as low because diagnostic methods, participant selection and breath-testing accuracy varied considerably between studies. Systematic review and meta-analysis
This means:
Some people with IBS may also have SIBO or IMO
Many people with IBS will not have SIBO
A positive breath test does not prove that SIBO is the only cause of the symptoms
A negative test does not explain what is driving the person’s IBS
SIBO treatment is not automatically appropriate for everyone diagnosed with IBS
The relationship is clinically relevant, but it should not be oversimplified into “IBS is always SIBO.”
Why do SIBO and IBS feel so similar?
Both may produce gas, bloating, distension, discomfort and altered bowel habits.
Carbohydrate fermentation can contribute to gas production in both conditions. People with IBS may also have visceral hypersensitivity, meaning normal amounts of gas or intestinal stretching can feel unusually painful or uncomfortable.
Constipation can further complicate the picture. Slower transit may increase fermentation and bloating, while methane production may itself be associated with slower transit.
The symptom alone does not reveal the underlying mechanism. Two people with similar bloating can have very different contributing factors and may therefore need different investigations and nutrition strategies.
Does bloating mean you have SIBO?
No.
Bloating may be associated with:
IBS
Constipation or incomplete bowel emptying
SIBO or IMO
Coeliac disease
Lactose or fructose malabsorption
Food intolerance
Pelvic-floor dysfunction
Menstrual or hormonal changes
Abdomino-phrenic dyssynergia
Gastroparesis or delayed gastric emptying
Inflammatory bowel disease
Gynaecological conditions
Other medical concerns
Self-diagnosing SIBO from bloating alone can lead to unnecessary testing, restrictive diets or repeated supplement protocols that do not address the actual cause.
Can you have SIBO without IBS?
Yes.
A person may develop SIBO in association with altered motility, previous surgery, anatomical changes or another medical condition without meeting the diagnostic criteria for IBS.
SIBO may also cause nutrient malabsorption or weight loss in more significant cases—features that are not typical diagnostic characteristics of IBS and require medical attention.
Can you have IBS without SIBO?
Yes.
IBS may be associated with several interacting mechanisms, including:
Altered gut–brain communication
Visceral hypersensitivity
Changes in intestinal motility
Previous gastroenteritis
Dietary triggers
Stress-related symptom amplification
Bile-acid changes
Altered fermentation
Changes in the gut microbiome
Pelvic-floor dysfunction or constipation
SIBO is only one possible consideration within a much broader clinical picture.
Is a microbiome test able to distinguish IBS from SIBO?
No.
A commercial gut microbiome test typically analyses a stool sample and primarily represents the microbial ecosystem of the large intestine. It cannot confirm or exclude an overgrowth within the small intestine.
A microbiome test may provide selected information about microbial composition, diversity and functional potential, but it is not a stand-alone diagnostic test for either SIBO or IBS.
If suspected SIBO is the clinical question, a suitably selected breath test may be more relevant.
If IBS is suspected, the assessment is based on symptoms, medical history and appropriate medical evaluation—not a microbiome score.
Are SIBO and IBS treated in the same way?
Not necessarily.
IBS management may involve a combination of:
Regular, nutritionally balanced meals
Adjusting fibre type and quantity
Identifying individual dietary triggers
A carefully supervised low-FODMAP intervention when appropriate
Constipation or diarrhoea management
Physical activity
Sleep and stress support
Gut-directed psychological therapies
Medications prescribed for the dominant symptoms
SIBO management may require:
Medical review and appropriate antimicrobial treatment
Assessment of possible underlying causes
Support for intestinal motility or constipation
Correction of nutrient deficiencies
Individualised dietary support during treatment
A plan to reduce the likelihood of recurrence
The American Gastroenterological Association advises that SIBO management should focus on correcting underlying causes where possible, addressing nutritional deficiencies and using antibiotics appropriately. AGA clinical practice update on SIBO
Antibiotics, herbal antimicrobials or highly restrictive diets should not be used simply because a person is bloated.
Does a low-FODMAP diet treat both conditions?
A low-FODMAP diet is an evidence-based dietary strategy for managing symptoms in some people with IBS. It reduces certain fermentable carbohydrates temporarily before foods are systematically reintroduced and personalised.
It is not intended to be a permanent, highly restrictive diet.
A low-FODMAP diet may also reduce fermentation-related symptoms in someone with SIBO, but symptom improvement does not confirm that SIBO has been eradicated. The diet does not identify or correct every underlying cause of SIBO.
Long-term unnecessary restriction may reduce dietary variety, fibre intake and enjoyment of food. Any elimination phase should have a clear purpose and a structured reintroduction process.
Should everyone with IBS be tested for SIBO?
No. Routine SIBO testing is not necessarily appropriate for every person with IBS.
Testing may be considered when:
Symptoms and risk factors create a reasonable suspicion of SIBO or IMO
Bloating or distension is persistent and pronounced
Constipation is accompanied by features suggesting methane production
Diarrhoea remains unexplained
There is a history of gastrointestinal surgery or impaired motility
Nutrient deficiencies or malabsorption are suspected
The result is likely to change the treatment approach
Before arranging testing, it is important to ask:
What clinical question are we trying to answer?
Is the selected test appropriate for that question?
Have other relevant conditions been considered?
Will the result meaningfully influence the next step?
When should you speak with your doctor?
Seek medical assessment if you experience:
Blood in the stool or black stools
Unexplained weight loss
Iron-deficiency anaemia
Fever
Persistent vomiting
Severe or worsening abdominal pain
Diarrhoea that wakes you at night
A new and persistent change in bowel habits
Difficulty swallowing
A family history of coeliac disease, inflammatory bowel disease or bowel cancer
Symptoms beginning later in life without an established explanation
These features should not be assumed to be IBS or SIBO. Nutrition consultations and commercial digestive testing should not delay appropriate medical investigation.
The bottom line
SIBO and IBS share several symptoms, but they describe different clinical problems.
IBS is a disorder of gut–brain interaction characterised by recurrent abdominal pain and altered bowel habits. It is diagnosed through a recognised symptom pattern and appropriate medical assessment.
SIBO refers to an excessive number or altered population of microorganisms in the small intestine. Breath testing may support the assessment when symptoms and risk factors create a reasonable clinical suspicion.
Some people may have both conditions, but SIBO does not explain every case of IBS, and bloating alone cannot distinguish between them.
A personalised assessment can help determine whether your symptoms are more consistent with IBS, suspected SIBO or IMO, constipation, food intolerance—or whether further medical investigation should come first.
Need help understanding your digestive symptoms?
If you experience persistent bloating, gas, abdominal discomfort, constipation, diarrhoea or food-related symptoms, I can help you review your health history, diet, bowel patterns and previous investigations.
Where appropriate, we can discuss whether SIBO breath testing, microbiome testing, medical referral or a personalised nutrition strategy may be the most useful next step.
I provide evidence-informed online nutrition consultations across Australia, with a particular focus on digestive health, SIBO, the gut microbiome, thyroid conditions and perimenopause.
This article is for educational purposes only and does not replace individual medical diagnosis, treatment or advice. Speak with your doctor about persistent, worsening or concerning gastrointestinal symptoms. Do not stop prescribed medication without consulting the prescribing practitioner.
Author
Ola Krawczyk is a Polish-Australian Clinical Nutritionist, accredited ATMS member, SIBO-Certified Practitioner and Microba Certified Practitioner specialising in gut health, SIBO, thyroid support and perimenopause nutrition.
Her professional approach is also informed by her personal experience with SIBO, hormonal health challenges and thyroid cancer followed by thyroid removal. Ola provides warm, personalised and evidence-informed online nutrition consultations across Australia through Clinical Nutrition by Ola.
Frequently asked questions
Is SIBO the same as IBS?
No. IBS is a disorder of gut–brain interaction characterised by abdominal pain and altered bowel habits. SIBO involves excessive numbers or an altered population of microorganisms in the small intestine.
Can SIBO cause IBS symptoms?
Yes. SIBO may cause bloating, abdominal discomfort, diarrhoea or constipation that resembles IBS. However, these symptoms do not prove that SIBO is present.
Can you have IBS and SIBO together?
Yes. Research suggests that positive SIBO tests are more common in people with IBS than in healthy controls, although test limitations make the exact degree of overlap uncertain.
Does IBS show on a colonoscopy?
No. A colonoscopy does not diagnose IBS. It may be recommended in selected circumstances to investigate warning signs or exclude other bowel conditions.
What test distinguishes SIBO from IBS?
SIBO may be investigated with hydrogen-methane breath testing. IBS does not have one confirmatory test; it is diagnosed from a recognised symptom pattern and appropriate medical assessment.
Does a stool microbiome test diagnose SIBO?
No. Stool primarily reflects the large-intestinal microbiome and cannot confirm or exclude overgrowth in the small intestine.
Should everyone with IBS have a SIBO breath test?
No. Testing is most useful when symptoms, medical history or risk factors create a reasonable suspicion of SIBO or IMO and the result is likely to change management.
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