Small intestinal bacterial overgrowth (SIBO) and irritable bowel syndrome (IBS) are common digestive conditions that often cause similar symptoms. Both can lead to bloating, stomach pain, gas, diarrhea, constipation, or changes in bowel habits.
Even though they may feel similar, SIBO and IBS are different conditions with different causes and treatments.
Understanding the difference can help your healthcare provider recommend the right testing and treatment.
SIBO vs. IBS at a Glance
SIBO
IBS
Caused by too many bacteria in the small intestine
A disorder that affects how the digestive system functions
Can often be confirmed with a breath test
Diagnosed based on symptoms after ruling out other conditions
Has a measurable underlying cause
Does not have a single identifiable cause
May improve with targeted antibiotics
Often managed with diet, lifestyle changes, and medications
Note: Some people have both SIBO and IBS at the same time.
What Is SIBO?
SIBO happens when too many bacteria grow in the small intestine.
Normally, most bacteria live in the large intestine. When bacteria move into the small intestine and multiply, they begin breaking down food too early.
This process creates hydrogen and methane gases that can cause digestive symptoms.
Common Causes of SIBO
SIBO may be linked to:
Slow movement of food through the intestines
Previous abdominal or intestinal surgery
Low stomach acid
Diabetes
Scleroderma
Hypothyroidism
Long-term use of certain medications, including proton pump inhibitors (PPIs)
What Is IBS?
IBS is a long-term condition that affects how the digestive system works.
Unlike SIBO, IBS does not cause visible damage to the digestive tract. The intestines may look normal during tests, but they do not function normally.
IBS may involve:
Changes in how the intestines move
Increased sensitivity to pain
Changes in communication between the brain and the digestive system
Types of IBS
IBS with Constipation (IBS-C): The main symptom is constipation with hard or infrequent stools.
IBS with Diarrhea (IBS-D): The main symptom is frequent loose or watery stools.
IBS with Mixed Bowel Habits (IBS-M): Patients experience both constipation and diarrhea.
Unclassified IBS (IBS-U): Symptoms do not clearly fit into one of the other IBS types.
SIBO vs. IBS Symptoms
Because these conditions share many symptoms, it can be difficult to tell them apart without testing.
Symptoms They Share
Both SIBO and IBS may cause:
Bloating
Abdominal pain or cramping
Excess gas
Diarrhea
Constipation
Changes in bowel habits
Feeling full quickly when eating
Nausea
Symptoms More Common With SIBO
SIBO may also cause:
Bloating that gets worse throughout the day
Unexplained weight loss
Vitamin B12 deficiency
Difficulty absorbing certain nutrients
Fatigue
Symptoms related to poor nutrient absorption
These problems are less common in uncomplicated IBS.
How Are SIBO and IBS Diagnosed?
Healthcare providers use different methods to diagnose each condition.
Diagnosing IBS
IBS is diagnosed by reviewing your symptoms and ruling out other digestive conditions.
Your provider may ask about:
How often you have abdominal pain
Changes in bowel habits
Stool consistency
How long symptoms have been present
Additional testing may be recommended to rule out other conditions.
Diagnosing SIBO
SIBO usually requires additional testing because symptoms alone cannot confirm the condition.
Breath Testing: A SIBO breath test measures hydrogen and methane gases after you drink a glucose or lactulose solution.
Results may suggest:
Hydrogen-positive SIBO: Hydrogen rises by 20 parts per million (ppm) or more within 90 minutes.
Methane-positive intestinal methanogen overgrowth (IMO): Methane reaches 10 ppm or higher during testing.
Small Bowel Aspirate: In some cases, a small sample of fluid from the small intestine may be collected during an upper endoscopy. Because this test is invasive, it is used much less often than breath testing.
Comparing SIBO and IBS
Feature
SIBO
IBS
Cause
Too many bacteria in the small intestine
Digestive system does not function normally
Diagnosis
Breath testing
Symptoms and medical evaluation
Measurable Test
Yes
No single diagnostic test
Common Treatment
Antibiotics and treating the underlying cause
Diet changes, medications, and symptom management
Treatment for SIBO vs. IBS
Treatment depends on which condition is causing your symptoms.
SIBO Treatment
Treatment may include:
Antibiotics to reduce bacterial overgrowth
Medications that improve intestinal movement
Treating underlying conditions that contribute to SIBO
Dietary changes during or after treatment
IBS Treatment
Treatment may include:
Medications for diarrhea or constipation
Medications that reduce abdominal cramping
Stress management
Behavioral therapies
Dietary changes
Your provider will recommend treatment based on your symptoms and medical history.
Diet and SIBO vs. IBS
Many patients with SIBO or IBS benefit from dietary changes. One commonly recommended approach is the Low FODMAP diet.
This eating plan reduces certain carbohydrates that are difficult to digest and may contribute to gas, bloating, and abdominal discomfort.
For IBS, a Low FODMAP diet may help reduce symptoms.
For SIBO, dietary changes are often used along with medical treatment, not as a replacement for treatment.
When Should You See a Gastroenterologist?
Ongoing bloating, stomach pain, gas, diarrhea, constipation, or changes in bowel habits should not be ignored, especially if symptoms continue or interfere with daily life.
Because SIBO and IBS have many of the same symptoms, a proper evaluation is important to determine the cause and recommend the right treatment.
The gastroenterology team at Charleston GI can evaluate your symptoms, determine whether breath testing or other diagnostic testing is appropriate, and create a personalized treatment plan.
No referral is needed to schedule an appointment with Charleston GI.
Frequently Asked Questions About SIBO & IBS
SIBO vs. IBS
Yes. Many people have both conditions. Research suggests some patients diagnosed with IBS may also have SIBO, and treating SIBO may improve digestive symptoms for certain individuals.
No. SIBO is a condition caused by excessive bacteria in the small intestine, while IBS is a functional digestive disorder. Although they are different conditions, SIBO can contribute to IBS-like symptoms in some patients.
The symptoms often overlap, making it difficult to tell without testing. SIBO-related bloating commonly worsens after meals and throughout the day. A SIBO breath test can help determine whether bacterial overgrowth may be contributing to your symptoms.
Symptoms & Causes
The type of gas produced during bacterial fermentation can influence symptoms:
Hydrogen: More commonly associated with diarrhea.
Methane: More commonly associated with constipation.
Foods such as garlic, onions, apples, cauliflower, and leafy greens contain fermentable carbohydrates (FODMAPs). In people with SIBO or IBS, these foods may be fermented more rapidly, leading to increased gas, bloating, abdominal pain, and distension.
As you eat throughout the day, intestinal bacteria ferment carbohydrates and produce gas. This can cause progressive bloating, often called “IBS belly” or “SIBO bloat,” that tends to improve overnight after fasting.
Yes. A gastrointestinal infection can affect gut nerves and digestive motility, increasing the risk of post-infectious IBS, SIBO, or both.
It can. Changes in bile flow after gallbladder removal may affect digestion and intestinal bacteria, which may contribute to chronic diarrhea or bacterial overgrowth in some people.
Diagnosis
IBS is often diagnosed based on symptoms after other serious conditions have been ruled out. If IBS treatments are not improving your symptoms, especially severe bloating, your gastroenterologist may recommend a hydrogen and methane breath test to evaluate for SIBO.
Treatment & Prevention
No. SIBO is often treatable, but it can return if underlying causes, such as slow intestinal movement or certain digestive conditions, are not addressed.
Untreated SIBO may continue to cause bloating, gas, abdominal discomfort, diarrhea, or constipation. In some cases, it can also interfere with nutrient absorption, including vitamin B12 and other essential nutrients.
No. A low-FODMAP diet helps reduce symptoms but does not cure either condition. SIBO often requires medical treatment, while IBS management may include dietary changes, medications, and lifestyle modifications.
It depends. Some probiotics may help people with IBS, while others may worsen symptoms during active SIBO. Your healthcare provider can recommend whether probiotics are appropriate based on your diagnosis and treatment plan.
Preventing recurrence often involves treating the underlying cause. Depending on the situation, this may include improving intestinal motility, managing digestive disorders, treating structural abnormalities, or addressing other contributing conditions.
Yes. The migrating motor complex (MMC) helps move food residue and bacteria through the small intestine between meals. If this process slows down, bacteria may remain in the small intestine and increase the risk of recurrent SIBO.
When to See a Gastroenterologist
You should see a gastroenterologist if you have persistent bloating, abdominal pain, excessive gas, diarrhea, constipation, or symptoms that do not improve with standard IBS treatment. A medical evaluation can help determine whether SIBO, IBS, or another digestive condition is causing your symptoms.
Charleston GI: Understanding the Low-FODMAP Diet – Explore dietary strategies designed to help identify trigger foods, alleviate symptoms, and manage flare-ups associated with IBS and SIBO.
Charleston GI: Types of IBS – Learn more about the four subtypes of irritable bowel syndrome—IBS-C, IBS-D, IBS-M, and IBS-U—and how identifying your specific pattern guides targeted treatment.
Charleston GI: IBS vs. IBD vs. Celiac Disease – Understand the key differences between functional bowel disorders, inflammatory bowel disease, and autoimmune conditions to better recognize your symptoms.
Charleston GI: Introduction to SIBO Breath Testing – An introductory guide explaining how SIBO breath testing works, why it is used, and how measuring gas levels helps evaluate bacterial overgrowth.
Charleston GI: What Happens During a SIBO Breath Test? – A step-by-step guide on what to expect during your appointment, from drinking the testing solution to providing timed breath samples.
Medical Disclaimer: This article is for educational purposes only and is not medical advice. Always consult a qualified healthcare provider regarding diagnostic or medical care.
