IBS vs SIBO: How to Tell the Difference
- Both SIBO and IBS cause bloating, gas, abdominal pain, and bowel changes, making them easy to confuse.
- SIBO results from excess bacteria in the small intestine, while IBS is a gut–brain interaction disorder without structural damage.
- SIBO is diagnosed with breath or fluid tests, while IBS is diagnosed by symptoms and exclusion of other conditions.
- Treatment for SIBO often involves antibiotics, while IBS treatment focuses on diet, stress management, and symptom control.
Bloating, diarrhea, constipation, stomach cramps. These symptoms can make daily life miserable and leave you wondering: Am I dealing with IBS or is it something else, like small intestinal bacterial overgrowth (SIBO)
Though may of their symptoms overlap, SIBO and IBS are distinct conditions with different causes and treatments. Understanding the key differences is essential for finding the right treatment.
Overlapping Symptoms
Both small intestinal bacterial overgrowth (SIBO) and irritable bowel syndrome (IBS) are gastrointestinal issues that share many of the same symptoms. The most common overlaps include:
- Gas and bloating that often worsen after meals
- Abdominal pain or cramping that may come and go
- Changes in bowel habits, including diarrhea, constipation, or both
- Fatigue and disrupted daily life
Because these symptoms overlap so much, it can be difficult for someone to know which condition they might be dealing with on their own.
| SIBO | IBS |
|---|---|
| Caused by excess bacteria in the small intestine where few should normally live | A functional gut disorder. Intestines look normal but don’t work properly |
| Symptoms: Bloating, gas, cramps, diarrhea (hydrogen type) or constipation (methane type), malabsorption, possible weight loss | Symptoms: Bloating, cramps, diarrhea, constipation, or both; no nutrient deficiencies |
| Complications: Can cause nutrient deficiencies (iron, B12) and weight loss | Rarely linked to nutrient deficiencies or weight loss |
| Diagnosis: Breath tests (hydrogen/methane) or small intestine fluid sampling (via endoscopy) | Diagnosis: Based on symptoms and exclusion of other conditions; no single confirmatory test |
| Treatment: Antibiotics to reduce bacterial overgrowth, diet adjustments, sometimes probiotics | Treatment: Diet changes (low FODMAP, fiber), medications for stool control, stress management, lifestyle support |
Key Differences
While the symptoms are similar, the underlying causes are what distinguish them. The key difference is that SIBO is an anatomical problem, while IBS is a functional disorder.
SIBO
SIBO is a condition where there is an excessive amount of bacteria, or the wrong type of bacteria, in the small intestine. This is a physical issue with the location and quantity of bacteria.
- Causes: Often linked to conditions that slow gut movement or change intestinal structure, such as diabetes, Crohn’s disease, or intestinal surgery.
- Complications: Can damage the intestinal lining, reduce nutrient absorption, and cause weight loss, anemia, or vitamin deficiencies.
Types of SIBO: Not all SIBO is the same; what makes one case different from another often comes down to the type of gas produced by the bacteria.
- Hydrogen-dominant: Bacteria produce hydrogen gas. It’s commonly linked with diarrhea, cramping, and bloating.
- Methane-dominant: Microorganisms in the gut produce methane. People with methane-dominant SIBO often struggle with constipation, bloating, and slower gut motility.
- Hydrogen sulfide-dominant: This less common type involves bacteria that produce hydrogen sulfide gas. Symptoms may include diarrhea, foul-smelling gas, and abdominal discomfort.
IBS
IBS is a functional disorder, meaning there's nothing visibly wrong with the intestines on scans. The issue lies in how the gut and brain communicate, leading to problems with gut motility and sensitivity.
- Causes: Exact cause is unclear. Likely involves stress, gut–brain signaling problems, altered motility, prior infections, and microbiome changes.
- Complications: Does not damage the intestines or cause malabsorption, but symptoms can be long-lasting and disruptive.
Types of IBS: IBS does not look the same for everyone. Doctors usually classify it into subtypes based on bathroom patterns.
- IBS-D: diarrhea is the main issue.
- IBS-C: constipation shows up most often.
- IBS-M: mixed type, with both diarrhea and constipation at different times.
- IBS-U: symptoms don’t clearly fit into the other groups.
How to Tell Them Apart
Tests for SIBO
- Breath tests (hydrogen or methane) measure gases from bacterial fermentation.
- Jejunal aspirate culture is the gold standard. Bacteria are sampled directly from the small intestine.
- Other tests may include blood work, vitamin levels, stool studies, or endoscopy
Evaluation for IBS
- Primarily a clinical diagnosis based on symptoms and history.
- Doctors may order tests to rule out other conditions, such as blood work, stool tests, colonoscopy, or celiac disease screening.
Why Diagnosis Matters
Getting the right diagnosis is important because treatments differ:
- Treating SIBO with antibiotics can reduce bacterial overgrowth and prevent nutrient deficiencies.
- Managing IBS focuses on symptom control, lifestyle changes, and gut–brain interaction therapies.
Treatment Options
SIBO Treatments
- Antibiotics: Common options include metronidazole, amoxicillin-clavulanate, or neomycin.
- Supportive care: Nutritional support, fluids, or dietary changes such as avoiding lactose.
- Addressing underlying causes: Improving gut motility or treating related diseases.
IBS Treatments
- Diet and lifestyle: More fiber, low-FODMAP diet, or avoiding gluten in some cases.
- Medications:: Lubiprostone, linaclotide, loperamide, rifaximin, antispasmodics, low-dose antidepressants.
- Probiotics: May help in some cases, though evidence is mixed.
- Stress-focused therapies: Cognitive behavioral therapy, gut-directed hypnotherapy, or relaxation strategies can reduce symptom severity.