What is SIBO?
SIBO stands for small intestinal bacterial overgrowth. It happens when there are more bacteria than usual in the small intestine. The small intestine is part of your digestive system that helps break down food and absorb nutrients.
Bacteria normally live throughout your digestive tract, especially in the large intestine (colon). In SIBO, too many bacteria grow in the small intestine, where there are usually fewer bacteria. These bacteria can ferment food before it is fully digested, causing gas and other digestive symptoms.
SIBO is usually not a primary disease by itself. It often develops because of another health condition or a change in anatomy that affects how food and bacteria move through the digestive tract. However, the exact underlying cause may not be identifiable in all cases.
Intestinal methanogen overgrowth
It should be noted that intestinal methanogen overgrowth (IMO), although associated with symptoms that overlap with SIBO, is a distinct condition. IMO results from an overabundance of methane-producing microorganisms known as methanogenic archaea, which are distinct from bacteria, and is commonly associated with constipation and alternating bowel habits.
What are the symptoms of SIBO?
Symptoms can vary from person to person. Some people have mild symptoms, while others have symptoms that affect daily life.
Common symptoms that often occur after eating include:
- Bloating (feeling of being too full that can happen after eating).
- Abdominal distention (visible protrusion of the abdomen after eating).
- Excess gas (i.e., flatulence)
- Excess belching or burping.
- Abdominal or belly pain or discomfort.
- Diarrhea (loose or watery stool 3 or more times a day).
- Constipation or alternating diarrhea and constipation. Constipation is more common when methane-producing organisms are involved.
- Nausea or upset belly.
- Feeling overly full after eating.
- Brain fog or difficulty concentrating.
In some cases, SIBO may interfere with the body’s ability to absorb nutrients from food. This can lead to vitamin deficiencies such as vitamin B12, vitamin D, or iron, weight loss, or malnutrition. These are more likely with certain underlying causes, such as prior bowel surgery.
What causes SIBO?
The digestive tract has natural defense mechanisms, including movement of the intestines (“housekeeping waves”) and the valve between the small intestine and the large intestine that help prevent excessive bacterial buildup. SIBO can happen when those systems are not working properly, often leading to stasis (slowing) in the small intestine.
Health conditions linked to SIBO include:
- Irritable bowel syndrome (IBS).
- Crohn’s disease.
- Celiac disease.
- Cirrhosis and other liver disease.
- Chronic pancreatitis.
- Short bowel syndrome.
- Some conditions that slow movement of the intestines, like gastroparesis, diabetes with nerve involvement, and scleroderma.
- Prior surgery that changes the anatomy of the digestive tract (for example, certain stomach or weight-loss surgeries, blind loops, or removal of the valve between the small and large intestine).
- Older age.
Not everyone with these conditions will develop SIBO, but they may increase your risk of SIBO.
How is SIBO diagnosed?
Your healthcare provider will ask about your symptoms, medical history, medications, and any conditions that may increase your risk of SIBO.
One common test is a breath test. During this test, you drink a special sugar solution and breathe into a collection device over 2-3 hours. The test measures gases (hydrogen and methane) produced by bacteria in your digestive tract. High hydrogen levels suggest SIBO, while high methane levels suggest IMO.
Fluid from the small intestine can also be collected during an endoscopy using a special catheter and sent to a laboratory to check for bacterial overgrowth. This is considered the reference standard but is more invasive, not readily available, and less commonly done.
Diagnosing SIBO can be challenging. Symptoms often overlap with other digestive conditions such as IBS, food intolerances, and celiac disease. No single test is perfect, and your healthcare provider may use several pieces of information to make a diagnosis.
How is SIBO treated?
Treatment depends on your symptoms, overall health, and any underlying condition contributing to SIBO.
Goals of treatment may include:
- Reducing extra bacteria.
- Improving symptoms.
- Correcting nutritional deficiencies.
- Treating the underlying cause when possible.
Your health care provider may recommend:
Antibiotics are the most commonly used treatment to reduce bacteria in the small intestine. Different antibiotics may be used depending on your symptoms and medical history. The goal is to improve symptoms rather than to eliminate all bacteria.
It is important to know that antibiotics (including rifaximin, a commonly used option) are not FDA-approved specifically for SIBO, so they are prescribed based on your provider’s judgment, and insurance coverage may vary.
An elemental diet is a nutritionally complete liquid formula that is absorbed early in the digestive tract. It can help reduce bacteria in the small intestine and may be used as an alternative to antibiotics.
Certain foods may worsen symptoms because bacteria use carbohydrates to produce gas.
Some people find symptom relief with dietary approaches such as a low-FODMAP eating plan, which reduces certain carbohydrates that can increase gas production. Diet changes may help manage symptoms but are not considered a cure for SIBO.
Learn more about managing SIBO with diet.
Managing the condition contributing to SIBO is often an important part of treatment. For example, improving control of Crohn’s disease, celiac disease, or other digestive disorders may help reduce symptoms and lower the risk of recurrence.
Can SIBO come back?
Some people experience recurring symptoms after treatment. Recurrence has been reported in up to 44% of people within 9 months.
Recurrence may happen because the condition that contributed to SIBO is still present. If symptoms return, talk with your healthcare provider. Additional evaluation or treatment may be needed.
Questions to ask your healthcare team
- Could SIBO be causing my symptoms?
- What testing do you recommend?
- What might be contributing to SIBO in my case?
- What treatment options are available?
- Should I work with a registered dietitian?
- Are there signs of vitamin or nutrient deficiencies I should watch for?
- What can I do if my symptoms come back?
When should I seek medical care?
Contact your healthcare team if you have:
- Ongoing bloating or gas that affects your daily life.
- Persistent diarrhea or constipation.
- Unexplained weight loss.
- Difficulty eating because of symptoms.
- Symptoms that do not improve with treatment.
Empowering you with information from an AGA Clinical Practice Update (Quigley et al., 2020)
Reviewed by
Ali Rezaie, MD, MSc, FRCPC, AGAF
Medical Director, GI Motility Program, and Professor of Medicine, Cedars-Sinai, Los Angeles, CA
Jessica D. Korman, MD
Capital Digestive Care, Washington, DC
AGA Patient Education Advisor
September 2026