In this article
Small intestinal bacterial overgrowth, or SIBO, is a condition in which very large numbers of bacteria grow in the small intestine (MedlinePlus). According to the American College of Gastroenterology (ACG), the most common way to indirectly measure the amount of bacteria in the small intestine is a hydrogen breath test (ACG).
This guide explains, in general terms, what SIBO is and how a breath test works.
What SIBO is
Healthy intestines normally contain many types of bacteria. The ACG describes SIBO as bacteria in the small intestine being out of balance and causing digestive symptoms. The imbalance may come from a loss of helpful bacteria or too much of certain types (ACG).
MedlinePlus notes that, unlike the large intestine, the small intestine usually doesn't have a large number of bacteria (MedlinePlus).
The ACG lists these among common symptoms (ACG):
- Belly pain
- Bloating
- Changes in bowel habits, such as diarrhea or constipation
- Extra gas
- Fatigue
- Nausea
Many of these symptoms are common and have many possible causes.
Why bacteria and breath are connected
Bacteria in the small intestine break food down into gas and nutrients. The ACG explains that extra bacteria may lead to extra gas (ACG). These gases leave the body through the breath, which is what a breath test measures.
How a breath test works, in general
The ACG describes the hydrogen breath test this way (ACG):
- The person drinks a sugar solution.
- Bacteria in the small intestine break the sugar down.
- The gases this produces leave the body through the breath.
- Breath samples are analyzed for hydrogen over about 3 hours.
The clinician who orders the test gives preparation instructions beforehand (ACG). MedlinePlus lists hydrogen and methane breath tests among several tests that may be used, alongside blood tests and other exams (MedlinePlus).
What's known about risk factors
The ACG lists several factors associated with SIBO (ACG):
- Structural changes in the intestine, such as narrowing after surgery or small pouches called diverticula
- Slowed movement of the intestine, including from some medicines
- Reduced stomach acid
- Conditions that affect absorption or immunity
- Diseases such as diabetes and thyroid disease
When to see a clinician
Questions about digestive symptoms, or about any change in health, are best discussed with a licensed clinician who knows a person's history. In a medical emergency, call 911 or go to the nearest emergency room.
Frequently asked questions
What does SIBO stand for? SIBO stands for small intestinal bacterial overgrowth. MedlinePlus also calls it small bowel bacterial overgrowth (MedlinePlus).
Is a breath test the only test used for SIBO? No. MedlinePlus lists hydrogen and methane breath tests among several possible tests, along with blood tests and other exams (MedlinePlus). The ACG describes the hydrogen breath test as the most common indirect measure (ACG).
Why does a breath test measure hydrogen? When bacteria in the small intestine break down the sugar used in the test, they produce gases, including hydrogen, that leave the body through the breath (ACG).
- American College of Gastroenterology. Small intestinal bacterial overgrowth (SIBO).
- MedlinePlus. Small bowel bacterial overgrowth.
The information in this article is for general educational purposes only. It is not medical advice and is not a substitute for diagnosis or treatment from a qualified clinician who knows your history. Don't start, stop or change any treatment based on this article. If you think you're having a medical emergency, call 911 or go to the nearest emergency room. Reading this article does not create a clinician-patient relationship with Tenor Health or any provider on our platform.
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