Quick Answer
Small intestinal bacterial overgrowth (SIBO) happens when too many bacteria, or the wrong types, grow in the small intestine. It can cause bloating, gas, abdominal pain, diarrhea and, in some cases, poor absorption of nutrients. SIBO usually develops because of another condition that slows the gut or changes its structure, so finding the underlying cause matters. It is most often evaluated with a breath test, which is useful but not perfect.
Who this is for: adults with ongoing bloating, gas or bowel changes who have heard of SIBO and want to know how it is identified
What SIBO Is
The small intestine normally has far fewer bacteria than the colon. SIBO is an excess or imbalance of bacteria in the small intestine.[1] These bacteria can ferment food earlier in digestion than usual, producing gas and sometimes interfering with how nutrients are absorbed.
A related condition, intestinal methanogen overgrowth (IMO), involves microbes that produce methane. Methane is more often linked with constipation, which is why breath tests for SIBO usually measure it too.[2]
Common Symptoms
SIBO symptoms overlap with many other digestive conditions, which is one reason it can be hard to identify.[1] Symptoms may include:
- Bloating, distension and gas
- Abdominal pain or discomfort
- Diarrhea, constipation or both
- Nausea or indigestion
- Greasy, foul-smelling or floating stools
- Fatigue or unintended weight loss
Over time, SIBO can make it harder to absorb fats, vitamins and minerals. Low vitamin B12, for example, can lead to anemia and nerve problems.[1]
Evaluating SIBO often starts with a close look at diet, symptoms and history.
Who Is More Likely to Develop SIBO
SIBO is usually a complication of another health condition rather than a problem on its own.[3] Risk factors include:[1, 2]
- Slow movement through the intestines, which can occur with diabetes, scleroderma, hypothyroidism or gastroparesis
- Past abdominal surgery, including some weight-loss surgeries, or structural changes such as adhesions or small bowel diverticula
- Low stomach acid, including from long-term acid-reducing medications
- Medications that slow the gut, such as opioid pain medicines
- Conditions such as celiac disease, irritable bowel syndrome, chronic pancreatitis, cirrhosis or immune deficiencies
- Older age
How SIBO Is Evaluated
Evaluation starts with your history, symptoms, medications and any past surgeries. Because symptoms overlap with other conditions, a provider may also check for problems like celiac disease, thyroid disease or anemia.
The most common test is a breath test. You drink a sugar solution, usually glucose or lactulose, then breathe into collection tubes at set times so hydrogen and methane can be measured.[2] Preparation matters. You typically avoid antibiotics for about four weeks and laxatives or motility medicines for about a week, eat a limited diet the day before and fast overnight.[2] Ask before stopping any prescription.
Breath tests are helpful but imperfect, and results can be falsely positive or negative.[2] In some cases, a gastroenterologist may take a fluid sample from the small intestine during an upper endoscopy, which is a more direct but more invasive test.[2]
How SIBO Is Treated
Standard treatment is a course of antibiotics, along with steps to address the underlying cause.[1] Diet changes, such as a short-term low-FODMAP or other modified eating plan, may help symptoms, though evidence for specific diets is limited.[2]
SIBO can come back, especially if the underlying cause continues.[1] Follow-up helps track symptoms, nutrient levels and whether more evaluation is needed.
How We Approach SIBO at Lake Forest Regenesis
Allana reviews your symptoms alongside your medical history, surgeries and medications to see whether SIBO is a reasonable possibility or whether another cause fits better. She may order labs to check for anemia, nutrient deficiencies, thyroid problems or celiac disease, and discuss whether breath testing makes sense for you. If SIBO is likely, the plan addresses both symptom relief and the factors that may have led to it, with follow-up to monitor progress. When symptoms are severe, keep coming back or come with red flags, she coordinates with a gastroenterologist.
When to See a Provider
Go to the ER for severe abdominal pain, a hard, swollen belly with vomiting, vomiting blood, or black or bloody stools. Book a visit if bloating, diarrhea or abdominal discomfort lasts more than a few weeks, especially if you have diabetes or a history of abdominal surgery. Unintended weight loss, anemia, trouble swallowing or persistent vomiting are red flags that usually call for a gastroenterologist.
Wondering if SIBO could explain your symptoms? Allana can review your history and help decide whether testing makes sense.
Frequently Asked Questions
Is SIBO the same as IBS?
No, but they can overlap. Some people with IBS symptoms have SIBO, and gastroenterology guidelines suggest breath testing may be considered for people with IBS.
Can I do a SIBO breath test at home?
Some kits are sold directly to consumers, but results still need to be interpreted alongside your history and other possible causes. Planning the test with a provider helps avoid confusing results.
Do probiotics help SIBO?
Research so far hasn't shown consistent benefit from specific probiotic products for SIBO. Talk with your provider before adding supplements.
Do acid-reducing medications cause SIBO?
Long-term use has been linked to a higher risk in many studies, but the relationship is complex. Don't stop a prescribed medication without talking to your provider.
References
- Cleveland Clinic. SIBO: symptoms, diagnosis, causes & treatment. Read the article
- Pimentel M, Saad RJ, Long MD, Rao SSC. ACG clinical guideline: small intestinal bacterial overgrowth. Am J Gastroenterol. 2020. Read the guidance
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Symptoms & causes of gas in the digestive tract. Read the article
This article is for general education and is not a substitute for individual medical advice. See our medical disclaimer.
