What is Small Intestinal Bacterial Overgrowth (SIBO), and How Do You Treat It?

Awareness and diagnosis of small intestinal bacterial overgrowth, or SIBO, is growing. Although we don’t know exactly how many people have SIBO, we do know that SIBO is underdiagnosed, and that there is a big overlap of SIBO with other common gastrointestinal disorders, such as irritable bowel syndrome (IBS). 

SIBO can cause a wide array of symptoms, including gas, bloating, and even malnutrition. Read on to learn more about SIBO’s: 

• Causes

• Symptoms

• Diagnosis

• Treatments

Small intestinal bacterial overgrowth defined

Small intestinal bacterial overgrowth (SIBO) is when there is an overgrowth of bacteria in the small intestine that causes problems, such as pain, gas, or bloating.

You may have heard of healthy gut bacteria — so if bacteria are healthy, why is SIBO a problem? Most gut bacteria is present in the large intestine, where it serves many important functions, including helping with the immune system, digesting food, and making important vitamins and nutrients, such as short-chain fatty acids.

But when bacteria in the small intestine overgrows, or when bacteria moves from the large intestine into the small intestine, it can cause SIBO — and bothersome symptoms. 

Causes of SIBO

There are many possible causes of SIBO, and there is a lot of overlap between SIBO and other gastrointestinal disorders, such as IBS, Crohn’s disease, and celiac disease.

In fact, up to 80% of people with IBS may have SIBO, and research is looking into whether SIBO may cause IBS. 

Your body has natural systems in place that prevent the unhealthy overgrowth of bacteria in the small intestine. However, when these systems don’t function well, SIBO can develop because of: 

• Decreased production of stomach acid (this can happen with age, stress, or medications)

• Certain medications, like proton pump inhibitors, antibiotics, or steroids, that can disrupt normal gut bacteria

• Anatomic abnormalities such as an intestinal obstruction, a fistula, or surgical removal of the intestine

• A slow-moving intestine, which might be cause by scleroderma or gastroparesis, for example

What are the symptoms of SIBO?

SIBO can lead to increased gas production by the bacteria, and symptoms may include:

• Diarrhea

• Bloating

• Gas

• Abdominal pain

• Weight loss 

More severe symptoms may include nutritional deficiencies including low levels of fat-soluble vitamins (vitamin A, vitamin D, vitamin E, and vitamin K). Vitamin B12 deficiency is also a common complication because it is normally absorbed in the small intestine. 

How is SIBO diagnosed?

There are two main ways to diagnose SIBO.

The first is with a sample from the intestine that can be tested for bacteria. This was previously considered the most accurate way to diagnose SIBO, but it is an invasive procedure with risks.

The second testing option is a breath test. This measures the exhaled gas produced by bacteria after you ingest a carbohydrate, such as lactulose or glucose. While this test is easier, cheaper, and non-invasive, there is an increased risk of incorrect results.

How do you treat SIBO?

The first step is to find and treat the underlying cause, if known. For example, if medications could be causing SIBO, make a plan with your provider to adjust them. Or maybe there is a structural problem in your intestine that needs surgery to fix. 

Next, treatment for SIBO includes the following:

• Selective antibiotics: This is a key part of treatment because certain antibiotics, such as xifaxan, will kill the bacterial overgrowth.

• Dietary changes: This is important because diet affects bacterial growth and gas production. Certain dietary eliminations, such as those in the low-FODMAPS diet, may be helpful.

There are some studies showing possible benefits of probiotics for SIBO symptoms, but others with conflicting results.

Should you adjust your diet if you have or are at risk of SIBO?

Diet changes may be helpful if you have SIBO or think you may be at risk. The most problematic foods are certain carbohydrates, as these can lead to fermentation in the gut. For some people, a low-FODMAPS diet may be recommended because this diet eliminates the carbs that can cause gut issues. The best dietary changes for you will depend on many factors and should be discussed with your healthcare provider. 

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Written by:

Christina Palmer, MD

Christina Palmer, MD, is a board-certified family physician with a special interest in chronic care management, women’s health, mental health, and preventive care. She has over 10 years of experience in primary care research, innovation, and practice.

Edited by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. An experienced and dedicated pulmonologist and hospitalist, she spent a decade practicing and teaching clinical medicine at academic hospitals throughout London before transitioning to a career in health education and health technology.

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