What is small intestine bacterial overgrowth (SIBO)?

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Small intestine bacterial overgrowth (SIBO) is getting more press lately, but what is it exactly and why does it happen? In this article, you’ll get an overview of what SIBO is, how it’s tested for and treated, and a few reasons why it occurs.

Setting the stage:

Normally, most of our native gut bacteria live in our large intestine. In SIBO, however, there are too many, or the wrong type, of bacteria in the small intestine. This imbalance leads to inflammation in the gut as well as the following symptoms. 


  • Abdominal pain or cramping
  • Diarrhea
  • Constipation
  • Excessive gas
  • Bloating
  • Reflux
  • Nausea
  • Increased reactivity to foods
  • Joint pain
  • Skin conditions
  • Brain fog
  • Weight loss/gain
  • Malabsorption of nutrients

As you can see, symptoms of SIBO are often gut-centered, but can include systemic issues and even nutrient deficiencies.

How and why does SIBO happen?

This shift of bacteria typically occurs because of improper motility in the small intestine and/or lowered digestive secretions and impaired gut immunity. If this sounds confusing, we’re about to break it down! 

Motility refers to the way things move through the gut. We want this to be a regular, smooth, and efficient process to make sure food and bacteria make it to the large intestine instead of getting backed up in the small intestine. Altered motility in the small intestine is one of the main reasons why people struggle with SIBO. The list of things that can affect normal motility is long, but common ones are food poisoning, autoimmune disease, thyroid disorders, structural obstacles in the gut, and chronic stress. 

Our digestive secretions provide another important protection against SIBO; if we’re not making enough, then we are more vulnerable to developing SIBO. By digestive secretions, we are mainly talking about stomach acid, digestive enzymes, and bile. All of these help to digest food in the small intestine so there’s less for microbes to eat and overgrow. Stomach acid and bile also have antimicrobial properties.

Finally, a strong immune system in our gut is an important part of preventing SIBO. Remember, most of our immune system is in the gut! We need it to be robust to help keep pathogenic (“bad”) bacteria from getting out of hand.  


The most common way SIBO is tested is by a lactulose (not lactose!) breath test. This measures the amount of hydrogen and methane gas in your breath. Note that this is not a perfect test and there is quite a bit of room for skewed results. Make sure your practitioner is literate in reading SIBO tests, as interpretation can be complex and nuanced. 

Treatment Options

SIBO is most commonly eradicated by one of the following ways.

The first is with antibiotics. Each round of antibiotic treatment typically lasts 2-3 weeks, and most commonly includes one called Xifaxan (or Rifaxamin) either alone or in combination with others. 

The second way is through antimicrobial herbs.  In a 2014 study, herbal antimicrobials were compared against the antibiotic Rifaximin for their effectiveness.  Results showed that these herbs were as effective at treating SIBO as the antibiotics.  

The third way is through something called an “elemental diet”, which is essentially a 2-3 week, liquid formula diet. This is usually not a first-line intervention, however.

Please consult with a practitioner to find the most appropriate path forward for your unique situation, health history, preferences, and budget.

What’s the role of food in SIBO?

Diet can be extraordinarily helpful in relieving symptoms and keeping people nourished throughout their SIBO journey. Low FODMAP diets are commonly recommended  because they restrict specific types of carbohydrates that bacteria eat. 

FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols. Limiting FODMAPs can bring symptom relief for SIBO, but it is NOT curative.

FODMAPs should not be eliminated long-term, as they are important fuel for our large intestine bacteria and support our overall nutrition. When people restrict FODMAPS for an extended time, studies have shown a decrease in butyrate-producing bacteria in the large intestine (more on butyrate another time, but suffice it to say it’s an extremely important substance for our gut health and to control inflammation!). 

Long-term restriction can also create a negative and fearful relationship with food that lowers quality of life. This often an under-recognized impact of restrictive diets like low-FODMAP.

The link between SIBO, Celiac, and IBS

Celiac disease and irritable bowel syndrome (IBS)  are very commonly linked with SIBO.  

Current research suggests that celiac disease is a predisposing factor for SIBO. Unmanaged celiac disease causes inflammation, disrupts motility, and alters the terrain of the gut in a way that increases risk for SIBO. In my practice, I often see overlap of the two conditions.

SIBO is also one of the main causes of IBS.  IBS and SIBO symptoms can mimic each other, so it’s helpful to work with a practitioner who can differentiate between the two. 

In Conclusion

SIBO is a complex condition that requires a very individualized approach. As with other digestive issues, the key is to reflect on WHY the SIBO occurred in the first place. That way, you can have the best chance to prevent it from coming back. 

If you’ve been struggling with SIBO, IBS, or other digestive issues and need support, feel free to book a call to see how we can resolve them together. 

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