Small intestine bacterial overgrowth (SIBO)

Dr Carly Polland ND in bloating digestive health SIBO 15 Aug 2024 • 3 min read

Author Bio

Dr Carly Polland ND | Clinical Lead at Biomesight

Dr. Carly Polland is an integrative physician focused on the intersection of endocrinology and immunology with the microbiome. Early in her clinical practice, she focused on hormonal imbalances, but she quickly realized these patients also had digestive issues and autoimmune disease. She dug into the research and realized the microbiome was connecting these symptoms. Standard stool testing was not useful in decoding the microbiome so she upgraded to microbiome testing like Biomesight. She has used this technology for over 6 years to help her patients modulate their microbiomes and improve their symptoms.

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One of the most common causes of digestive symptoms that is often overlooked is small intestine bacterial overgrowth (SIBO). In the small intestine, there is normally a very small population of bacteria. This population is distinct from the large intestine microbiome. But when motility in the small intestine becomes impaired, this small population can bloom into a larger population. This results in bacteria in the small intestine fermenting your food in the small intestine. This results in gas and other bacterial waste that can damage the small intestine, resulting in loss of digestive enzymes, impaired barrier function, inflammation, and nutrient deficiencies. 

In terms of digestive symptoms, it is important to understand that SIBO does not present the same in every person. What is considered the hallmark symptom is abdominal distention that looks like a pregnant belly. But you do not have to have this symptom to have SIBO. 

Symptoms can include a combination of:

• Gas
• Bloating
• Abdominal distention
• Heartburn 
• Burping
• Diarrhea
• Alternating constipation and diarrhea
• Nausea
• Abdominal pain

Now the symptom of bloating is a tricky one because it can mean different things to different people. It is important to understand that when we talk about bloating in the context of SIBO, we are talking about a feeling of pressure in your abdomen. This may or may not include changes in abdominal girth, which is abdominal distention. The distention can be minimal, where it just feels like your pants fit tighter or it can be significant, where you look 6 months pregnant by the end of the day. 

The most common presentation of SIBO that I see is mild bloating with changes in bowel consistency and frequency. The bloating is typically best in the morning and it gradually builds throughout the day. By the end of the day, we see gas and bloating. Typically, stools are looser and just more erratic, not always feeling like you completely evacuate. 

SIBO can also have a myriad of symptoms outside the digestive tract, particularly brain fog and fatigue. I also see atopic dermatitis, acne, joint pain, period irregularities, thyroid irregularities, mood disorders, and more with SIBO. 

When should you suspect SIBO? When you have digestive symptoms and…

• You have a history of food poisoning.
• You have a history of abdominal or pelvic surgeries.
• You have endometriosis.
• You have a connective tissue disorder such as scleroderma or Ehlers Danlos.
• Digestive symptoms started after a viral illness.
• You have diabetes.
• You have celiac disease or Crohn’s disease.
• You have been diagnosed with IBS.
• You have abdominal or pelvic adhesions.
• You have impaired exocrine pancreatic function.
• You have been diagnosed with Lyme disease
• You have been exposed to mold or a water damaged building.
• You have been diagnosed with chronic fatigue syndrome.

The available clinic test for SIBO is a breath test. Glucose, lactulose or even fructose can be used as the substrate for the breath test. A few research studies suggest that glucose is superior, however, it is absorbed in the beginning of the small intestine, so it cannot assess the entire small intestine. Lactulose is not absorbed, so it is most often used by SIBO practitioners. Dr. Jason Hawrelak actually recommends doing all three substrates (as separate breath tests on 3 consecutive days) to more thoroughly assess for SIBO. Because each substrate is not perfect. False negatives and false positives are a possibility with the breath test. When it is a true positive, the gas levels on the test can give you a rough idea of how many treatment rounds you may need as well as what gases are involved, which will guide treatment. Most breath tests only assess for hydrogen and methane but one also assesses for hydrogen sulfide (Trio-Smart).

It is important to note that there are no blood tests or stool tests that can assess for SIBO or tell you anything about the bacteria involved in SIBO. This is a common misconception. So if you suspect you have SIBO, do not expect a stool test to diagnose it. In recent years, Dr. Mark Pimentel has confirmed that hydrogen SIBO is caused by overgrowth of Escherichia and Klebsiella and hydrogen sulfide SIBO is caused by overgrowth of Fusobacterium and Desulfovibrio (1). It is important to note that methane overgrowth is not SIBO — it is a separate condition called intestinal methanogen overgrowth (IMO). Typically, the methanogen overgrowth is actually in the large intestine but Methanobrevibacter smithii can also be overgrown in the small intestine. 

The three main treatment options are antibiotics, herbs, and the elemental diet. Not all people will respond to all treatments, but the vast majority of the time, one of the treatment options will work. You may just have to try a few treatments before you find the right one. Antibiotics may include rifaximin, neomycin, metronidazole, trimethoprim/sulfamethoxazole, amoxicillin-clavulanic and many others. Rifaximin is the antibiotic of choice because it is not absorbed into the bloodstream and is deactivated before it reaches the large intestine. So it does not harm the large intestine microbiome. However, insurance does not always cover rifaximin, so some doctors will prescribe other antibiotics. The standard herbs are berberine, though neem, oregano, allicin, and uva ursi are also used. If there are no concerns about a fungal overgrowth or disordered eating, the elemental diet may be a good option.

When it comes to treatment, choosing the right treatment is only the first step. The treatment then needs to be used for the right amount of time and followed up with the right preventative treatments. So choosing the right practitioner to guide you will be very important to your success. You should look for a practitioner who has prescriptive authority. While prescriptions are not always necessary to treat SIBO, for many patients, they are a superior treatment option and sometimes necessary. You should also look for a practitioner with at minimum, 20 hours of training in SIBO. Ideally, they have been trained by Dr. Allison Siebecker or Dr. Nirala Jacobi. They should also be staying up to date on the latest research, so ask if they follow Dr. Mark Pimentel. I see so many patients fail SIBO treatment because it was not done correctly, so finding a knowledgeable practitioner is very important.

For the vast majority of digestive patients that present to my practice, we start with the small intestine. Patients either do a lactulose breath test or we try a SIBO treatment trial. And even if the breath test comes back negative, we will often do a treatment trial. Over 60% of patients have improvement in symptoms. So please consider whether or not your symptoms are SIBO and discuss breath testing and treatment with your doctor. 

References

1. Leite G, Rezaie A, Mathur R, et al. Defining Small Intestinal Bacterial Overgrowth by Culture and High Throughput Sequencing. Clin Gastroenterol Hepatol. 2024;22(2):259-270. doi:10.1016/j.cgh.2023.06.001