What is SIBO?

So far in our discussions about comprehensive stool analyses, we have discussed a few different imbalances we can see in the gastrointestinal microbiome – growth of unwanted microbes/infectious organisms, lack of beneficial bacteria, and potentially pathogenic overgrowth of expected/commensal bacteria. Today we will be introducing a new imbalance: growth of normal/expected bacteria in an abnormal location.


What is SIBO?

SIBO stands for small intestinal bacterial overgrowth. Normally, there should not be a significant amount of bacteria in our small intestine. In SIBO, bacteria we would normally find in our large intestine, start to populate the small intestine where they do not belong.


How Does SIBO Develop?

The GI tract has built in protections to help prevent bacteria from colonizing in the small intestine. One of these protections is enzymatic secretions. Hydrochloric acid, produced in the stomach, helps with the breakdown of food and directly suppresses bacterial growth. Pancreatic enzymes, brush border enzymes, and bile help with food digestion. This helps to ensure there aren’t undigested food particles serving as substrate for the bacteria to ferment and flourish. A second protection is the migrating motor complex (MMC). The MMC is a pattern of electromechanical activity in the GI tract’s smooth muscle that occurs in between meals at intervals of every 90 minutes. Consuming any calories (and even zero calorie sweeteners like stevia) will stop the MMC. Its job is to sweep undigested material through the GI tract. A third protection is the ileocecal (IC) valve, which is a small segment between the small and large intestine. This valve is supposed to prevent back flow of the large intestine’s contents back into the small intestine.

So if there aren’t supposed to be bacteria in the small intestine, how do they get there? Basically anything that interferes with the three protections we just discussed can increase the risk of SIBO developing. Certain factors decrease motility and affect the MMC like hypothyroidism, medications like opiates, diabetic neuropathy, and gastroparesis. Structural or anatomic abnormalities can also affect motility, like diverticulosis, adhesions, or bowel resection. High stress, hypochlorhydria, and medications like immunosuppressants and PPI’s are a few other risk factors for developing SIBO.
What are some indications you might have SIBO?

When bacteria are present in the small intestine in larger  than desired amounts, they can ferment poorly digested, fermentable carbohydrates. This fermentation process releases hydrogen gas. Other organisms called Archaea, can also use this hydrogen to produce methane gas. This gas production results in the common symptoms of SIBO – bloating, gas, abdominal pain diarrhea and/or constipation. There are a few hallmark symptoms I tend to see in patients with SIBO. The first is that the bloating gets worse throughout the day/is at its worst in the evening. The second is that the symptoms tend to get worse when they make healthier diet changes/they are experiencing completely unpredictable food sensitivity reactions. The third is that there symptoms often get worse when they introduce probiotics and/or prebiotics.

Common Signs/Symptoms:

  • Fatty stools
  • Gas
  • Bloating
  • Heartburn
  • Nausea
  • Constipation and/or diarrhea
  • Increasing food sensitivities
  • Persistent iron deficiency or B12 deficiency
  • Rashes

Other Associated Conditions:

  • Fibromyalgia
  • Chronic fatigue syndrome
  • Diverticulitis
  • Interstitial cystitis
  • Restless leg syndrome
  • Rosacea
  • Diverticulitis

Testing for SIBO

Since we have been discussing the comprehensive stool analysis in previous blogs, let’s quickly review some signs that might point to SIBO on this specific test (this, however, is not the gold standard for diagnosing SIBO).

  1. High Relative Abundance
    The stool analysis cannot identifyLOCATION of bacteria and therefore is not diagnostic of overgrowth in the small intestine, however high relative abundance in the stool sample can be a potential indicator of bacterial overgrowth in the small intestine as well.
  2. Methanobrevibacter smithii
    Methanobrevibacter smithii is measured on PCR. The species within Methanobrevibacter are anaerobic archaea that produce methane. Methane production is a hallmark of constipation type SIBO. Methane slows down transit time in the GI tract.
  3. Fat Malabsorption
    High fecal fats seen in the stool indicate either issues with fat digestion or fat absorption. Fat malabsorption is another sign of SIBO. The bacteria in the small intestine can deconjugate bile acids, preventing micelle formation/fat absorption.

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The gold standard for diagnosing SIBO is breath testing. This allows us to identify if there are large numbers of bacteria in the small intestine specifically (vs. a stool analysis, which can only tell you if there are a lot of bacteria in the entire GI tract). Patients drink a lactulose solution and then hydrogen and methane are measured every 15-20 minutes over the course of 2-3 hours. Bacteria and archaea ferment the sugar into hydrogen or methane. The gas diffuses into the blood stream and is transported to the lungs where it is expired (and can be captured for testing). Timing of the gas spikes reflects location. Spikes within the first 90 minutes point to the small intestine. Here is an example of Genova’s 2 hour breath test.

This is an example of a positive result for both hydrogen and methane because the hydrogen increased for the 20 parts per million (ppm) and the methane increased more than 10 ppm within 90 minutes.
Treating SIBO

There are a few elements in a comprehensive SIBO treatment protocol. We must remove the bacteria in the small intestine, stimulate motility and digestion, and address any other underlying causes of the SIBO, like hypothyroidism for example.

  1. Anti-microbials
    1. Either herbal anti-microbials or antibiotics can be used to remove the unwanted bacteria in the small intestine. Both have been shown to be effective, but the herbal anti-microbials will need to be used for a longer period of time. Depending on the level of gas measured on the breath test, multiple treatment rounds might be needed for full eradication.
  2. Prokinetics
    1. A prokinetic is an agent that can amplify and co-ordinate gastrointestinal motility. These are different than laxatives, which promote bowel movements. As we discussed earlier, MMC’s, those coordinated, peristaltic contractions that help to clear out the intestine can be dysfunctional in SIBO. Prokinetics help to regulate motility. Again, these can be prescription, like erythromycin or LDN, or natural, like ginger or D-limonene.
  3. Digestive secretions
    1. Digestive enzymes help to ensure that food is properly broken down and absorbed. Poorly digested, unabsorbed food particles serve as a substrate for the bacteria to ferment in the small intestine. Digestive secretions like HCl and bile also help to directly suppress growth of unwanted bacteria. Bitter herbs can be taken in tincture form. These help to stimulate the release of your own digestive enzymes. Broad spectrum digestive enzyme capsules can also be used.
  4. Dietary changes
    1. Dietary changes can be helpful for symptom improvement and even for eradication. The low FODAMP diet consists of avoiding specific types of carbohydrates. FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols. These are types of carbohydrates that the body might not be able to absorb well and certain bacteria can feed on them, promoting overgrowth and symptoms of gas production. The elemental diet contains pre-digested nutrients (amino acids, essential vitamins and minerals, MCT and simple sugars) in their simplest forms to allow for easy absorption. It limits digestive function to allow for rest and repair and also essentially “starves” the bacteria in the small intestine since all of the nutrients are absorbed and therefore do not provide a fermentable substrate for them. Elemental diets have been shown to normalize breath test results even as a stand-alone treatment. Another strategy to implement as part of a SIBO protocol, or as part of a relapse prevention protocol, is to set meal times and restrict snacking. As we discussed earlier, the MMC occurs every 90 min, but is stopped by consuming food. Leaving a few hours between meals and fasting overnight allows the MMC to clear out the intestine properly.

Relapse after SIBO treatment is very common. Bacteria can repopulate within 2 weeks of finishing anti-microbial treatment or an elemental diet. There is no one size fits all approach to treating SIBO. It is best to work with a doctor who can help you to identify the underlying imbalances that caused you to develop SIBO in the first place. This way you cannot only eradicate the bacteria from the small intestine, but also get on a proper treatment protocol that ensures the bacteria don’t just repopulate again after treatment.


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