All About SIBO

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All About SIBO: Small Intestinal Bowel Overgrowth

Peptic ulcer was once thought to be psychogenic and stress-related. We now know it is due to infection with H. pylori. Irritable bowel syndrome was also, until recently, believed to be psychogenic. It is now accepted to be multi-factorial in nature and highly related to the microbiome. Sounding familiar? The next condition first believed to be psychogenic is SIBO, small intestinal bowel overgrowth.

SIBO is believed to be caused by two factors. First, failure of the gastric acid barrier or too low stomach acid. Second, a failure of intestinal clearance (poor motility) which promotes bacterial overgrowth.

Who should be assessed for SIBO?

  • Those with ME/CFS with digestive issues

  • All with fibromyalgia

  • Those with IBS and IBD

  • Those who chronically used antacids and opioids

  • Those with any other hard to define chronic condition with digestive symptoms

The Community that is Your Small Intestine

Up to 70% of the total microbiota resides in the lower colon and are most talked about. The 30% of the stomach and small intestine are just as important to the host. Naively, we once believed the stomach and upper small intestine were sterile. This seemed intuitive given the hostile milieu of bile acids, water abundance, protein destructive enzymes, and carbon dioxide.

So how many microbes should be in the small intestine?

The first part of the small intestine, the duodenum, has a microbial mass of about 10^3-4 cells per mL. The next section, the jejunum, contains roughly 10^4-5 cells/mL. Lastly, the ileum, which connects the small intestine to the large, contains about 10^8 cells/mL.  SIBO is defined as bacterial populations exceeding 10^5-6 cells/mL.


Who is at Risk of SIBO?

Several factors have been associated with increased risk of SIBO. These include being female, an older age, predominant symptom of bloating and flatulence, and diarrheal subtype of IBS. Furthermore, those who chronically take proton-pump inhibitors have a 7-fold increase incidence of SIBO. Chronic use of opioid pain relievers also greatly increases bacterial overgrowth and contributes to SIBO.

Nutritional Consequences of SIBO

Overgrowth of bacteria in the small intestine can essentially “crowd-out” normal digestive processes at the intestinal surface. The activity of digestive enzymes can be greatly hindered which leads to a disrupted ability to breakdown carbohydrates and proteins. A low FODMAP diet may be the best, first option as it eliminates indigestible foods and difficult to digest foods such as lactose and fructose.

B12 deficiency may occur with long standing SIBO. The gut bacteria sequester vitamin B12 and convert it to unusable forms. Bacteria are also responsible for a large percentage of folate production. With SIBO, one might see excesses of folate.

Bacterial overgrowth produces a number of toxic compounds: D-lactate and serum amyloid A. These can promote inflammation, damage the border of the intestinal cells resulting in malabsorption, and increase permeability. D-lactate in particular has been associated with brain fog and encephalopathy. Some studies have even shown increased level of serum endotoxins (LPS), inflammatory cytokines and chemokines, and endogenous production of ethanol due to SIBO. One can imagine the systemic symptoms these effects could cause. Headaches. Wide spread pain. Disrupted sleep. Brain fog. Fatigue. Etc.

Does Fasting Make GI Symptoms Worse?

During fasting a migrating motor complex (MMC) develops approximately every 90-120 minutes to sweep residual debris through the GI tract. Our gut’s “street cleaner,” if you will, the MMC produces rhythmic waves of electrical impulses. Abnormalities in the MMC can prevent bacterial clearance and predispose to SIBO. If fasting worsens your gut symptoms, treatment of SIBO may be the first order of business.

How to Test for SIBO

Small intestine aspirate remains a standard to diagnosis SIBO. However, it is invasive, expensive, and not very accurate. An endoscopic sample of intestinal contents is sampled and cultured. This technique can only measure culture-able microbes, which severely limits its usefulness. Indeed >50% of the bacterial species in the gut cannot be cultured. Further, overgrowth may be occurring distal to the site of sampling. This testing gives a high rate of false negatives.

Glucose and lactulose hydrogen breath tests are now more commonly used to evaluate SIBO, but are still imperfect. Ingestion of these sugar solutions is followed by measurement of hydrogen and methane breath gases, which are produced by the flora in response to the ingested substrates. This is a type of fermentation test.

The lactulose challenge is better than glucose since glucose is mostly absorbed in the proximal small intestine and may not reach the area of SIBO. Glucose breath testing then gives a high rate of false negatives. The lactulose drink challenge is more specific. However, fast gut transit time can severely determine the results of this test. Those with a fast transit time may pass the challenge before bacteria can adequately ferment it to give a result.

A rise in hydrogen greater than 20 parts per million (ppm) above baseline, 90-120 minutes following ingestion of a 10 g lactulose challenge is diagnostic of SIBO.

SIBO and Fibromyalgia

A 2004 study showed that all 42 patients with fibromyalgia had positive SIBO breath testing when compared with controls. Interesting enough, the same group found those with the highest degree of hydrogen in the breath had the most severe fibro pain.

Indirect SIBO Testing

A molecular assessment of GI ecology provides lots of valuable information that may point to SIBO.  This can be achieved by looking at urinary markers. Bacteria of the upper small intestine convert tryptophan to indole. Indole is later excreted in the urine as indican, which in excess may point to a diagnosis of SIBO. Other urinary markers include D-lactate. Lactic acid is the byproduct of carbohydrate fermentation and is detectable in excess in the urine of those with SIBO. These markers are commonly evaluated on an organic acid test and can be used with the whole clinical picture to diagnose SIBO.

How to Treat SIBO

A course of oral antibiotics is most effective in eliminating SIBO. Rifaximin 550 mg taken three times daily for 14 days is widely used. If unresponsive, short courses of other antibiotics, such as ciprofloxacin, may be indicated until symptoms resolve.

Natural SIBO treatments have been evaluated sparingly. A 2014 study showed SIBO improvement comparable to Rifaximin with the use of 4 weeks of Dysbiocide and FC Cidal or Candibactin-AR and Candibactin-BR. You can find these supplements in the dispensary.

Probiotics for SIBO

The research surrounding probiotics for treatment of SIBO are mixed. High dose S. boulardii, Lactobacillus casei, and the commercial VSL #3 have all been evaluated for SIBO with mixed results. They will work for some, and have no effect in others.



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