Small Intestine Bacterial Overgrowth

Some research suggests that 81% of people with chronic fatigue syndrome, 84% of people with fibromyalgia, 54% of people with hypothyroidism and up to 78% of people with IBS have small intestine bacterial overgrowth (SIBO)

Hydrogen breath tests are widely used to explore what’s going on in functional gastrointestinal disorders. Small intestinal bacterial overgrowth (SIBO) and carbohydrate malabsorption are disorders detected by these tests that have been shown to be of great importance for symptoms of gastrointestinal diseases.

Glucose hydrogen breath test is more acceptable for diagnosis of small intestine bacterial overgrowth whereas lactose and fructose hydrogen breath tests are used for detection of lactose and fructose maldigestion respectively. Lactulose hydrogen breath test is also used widely to measure the orocecal transit time for GI motility.

Basic Principle of SIBO Breath Test

Bacteria in the bowel generally produce hydrogen gas on fermentation of carbohydrates. In bowel, bacteria can only do this when dietary carbohydrates are not absorbed in small intestine and stay as undigested material as it travels along the digestive tract into large intestine. Though some of the hydrogen gas produced by the bacteria is expelled as flatus or in making other molecules such as sulphides, acetate and short chain fatty acids but most of the gas is absorbed across the lining of the large intestine into blood stream. The gas is then transported to lungs via the blood stream and from blood it is exchanged into the airways of lungs and breathed out. The only source of hydrogen gas in the breath can be from bacterial fermentation in the bowel. The same applies to the gas called methane which is exhaled by some people and not all. The bacteria in their large bowel make methane from the hydrogen. The amount of hydrogen and methane gases breathed out from the lungs can be easily measured by taking a breath sample, and measuring by a breath-testing machine.

Types of Hydrogen Breath Tests

I am not going to discuss al of the options or discuss any in detail. But I do want to highlight some key points.

1. Glucose hydrogen breath test – the best breath test for detecting small intestine bacterial overgrowth.

2. Lactose hydrogen breath test

“Lactose intolerance depends not only on the expression of lactase but also on the dose of lactose, intestinal flora, gastrointestinal motility, small intestinal bacterial overgrowth and sensitivity of the gastrointestinal tract to the generation of gas and other fermentation products of lactose digestion.”

3. Fructose hydrogen breath test

“It has been reported that prevalence of fructose intolerance (FI) in patients with functional GI disorders (FGID) range between 38 and 75 %.”

“2 studies reported a prevalence of fructose malabsorption in functional dyspepsia or unexplained GI symptoms of 40-55% and 73%, respectively. Therefore, it seems to be reasonable to perform routine fructose H2 breath tests in patients with unexplained abdominal symptoms who have had an unremarkable medical check-up including laboratory tests, physical examination, ultrasound and endoscopy and in the absence of “red flags” (e.g., unintended weight loss, rectal bleeding, fever, severe diarrhea or vomiting, persistent pain in the upper or lower right abdomen, family history of inflammatory bowel disease or colon cancer.”

4. Lactulose hydrogen breath test

“Of the 2,390 patients with IBS-like symptoms, 848 (35%) were symptomatic lactose malabsorbers and 1,531 (64%) symptomatic fructose malabsorbers. A combined symptomatic carbohydrate malabsorption was found in 587 (25%) patients. Out of 460/659 patients with early significant H2 increase in the lactose and fructose test who underwent a glucose breath test, 88 patients had positive results indicative of small intestine bacterial overgrowth.”

Take away message – fructose and lactose malabsorption and small intestine bacterial overgrowth are common issues in people with IBS-like symptoms.

I recommend the lactulose breath test as a starting point to assess for small intestine bacterial overgrowth. One of the reasons being SIBO can cause a lactose intolerance. We must find the root cause!

It is important to appreciate that other tests will likely be important alongside a hydrogen breath test. As discussed in my e-book on SIBO, we must try and understand the cause of the overgrowth in the first place.

We have five endogenous mechanisms to protect us from SIBO:

These were detailed in a great article (Kopacova, 2010) and include:

  1. Secretion of hydrochloric acid produced in the stomach (Brechmann et al., 2017)
  2. Gut motility (and thus knowledge of: (1) ‘The Migratory Motor Complex’ (2) The Vagus Nerve (3) Interstitial cells of Cajal, is important)
  3. An intact ileo-cecal valve (a sphincter muscle valve that separates the small intestine and the large intestine)
  4. Secretory immunoglobulins (also known as antibodies, which are produced by white blood cells. They aid in the destruction of antigens, such as bacteria or viruses.)
  5. Bacterio-static properties of pancreatic juice and bile (bile stops bacteria from reproducing)

One or more of these defence mechanisms needs to fail for SIBO to occur

If you would like more information I have a comprehensive e-book/PDF on SIBO available from my online shop: click here.

More can also be accessed via Dr. Siebecker’s website: www.siboinfo.com

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