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Small Intestinal Bacterial Overgrowth

What is SIBO?

Small Intestine Bacterial Overgrowth (SIBO) is used to describe a condition in which abnormally large numbers of bacteria (at least 100,000 bacteria per ml of fluid) are present in the small intestine and the types of bacteria in the small intestine resemble more the bacteria of the colon than the small intestine.

The entire gastrointestinal tract, including the small intestine, normally contains bacteria. The number of bacteria is greatest in the colon (at least 1,000,000,000 bacteria per milliliter (ml) of fluid) and much lower in the small intestine (less than 10,000 bacteria per ml of fluid). The types of bacteria within the small intestine should differ to the types of bacteria within the colon. Small intestinal bacterial overgrowth (SIBO) is also known as small bowel bacterial overgrowth (SBBO).

What causes SIBO?

The gastrointestinal tract is a continuous muscular tube through which digesting food is transported on its way to the colon. The coordinated activity of the muscles of the stomach and small intestine propels the food from the stomach, through the small intestine, and into the colon. Even when there is no food in the small intestine, muscular activity sweeps through the small intestine from the stomach to the colon.  The muscular activity that sweeps through the small intestine is important for the digestion of food, but it also is important because it sweeps bacteria out of the small intestine and thereby limits the numbers of bacteria in the small intestine. Anything that interferes with the progression of normal muscular activity through the small intestine can result in SIBO. Simply stated, any condition that interferes with muscular activity in the small intestine allows the bacteria to stay longer and multiply in the small intestine.  The lack of muscular activity also may allow bacteria to spread backwards from the colon and into the small intestine.

SIBO Symptoms

The main symptoms of SIBO are typically those of IBS:  abdominal bloating (gas, belching or flatulence), abdominal pain, constipation and/or diarrhoea. 

An emerging new train of thought is that SIBO might underlie Irritable Bowel Syndrome and there are some recent studies which appear to confirm this theory, a study by Pimentel et al (2003) found SIBO to be present in 84% of patients tested although other studies have suggested that this figure may be lower and closer to 50%.  In my clinical experience around 52% of IBS patients also have SIBO.

It is also possible that SIBO could be associated with other disorders either as a cause or as an effect of another disease or condition, such conditions includes:

  • Heartburn
  • Nausea
  • Leaky Gut
  • Food Intolerance
  • Joint Pain
  • Fatigue
  • Eczema
  • Asthma
  • Depression
  • Steatorrhea
  • Anemia (Iron or B12)
  • Acne Roseacea
  • Celiac Disease
  • Chronic Prostatitis
  • CLL (Chronic Lymphocytic Leukemia)
  • H pylori Infection
  • Hypochlorhydria
  • Hypothyroid/ Hashimoto’s Thyroiditis
  • Restless Legs Syndrome
  • Crohn’s Disease
  • Ulcerative Colitis
  • Interstitial Cystitis

As a general rule if the symptoms of IBS as well as one of the above conditions then SIBO should be considered.

Hydrogen Breath test

There is a simple, inexpnsive and non-invasive test which can be used to identify SIBO which is the Hydrogen Breath Test.  Breath testing measures the hydrogen and methane gas produced by the bacterial fermentation of special types of sugars which are not absorbable by humans, only by bacteria.  The gases produced diffuse into the blood, and then into the lungs, for expiration. Hydrogen and Methane are only produced by bacteria, not by humans. The gas is measured over a 2-3 hour period (the typical small intestinal transit time) and compared to the starting level. 

Lactulose Breath Test (LBT)

Lactulose cannot be digested by humans; we are dependent on bacteria to do this.  When bacteria digest lactulose, they produce gas. The levels of the gases created (Hydrogen and Methane) indicate bacterial overgrowth.
The lactulose test can diagnose overgrowth in the distal end of the small intestine which is the portion closest to the colon and thought to be most prevalent.  However the test is not as sensitive as the glucose breath test.

Glucose Breath Test (GBT)

Glucose is usually absorbed within the top two feet of the small intestine; so if Hydrogen and methane is found in this test it indicates an overgrowth in upper end of the SI closest to the stomach.
This test has its advantages; it is better at diagnosing bacterial overgrowth of the top portion of the small intestine but cannot identify an overgrowth further along the gut.

Treatment Approaches

There are 4 main treatment approaches for SIBO:

1. Antibiotics, prescribed by a GP.  Typical course is 1-2 weeks, SIBO can and often des rebound if care isn’t taken to prevent it coming back.  For this reason Antibiotics is not my recommended course of action!
2. Herbal antibiotics which may include Enteric coated peppermint, Golden seal, Oregano or Grapefruit Seed Extract.  Acobinationof these is most often recommended
3. Elemental Diet (such as Ensure Plus or Vivonex) these shakes contain pre-digested foods and ensure that the bacteria have nothing to feed on. A two week course is needed.
4. Specific Carbohydrate Diet – This starves the bacteria and takes longer than antibiotics. The length of time needed on the SCD diet varies enormously and can be a number of weeks to a year or two.

Each of the treatment options can be used individually but two or more approaches used simultaneously get the best results.  Please contact me for more information on SIBO.