Small Intestinal Bacterial Overgrowth

Small Intestinal Bacterial Overgrowth

What is SIBO?

Small Intestine Bacterial Overgrowth (SIBO) is a chronic bacterial infection of the small intestine.  The infection is of bacteria that normally live in the gastrointestinal tract but have abnormally overgrown in a location not meant for so many bacteria. 

The Problem
The bacteria interfere with our normal digestion and absorption of food and are associated with damage to the lining or membrane of the Small Intestine.

  • They consume some of our food which over time leads to deficiencies in their favorite nutrients such as iron and B12, causing anemia.
  • They consume food unable to be absorbed due to lining damage of the small intestine, which creates more bacterial overgrowth.
  • After eating our food, they produce excess gas within our Small intestine. The gas causes abdominal bloating, abdominal pain, constipation, diarrhea or both (the symptoms of IBS).  Excess gas can also cause belching and flatulence.
  • They can cause fat absorption leading to deficiencies of vitamins A & D and fatty stools.
  • Through the damaged lining, larger food particles not able to be fully digested, enter into the body which the immune system reacts to.  This causes food allergies/ sensitivities.
  • Bacteria themselves can also enter the body/bloodstream.  Immune system reaction to bacteria and their cell walls causes chronic fatigue and body pain and burdens the liver.
  • Finally, the bacteria excrete acids which in high amounts can cause neurological and cognitive symptoms.

 

 In general, SIBO is substantially underdiagnosed. There are several reasons for this fact. Some patients may not seek healthcare or SIBO may not be properly diagnosed by medical investigations. SIBO might be asymptomatic or with non-specific symptoms only, and last but not least, all symptoms might be incorrectly ascribed to the underlying disease (leading to SIBO). Of course, diagnostic yield also depends on the methods used for investigation. According to different studies with the investigation of small sets of clinically healthy people as a control, findings consistent with SIBO were found in 2.5% to 22%.

For instance, the prevalence of SIBO in patients fulfilling diagnostic criteria for irritable bowel syndrome was 30%-85%.  The prevalence of SIBO in coeliac disease non-responding to a gluten-free diet was up to 50%. In liver cirrhosis, SIBO was diagnosed in more than 50% of cases. In a small group of elderly people (70 to 94 years old) with lactose malabsorption, SIBO was documented in 90%.  An interesting study was performed on asymptomatic morbidly obese subjects and SIBO was found in 17% as compared to 2.5% in non-obese persons

Diagnostic Testing:

Unfortunately there is no perfect test.  The small intestine (SI) is a hard place to get to.  If we want to see or sample the SI, endoscopy only reaches into the top portion, and colonoscopy only reaches into the end portion.   The middle portion, which is substantial (about 17 feet) is not accessible, other than by surgery.  And stool testing predominantly reflects the large intestine (LI).  Luckily, there is a non-invasive test which is commonly used in SIBO research; the Hydrogen Breath Test.

Hydrogen Breath Test

A hydrogen breath test can be used to diagnose several conditions:  H pylori infection, carbohydrate malabsorption (ex. lactose) and SIBO. Breath testing measures the hydrogen & methane gas produced by bacteria in the Small Intestine that has diffused into the blood, then lungs, for expiration.  Hydrogen & Methane are gases produced by bacteria, not by humans.  The gas is graphed over the SI transit time of 2 or 3 hours & compared to baseline.  Patients drink a sugar solution of glucose or lactulose after a 1 or 2 day preparatory diet.  The diet removes much of the food that would feed the bacteria, allowing for a clear reaction to the sugar drink. There are two (2) types of tests may be used: Lactulose or Glucose.

Lactulose Breath Test (LBT)

Humans can’t digest or absorb lactulose.  Only bacteria have the proper enzymes to do this.  After they consume lactulose, they make gas.  If there is an overgrowth, this will be reflected in the levels of Hydrogen and/or Methane. The advantage to this test is that it can diagnose overgrowth in the distal end of the Small Intestine, thought to be more common.  The disadvantage is that it cannot diagnose bacterial overgrowth as well as the Glucose Breath Test (GBT).

Glucose Breath Test (GBT)

 Both humans and bacteria absorb glucose.  Glucose is absorbed within the first three feet of the Small Intestine, therefore if the bacterial gases of Hydrogen and/or Methane are produced during this test, it reflects an overgrowth in the proximal/upper end of the SI (within the first two feet).

The advantage to this test is that it successfully and accurately diagnoses proximal overgrowth.  The disadvantage is that it cannot diagnose distal overgrowth, occurring in the latter 17 feet of the SI, which is thought to be more common.

How is the test performed?

The test is performed either at home with a take home kit or in a medical office that has a breath testing machine such as a hospital, doctors office, or clinic lab.  It takes 1-3 hours in the morning after a 12 hour fast the night before and a special diet the day before.  At home kits may be obtained from numerous laboratories. 

Which Test Is Best?

Physicians and studies use both glucose and lactulose.  We currently use the 3 hour lactulose test in our office and have good results with this method.

 

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