Small Intestinal Bacterial Overgrowth (SIBO) A Gut Related Diagnosis That Is Under Diagnosed

What is SIBO?

Simply put, Small Intestine Bacterial Overgrowth 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.  (1)

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 SI (leaky gut syndrome, which I prefer to call leaky SI in this case).

  • 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 SI lining damage, which creates more bacterial overgrowth (a vicious cycle).
  • After eating our food, they produce gas/ expel flatus, within our SI.  The gas causes abdominal bloating, abdominal pain, constipation, diarrhea or both (the symptoms of IBS).  Excess gas can also cause belching and flatulence.
  • They decrease proper fat absorption by deconjugating bile 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 (endotoxin) 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.

Human intestinal microbiota create a complex polymicrobial ecology. This is characterised by its high population density, wide diversity and complexity of interaction. Any dysbalance of this complex intestinal microbiome, both qualitative and quantitative, might have serious health consequence for a macro-organism, including small intestinal bacterial overgrowth syndrome (SIBO). SIBO is defined as an increase in the number and/or alteration in the type of bacteria in the upper gastrointestinal tract. There are several endogenous defence mechanisms for preventing bacterial overgrowth: gastric acid secretion, intestinal motility, intact ileo-caecal valve, immunoglobulins within intestinal secretion and bacteriostatic properties of pancreatic and biliary secretion. Aetiology of SIBO is usually complex, associated with disorders of protective antibacterial mechanisms (e.g. achlorhydria, pancreatic exocrine insufficiency, immunodeficiency syndromes), anatomical abnormalities (e.g. small intestinal obstruction, diverticula, fistulae, surgical blind loop, previous ileo-caecal resections) and/or motility disorders (e.g. scleroderma, autonomic neuropathy in diabetes mellitus, post-radiation enteropathy, small intestinal pseudo-obstruction). In some patients more than one factor may be involved. Symptoms related to SIBO are bloating, diarrhoea, malabsorption, weight loss and malnutrition. The gold standard for diagnosing SIBO is still microbial investigation of jejunal aspirates. Non-invasive hydrogen and methane breath tests are most commonly used for the diagnosis of SIBO using glucose or lactulose. Therapy for SIBO must be complex, addressing all causes, symptoms and complications, and fully individualised. It should include treatment of the underlying disease, nutritional support and cyclical gastro-intestinal selective antibiotics. Prognosis is usually serious, determined mostly by the underlying disease that led to SIBO. (2)

The overall prevalence of SIBO in the general public is unknown. 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%. (2)

In particular diseases and disorders, literature data on prevalence differ substantially. For instance, the prevalence of SIBO in patients fulfilling diagnostic criteria for irritable bowel syndrome was 30%-85%[911,16,18,19]. The prevalence of SIBO in coeliac disease non-responding to a gluten-free diet was up to 50%[20]. In liver cirrhosis, SIBO was diagnosed in more than 50% of cases[21,22]. In a small group of elderly people (70 to 94 years old) with lactose malabsorption, SIBO was documented in 90%[23]. An interesting study was performed on asymptomatic morbidly obese subjects and SIBO was found in 17% (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. (1)

Hydrogen Breath Test

A hydrogen breath test can be used to diagnose several conditions:  H pylori infection, carbohydrate malabsorption (ex. lactose) and SIBO.

SIBO Breath Test
Breath testing measures the hydrogen (H) & methane (M) gas produced by bacteria in the SI that has diffused into the blood, then lungs, for expiration.  H & M 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.
Two 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 H and/or M.

The advantage to this test is that it can diagnose overgrowth in the distal end of the SI, 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 SI, therefore if the bacterial gases of H and/or M 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 at a facility 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 breath testing laboratories.  Lactulose kits require a physician prescription.

Which Test Is Best?

Physicians and studies use both glucose and lactulose.  I currently use the 3 hour lactulose test and have good results with this method.

Test Interpretation

Doctors vary widely in how they interpret SIBO breath tests.  What one physician calls negative, another call positive. There is no universally accepted standard among physicians at present.
For a detailed explanation of various positive standards and interpretation with case examples, please see my article on test interpretation or either one of my SIBO class videos.

Articles:
SIBO: The Finer Points of Diagnosis, Test Interpretation, and Treatment by Drs Siebecker & Sandberg-Lewis
How to Interpret Hydrogen Breath Tests by Dr Ghoshal
Implementation and Interpretation of Hydrogen Breath Tests by Dr Eisenmann et al

 

RESOURCES:

(1) http://www.siboinfo.com/overview.html

(2) Small intestinal bacterial overgrowth syndrome; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2890937/