SIBO – Small Intestinal Bacterial Overgrowth (an important diagnosis to gut symptoms)

 In Digestive System

The small intestine, or small bowel as it is sometimes called, is an integral part of the digestive process. Its job is to absorb nutrients and minerals from the food you eat. Despite the name, the small bowel is not small. It stretches about 20 feet from end to end and is made up of three distinct sections. A lot can go wrong inside that long path of intestine including a condition that you might not be familiar. It’s called small intestinal bacterial overgrowth (SIBO).

What is Small Intestinal Bacterial Overgrowth?

SIBO is an overgrowth of aerobic and anaerobic microbes in the small bowel. These bacteria generally live in the large intestine. There are bacterial concentrations throughout the GI tract, and that’s healthy, but the population in the small intestine is scarce, typically only 10,000 bacteria per milliliter of fluid.

What Causes SIBO?

In a healthy gut, bacteria overgrowth should not happen. The body has a way of protecting the small intestine from it with:

  • Gastric acid
  • Pancreatic and biliary secretions
  • Small bowel movement called peristaltic waves

There is also a valve between the small and large intestine designed to keep the bacteria where they belong. SIBO develops when one of these safeguards fails. For example, if for some reason the small bowel stops moving, bacteria can start to divide and ascend up the bowels.

The Cleveland Clinic also lists antibiotics as a possible cause of SIBO. There is a delicate ecosystem in the intestinal tract one that requires the good bacteria to keep the harmful bacteria in check. Antibiotics can kill off enough of the good bacteria so that the bad takes over. The clinic also states a gastrointestinal obstruction or radiation therapy might trigger SIBO.

What are Medical Conditions That Can Cause SIBO

SIBO can be a symptom of another condition, too, such as:

  • IBS
  • Neuromuscular diseases like restless leg syndrome
  • Inflammatory Bowel Disease
  • Pancreatic disease
  • Celiac disease
  • Hypothyroidism
  • Liver disease
  • Diabetes
  • Fibromyalgia
  • Rosacea
  • Parkinson’s disease

What are the Risk Factors for SIBO?

Besides the conditions listed, the other risk factors for small bowel intestinal overgrowth include:

  • Obesity
  • Advanced age
  • Medication like antibiotics, gastric acid suppressors or opioid pain meds
  • GI infection
  • Surgery
  • Strictures, which are kind of like scar tissue that causes narrowing of a passage

An organ system dysfunction can put you at risk, as well, such as kidney failure.

What are the Symptoms of Small Intestinal Overgrowth?

Many symptoms point to SIBO, but abdominal bloating or distention is the hallmark sign of this problem. Other potential symptoms include:

  • Excessive gas
  • Belching
  • Abdominal cramps
  • Diarrhea
  • Constipation
  • Nausea
  • Heartburn

Some people develop nutrient deficiencies from SIBO, too. For example, their body might not have enough iron or vitamin B12.

How is SIBO Diagnosed?

The Gold Standard test for small intestine bacteria overgrowth requires a surgeon to take a small amount of fluid from the small bowel using an endoscope. A lab will use that fluid to culture bacteria and see what grows. The culture gives them an idea of what the bacteria population is like in the small intestine.

There are some downsides to this process, though. For one thing, it’s invasive. It can also be limiting. The endoscope can only reach the top of the small bowel, and so the test doesn’t offer a full view of the bacteria growing in the entire 20 feet.

A less invasive means of diagnosis is the breath test.  First, a sample of the patient’s breath is taken first as a reference point.  The patient then drinks a liquid that moves through the intestinal tract. If there are bacteria, they will take this liquid and ferment this, therefore, producing gases such as hydrogen and methane.  These gases are dented with subsequent breath collections.

There are many advantages to this test over the other one. For one thing, it is not invasive like the endoscopy procedure. It also tests the entire small bowel as opposed to just the top section.

What is the Treatment for SIBO?

The ultimate result of any treatment is to restore the healthy bacterial balance of the small intestine. Typically that involves antibiotic therapy. The downside to antibiotics is the overgrowth may come back.

Doctors will approach treatment of SIBO with three goals in mind:

Eliminating the overgrowth – Antibiotics can accomplish this goal. The ones typically prescribed for SIBO include:

  • Rifaximin
  • Rifaximin plus neomycin
  • Amoxicillin-clavulanate
  • Metronidazole with a cephalosporin
  • Metronidazole with trimethoprim/sulfamethoxazole
  • Botanicals like oregano oil

Providing good nutritional support – Nutritional support is necessary to prevent some problems that can occur with SIBO like:

  • Weight loss
  • Fat-soluble vitamin deficiency
  • Vitamin B12 deficiency
  • Iron deficiency
  • Low serum bile acids
  • Low red blood cell folate levels

The health care provider might recommend a specialized diet to control overgrowth of bacteria.  These diets include the elemental diet and the low FODMAP diet.

Correcting the underlying problem – SIBO is a symptom that something else is going on to cause the overgrowth. The treatment plan will look for this cause and treat it to prevent an occurrence.

Retesting during the treatment can provide feedback on how well it is working and allow the care team to make adjustments where necessary.

Small intestinal bacterial overgrowth can be a difficult condition to treat. It is a complex disease, and the treatment that works for one person might not work the next.


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