Small Intestinal Bacterial Overgrowth


The small bowel or the small intestine is a part of the gastrointestinal tract that normally accommodates bacteria. The colon has the greatest available number of bacteria while the small intestine contains much lower. In addition, the bacteria within the colon and those in the small intestine are not similar with each other.

Small Intestinal Bacterial Overgrowth

Small intestinal bacterial overgrowth (SIBO) also medically known as Small bowel bacterial overgrowth syndrome (SBBSOS) is referred to as a condition where there is an abnormally large amount of bacteria is growing within the small intestine, with at least 100,000 bacteria per ml of fluid. The kind of bacteria that is present inside the small intestine is much more similar with the bacteria located in the colon.

Small Intestinal Bacterial Overgrowth Symptoms

Small intestinal bacterial overgrowth has no specified clinical features or even physical findings that could make the diagnosis of the condition. Instead, SIBO must be taken into consideration that the existence of many compiled non-specific symptoms that occur each by themselves should not be alarming, unless they appear all together.

Symptoms of SIBO may include:

  • Abdominal pain
  • Abdominal cramps
  • Excess gas in the alimentary canal
  • Bloating
  • Diarrhea that is usually watery
  • Indigestion
  • Constipation
  • Weight loss

Not all individuals with SIBO experience all of these symptoms. As the disease progresses, the overgrowth of bacteria restrains the ability of the body to correctly absorb nutrients from the diet. This could result to electrolyte and vitamin abnormalities, problems with fat absorption, and protein insufficiency.


When the small intestine has too many bacteria, these organisms eat up the nutrients that are supposedly absorbed into the body. As a result, a person with Small Intestinal Bacterial Overgrowth can become malnourished.

The nutrient breakdown inside the small intestine caused by the excess bacteria could damage the intestinal lining as well. This will make it more difficult to absorb nutrients for the body.

There are a lot of conditions related with SIBO and a few are commonly known such as:

  • Diverticuli (out-pouchings) of the small intestine wherein the bacteria is allowed to multiply and live without being swept away.
  • Muscular and neurological conditions could change the normal activity of muscles in the intestine. Scleroderma directly harms the intestinal muscles. Diabetes mellitus harms the nerves that manage the intestinal muscles. In those cases, SIBO can develop due to the abnormal activity of the muscles in the small intestine.
  • Irregular or partial blockage of the small intestine could affect the transport of bacteria and food through the small intestine and may lead to SIBO. The causes of the blockage that result to SIBO involve Crohn’s disease and scarring from previous surgery.

Predisposing factors which might lead to SIBO are:

  • An impaired motility or movement of the small bowel or anatomical changes that ends up with stasis
  • Disorders that arise in the immune system
  • Health conditions that allows more bacteria from the colon to enter the small bowel

small intestine bacterial overgrowth causes pathogenesis symptoms


The onset of Small Intestinal Bacterial Overgrowth symptoms is not specific and it might take time for the physician to consider the condition as a possible cause. The clues might come from other diseases related with malabsorption of vitamins, proteins, and fats. It is essential to find out those causes and also the potential causes of SIBO.

The diagnostics tests may involve:

  • Blood tests – May be useful for finding the different causes of vitamin deficiencies, anemia, and electrolyte imbalance
  • Upper GI endoscopy – Permits the gastroenterologist to assess the inside of the upper area of the small intestine and take small samples of tissue that may be studied under the microscope. Fluid samples from the jejunum and duodenum can also be examined for possible abnormalities that are linked with SIBO.
  • Breathe tests – These are done to evaluate the byproducts of digestion particularly those that accountable on the bacteria inside the intestine.  The tests involve D-xylose, hydrogen breath test, and bile acid.


Dietary treatments for Small Intestinal Bacterial Overgrowth can be used without any other antibiotics or treatment. The diet could decrease the number of bacteria although the rate is slower compared to antibiotics.

SIBO Specific Diet is a combination of:

  • Low FODMAP diet – This type of diet can reduce symptoms of SIBO, which involves the limiting of foods high in polyols, fructose, galactans, lactose, and fructans.
  • Specific Carbohydrate Diet (SCD) – It is a restrictive type of diet that can treat a number of systemic and gastrointestinal diseases including SIBO.


The treatment for SIBO focuses on treating and managing any underlying conditions associated with it. The main goal is to restrain the symptoms of the condition since the disease that caused the SIBO often is not possible to correct.

Antibiotics are very effective for this disease, but clinical signs mostly recur when they are stopped. Some physicians find it obligatory to treat the patient with certain antibiotics repeatedly or perhaps continuously.

In some other cases, motility-speeding drugs are prescribed by the physician to speed up the intestinal movement.

Getting enough nutrition and fluids are also helpful. An individual who is malnourished might need nutrition that is given through a vein which is called total parenteral nutrition (TPN). An individual who is dehydrated may be in need of intravenous (IV) fluids in a hospital.


  • Small intestinal bacterial overgrowth (SIBO) facts What causes SIBO? Who is at risk for SIBO? What are the signs and symptoms of SIBO? How is the diagnosis of SIBO made? What is the treatment for SIBO? Can SIBO be prevented? What is the prognosis for SIBO? at
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  • Menees SB, Maneerattannaporn M, Kim HM, Chey WD (2012). The efficacy and safety of rifaximin for the irritable bowel syndrome: a systematic review and meta-analysis. Am J Gastroenterol 107: 28–35.
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