SIBO (Small Intestinal Bacterial Overgrowth)

SIBO (Small Intestinal Bacterial Overgrowth)

Things to know about small intestinal bacterial overgrowth (SIBO)

 Picture of SIBO (Small Intestinal Bacterial Overgrowth)

Picture of SIBO (Small Intestinal Bacterial Overgrowth)

  • SIBO stands for small intestinal bacterial overgrowth.
  • SIBO can be considered to be of two types. One is associated with identifiable diseases or conditions of the intestines. The other is not.
  • SIBO of either type can give rise to similar symptoms including indigestion, diarrhea, bloating, abdominal pain, and diarrhea or loose stools.
  • The type associated with intestinal diseases and conditions may result in, the inability of the body to absorb nutrients from the intestine and may lead to malnutrition and vitamin deficiencies that may help direct testing to find the diagnosis. This article deals only with SIBO associated with intestinal diseases and conditions.
  • The diagnosis is often one of exclusion, making sure that other causes of the symptoms are not present.
  • Blood tests, breathing tests, and biopsies or tissue samples from the small intestine may be required to diagnose either type of SIBO.
  • Antibiotics may be prescribed but the type and length of treatment depend upon the patient and the symptoms.
  • Any underlying illness will also need to be addressed at the same time once therapy is started for SIBO.
  • The prognosis depends upon how well the associated illnesses are managed and the response to therapy. Relapse is relatively common.

SIBO and IBS: FODMAP Foods to Eat and Foods to Avoid

FODMAP is an acronym for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. High FODMAP foods have a lot of simple carbohydrates and sugar alcohols that aren’t absorbed by the gut very well, and can pose a problem particularly if you have IBS or another bowel condition that puts you at risk for the condition. Examples of foods high in FODMAPs (foods that sit and ferment in the gut) include:

  • Beans
  • Lentils
  • Wheat
  • Dairy products

How does normal gut bacteria cause SIBO?

The small intestine is a relatively clean place. The stomach receives food, mixes it with acid and digestive juices, and turns it into a clean slurry that is pushed through the three parts of the small intestine (duodenum, jejunum, ileum) where the nutrients are absorbed into the body. The refuse is dumped into the large intestine, or colon, where water is absorbed and the feces become more solid and are eliminated from the body.

The normal bacteria (flora) of the gut, perform important functions, helping to digest certain vitamins like folic acid and vitamin K, and they protect the intestine from being invaded by disease-causing bacteria. However, if the normal function of the intestine is compromised, bacterial overgrowth may occur. This may be the result of a lack of adequate stomach acid, damage to the intestine by toxins like alcohol, or a decrease in the speed at which the small intestine transfers material to the colon.

The colon is not as clean as the small intestine and reflux, or backflow, of stool into the small intestine can colonize it with colonic bacteria.

This article will discuss only the type of SIBO associated with intestinal diseases and conditions.

Associated SIBO: Types of other diseases or conditions associated with it

Small intestine bowel overgrowth is often associated with another illness that affects the function of the small intestine. The body has many protective mechanisms to keep bacteria under control, including stomach acidity and intestinal motility, the ability of the intestine to move its contents downstream at an appropriate speed. Bacterial growth is hindered by the presence of bile and immunoglobulins. Finally, the ileocecal valve prevents stool from refluxing from the colon (large intestine) into the ileum or the last part of the small intestine.

Any illness or disease that affects the body’s defense mechanism puts a person at risk for SIBO, but the majority of people develop SIBO because of an intestinal motility problem. These may include:

  • complications from gastric bypass surgery,
  • bowel strictures and adhesions that can lead to intermittent bowel obstructions,
  • diverticuli or outpouchings of the small intestine, and
  • tumors.

Bowel motility may be affected by neurologic diseases including:

  • myotonic dystrophy, 
  • Parkinson’s disease, and
  • a rare condition called intestinal pseudo-obstruction.

People with diabetes with autonomic dysfunction (nerve damage) may also develop dysmotility.

Other intestinal diseases that may be associated with SIBO include:


What is irritable bowel syndrome or IBS? See Answer

SIBO symptoms and signs

There are no specific complaints or physical findings that can make the diagnosis of SIBO. Instead, small intestine bacterial overgrowth should be considered in the presence of a compilation of many non-specific symptoms; each by itself would not be worrisome but together can point to the potential diagnosis.

Initial symptoms are specific to the gastrointestinal tract and abdomen and include:

A person with SIBO does not need to have all of these symptoms.

As the disease progresses, the bacterial overgrowth inhibits the body’s ability to properly absorb nutrients from the diet. This can lead to vitamin and electrolyte abnormalities, protein deficiencies, and difficulties with fat absorption.

Inability to absorb vitamin B12 can lead to symptoms of pernicious anemia, including a low red blood cell count and peripheral neuropathy. Anemia also may be due to iron deficiency. Decreased Vitamin A may lead to night blindness. The metabolic bone disease may be due to Vitamin D deficiency and decreased calcium. This may also lead to muscle twitching and spasms.

Malnutrition may result in weight loss, and progress to excessive muscle wasting (cachexia). Inability to absorb fats in the diet may lead to steatorrhea (excess fat in the feces) that results in foul-smelling oily stool, and may cause some anal leakage or fecal incontinence.

Is there a test to diagnose the condition?

The initial symptoms of small intestine bacterial overgrowth are non-specific and it may take time for the person and health care professional to consider SIBO as a potential cause. The clues may come from illnesses associated with the malabsorption of proteins, fats, and vitamins. When there is malabsorption it is important to look for SIBO.

Blood tests may be ordered to look for different causes of anemia, electrolyte imbalance, and vitamin deficiencies.

Breath tests may be considered to diagnose SIBO by looking for the byproducts of digestion, especially those produced by bacteria. Upper GI endoscopy allows a gastroenterologist to look at the inside of the upper part of the small intestine and take biopsies or small bits of tissue that can be examined under the microscope. Biopsies can determine if there is damage to the lining of the intestine that may be giving rise to the symptoms either through the mechanism of bacterial overgrowth or via another mechanism.

While these diagnostics tests are being performed, it is appropriate for the health care professional to look for conditions that are associated with SIBO. If such a condition is already known, then maximizing treatment of the associated condition may be undertaken at the same time the diagnosis of which SIBO is being considered and tested.

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Antibiotic and probiotic treatment for SIBO

The treatment for SIBO includes controlling and treating any underlying associated illness. The goal is to control the symptoms of small intestine bacterial overgrowth since it may not be possible to “cure” the disease.

Antibiotics are one of the treatments that help control excess bacteria. Not all the bacteria in the intestine must be eradicated since some are required to help with normal digestion.

Amoxillin-clavulanate (Augmentin) and rifaxamin (Xifaxan) are the two common first-line antibiotics that may be prescribed. Depending upon the situation, other antibiotics may also be considered, including:

While a single course of antibiotics for 1-2 weeks may be sufficient, SIBO tends to relapse, and sometimes repeated courses of antibiotics may be required. In some people, the antibiotics will be routinely cycled, meaning that they will alternate 1-2 weeks on the antibiotic with 1-2 weeks off.

In addition, underlying vitamin and nutrient deficiencies due to malabsorption should be treated.

How can the condition be prevented?

Since SIBO usually is a secondary illness that occurs because the intestine has in some way been affected by another disease, it is important to keep chronic diseases properly treated and under control as best as possible.

Does SIBO relapse? What’s the prognosis?

Small intestine bacterial overgrowth is usually associated with another underlying illness. Even with appropriate treatment, the relapse rate is high and often depends upon how well the underlying illness is managed and controlled.


IBS – Irritable Bowel Syndrome: Symptoms, Diet, Treatment See Slideshow

Medically Reviewed on 8/8/2022



Tursi A, Brandimarte G, Giorgetti GM, Elisei W. Assessment of small intestinal bacterial overgrowth in uncomplicated acute diverticulitis of the colon. World J Gastroenterol. 2005;11:2773–2776