What is SIBO?

SIBO or Small Intestinal Bacterial Overgrowth is a condition in which there is excessive accumulation of bacteria in the small intestine.

There are two types of SIBO, methane dominate or hydrogen dominate. Methane and hydrogen are the gasses that are released by the overgrowth bacteria. Hydrogen dominate is more often causes chronic diarrhea and may even cause malnutrition and unintentional weight loss since the bacteria use up the body’s nutrients. Methane dominate, on the other hand, is more likely to cause constipation and weight gain.

Symptoms of SIBO

SIBO mainly affects the gut, and symptoms include1:

  • Bloating
  • Diarrhea
  • Abdominal pain/discomfort
  • Abdominal distension
  • Constipation
  • Indigestion
  • Gas
  • Weight loss
  • Weakness

Who is at Risk of developing SIBO?

Structural abnormalities of the small intestine may affect the way food moves. The lack of movement can cause a bacterial imbalance. The risk factors for SIBO include:

Age ­– SIBO can occur in older people because of an age-related decrease in gastrointestinal (GI) motility, which can be due to the ingestion of many medications, reduced bowel movement, malnutrition, and lowered gut immune function.

Irritable Bowel Syndrome – Since symptoms of irritable bowel syndrome are similar to SIBO, such as bloating, cramping, distention, and abdominal discomfort, some studies have found an overlap between the two conditions. Even though some studies failed to replicate these findings, delayed transit and disordered motility in irritable bowel syndrome could potentially account for the occurrence of SIBO.

Anatomic Abnormalities – Proper structural anatomy of the small intestine is crucial for its normal movement. Lack of movement can lead to bacterial imbalance, which can cause SIBO. Anatomic abnormalities can include:

  • Small-bowel obstruction – a blockage in the small intestine that is caused by scar tissue, hernia, cancer, or as a result of prior surgeries.
  • Small-bowel diverticula –  a condition in which there are small pouches called diverticula in the small intestine
  • Adhesions – commonly known as scar tissue developed from multiple abdominal surgeries or radiation therapy.
  • Fistula – an abnormal connection between two parts of the bowel.
  • GI tract surgeries- surgical procedures such as Roux-en-Y or gastric bypass surgery can lead to the small intestine’s abnormal motility, leading to bacterial overgrowth.

Certain Medications – certain medications may sometimes be the cause of SIBO2:

  • Narcotics
  • Frequent use of antibiotics, which can affect the bacteria in the small intestine
  • Anti-spasm medications that treat irritable bowel syndrome
  • Protein-pump inhibitors (PPIs) that reduce stomach acid production to control heartburn

Certain Medical Conditions – certain medical conditions can interfere with how the intestines normally work, leading to SIBO. These medical conditions include3,4:

  • Coeliac disease
  • Crohn’s disease
  • Scleroderma
  • Diabetes mellitus
  • Lupus
  • Liver cirrhosis
  • Immunodeficiency syndromes – such as AIDS, IgA deficiency, chronic lymphocytic leukemia, and immunoglobulin deficiencies.
  • Chronic pancreatitis
  • Chronic fatigue syndrome
  • End-stage renal disease
  • Myotonic muscular dystrophy
  • Chronic intestinal pseudoobstruction
  • Cystic fibrosis


If you are experiencing symptoms of SIBO, it is essential to see a doctor for a proper diagnosis since symptoms can often be mistaken for many other medical conditions. A gastroenterologist is a doctor that specializes in the digestive system and can help diagnose SIBO by ordering tests to check the bacterial growth in your gut. Common tests for SIBO diagnosis include:

  • Breath testing­ is a non-invasive, most widely available, and least expensive test for diagnosing SIBO. In SIBO, the excess bacteria in the small intestine can release hydrogen and methane gases. The breath test measures the presence of hydrogen and methane that you breathe out after drinking a sugary beverage. During the test, you breathe into a tube at regular intervals of 15 minutes for 3 hours. If there is a rapid increase in hydrogen and methane gases after breathing out, it may indicate SIBO3,4.
  • Small-bowel jejunal aspiration and culture is the most widely accepted test for diagnosing SIBO.  It is an invasive test in which your doctor will pass a long thin tube called an endoscope down your throat through your upper digestive tract to your small intestine. A sample of your intestinal fluid will be taken and tested in the laboratory to produce a culture. The culture helps to observe the growth of bacteria.
  • Blood tests can be taken in addition to other tests to look for any vitamin deficiencies or anemia.
  • Stool tests help determine fat malabsorption, which can indicate SIBO.
  • Imaging tests such as X-ray, CT scan, or MRI can help look for structural abnormalities of the small intestine.

Treatment and management of SIBO

Since there are many different types and levels of SIBO, treatment varies according to the patient’s medical condition and addresses all the causes, symptoms, and complications of SIBO. Your doctor will help determine the best treatment option for you, depending on your medical tests. SIBO treatment aims to correct the cause, treat the bacterial overgrowth, and provide nutritional support in patients with weight loss or vitamin deficiency3. The following are the common treatment options for SIBO:

  • Antibiotic Therapy – Antibiotics is the mainstay of treatment for SIBO since it helps reduce or eliminate bacterial overgrowth and reverses the mucosal inflammation associated with bacterial overgrowth and malabsorption. Antibiotics help produce a remarkable improvement of symptoms in most SIBO patients. The choice of antibiotics differ according to the following conditions:
  • Hydrogen-predominant bacterial overgrowth: The primary treatment is rifaxamin 1650 mg/day for two weeks5.
    • Methane-predominant bacterial overgrowth: This type of SIBO is harder to treat; therefore, a combination of neomycin 1000 mg/day and rifaximin 1650 mg/day is given for two weeks as treatment5.

Other antibiotics for SIBO treatment include4:

  • Amoxicillin–clavulanic acid
    • Cephalexin + metronidazole
    • Trimethoprim-sulfamethoxazole
    • Ciprofloxacin
    • Colistin + metronidazole
    • Doxycycline
    • Tetracycline
    • Minocycline
    • Chloramphenicol
  • Surgery – Surgical intervention is considered when it is possible to correct gastrointestinal abnormalities such as blind loops, bowel obstruction, enterocolic fistula, and multiple small intestinal diverticula3.
  • Nutritional support – In patients with nutritional deficiencies or weight loss, nutritional support is crucial in addition to antibiotics in the management of SIBO. Malabsorption can cause the loss of macronutrients and micronutrients, such as omega-3 fatty acids and liposoluble nutrients, such as vitamins A, D, E, and K5. Monthly intramuscular injections of vitamin B12 can help manage cobalamin deficiency. Pancreatic enzyme supplementation can improve the breakdown and absorption of protein, fat, and starch in patients with steatorrhea. Correcting other deficient nutrients, such as calcium, magnesium, and iron may also be necessary4,6.

Some of the dietary therapies to prevent the recurrence of SIBO, repair the intestinal lining, or provide an optimal nutritional status include:

  • Lactose-free diet – If damage to the small intestine occurs, it may cause the inability to digest lactose; therefore, a lactose-free diet or the substitution of a large proportion of dietary fat with medium-chain triglycerides will be essential6.
  • FODMAP diet – A low fermentable oligosaccharide, disaccharides, monosaccharides, and polyols (FODMAP) diet can help prevent intestinal distress and diarrhea, cramping, constipation, stomach bloating, and gas symptoms6.
  • Elemental diet – An elemental diet is a liquid formula that contains all the predigested essential nutrients in their simplest form so that they are easy to absorb. This diet prevents the delivery of nutrients to bacteria in the small intestine’s distal portion to prevent SIBO7.
  • Specific Carbohydrate diet (SCD) – The SCD diet is a restrictive diet that allows some carbohydrates but restricts others. In this diet, starches, grains, and processed foods are prohibited, but fruits and vegetables are permitted. This diet can help with SIBO treatment because it restricts the carbohydrates that don’t get fully digested and remain in the gut, which allows the overgrowth of harmful bacteria8.
  • Gut and Psychology Syndrome diet (GAPS) – the GAPS diet is similar to the SCD diet with a few changes. In the GAPS diet, fewer beans are permitted. In addition, grains, refined food, pasteurized dairy, and starchy vegetables are prohibited8.
  • Bi-phasic diet – The bi-phasic diet combines the low-FODMAP and SCD diets and consists of two phases. Phase 1 focuses on repairing damage to the intestinal lining and maintaining proper digestion. All grains, legumes, dairy, sugar, certain vegetables, canned foods, processed foods, fermented foods and alcohol are avoided. During phase 2, antimicrobials are introduced to remove the remaining bacteria and fungi from the small intestine. Some prohibited food from phase 1 is permitted for some bacteria to grow for the antimicrobials to be more successful.
  • Vegan and vegetarian diets – Vegan and vegetarian diets rich in fiber can effectively manage symptoms of SIBO since these diets increase the production of short-chain fatty acids and inhibit invasive bacteria7.
  • Recurrent SIBO – Approximately 45 percent of patients experience a relapse of SIBO symptoms after completing antibiotic therapy. Recurrence is treated with either the same or alternative antibiotics. If recurrence occurs within three months, a second course of antibiotics is given. If recurrence occurs beyond three months, antibiotics are only prescribed after a positive carbohydrate breath test.

Other potential forms of treatment include:

  • Probiotics and prebiotics – Probiotics and prebiotics have been suggested for SIBO treatment because they help strengthen the gut’s barrier function, modify the bowel’s inflammatory response, and inhibit several pathogens. However, research studies show mixed results and further studies are needed.
  • Prokinetics – Prokinetics help improve gastrointestinal motility and can potentially be used for SIBO treatment when combined with antibiotics. However, more studies are needed to define the role of prokinetics in SIBO treatment.

SIBO Complications

SIBO complications range from mild to severe. Mild complications include diarrhea and minimal vitamin deficiencies. Severe complications are caused due to fat-soluble vitamin deficiencies and include malabsorption and neuropathies. Early recognition and treatment of SIBO can help avoid malnutrition and weight loss leading to morbidity and mortality. If SIBO is left untreated, it can lead to intestinal failure.

Prevention Prevention is crucial in the management of SIBO. Addressing the root cause of SIBO can help prevent a reoccurrence. Correction of physical defects in the small intestine or treating the underlying medical condition can help prevent SIBO. The removal of protein pump inhibiting drugs (PPIs) and antacids can also help prevent SIBO since they reduce hydrochloric acid, a risk factor of SIBO. Dietary and lifestyle changes may also be essential for the reoccurrence of SIBO.


  1. Dukowicz, A. C., Lacy, B. E., & Levine, G. M. (2007). Small intestinal bacterial overgrowth: a comprehensive review. Gastroenterology & hepatology3(2), 112–122.
  2. Krajicek, E. J., & Hansel, S. L. (2016). Small Intestinal Bacterial Overgrowth: A Primary Care ReviewMayo Clinic proceedings91(12), 1828–1833. https://doi.org/10.1016/j.mayocp.2016.07.025.
  3. Bures, J., Cyrany, J., Kohoutova, D., Förstl, M., Rejchrt, S., Kvetina, J., Vorisek, V., & Kopacova, M. (2010). Small intestinal bacterial overgrowth syndrome. World journal of gastroenterology16(24), 2978–2990. https://doi.org/10.3748/wjg.v16.i24.2978
  4. Singh, V. V., & Toskes, P. P. (2003). Small bowel bacterial overgrowth: presentation, diagnosis, and treatment. Current gastroenterology reports5(5), 365–372. https://doi.org/10.1007/s11894-003-0048-0
  5. Sorathia, S. J., & Rivas, J. M. (2020). Small Intestinal Bacterial Overgrowth. In StatPearls. StatPearls Publishing.

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