SIBO symptoms, risk factors and causes

SIBO symptoms, risk factors and causes

SIBO is shortcut for Small Intestinal Bacterial Overgrowth. It happens when the bacteria in the gut get out of balance and overgrow. SIBO refers to a condition in which abnormally large numbers of bacteria are present in the small intestine and the types of bacteria which are present in the small intestine resemble more the bacteria of the colon than the small intestine. The number of bacteria is usually defined as at least 100,000 bacteria per ml of fluid. Many conditions are associated with SIBO, including Crohn’s disease, scleroderma, diabetes and others. There are some similarities between the symptoms of SIBO and IBS (irritable bowel syndrome) [1]. There are some theories that SIBO can be responsible for the symptoms of at least some people diagnosed with IBS. The small intestine or small bowel is part of our gastrointestinal tract which connects the stomach with the colon. The main function of the small intestine is to digest and absorb food into the body. The small bowel is approximately 21 feet in length. It begins at the duodenum which is followed by the jejunum and then the ileum. It is known that the entire gastrointestinal tract in which small intestine is also included, contains bacteria. The number of bacteria which is present in the small intestine is much lower and in the colon is greatest. Also the types of bacteria which are present in the small intestine are different than the types of bacteria which are present in the colon. But in some studies are suggested that SIBO and its symptoms can happen with smaller number of bacteria, for example 10,000 per ml of fluid. When some patient has a typical case of this condition, then the patient can experience symptoms which fluctuate in intensity over months, years or even decades before the diagnosis is made. It is known that the symptoms of SIBO tend to be chronic. [2]

SIBO symptoms, risk factors and causes

Symptoms: Here are the most common signs and symptoms of SIBO:

  • Fat malabsorption
  • B12 deficiency, as well as other vitamins and minerals
  • Chronic illnesses, such as diabetes, chronic fatigue syndrome, fibromyalgia, autoimmune diseases and neurological disorders
  • Food intolerances such as fructose, lactose, casein, gluten and more
  • Diagnosis of inflammatory bowel disease or irritable bowel syndrome
  • Constipation (much less common than diarrhea)
  • Abdominal pain or cramping
  • Diarrhea
  • Bloating
  • Gas

Causes: We know that our gastrointestinal tract is uninterrupted muscular tube through which digested food is transported on the way to the colon. This coordinated activity of the muscles of the small intestine and stomach propels the food from the stomach through the small intestine and it finish into the colon. Also when there is no food in the small intestine, the muscular activity sweeps through the small bowel from the stomach to the colon. The muscular activity which sweeps through the small bowel is important for the digestion of food but also it is important it sweeps bacteria out of the small bowel and at the same time, it limits the number of bacteria in the small bowel. Anything which can interfere with the progression of normal muscular activity through the small intestine can lead to SIBO. Any condition which is interfering with the muscular activity in the small intestine is allowing bacteria to stay longer and to multiple in it. Also the lack of muscular activity is allowing the bacteria to spread backward from your colon to your small intestine. The neurological and muscular diseases can alter the normal activity of your intestinal muscles. The intermittent or the partial obstruction of your small bowel interferes with the transport of food and bacteria through your small intestine and this can result in SIBO. [3]

SIBO symptoms, risk factors and causes

SIBO symptoms, risk factors and causes

Risk factors: Here are some factors which can increase the risk of SIBO [4,5]:

  1. Medications:
  • Gastric acid suppression
  • Recurrent antibiotics
  1. Organ system dysfunction:
  • Malnutrition
  • Celiac disease
  • Crohn’s disease
  • Immunodeficiency states
  • Pancreatitis
  • Renal failure
  • Cirrhosis
  1. Elderly 
  2. Metabolic disorders:
  • Hypochlorhydria
  • Diabetes
  1. Irritable bowel syndrome [1]
  2. Motility disorders:
  • Chronic intestinal pseudo – obstruction
  • Celiac disease
  • Small bowel dysmotility
  • Gastroparesis
  1. Structural/anatomic:
  • Gastric resection
  • Fistulas between proximal and distal bowel
  • Resection of ileocecal valve
  • Surgically created blind loops
  • Small intestine structures (Crohn’s disease, medications, radiation)
  • Small intestine diverticula


[1] Ghoshal UC, Shukla R, Ghoshal U. Small intestinal bacterial overgrowth and irritable bowel syndrome: A bridge between functional organic dichotomy. Gut Liver. 2017;11(2): 196–208.

[2] Saffouri GB, Shields-Cutler RR, Chen J, et al. Small intestinal microbial dysbiosis underlies symptoms associated with functional gastrointestinal disorders. Nature Communications. 2019;10.

[3] Sachdev AH, Pimentel M. Gastrointestinal bacterial overgrowth: pathogenesis and clinical significance. Therapeutic Advances in Chronic Disease. 2013;4(5):223–31.

[4] Dukowicz AC, Lacy BE, Levine GM. Small intestinal bacterial overgrowth: A comprehensive review. Gastroenterology & Hepatology. 2007;3(2):112–22.

[5] Rao S, Bhagatwala J. Small intestinal bacterial overgrowth: Clinical features and therapeutic management. Clinical and Translational Gastroenterology. 2019;10(10).


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