Small Intestinal Bacterial Overgrowth (SIBO) – How It Is Caused?


Small intestinal bacterial overgrowth (SIBO) is a condition where excessive bacteria grow in the small intestine. This leads to poor nutrient absorption, abdominal discomfort, and other symptoms. Understanding what causes SIBO and how to prevent it can help manage this challenging gastrointestinal disorder. 

What Is Small Intestinal Bacterial Overgrowth (SIBO)?

SIBO occurs when abnormally large amounts of bacteria proliferate in the small intestine rather than remaining limited to the colon.

Normally less than 104 colony-forming units per mL of bacteria reside in the upper GI tract. In SIBO, bacterial counts exceed 105 or 106 CFU/mL. These excessive bacteria interfere with the small intestine’s digestive and absorptive functions.

Causes Of Small Intestinal Bacterial Overgrowth

Causes Of Small Intestinal Bacterial Overgrowth

SIBO may be caused by:

✔ Diverticuli in the small intestine that harbor bacteria

✔ Scarring or adhesions from surgery that slow motility

✔ Diseases affecting the intestines like Crohn’s or celiac 

✔ Medications including PPIs, narcotics, and anticholinergics

✔ Autoimmune disorders like scleroderma and diabetes

✔ Structural issues like fistulas or strictures

✔ Hypochlorhydria allows bacteria to survive stomach acid

The overgrowth is often made up of microbes from the mouth that don’t belong in the lower digestive tract like Streptococcus and Escherichia coli.

Signs & Symptoms of Small Intestinal Bacterial Overgrowth

Common symptoms of SIBO include:

✔ Diarrhea, constipation or both

✔ Abdominal pain, bloating, or distension

✔ Excess gas and belching

✔ Nutritional deficiencies 

✔ Weight changes – unintentional loss or gain

✔ Fatigue and weakness

✔ Nausea

✔ Acne, eczema, or rashes

Joint pain

✔ Headaches

✔ Depression and anxiety

✔ Brain fog and memory loss

Symptoms may vary based on the location and types of bacteria involved. Symptoms often worsen after fiber intake.

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How To Avoid Small Intestinal Bacterial Overgrowth (SIBO)?

Preventive strategies for SIBO include:

✔ Avoiding unnecessary antibiotics that disrupt gut flora

✔ Managing diabetes, scleroderma, and other underlying conditions 

✔ Eating small, frequent meals instead of overeating

✔ Chewing thoroughly and eating slowly

✔ Staying well hydrated with water between meals

✔ Minimizing alcohol and caffeinated beverages

✔ Quitting smoking to improve GI functioning

✔ Taking probiotic supplements to maintain healthy gut bacteria

✔ Avoiding unnecessary PPIs and anticholinergic drugs when possible

✔ Treating GI issues like ulcers, strictures, and diverticuli 

Early intervention for any motility issues or structural problems can help prevent progression to SIBO.

Precautions While Having SIBO

People with SIBO should:

✔ Follow a low FODMAP diet to ease symptoms

✔ Replenish nutrients through diet or supplements as needed

✔ Avoid alcohol, caffeine, and carbonated beverages

✔ Reduce fiber intake from fruits, vegetables, beans, and grains

✔ Limit fat intake which stimulates intestinal contractions

✔ Keep well hydrated and drink in between (not during) meals

✔ Take antibiotics or antimicrobials only if prescribed by a doctor

✔ Seek guidance from a dietician to ensure adequate nutrition

✔ Avoid probiotics during antibiotic treatment as they can be ineffective

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SIBO arises when excess bacteria populate the small intestine, leading to malabsorption and uncomfortable symptoms. Controlling underlying medical conditions and avoiding unnecessary antibiotic use can help prevent SIBO.

A combination of antibiotics, proper diet, nutritional support, and hydration is key to managing SIBO. Working with a knowledgeable gastroenterologist provides the greatest chance of successfully overcoming this challenging condition.


Q: What are the most common SIBO symptoms?

A: Abdominal pain, bloating, diarrhea or constipation, malnutrition, weight changes, and fatigue are the most frequently reported SIBO symptoms.

Q: What antibiotics treat SIBO?

A: Rifaximin, metronidazole, amoxicillin, tetracycline, and neomycin are some of the antibiotics used for treating SIBO.

Q: Can SIBO go away on its own?

A: In some mild cases, SIBO may resolve with dietary changes to discourage bacterial overgrowth. But most cases require antibiotic treatment.

Q: Is SIBO technically an infection? 

A: No, SIBO is an overgrowth of microbes normally present in the intestines rather than infection with new microorganisms.

Q: Does SIBO always cause diarrhea?

A: Not always – some people with SIBO experience constipation. Symptoms depend on the location and types of bacteria contributing to the SIBO.

Dr. Jun Ren is a dedicated and experienced registered dietitian and nutritionist who is committed to helping people achieve their health goals through personalized nutrition plans. With a passion for promoting healthy eating habits and preventing chronic diseases, Dr. Ren has been able to assist numerous clients in improving their overall quality of life.

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