Small bowel bacterial overgrowth

Other Names:
Bacterial dysbiosis of the intestine

Small bowel bacterial overgrowth (SBBO) is a proliferation of colonic-type bacteria in the upper gastrointestinal tract (the stomach, duodenum and jenjunum). It only occurs when the normal defenses against bacterial proliferation are reduced by factors such as slowed peristalic motion, reduced gastric acidity, exposure to antibiotics and surgical resection of the small intestine.  SBBO causes malabsorption, lethargy, fatigue and various gastrointestinal symptoms. It is difficult to eradicate, and is principally treated by trying to eliminate the overgrown population of microbes with various antimicrobial drugs. It often requires continued treatment.

Bacterial overgrowth has a number of other undesirable effects, including reduced stomach acidity, reduced nutrient absorption, increased inflammation, and raising the risk of stomach cancer.


Researchers in Italy detected small bowel bacterial overgrowth (SIBO) in 50% of patients using proton pump inhibiting drugs (PPIs) for reducing stomach acid, compared to only 6% of healthy control subjects. The prevalence of SIBO increased after one year of treatment with PPIs.

Fermentation of malabsorbed carbohydrates produces hydrogen gas in the intestines. Hydrogen gas is the preferred energy source for Helicobacter pylori which colonises the stomach and reduces acid production there for its own survival. Elevated levels of hydrogen gas are also associated with other nasty bugs such as Salmonella, E. coli and Campylobacter jejuni, the leading cause of bacterial human diarrhea illnesses in the world. Excessive fructose, certain types of fiber and starch, and particularly wheat, increase hydrogen production, and thus increase the risk of infection by H. pylori and other pathogenic bacteria.


A high carbohydrate diet promotes bacterial overgrowth.  A low-carb (LC) diet would reduce bacterial overgrowth.  It is not the amount of carbohydrates that is important, but the type of carbohydrates. The theory is that the longer chain carbohydrates (disaccharides and polysacharides) are the ones that feed bad bacteria in our guts, while short chain carbohydrates (monosacharides) don’t pose a problem. 

Narrower Problems:
Helicobacter pylori infection
Related Problems:
Problem Type:
E: Emanations of other problems
Date of last update
12.07.2019 – 11:48 CEST