Small bowel bacterial overgrowth

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.

Dysbiosis literally means that the ecology of the gut is out of balance, with dysfunctional organisms, such as certain bacteria and the fungus Candida albicans, in greater abundance than optimal, and with beneficial organisms, like Lactobacillus spp., in lower abundance. Many symptoms of dysbiosis are attributed to "leaky gut", or an increase in intestinal permeability. If otherwise healthy foods do not get properly digested, the undigested food particles may pass inappropriately through a leaky intestine into the blood stream, where they are branded as foreign and undesirable by the body's immune guards. The immune system dispatches proteins to attack these foreign particles. Undigested foods then become part of the overall suppressive load on the immune system. If the intestines are unbalanced (dysbiotic) and leaky, bacteria and parasites can also pass through the defensive intestinal barrier, enter the circulatory system (lymph and blood) and invade the organs, precipitating further immune responses. Circulating immune complexes can then trigger a variety of so-called autoimmune diseases, such as arthritis and lupus. This has some support in recent medical literature on mucosal immunity and intestinal permeability, but the matter is not uniformly accepted by the medical mainstream.

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.