Definition of Small bowel bacterial overgrowth:

Small bowel bacterial overgrowth is a condition in which abnormally large numbers of bacteria grow in the small intestine.

Causes, incidence, and risk factors:

Normally, the small intestine contains a relatively low number of bacteria. This is different from the large intestine, which contains large numbers of bacteria.

The abnormally large numbers of bacteria in the small intestine use for their growth many of the nutrients that a person would normally absorb. As a result, a person with small bowel bacterial overgrowth may not absorb enough nutrients and will be malnourished. In addition, the breakdown of nutrients by the bacteria in the small intestines can damage the cells that line the intestinal wall.

In addition, the breakdown of nutrients by the bacteria in the small intestines can damage the cells lining the intestinal wall.

Too much growth of bacteria in the small intestine can occur with many different conditions, including:

• Complications of diseases or surgery that create pouches or blockages in the small bowel, such as Crohn's disease
• Diseases that lead to movement problems in the small bowel, such as diabetes and scleroderma
• Immunodeficiency such as AIDS or immunoglobulin deficiency
• Short bowel syndrome caused by surgically removing a large part of the small intestine
• Small bowel diverticulosis, in which small sacs occur in the inner lining of the intestine, allowing too much growth of bacteria. Although these sacs can occur anywhere along the intestinal tract, they are much more common in the large bowel than in the small bowel.
• Surgical procedures, such as a Billroth II type of stomach removal (gastrectomy) that creates a loop of small intestine where excessive intestinal bacteria can grow.