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

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 many of the nutrients for their growth that a person should absorb. As a result, a person with the condition 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 lining the intestinal wall.

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

• A problem with the immune system (immunodeficiency), such as AIDS or immunoglobulin deficiency
• Complications of diseases or surgery that create pouches or blockages in the small bowel, such as Crohn's disease
• Diseases that slow small bowel movement, such as diabetes and scleroderma
• Short bowel syndrome caused by surgically removing a large part of the small intestine
• Small bowel diverticulosis, in which small sacs of the inner lining of the intestine stick out, 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 intestinal bacteria can grow excessively

The most common symptoms are:

• Abdominal pain and cramps
• Bloating
• Diarrhea (usually watery)
• Fullness

Other symptoms may include:

• Fatty, floating stool
• Weight loss

Low red blood cells (anemia) is a sign.

The goal is to treat the cause of the excess intestinal bacteria growth. For certain conditions, antibiotics or drugs that speed intestinal movement (motility-speeding drugs) may be considered.

Treatment also involves getting enough fluids and nutrition.

Someone who is dehydrated may need intravenous (IV) fluids in a hospital. If the person is already malnourished, a type of nutrition given through a vein (total parenteral nutrition (TPN)) may be necessary.

Severe cases lead to malnutrition. Other possible complications include:

• Dehydration
• Excess bleeding due to vitamin deficiency
• Liver disease
• Osteoporosis

Prather C. Inflammatory and anatomic diseases of the intestine, peritoneum, mesentery, and omentum. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 145.