Most of the time, unlike the large intestine, the small intestine does not have a large number of bacteria. Excess bacteria in the small intestine may use up the nutrients needed by the body. As a result, a person may become malnourished.
The breakdown of nutrients by the excess bacteria can also damage the lining of the small intestine. This can make it even harder for the body to absorb nutrients.
Conditions that can lead to overgrowth of bacteria in the small intestine include:
Complications of diseases or surgery that create pouches or blockages in the small intestine. Crohn disease is one of these conditions.
Diseases that lead to decreased movement of the small bowel, such as diabetes and scleroderma.
Immunodeficiency, such as AIDS or immunoglobulin deficiency.
Small bowel diverticulosis, in which small, or, at times, large sacs occur in the wall of the intestine. These sacs allow too many bacteria to grow.
Surgical procedures that create a loop of small intestine where excess bacteria can grow. An example is a Billroth II type of stomach removal (gastrectomy).
Some cases of irritable bowel syndrome (IBS).
Symptoms
The most common symptoms are:
Abdominal fullness
Abdominal pain and cramps
Bloating
Diarrhea (most often watery)
Gassiness
Other symptoms may include:
Fatty stool
Weight loss
Exams and Tests
Your health care provider will perform a physical exam and ask about your medical history. Tests may include:
Rej A, Chew TS, Sanders DS. Gastroenterology. In: Penman ID, Ralston SH, Strachan MWJ, Hobson RP, eds. Davidson's Principles and Practice of Medicine. 24th ed. Philadelphia, PA: Elsevier; 2023:chap 23.
Sundaram M, Kim J. Short bowel syndrome. In: Yeo CJ, ed. Shackelford's Surgery of the Alimentary Tract. 8th ed. Philadelphia, PA: Elsevier; 2019:chap 79.
Review Date:
5/4/2022
Reviewed By:
Michael M. Phillips, MD, Emeritus Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.