Small Intestinal Bacterial Overgrowth (cont.)
Bhupinder Anand, MD
In this Article
What are small intestinal bacteria overgrowth symptoms?
The symptoms of SIBO include:
A small number of patients with SIBO have chronic constipation rather than diarrhea. When the overgrowth is severe and prolonged, the bacteria may interfere with the digestion and/or absorption of food, and deficiencies of vitamins and minerals may develop. Weight loss also may occur. Patients with SIBO sometimes also report symptoms that are unrelated to the gastrointestinal tract, such as body aches or fatigue. The reason for these symptoms is unclear. The symptoms of SIBO tend to be chronic. A typical patient with SIBO can experience symptoms that fluctuate in intensity over months, years, or even decades before the diagnosis is made.
What is the normal relationship between bacteria and the small intestine?
At birth, there are no bacteria in the gastrointestinal tract. During birth, however, bacteria from the mother's colon and vagina are swallowed by the infant, and, within a few weeks or months, they populate the infant's gastrointestinal tract.
The relationship between normal intestinal bacteria and their human host is complex. The relationship is symbiotic, which means that each benefits from the other. The bacteria benefit from the warm, moist environment of the small intestine that is ideal for growith as well as the constant flow of food passing down the gastrointestinal tract provides a ready source of nutrition. The human host benefits in several ways. For example, the normal bacteria stimulate the growth of the intestinal lining and the immune system of the intestine. They prevent the growth of disease-causing bacteria within the intestine. They produce vitamin K, which is absorbed and used by the host. In fact, the bacteria are important even for the muscular activity of the small intestine, without bacteria, there is reduced muscular activity.
There is a delicate balance between the bacteria of the gastrointestinal tract and the human host. The gastrointestinal tract, particularly the small intestine, contains an extensive immune system. The immune system protects the intestine from disease-causing viruses, bacteria, and parasites. (The effects of the immune response have been experienced by anyone who has experienced gastroenteritis.) The interesting fact is that the intestine does not attack the normal bacteria within it, only disease-causing bacteria. Somehow, the intestine becomes tolerant of the normal bacteria and does not mount an attack against them. The intestine has other ways that may be important in protecting it from bacteria, both normal and disease-causing. As mentioned previously, muscular activity keeps the numbers of bacteria within the intestine at a low level. Mucus that is secreted into the intestine coats the intestinal lining and prevents the bacteria from coming into contact with the lining. The intestine secretes antibodies that can block, and sometimes kill, bacteria as well as substances that prevent the growth of bacteria. Finally, the lining of the intestine can produce receptors for toxic substances produced by bacteria and can prevent the substances from exerting their toxic effects.
Medically Reviewed by a Doctor on 3/26/2012
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