Small intestinal bacterial overgrowth (SIBO) is caused by an excessive growth of bacteria in the small intestine due to dysfunctions in several key digestive processes or anatomical alterations. The main causes include:
- Low stomach acid (hypochlorhydria), which reduces the ability to kill bacteria entering the small intestine and allows undigested carbohydrates to accumulate, feeding bacterial growth.
- Dysfunction in the migrating motor complex (MMC), a specific pattern of gut motility that normally clears bacteria from the small intestine, leading to bacterial stasis when impaired.
- Problems with intestinal nerves or muscles, or structural abnormalities such as adhesions, strictures, or resection of the ileocecal valve, which impede normal movement of intestinal contents and bacteria.
- Altered bile flow and enzyme production, reducing the natural antibacterial effects and digestion of carbohydrates.
- Stress, which lowers stomach acid and bile production, weakens the immune system, and slows gut motility.
- Certain medical conditions and surgeries, including diabetes, celiac disease, Crohn's disease, scleroderma, bowel obstructions, and gastric surgeries, may also predispose individuals to SIBO by impairing intestinal motility or altering anatomy.
- Immune system deficiencies can increase susceptibility to SIBO.
These causative factors lead to bacterial multiplication in the small intestine, disrupting normal digestion and producing symptoms typical of SIBO.
