The Real Cause of SIBO — Why Everything You’ve Been Told Is Incomplete — What SIBO Actually Is — And What It Isn’t

Small intestinal bacterial overgrowth is defined as an abnormal increase in the number and type of bacteria colonizing the small intestine &#8212; organisms that belong in the colon, now established in a compartment where they have no business being. The diagnostic threshold is more than 10&#179; colony-forming units per milliliter of small intestinal fluid, though this cutoff has been debated for decades and matters far less than the question almost no one is asking: Why is the small intestine &#8212; a compartment that your body works extraordinarily hard to keep nearly sterile &#8212; suddenly hospitable to bacterial colonization? The small intestine is not passively sterile. It is actively, aggressively, metabolically hostile to microbial colonization. Your body maintains this hostility through five overlapping defense systems operating simultaneously, every hour of every day. When all five hold, bacteria cannot gain a foothold. When one begins to crack, the others compensate. But when two or three fail at once &#8212; which is the actual situation in most people with chronic, treatment-resistant SIBO &#8212; the entire system collapses, and bacterial colonization becomes not just possible but inevitable. Those five barriers are: gastric acid, which kills the majority of organisms before they ever reach the small intestine; the migrating motor complex, the interdigestive sw