Which of the following is a cause of Secondary SIBO/dysbiosis?

• A. Excess substrate in the intestinal lumen for bacteria to feed
• B. Decreased clearance of bacteria from the small intestine
• C. Abnormal anatomy
• D. Regular exercise

Answer: (B)

Secondary SIBO/dysbiosis happens when the small intestine’s ability to clear bacteria is impaired, allowing bacteria to linger and multiply. Decreased clearance from motility problems means bacteria that should be moved along or washed out stay in the small intestine, leading to overgrowth and an imbalanced microbiota.

Excess substrate can help bacteria grow, but it isn’t the primary driver on its own unless clearance is also compromised. Abnormal anatomy can predispose to stasis and overgrowth as well, but the core mechanism in secondary cases is reduced clearance. Regular exercise tends to improve motility, so it wouldn’t be a cause.