Dr. Trisha Pasricha, a Harvard gastroenterologist, breaks down the mechanics of bowel movements and farts—covering propulsion, pliability, pelvic floor function, gut-brain links and odor chemistry. She debunks common myths and outlines norms for frequency, transit time, fiber use, toilet positions, definitions of constipation and incontinence, plus diet and hydration impacts.

• 99% of farts are odorless; smelly ones come from hydrogen sulfide, which Pepto-Bismol can reduce.
• Bowel movements rely on three Ps—Propulsion, Pliability and Pelvic Floor—and bowel cleanses are useless and risky.
• Transit time matters more than frequency, and she recommends fiber "maxxing" plus capping toilet time at five minutes, using specific positions to aid propulsion.
• TRPV1 and PIEZO2 receptors drive the urge to defecate, and factors like coffee, alcohol, NSAIDs and hydration all influence gut function.