Jonathan Long is a biochemist who studies the chemicals produced during exercise. In Long’s world, “you always start with molecules,” which offer “clean handles” to understanding complex processes. His lab has identified a chemical produced in the digestive tract during exercise that can make a person stop eating. Long now studies this “gut-brain axis” for ways to treat obesity, diabetes, and, perhaps, even age-related conditions like dementia, as he tells host Russ Altman on this episode of Stanford Engineering’s The Future of Everything podcast.