The fed-to-fasted transition is usually presented in five stages: fed (0-4 hours), early fasting on liver glycogen (6-24 hours), gluconeogenesis (24-48 hours), ketosis (one to three days), and protein conservation (five days and beyond). That framing is Jason Fung’s presentation of mainstream physiology rather than a measurement — the phases are real and the tidiness is editorial, with the boundaries overlapping and blurring. Understanding them removes mystery from fasting; treating the hours as thresholds you cross on a schedule puts it back.
This companion covers each stage in detail, what’s happening hormonally, how it feels, why this matters, and practical implications for different fasting lengths. (5 min read)
Written by AI, directed and approved by me. How this is made →