Ketones, Autophagy, and the Practice of Fasting

Zoe "You mentioned that fasting triggers autophagy. And in our last session, you said ketones rise during fasting. What's the relationship between rising ketones and autophagy?"

Dr. Lee "Excellent question. We'll go deeper later, but in short: rising ketones promote autophagy. Ketones aren't just an energy substrate — they also serve as signaling molecules that activate autophagy. Figure 3-10 shows the trajectory of my own ketone levels during a 10-day fast. By day 2, ketones had already risen to about 4 mM. This was likely because I have a low body weight relative to my height, and I had already been on a ketogenic diet for several days beforehand. In that state, autophagy was likely proceeding rapidly inside my cells."