In part two of his series on caloric restriction and fasting, Dr. David Sinclair shifts from the science of why eating less extends life to the practical question of how to make it work in real life. He introduces chrononutrition—the idea that your body doesn't just care what you eat but when—and explains how the clocks in your liver, pancreas, gut, and fat cells are set by mealtimes, why insulin sensitivity is highest in the morning, and how late-night eating creates a kind of “metabolic jet lag.” Drawing on work from colleagues like Satchin Panda and Valter Longo, he lays out the measurable benefits of time-restricted eating, from weight loss and better blood pressure to a sharper brain and a lower biological age.

Sinclair then walks hour by hour through what actually happens inside the body during a fast—from burning through glycogen to gluconeogenesis, ketosis, and the deep cellular cleanup of autophagy and chaperone-mediated autophagy. Getting personal, he shares his own three-day fast and real-time glucose-monitor data, describes his 18:6 eating window, and explains how continuous glucose monitoring taught him which foods spike his blood sugar. He closes by contrasting all of this with the modern pattern of constant eating—and the insulin resistance, ectopic fat, and accelerated aging it drives—before busting the most common fasting myths, starting with whether fasting makes you lose muscle.