I Replaced 16:8 Fasting With This and Everything Got Better

0:00 – 3:33

The Cortisol Trap: When Daily Fasting Becomes Chronic Stress

The speaker opens with a confession: after years of being the biggest advocate for 16:8 fasting, he's completely changed his approach. The problem isn't fasting itself (he still loves it), but what daily fasting does to your cortisol rhythm. When you skip breakfast every single morning for years, you're training your body to wake up in a slightly stressed state, day after day. Over time, this flattens your circadian cortisol curve, which can lead to insulin resistance and metabolic dysfunction. The exact things fasting is supposed to fix. Here's the biological mechanism: when you wake up, cortisol naturally peaks (the cortisol awakening response) to give you alertness and energy. That peak is supposed to gradually decline through the day, and one of the signals that helps cortisol come down is food. When you eat, especially protein and carbs, you signal to your HPA axis that resources are available, so cortisol can stand down. When you skip breakfast every day, that signal never comes. Cortisol stays elevated to keep blood glucose stable through gluconeogenesis, a stress-driven process. Think about our ancestors, the speaker urges. They didn't wake up and refuse to eat when food was accessible. If they had food, they ate it. The only time they fasted through the morning was when there genuinely was no food. We don't live in that situation now (we have food available all the time, which is part of our problem), but our ancestors weren't choosing chronic daily restriction with a fridge full of eggs 10 feet away. That's a modern behavior our biology has no framework for. A study in Endocrinology Metabolism found that fasting powerfully increases cortisol secretion and, more importantly, alters the timing of the circadian cortisol curve. Another study in Frontiers of Nutrition found that even a single day of fasting can increase cortisol rhythm amplitude (which is fine and helps burn fat), but imagine doing that every morning for years. You're reprogramming your HPA axis to run hot. A flattened cortisol rhythm can lead to all kinds of metabolic issues and even fat storage, which could explain why some people start to struggle after doing 16:8 for a while. They need to change it up. Period. The fix isn't to stop fasting, he says. It's to stop fasting the wrong way.