For the first few hours without food, your body simply finishes digesting your last meal. Then the safety net disappears. Blood sugar falls, stored glycogen in your liver is mobilized, and by around 12 hours your system flips into burning fat, producing ketones to keep your brain running. Around 16 hours, damaged cell parts are broken down and recycled in a deep internal clean-up that many people credit with sharper thinking and easier weight loss.
As you pass 24–36 hours, fat-burning intensifies, inflammation may drop, and growth hormone surges to protect muscle. This is where advocates talk about “deep healing” and maximum cellular repair. Yet the story is not one‑sided: prolonged fasting can trigger gallstones, mood crashes, digestive issues, and overwhelming cravings. Because bodies respond so differently, extended fasts should never be copied from a video or trend. They belong in a plan made with a medical professional who knows your history, your limits, and your life.
