6 Stages of Fasting: What Happens to Your Body From 12 to 72 Hours

What happens to your body when you fast for 12, 16, 18, 24, 48, or 72 hours? Fasting is not one single biological state. As time passes without food, your body gradually changes how it uses energy, regulates hormones, and responds to the absence of nutrients. In this video, we explore the **6 stages of fasting**, from the familiar overnight fast to the much more demanding 72-hour extended fast. ### What You'll Learn ⏱️ **12-Hour Fast:** The overnight baseline, glycogen, and insulin ⏱️ **16-Hour Fast:** Stored fat use, insulin changes, and intermittent fasting ⏱️ **18-Hour Fast:** Ketone production and the metabolic fuel shift ⏱️ **24-Hour Fast:** Autophagy research, cellular recycling, and growth hormone ⏱️ **48-Hour Fast:** Extended fasting, immune-cell research, and electrolyte concerns ⏱️ **72-Hour Fast:** Deep extended fasting, emerging research, and serious safety risks You'll also learn why **longer fasting is not automatically better**, why fasting timelines vary between individuals, and why breaking a fast deserves careful attention. This is a science-based exploration of **fasting physiology, intermittent fasting, ketosis, fat burning, metabolism, and autophagy**. ⚠️ **Health Disclaimer:** This video is for educational purposes only and is not medical advice. Fasting responses vary, and hour-based stages are simplified explanations rather than universal biological switches. Extended fasts, especially 48- and 72-hour fasts, can carry significant risks and should not be attempted casually. People who are pregnant or nursing, have a history of disordered eating, have diabetes, or take blood-pressure or glucose-lowering medication should consult a qualified healthcare professional before changing their eating pattern. 6 stages of fasting, stages of fasting, fasting stages, fasting timeline, fasting hour by hour, what happens when you fast, what happens to your body when you fast, what happens to your body when you stop eating, fasting explained, fasting science, 12 hour fast, 16 hour fast, 18 hour fast, 24 hour fast, 48 hour fast, 72 hour fast, 3 day fast, intermittent fasting, 16 8 intermittent fasting, extended fasting, fasting metabolism, fat burning during fasting, ketosis explained, ketones and fasting, insulin and fasting, glycogen depletion, autophagy explained, autophagy fasting, growth hormone fasting, metabolic switching, cellular repair, fasting for beginners, OMAD fasting, one meal a day, health science, biology explained, nutrition science 💬 **Which fasting duration have you tried or are you curious about: 16, 18, 24, 48, or 72 hours?** Stages of fasting · Fasting timeline · Intermittent fasting What happens when you fast · 16-hour fast · 24-hour fast · 72-hour fast Autophagy · Ketosis · Fat burning · Metabolism · Fasting science 🔔 Subscribe for more science-based videos explaining what happens inside the human body, hour by hour. #IntermittentFasting #FastingStages #Autophagy #HealthScience #WeightLossJourney #Biohacking #Longevity #MetabolicHealth #HealthyLiving #ScienceExplained