What happens to your body when you fast

When you fast, your body initially burns through stored glucose (glycogen) in the liver and muscles for energy, which typically takes 12 to 24 hours. Once glycogen is depleted, your body shifts to burning fat, converting fatty acids into ketones for fuel, a state called ketosis. Insulin levels drop significantly, which promotes fat burning and cellular repair processes like autophagy, where cells break down and recycle damaged components. Hormonal changes also occur, including increased norepinephrine and growth hormone levels, which help preserve muscle mass and maintain metabolism. Short-term fasting can reduce inflammation and improve insulin sensitivity. However, extended fasting without proper hydration or electrolytes can lead to fatigue, dizziness, and muscle loss.