Tracking your fasting and eating windows in real-time is the single most important habit for intermittent fasting success. Use our interactive web timer below to start your fast, monitor your biological stage progression from glucose burning to ketosis and deep cellular autophagy, or download our iOS app for automatic background lock-screen notifications.

The 4 Metabolic Stages of Intermittent Fasting

1. Hours 0 – 4 (Fed State): Your body processes food from your last meal. Blood glucose is elevated, insulin is high, and energy is drawn directly from circulating nutrients.
2. Hours 4 – 12 (Early Fast): Stomach empties and circulating insulin drops significantly. The liver breaks down stored glycogen to maintain normal blood sugar levels.
3. Hours 12 – 16 (Fat Burning & Ketosis): Liver glycogen stores become depleted. Your body switches to burning stored body fat for fuel, generating ketone bodies (beta-hydroxybutyrate).
4. Hours 16 – 24+ (Deep Autophagy): Nutrient deprivation activates AMPK and suppresses mTOR, triggering cellular recycling of damaged proteins and senescent cells.

Medical References

• de Cabo R, Mattson MP. (2019). Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine.
• Barnosky AR et al. (2014). Intermittent fasting vs daily calorie restriction. Transl Res.