Intermittent Fasting Calculator
Track your fasting window, eating window, and observe your body's journey through blood sugar stabilization, ketosis, and cellular autophagy.
Break your fast at 12:00 PM tomorrow. Eating window open until 8:00 PM (8 hours).
Intermittent Fasting Protocols & Biological Adaptations
Comparison of popular time-restricted feeding windows:
| Protocol | Fasting / Eating Split | Metabolic Characteristics | Ideal Use Case |
|---|---|---|---|
| 14:10 Circadian | 14h Fast / 10h Eat | Gentle insulin reset; stabilizes nocturnal blood glucose | Beginners and hormonal sensitivity management |
| 16:8 Leangains | 16h Fast / 8h Eat | Metabolic switch flips; active fat oxidation; mild autophagy | Sustainable fat loss & daily body recomposition |
| 18:6 Advanced | 18h Fast / 6h Eat | Elevated circulating ketones; accelerated cellular autophagy | Experienced fasters seeking enhanced metabolic flexibility |
| 20:4 Warrior | 20h Fast / 4h Eat | Deep ketosis, high growth hormone (GH) secretion, maximal autophagy | Advanced practitioners & deep digestive rest |
Frequently Asked Questions
What is the 'Metabolic Switch' in intermittent fasting?
In a seminal New England Journal of Medicine review (de Cabo & Mattson, 2019), the metabolic switch describes the point around 12–16 hours of fasting when liver glycogen stores are exhausted, and cellular metabolism switches from glucose-based energy to adipose fatty acids and ketone bodies (acetoacetate and β-hydroxybutyrate).
When does cellular autophagy actually begin during a fast?
Autophagy (the Nobel Prize-winning cellular self-cleaning process) begins to ramp up significantly between 16 and 24 hours of fasting as intracellular amino acids decline, activating the master energy sensor AMPK and downregulating the mTOR growth pathway.
What breaks an intermittent fast?
Any caloric macronutrient intake—such as carbohydrates, proteins, or fats (>10–15 calories)—triggers insulin secretion and mTOR activation, temporarily pausing the fasting state. Pure water, unsweetened black coffee, plain green tea, and zero-calorie electrolytes do not break a metabolic fast.
Which fasting protocol is best for beginners?
The 14:10 or 16:8 protocol is recommended for beginners. Fasting for 16 hours (e.g., stopping food intake at 8:00 PM and breaking fast at 12:00 PM the next day) captures the key hormonal benefits of fat oxidation without excessive hunger.
Scientific References
- de Cabo R, Mattson MP. (2019). Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine, 381(26), 2541–2551. PMID: 31881139.
- Anton SD, Moehl K, Donahoo WT, et al. (2018). Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity, 26(2), 254–268. PMID: 29086496.
- Panda S. (2016). Circadian physiology of metabolism. Science, 354(6315), 1008–1015. PMID: 27885004.
