Fasting stages chart

The 8 stages of a fast

1. 0 to 4 hBlood Sugar RisingYour body is digesting your last meal and using that energy. Insulin is elevated.Main fuel: Glucose from your meal
2. 4 to 12 hBlood Sugar FallingBlood sugar settles back to normal and insulin starts to drop.Main fuel: Glucose and stored glycogen
3. 12 to 16 hFuel SwitchYour liver's glycogen is getting low, so your body starts turning to fat for fuel.Main fuel: Glycogen, then more and more fat
4. 16 to 24 hFat BurningYour body starts burning stored fat for energy. Stay hydrated!Main fuel: Mostly stored fat
5. 24 to 36 hKetosisFat is now your main fuel, and your liver turns more of it into ketones.Main fuel: Fat and ketones
6. 36 to 48 hAutophagyCells may start clearing out old components, a natural recycling process.Main fuel: Fat and ketones
7. 48 to 72 hDeep RenewalGrowth hormone levels may rise, helping to preserve muscle.Main fuel: Fat and ketones
8. 72 h and beyondImmune ResetExtended fasting territory. Only continue with medical guidance.Main fuel: Fat and ketones

Typical times after your last meal. They vary from person to person.

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How to read the chart

The chart shows the eight stages Fasting Tracker marks on its timer, from Blood Sugar Rising at your last meal to Immune Reset at 72 hours, with the hour each one typically begins and your body's main fuel. These hours are typical averages, not a schedule: your last meal, how active you are and your metabolism all change the timing, and the later stages, such as autophagy, haven't been timed in people ^1,2.

1. 0 hBlood Sugar RisingYour body is digesting your last meal and using that energy. Insulin is elevated.
2. 4 hBlood Sugar FallingBlood sugar settles back to normal and insulin starts to drop.
3. 12 hFuel SwitchYour liver's glycogen is getting low, so your body starts turning to fat for fuel.
4. 16 hFat BurningYour body starts burning stored fat for energy. Stay hydrated!
5. 24 hKetosisFat is now your main fuel, and your liver turns more of it into ketones.
6. 36 hAutophagyCells may start clearing out old components, a natural recycling process.
7. 48 hDeep RenewalGrowth hormone levels may rise, helping to preserve muscle.
8. 72 hImmune ResetExtended fasting territory. Only continue with medical guidance.

Why the timing varies

The metabolic switch from sugar to fat typically happens somewhere between 12 and 36 hours after your last meal: earlier if you're active, later if your liver started the fast full of glycogen ¹. A walk after your last meal and a lighter, lower-carbohydrate dinner can bring it forward. To see where you are right now, use the fasting stage calculator.

Which stage does your plan reach?

Plan	Fast	Eat	Level	Stage your fast reaches	In the app
13:11 Circadian	13 h	11 h	Beginner	Fuel Switch	Free
14:10 Gentle Start	14 h	10 h	Beginner	Fuel Switch	Free
16:8 Leangains	16 h	8 h	Intermediate	Fat Burning	Free
18:6 Fat Burner	18 h	6 h	Intermediate	Fat Burning	Free
20:4 Warrior	20 h	4 h	Advanced	Fat Burning	Pro
OMAD, One Meal a Day	23 h	1 h	Advanced	Fat Burning	Pro
24 hours, Full Day	24 h	None that day	Expert	Ketosis	Pro
36 hours, Monk Fast	36 h	None for a day and a half	Expert	Autophagy	Pro

Most daily plans sit at the start of the switch, around 12 to 16 hours, and repeat it every day without the strain of long fasts ³. The stages after 24 hours belong to occasional long fasts. Read what's known about them in what happens after 36 hours.

Printing tips

• Print it on A4 or US Letter paper, in colour or black and white.
• Circle the stage your plan reaches, so you know what you're aiming for.
• Keep it on the fridge or by your desk for the hungry moments: knowing you're nearly at the next stage helps.

Sources

1. Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018;26(2):254-268. doi.org/10.1002/oby.22065
2. Jamshed H, Beyl RA, Della Manna DL, et al. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019;11(6):1234. doi.org/10.3390/nu11061234
3. Mattson MP, Moehl K, Ghena N, et al. Intermittent metabolic switching, neuroplasticity and brain health. Nat Rev Neurosci. 2018;19(2):63-80. doi.org/10.1038/nrn.2017.156