HOME / FASTING / 20:4
Twenty hours without food, four hours to eat. It spends two hours inside Ketosis Entry, and it is the shortest schedule where the fast is the main feature of your day rather than the background of it.
Harder socially than physically. A four hour window means most days have one meal and one smaller one.
20h
Fasting
4h
Eating window
5
Stages reached
Five of the nine stages, with the sixth left for longer fasts. On the timer screen Ketosis Entry shows as KETOSIS, where space is tight.
A day on 20:4
Planning matters more here than on any shorter schedule, because there is no room to make up a missed meal later.
3PM TO 7PM
Late lunch and an early dinner. Keeps the window inside normal social hours, which is the part worth planning around.
5PM TO 9PM
Eat with everyone else and finish later. The trade is a longer stretch fasted through the working day.
A FEW DAYS A WEEK
Many people run 20:4 on two or three days and 16:8 on the rest. Burn logs each fast against the plan you set for it.
Eating in four hours
Four hours is not much room to hit a day's protein. Lead with it rather than filling up on everything else first.
A meal and a substantial second one sits better than a single very large meal after twenty hours.
Twenty hours without food means twenty hours without sodium. Most of the headaches and fatigue at this length are electrolytes.
Burn's Struggle Support holds six tools, including a symptom check and a breathing exercise, for the stretch between hour 14 and your window opening.
See the tools →
A 20:4 asks for hunger management, a planned window and consistent hydration. Those are habits you build on shorter schedules first.
FIRST
If 16 hours still takes effort most days, twenty will not go well.
THEN
Six hours teaches you how to fit a day's food into a short window. Four hours assumes you already know.
THEN
See how it fits your week before committing to it daily.
Burn names Ketosis Entry at 18 hours because a timer has to draw a line. Onset varies with your last meal, your activity, your sleep and your metabolism, and Burn does not measure ketosis, autophagy, or metabolic state.
Speak to a doctor before starting if you are pregnant or breastfeeding, have a history of eating disorders, manage diabetes, take medication timed to meals, or are under 18. Stop and eat if you feel unwell, whatever the timer says.
Burn names every stage you reach, buzzes your wrist at each boundary, and keeps the history so you can see which weeks held.
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