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Practical answers to the questions people actually have once they start: what breaks a fast, what to do when you are hungry, how to keep going past the first week, and how fasting fits around work, training, and family meals.
The science section explains the biology. These guides tell you what to do about it.
Getting started
Read these in order and the first four weeks get considerably easier.
01
Including the two days that take the most planning.
02
The small adjustments that remove most of the difficulty.
03
Building a habit that survives a bad week.
04
What to eat first, and why the timing matters more than the food.
When it gets hard
Hunger, headaches, low energy, feeling cold, trouble sleeping. All of it is common, most of it passes, and some of it means you should eat. These guides say which is which.
Fasting around a life
Fasting around a full calendar, not an empty one.
Training fasted, when to eat around a session, and what to expect from strength work.
How your eating window affects how you sleep, and what to do about a late dinner.
Dinner plans, work lunches, and holidays, without abandoning the schedule entirely.
Everything in this section
Starting out, and keeping it going.
Coffee, tea, supplements, and diet drinks.
What is normal, and what means stop.
The two things worth getting right.
The science section covers one process at a time: the fuel your body switches to, the signals behind the switch, and how each claim is measured.
Go to the science section →If you are pregnant or breastfeeding, have a history of disordered eating, manage diabetes, or take medication timed with food, speak to a clinician first. Nothing in these guides is medical advice.
Read the safety guidance →Burn includes an education library you can read during a fast, without leaving the app.
Download free on the App StoreiPhone, iPad, and Apple Watch. Requires iOS 18 or watchOS 11.