Values are modelled from published fasting studies, not measured from you. Timing shifts by hours between people.
Tap any stage to read what's happening and how good the evidence is.
Hunger comes in waves that pass on their own. These are the things that make riding one easier.
Most people who feel terrible on a fast are short on salt, not willpower. Match the symptom to the mineral.
These ranges vary widely between sources, and most of those sources sell electrolyte powder. Treat them as a starting point, not a prescription.
Do not supplement sodium or potassium without asking your doctor if you have high blood pressure, kidney disease or heart failure, or if you take a diuretic, ACE inhibitor, ARB, or a potassium-sparing medication. Potassium in particular can cause dangerous heart rhythm problems in the wrong circumstances.
The question isn't only whether a pill breaks your fast — it's whether you'll absorb it at all.
Worrying about the four calories in a vitamin capsule misses the point. Timing them so they actually work is the part that matters.
Strictly, anything with calories does. Practically, it depends what you're fasting for.
If your goal is weight loss, the calorie threshold is what matters and a splash of cream is noise. If it's ketosis or autophagy, protein and carbohydrate are what break the state — fat is the least disruptive of the three.
Tap to set it as your goal. Longer isn't automatically better — the one you'll keep wins.
Established is replicated human physiology. Animal-derived is mostly rodent work — mice run far faster metabolisms, so hour-for-hour translation is unreliable.
Autophagy is the most oversold claim in fasting. It can't be measured in a living person without tissue sampling, so any app naming the exact hour it "switches on" is guessing. This one won't.
A 2025 BMJ meta-analysis found intermittent fasting gives broadly similar results to ordinary calorie restriction. Fasting is a structure that makes eating less easier — not magic on the clock.
Chest pain, fainting, persistent dizziness, palpitations or confusion mean end the fast immediately and seek medical attention. These are not part of the process.
Sodium, potassium and magnesium need replacing. Most people who feel awful on a long fast are short on electrolytes, not willpower. Break a long fast small and gently.
Educational reference, not medical advice. Fasting interacts with medication in ways that need a clinician.
Sets the ring target. You can always go past it.
Forgot to hit start? Backdate it — the timer catches up.
Logged against the hour you're in. Over a few fasts this builds your own hunger curve — most people find it peaks and then fades.