nüchtern — free, private fasting tracker

• Time since eating — the clock on the Fast tab. Note when you actually finished your last meal (tap “Adjust start time”).
• Water — sip steadily; pale-yellow urine is the target. Don't wait until you're thirsty.
• Electrolytes — on fasts past ~16–18h, add a little salt; consider potassium & magnesium too. They carry no calories and won't break the fast.
• How you feel — steady energy, clear head, mild hunger waves are normal. Dizziness, a racing heart, or confusion are not.
• The re-feed — break the fast gently. Start small (broth, a little protein or fruit), then a proper meal. The longer the fast, the gentler the return.

Treat this like training, not a test of willpower. A sensible ladder: get comfortable at 13h, then 16h, then 18h. Hold each rung for a week or two before adding the next. Most people do best with regular 16–20h fasts, and an occasional 24–36h fast once or twice a month for the deeper autophagy benefits. Only step into multi-day territory once shorter fasts feel genuinely easy, and not without a doctor's blessing.

The science here reflects a typical healthy adult; individual timing varies with your last meal, activity and metabolic health. Grounded in research featured in the documentary “Fasting: Awakening the Rejuvenation from Within” (Gilman & de Lestrade) and current work on ketosis and autophagy. Yoshinori Ohsumi mapped the mechanism of autophagy in yeast, receiving the 2016 Nobel Prize in Physiology or Medicine for it; when it switches on in a fasting human is a much less settled question.

This tab keeps things brief on purpose. There's a dedicated reference page with the fuller picture: a visual, hour-by-hour walkthrough of every metabolic phase, plain-language explanations of the medical terms, and what research says about the deeper benefits. It's in English and German.

Read the full Science of Fasting guide →

Read the daily-living guide: light, sleep, movement & calm →