Fasting and sleep: timing is everything
Fasting and sleep are a loop: your window placement shapes your sleep, and your sleep shapes how hard tomorrow's fast feels.
Most fasting advice treats the window as a calorie tool. It's also a circadian tool — when you eat is one of the strongest signals your body clock gets. Place the window well and sleep improves; place it badly and both suffer.
Close the kitchen 3+ hours before bed
Late, heavy meals raise core temperature and keep digestion running right when your body wants to downshift — a classic cause of shallow sleep. An eating window that ends mid-afternoon to early evening gives digestion time to finish before lights out.
Why bad sleep makes fasting brutal
One short night raises ghrelin (hunger) and drops leptin (fullness) the next day — which is why the day after bad sleep feels like endless snack cravings. If you slept badly, don't force a long fast: eat when genuinely hungry, and go again tomorrow. Rigidity here is how streaks die.
Placing your window for sleep
- Early-to-mid windows (e.g., 9 am – 5 pm) tend to be best for sleep — dinner is done long before bed.
- Social-evening windows (e.g., 12 pm – 8 pm) work fine if you keep the final meal moderate and finish by ~8.
- Whatever you pick, consistency beats perfection — a regular window trains your clock; a shifting one confuses it.
Build a window that fits your nights
Kairo maps your eating window from your real wake time — and adapts it on poor-sleep days.
Build my plan — freeGeneral information only, not medical advice. Consult a healthcare professional before starting any fasting routine, especially if you are pregnant, under 18, have a medical condition, or a history of disordered eating.