Fasting across time zones, night shifts and clock changes

A fasting schedule is easy to follow when every day looks the same. Travel, night shifts and the two clock changes of the year complicate the arithmetic. One rule settles most cases: count elapsed hours, not the time on the wall.

Elapsed time is what counts

A fast is a duration. If you stopped eating at 20:00 in Paris and land in New York six time zones west, your watch says less time has passed than really has. Sixteen hours after your last meal is still sixteen hours, whatever the local clock shows.

A tracker should store the moment your fast began as a fixed point in time and compute the rest from it. That is how Volvelle works: the elapsed time stays correct when your iPhone changes time zone.

Flying east or west

Two simple approaches:

• Keep counting. Finish the fast you started, by elapsed hours, then eat at the next sensible local mealtime.
• Reset on arrival. Treat the travel day as an exception, eat when it is practical, and start your usual window on local time the next day.

Neither is more correct. Long-haul days are irregular, and a log that shows a shorter or longer fast on that date is simply accurate.

Clock changes

When clocks go forward or back, a fast that spans the change lasts one hour less or more than the wall clock suggests. If your fast began at 20:00 and the clocks go back overnight, noon arrives after seventeen hours, not sixteen. A tracker that counts elapsed time shows the right figure.

Night shifts

The numbers in a plan do not assume daytime. On nights, place the eating window around your waking hours and your main meal, and keep the same window across a run of shifts where you can. If your days differ, a weekly schedule with a different plan for each day is easier than adjusting by hand. Choosing your window follows the same steps.

Past midnight

Most fasts start one evening and end the next day. When you review your history, check how the fast is attributed: usually to the day it ended. Knowing the convention avoids thinking a day is missing.

A word on medication

If you take medication at fixed times or with food, travel and shift work are a reason to ask your doctor how to adapt, before changing your meal times. See who should talk to a doctor before fasting.

This guide is general information, not medical advice. Talk to a doctor before you start fasting.