Some travellers use a short fast, timed to end at breakfast in the new time zone, to help their body adjust after a long flight. This page explains the idea behind it, how the approach is usually done, example schedules for common routes, and who should not try it. The evidence is promising but limited: much of the underlying science comes from animal studies, and human studies are few and small, so treat this as one option alongside light exposure and sleep timing rather than a sure fix.
Table of Contents
The Idea Behind It
The body has a central “master clock” in the brain, which is set mainly by light, and many peripheral clocks in organs such as the liver and gut, which are strongly influenced by when you eat. After crossing several time zones, these clocks are out of step with local time and with each other, which contributes to jet lag symptoms such as poor sleep, daytime tiredness, and digestive upset.
A common rule of thumb is that the body adjusts by roughly one time zone per day, often more slowly when travelling east. In animal studies, a period without food followed by a meal at a new time can shift some body clocks toward the new feeding time, and research in mice has suggested that a fast of around 16 hours may make food timing a stronger signal. The idea for travellers is to use a fast and a well-timed first meal to send a clear “morning” signal in the new time zone.
This idea has been around since the 1980s, when a feeding-and-fasting schedule known as the Argonne anti-jet-lag diet was developed at a US national laboratory. A small number of human studies of approaches like this have reported less jet lag, but the evidence is limited and of mixed quality. It is reasonable to try if you are healthy, but it will not work for everyone.
The Basic Approach
The usual version is simple: avoid eating for roughly 12–16 hours before breakfast time at your destination, then eat a normal breakfast at local breakfast time and follow local meal times from then on.
Step 1: Work out breakfast time at your destination
Pick the time you would normally eat breakfast in the destination time zone, typically around 7–8 AM local time, on the first morning you will be there.
Step 2: Count back 12–16 hours
That is roughly when your last meal before the fast would be. If the timing would mean a fast much longer than 16 hours, adjust the plan (see the examples below) rather than extending the fast.
Step 3: Drink water during the fast
Water, and plain tea or coffee in moderation, are the usual fasting drinks. Cabin air is dry, so drink regularly.
Step 4: Eat breakfast at local breakfast time
Have a normal, balanced breakfast at the destination’s morning meal time, even if you do not feel hungry.
Step 5: Follow local meal times
Eat lunch and dinner at normal local times. Try not to eat at the times you would have eaten back home.
Example Schedules by Route
Flight times vary, so these are illustrations of the principle rather than exact plans.
In-Flight Practicalities
Declining meal service
Let the cabin crew know you do not want the meal. On long-haul flights, the smell of meal service can be the hardest part; headphones and a window seat can help.
Stay hydrated
Humidity in aircraft cabins is usually low. Drink water regularly, go easy on alcohol, and do not overdo caffeine. Dehydration can add to headaches and tiredness.
Electrolytes
On long flights, some people find a small amount of salt or an electrolyte drink helps with headaches. If you have high blood pressure, heart, or kidney problems, check with your healthcare provider before adding salt. See electrolytes and fasting.
Sleep on the destination’s schedule if possible
If it is night at your destination during the flight, try to sleep; if it is daytime there, try to stay awake. An eye mask and ear plugs or noise-cancelling headphones can help.
Move regularly
Long periods of sitting increase the risk of blood clots (deep vein thrombosis). Get up and walk when it is safe to do so, flex your ankles and calves in your seat, and stay hydrated. If you have risk factors for blood clots, ask your healthcare provider about travel precautions.
The First Meal
In this approach, the first meal at local breakfast time is the signal you are aiming for, so timing matters more than making it perfect.
What to eat
- A source of protein, such as eggs, yoghurt, fish, or beans
- Some carbohydrate, such as oats, wholegrain bread, or fruit
- A normal-sized breakfast, not just a snack
- Coffee or tea is fine if you normally have it in the morning
What to avoid
- A very large, heavy meal right after a fast, which can cause stomach discomfort
- Alcohol
For more on ending a fast comfortably, see how to break a fast.
Combining With Light Exposure
Light is the strongest signal for the brain’s master clock, so meal timing works best alongside sensible light exposure.
After travelling east (usually harder)
- Get outdoor daylight in the morning at your destination
- Keep evening light and screens dim
- Eat breakfast at local time
After travelling west (usually easier)
- Get daylight in the afternoon and early evening
- Try to stay up until a reasonable local bedtime
The best timing for light depends on how many time zones you crossed. For large shifts, the rules become more complicated, and some travellers use online jet lag planners based on published guidance.
Caveats and Who Should Avoid It
Results vary
Some people find it helps; others notice little difference. It may reduce symptoms but is unlikely to prevent jet lag entirely.
Short trips
For a short trip of a day or two, many people prefer to stay roughly on home time rather than adjust at all.
Health conditions and medications
Do not skip meals while travelling without medical advice if you have diabetes (especially if you use insulin or sulfonylureas), take medication that needs to be taken with food, or have other significant health conditions. Time-zone changes can also affect medication schedules, so ask your healthcare provider or pharmacist how to time doses. See our medications guide.
Pregnancy, under-18s, and underweight
Fasting is not recommended for people who are pregnant or breastfeeding, under 18, or underweight.
Important arrivals
If you need to perform well soon after landing, being hungry may make you feel worse. It may be better to eat normally and focus on light and sleep instead.
History of disordered eating
Anyone with current or past disordered eating should not use fasting for jet lag. Travel disrupts eating patterns enough without adding deliberate restriction.
Frequently Asked Questions
Does this work for shift workers?
Shift work raises similar body-clock issues, and research on meal timing in shift workers is ongoing. There is no well-established fasting protocol for shift changes. Regular meal times within each schedule, and avoiding large meals in the middle of the night, are commonly suggested. If you have health conditions, discuss changes with your healthcare provider.
Can I do this if I don’t already fast?
A single 12–16 hour fast is similar to an early dinner followed by a late breakfast, and most healthy adults tolerate it. People who never fast may find the hunger more noticeable. If you feel dizzy or unwell, eat something.
What about the return trip?
The same principle applies: aim for your first meal at breakfast time in your home time zone, and use daylight to help your body clock adjust back.
Should I take melatonin too?
Melatonin is one of the more studied options for jet lag, particularly for eastward travel, and is usually taken around local bedtime for a few nights. Rules on availability vary by country, and it can interact with some medications and cause drowsiness. Ask your healthcare provider or pharmacist whether it is suitable for you and what dose to use.
Coffee on the flight: yes or no?
Plain coffee does not break a fast. Moderate amounts are fine for most people, but caffeine late in your destination’s day can make it harder to sleep. See coffee and fasting.
Do airlines accommodate this?
You can usually decline meals simply by telling the crew. Some airlines let you indicate at booking or boarding that you do not want to be woken for meals.
The Bottom Line
A short fast of around 12–16 hours that ends with breakfast at local time is a simple, low-cost approach some travellers use to help adjust to a new time zone. The idea is based on how meal timing affects the body’s clocks, but human evidence is limited and results vary. It works best alongside well-timed daylight, sleep on the local schedule, and good hydration. Avoid long fasts, and do not use this approach if you have diabetes, take medication that requires food, are pregnant, under 18, or have a history of disordered eating, unless your healthcare provider agrees.