Over years of travel and research, I’ve settled on the following protocol for combating and preventing jet lag while traveling across time zones. As with all things, YMMV but this is based on work from other folks as well so definitely has a wider use basis.
The whole goal in fighting jet lag is to adjust your body to your destination timezone as quickly as possible, and the thing most in your control when traveling to do this with is food
Fast for 16 hours going into breakfast in your destination timezone.
eg, if you’re flying NYC to London and plan to eat breakfast at 8am GMT (either on the plane or ground), you would eat your last meal 16 hours before at 1pm Eastern
Hydrate, Hydrate, Hydrate
Drink lots of water and only water. Planes dry you out and dehydration is your enemy with jetlag
Sparkling water is great too while fasting since it helps you feel more full.
Shift Your Sleep Schedule
If you can start waking up earlier or later the day or two before your trip (based on which direction you’re going) all the better
Get Sunlight in Your Destination
Especially for big time zone changes, getting lots of sunlight during the day helps your body reset its circadian rhythm faster
Sleep in Your Destination Time Zone
Start moving your sleep to your new time zone and if you can sleep in the plane at “night” in your destination, great.
Unless absolutely necessary, don’t nap on your first day. Power through and go to be around 8pm if you need to but naps will often keep you up and night and make the overall adjustment period longer.
Whenever possible, try to land between about 10am and 2pm in your destination - this will make it easier to get the sunlight at appropriate times while also being late enough that you’ll be less tempted to take a nap during the day.