In short
Jet lag is not tiredness, it is a clock running on the wrong meridian, and it resolves at roughly one time zone per day on its own. The lever that speeds this up is light, timed by direction: after flying east, seek morning light and avoid the very early hours; after flying west, hold light into the evening. Caffeine manages the symptoms but barely moves the clock, and protects the day at the price of the night if timed late. The layers keep their usual local time anchors from day one.
Most travel advice treats jet lag as fatigue. It is navigation: the clock is set for a city you are no longer in, and the job is to move it.
01What jet lag actually is
The circadian clock re-entrains slowly. The clinical literature puts the natural rate at about one time zone per day, which is why a six zone trip costs most of a week when left alone, and why eastward travel, which demands the clock shift earlier, is reliably harder than westward, which lets it drift later, the direction it prefers.1 Sleeping badly is the visible symptom. The underlying problem is that cortisol, temperature, digestion and alertness are all still firing on origin time.
02The one rule that matters
Light shifts the clock in opposite directions depending on when it lands. The hinge is the core body temperature minimum, which sits roughly two hours before your habitual wake time: light after it moves the clock earlier, light before it moves the clock later.2 Every practical instruction in this protocol is that one curve, applied. Get the light timing right and everything else is refinement.
03Flying east
East means advancing the clock, the hard direction. On arrival, seek bright outdoor light in the local morning and avoid light in the very early hours, when your body clock still reads it as night and would shift the wrong way; as the days pass, the safe window moves earlier with you.2 If the trip matters enough to prepare for, the clock can be moved before departure: shifting sleep earlier by an hour a day for a few days, with bright light on waking, takes zones off the bill before boarding.3
04Flying west
West is the easy direction, because delaying the clock is what it does naturally. Hold bright light into the local evening, stay up until a reasonable local bedtime, and avoid the trap of the 4 am supermarket run: early waking is normal for the first days, and lying in darkness is better than feeding the old clock with light.3
05Caffeine, meals, melatonin
Caffeine is a symptom tool, not a clock tool. It will hold the afternoon of the first days together, and the same meta-analytic numbers apply abroad as at home: taken late it costs the night that re-entrainment depends on, so it belongs in the local morning only.4 Meal timing is a weaker signal: human evidence suggests it nudges peripheral rhythms more than the central clock, so eating on local time is sensible housekeeping rather than a lever.5
The honest note on melatonin
Melatonin is the one supplement with an authorised EU claim for jet lag, at a minimum of 0.5 mg taken close to bedtime on the first days of travel.6 LAYER ZERO does not contain it, and in several EU countries it is regulated as a medicine rather than a food. We say it plainly because they are different jobs: melatonin shifts the clock; the layers keep the day standing while the clock moves. This protocol is built on light because light is the strongest tool available to everyone.
06The research horizon
Travel science has been refining its two main instruments. On melatonin, a 2024 dose-response meta-analysis of 26 randomised trials in the Journal of Pineal Research found the sleep-promoting effect peaks around 4 mg taken about three hours before target bedtime, notably earlier and higher than the folk-standard tablet at lights-out; for shifting the clock itself, small doses timed to your internal evening remain the standard, and the two jobs should not be confused.7 A 2025 review in Experimental Physiology consolidated the athlete travel playbook, confirming the direction-specific core this protocol teaches: eastward means advancing the clock with morning light, westward means delaying it with evening light.8 One honest note on the app ecosystem: circadian travel apps are built on solid phase-response science, but independent trials of the apps themselves have not been run yet, so treat them as good calculators rather than proven interventions. The light does the work either way, and light is free at every destination.
07Where the system sits
The system's answer to travel is continuity: LAYER ONE with the local morning, LAYER TWO through the local day, LAYER THREE 60 to 90 minutes before local bed, from the first day. The layers do not shift the clock; they keep the day's structure standing while light does the shifting.
In the system
The clock this protocol moves is described in the circadian day. The morning anchor it relies on is morning light, and the caffeine arithmetic is in optimising caffeine timing. To place your own layers, the protocol builder takes about three minutes. Build your protocol →
Sources
Next in this thread
The circadian dayThe clock jet lag disrupts, and the physiology this protocol steers by.→How we handle evidence. This protocol is built on the clinical jet lag literature and the human phase response to light, with the melatonin question answered plainly rather than avoided. Educational content, not medical advice.