Jet lag is the unpleasant experience of not adjusting quickly to a ‘local’ sleep cycle – this occurs when the circadian rhythms are out of alignment, both with the local pattern of day and night, and with each other, as different body rhythms adjust at different rates. We know from research that the ‘master’ body clock, located in the brain, responds most to light, while other parts of our bodies are more influenced by meal times. Jet lag might be made worse if the clocks in different parts of our bodies are out-of-sync with each other and with the local time.