Not eating for 12-16 hours can help people quickly reset their sleep-wake cycle, according to a new study from the Harvard Medical School. This discovery can drastically improve a person's ability to cope with jet lag or adjust to working late shifts.

Scientists have long known that our circadian rhythm is regulated by our exposure to light. Now they have found a second "food clock" that takes over when we are hungry. This mechanism probably evolved to make sure starving mammals don't go to sleep when they should be foraging for food.

The lead researcher Clifford Saper explains:

The neat thing about this second clock is that it can override the main clock ... and you should just flip into that new time zone in one day.

It usually takes people a week to fully adjust to a new time zone or sleeping schedule. To think that this new "food clock" hack can help you change your internal clock in one day is mind boggling.

How does it work?

Simply stop eating during the 12-16 hour period before you want to be awake. Once you start eating again, your internal clock will be reset as though it is the start of a new day. Your body will consider the time you break your fast as your new "morning."

For example, if you want to start waking up at 2:00 am, you should start fasting between 10:00 am or 2:00 pm the previous day, and don't break your fast until you wake up at 2:00 am. Make sure you eat a nice healthy meal to jumpstart your system.

Another example: If you are travelling from Los Angeles to Tokyo, figure out when breakfast is served in Tokyo, and don't eat for the 12-16 hours before Tokyo's breakfast time.

Why does this work?

Like everything else in our evolutionary history, it has to do with survival:

"For a small mammal, finding food on a daily basis is a critical mission. Even a few days of starvation, a common threat in natural environments, may result in death," the study said. "Hence, it is adaptive for animals to have a secondary "master clock" that can allow the animal to switch its behavioral patterns rapidly after a period of starvation to maximize the opportunity of finding food sources at the same time on following days." The shift is a survival mechanism in small mammals that forces them to change their sleeping patterns, Fuller suggests. One starvation cycle is enough to override the traditional light-based circadian clock, the study suggests. "This new timepiece enables animals to switch their sleep and wake schedules in order to maximize their opportunity of finding food." "A period of fasting with no food at all for about 16 hours is enough to engage this new clock," says Saper. "So, in this case, simply avoiding any food on the plane, and then eating as soon as you land, should help you to adjust — and avoid some of the uncomfortable feelings of jet lag." CBC (quoting study published in the May 22 issue of Science.

For more information, check out Science Friday's interview with lead researcher Clifford Saper.