Scientists have long maintained that meal times affect the body clock, which has a natural period of about 24.2 hours. But, they've always said that the key factor is light.

Now, a team at Harvard University has found that the brain has a second feeding clock, which keeps track of meal times rather than daytime and when food is scarce, it actually overrides the master clock.

Thus, frequent air travellers can keep tiredness at bay by not eating, the Harvard researchers reported in the latest edition of the Science journal.

According to lead researcher Clifford Saper, travellers may be able to use the feeding clock to adapt to changes in time zones which leaves them feeling groggy and jet-lagged.

"If, for example, you are travelling from the US to Japan, you are forced to adjust to an 11-hour time difference. Because the body's biological clock can only shift a small amount each day, it takes the average person about a week to adjust to the new time zone. And, by then, it's often time to turn around and come home. A period of fasting with no food at all for about 16 hours is enough to engage this new clock.

"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," he said.

The researchers came to the conclusion after analysing the brain function in laboratory mice, which were missing a key clock gene, Bmal1.

Subsequently, they placed the gene into a viral vector, which enabled the animals to restore a functional biological clock to only one spot in the brain at a time.

"We discovered that a single cycle of starvation followed by re-feeding turns on the clock, so it effectively overrides the suprachiasmatic nucleus and hijacks all of the circadian rhythms onto a new time zone that corresponds with food availability.