Fasting before a long flight may help prevent jet lag, researchers at the Harvard Medical School have found. Our internal body clock usually tells us when to sleep and eat based on the amount of light received. But, according to research by Dr. Clifford Saper, a second clock takes over when food is scarce. Manipulating this clock could help travellers adjust to new time zones. "A period of fasting for about 16 hours is enough to engage this new clock," said Saper.