Skip the pretzels: starving may fend off jet lag

CHICAGO (Reuters) - Starving yourself before a long flight may help prevent jet lag, U.S. researchers said on Thursday.

Normally, the body's natural circadian clock in the brain dictates when to wake, eat and sleep, all in response to light. But it seems a second clock takes over when food is scarce, and manipulating this clock might help travelers adjust to new time zones, they said.

"A period of fasting with no food at all for about 16 hours is enough to engage this new clock," said Dr. Clifford Saper of Harvard Medical School, whose study appears in the journal Science.

He said a person from the United States traveling to Japan must adjust to a 11-hour time change.

"Because the body's 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 come home," Saper said in a statement.

Saper and colleagues knew that when food is scarce, animals are able to override their normal biological clock to improve their chances of finding food.

Studies have shown that mice fed only during the time when they normally sleep shift their body clocks to this new schedule. "They would be awake and alert and ready to go an hour or two before a meal was due to appear to have maximal chance of getting the food," Saper said in a telephone interview.

"This is built into the brain. The problem is, nobody knew how it worked," he said.

He and colleagues set out to find this mechanism. They used a group of mice that had been genetically engineered to lack a master gene called BMAL1 that regulates the body's clock. They put this gene into the shell of a hollowed-out virus that acted as a vector to deliver the gene only to brain cells they were interested in studying.

When they put it into a small region of the hypothalamus known as the suprachiasmatic nucleus, which serves as the body's primary clock, the mice adjusted to a light-based schedule for waking and sleeping, but not eating.

"If you don't wake them up they will starve to death," Saper said.

However, when they restored the gene only in a section of the hypothalamus called the dorsomedial nucleus, which helps organize waking and feeding schedules, the mice adjusted to the eating schedule, but not daylight.

Saper said when food is scarce, this second clock can override the body's primary clock. He said these same clock genes are known to be in all mammals, including humans.

While skipping meals ahead of a long flight or night shift has not been proven to work in humans, it may be worth a try.

"I'm certainly going to do it the next time I go to Japan," he said.

(Editing by Maggie Fox)