Study: Mealtime Changes Could Combat Jet Lag

W A S H I N G T O N, Jan. 19, 2001 -- The timing of meals may play an important rolein resetting body clocks, concludes a study that could aidscientists hunting ways to combat long-distance travelers’ jet lag.

The discovery, published in today's edition of the journalScience, is in rats, not travelers, scientists cautioned.

Still, "it's a noninvasive to change your eating habits," noteslead researcher Michael Menaker, a University of Virginiabiologist. "This would give you a reason to try it."

But more important than the nuisance of jet lag, Menakerstressed, the discovery that the liver resets its own biologicalrhythms according to eating habits also could point the way tobetter therapy for serious liver diseases.

Controlling Circadian Rythms

Everyone has a sort of master clock in the brain that controlstheir "circadian rhythms," biological patterns such as sleep andbody temperature. This brain clock is very light sensitive, thereason most people sleep at night and wake during the day. Travelto a greatly different time zone, however, and it can take a whilefor that master brain clock to adjust.

Then scientists discovered the brain-based clock isn't the onlycontrol of circadian rhythms. Other organs seem to have their ownclocks that supplement the brain's master clock. Perhaps that's whysleep problems aren't the only jet lag symptom; lots of suffererscomplain of stomach upset and other problems, too.

Menaker simulated jet lag by exposing rats to light six hoursearlier than they'd normally wake. While the light-sensitive brainclock could adjust in a few days, the rats' separate livercircadian rhythms were out of sync for up to two weeks.

The liver helps control food metabolism. So Menaker, workingwith scientists in Norway and Japan, wondered if changing mealtimeswould reset the liver's own circadian rhythm and thus help readjustthe overall body clock.

They tested rats genetically engineered to carry afluorescent-stained clock-related gene — when and how much therats' liver tissue glowed under a microscope showed allowedmeasurement of the liver's circadian rhythms.

Rats normally sleep during the day and feed at night. Allow themfood only for four hours during daylight and they rapidly act likeday is night, pumping away on their exercise wheels for a few hoursbefore the food appears. Are they just hungry? Check those livergenes under the microscope, and Menaker found that the circadianclock in the liver had shifted by 10 hours after just two days ofadjusted mealtimes.

The finding is "very important," said circadian rhythm expertDavid Earnest of Texas A&M University. "What it proves for thefirst time is that feeding cycles can directly act … on therhythms expressed within peripheral tissues like liver,"independent of the brain's master clock.

That doesn't mean eating habits are more important than lightexposure for a person trying to prevent jet lag, Earnest cautioned— but that changing meal times might "be an added bonus" inhelping reset the body clock after a long trip.

Indeed, "it's reasonable that … if you're going to Europe,you should a few days before start eating dinner on Europeantime," Menaker said. "The brain will shift more quickly once youget there," meaning the two organs might be in sync sooner thanksto the liver's head-start.

But the discovery might have much more medically importantramifications: Doctors know that some diseases are worse at certaintimes of day and thus try timing some medications, a field calledchronotherapy. Some cholesterol drugs, for instance, work best whentaken before bed so they target a cholesterol-affecting liverenzyme most active at night.

Radiation for liver cancer works on a similar pattern, Menakersaid — it may work best with fewest side effects in the middle ofthe night, when patients can't get it. Yet if patients could resettheir liver clock by altering meal times, "you might get quite anadvantage," he said.

Menaker cautions that's just a theory, but that "it's likelyall the peripheral organs have their own oscillators," orcircadian clocks, something he is beginning experiments to test.