Avoiding food may be a way for travellers to curb the effects of jet lag, a new study says.
Researchers from Harvard Medical School and the Beth Israel Deaconess Medical Center in Boston say they found that mice have a second internal clock based on food. This clock can override the body's usual light-based clock that regulates eating and sleeping habits.
They say that if the mice endured a period of starvation followed by a healthy feeding, the food-based clock was activated and esentially reset their sleep-wake patterns.
The researchers say that their findings may apply to humans when they travel or face changes in shift work and they need to overcome disrupted eating and sleeping patterns more quickly.
Normally, cells in the brain's hypothalamus region dictate patterns of eating, sleeping and hormone activity. In this cycle, known as the circadian rhythm, these cells receive signals from the eyes as they process changes in the daily cycle of light and dark.
"When food is readily available this system works extremely well," the study's senior author, Dr. Clifford Saper, said in a statement.
"Light signals from the retina help establish the animals' circadian rhythms to the standard day-night cycle."
However, the researchers found that when mice could not find food during their normal waking periods, their patterns would change according to the availability of food, which could be during times when they would normally be asleep.
Saper, chairman of the department of neurology at Beth Israel Deaconess Medical Center and a neurology professor at Harvard, used a hypothetical trip to Japan to illustrate how these new findings might help travellers.
A person making the journey from the United States to Japan would need to adjust to an 11-hour time difference. But the body's internal clock can only adjust a small amount each day, so it can take up to a week to adapt to the new time zone.
However, tapping into the food-based clock could significantly shorten the adjustment time.
"A period of fasting with no food at all for about 16 hours is enough to engage this new clock," Saper said in a statement.
"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."
The study was published Friday in the journal Science.
Abstract:
Differential Rescue of Light- and Food-Entrainable Circadian Rhythms
Patrick M. Fuller, Jun Lu, Clifford B. Saper
When food is plentiful, circadian rhythms of animals are powerfully entrained by the light-dark cycle. However, if animals have access to food only during their normal sleep cycle, they will shift most of their circadian rhythms to match the food availability. We studied the basis for entrainment of circadian rhythms by food and light in mice with targeted disruption of the clock gene Bmal1, which lack circadian rhythmicity. Injection of a viral vector containing the Bmal1 gene into the suprachiasmatic nuclei of the hypothalamus restored light-entrainable, but not food-entrainable, circadian rhythms. In contrast, restoration of the Bmal1 gene only in the dorsomedial hypothalamic nucleus restored the ability of animals to entrain to food but not to light. These results demonstrate that the dorsomedial hypothalamus contains a Bmal1-based oscillator that can drive food entrainment of circadian rhythms.
