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July 31, 2006 -- Raiding the refrigerator in the wee hours? Your body clock -- which affects patterns of eating and sleeping -- may play a role.
A new study shows that mice learned to expect food at odd hours after snacking when they would normally be sleeping.
And the mice had a hard time breaking the habit.
"Somewhere in the body, they clearly remembered this time of day," says Masashi Yanagisawa, MD, PhD, in a news release from the University of Texas Southwestern Medical Center at Dallas.
Certain body-clock genes in the mice's brains may be part of the reason, the researchers note.
Their study is due to appear in Proceedings of the National Academy of Sciences' Aug. 8 early online edition.
Chow Time
Yanagisawa and colleagues studied two groups of mice.
One group got a restricted amount of food every four hours. The other group got unlimited food around the clock.
All of the mice lived on a 12-hour light-dark cycle. That is, they spent 12 hours in darkness, followed by 12 hours of light, day after day.
Mice normally eat in the dark; they're more comfortable scurrying around under cover of darkness.
But the restricted-food group got some of their chow at an unusual time, in the middle of the light cycle.
That's like eating in the middle of the night for people, the researchers note.
Tinkering With the Body Clock
The mice in the restricted-food group came to expect their unusually timed snack, and it was hard to change their ways.
Those mice became more active during the two hours before their midday snack. Certain body-clock genes in their brains also switched on in sync with the feeding schedule, the study shows.
The pattern was tough to stop. After two days without any food at all, the body-clock genes still turned on in sync with the unusual feeding schedule.
If the findings apply to people, eating late at night might train body-clock genes to expect food at those times.
But because the study was on mice, that's not certain yet.
SOURCES: Mieda, M. Proceedings of the National Academy of Sciences of the United States of America, Aug. 8, 2006, early online edition. News release, University of Texas Southwestern Medical Center at Dallas.