Late-Night Snack Attack? Why It Happens

Love that bowl of ice cream around 10 p.m.?

You may have tried to give it up knowing you don't need the extra calories, but failed. Guess what? It's not your fault. Just like you have a body clock, you also have a food clock.

Eating late at night may genetically change an area of the brain so that it comes to expect food at that time, researchers at the University of Texas Southwestern Medical Center have discovered. So when you try to kick the habit, your genes actually activate at the expected mealtime, making it extra difficult not to indulge in that late-night bowl of ice cream.

At least that's the way it works in mice. In experiments with laboratory mice, study leaders Dr. Masashi Yanagisawa and S. Clay Williams found that food turns on body-clock genes in a particular area of the brain even when the food cycle is interrupted.

The daily ups-and-downs of waking, eating and other bodily processes are known as circadian rhythms, which are regulated by many internal and external forces. One class of genes involved in these cycles is known as Period or Per genes. When food is freely available, the strongest controlling force is light, which sets a body's sleep/wake cycle, among other functions. Light acts on an area in the brain called the suprachiasmatic nucleus, or SCN. Destroying the SCN doesn't affect the body clock that paces feeding behavior, so the circadian pacemaker for feeding must be somewhere else.

To find out where it is, the UT Southwestern research team set mice on a regular feeding schedule, then examined their brain tissue to find where Per genes were turned on in sync with feeding times. The researchers put the mice on a 12-hour light/dark cycle, and provided food for four hours in the middle of the light portion. Because mice normally feed at night, this pattern is similar to humans eating at inappropriate times. The mice soon fell into a pattern of searching for food two hours before each feeding time. They also flipped their normal day/night behavior, ignoring the natural cue that day is their usual time to sleep. After several days, the researchers found that the daily activation cycle of Per genes in the SCN was not affected by the abnormal feeding pattern.

When the extra feeding times were stopped, genes in the mice continued to turn on in sync with the expected feeding time. "They started to show the same pattern of anticipatory behaviors several hours before the previously scheduled time of feeding," said Yanagisawa "So somewhere in the body, they clearly remembered this time of day."

The study findings were published in the Proceedings of the National Academy of Sciences, August 2006.

--From the Editors at Netscape

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