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Sleep the Weight Off

A good night's rest can prevent weight gain. Not resting can put on extra pounds.

Worried about gaining weight? Just sleep on it. If you didn't need another reason to get eight hours of sleep a night, try this one: Not resting can put on extra pounds.

Eons of evolution set our internal clocks to make us rest at night and run around in the day. Remember how hard it was to go to bed as a kid when it was still light outside? But modern-day life, with its swing shifts and all-night lighting, often manually overrides nature's schedules. The result: Our bodies become confused.

No one fully understands the consequences of that confusion, but new research out of Northwestern University points at weight gain as one result of behaving counter-clockwise.

The sun goes up, the sun goes down, and the Earth goes round and round. It's been happening for all the days of our lives, not to mention those of our amoeba ancestors. That daily cycle is built into our very fiber, into our genetic code; we run on circadian rhythms that tell us when to rise, when to sleep and when to eat.

When Northwestern researchers fiddled with one of the circadian clock genes in test mice, conveniently known as CLOCK, the animals stayed up when they would normally sleep and snacked all the time. They also developed symptoms that could lead to diabetes, like insulin resistance and high blood sugar levels. Ultimately, the circadian cycle-confused rodents gained more weight on the very same diet as mice whose clocks ran straight.

The physical results are important, but so to is where researchers found the CLOCK gene. It was all over the place. Especially intriguing was its location in areas of the brain that control metabolism and appetite, and in cells that metabolize sugar.

So why do we care about a bunch of mice with a gene changed in the laboratory? Humans and mice aren't so different, at least not in the genetic scheme of things, and their clock genes are nearly identical. The mice model what happens when our own circadian clocks get reset. Scientists think that as much as any genetic mutation, people's behaviors might be resetting their clocks and leaving them prone to weight gain.

When we fly across time zones or don't sleep we throw off our internal timepiece. But as the profusion of CLOCK genes shows, that clock isn't centrally located. Instead it's in a bunch of different systems.

Each part of the body that has a piece of the clock starts running on its own time, and suddenly—chaos. It's that cacophony of signals, say researchers, that leads to a breakdown in how the clock works. Hence changes in sleep patterns, metabolism, and eating habits.

Northwestern's mouse model isn't the only development showing a connection between fighting nature's timepiece and gaining weight. Scientists at Columbia University, found that people who didn't get the requisite number of hours of sleep did indeed gain weight—especially individuals between the ages of 32 and 49.

At the University Chicago researchers showed that people who fought their timepiece settings changed their levels of two important hormones related to fat metabolism, leptin and ghrelin. Coincidentally, leptin decreases appetite, and ghrelin increases it. Any guesses as to what happened when people didn't get enough rest? You got it, leptin went down and ghrelin went up.

What happens when we try to turn off a clock set millennia ago isn't completely understood. But mounting evidence seems to suggest that if you're concerned about putting on the pounds, or about taking them off—get a good night's sleep.