Insufficient sleep affects appetite and satiety hormones as well as fat cells, according to the nation's top sleep experts.

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If you want to lose weight, be sure to get enough sleep.

Most people know they should cut calories and exercise more to trim down, but there's now significant scientific evidence that another critical component to weight control is avoiding sleep deprivation, sleep scientists say.

"There is no doubt that insufficient sleep promotes hunger and appetite, which can cause excessive food intake resulting in weight gain," says Eve Van Cauter, director of the Sleep, Metabolism and Health Center at the University of Chicago. She has spent 15 years studying the topic.

Sleep deprivation probably affects every process in the body, she says. "Our body is not wired for sleep deprivation. The human is the only mammal that does this."

Her research and that of others may help explain why so many people who are chronically sleep-deprived also are overweight, and it could be part of the reason sleepy college students, new parents and shift workers pack on pounds.

STORY: If you don't snooze, you lose

Studies have shown that when people don't get enough sleep they:

• Have increased levels of a hunger hormone called ghrelin and decreased levels of the satiety/fullness hormone called leptin, which could lead to overeating and weight gain.

• Consume about 300 calories a day more than when they are well-rested. Overall, most of the extra calories came from high-fat foods.

• Snack more and do less physical activity.

• Eat more than what is needed to cover the energy cost of staying awake longer, especially at night, which can lead to significant weight gain.

Research has showed that when study participants didn't get enough sleep for five days, they consumed more carbohydrates and gained nearly 2 pounds in that time. "When people are sleepy, they make poor food choices and are more likely to eat more than they need," says Kenneth Wright, director of sleep and chronobiology laboratory at the University of Colorado in Boulder.

When those folks got enough sleep, they reduced their intake of both carbohydrates and fats, Wright says.

Other research shows that too little sleep also plays havoc with your fat cells, which could lead to weight gain and type 2 diabetes, and that making sure you get enough sleep will help fight a genetic predisposition to gain weight.

Van Cauter says sleep deprivation affects the body in many different ways. For instance, it activates a small part of the hypothalamus, the region of the brain that also is involved in appetite regulation.

In addition to ghrelin and leptin, there are many other hormones involved in appetite regulation that sleep deprivation may affect, she says. "We are looking at endocannabinoids, which are increased in the afternoon in people who are sleep-deprived. These hormones promote eating for pleasure, which is called 'hedonic eating.'"

Another recent discovery is that not getting enough sleep reduces fat cells' ability to respond properly to the hormone insulin, which is crucial for regulating energy storage and use, Van Cauter says.

Plus, insulin promotes the release of leptin, so if your fat cells are less insulin-sensitive, you will make less leptin, which is associated with an increase in food consumption and weight gain, she says.

Insulin and leptin contribute independently to fat intake or storage, says Matthew Brady, an associate professor of medicine at the University of Chicago and senior author of the study on sleep deprivation and fat cells. "There is a growing body of evidence that agrees that sleep deprivation can lead to greater chance of weight gain."

So how can you know if you're getting enough sleep?

Sleep needs vary, but in general, most young adults need seven to nine hours a night, Van Cauter says. Some people can do with less, and others need more. As people grow older, their need for sleep decreases to about seven to eight hours a night, she says.

Yet, many people don't know exactly how much sleep they need.

Van Cauter recommends trying to get a handle on your sleep needs by doing this: The next time you're on vacation, go to bed at your usual time, but do not use an alarm clock to wake up. The first couple of days, you may sleep more than usual. That way you will pay your sleep debt, she says.

Then, when your sleep has stabilized, record how much you sleep, plus or minus 15 minutes, she says. That is your sleep need or capacity.

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