WEDNESDAY, Sept. 1 (HealthDay News) -- Teens who sleep less than eight hours a night are more likely to eat a high-fat diet that puts them at risk for obesity and the many health problems connected with it, new research shows.

The study, published in the Sept. 1 issue of the journal Sleep, found that these sleep-deprived teens consumed 2.2 percent more calories from fat, and ate more snacks than those who slept eight hours or more a night. They also ate more total calories.

"There's been a lot of research over the last five years implicating insufficient sleep with obesity," said study author Dr. Susan Redline, of Brigham and Women's Hospital and Beth Israel Deaconess Medical Center in Boston.

"Some experimental studies on sleep deprivation in controlled laboratory environments show a craving for fatty foods among the participants" who got less sleep, she said.

Redline, a professor of medicine with the school's division of sleep medicine, said sleep-deprived teens may suffer from metabolic disturbances that have been linked to obesity and insulin resistance in other research with shift workers whose sleep was also irregular.

Metabolism is the body's process for turning calories into energy. Lack of sleep can affect metabolism by changing the level of appetite-regulating hormones like leptin and ghrelin, setting the stage for poor eating habits, Redline explained.

In addition to being a possible cause of metabolic problems, fewer hours of sleep provided teens with "more opportunities to eat," Redline said.

Teens need about nine hours of sleep every night to feel rested and alert the next day, but few teens get that amount, experts said.

"I almost never see anyone who is sleeping more than seven hours a night," said Dr. Paula Elbirt, an associate professor of pediatrics and adolescent medicine at Mount Sinai Medical Center in New York City. Insufficient sleep among teens is "the rule, not the exception," she said.

Elbirt said the "adolescent lifestyle" encourages teens to stay up late. Socializing on cell phones and computers, playing video games and watching television keep teens awake into the middle of the night, she said, noting that daily stress may be an underlying reason for staying up late.

Elbirt said that while the "prevailing view is that a calorie is a calorie," there is some evidence that calories from fat are more likely to be metabolized into more stored fat. Also, the more fat you eat, the more you crave, she said.

Teens are also "phase-delayed" according to the study, meaning that their circadian rhythm is shifted in a way that makes them alert at night and sleepy in the morning, eating into the night hours.

And because school starts early for most teens, they tend not to get the sleep they need, experts said.

"All of us have a clock system inside us and it keeps 24-hour time," said Dr. Kenneth P. Wright Jr., an associate professor of integrative physiology at the University of Colorado in Boulder. "In adolescence, this system changes, and it drives a lot of our behaviors, like when we sleep."

Wright, at the school's Center for Neuroscience, likened adolescents to people "on the East Coast, living on a West Coast time" clock.

The study measured the hours slept of 240 teens for five to seven consecutive 24-hour periods on weekdays. The teens wore wrist meters measuring their movements to determine wakefulness and sleep. They were interviewed twice within 24 hours of eating about what foods they ate, the amount they ate, and when and where.

Teens who slept less than eight hours a night consumed, on average, 1,968 calories a day. Those who slept eight hours or more averaged 1,723 calories a day. The teens slept a little less than an average of eight hours a night. Only 34 percent of the participants slept eight hours or more.

Wright cited the study's "strong methodology," calling it a "step forward" in examining the relationship between lack of sleep and obesity.

"When we think of adolescents and lack of sleep, we think of drowsy driving, and learning is impaired, but this study also shows that there are real health consequences for teens," said Wright. "It supports the notion that sleep is important for our health."

More information

For more information on sleep and teens, go to the National Sleep Foundation.