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    The Evidence Against Sleep Loss continued...

    During the 15-year study period (since 1989) researchers found that short sleep was associated with low leptin levels. They show a 15% increase in ghrelin and a 16% decrease in leptin in people who consistently got only five hours of sleep.

    "It shows that there is a regulatory problem," Mignot tells WebMD. "In natural evolution, when you were more active, you needed to eat more calories, so you had this natural reaction that increased your appetite and your sleep." Compare that with today, when people aren't as physically active yet burning the candle at both ends, either in traffic or in front of the TV. Also, food is more readily available. All those factors have caused increase in weight.

    Researchers also show an association between sleep duration and BMI. Those getting three hours of sleep had a 5% increase in body weight. "That's not an enormous amount, but the effect might be underestimated," says Mignot. "Still, it's something we can do something about. It may be the reason why dieting has been so disappointing for so many people."

    Sleep Loss Affects Cravings

    In the second study, 12 healthy males in their 20s were studied to see how sleep loss affected both leptin and ghrelin levels. The young men got only four hours of sleep for two nights, then two nights of 10 hours in bed (average of 9 hours of sleep). Hormone levels were measured before, during, and after the sleep periods. They also completed questionnaires to assess their hunger and desire for different foods.

    After a night of four hours of sleep, sleep restriction resulted in a 24% increase in hunger and a 23% increase in appetite, reports study co-researcher Esra Tasali, MD, a sleep specialist at the University of Chicago Medical Center. "If allowed to increase their food intake, they would likely eat an extra 550 calories a day," Tasali tells WebMD, whose study appears in Annals of Internal Medicine.

    As the sleepy guys got hungry, their food choices also changed. High calorie, high-carb foods were most appealing -- sweets, and salty and starchy foods -- after two nights of little sleep. Fruit, vegetables, and dairy products were at the low end of the craving scale.

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