BEIJING, July 10 -- If an improved diet and extra trips to the gym fail to help shed those excess pounds, a growing body of research is shining light on a new way to get to a new you: Do nothing.

    Do nothing, that is, but sleep.

    As millions of Americans move through life weary and sleep-deprived, scientists are uncovering more and more evidence that insufficient slumber may cause hormonal shifts that boost both hunger and appetite -- particularly for fat-laden carb catastrophes like jelly-filled donuts and super-sized fries.

    "We all need to be aware there is a relationship between sleep and obesity," says J. Catesby Ware, chief of the division of sleep medicine at Eastern Virginia Medical School, and director of the Sleep Disorder Center at Sentara Norfolk General Hospital in Norfolk, Va.

    Ware and his colleagues found signs of this link in a recently completed study of more than 1,000 men and women that indicated those who reported sleeping less also weighed more.

    He is now in the midst of new research focusing on another group of 1,000 individuals that is quantifying specific daily sleep habits, with preliminary data reinforcing his previous observation -- less sleep equals a bigger belly.

    "There are a number of research studies that all support the thesis that too little sleep leads to weight gain," Ware said. "How that happens is still somewhat unclear, but there are hormonal secretions that are affected with sleep loss that apparently affect appetite and eating."

    Other researchers are working to unravel the mechanism behind the mystery.

    Eve Van Cauter, a professor of medicine at the University of Chicago, recently found that when 12 healthy men in their 20s were instructed to sleep just four hours a night for two nights straight, they reported an increase in feelings of hunger by 24 percent.

    What's more, Cauter and her colleagues noted that levels of the hormone leptin, which delivers feelings of satiation to the brain, decreased by 18 percent among the men.

    Conversely, levels of the hormone ghrelin, which sparks hunger, shot up 28 percent -- prompting cravings for candy, cookies and cake.

    Dr. Phyllis Zee, a professor of neurology at the Northwestern University Feinberg School of Medicine, said that while researchers continue to be stymied by the exact nature of the sleep-weight connection, the relationship is undeniable.

    "This kind of short-term sleep deprivation study supports the relationship we see in the larger population-based studies, which shows that if you restrict sleep, the hormonal and metabolic profiles begin to resemble those of people who are pre-diabetic, while bringing about autonomic changes that can be related to the development of cardiovascular disease," added Zee, director of the Sleep Disorders Center at Northwestern Memorial Hospital in Chicago.

    According to several polls by the National Sleep Foundation, many Americans of all ages barely meet or fail to meet the minimal daily sleep requirements most physicians and researchers recommend.

    In its most recent 2005 survey, the NSF found that more than 70 percent of adults over the age of 18 get less than eight hours of sleep a night on weekdays -- and 40 percent get less than seven hours.

    A 2003 poll found that, on average, American adults between the ages of 18 and 54 sleep just 6.7 hours a night during the week, and seven hours a night on weekends.

    Among older adults -- those between 55 and 84 -- 13 percent sleep less than six hours a night during the week, while 11 percent have a similar sleep pattern on weekends.

    Against such a national backdrop of sleep deprivation, researchers concur that the battle of the bulge may ultimately best be waged beneath the sheets.

    "Between seven and eight hours seems to be a fairly magical number for sleep duration," said Zee. "People who report, on average, getting between seven and eight hours of sleep are the ones who appear to have the lowest risk" of weight gain.

    Ware agreed: "By sleeping more, you gain on all fronts. If you are obese and are trying to lose weight, it's almost a no-brainer."