There will be no big marketing budget behind this diet breakthrough, no FDA approvals, no celebrity endorsements: Research published this month in the Annals of Internal Medicine (one of the the big kahunas of peer reviewed medical journals) establishes that sleep--and sleep alone--is one of the most powerful diet tools ever identified.
There's not a diet pill on the planet that could accomplish what sleep did in this study, which compared two groups of overweight non-smokers on calorie restricted diets for 14 days. One group clocked 8.5 hours of sleep per night, and the other logged 5.5 hours of sleep per night (which the authors point out is a "norm" for people in this day and age.) Both groups ate roughly 1,450 calories a day. After two weeks, the people who slept more lost more fat than the group who slept less. More than half of the weight loss during the 8.5 hours of sleep was fat versus only one quarter of the weight loss during the 5.5 hours of sleep. People literally burned fat while they slept.
Even more startling, the folks who slept less lost more muscle (60% more muscle was lost by the sleep-deprived group.) Those three hours of lost sleep caused a shift in metabolism that made the body want to preserve fat at the expense of muscle. And that's not all that happened: When the researchers compared circulating blood levels of appetite-regulating hormones in the two groups they found those who slept for three fewer hours had produced more of the appetite stimulating hormone ghrelin. They woke up hungrier!
Most of us assume our bodies burn more calories when we are awake longer, but that's not true. The metabolic rate is down-regulated with less sleep. Translation: When you sleep less, your body starts to burn calories at a slower rate to preserve energy. In the study, people burned on average 400 more calories by sleeping for 3 more hours--that's an additional 2,800 calories burned in just one week. With less sleep, the body seeks to meet the increased metabolic needs of longer waking hours by shifting into a lower gear, so to speak, that burns fewer calories and less fat.
Bottom Line: If you want to burn fat, preserve muscle and wake up less hungry when you are dieting, sleep more...8.5 hours a night to be exact.