Researchers at the Mayo Clinic in Rochester, Minnesota, tracked the sleep and diet patterns of 17 healthy men and women, ages 18 to 40, for three days. They slept an average of six and a half hours. Next, for eight days in a sleep lab, one group snoozed to their hearts' content, while the other slept for two-thirds of their usual duration. Participants ate and drank whatever they wanted during the study, and researchers tracked how many calories participants ate and burned each day. Guess what? The sleep-deprived group (who clocked in at 5.2 hours of sleep) wound up consuming an extra 549 calories a day -- and the comparison group ate about 143 fewer daily calories than usual.
So how much sleep is enough? Seven to eight hours of nightly shut-eye is optimal, experts say -- previous studies indicate that any less can lead to weight gain. One way this happens: Sleep deprivation causes insulin resistance, affecting how your metabolism processes fat and leading to weight gain, SELF reported in this year's February issue.
With this study, one of the most surprising things was the group that snoozed less didn't expend more calories than the group that slept more, says Andrew Calvin, M.D., fellow in cardiovascular disease and assistant professor of medicine at Mayo Clinic, Rochester.
"I think we assume that if we're awake longer, we're going to burn more calories because we're moving longer," Calvin says. But that didn't happen here.
The study was too short for researchers to tell whether participants gained weight. But, Calvin says, "If this were to happen on a regular basis with people, we would expect a significant weight gain." Consume 549 extra calories every day for one week, and you'd gain a pound of weight, he says.
The researchers also noticed that sleep-deprived participants' hormone levels changed. Levels of the hormone leptin, which tells your brain when to stop munching, went up, while levels of ghrelin, the hormone that tells the brain when you're hungry, went down. Calvin expected the opposite, but says the changes were probably a result, not a cause, of consuming the extra calories. In fact, that's the pattern experts typically see among people who are overweight, Calvin says.
Not getting enough snooze time can affect your body in other ways, too. Too little sleep can weaken your immune system and cause your reaction time and memory to lag, SELF reported in January 2010. Getting fewer than five hours of sleep can even double your risk for developing type 2 diabetes.
If you have trouble falling asleep or snoozing soundly, try a healthy bedtime snack or turn off your computer, TV and smartphone one to two hours prior to lying down. Who couldn't use a little more rest?