A good night's rest could be just what you need to stay slim. Researchers at the University of Pennsylvania have uncovered direct evidence that sleep deprivation is tied to weight gain in the largest study to date of healthy individuals in a controlled laboratory setting.

It is becoming apparent that America's sleep is under siege. The number of 'short sleepers' — people who get the less than six hours per night — has streadily risen since 1975. A national health survey conducted between 2004 and 2007 found that one out of every three adults is a short sleeper.

This pattern is suspected to negatively impact our energy levels and daily metabolism, potentially increasing our appetites throughout the day and leading to weight gain.

Unlike prior work that asked people to self-report their eating and sleeping habits, which is prone to bias, scientists at Penn recruited 225 adults to participate in a two-week sleep study at the Sleep and Chronobiology Laboratory at the Hospital of the University of Pennsylvania.

By monitoring these subjects in the lab, they could directly assess how sleep deprivation changed people's dietary habits.

A Late Date With The Refrigerator

People who were forced to stay up late consumed 30 percent more calories and gained about eight times the weight (average: 2.13 vs. 0.24 lbs) compared to individuals allowed 10-12 hours of sleep over this short two-week study period.

"Although previous epidemiological studies have suggested an association between short sleep duration and weight gain/obesity, we were surprised to observe significant weight gain during an in-laboratory study," said lead author Andrea Spaeth, a doctoral candidate in the psychology department at the University of Pennsylvania.

All of the volunteers were provided three meals day at set times, which they picked from a broad collection of menus, but they were also allowed to snack as much as they wanted during the day and night.

Subjects who stayed up late ate more snacks, especially on the initial days when bedtime was delayed. Most of this snacking was done during the twilight hours of 10 p.m. to 4 a.m. and consisted of a higher percentage of fatty foods.

Participants were either Caucasian or African American, and interestingly, the latter put on more pounds when sleep deprived.

"African Americans, who are at greater risk for obesity and more likely to be habitual short sleepers, may be more susceptible to weight gain in response to sleep restriction," continued Spaeth. "Future studies should focus on identifying the behavioral and physiological mechanisms underlying this increased vulnerability."

Sleep-deprived males in both racial groups gained about twice the pounds as sleep-deprived women.

Last week, the American Medical Association classified obesity as a disease, which should reinvigorate efforts to curb the exorbitant levels of the disorder recorded in the U.S.

Rectifying sleep disorders may offer a simple option for reducing obesity. Sleep apnea, which leads to interruptions in breathing, has been tied to obesity, as the restless nights caused by the condition have been linked to having less energy for exercise and daily activities. In turn, extra pounds can bulk up the muscles and tissues in one's airways, possibly establishing a vicious cycle.

Source: Spaeth AM, Dinges DF, Goel N. Effects of Experimental Sleep Restriction on Weight Gain, Caloric Intake, and Meal Timing in Healthy Adults. Sleep. 2013.