Eating less late at night could be key to feeling more alert and being able to concentrate despite sleep deprivation, according to a new study.

"Adults consume approximately 500 additional calories during late-night hours when they are sleep restricted," says senior author David F. Dinges, PhD, director of the Unit for Experimental Psychiatry and chief of the division of Sleep and Chronobiology.

Working with 44 participants between the ages of 21 and 50, the researchers gave them unlimited, "free-range" access to food and beverages during the day, but capped their sleep at just four hours for three consecutive nights.

On the fourth night, 24 of the participants were given access to nothing but water between 10pm and their 4am bedtime, while the remaining 20 continued free-range access to nourishment.

At 2am each day, the researchers assessed participants' working memory, cognitive skills, sleepiness, stress level and mood.

On the fourth night, participants who had fasted performed better on the tests, specifically in the domains of reaction time and concentration than their free-range counterparts.

Meanwhile, the free-rangers showed attention lapses and slow reaction times, according to the study, which will be presented at SLEEP 2015, the 29th annual meeting of the Associated Professional Sleep Societies, LLC.

Hailing from the Perelman School of Medicine at the University of Pennsylvania, this same research team conducted the 2013 study concluding that those with late bedtimes and chronic sleep deprivation eat more than others and gain weight easily.

"Short sleep duration is a significant risk factor for weight gain and obesity, particularly in African Americans and men," says senior author Dr. Namni Goel.

Dr. Goel and associates concluded in a related study that individuals reduce their calorie intake to compensate for the reduced morning resting metabolism that is the result of sleep deprivation.

"This research suggests that reducing the number of calories consumed can help prevent that weight gain and some of the health issues associated with obesity in Caucasians and particularly in African Americans."