Night owls are more likely to gain weight than people who get good sleep because they tend to graze the kitchen for junk food in the wee hours, a new study suggests.

Researchers at the University of Pennsylvania found that people who were kept up until 4 a.m. in a sleep lab ate more than 550 additional calories during the late-night hours.

"People consumed a substantial amount of calories during those late-night hours when they would normally be in bed," said study author Andrea Spaeth, a doctoral candidate in the psychology department at the University of Pennsylvania. "Those calories also were higher in fat compared to the calories consumed at other times of day."

As a result, subjects kept up late gained more weight during five days of sleep deprivation than people in a control group who were allowed to get good sleep, Spaeth said.

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