In a recent study, researchers found that normal-weight young men ate a Big Mac’s-worth of extra calories when they’d gotten four hours of sleep the night before compared to when they slept for eight hours.

Given the findings, and the fact that people have been sleeping less and getting fatter over the past few decades, “sleep restriction could be one of the environmental factors that contribute to the obesity epidemic,” they write in the American Journal of Clinical Nutrition.

A number of studies have linked shorter sleep duration with higher body mass index (BMI) -- a measure of weight in relation to height used to gauge whether someone is overweight or obese. But no experimental studies to date have actually looked at what happens to a normal-weight person’s eating patterns when he or she sleeps less.

To investigate, Dr. Laurent Brondel of the European Center for Taste Sciences in Dijon, France, and colleagues looked at sleep, eating, and energy expenditure in 12 healthy young men across two 48-hour sessions.

After the night of short sleep, the researchers found, the men took in 22 percent more calories, on average, than when they were allowed to sleep for eight hours. They ate more at breakfast and dinner, but not at lunch. The average calorie increase was about 560.

It’s possible that people might eat more after a short sleep because mammals have evolved to store up calories in the summer, when nights are short and food is plentiful, Brondel and his colleague Dr. Damien Davenne of the University de Caen in Caen, France noted in an email to Reuters Health.

The findings make it clear that people need to do their best to get an adequate amount of sleep so their bodies can function properly.