People who are trying to stay trim may want to make sure they get plenty of sleep.
In a study, researchers found that normal-weight young men ate a Big Mac's-worth of extra kilojoules 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.
How the study was done
To investigate, Dr Laurent Brondel of the European Centre 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.
Two days served as a control period, during which the study participants stuck to their normal routines but kept track of their sleep, eating and activities in a diary.
During the second two-day period, the men went to bed at midnight and woke up at 8am on one day, and on the other day went to bed at 2am and woke up at 6am.
They were allowed to eat as much as they liked.
What the results showed
After the night of short sleep, the researchers found, the men took in 22% more kilojoules, on average, than when they were allowed to sleep for eight hours.
They ate more at breakfast and dinner, but not at lunch.
It's possible that people might eat more after a short sleep because mammals have evolved to store up kilojoules 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.
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, Brondel and Davenne add. "It is time to understand that sleep is not just losing time, besides the recovery processes that occur, there are many other functions (energy conservation, memory and so on) which are going on." - (Reuters Health, April 2010)