Four hours less sleep = 560 more calories

We tend to eat more when we sleep less. So much so that researchers are now asking whether lack of sleep is one of the causes of increased obesity – especially in younger people.

A study published in the American Journal of Clinical Nutrition this month found that normal-weight young men ate 560 more calories during the day after sleeping for just four hours compared to sleeping for eight – that’s an increase equivalent to a Big Mac's-worth of extra calories for every night of sleep deprivation.

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

A number of previous studies have linked shorter sleep duration with higher body mass index (BMI). But this is the first to actually look at what happens to a normal-weight male’s eating patterns when he sleeps less.

22% more calories

The first two day period served as a control. 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 8 a.m. on one day, and on the other day went to bed at 2 a.m. and woke up at 6 a.m. They were allowed to eat as much as they liked.

After the night of short sleep, the researchers found, the men took in 22% 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 told Reuters.

The findings make it clear that people need to do their best to get enough sleep so their bodies can function properly. ‘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,’ Brondel warns.