People who got very little sleep ate more but didn't burn any extra calories in a new study that adds to evidence supporting a link between sleep deprivation and weight gain.
Although the findings don't prove that sleeplessness causes people to pack on extra pounds, or exactly how the relationship between sleep and body weight might work, they do show that "sleep should be a priority," said Michael Grandner, who studies sleep and sleep disorders at the University of Pennsylvania in Philadelphia.
"If you're making your diet a priority and trying to be healthy, don't forget that getting healthy sleep is probably an extremely important part of being healthy," Grandner, who was not involved in the new work.
Previous studies have tested the link between sleep and diet and weight in multiple ways, Grandner explained. Some surveyed large populations of people with questions about their sleeping and eating habits and tracked their future health conditions. Others, including the new report, looked at a smaller group of people very closely, manipulating their sleep schedule and observing how their food cravings and appetite responded.
Both kinds of research have generally supported the idea that less sleep is associated with more extra weight.One recent study in Sweden found, for example, that young men who were sleep-deprived ate about the same amount of food as usual, but burned between 5 and 20 percent fewer calories than when they were well-rested.
Approximately 50 to 70 million Americans -- including a significant number of shift workers -- suffer from chronic sleep loss and sleep disorders, according to the National Institutes of Health.
For the current study, Marie-Pierre St-Onge of the New York Obesity Research Center at St. Luke's-Roosevelt Hospital and colleagues recruited thirty men and women in their 30's and 40's, all of roughly normal weight. The participants lived and slept in a research center during two different five-night periods.
During one of those visits, they were allowed to sleep for nine hours each night. During the other, participants were only permitted four hours of shut-eye. Both times, they were fed a strict diet for the first four days of their stay and then were allowed to eat whatever they wanted on the fifth and final full day.
Researchers tracked how much energy they burned on a daily basis, and also asked participants how energetic they felt.
The tests showed that regardless of which sleep schedule they were on, people burned a similar amount of calories -- about 2,600 per day.
But when they were sleep-deprived, they fed themselves about 300 more calories on average on the final day of the study compared to when they had been sleeping normally. Well-rested participants ate an average of 2,500 calories that day, compared to 2,800 when they were running on less sleep.
If that kept up in a person's normal daily life, it would put the sleep-deprived at higher risk of obesity.
Participants also said they felt more sluggish and less energetic after a few days on the short sleep schedule.
There are a few possible explanations behind the link between sleep and eating, researchers explained. One is that shut-eye is important for the hormones that help control how much we eat.
Sleep "seems to play a role in how your body manages the hormones that control how hungry you are, when you're hungry (and) what kinds of foods you're hungry for," Grandner said.
Another explanation is that when we're tired, we're less good at making healthy eating decisions.
"It's possible that when you're on short sleep you're more susceptible to giving in to your desires," St-Onge told . "You walk past a (food) cart or a bakery and it smells so good...If you're sleep-deprived you may be like, 'Oh, what the heck,'" she said.
Grandner added that it's possible the link goes both ways, and that eating too much of certain kinds of foods can disrupt a person's sleep schedule. Or, someone that has a stressful job may sleep too little and also eat too much as a result.
Too little sleep has also been tied to a host of other health problems, he said, including heart disease and diabetes -- which have their own associations with weight, complicating the picture even further.
"People always want to say if you sleep more you'll lose weight," St-Onge said. While her study didn't set out to show whether that's the case, "if you're trying to control your weight, it would be helpful not to be sleep-deprived," she concluded.
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