FRIDAY, June 28 (HealthDay News) -- 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 of the morning, 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.
Late-night overeating is likely the result of hormonal changes
that occur in people who are sleep-deprived, said Dr. W.
Christopher Winter, medical director of the Martha Jefferson Sleep
Medicine Center in Charlottesville, Va.
They tend to experience an increase in their levels of ghrelin,
a hormone that stimulates hunger cravings, and a decrease in levels
of leptin, a hormone that makes people feel full.
"Now you're in a situation where you are craving bad food and more of it, and your body feels less full when it gets that bad food," Winter said.
The research team monitored the eating habits of about 200
people who, for five days straight, were kept up until 4 a.m. and
then allowed only four hours of sleep. They remained in the lab the
whole time, going through in groups of four or five at a time.
Subjects were allowed to eat whenever they liked, and trained
monitors in the sleep lab maintained a running tally of the amount
consumed and the times at which they ate.
Researchers then compared their calorie intake and weight gain
to that of a control group allowed a good night's sleep in the same
lab with the same food availability.
"The only difference between the two groups was sleep," Spaeth said. "They lived in a suite, and in the suite there was a kitchen with a fridge and microwave."
The eating habits of the control group remained unchanged. The
sleep-deprived group began eating additional calories between 10
p.m. and 4 a.m., and they tended to eat fattier foods during that
time period. "That does kind of mimic the real world, when you're
up late at night and you drift over to your fridge," Spaeth
There was one key difference between the lab and the real world.
Since the study took place in a hospital, the suite's kitchen was
stocked with hospital food. "I'm wondering if the effect would be
stronger in the real world, where you have access to more
calorically dense foods," Spaeth said.
The findings are published in the July issue of the journal
Previous studies have shown a link between inadequate sleep and
weight gain, Winter said, but this research is valuable because it
provides precise observations in a laboratory setting.
"Anytime you're dealing with studies in the field, you're often relying on some sort of food diary or the recall of the patient," Winter said. "It's amazing how much food a person can eat and not remember. It's hard to keep track of people in terms of their eating and in terms of their sleep. When people are in a lab, they can perfectly control conditions and report them."
Blacks gained more weight than whites, and males gained more
weight than females. Researchers currently are undertaking
follow-up research involving detailed calorie counting to try to
explain these differences, Spaeth said.
The study adds more weight to the growing mound of evidence
suggesting that people who want to control their weight need to get
seven to eight hours' sleep a night, Winter said.
People who can't get a good night's sleep -- such as people who
are traveling or working late to meet a deadline -- need to pay
extra attention to their food cravings, he added.
"God knows I'm aware of it," Winter said. "I'm usually traveling a lot, and I can feel myself craving food I don't really need and didn't know I wanted. I know when I'm going through an airport late at night and I see chocolate-covered pretzels, I know I'm not craving them because I'm hungry. I think if patients are more aware of those things, they're going to say, 'I'm not going to eat this because I'm not hungry, and it's not going to do me any good.'"
For more on eating behaviors, go to the
U.S. National Library of Medicine.
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