Apparently, we’re not sleeping as much as we used to. More than a third of adults report sleeping less than 7 hours a night. And that’s a fairly new development. We’re sleeping significantly less than we were 20 or 30 years ago.
It’s not hard to imagine why. “It’s due to light, our gadgets, noise in the neighborhood, stress, people working two jobs,” says Erin Hanlon, assistant professor in the department of medicine at the University of Chicago. “The list of reasons goes on and on.”
But the consequences of not getting enough sleep are much greater than nodding off while sitting at your desk. New research is showing how too little sleep can affect our health, starting with our waistlines.
“Studies have consistently associated insufficient sleep with an increased risk of obesity,” notes Hanlon.
For example, researchers tracked more than 68,000 women in the Nurses’ Health Study from 1986 to 2002.1 “We found that women who reported less sleep—5 or 6 hours—gained more weight than those who reported getting 7 or 8 hours of sleep,” explained Sanjay Patel at a recent National Academy of Medicine webinar on “The Potential Role of Sleep in Obesity Prevention and Management.” Patel is the director of the Center for Sleep and Cardiovascular Outcomes Research at the University of Pittsburgh.
And women who slept no more than 5 hours a night were 28 percent more likely to gain at least 30 pounds over those 16 years than women who slept 7 hours a night. Women who slept 6 hours were 12 percent more likely to gain that much.
Why? “One explanation is that they’re eating more,” Michael Grandner, director of the Sleep and Health Research Program at the University of Arizona College of Medicine, told the webinar viewers.
In the largest study done so far, “about 200 people were sleep deprived in a laboratory for 5 nights, to simulate a sleep-restricted workweek,” said Grandner.2 They were allowed only 4 hours in bed each night, “and they had unlimited access to food in the lab kitchen.”
After the 5 days, “the sleep restricted subjects [had] gained about 2 pounds,” said Grandner, while the control group, which was allowed to sleep for up to 10 hours a night, gained virtually no weight.
And it wasn’t because they ate more than the control group at breakfast or lunch. They ate more only at night, when the control group was asleep.
“It’s been shown over and over again that when you keep people up for extended periods of time, they start eating between 300 to 550 [extra] calories per day,” noted Grandner. “What seems to be clear across studies is that people start craving energy-dense food.”
There’s a slight bump in calorie burning when you’re up at night, he added, “but the amount of calories you start craving is much greater than energy needs.”
What’s driving that increased appetite? Hanlon’s team is trying to find out.
She randomly assigned 14 people to spend either 4½ or 8½ hours in bed for four nights each.3 On the fifth day, the people weren’t allowed to eat until 3 p.m. No matter how long they had slept, “they ate about 2,000 calories—90 percent of their calorie needs—at that meal,” says Hanlon.
But that didn’t stop them from eating more when they were given snacks in their rooms right after that meal. “When they had normal sleep, they ate another 600 calories of snacks, but when they were experiencing short sleep, they ate another 1,000 calories,” says Hanlon.
Why? Their levels of ghrelin (which boosts appetite) were higher, while their leptin (which curbs appetite) was blunted after short sleep.
What’s more, endocannabinoid peaks were higher when people got less sleep. “The endocannabinoid system helps regulate appetite,” explains Hanlon. If the name sounds familiar, it’s because the cannabinoids in marijuana and the endocannabinoids our bodies make bind to the same receptors in the brain, fat cells, muscles, and elsewhere.
“We know that marijuana causes people to eat when they’re not hungry,” says Hanlon. “It engages the same feeding pathways that our endocannabinoids do.”
That could explain the 400 extra calories’ worth of snacks. “Despite saying that they felt full, the short-sleepers had a stronger desire to eat, and they ate more,” says Hanlon.
Other studies find an increase in impulsive behavior after short sleep. “So your reward system is saying ‘Eat that Snickers’ more than usual, and you’re less able to inhibit your response to it,” says Hanlon.
And it’s more likely to be Snickers than broccoli. In some studies, notes Hanlon, people who get less sleep “have an increased appetite for high-carb and high-fat foods.”
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