Less sleep may mean more weight
Getting too little sleep can have all kinds of negative consequences, including making you cranky and impairing your driving. A growing body of evidence suggests another possibility: making you fat.
That intriguing prospect has researchers busily conducting studies on the potential relationship between shut-eye and BMI.
Although it might seem intuitive that under-sleeping leads to overeating, science hasn't yet found a direct cause-and-effect relationship between lack of sleep and being overweight.
“There is a very, very strong link,” says Jim Hill, director of the Colorado Nutrition Obesity Research Center at the University of Colorado and a spokesman for the American Society for Nutrition. “People with sleep problems tend to have obesity. Why? That's where the research is.”
In a recent study, Marie-Pierre St-Onge of the New York Obesity Nutrition Research Center at St. Luke's-Roosevelt Hospital found that sleep-deprived people tend to burn the same number of calories — in her study, about 2,600 per day — as people who enjoy a full night's sleep. But her research, published in the August issue of the American Journal of Clinical Nutrition, found that sleep-deprived subjects consumed about 300 more calories per day (2,800 vs. 2,500) than the well-rested subjects. Because it takes just 3,500 calories to add a pound to your body, St-Onge says, “if people kept that up for a while, it would add up really, really quickly.”
Do sleep deficits actually cause people to become overweight? Does being overweight cause people to not get enough sleep? Do the two conditions share some underlying factor?
Michael Breus knows those questions need answers. But he's not waiting for all the dots to be connected. The prominent sleep disorders specialist has recently published “The Sleep Doctor's Diet Plan: Lose Weight Through Better Sleep” (Rodale/Mindworks, 2011). (Although the book touts Breus as the Sleep Doctor, he is a psychologist with a Ph.D., not a physician.)
Breus spells out, and supports by citing research, several means by which too little sleep could lead to weight gain. When you're sleep-deprived, your body moves into a different mode, he says. “On a physical level, the key things are hormones,” Breus says. When you lack sleep, “your metabolism slows down. Your body is trying to conserve energy stores” to carry you through the longer period of wakefulness. That slowdown triggers the release of cortisol, a hormone that your body secretes in response to stress and that boosts your appetite: Your body senses it needs more energy, so it demands more food.
Sleep deprivation also causes your body to release more ghrelin, the hormone that signals hunger, and less leptin, the hormone that tells your body it's full, Breus says. When those hormones are out of whack, your body wants more food and lacks the sensitivity to know when to stop eating. That hormone cocktail, combined with being awake for more hours a day, can send you snacking into the wee hours.
“The later you're up at night, the greater the likelihood that you're going to eat,” and “you're more likely to eat high-fat, high-carb foods,” Breus says. Such “comfort foods ... literally act like calming agents by increasing serotonin,” a hormone that promotes calm and contentment.
And that's just the hormones. Breus notes that a healthful night's sleep — about 7½ hours for most adults — allows you to enjoy five 90-minute sleep cycles, each including a deeply restful rapid-eye movement, or REM, phase. Those cycles include increasing amounts of REM as your sleep progresses, so losing one or two sets of REM at the end of your sleep time digs deep into your total REM time, Breus says. You burn more calories during REM than during other parts of the sleep cycle, and those unburned calories can add up to weight gain, he says.
Hill agrees that lack of sleep can “really screw up the whole neuroendocrine chain,” making you eat more by “disrupting the hormones that control hunger and satiety.”
But he urges caution. “I'm convinced (sleep deprivation and obesity) are linked, but I don't believe the science has proved it.
“We have to be very careful that we're not giving the wrong message,” Hill says. “I don't think it's going to be as simple as you fix the sleep, you fix the obesity.”