how sleep affects your weight

Want to be slim and healthy? Get into bed. At night. To sleep, of course.

True, those of you who collect weird statistics may know that being, um, intimate burns about 120 calories every 30 minutes for men and 90 for women which, as scientists at the University of Quebec note, is about half what they’d spend during a 30 minute jog. But when it comes to waist size and weight, what matters most in bed is how long you stay there. Sleeping, that is.

According to the Centers for Disease Prevention and Control (CDC), more than one in every three American adults gets less than the recommended seven to nine hours of sleep a night. The National Center for Health Statistics says that the same number of us aren’t just a few pounds over our jeans size, but actually obese, defined as a BMI (body mass index) of 30 or more, for example, 169 pounds for a person 5’3” tall and 207 pounds for a person 5’9” tall.

In a moment of scientific agreement, researchers on both side of the Atlantic think they can draw a straight line connecting these two facts. At the Mayo Clinic, Andrew Calvin, MD, says that when people don’t get enough sleep, they eat more, wolfing down about 500 extra calories a day, enough to pack on an extra pound in just one week. And a study at the University of Leeds’ Institute of Cardiovascular and Metabolic Medicine and School of Food Science and Nutrition in England found that people sleeping only six hours a night were likely to have waistlines 1.18110236 inches (3 cm) larger than those sleeping for nine hours.

Not surprisingly, the sleep-deprived also had higher BMIs, a situation increasingly linked to a myriad of unpleasant health issues including, but not limited to, high blood pressure, more “bad” cholesterol, less effective glucose metabolism leading to an increased risk of diabetes, lower levels of thyroid hormones, and higher levels of C-reactive protein (CRP), a measure of inflammation considered a risk for heart disease.

What’s happening here? As Eve Van Cauter, director of the Sleep, Metabolism and Health Center at the University of Chicago, explains, we humans are the only mammals who don’t sleep on a regular basis. When we don’t get enough rest, ghrelin, a hormone that stimulates appetite, goes into overdrive, while leptin, a hormone that tells you you’ve had enough to eat, pulls back. At the same time, you produce more endocannabinoids, chemicals that trigger what Van Cauter calls “hedonic eating,” that is, “eating for pleasure.”

Sleep deprivation also affects your fat cells, the ones your body uses to store fat. You pretty much have the same number of fat cells as long as you live, but they can change shape, expanding to store more fat or contracting so you are slimmer. Sleep deprivation appears to makes fat cells less responsive to insulin. When that happens you make less leptin, which means you are likely to eat more and gain weight.

Conclusion? As it says at the top, get enough sleep. Your mirror will show you the difference.

Carol Ann Rinzler is the author of “Nutrition for Dummies” (6th edition). Her latest book is “Is It Safe to Kiss My Cat?”