Contrary to what many people think, sleep is not an inactive state. During sleep our bodies are doing lots of important work—repairing cells and tissues, restoring full, healthy function to our immune system, consolidating memories and rebooting the neural cells and networks of the brain. We’re burning calories the whole time. For a 150-pound person, the estimated calorie burn over a 7-hour night of rest is just over 440 calories. That’s a 40-minute jog on a treadmill!
Getting plenty of high-quality rest is an important—and still overlooked– factor in weight control. Here are some of the ways you can harness your sleep routine and your overnight rest to help your body burn more calories and stay metabolically healthier.
Activate your body’s ‘thinning’ fats
It might surprise you to learn there isn’t just one type of fat—and certain kinds of fat actually work to burn energy, rather than storing it. Brown fat and beige fat both appear to have significant metabolic benefits. In contrast to white fat, these so-called “thinning fats” burn calories, help keep insulin working properly, help regulate blood sugar, and guard against obesity. Studies in mice show that animals with higher amounts of brown fat are leaner, and have better metabolic health. Research involving humans has shown brown fat is linked to lower body mass. On the other hand, a lack of brown fat in mice is associated with higher insulin resistance, higher blood sugar, and diabetes. Scientists recently discovered beige fat activates a protein that works to burn calories and generate heat in the body, and may have significant benefits in combating obesity and metabolic disorders.
What do these metabolically beneficial fats have to do with sleep? Sleep can contribute to the increase of these “good” fats in at least a couple of ways. Research has shown that the sleep hormone melatonin contributes to the increase of both brown fat and beige fat. Regularly getting enough high-quality sleep, sticking to a consistent sleep-wake cycle, and protecting daily circadian biorhythms from disruption are all ways to encourage your body’s natural melatonin production, which may help your body make more of these weight-loss promoting fats.
Both brown and beige fat are sensitive to temperature and can be stimulated by exposure to cool nighttime temperatures. Research shows sleeping overnight in cool environments increases brown and beige fat, by triggering the body to convert white fat to these energy-burning fats. (More on the importance of a cool bedroom for weight loss in a minute.)
Limit blue light exposure
Blue light aggressively suppresses melatonin, throws daily biorhythms out of sync, and inhibits sleep. Research shows this blue light delays melatonin production for more than twice as long as other light wavelengths, and alters circadian rhythms by twice the degree.
Where do we get exposure to blue light? Pretty much everywhere, these days. Sunlight contains blue light. But this short wavelength light is found in especially high concentrations in digital screens and energy efficient lighting, including LED and fluorescent lights. In today’s world, we're exposed to more blue light than ever before, including at the worst times for sleep and melatonin production—during the evening hours before bed. A 2017 study found blue light exposure between the hours of 9-11 p.m.—prime time for Netflix, and that evening scroll through social media on your phone or computer—significantly reduced melatonin production, shortened sleep time, and led to more restless sleep.
Too much bright light exposure, particularly in the evenings, compromises our sleep and health—including greater potential for weight gain. Blue light’s suppression of melatonin may inhibit the weight-regulating benefits of this hormone and of sleep itself.
Set an earlier bedtime
Later bedtimes have been linked to several factors that promote weight gain, including more late-night snacking and a stronger preference for high-calorie foods. Research has demonstrated a relationship between going to bed later and gaining weight. What’s behind this connection? There are likely to be several factors at play. Among them, staying up later simply leaves us with more waking time to eat, and to be tempted by the most calorie-dense foods (think sugary sweets and salty fried snacks). Self-control—what we often think of as “willpower”—is a deeply complicated cognitive process, one that scientists are still working to understand.
Are we less able to resist ice cream and cookies and potato chips at night, after a long day of decision-making, discipline, and focus? Probably so—and studies show that for people who are sleep deprived, cravings for junk food become even harder to resist. But there’s little question that removing the temptation is easier than resisting it—and that’s what an earlier bedtime can do. More time in the evenings sleeping means less time available for snacking, at the time when many of us are most tempted.
With so many of us chronically sleep deprived, an earlier bedtime also helps ensure that we get enough sleep on a nightly basis. A single night of insufficient sleep can send hunger hormones from spiking, sending our appetites on the rise. Being short on sleep also makes us more prone to stress and for many of us, to emotional eating.
Going to bed earlier isn’t easy for everyone. In addition to busy schedules and lots of responsibilities that get pushed to the nighttime hours, some chronotypes are more driven to stay up late than others. Early-rising Lions and sleep-craving Bears are more likely to welcome an earlier bedtime than restless Dolphins and late-to-bed, late-to-rise Wolves. If you’re one of these evening types, don’t give up: even a small, gradual shift to an earlier bedtime can bring you more sleep, and help keep your waistline in check.
Get light exposure early in the day
Evening light exposure interferes with melatonin production—and that can make it easier for our bodies put on weight. But light exposure isn’t all bad for sleep and weight. Far from it. Early in the day exposure to light helps to strengthen our daily, 24-hour circadian rhythms, in part by reinforcing the natural decline of melatonin that happens to us every morning. When melatonin levels drop, you become more alert and ready to be active. That sends you into your day more energized—and apt to burn more calories throughout the day.
Morning light also sends powerful cues to your brain that help keep your daily biorhythms in sync. These circadian biorhythms exert a great deal of control over sleep-wake patterns. Your next night’s sleep may be the last thing on your mind when you’re just getting your day underway. But by shoring up circadian rhythms, this early-day light exposure can have a direct effect on how well you sleep at night—and sleeping well makes it easier to lose weight and maintain a healthy weight. What’s more, our biorhythms do a lot more than control our sleep—they influence nearly every part of our daily physiology, from metabolism and digestion to hormone production—including hormones that regulate hunger and fullness.
Sleep in a cool bedroom
Keeping your bedroom cool is one of the most comfortable, relaxing, sleep-promoting choices you can make for your nightly sleep environment. A cool bedroom can help you sleep better, able to fall asleep faster and wake less often throughout the night. A cool nighttime environment also encourages your body to burn more calories. And, as studies show, a colder bedroom stimulates the production of beige and brown fats, which burn energy (aka calories), and help to protect metabolic health.
What’s behind the connection between a cool bedroom, sound sleep, and weight loss? Staying cool at night stimulates your metabolism. Essentially, you need to burn more calories to keep warm.
As I’ve talked about before, a cool environment is naturally more conducive for sleep. By cool, I’m talking about a bedroom temperature of between 62-68 degrees Fahrenheit, with the optimal temperature being right in the middle, at about 65 degrees. In the evenings as we move closer to sleep, our bodies undergo a natural, gradual drop in temperature. (Like so much else going on in the body, daily thermoregulation, or rise and fall in body temperature, is regulated by circadian rhythms.) Sleeping in a cool room can enhance that natural body temperature decline that is part of our transition to sleep. The fall in body temperature that happens in this transition to sleep occurs alongside the rise in melatonin that’s both essential for sleep and helps to weight control.
Maintaining a cool sleep environment also has a direct effect on sleep quality and sleep quantity. Warmer nighttime temperatures are linked to more restless sleep with more frequent awakenings throughout the night, and less time spent in slow wave sleep and REM sleep, two deeply restorative sleep stages. Sleeping in a cool bedroom will help you fall asleep more easily and sleep more soundly. Sleeping better gives powerful, fundamental assistance to weight loss.
Cool temperatures also increase the body’s stores of beige and brown fats, the “thinning” fats that burn calories, rather than storing them. A 2014 study found that brown fat increased significantly when people were exposed to cool overnight temperatures. After a month of sleeping in a 66-degree Fahrenheit nighttime environment, researchers measured an average 42 percent increase in the participants brown fat, along with an average 10 percent increase in their fat metabolism. The healthy, young adults in the study also showed better insulin sensitivity and beneficial changes to appetite hormones after the month of cool overnights. When scientists had the study participants return to a warmer nighttime sleep environment, these weight-promoting benefits diminished or reversed altogether.
Don’t just stop with turning down your thermostat! Sleeping in the nude is another comfortable way to regulate your nighttime sleep temperature and sleep more comfortably and soundly while burning more calories and increasing your calorie-burning fats.
To help cool down and achieve the ideal sleep temperature at night, I recommend to my patients the Chilipad, a mattress topper that helps to regulate body temperature throughout the night, for optimal temperatures all night long. This sleep system lets bed partners regulate their temperatures independently of one another. For each sleeper, the pad will lower temperatures early in the night, to encourage sleep and melatonin rise, and bring temperatures slightly up near to morning, when a warmer temperature helps to stimulate alertness.
Eat a sleep-friendly snack
Having an after dinner, pre-bed snack is a ritual in millions of homes. For sleep and for weight control, it’s important to keep snacking reasonably light in the evening hours. Research has clearly shown that the when of eating is really important and that people who eat a greater share of their daily calories at night are very likely to throw their circadian rhythms out of sync and gain weight.
But let’s face it—most people will go looking for a nighttime snack at least occasionally, if not regularly. The goal is to snack smart. For sleep and weight control, that involves a balance of protein and complex carbohydrates. Studies indicate that a protein-rich bedtime snack does not contribute to weight gain, and may have benefits for metabolism and muscle recovery.
With attention to these sleep habits and a commitment to making sleep a priority every day, you really can leverage your sleep to help you lose weight and stay at a healthy weight as you age.
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