The desire to burn fat is one of the most commonly cited health and fitness goals. There are many ways to accomplish that objective through diet and exercise. Eat the right food and stay active, and you can burn calories and fat while building lean muscle. That’s great for roughly 2/3 of the day when you’re awake, but what about that other 1/3 when you’re asleep?
The human body is constantly burning calories for fuel, even when asleep. According to Dr. Michael Breus, aka The Sleep Doctor, a 150-pound person can burn about 440 calories over a 7-hour night of rest. This can translate into fat loss over time, but science shows sleeping at cooler temperatures not only produces better, more restful sleep — but it also boosts metabolism and alters our fat stores.
THE SLEEP-FAT CONNECTION
A 2014 study published in the Diabetes journal tested different sleeping temperatures on adult males over a four-month period. Each slept for one month at temperatures of 75ºF (23.8ºC), 66ºF (18.8ºC), 75ºF (23.8ºC) again and 81ºF (27.3ºC). After a month of sleeping at 66ºF, the participants displayed a 42% increase in brown fat volume (a good thing) and a 10% increase in fat metabolic activity. These changes returned to baseline amounts after a month at 75ºF and actually reversed at 81ºF.
Brown fat burns calories in a process known as thermogenesis, which creates heat and helps maintain body temperature. White fat, on the other hand, stores energy. It’s a characteristic of obesity that increases risk of Type 2 diabetes and other diseases.
Additional research from the University of Kentucky School of Medicine found that, in response to cold, white fat cells can take on the characteristics of brown fat cells. This can occur whether you’re working out in frigid temperatures, recovering in a cryochamber, or sleeping with the AC on full blast. The authors noted this shift from white to brown fat is a defense against obesity, as it results in the body burning extra calories rather than converting them into fat tissue.
Another nod for sleeping cooler comes from a recent study published in the Endocrine Society’s Journal of Clinical Endocrinology & Metabolism. It found short-term cold exposure may activate brown fat to help people burn 15% more calories. In addition to greater calorie expenditure, study participants exposed to colder temperatures also displayed healthier blood profiles.
SLEEP AFFECTS FOOD CHOICES
According to the National Sleep Foundation, optimal sleep temperature can vary by person, but a good range to shoot for is 60–67ºF, with most research suggesting around 65ºF. We now know sleeping in a colder room increases brown fat and burns more calories during those 7–8 hours of shuteye. But a good night’s sleep is about more than chemical reactions in the body. It’s also about feeling alert and making good choices when you’re awake.
A 2018 Cleveland Clinic study found getting adequate sleep helps to fight off junk food cravings. The impact is twofold. People who are feeling lethargic due to lack of sleep tend to want food for energy, and then they choose high-calorie foods loaded with sugar and fat. These foods may provide an initial rush of energy, but that doesn’t last, and the extra calories lead to weight gain.
THE BOTTOM LINE
The importance of sleep can’t be overstated. Adequate sleep can fend off disease and weight gain and improve everything from your work and relationships to what you eat. Try sleeping in a cooler room, and see how it impacts your waking hours.
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