Here's a new way to burn fat: Turn up the air conditioning, strip down to your skivvies, and embrace the deep chill. According to two new studies, by acclimating your system to colder temperatures, you can train your body to burn more fat overall.
Humans have several different types of fat, including white fat – the stuff that we pile on by eating too much junk and not exercising. There's also brown fat, discovered just a few years ago, the main purpose of which is to keep us warm. According to Stephan Guyenet, an obesity researcher at the University of Washington, who was not involved in either study, brown fat works like an internal fireplace, pulling glucose from the blood and from white fat stores in order to keep up the body's core temperature. Put simply, brown fat burns white fat. The other, more common way we stay warm is by shivering. Basically, when the brain senses cold, the muscles start contracting to generate heat. Both body-warming methods work just fine, but the brown fat way also leads to weight loss.
In the first study, the researchers wanted to see whether brown fat could be trained to start generating heat before the body began shivering, if people became used to cooler temperatures. They put participants in a 60-degree room for one hour the first day, two hours the second day, and four hours on days three through 10. After just 10 days, the participants' brown fat activity had increased significantly, proving that, yes, it can be trained.
"If you spend one or two days in a 60-degree room, you're probably going to feel cold and start shivering," Guyenet says. "But if you stay in that room for longer, say for two weeks, your body won't need to shiver anymore because it's been gradually acclimated to activating the brown fat. Still, your core temperature in that room stays the same, so it becomes about which of the two mechanisms the body uses to stay warm. If it relies on brown fat, it can contribute to overall fat loss."
The second study exposed participants to 63 degrees two hours a day for six weeks. At the study's end, their average body fat mass decreased about 5 percent. "These results are especially telling about brown fat's impact because these people were lean to begin with," says Guyenet. "It's pretty tough for lean people to lose that much weight."
Even though brown-fat training has promise, more studies need to be done before calling it a surefire weight-loss strategy, says Guyenet. Still, he has heard of people who've tackled cold training on their own and lost weight.
So, if you're curious — and you're not planning to ditch your workouts for couch time in your boxers — there's no harm in tinkering with the thermostat or finding a meat locker to see what happens to your body.