It’s tempting to crank up the indoor heat during winter, but scientists say it could be making us fat. Keeping your house cool has benefits beyond reducing heating costs, because cold temperatures activate a substance called brown fat that adults carry on their upper back and neck. (Babies have it, too, since they can’t shiver effectively.) Also known as brown adipose tissue, brown fat acts as an internal furnace that consumes many calories, unlike regular fat, which stores extra energy and calories. The only catch is that brown fat must be activated first in order to start burning calories, and cool temperatures can do that.
A new study from Britain links rising indoor temperatures to obesity. Central heating has become common in American and British homes since 1960, and room temperatures and obesity have risen simultaneously. The average temperature of living rooms in Britain was 64.9 degrees Fahrenheit in 1978, creeping upward to 70.3 degrees by 2008. Bedrooms in the U.K. were kept at 59 degrees in 1978 and climbed to 65.3 by 1996. U.S. bedrooms were 66.7 degrees in 1987, up to 68 by 2005.
The paper’s lead author Fiona Johnson explains that people now heat their entire houses. Historically, only the main room with a woodstove or fireplace got really warm, while bedrooms stayed cool, but nowadays people don’t have to adjust as they move through the house. Add the extra hours of commuting in a heated car, with less time spent outside, and suddenly our bodies lose their brown fat because it’s never activated. Dr. Johnson explains: “It’s kind of ‘use it or lose it.’ If you’re not exposed to cold, you’re going to lose your brown fat, and your ability to burn energy is affected. But you can get it back.”
Former NASA scientist Ray Cronise has made similar discoveries: “We can use thermal temperature to supercharge weight loss… In environments as mild as 60 degrees, some of these people saw metabolism rates boost by as much as 20 percent.” Tim Ferriss, author of The 4-Hour Body, explains how "thermal dieting" -- taking cold showers, drinking ice water, going for frigid walks -- can burn calories. Admittedly, it sounds a bit extreme, so I was relieved to see Dr. David Katz, a Yale professor, express skepticism, suggesting that if people are desperate to lose weight, it's best to focus on diet and exercise.
I grew up in a very cool house, where a wood-burning cookstove heated the main floor during the day and the bedrooms upstairs were frigid in winter. The rule was that, if I felt cold, I had to put on another layer of clothing before complaining. Usually that second sweater or pair of socks did the trick; I’ve realized that most people don’t dress properly to handle a cool house, hence their thermostat addiction. I still like the idea of gradually turning down the heat, but mostly because it will save energy and money.