Among the many, many, many reasons I love summer is the fact that, in my mind, it's my best-looking season. My hair bleaches out a little, I get a tan on (despite the SPF, I'm not a madwoman), and for whatever reason, I always seem to drop a few pounds without consciously doing a thing. Vanity! Not even ashamed.
I generally assumed the last perk was a result of the heat. You know, I'm sweating, my body temp is up, I must be burning a few extra calories during my usual exercise sessions. Thank you, summer!
But recently I read a few studies that have found that cold temperatures activate the body's stores of brown fat, the "good" type of fat that actually burns up calories. (It's one reason to take a real winter vacation.) It got me thinking: Is my unintentional summer slim down just because I'm actually craving salads? Am I really burning more calories in the winter, just negating them with the extra mashed potatoes and hot chocolate I'm consuming (not together)?
To put my mind at ease, I turned to Jessica Matthews, an assistant professor of exercise science at Miramar College in San Diego and a senior advisor for health and fitness education for the American Council on Exercise. "Overall, given that exercise itself raises the body's temperature, the reality is that in hotter temperatures the body needs to expend additional energy beyond the demands of working muscles in order to thermoregulate, or keep the body's temperatures from rising too greatly," she says. (10 Must-Know Tips for Exercising in Hot Weather.)
Translation: Basically what she's saying is that yes, in the summer you probably burn a few extra calories while working out or while at rest, because your body needs to work that much harder to cool itself back down compared to when it's chillier out.
Here's the twist, though. If you're so cold you start to shiver, you may burn a few extra calories than you would in warmer temperatures. "Shivering requires the body to work harder in order to thermoregulate, though the exact effect on calorie expenditure depends on a number of factors—time of exposure, temperature, wind chill, etc.," says Matthews.
As for how cold temperatures affect your brown fat, right now it's hard to say, Matthews says. Most of the research about the relationship with temperature, brown fat, and calorie burn has been done in mice, and it may still be too early to tell how it affects humans.
Bottom line, says Matthews: In general, how many calories you burn depends on a lot, not just temperature. In fact, the difference caused just by the thermostat is probably pretty small, compared to the impact things like exercise and eating well makes. If you're interested in boosting your calorie burn, you're better off using these tips instead.