Could global warming be making you fat? Year-round warmth is a luxury that might affect your body weight and your health.
During Michael Phelps’s 2008 Olympic gold-medal streak in swimming, Ray Cronise, a former materials scientist at NASA, heard the widely circulated claim that Phelps was eating 12,000 calories a day. Phelps’s intake was many thousands of calories more than what most elite athletes need. Running a marathon burns only about 2,500 calories. Phelps would have to have been aggressively swimming during every waking hour to keep from gaining weight. But then Cronise figured it out: Phelps must have been burning extra calories simply by being immersed in cool water.
Fascinated, Cronise began a regimen of cold showers and shirtless walks in winter. When he began measuring his metabolism during and after cold exposure, he found that his body was burning a tremendous amount of energy. He lost 26.7 pounds in six weeks.
His findings have helped drive a theory gaining momentum among scientists: that people can harness environmental thermodynamics in pursuit of weight loss. Because the human body uses energy to help maintain a normal temperature, exposure to cold expends calories.
Cronise’s preliminary experiments led him to put together what is now a pretty high-tech lab in his Huntsville, Alabama, home, where he conducts miniature scientific studies, mostly on himself. All of this has attracted publicity—and criticism. Detractors have raised concerns about regularly exposing one’s skin to cold (Cronise shared these worries). Some even accused him of diverting people away from solid principles of weight management and toward dubious shortcuts.
To the contrary, Cronise believes that his weight-loss story has been misunderstood and may distract people from the important issue of nutrition. “You can’t freeze yourself thin,” he told me. But his interest in altering metabolism through exposure to mild cold—which he defines as 55 to 65 degrees Fahrenheit—has only grown. Such temperatures are far enough below the socially accepted range that people plunked into a 50-something-degree office would complain to no end.
Unless, maybe, they believed it was good for them.
A Double Whammy: Overfed and Overheated
The notion that thermal environments influence human metabolism dates back to studies conducted in the late 18th century by the French chemist Antoine Lavoisier, but only in the past century has it really become relevant to daily life. Cronise believes that our thinking about obesity and metabolic diseases like diabetes doesn’t address the fact that most people are rarely cold today. Many of us live almost constantly in environments above 70 degrees Fahrenheit. When we are somewhere colder, most of us quickly put on a sweater or turn up the thermostat.
We don’t really experience seasonal variations in temperature the way our ancestors did. Even people in tropical regions used to get cold on rainy nights, Cronise pointed out, in a quick rejoinder to my observation that not all parts of the world have four seasons. Most other species display clearly ingrained biological responses to the seasons; why would humans be any different?
A recent article Cronise coauthored with scientists Andrew Bremer and David Sinclair proposes what the trio calls the Metabolic Winter hypothesis: Obesity is only in small part due to lack of exercise and mostly due to a combination of chronic overeating and chronic warmth. Seven million years of human evolution were dominated by two challenges: food scarcity and cold. “In the last 0.9 inches of our evolutionary mile,” they write, pointing to the fundamental lifestyle changes brought about by refrigeration and modern transportation, “we solved them both.” Other species don’t exhibit nearly as much obesity and disease as we warm, overfed humans and our pets do.
In June 2014, Francesco Celi, a National Institutes of Health researcher, published a study that found that when people cool their bedrooms from 75 degrees to 66 degrees, they gain brown fat, which burns calories to generate heat. (Brown fat is considered good; white fat, by contrast, stores calories.) Another 2014 study found that, even after controlling for diet, lifestyle, and other factors, people who live in warmer parts of Spain are more likely to be obese than people who live in cooler areas.
Harnessing the Power of Chill
Cronise is currently testing whether, with a low-calorie diet and a cool environment, he can maintain a healthy weight and low body-fat ratio without going to the gym. He doesn’t turn on the heat in his home until the coldest days of winter, which at times means letting the indoor temperature dip into the 50s. He trained himself to sleep without blankets.
Even on the hottest nights, I feel like I need the weight of a blanket, or at least a sheet, to sleep. Cronise was able to wean himself from blankets gradually, by learning to sleep with them first folded down partway, and then folded farther, and then, eventually, all the way down to his feet.
But Cronise is more reasonable than his anti-blanket rhetoric might suggest. Mild cold exposure might be as simple as forgoing a jacket when you’re waffling over whether you need one, not layering cardigans over flannels, or turning off the space heater under your desk.
And there are devices like the Cold Shoulder, an ice vest invented by Wayne Hayes, an associate professor at the University of California at Irvine who was inspired by Cronise’s research. Hayes claims that wearing it for an hour burns up to 250 calories, though his data are very rough. A little more than a year ago, he began selling the vest out of his Pasadena apartment. (Name notwithstanding, people won’t ignore you when you wear it.)
“The first time you put it on, it’s a bit shocking, to be honest,” Hayes warned me. But after wearing it a few times, he said, most people barely notice it. (That was my experience.) Hayes recommends wearing the vest twice a day until the ice melts—which can take an hour or longer—though he has himself worn it as many as three or four times in a single day.
“If you buy more than one,” he said, drifting into salesman mode and only half kidding, “you can cycle them throughout the day and wear them every waking hour.”