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Cronise’s latest ideas are laid out in a 2014 article he co-authored with Andrew Bremer, who was then at Vanderbilt University (he is now at the National Institutes of Health), and the Harvard geneticist David Sinclair, who is well known for his recent work on resveratrol (the “anti-aging” antioxidant found in red wine) and sirtuins—enzymes that help control metabolism. Sirtuins are active during times of stress, including when a person is hungry, and are thought to be related to the known life-prolonging effects of very-low-calorie diets.
Cronise, Bremer, and Sinclair propose what they call the “Metabolic Winter” hypothesis: that obesity is only in small part due to lack of exercise, and mostly due to a combination of chronic overnutrition 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 chronic disease as we warm, overfed humans and our pets do. “Maybe our problem,” they continue, “is that winter never comes.”
Their article joins a growing body of research on the metabolic effects of cold exposure, some of which I’ve reported on previously. Earlier last year, in the journal Cell Metabolism, researchers from the National Institutes of Health likened these effects to those of exercise, arguing that a better understanding of endocrine responses to cold could be useful in preventing obesity. The lead researcher in that study, Francesco Celi, published more research in June, finding that when people cool their bedrooms from 75 degrees to 66 degrees, they gain brown fat, the metabolically active fat that burns calories to generate heat. (Having brown fat is considered a good thing; 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 the cooler parts.
Meanwhile, Wouter van Marken Lichtenbelt, a professor at Maastricht University, in the Netherlands, has headed up a spate of recent research on the weight-loss effects of “non-shivering thermogenesis,” the technical name for the calorie-burning, heat-generating metabolic phenomenon that occurs in the mild cold that Cronise champions. “Mild cold exposure increases body energy expenditure without shivering and without compromising our precious comfort,” Lichtenbelt and colleagues wrote in an April paper.
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 does not turn on the heat in his Alabama home until the coldest days of winter, which at times means letting the indoor temperature dip into the 50s. And he has—most amazing, to me—trained himself to sleep without blankets. When he talks about the practice, he uses blanket as a verb, as in: People used to blanket because bedrooms had no heat. Now we heat bedrooms and we blanket.
Even on the hottest nights, I feel like I need the weight of a blanket, or at least a sheet, to sleep. But like eating sweets or turning up the heat, he sees sheeting and blanketing as acquired habits that can be changed. He was able to wean himself from blankets gradually, by learning to sleep with them first folded down partway, and then folded further, and then, eventually, all the way down to his feet. Cold really isn’t that miserable, he insists, once you’ve gone through withdrawal and adapted to it.
Cronise said that when people tell him they need a blanket to sleep, he asks them, “Do you walk around in a blanket all day?” (Given the choice, some of us would.) But Cronise is more affable and reasonable-sounding than his anti-blanket rhetoric might suggest. The mild cold exposure he advocates might be as simple as forgoing a jacket when you’re waffling over whether you need one, not layering cardigans over flannels despite the insistence of the fall catalogs, or turning off the space heater under your desk. And if you don’t want to annihilate the environment by running the air conditioner to get a taste of sweet, calorie-burning, metabolism-enhancing cold in the summer, there are devices like the ice vest, which really isn’t as terrible as it sounds.
“The first time you put it on, it’s a bit shocking, to be honest,” Wayne Hayes, the vest’s inventor, warned me. “You feel like, Holy @#$%&, this is cold.” But after wearing it a few times, he said, most people barely notice they have it on. That was my experience. (Hayes’s wife has become so used to the vest that she wears it under her clothes instead of over them.) 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.”
