Is the fact that Americans can be warm year-round one reason they are so obese?

That's the theory of Ray Cronise, former NASA materials scientist.

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.

If you want to try this out for yourself, the article mentions a device called the Cold Shoulder, a vest that holds ice packs, which you can wear around the house to try to burn more calories. You can buy the Cold Shoulder weight loss vest on Amazon for $149.

This still all sounds speculative, but I do sleep much better in really cold rooms. When I'm in a hotel and need a good night's sleep, I always crank up the A/C and bury myself under the covers.

I came home from vacation in Del Mar to a 63 degree apartment in San Francisco today, and I'm not going to turn on the heat. Damn it is cold.