Johnson notes that gains from turning down the heat would be tempered by people's natural responses to feeling chilly: seeking more clothes and more food. But evidence suggests layering up and eating more don't completely negate the extra energy expenditures from cold exposure, she said.
All of this points to a connection between shrinking cold exposure and expanding waistlines. However, Johnson notes that direct evidence still is lacking, as is information on how cold one would have to be or for how long to have what effects.
"It is perhaps too early to tell people to turn down the thermostat or make sure they get cold," she said.
It is certainly a case for doing studies to expose people to cold and seeing what effect this has on brown fat levels, energy expenditure, capacity to create heat, and body weight.
Small effects could add up, said Arne Astrup of the University of Copenhagen.
"Even 100 calories a day can mean a lot over a year or in the long term," Astrup said, citing a 2003 Science paper that suggested that reducing net calorie intake by 100 per day could prevent weight gain for most of the population.