UNCHANGING TEMPERATURES

The theory: Call it the Goldilocks Syndrome. If people rarely get too cold or too hot, but almost always stay “just right” in their temperature comfort zone – as Americans do, these days, year-round – they will gain weight.

The research: Environmental temperature can affect weight. A 2002 study of Dutch men found they burned more calories when in a room that was a chilly 61 degrees than when it was a cozier 72 degrees.

That same year, a study with Dutch women found they consumed fewer calories in a too-toasty 81-degree room than in a 72-degree room, because they chose lower-calorie foods to eat. That fits with other science. Studies of people (and pigs) have found they eat less in hot environments.

If the effects seen in short-term experiments hold over time, you’d expect that people who experience sizable temperature variations would be thinner than people who live in conditions that always suit them.

This could only be implicated in the widespread widening of Americans if they’re staying in their comfort zone more than they did 30 years ago – and it seems that they are. Although most homes were heated in the 1970s, better units and better insulation now help keep people in those homes warmer in winter. But greater progress has probably been made in beating the summer heat. Data from the Air-Conditioning, Heating and Refrigeration Institute show that nearly 90% of new homes are now built with central air conditioning, while only about one-third were in the 1970s. And Americans are even more likely to stay cool on the road. Almost every new car has AC now, whereas only about 60% used to back then.

Our experts weigh in: “I am very skeptical about this one,” says James Hill of the University of Colorado, and Susan Roberts of Tufts University calls it “small stuff.” But Dr. George Bray of Louisiana State University thinks there may be something to it. He notes that temperature affects energy intake and output – so the more the temperature varies, the more a person’s energy balance may bounce around.