Air conditioning may contribute to weight gain.

Air conditioning helps you to gain weight through two mechanisms: you eat more and you burn fewer calories maintaining your body temperature.

You Don’t Eat in the Heat

A report published in the International Journal of Obesity says that you eat less when you are overheated.

“Restaurateurs report that when their air conditioning goes out, they lose business. People don’t want to eat a lot in the heat,” says David Allison, the leader of the study team and a professor of biostatistics at the University of Alabama at Birmingham.

This idea is backed up by research by John de Castro, a University of Georgia State psychologist. De Castro found people eat more as the weather cools. People’s daily intake is 200 calories per day greater in fall than in the rest of the year. With air conditioning, every day is a fall day.

Interestingly, residential air conditioning started becoming more common in 1980, and obesity rates have steadily risen since 1980. Just a coincidence?

You Don’t Burn as Many Calories

Air conditioning and heating help keep you in “the thermoneutral zone,” a temperature range where you do not have to regulate your body temperature.

When your body is above or below this zone, you need to burn calories to maintain your body temperature at the right level.

You might think this isn’t a lot of calories, but an adult 154 pound male burns an average of 75 calories per hour to maintain his normal body temperature. Over the years, reducing that amount by even a little can add up to a lot of extra calories and weight.