Air conditioning & no sleep makes you fat?

Obesity is just as likely to be caused by lack of sleep and too much air-conditioning as it is by a sedentary lifestyle and aggressive marketing by the food industry, according to a research article that challenges the conventional wisdom.

David Allison, an obesity researcher at the University of Alabama at Birmingham, US, and colleagues have published a paper questioning the importance of what they call the "Big Two" obesity factors: overeating as a result of junk food marketing and lack of exercise.

The researchers drew up a list of 10 factors that might have as much or more to do with increasing waistlines as the Big Two. For instance, they point out that studies show that people who do not get enough sleep have increased appetites. Notably the amount of sleep an average US adult gets has decreased from nine hours to seven hours in the last several decades.

Heating and air conditioning might also be to blame. When people and animals go above or below a "thermoneutral" ambient temperature, they lose weight - if it is too cold they burn fat to stay warm, and if too hot their appetites decrease. But studies show that people are keeping their houses warmer in the winter and cooler in the summer than they did a few decades ago, so these natural influences on weight are negated.

Other possibilities include the decrease in the number of people who smoke - which suppresses appetite - environmental endocrine disruptors, an ageing population, and an increase in babies born to older women - which are more likely to be obese. Another possibility is that overweight people are more likely to marry one another and give birth to children genetically predisposed to be overweight themselves. Article here.