Sleep loss, air conditioning may be making us fat

"Super-sized" fast food meals and TV time shouldn't take all the blame for the U.S. obesity problem, according to a research review published Tuesday.

In fact, a group of researchers contend, a number of aspects of modern living - from lack of sleep to exposure to environmental chemicals to living with air conditioning - may be feeding Americans' weight woes.

Writing in the International Journal of Obesity, they argue that obesity research and prevention efforts need to look beyond the "Big Two" - food industry practices, like beefed-up portion sizes and added sugar; and reduced physical activity from factors such as cuts in school gym classes.

That's not to say that diet and exercise aren't important, said report co-author Dr. David B. Allison of the University of Alabama at Birmingham

However, he told Reuters Health, the evidence linking obesity to food industry marketing and lack of gym class is circumstantial.

It's equally plausible that a range of other factors are also involved, Allison and his colleagues point out.

Lack of sleep is one, they say. Research in animals and humans suggests that chronic sleep deprivation boosts appetite and eating, and studies also show that U.S. adults and children are sleeping less than they used to. In recent decades, adults have gone from sleeping for an average of 9 hours to about 7 hours, the researchers point out.

There is also evidence that industrial chemicals that act as endocrine disruptors may increase body fat. These chemicals, which are used in products such as pesticides and plastics, alter hormonal activity when they get into the body. Studies suggest that people have been increasingly exposed to these chemicals through the food chain in recent decades.

Another factor potentially weighing Americans down is air conditioning. The body burns calories when forced to regulate its own temperature and, Allison noted, people tend to eat less in hot, humid weather.

He and his colleagues cite 10 potential obesity risk factors in all, including: increased rates of older mothers, whose children may be more prone to excess weight gain; a range of medications, such as antidepressants, which can promote weight gain; and a decrease in smoking rates, because people often gain weight when they quit and the absence of nicotine, an appetite suppressant.

No one is suggesting that people should stop taking their prescriptions, keep smoking or swelter in the July sun, according to Allison. When it comes to any one person's weight, he said, "what ultimately matters is calorie intake and calorie expenditure."

That means diet and exercise is still key.

But, Allison argued, researchers and policymakers should be "open-minded" about the potential contributors to the obesity problem and not assume that the answer lies in simple fixes like ridding schools of vending machines or installing sidewalks in the suburbs to encourage walking.