June 27 (Bloomberg) -- The growing problem of obesity in the past three decades could be attributed to an increase in anti- depressants, air conditioning and the declining number of smokers, according to a study.

These factors are among 10 listed by researchers who want the public and other academics to examine reasons for the rapid surge in obesity since 1970. They said too much attention has been paid to the ``Big Two'' -- food-marketing practices and a decline in physical activity.

``What we refer to as the `Big Two' are not the overall major causes of obesity, and certainly are not the sole causes,'' said one of the study's authors, David Allison, from the University of Alabama at Birmingham. ``There are multiple other causes likely to be important.''

The report, published today in the International Journal of Obesity, cited a study that found no association between obesity and proximity to fast-food restaurants in more than 7,000 children. The report also said Pathways, a large childhood obesity prevention program that emphasizes physical education classes, had no effect on body mass index rates, a method for measuring size.

Allison said another factor that merits attention includes the increase of psychotropic medications such as anti-psychotics, anti-depressants and mood stabilizers, as well as contraceptives and antihistamines, all of which can cause weight gain.

Air Conditioning

An increase in air conditioning also could be an important aspect to the increase in obesity. Mammals burn energy keeping their bodies within a certain temperature range, so the more we live and work in temperature-regulated environments, the less likely we are to expend energy. People also eat less when they are too warm.

``Yesterday in Alabama, it was 100 degrees,'' Allison said last week in an interview. ``If you were here in 1960, with no air conditioning in a car or restaurant, you probably wouldn't want to go to the all-you-can-eat buffet.''

Other causes listed in the report include adults getting less sleep, mothers giving birth later in life and an increase of endocrine disruptors, or industrially produced materials such as PCBs, DDT, and other pesticides, in the environment.

Further research shows smokers weigh less than non-smokers, and that people who quit smoking gain weight. Not that the Allison thinks people should take up smoking, quit their medications, or spend their summers sweating.

``I haven't made any personal changes,'' he said. ``This isn't the kind of paper where I would say the public should run out and take personal action.''

Allison's goal is to generate additional research in these areas and prompt people to question decisions to spend tax money on public policy programs to reduce obesity without solid evidence.

To contact the reporter on this story: Ryan Flinn in San Francisco at rflinn@bloomberg.net.

Last Updated: June 27, 2006 00:04 EDT