An imbalance of female sex hormones among men in Western nations may be playing a key role in obesity epidemic, according to a recent study.

Researchers from the University of Adelaide in Australia found that obesity among Western men could be linked with exposure to substances containing the female sex hormone estrogen - substances that are more often found in affluent societies, such as soy products and plastics.

"Exposure to estrogen is known to cause weight gain, primarily through thyroid inhibition and modulation of the hypothalamus. Soy products contain xenoestrogens, and we are concerned that in societies with a high dietary saturation of soy, such as the United States, this could be working to 'feminize' the males," Maciej Henneberg, co-author of the study, said in a statement. "This would allow men in those communities to artificially imitate the female pattern of weight gain."

He said that the source of xenoestrogen is polyvinyl chloride, known as PVC, a product in prominent use in most wealthy countries, "from plastic medical devices to piping for our water supplies."

For the study, researchers compared obesity rates among men and women from around the world with measures such as Gross Domestic Product to determine the impact of affluence on obesity.

James Grantham, co-author of the study and medical student, found that while it was normal for women in the developing world to have significantly greater levels of obesity than men, the developed world offers quite a different picture.

"Hormonally driven weight gain occurs more significantly in females than in males, and this is very clear when we look at the rates of obesity in the developing world," Grantham said in a statement. "However, in the Western world, such as in the United States, Europe and Australia, the rates of obesity between men and women are much closer. In some Western nations, male obesity is greater than female obesity."

He added that while poor diet is "no doubt" to blame, there is surely more to it than simply a high caloric intake.

Henneberg said micro-evolutionary changes may be occurring within Western societies that could also be leading to changes in testosterone and estrogen in men.

"This would certainly explain the various concerns about sperm count reductions among men in developed nations," he said.

The researchers said further research is needed to better understand whether or not environmental factors are leading to a "feminization" of men in the Western world.

The findings were recently published in the online journal PLOS ONE.