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Female hormones may be making western men fat and infertile, according to a new study.

Researchers from the University of Adelaide believe that exposure to estrogen may be fueling the male obesity epidemic. Experts explain that exposure to common substances found in affluent societies like soy products and plastics, which contain the female sex hormone, are making Western men fat.

The study compared Gross Domestic Product and obesity rates among men and women worldwide. While it was normal for women in developing countries to have significantly higher rates of obesity, the findings revealed little difference between sex and obesity in the western world.

"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," researcher James Grantham said in a news release.

"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.

"While poor diet is no doubt to blame, we believe there is more to it than simply a high caloric intake," Grantham said.

"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. This would allow men in those communities to artificially imitate the female pattern of weight gain," co-author Professor Maciej Henneberg, a Wood Jones Professor of Anthropological and Comparative Anatomy, said in a statement.

"Another well-established source of xenoestrogen is polyvinyl chloride, known as PVC. This product is in prominent use in most wealthy countries, from plastic medical devices to piping for our water supplies," he said.

Researchers said the latest findings could also explain why western men have significantly lower sperm counts than those living in developed nations.

The findings were published in the online journal PLOS ONE.