The modern lifestyle of super-sized french fries and couch potatoes often takes the blame for the rising rates of obesity and diabetes in the U.S. -- perhaps rightly so. But growing evidence suggests another factor in the dual epidemics: modern chemicals.
Exposure to even minuscule amounts of synthesized substances -- used in everything from pesticides to water bottles -- can scramble hormone signals, scientists say. This interference can trick fat cells into taking in more fat or mislead the pancreas into secreting excess insulin, a hormone that regulates the breakdown of fat and carbohydrates.
Among the most ubiquitous and scrutinized of these so-called endocrine disruptors is bisphenol A, better known as BPA. The chemical is a common ingredient in plastics and food-can linings.
"When you eat something with BPA, it's like telling your organs that you are eating more than you are really eating," says Angel Nadal, a BPA expert at the Miguel Hernandez University in Spain.
Nadal's latest research, published last week in PLoS ONE, finds that the chemical triggers the release of almost double the insulin actually needed to break down food. High insulin levels can desensitize the body to the hormone over time, which in some people may then lead to weight gain and Type 2 diabetes.
To achieve this feat, BPA fools a receptor into thinking it is the natural hormone estrogen, an insulin regulator. Nadal's team found that even the tiniest amounts of BPA -- a quarter of a billionth of a gram -- did the trick. The effect disappeared when the researchers stripped the specific receptors from the study mice, evidence that they had in fact pinpointed BPA's chemical mechanism, which had previously eluded scientists.
In laboratory tests of human cells, the response was even more pronounced.
"That pretty much nails it," Bruce Blumberg of the University of California, Irvine, who was not involved in the new study, told The Huffington Post. He notes that despite the prior associations made between BPA and metabolic problems, including obesity and diabetes, doubt had lingered because of a lack of understanding about how the phenomenon occurred. Long-term studies of children -- tracking BPA exposures and health outcomes -- remain ongoing around the world.
An estimated 90 percent of people in developed countries have BPA circulating in their blood at levels often higher than the threshold for causing hormone disruption used in Nadal's study. This high incidence is due not only to exposures from leaching food packages but also BPA-infused cash register receipts, dental sealants and toilet paper.
"People are seeing effects of BPA down to 1000-fold below [Nadal's threshold]," adds Frederick vom Saal, another expert in endocrine disruptors at the University of Missouri-Columbia. "It takes so little of this chemical to cause harm."
The chemical industry disagrees. "BPA is one of the most thoroughly tested chemicals used today and has a safety track record of 50 years," says Kathryn Murray St. John, a spokesperson for the American Chemistry Council, a lobbying group for the plastics industry. She highlights recent regulatory rulings in favor of the safety of BPA.
Vom Saal, who also wasn't involved in the Spanish study, explains why the "standard estimates of safety" may be invalid. Minute amounts of the chemical may be even more potent than larger quantities, he says, which can flood the receptors and essentially turn them off, stopping the flow of insulin. In other words, the dose does not make the poison -- at least not in the ordinary sense. Yet the traditional dose-response assumption remains the basis for most regulatory tests that have deemed the chemical safe.
The consequences of the continued widespread use of BPA could be most dire for pregnant women and developing fetuses, who appear to be particularly sensitive.
"The fetus is not only exposed to BPA but also to higher levels of insulin from the mother, making the environment for the fetus even more disruptive," says Nadal. "This is a very delicate period."
Previous studies have suggested that the environmental chemicals in the womb can preprogram weight gain later in life. BPA, for example, may tell a growing fetus to develop more fat cells.
Nadal adds that BPA is just one of a larger cocktail of at least 20 endocrine disruptors commonly used in everyday items, including phthalates, nicotine, dioxin, arsenic and tributyltin. Further, obesity and diabetes aren't the only risks posed by the chemicals. Studies also hint at links with cancer, infertility, heart disease and cognitive problems.
Overall, half of the developed world is now overweight and one in six is obese -- about double the numbers of 30 years ago. Approximately 250 million people suffer from diabetes worldwide.
Sure, our lifestyle has changed over the decades in parallel with the increased use of BPA. Yet scientists have noticed the same fattening trend in newborns, lab rodents, pets and wildlife that live in close proximity to humans. Have babies or mice really changed how much they eat or exercise? Experts highlight this as further evidence that more than just caloric intake is driving the current epidemics of obesity and Type 2 diabetes.
"The scary thing is, this is occurring in children. Thirty years ago, we called Type 2 diabetes 'adult-onset,'" vom Saal says. That's not the case anymore.