A human body, when taking in more calories than it expends, makes fat faster than you can say couch potato.
But a growing stack of laboratory research suggests that some of the chemicals used in everyday items predispose an individual to the battle of the bulge, despite normal diet and exercise.
Scientists describe these chemicals as "obesogens" because of way they effect how we develop and store fat.
Researchers are discovering that our bodies mistake certain man-made chemicals used in plastics, food wrappers and fragrances, for example, for naturally occurring hormones that regulate the production and storage of fat cells.
The scientific results from multiple laboratories are preliminary. Yet, the data say the same thing: Chemicals that affect our hormone system -- often called endocrine-disrupting chemicals -- are playing some role in the global epidemic of excessive weight.
"Despite what we've heard, diet and exercise alone are insufficient to explain the obesity epidemic," according to Dr. Bruce Blumberg, professor of developmental and cell biology and pharmaceutical sciences at the University of California in Irvine.
As Blumberg, co-author of a review article in the August 2009 issue of Molecular Endocrinology called "The Case for Obesogens." points out, the obesity epidemic roughly correlates with the rise in the use of industrial chemicals, including plastics and pesticides, following World War II.
The U.S. Centers for Disease Control and Prevention and other international laboratories are tracking levels of hundreds of chemicals in people, and dozens of these substances found are known to disrupt the hormone system.
Such measurements, called biomonitoring, demonstrate that toxic substances not only insult the environment but also toll human bodies. The health effects of our chemical body burden are just beginning to be understood, but there are reasons for concern.
Man-made substances that mimic a body's natural hormones can cause serious problems at tiny doses - especially when they cross the placenta to expose a fetus during a critical developmental period.
With certain obesogens, it appears that early post-natal exposures also are critical.
Among the chemicals linked to weight gain are several I write about in The Body Toxic: How the Hazardous Chemistry of Everyday Things Threatens Our Health and Well-being (North Point Press/Farrar, Straus and Giroux). They include:
Globally, the tallies of overweight adults and children are a staggering 1.6 billion and 155 million, respectively. Those considered obese number 400 million adults, and between 30 million and 45 million children.
It would be ridiculous to suggest that chemicals are the main culprits behind the world's expanding waistline. Eating too much and exercising too little go a long way on the path to pudginess.
But with legions of people at risk for type 2 diabetes, high blood pressure, cardiovascular disease and certain cancers because of excessive weight, we simply cannot afford to ignore any contributing factors.
Certainly, we can take individual steps to reduce our exposures to hormone-disrupting obesogens. To name a few:
But the long-term solution to our toxic problem requires a fundamental shift in the way we use industrial chemicals so that public health and environmental protections are the top priorities.
The European Union recently instituted sweeping changes that mean chemical companies will lose access to the EU's 500 million consumers and $11 trillion (US) market unless they can prove their substances do no harm.
In the United States, it's time to do the same by supporting measures such as the Kid-Safe Chemicals Act, which would require that all chemicals be proven safe for children before they can be sold.
It makes no sense to continue to let loose untested chemicals, chasing down the ones that create messes in places and people after the harm has been done.
Your children and grandchildren -- and their waistlines -- will thank you for it.
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