Obesogens: An Environmental Link to Obesity

Convincing evidence suggests that diet and activity level are not the only factors in the rising worldwide obesity trend — chemical “obesogens” may alter human metabolism and predispose some people to gain weight.

| February 21, 2012

atrazine label

Atrazine, an agricultural herbicide, is on the list of potential chemicals that can cause weight gain.


The herbicide atrazine is in the news for multiple reasons these days.  In addition to concerns that this widely used pesticide may cause cancer, evidence has recently surfaced showing that, for more than a decade, Syngenta has spent millions of dollars to pay scientists and journalists to deny and deflect the growing documentation of the human health dangers posed by atrazine. Plus, cancer is not the only concern with this chemical; a new report from the National Institute of Environmental Health Sciences names atrazine among a group of endocrine-disrupting chemicals that are “obesogens” — meaning they are suspected of contributing to the obesity epidemic now underway in this country. Here are links to these important stories: It's Time to Ban Atrazine, Syngenta Spends Millions to Deflect Evidence Against Atrazine Herbicide. — MOTHER

Obesity has risen steadily in the United States over the past 150 years,with a marked uptick in recent decades.  In the United States today more than 35 percent of adults  and nearly 17 percent of children aged 2 to19 years are obese.  Obesity plagues people not just in the United States but worldwide, including, increasingly, developing countries. Even animals — pets, laboratory animals, and urban rats — have experienced increases in average body weight over the past several decades, trends not necessarily explained by diet and exercise. In the words of Robert H. Lustig, a professor of clinical pediatrics at the University of California, San Francisco, “[E]ven those at the lower end of the BMI [body mass index] curve are gaining weight. Whatever is happening is happening to everyone, suggesting an environmental trigger.

Many in the medical and exercise physiology communities remain wedded to poor diet and lack of exercise as the sole causes of obesity. However, researchers are gathering convincing evidence of chemical “obesogens” — dietary, pharmaceutical, and industrial compounds that may alter metabolic processes and predispose some people to gain weight.

The idea that chemicals in the environment could be contributing to the obesity epidemic is often credited to an article by Paula Baillie-Hamilton, published in the Journal of Alternative and Complementary Medicine in 2002. Her article presented evidence from earlier toxicologic studies published as far back as the 1970s in which low-dose chemical exposures were associated with weight gain in experimental animals. At the time, however, the original researchers did not focus on the implications of the observed weight gains.

The role of environmental chemicals in obesity has garnered increased attention in academic and policy spheres, and was recently acknowledged by the Presidential Task Force on Childhood Obesity and the National Institutes of Health (NIH) Strategic Plan for Obesity Research. “Over the past ten years, and especially the past five years, there’s been a flurry of new data,” says Kristina Thayer, director of the Office of Health Assessment and Translation at the National Toxicology Program (NTP). “There are many studies in both humans and animals. The NTP found real biological plausibility.” In 2011 the NIH launched a 3-year effort to fund research exploring the role of environmental chemical exposures in obesity, type 2 diabetes mellitus, and metabolic syndrome.

What Are Obesity and Overweight?

For adults obesity is defined as having a BMI of 30 or more, whereas overweight is defined as having a BMI of 25 or more. Defining obesity is a bit more complicated for children; it depends on the age and sex of the child. Children are considered obese if they are at or above the 95th percentile of the sex-specific growth charts, and overweight if they are between the 85th and 95th percentiles.

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