Obesogens: An Environmental Link to Obesity

Obesity has risen steadily in the United States over the past 150 years,1 with a marked uptick in recent decades.2 In the United States today more than 35% of adults3 and nearly 17% of children aged 2–19 years are obese.4 Obesity plagues people not just in the United States but worldwide, including, increasingly, developing countries.5 Even animals—pets, laboratory animals, and urban rats—have experienced increases in average body weight over the past several decades,6 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.”7 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.8,9 Obesity is rising steadily around the world. Convincing evidence suggests that diet and activity level are not the only factors in this trend—chemical “obesogens” may alter human metabolism and predispose some people to gain weight. Fetal and early-life exposures to certain obesogens may alter some individuals’ metabolism and fat-cell makeup for life. Other obesogenic effects are linked to adulthood exposures. Joseph Tart/EHP; woman: gokhanilgaz/iStockphoto; fat cells: David M. Phillips/Photo Researchers, Inc.; fetal development cycle: Dragana Gerasimoski/Shutterstock.com; french fries: Richard Peterson/Shutterstock.com 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 2002.10 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 Obesity11 and the National Institutes of Health (NIH) Strategic Plan for Obesity Research.12 “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.13 What Are Obesity and Overweight? The concept of obesogens has spread into the public awareness, too, with documentaries such as “Programmed to be Fat?” which aired on the Canadian Broadcasting Corporation (CBC) Network in January 2012 and a session on obesogens at the Society of Environmental Journalists annual conference in October 2011.14