Chemicals May Play Role in Rise in Obesity

By Elizabeth Grossman
Special to The Washington Post
Monday, March 12, 2007

Too many calories and too little exercise are undeniably the major factors contributing to the obesity epidemic, but several recent animal studies suggest that environmental exposure to widely used chemicals may also help make people fat.

The evidence is preliminary, but a number of researchers are pursuing indications that the chemicals, which have been shown to cause abnormal changes in animals' sexual development, can also trigger fat-cell activity -- a process scientists call adipogenesis.

The chemicals under scrutiny are used in products from marine paints and pesticides to food and beverage containers. A study by the Centers for Disease Control and Prevention found one chemical, bisphenol A, in 95 percent of the people tested, at levels at or above those that affected development in animals.

These findings were presented at last month's annual meeting of the American Association for the Advancement of Science. A spokesman for the chemical industry later dismissed the concerns, but Jerry Heindel, a top official of the National Institute of Environmental Health Sciences (NIEHS), who chaired the AAAS session, said the suspected link between obesity and exposure to "endocrine disrupters," as the chemicals are called because of their hormone-like effects, is "plausible and possible."

Bruce Blumberg, a developmental and cell biologist at the University of California at Irvine, one of those presenting research at the meeting, called them "obesogens" -- chemicals that promote obesity.

Blumberg began to suspect a link while trying to pinpoint how one endocrine disrupter, tributyltin, affects genetic mechanisms in the reproductive system. Tributyltin is used as a marine and agricultural fungicide, an antimicrobial agent in industrial water systems, and in plastics; it can cause serious sexual abnormalities in marine animals.

"What we discovered," Blumberg said, is that tributyltin disrupted genetic interactions that regulate fat-cell activity in animals. "Exposure to tributyltin is increasing the number of fat cells, so the individual will get fatter faster as these cells produce more of the hormones that say 'feed me,'" Blumberg said. The exposed animals, he added, remain predisposed to obesity for life.

Retha R. Newbold, a developmental biologist at the NIEHS, has seen similar lifetime effects in her work with diethylstilbestrol (DES), a potent synthetic estrogen she has studied for 30 years.

Whether its effects include promoting obesity has yet to be determined, but its effects on animal metabolism -- it is also used to fatten livestock -- are similar to those caused by bisphenol A, a chemical most people now encounter daily.

"Exposure to bisphenol A is continuous," said Frederick vom Saal, professor of biological sciences at the University of Missouri at Columbia. Bisphenol A is an ingredient in polycarbonate plastics used in many products, including refillable water containers and baby bottles, and in epoxy resins that line the inside of food cans and are used as dental sealants. In 2003, U.S. industry consumed about 2 billion pounds of bisphenol A.

Researchers have studied bisphenol A's effects on estrogen function for more than a decade. Vom Saal's research indicates that developmental exposure to low doses of bisphenol A activates genetic mechanisms that promote fat-cell activity. "These in-utero effects are lifetime effects, and they occur at phenomenally small levels" of exposure, vom Saal said.

Research into the impact of endocrine-disrupting chemicals on obesity has been done only in laboratory animals, but the genetic receptors that control fat cell activity are functionally identical across species. "They work virtually the same way in fish as they do in rodents and humans," Blumberg said. "Fat cells are an endocrine organ."

Bonnie - they can take as many "next steps" as they want to study this. Chemical exposure contributing to obesity is a reality, period. Simply, it is very difficult to eliminate the toxic load that we ingest on a daily basis. So our bodies' create as much adipose (fat) tissue as possible to encapsulate the toxins. Hence, weight gain.

I want to clarify that this is one of many reasons why humans become overwieght/obese.