Do chemicals contribute to obesity?

RALEIGH -- The number of American adults who are obese has more than doubled in the past 30 years, and obesity is dramatically on the rise in Asia, Latin America and the Middle East. But there may be more at work than people eating more calories than they burn.

Scientists have come across clues that chemicals in the environment may contribute to the obesity epidemic and the subsequent rise in diabetes worldwide.

But some clues are fuzzy, others difficult to interpret.

"We have too many questions," Dr. Michael Gallo, a renowned toxicologist at the University of Medicine and Dentistry of New Jersey, said this month during a three-day national toxicology workshop in Raleigh.

The workshop brought together more than 200 scientists from universities, research institutes and federal agencies, including the Environmental Protection Agency, the Food and Drug Administration and the National Institutes of Health.

The scientists worked on to-do lists aimed at filling data gaps. Among the potential obesogens were nicotine, pesticides and the plastic additives bisphenol A and phthalates - the same chemicals under scrutiny at the EPA in Research Triangle Park, where researchers are testing whether they also cause cancer, disrupt reproduction or damage unborn life.

That smoking is bad is well known, said Alison Holloway, an associate professor in the department of obstetrics and gynecology at McMaster University in Ontario. Holloway's group, which looked at nicotine and obesity, found evidence that smoking during pregnancy increases the risk of obesity in the offspring.

Much less is known about smoking and diabetes and of the risks of secondhand smoke, Holloway said.

Data linking pesticides to obesity and diabetes are also limited. The scientists found some evidence that exposure during the first trimester of pregnancy has led to an increase in gestational diabetes among farm wives.

But the least data are available on bisphenol A and phthalates - and what's there is unclear.

"There's a lot of work to do," said Kim Boekelheide, professor of pathology and laboratory medicine at the Brown University School of Medicine in Rhode Island.