One of the puzzles of the modern world is why we humans are growing so tubby. Maybe these two mice offer a clue. They're genetically the same, raised in the same lab and given the same food and chance to exercise. Yet one is svelte, while the other looks like, well, an American.
The only difference is that one was exposed at birth to just one part per billion of an endocrine-disrupting chemical. The brief exposure programmed the mouse to put on fat, and although there were no significant differences in caloric intake or expenditure, it continued to put on flab long after the chemical was gone.
That experiment is one of a growing number of peer-reviewed scientific studies suggesting that one factor in the industrialized world's obesity epidemic (along with Twinkies, soda and television) may be endocrine-disrupting chemicals. These chemicals are largely unregulated — they are in food, couches, machine receipts and shampoos — and a raft of new studies suggest that they can lead to the formation of more and larger fat cells.
Before I describe some of this research, a more basic issue: Why should an op-ed columnist write about scholarship published in scientific journals? Don't pundits have better things to fret about, like the feuding between Democrats and Republicans? One answer is that obesity is an important national problem, partly responsible for soaring health care costs. Yet the chemical lobby, just like the tobacco industry before it, has impeded serious regulation and is even trying to block research.
A second is that journalists historically have done a poor job covering public health issues — we were slow on the dangers of tobacco and painfully delinquent in calling attention to the perils of lead — but these are central to our national well-being. Our lives are threatened less by the Taliban in Afghanistan than by unregulated contaminants at home.
Endocrine disruptors are a class of chemicals that mimic hormones and therefore confuse the body. Initially, they provoked concern because of their links to cancers and the malformation of sex organs. Those concerns continue, but the newest area of research is the impact that they have on fat storage.
Bruce Blumberg, a developmental biologist at UC Irvine, coined the term "obesogen" in a 2006 journal article to refer to chemicals that cause animals to store fat. Initially, this concept was highly controversial among obesity experts, but a growing number of peer-reviewed studies have confirmed his finding and identified some 20 substances as obesogens.
The role of these chemicals has been acknowledged by the presidential task force on childhood obesity, and the National Institutes of Health has become a major funder of research on links between endocrine disruptors and both obesity and diabetes.
Among chemicals identified as obesogens are materials in plastics, canned food, agricultural chemicals, foam cushions and jet fuel. For example, a study in the fall found that triflumizole, a fungicide used on many food crops, like leafy vegetables, causes obesity in mice.
Just this month, a new study in the journal Environmental Health Perspectives found that endocrine disruptors that are sometimes added to PVC plastic cause mice to grow obese and suffer liver problems — and the effect continues with descendants of those mice, generation after generation. Another study found that women with a pesticide residue in their blood bore babies who were more likely to be overweight at the age of 14 months.