Pollutants acting on genes in the developing fetus and newborn are believed to turn more precursor cells into fat cells, which stay with you for life. And they may alter metabolic rate, so that the body hoards calories rather than burning them, writes Sharon Begley in a recent issue of the Newsweek.
In 2002, an unknown Scottish academic published a paper about the link between obesity and synthetic chemicals.
In Japan, scientists were finding that bisphenol A (a chemical compound used to make plastic drinking bottles and baby bottles, among other things) pushed certain cells to become fat cells in experiments performed in the lab and also acelerated the growth of existing fat cells. If their results held true outside the lab in people, it would mean that BPA, and potentially other synthetic chemicals, were in fact contributing to obesity.
In 2006, Bruce Bloomberg at the University of California, Irvine exposed pregnant mice to a chemical called tributyltin, which is found in marine paints and plastics and often ends up in people through drinking water.
The tributyltin activated a receptor called PPAR gamma, which acts like a switch for cells' fate: in one position it allows cells to remain fibroblasts, in another it guides them to become fat cells. (It is because the diabetes drugs Actos and Avandia activate PPAR gamma that one of their major side effects is obesity.) The effect was so strong and so reliable that Blumberg thought compounds that reprogram cells' fate like this deserved a name of their own: obesogens.
Also researchers at Michigan State University said that the daughters of women who ate Lake Michigan fish laced with the toxic remnants of DDT were at greater risk of becoming obese.
They studied the adult daughters of 250 West Michigan mothers who ate Lake Michigan fish to gauge their offsprings' exposure to DDE, a breakdown product of DDT.
The study, published in the March edition of Occupational and Environmental Medicine, found that women with intermediate levels of DDE in their bodies gained an average of 13 pounds of excess weight. Women with higher levels of DDE gained more than 20 pounds of excess weight.
"What we have found for the first time is exposure to certain toxins by eating fish from polluted waters may contribute to the obesity epidemic in women," said Janet Osuch, a professor of surgery and epidemiology at MSU's College of Human Medicine and one of the lead authors of the study.
Osuch said prenatal exposure to toxins is increasingly being looked at as a potential cause for the rise in obesity seen worldwide.
The federal government banned DDT in 1973 after studies showed the chemical killed songbirds and drove bald eagles to the brink of extinction by disrupting the birds' reproductive cycle. The chemical and its byproducts are still found in some species of fish and other marine life.
Lake Michigan fish are far cleaner now than in the 1970s, but DDT and DDE are persistent compounds that accumulate in the fatty tissue of fish and humans.
The state of Michigan recommends that women and children limit consumption of most species of Lake Michigan fish to one meal per month. Studies have shown that removing all fat and skin from fish can reduce exposure to persistent toxins.
Apart from bisphenol, other obsesogens thus far identified are -
Phthalates: Found in "toys, food packaging, hoses, raincoats, shower curtains, vinyl flooring, wall coverings, lubricants, adhesives, detergents, nail polish, hair spray and shampoo."
PCBs: Used as coolants and lubricants in electric equipment and have also been added to plastics, inks, adhesives, paints, and flame retardants. PCBs are not only into the products we buy but is in the air and water, and many people are exposed to them through eating certain kinds of fish -- especially the ones highest on the food chain.
Perfluoroalkyl compounds - used in stain repellents and nonstick-cooking surfaces.
These chemicals known as "endocrine disruptors," have effects on male and female reproduction, breast development and cancer, prostate cancer, neuroendocrinology, thyroid, metabolism and obesity and cardiovascular endocrinology, said the Endocrine Society in June last.
Results from animal models, human clinical observations and epidemiology studies converge to implicate EDCs as a significant concern to public health, the statement added.
The more dangerous chemicals are allowed to proliferate in our air, water, food and the products around our homes, the greater the threat to our own health, and the more of a burden it places on a health care system teetering at the edge of catastrophe, warns Tara Lohan, writing in Alternet.