I first heard the word ‘obesogens’ two years ago from a colleague, who had been trolling the web in search of stories. “They’re chemicals that make us fat,” she said. “Come on; we’re fat because we eat too much and we don’t exercise enough.” “Well there’s this guy called Blumberg…” Bruce Blumberg coined the term ‘obesogens’ in 2005, after getting the results of a ground-breaking study of pregnant lab mice fed a marine pesticide called tributyltin.
In the 1990s he’d been looking for sex reversals in snails and flounder as a result of the pesticide. Much to his surprise, he discovered that it was also turning reproductive cells into fat cells. Then he came across a review in “The Journal of Alternative and Complementary Medicine”. A Scottish doctor was suggesting a link between environmental chemicals like DDT, dioxins and organochlorines, and rising rates of obesity. Dr. Paula Baillie-Hamilton had discovered that researchers had been reporting pathological weight loss as a result of ingestion of these chemicals, but failed to highlight any weight gain they may have found. Weight loss was the problem for which they were watching. Weight gain seemed like a healthy thing. But in very low doses, they were definitely seeing weight gain.
Blumberg decided to launch a mouse study, using the same pesticide, the endocrine-disrupting tributyltin. He wanted to know if fetal exposure would lead to overweight baby mice.
“We found out that a single prenatal exposure to tributyltin at day 16 of development could cause mice to be born with more fat stored at birth and to become fatter later in life.”
There were other researchers discovering similar effects. Around the time Blumberg was searching for the hormone receptor that was causing the growth of fat cells in the frog’s testes, Retha Newbold, a government researcher in North Carolina specializing in the now banned drug D.E.S., was told by her lab technicians that she would need bigger cages because her mice were getting too fat for them. D.E.S., like tributyltin, is an endocrine disruptor. After reading Baillie-Hamilton’s review, she began designing her own study.
In Missouri, Fred Vom Saal, an expert on the health effects of bisphenol A (BPA), was also getting fat lab mice as a results of trace amounts of BPA. Not surprisingly, BPA is also an endocrine disruptor.
Obesity in Canada has doubled in less than thirty years. Every second adult in the western world is overweight. We have all presumed this is because of the widespread adoption of a western lifestyle full of fattening food and low levels of exercise. But some epidemiologists noted that even newborn babies were fatter than they used to be. As well, animals that live in proximity to people, like farm and lab animals, have become fatter since the 1950s. Was something programming us in the womb to be a little fatter than we should be?
Follow-up studies by Newbold and Vom Saal were positive. By 2007 there was enough evidence for the existence of obesogens that grant money for more studies began flowing from the National Institute of Environmental Health Sciences in North Carolina. Europeans were getting fatter too, so in 2008 the European Union launched a five-country study called Obelix, to study every aspect of the obesogen hypothesis. The study would carry out animal testing, epigenetic testing and perhaps most important, epidemiological studies. It’s one thing for lab mice to be getting fatter; but was the same effect happening in humans? Only large population studies could find out because laboratory tests couldn’t ethically be carried out on people.
The epigenetic studies are important because it’s possible exposure to endocrine disruptors in utero could be programming a multi-generational change in how our DNA is expressed.
But all of these endocrine disrupting chemicals had been tested by government and industry labs and declared safe. Industry toxicologists I talked with were quite certain their tests assured us that the levels allowed in the environment would do no harm. Yet academic endocrinologists like Vom Saal were finding that very small doses – 2 parts per billion – of BPA, lead to overweight litters of lab mice when the safe dose established by toxicologists of 50,000 parts per billion did nothing. How could tiny amounts have a negative effect, when much larger amounts have no effect? Endocrinologists call this a “non-monotonic dose response curve”. Industry toxicology experts don’t buy it; academic endocrinologists have no doubt it happens. (We worked hard in the documentary to explain this effect.)
Everyone I talked with agreed the lab tests are difficult to get right. And they all believe more testing must be done, especially human studies, before they can be sure that obesogens are really contributing to the obesity epidemic. In the meantime though, they suggest that the precautionary principle be applied: if we have any doubt about the safety of a chemical or drug, and it’s not essential, it should be pulled from use.
Retha Newbold has little doubt what is going on. “What we’re doing with these developmental exposures,” she said to me, “is that we’re programming people so that they will develop obesity later on in life and that’s something that’s going to be passed on to future generations. I think we have to really be concerned that our focus is on prevention.”
Bruce Mohun, Director and Co-writer
Bruce Mohun is a science journalist, and a TV director, writer and host. Over the last twenty years, his programs have aired on CBC, Discovery, Knowledge, TVOntario, Access, and SCN. In 2010 he directed THE DOWNSIDE OF HIGH for CBC TV’s The Nature of Things, which won the Gold World Medal for Best Health & Medicine Documentary at the 2011 New York Festivals. He is a past winner of the Science Council of British Columbia’s Eve Savory Award for Science Communication, and the Canadian Federation of Biological Sciences’ Gordin Kaplan Award for Science Communication. He was also one of the first North American journalists to produce a multi-part series on global warming, which aired on Knowledge and was screened at the New York Film Festival and the Image and Science Film Festival in Paris.