Does pollution play a role in weight loss?

Kim Ridley | April 2007 issue
Waistlines around the world are expanding at an alarming rate: More than 1 billion people are overweight. While the obesity epidemic is usually blamed on individuals, who eat too much and exercise too little, scientists are beginning to suspect that the situation is more than just a simple matter of calories. Some are now investigating the influence of another factor: pollution.
Most people who diet eventually regain the weight they’ve lost—and pack on even more pounds. Although this rebound effect has been portrayed as an evolutionary safeguard built into our bodies from the old feast-or-famine days, The Ecologist (Dec. 2006) reports that researchers are finding that some industrial chemicals, particularly the notorious “endocrine disruptors,” dramatically affect human metabolism and appetite control.
Many industrial chemicals, including certain compounds in pesticides, as well as polybrominated flame retardants, and phthalates—which are ubiquitous industrial plasticizers used in everything from PVC plastic to cosmetics—mimic or block the effects of hormones in the body. Growing evidence is beginning to link these endocrine disruptors to obesity, in addition to other health problems including cancer and developmental defects.
The body typically stashes toxins absorbed from food, water, and other sources in fat cells. In the late 1990s, a research team led by Professor Angelo Tremblay of Laval University in Quebec began studying the effects of organochlorines like DDT, dioxins and PCBs on the metabolisms of people enrolled in weight-loss programs. Building on earlier work by Italian researchers, the Canadian team found that levels of industrial pollutants in the dieters’ blood rose as they lost weight. As people lose weight, fat cells shrink and release the contaminants back into the bloodstream.
Tremblay and his colleagues further reported that as these levels rose, the levels of thyroid hormones necessary to maintain an efficient metabolism plummeted. “If I were to put this in journalistic terms, I might say that the organochlorines essentially shut down the metabolic furnace that helps the body burn fat,” Tremblay told The Ecologist. The Canadian team’s research continues to confirm that these chemicals may be among the major contributors to rebound weight gain.
Adding to the evidence is research by Dr. Paula Baillie-Hamilton, author of The Detox Diet. After extensively examining the effects of various classes of chemical pollutants on the body’s weight-control system, she made a surprising and counterintuitive discovery: Some of the same chemicals that cause weight loss in high doses can lead to weight gain at the very low levels at which we are exposed to them in everyday life.
Other common chemicals are believed to trigger obesity in different ways. For example, some research suggests that industrial chemicals such as bisphenol A (found in materials including hard clear-plastic bottles, food can linings and some dental resins) and organotins (stabilizers used in everything from PVC plastic to agricultural pesticides to wood preservatives) transform “baby” fat cells into full-fledged mature fat cells. As these fat cells proliferate, it becomes more difficult to lose weight and keep it off.
Dr. Leo Galland, author of The Fat Resistance Diet, thinks industrial pollutants may also trigger allergic responses that can cause or exacerbate chronic inflammation. Galland contends that inflammation causes the body to release chemicals that make it more resistant to leptin, a hormone produced only by fat cells that affects appetite, fat stores and metabolism.
Of course, couch potatoes who gorge on junk food and don’t get any exercise are going to get fat. But if losing weight is a simple matter of calorie counting, why do so many dieters fail? That’s still an open question, but it’s becoming clear that pollution merits much more investigation.