Could dieting pollute us?

I just stumbled across a thought-provoking study that I have to share. Korean researchers publishing in the International Journal of Obesity have found that weight loss is associated with higher blood levels of persistent organic pollutants (POPs)—chemicals used to make pesticides and solvents that are notorious for accumulating in our bodies and in the environment. The researchers believe that POPs, which typically build up in fat, get released into the bloodstream when fat is burned. There, they could potentially cause health problems, increasing the risk for cancer, nervous system and reproductive damage (in part because many are considered endocrine disruptors).

The scientists conducted the study by interviewing 1099 adults about the weight changes they experienced over the course of the previous 10 years and the previous year. Then they compared these reported changes to the subjects’ current blood POP levels collected as part of the US National Health and Nutrition Examination Survey. (It’s important to note that they did not actually measure the POP levels at the earlier time periods.) They found that blood POP levels were higher in people who had reported long-term weight loss (and, to a lesser degree, short-term weight loss), and that POP levels were lower in people who had gained weight.

The study would have been more compelling if the researchers had measured the “before” and “after” POP concentrations; they were also relying on potentially inaccurate self-reports. But nevertheless, the findings are interesting. Plus, other studies have tracked POP levels and weight over time. For instance, a 2000 study published in the International Journal of Obesity and Related Metabolic Disorders collected blood samples from 39 obese people before and after they dieted for 15 weeks. The authors reported finding statistically significant increases in the blood levels of 15 organochlorine pesticides in the subjects after they dieted. And a 2006 study published in Obesity Surgery reported similar results in morbidly obese people who underwent bariatric surgery—their blood levels of organochlorine pesticidies spiked by more than 50 percent after surgery, and the more weight they lost, the higher their chemical levels rose—a finding that suggests that the chemical increases are not related to dietary changes.

Granted, these studies do not prove that weight loss causes increases in blood chemical levels. (I feel like I’m going to be writing a variant of that sentence in every post.) There could be other factors involved. And of course we all know that there are many health benefits associated with weight loss, so I’m not saying we start living on a diet of bacon and Dunkin’ Donuts, delicious—oh so delicious!—as that might sound. But there is some literature, including studies in PLoS Medicine and the Journal of Internal Medicine, suggesting that weight loss can be accompanied by health problems and even an increased risk of death. Most researchers have attributed these findings to the fact that weight loss can be the result of cigarette smoking or underlying illness, but it’s interesting to wonder whether circulating chemicals could be playing a role, too. Maybe; maybe not. It’s too soon to tell, but it’s certainly an interesting question.

Lim JS, Son HK, Park SK, Jacobs DR Jr, & Lee DH (2010). Inverse associations between long-term weight change and serum concentrations of persistent organic pollutants. International journal of obesity (2005) PMID: 20820170

Chevrier, J., Dewailly, �., Ayotte, P., Mauriège, P., Després, J., & Tremblay, A. (2000). Body weight loss increases plasma and adipose tissue concentrations of potentially toxic pollutants in obese individuals International Journal of Obesity, 24 (10), 1272-1278 DOI: 10.1038/sj.ijo.0801380

Hue, O., Marcotte, J., Berrigan, F., Simoneau, M., Doré, J., Marceau, P., Marceau, S., Tremblay, A., & Teasdale, N. (2006). Increased Plasma Levels of Toxic Pollutants Accompanying Weight Loss Induced by Hypocaloric Diet or by Bariatric Surgery Obesity Surgery, 16 (9), 1145-1154 DOI: 10.1381/096089206778392356

Sørensen, T., Rissanen, A., Korkeila, M., & Kaprio, J. (2005). Intention to Lose Weight, Weight Changes, and 18-y Mortality in Overweight Individuals without Co-Morbidities PLoS Medicine, 2 (6) DOI: 10.1371/journal.pmed.0020171

Drøyvold WB, Lund Nilsen TI, Lydersen S, Midthjell K, Nilsson PM, Nilsson JA, Holmen J, & Nord-Trøndelag Health Study (2005). Weight change and mortality: the Nord-Trøndelag Health Study. Journal of internal medicine, 257 (4), 338-45 PMID: 15788003

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