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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20 Responses to Could dieting pollute us?

  1. Jason Snyder says:

    If burning fat releases these chemicals into the bloodstream, the subjects obviously already had them stored in the fat; is it that much less harmful to have high levels in our body fat to begin with? It seems like the moral of the story is that you’re really just better off to maintain a healthy lifestyle and avoid putting on extra weight as you age.

  2. Ken says:

    This has been known for a long time to anyone serious about fasting. When I first started fasting, I would only go a few days at a time before eating again to limit the buildup of toxins coming out into the blood. I experienced headaches and queasiness. With regular fasting and a change in diet (attempting to limit the source), I feel that I now have flush the majority of those toxins out of my body. Currently I do a week-long fast once a quarter because I don’t think I will every be able to completely eliminate toxins coming into my body. And now when I fast, I don’t feel horrible at all like I used to.

    I understand the need for a catchy title, but doesn’t it seems a little improper?

  3. Hi Ken, Thanks for sharing. That’s really interesting and makes a lot of sense. And yes: I try to keep my titles short and sweet, but you’re right, in doing so I’m unable to capture a lot of the nuances. Sorry if it seems inappropriate.

    Jason, that’s a good question. The implication from the study (although the researchers did not come out and say it) was that having these chemicals in the bloodstream is indeed more harmful than having them stored in fat. Certainly, as fat is considered an endocrine organ, chemicals that are stored there might be able to affect hormone signaling; if they are circulating throughout the bloodstream, though, they might be more likely to directly affect other organs. But I’m speculating here.

  4. Travis says:

    This is a fascinating topic, especially for people like myself who study the health impact of weight loss .

    I think it’s important to point out that obesity itself is associated with increased POP concentrations in the blood stream (e.g., to support your argument that a diet of donuts and bacon are not necessarily the right approach :) But the consistent finding that weight loss also increases POP levels is definitely concerning, since these increased concentrations of POPs may then make an individual more likely to regain their lost weight, among other things.

    All that being said, I think the benefits of weight loss are likely to substantially outweigh the risks of an increased concentration of POPs. I also wonder how long these increased concentrations could persist post weight loss, since these individuals now have less fat tissue to store the POPs. As you say, the findings so far raise a lot of interesting questions!


  5. bmossop says:

    Very nice post, Melinda! Just curious, in your reporting, did you come across any data of how exercise/physical activity factors into the equation? Knowing chronic physical activity changes the way lipids are metabolized (and decreases organochlorine peptides themselves), I wonder wheter POP levels during dieting are different when someone also exercises during weight loss??

  6. Thanks, Brian! That’s a really good question, and I haven’t looked into it (but should). That said, the 2000 study I referenced in the International Journal of Obesity and Related Metabolic Disorders did do a follow-up with the subjects after they completed the first analyses. The follow-up lasted for 18 weeks and involved keeping the subjects on low-fat diets and some kind of exercise regimen. When they analyzed the subjects’ blood for POPs after this period, the researchers wrote that “their observations persisted,” which I guess means that the POP levels stayed about the same. However, I don’t have access to the full study—just the abstract—so I don’t have more details. Sorry!

  7. Hi Travis! Thanks for the comment. And I agree—although I am no expert in this area, I would imagine the benefits of weight loss far outweigh these potential risks. I just think it’s an interesting finding and worth considering.

  8. mangrist says:

    I was going to say “Pass the Twinkies” until Travis had to go and ruin it for everyone…

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  10. susie says:

    i wonder what size they wear!!!!!!!!!!!!!!!?????????????????????

  11. susie says:

    someone answer our ????S.they look like a tootsie roll or a turd………..from three weeks ago

  12. margret bertha says:

    yeah susie keep talking!!!!!!!!!!!

  13. susie says:

    thanks margret??????????!!!!!!!!!!!!!!ill keep talking

  14. susie says:

    i wonder where they got those pants because i need them for more attention!!!!!!!!!!!!!!!

  15. gabs says:

    me too

  16. gabs says:

    i think a gorrilla could fit in them

  17. gabs says:

    i think we would be showing to much

  18. gabs says:

    i think they are pregnant

  19. Tabs says:

    How did you figure that out????p.s. cute name!!!!

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