According to an article in Environmental Health Perspectives, exposure to a class of chemicals commonly found in soap and plastics could be fueling the obesity epidemic and insulin resistance in men. The study was based on urine, blood samples and other data collected for the National Health and Nutritional Examination survey (NHANES) — a large government survey — between 1999 and 2002.

The chemicals, known as phthalates, have already been implicated as a cause of male reproductive problems, including low testosterone and low sperm counts. Researchers caution that it is still too soon to know whether phthalates are causing obesity and diabetes.

Of the adult men in the study, 1,451 had data on phthalate exposures, obesity and waist circumference. Of these, 651 also had data necessary to calculate insulin resistance. The analysis determined that more than 75 percent of the U.S. population has measurable levels of several types of phthalates detectable in their urine. Men with the highest levels of phthalates had more belly fat and insulin resistance, even after adjusting for the other factors.

The researchers admit that there was one drawback of the data, and therefore, of the study: there was no information on hormone levels and there was no long-term data.

While there’s no conclusive evidence that phthalates are directly causing obesity and diabetes, researchers believe they could definitely be part of the problem. For example, in animal studies, phthalates have been shown to have an effect on thyroid hormone, which could be a pathway to obesity.

“It’s a complex, multi-factorial problem,” says Dr. Ted Schettler, science director for the Science and Environmental Health Network. “What the authors are suggesting is that a chemical exposure may be one among many factors. The study is certainly hypothesis-generating. It clearly makes a case that this potential link ought to be studies in more detail in more systematic ways.”

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