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Chemical compounds used in the manufacturing of non-stick pots and pans, stain-resistant clothing and carpets, and food packaging might be putting people at risk of becoming obese. A new study found an association between chemicals called perfluoroalkyl substances (PFASs) and high levels of obesity, which scientists hypothesize could be disrupting the body’s ability to burn calories properly.

The team at Harvard University led by Qi Sun, an associate professor at the university’s Department of Nutrition, analyzed the records for 621 overweight and obese individuals who were followed for two years as they dieted.

Over the first six months of the trial, participants had lost 6.4 kg, but somewhat expectedly regained 2.7 kg over the course of the following 18 months. What was surprising, however, was that those who gained the most weight back also had the highest blood concentrations of PFASs, and this was particularly true for women.

According to the study published in the journal PLOS Medicine, women with the highest PFAS levels gained about 2 kg more than those with the lowest levels of PFASs. Upon closer investigation, the researchers found that those with PFAS levels in their blood also burned calories slower, having a lower resting metabolic rate.

The scientists were quite fortunate to complete their investigation: the diet trials were conducted in the 2000s, and along the years the samples had been drained for other research.

“When this project was funded, plasma samples collected from study participants in the POUNDS-Lost trial were almost depleted because they were used for other projects over the years. These precise samples have to be shared among trial investigators. One of the most memorable and happiest moments was when Dr. Jeremy Furtado (our lab director) finally found enough samples in freezers!” Sun told ZME Science in an email.

PFASs have been employed in the manufacturing of a wide range of products in the last 60 years from food wrapping to pots to clothing. These are very persistent chemicals that, once in the bloodstream, stay there and accumulate, potentially causing chronic illnesses. Highly fluorinated chemicals have been previously associated with kidney and testicular cancer, elevated cholesterol, decreased fertility, thyroid problems, and hormone disruption.

The new findings now suggest that PFASs are also obesogenic — chemicals that promote excess weight gain and obesity. PFASs may be acting on a pathway that slows down the metabolism, though more research is needed to investigate this relationship, as this cannot be determined from a causal study.

“Given this is the first human study that linked PFASs with weight regain after dieting, I would like to call for replications and further research for mechanisms. Having said this, I think the public should be aware of the issue of PFASs exposures and associated potential health consequences,” Sun told ZME Science.

“I personally avoid using products that contain PFASs whenever possible. For example, I primarily use cast iron instead of nonstick cookware to cook dinner and do not eat fast foods, including popcorn, that can be contaminated by PFASs through contact with food packaging materials,” he advises.