Many doctors still don’t know about, or acknowledge, the chemical link to weight gain and obesity – and yet the studies continue to pile up.
Most recently a class of chemicals used in many industrial and consumer products was linked with greater weight gain after dieting, particularly among women, according to a study led by Harvard T.H. Chan School of Public Health.
The chemicals – perfluoroalkyl substances (PFASs) – have been linked with cancer, hormone disruption, immune dysfunction, high cholesterol, and obesity.
The study, published in PLOS Medicine, also found that higher blood levels of PFASs – known as ‘obesogens’ because they may upset body weight regulation – were linked with lower resting metabolic rate (RMR), or slower metabolism after weight loss. Metabolism refers to the chemical processes in the body that convert energy from food, commonly known as “burning calories.”
People with a lower RMR, or slower metabolism, burn fewer calories during normal daily activities and may have to eat less to avoid becoming overweight.
“Obesogens have been linked with excess weight gain and obesity in animal models, but human data has been sparse. Now, for the first time, our findings have revealed a novel pathway through which PFASs might interfere with human body weight regulation and thus contribute to the obesity epidemic,” said senior author Qi Sun, assistant professor in the Department of Nutrition at Harvard Chan School.
» A new study has found that exposure to perfluorinated chemicals, found in many everyday items including cookware and cosmetics, may slow the metabolism, making weight loss difficult.
» Perfluoroalkyl substances (PFASs) have been linked with cancer, hormone disruption, immune dysfunction, high cholesterol, but they also act as obesogens, chemicals that upset body weight regulation.
» PFASs can be hard to avoid but individuals can take some steps to keep them out of their homes.
PFASs have been used for more than 60 years in products ranging from food wrappers to clothing to pots and pans, and studies have shown that they’ve contaminated drinking water near industrial sites, military bases, and wastewater treatment plants. These chemicals can accumulate in drinking water and food chains and persist for a long time in the body.
The researchers analyzed data from 621 overweight and obese participants in the Prevention of Obesity Using Novel Dietary Strategies (or POUNDS LOST) clinical trial, which was conducted in the mid-2000s.
This unique trial tested tested the effects of four heart-healthy diets on weight loss over a period of two years. Researchers looked at the possible connection between the amount of PFASs in participants’ blood as they entered the study and their weight loss or gain over time.
Women particularly vulnerable
During the first six months of the trial, participants lost an average of 6.4 kg, but regained 2.7 kg over the course of the following 18 months. Those who gained the most weight back also had the highest blood concentrations of PFASs, and the link was strongest among women. On average, women who had the highest PFAS blood levels (in the top third) regained 1.7-2.2 kg more body weight than women in the lowest third.
In addition, the study found that higher blood concentrations of PFASs were significantly associated with lower resting metabolic rates.
“We typically think about PFASs in terms of rare health problems like cancer, but it appears they are also playing a role in obesity, a major health problem facing millions around the globe,” said study co-author Philippe Grandjean, adjunct professor of environmental health at Harvard Chan School. “The findings suggest that avoiding or reducing PFAS exposure may help people maintain a stable body weight after they successfully lose some weight, especially for women.”
How to lower your exposure
PFAS are used in many consumer products. They are used in food packaging, such as fast food wrappers and microwave popcorn bags; waterproof and stain resistant fabrics, such as outdoor clothing, upholstery, and carpeting; nonstick coatings on cookware; and cleaning supplies, including some soaps and shampoos.
People can be exposed to these chemicals (and may others which also have an obesogenic effect) in house dust, indoor and outdoor air, food, and drinking water.
Once they are in the environment, for instance in the water supply they are very difficult to avoid. As consumers we can take a stand against PFASs by refusing to purchase products containing PFCs, such as:
For more on obesogens see our article Programmed to be Fat?
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