- Changes in diet and exercise do not fully explain the steep rise in overweight and obesity over recent decades.
- One theory claims that chemicals in everyday plastic products promote weight gain by changing human metabolism.
- A new study found that a range of plastic household items contain thousands of chemicals, many of them unknown.
- One-third of the items contained chemicals that, after extraction, caused the growth and proliferation of mouse fat cells in the lab.
Chemicals in plastic household items such as drinks bottles, yogurt pots, and freezer bags may be contributing to the global epidemic of obesity, a new study suggests.
The chemicals may alter human metabolism by promoting the growth of fat cells, or adipocytes.
According to the World Health Organization (WHO), the number of people with obesity has nearly tripled globally since 1975.
The WHO estimates that in 2016, more than 1.9 billion adults were overweight. Of these individuals, more than 650 million had obesity.
Having excess body weight increases a person’s risk of type 2 diabetes, cardiovascular disease, hypertension, non-alcohol-related fatty liver disease, stroke, and certain types of cancer.
Research suggests that factors such as changes in diet are insufficient to explain the scale of the obesity epidemic and the speed with which it has spread around the world.
One possible culprit is the effect of synthetic chemicals in our environment called endocrine disruptors. These influence the endocrine system, which includes the hormones that regulate appetite, metabolism, and weight, among other bodily functions.
The most well-known endocrine disruptors are bisphenol A and phthalates, which are present in some plastics.
These chemicals affect human development and fertility, and lab-based experiments indicate that they may also promote obesity.
However, plastics contain thousands of chemicals. Products made from plastic comprise one or more polymers, but manufacturers also add chemical fillers and additives to achieve the desired properties.
A 2019 study estimates that plastic food packaging alone could contain more than 4,000 known substances that appear in chemical databases.
Unidentified chemicals
However, biologists at the Norwegian University of Science and Technology in Trondheim suspected that there might be many unknown chemicals in plastic products that do not appear in the databases.
They used methanol to extract chemicals from 34 everyday products, including freezer bags, yogurt pots, drinks bottles, vegetable trays, scouring pads, and coffee cup lids.
Crucially, they used a technique called nontarget high resolution mass spectrometry, which identifies both known and unknown substances, to find chemicals.
They detected a total of 55,300 chemical features and tentatively identified 629 substances that are already in databases, including 11 that are known to disrupt metabolism.
Finally, they tested extracts from each of the products on a type of mouse precursor cell that can differentiate into fat cells.
They compared the effect of the extracts with those of a reference chemical — a diabetes drug called rosiglitazone (Avandia) that has well-known metabolic effects.
The chemical cocktails from four out of the 34 products transformed precursor cells into adipocytes that were larger and contained more fat than rosiglitazone-treated cells. Chemicals from 11 of the products induced the formation of adipocytes.
The results have been published in Environmental Science & Technology.
Not the usual suspects
“It’s very likely that it is not the usual suspects, such as bisphenol A, causing these metabolic disturbances,” says first author Johannes Völker, Ph.D., who is affiliated with the university’s biology department.
“This means that other plastic chemicals than the ones we already know could be contributing to overweight and obesity,” he adds.
The scientists report that chemical cocktails from PVC and PUR products were most likely to promote the creation of fat cells, whereas those from PET, HDPE, and PLA products were inactive.
They emphasize that food packaging is not the only potential source of metabolism-disrupting chemicals.
The substances may also find their way into the body through the skin — for example, from plastic shower slippers or when inhaling dust that has been in contact with plastic flooring.
In their paper, the authors conclude:
“Given the potency of the extracted mixtures and considering our close and constant contact with plastics, our results support the idea that plastic chemicals can contribute to an obesogenic environment and, thus, the obesity pandemic.”
However, they acknowledge that the results are not definitive, since the experiments took place in cells growing in dishes in the lab rather than in whole animals.
“It is too early to quantify the contribution of plastic chemicals to obesity from a public health perspective, mainly because our work was done in vitro, not in vivo, and the causative chemicals remain unknown,” said senior author Martin Wagner, Ph.D., an associate professor of biology at the university.
“So, we cannot draw a causal link to what is happening in human populations so far,” he told Medical News Today.
However, he pointed out that there is good evidence from in vivo and epidemiological studies that bisphenol A is associated with obesity.
In a tweet, he called for manufacturers to make their plastics chemically simpler and safer.
Criticism of the study
The researchers used methanol to extract chemicals from the plastics, which may not reflect what happens under everyday conditions.
“The authors are studying extraction rather than migration,” said Chris Howick, who is chairperson of the product safety committee at the British Plastics Federation.
“The authors are removing ingredients that would normally remain in the sample throughout its lifetime — as an example, flexible PVC products do not generally become brittle over their lifetimes since the plasticizer remains in the product,” he told MNT.
However, Prof. Wagner said that in a previous study, his team demonstrated that many chemicals do, in fact, leach from plastic products in a standard test for food contact materials that uses water only.
“We also found that these migrates induced in vitro toxicity, including endocrine-disrupting effects,” he said.
“For the metabolism-disrupting compounds, we have not done this type of experiment yet, so it is too early to tell if these also leach,” he added.
In their new paper, the authors also acknowledge that they analyzed plastic packaging that had contained food or personal care products.
“Because chemical migration is not a one-way street, we cannot exclude the possibility that compounds from the contents migrated into the packaging,” they write.
“This is an ever-present challenge in migration studies, and it is common, especially for food with a high fat content, for migration of food into the plastics to exceed any migration from the plastic into the food,” said Howick.
He also pointed out that certain foods have well-established effects on the endocrine system.
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