According to a major scientific study, chemical pollution of the environment amplifies the global epidemic of obesity.
The idea that toxins called “obesogens” can affect how the body controls weight is not yet part of mainstream medicine. But the dozens of scientists behind the review argue that the evidence is now as strong as it should be. “This is essential because the current clinical management of obese patients is woefully inadequate,” they said.
The most disturbing aspect of the evidence is that certain weight-increasing chemical impacts can be passed down from generation to generation by altering how genes work. Pollutants cited by researchers as increasing obesity include bisphenol A (BPA), which is widely added to plastics, as well as certain pesticides, flame retardants and air pollution.
Global obesity has tripled since 1975, with more people obese or overweight than underweight, and increasing in all the countries studied. Nearly 2 billion adults are now overweight and 40 million children under five are obese or overweight.
“Clinicians focus on calories – if you eat more calories, you’re going to get fatter,” says Dr. Jerrold Heindel, lead author of one of the three review articles, and formerly at the US National Institute of Environment Health Sciences. “So they wait until you become obese and then they will consider giving you diet, medication or surgery.
“If it really worked, we should see a drop in obesity rates,” he said. “But it’s not – obesity continues to rise, especially among children. The real question is: why are people eating more? The obesogenic paradigm focuses on this and provides data that indicates these chemicals are what can do this.
Moreover, according to the scientists, the approach offers the potential to prevent obesity by avoiding exposure to pollutants, especially in pregnant women and babies: “Prevention saves lives, while costing much less than any [treatment].”
The evidence for obesogens is presented by over 40 scientists in Three review papers, published in the peer-reviewed journal Biochemical Pharmacology and citing 1,400 studies. They say these chemicals are everywhere: in water and dust, food packaging, personal care products and household cleaners, furniture and electronics.
The review identifies about 50 chemicals as having good evidence of obesogenic effects, from experiments in human and animal cells and from epidemiological studies in people. These include BPA and phthalates, also a plastic additive. A Analysis 2020 out of 15 studies found a significant link between BPA levels and obesity in adults in 12 of them.
Other obesogens are pesticides, including DDT and tributyltin, old flame retardants and their newer substitutes, dioxins and PCBs, and air pollution. Several recent studies establish a link between exposure to looks dirty early in life to obesity.
The review also names PFAS compounds — called “eternal chemicals” because of their longevity in the environment — as obesogens. They are found in food packaging, kitchen utensils and furniture, including certain child car seats. A two-year randomized clinical trial published in 2018 found that people with the highest levels of PFAS regained more weight after dieting, especially women.
Some antidepressants are also well known to cause weight gain. “It’s proof of principle that chemicals made for one thing can have side effects that interfere with your metabolism,” Heindel said. Other chemicals with evidence of being obesogenic included certain artificial sweeteners and triclosan, an antibacterial agent banned from certain uses in the United States in 2017.
How it works
Obesogens work by disrupting the body’s “metabolic thermostat,” the researchers said, making it easier to gain weight and harder to lose weight. The balance between the body’s energy intake and expenditure through activity is based on the interaction of various hormones from the fatty tissues, intestine, pancreas, liver and brain.
Pollutants can directly affect the number and size of fat cells, alter the signals that make people feel full, alter thyroid function and the dopamine reward system, the scientists said. They can also affect the microbiome in the gut and lead to weight gain by making it more efficient to absorb calories from the intestines.
“It turns out that chemicals dumped into the environment have these side effects, because they make cells do things they wouldn’t otherwise do, and one of those things is depositing fat,” said Professor Robert Lustig of the University of California. , San Francisco, and lead author of another of the reviews.
The early years of a child’s development are the most vulnerable to obesogens, the researchers wrote: “Studies have shown that in utero and early life exposures were the most sensitive times, because this altered programming in a irreversible damage to various parts of the metabolic system, increasing susceptibility to weight gain.”
“We have four or five chemicals that will also cause transgenerational epigenetic obesity,” Heindel said, referring to changes in gene expression that can be inherited. A 2021 study found that the level of obesity in women significantly correlated with the level of exposure of their grandmothers to DDT, even though their granddaughters were never directly exposed to the now banned pesticide.
“People need to know that [obesogenic effects] are happening,” Lustig said. “Because it affects not just them, but their unborn children. This problem will affect generation after generation until we get it under control.
cause and effect
Directly proving a causal link between a hazard and an impact on human health is difficult for the simple reason that it is unethical to perform harmful experiments on people. But strong epidemiological evidence can stack up to an equivalent level of evidence, as in the case of smoking and lung cancer.
Lustig said that point had been reached for obesogens, 16 years after the term was first coined. “We will never have randomized controlled trials – they would be illegal and unethical. But now we have the evidence for obesogens and obesity.
The obesogenic paradigm has not been taken up by mainstream researchers until now. But Professor Barbara Corkey, of the Boston University School of Medicine and former president of the Obesity Society, said: “The original worldview was that obesity is caused by eating too much and exercising too little. And this is nonsense.
“That’s not the explanation because all creatures on Earth, including humans, eat when they’re hungry and stop when they’re full. Every cell in the body knows if you have enough food,” said she said. “Something has disturbed this normal detection apparatus and it is not willpower.
“Overweight and obese people go to extreme lengths to lose weight, and the diet industry has done extremely well,” Corky said. “We learned that it does not work. When the medical profession does not understand something, we always blame the patients and unfortunately, people are still held responsible for [obesity].”
Lustig said, “Greediness and laziness are just the outward manifestations of these biochemical disturbances that occur below the surface.”
How much of the obesity pandemic may be caused by obesogens is not known, although Heindel said they will have an “important role.”
Lustig said: “If I had to guess, based on all the work and reading I’ve done, I’d say obesogens will make up about 15% to 20% of the obesity epidemic. But that’s He attributes the rest to processed diets, which themselves contain obesogens.
“Fructose is the main driver of a lot of this,” he said. “It distributes energy to fat in the liver and is a prime obesogen. Fructose would cause obesity even if it had no calories. A small 2021 trial found that an ultra-processed diet caused more weight gain than an unprocessed diet, despite containing the same calories.
Reducing exposure to obesogens is difficult, given that there are 350,000 man-made chemicals today, many of which are ubiquitous in the environment. But those known to be harmful can be withdrawn from sale, just like what’s happening in europe.
Heindel said mothers-to-be in particular could adjust what they eat and monitor what their children play with in their early years: “Studies have shown that changing diets can in about a week lead to a significant drop in several obesogens”.
Lustig said: “This cause is very widespread and pernicious, and it is also lucrative for many [chemical] businesses. But we have to approach it rationally. To do this, the “knowledge gap” among doctors, regulators and policymakers must be closed, the scientists said.
“Now is the time [obesity researchers and clinicians] should start paying attention and if they think the data isn’t strong enough, tell us what more needs to be done,” said Heindel, who is hosting a conference to address this issue.
Corkey is still not fully convinced by the obesogenic paradigm, but said the concept of environmental toxins is probably the right direction to go. “Is there any proof? No, there isn’t,” she said. “It’s a very difficult problem, because the number of chemicals in our environment has just increased astronomically.
“But there is no alternative hypothesis that makes sense to me and I would certainly challenge anyone with a better testable idea to come up with it,” she said. “Because it’s a serious problem that impacts our societies enormously, especially children. The problems are getting worse, not better – we’re going in the wrong direction as it is.
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