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Why is long-term weight loss so hard? These scary chemicals are partly to blame


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People have been told for years that losing weight and keeping it off is as simple as eating less and exercising more. But not only is this conventional wisdom vague and even a little shame-y, it also fails to account for other factors that can have a profound influence on weight.

One glaring oversight in the energy balance equation: obesogens, or chemicals that encourage fat storage. They’re part of a larger group of toxins called endocrine disruptors, which mess with your hormones, and are found in food, plastics, product packaging, household items, the environment… the list goes on. And there’s been some compelling evidence over the past decade or so to suggest that these sneaky chemicals can make it tough to lose weight and keep it off long-term.

“Doctors tell us it’s all about calories in, calories out, and that all calories are the same. And it’s not true,” says Bruce Blumberg, PhD, professor of developmental and cell biology and pharmaceutical sciences at the University of California, Irvine. He helped coin the term “obesogen” in 2006, and his new book, The Obesogen Effect, takes a closer look at what we know about them—just in time for spring detox season.

Could obesogens be sabotaging your weight-loss efforts? Keep reading for the 411.

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Why obesogens make it hard to lose weight
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Where are obesogens found?

Time to double-down on your commitment to avoiding the Dirty Dozen— according to Blumberg, conventionally grown food is a top source of obesity-promoting chemicals. “The vast majority are coming in through the diet as contaminants from food, like pesticides or fungicides,” he explains.

Other edible obesogens include artificial sweeteners (such as aspartame and saccharine), MSG (monosodium glutamate, often found in Chinese food), soy, and fructose. While it’s not entirely surprising that high-fructose corn syrup falls in the latter category, it also includes so-called healthy sweeteners like honey and agave syrup.

The packaging of food can also contain obesogens, says Blumberg. BPA (bisphenol-A), which is often found in plastic packaging and canned foods, is a big one. And these chemicals are also found outside of the kitchen. Parabens (often found in beauty products) and phthalates (found in many things including plastic, vinyl, paint, air fresheners, and beauty products) are also known obesogens, along with many air pollutants. So, basically, they’re everywhere.

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Why obesogens make it hard to lose weight
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Different obesogens affect weight in different ways

The term obesogen refers to any chemical that has the potential to promote weight gain—and they don’t all work the same way.

“They can [cause weight gain] by acting on cells, making more and bigger fat cells,” explains Blumberg. “They can also act on your metabolism so you burn fewer calories. They can affect appetite and satiety, so you feel like you’re hungrier, or they can alter your microbiome—the composition of the bacteria that live in your intestines, which also has an important role in what happens to the food that you eat.” 

One obesogen that’s been well-researched is TBT (tributylin), which has been found to contaminate seafood. It activates two hormone receptors, stimulating pre-fat cells to become fat cells. It can also stimulate stem cells to become pre-fat cells through a similar mechanism, Blumberg explains.

As for the other 50 or so obesogens? Scientists have an idea of how they work, but it’s hard to say exactly what role many of them play in weight gain. “Another known obesogen that’s well-reviewed is DBT. DBT is an estrogen, and exposing young animals to estrogens will make them [gain] fat,” says Blumberg, who adds that the chemical is found in vinyl floors and blinds. “But DBT gets metabolized to an anti-androgen called DDE, which also [promotes fat gain]. So is it the direct effect of DBT that makes the animals fat, or is it an indirect effect of DBT being metabolized to DDE? We simply don’t know, but we can guess probably one of those.”

Ultimately, more research is needed to determine exactly how each obesogen acts in the body to promote fat gain—but we do know that they have this end result, says Blumberg. And since we’re exposed to so many obesogens, most of us likely experience a combination of the aforementioned side effects, making sustainable weight loss even trickier.

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Why obesogens make it hard to lose weight
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Obesogens have an impact on future generations

It’s also important to note that you aren’t the only one affected by your own obesogen exposure, says Blumberg. Your children may, in turn, be genetically susceptible to weight issues, if his research on obesogens’ effect on mice is any indication.

“If we expose a mouse to a very low dose of TBT, the babies will become a little [heavier], then the grandbaby, the great grandbaby, and the great-great grandbaby,” says Blumberg. “They respond differently to diet [than mice whose ancestors weren’t exposed to TBT].”

These great-great-grandmice have what’s called a thrifty phenotype, says Blumberg. “The thrifty phenotype was recognized in the past from dietary studies in humans,” he says. “It means that if you and I both eat the same amount of calories and I have a thrifty phenotype and you don’t, I’ll store more of those calories than you will.” (In the hunter-gatherer days thousands of years ago, this was a survival advantage.)

Translation: Some people are ancestrally programmed to hold onto calories in a way that others aren’t, and obesogens play a role in this. That makes maintaining weight loss more challenging, because you’re fighting against the body’s natural inclination—no matter how many HIIT classes you take or how much sugar you cut from your diet. 

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Why obesogens make it hard to lose weight
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How to minimize your obesogen exposure

The sad truth is, obesogens are nearly impossible to avoid entirely, and you’d drive yourself crazy if you actually tried to do so. They’re everywhere in our environment—think wall paint, medical devices, building materials, electronics, furniture, and more.

We do, however, have some control over obesogens in the food we eat, says Blumberg. “The more processed the food, the more obesogens are in it, generally speaking,” he says. His advice: Go for ingredients that are whole, fresh, and unprocessed. Also, buy organic, grass-fed, and wild when you can—this will help you avoid obesogenic pesticides and fungicides. And if you don’t have one already, invest in a household water filter to clean up your H2O at home and switch to beauty products without parabens and phthalates.

Because ultimately, it’s not a bad idea to cut some chemicals from your life—even if weight loss isn’t your end goal.

Inspired to spring-clean your space of harmful chemicals? Check out the Environmental Working Group’s Healthy Home Guide for tips—and maybe think twice before lighting your favorite scented candle

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