A Toxicological Perspective on How We Became So Fat

By Julia Tobacyk posted 03-14-2018 15:01


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Americans have only gotten bigger and fatter over time. Statistics show that up to 30 percent of the adult American population is now classified as obese. Yet, a simple question remains unanswered: how did we get so fat? The most basic macro-level explanation is that not only did food production increase, but food became less expensive than ever; therefore people started eating more food, especially processed food.

There are many other competing hypotheses explaining the roots of the obesity epidemic, such as fast food restaurants, Facebook, too little sleep, too much salt, fat and sugar, life stress, and even drugs, particularly some classes of antidepressants.

However, at the “Adipocyte Toxicology and Obesogens” Scientific Session at the 2018 SOT Annual Meeting and ToxExpo, toxicologists from all around the world came together to discuss another cause of obesity: chemicals in the environment. These chemicals, called obesogens, dysregulate our overall fat metabolism. What’s scary is that many of the obesogens discussed during the session are ubiquitous in our daily lives—ranging from phthalates in plastics to pollutants and chemical contaminants in our food and drinking water. 

The first speaker, Bruce Blumberg, University of California Irvine, discussed an even more terrifying problem: your grandparents’ diet and lifestyle might have a strong influence on your metabolism. So, if you are struggling with those extra pounds, then perhaps it is reasonable to blame your grandparents for your predisposition for obesity. Dr. Blumberg showed that merely exposing pregnant mice to tributyltin, an environmental contaminant, through drinking water at minuscule doses made their offspring (up to the F4 generation!) already predisposed to obesity. Shockingly, none of the offspring were ever exposed to tributyltin throughout their lifetime, suggesting that there is an inherited predisposition to obesity. Dr. Blumberg explains this phenomenon as illustrating the “thrifty phenotype,” meaning that disturbances during pregnancy (like exposure to tributyltin) can cause permanent metabolic changes that are inherited generations later.

However, there are even more chemicals in our environment that act as obesogens. Michele La Merrill, University of California Davis, provided a thorough review that investigated the link between exposure to the pesticide dichloro-diphenyl-trichloroethane (DDT) and obesity. It comes as no surprise that Dr. La Merrill concluded that DDT and its metabolite Dichlorodiphenyldichloroethylene (DDE) carry an obesogenic potential.

On a positive note, tributyltin compounds have been banned from industrial use since the 1980s. Currently, the tributyltin findings serve as a paradigmatic case allowing scientists to say, “Indeed, there are chemicals in the environment that make us fat.” Similarly, DDT was banned as a pesticide worldwide under the Stockholm convention in 2001. So, why do we care about the effects of banned chemicals? After all, regulatory agencies have already taken the steps to reduce human exposure to those chemicals.

Well, scientists care. Chances are that the environment is filled with hundreds of unknown chemicals that act as obesogens. Chad Deisenroth, US Environmental Protection Agency, tackled this challenge and discussed his integrated approach for detecting such chemicals that might have an obesogenic potential. It is hypothesized that the common denominator of obesogens is that they activate PPARG, a master regulator of adiposity. By dissecting and clarifying the mechanism of toxicity of obesogens, such as tributyltin and DDT, it might be easier to predict other chemicals that have obesogenic properties before they are used for industrial purposes. 

Certainly, some chemicals in the environment can make us fat. But, so does poor nutrition, lack of exercise, genetics, too little sleep, and too much stress. Even though every one of these hypotheses is convincing, nobody knows what is the true cause of the increased obesity rates worldwide. How big of a role do obesogens play in the global obesity epidemic? That’s a question yet to be answered.

This blog was prepared by an SOT Reporter. SOT Reporters are SOT members who volunteer to write about sessions and events they attend during the SOT Annual Meeting and ToxExpo. If you are interested in participating in the SOT Reporter program in the future, please email SOT Communications Director Michelle Werts.