Why Are Animals Getting Fat?

We’ve all heard about the obesity epidemic. People are getting fatter, and this may relate to Type 2 diabetes rates. But did you know that animals are getting fatter too? What do fat animals tell us about human weight issues?


In people, fat is always blamed on eating too much and not moving enough. Or maybe your genes have something to do with it. Anyway, it’s your fault. But would you say that to an overweight raccoon?

You’ve probably seen fat pets. Some owners overfeed their cats and dogs. Increasing weights in farm animals could also be due to increased feeding.

But how do you explain the rising weights of lab animals? They have been fed a standard diet and kept to a standard lifestyle for at least 50 years. According to this article in ProPublica, captive chimps “living in highly controlled environments with nearly constant living conditions and diets” increased in weight by over 30% between 1985 and 2005.

And what is making zoo animals and wild animals fatter? Nearly every species studied has grown in the last 30 years.

Why is this happening? An article by science writer Robin Marantz Henig in a recent issue of Prevention goes over many causes.

Henig reports that numerous industrial chemicals are associated with weight gain in laboratory animals. Now, we know that association does not prove causation, but in many cases, probable pathways from these chemicals to weight gain have been shown.

According to Henig, these chemicals (called “obesogens”) work in at least three ways: They may increase the number of fat cells or increase their fat storage capacity. They might slow down our metabolism and promote fat storage. They may even act to make us hungrier more of the time.

It is also possible that bodies produce more fat as a place to store these chemicals instead of having them circulate through the body. So fat may be an animal or human’s way of protecting itself in a toxic environment.

Obesogens are everywhere. Henig writes,

If you’ve ever eaten seafood, plugged in an air freshener, handled a cash register receipt, eaten canned vegetables, sat on a couch treated with flame retardant, or cooked in a nonstick pan, you’ve already been exposed.

The worst exposures are probably before birth. Once these chemicals affect your genes, you, your children, and your grandchildren will likely be fat.

Many of these chemicals seem to increase fatness by increasing insulin resistance. So they may well cause diabetes. And in fact, many farm animals and pets are getting diabetes.

As I wrote here in 2012, it is possible that the entire statistical link between fatness and diabetes is explained by toxic chemicals.

What are some of these chemicals?
Dozens of chemicals can cause long-term weight gain. One is the fungicide tributyltin (TBT). Ships used to be coated with it. Now it’s in the water, in seafood, and in everyone’s body. When pregnant mice were fed a single dose of TBT, their offspring were 15% fatter than those of mice who hadn’t been exposed.

The pesticide DDT is another obesogen. The plasticizer bisphenol A (BPA) imitates hormones such as estrogen in ways that cause fatness. Many personal care and homecare products include phthalates, a class of chemicals that disrupts the endocrine system, especially the thyroid.

Perfluorooctanoic acid, used in products such as Teflon, is a potent obesogen. Many more are in Henig’s article. And more are described here and here. There are hundreds of them.

A surprising entry on the list is antibiotics. They can kill off healthy gut bacteria and promote bacteria that cause weight gain.

One obesogen to watch out for is brominated vegetable oil, or BVO. It was banned in Europe as a flame retardant for health reasons but is still added to soft drinks here.

Why I’m angry about this
So we’re dumping thousands of chemicals into the environment, and many of these affect our body functions. A lot of them make people fat; some promote diabetes. That’s sad, but the people doing it didn’t know about these effects. Now that they know, maybe they’ll change, right?

Fat chance. This research is not new. Studies on animals’ getting fatter have been around since the 90’s. Some were collected in an overview published in 2002 called “Chemical toxins: a hypothesis to explain the global obesity epidemic.” (Abstract here.)

People KNOW this. They’ve known for years. And yet I hadn’t heard about it until two years ago, despite writing every week about health, diabetes, and fat. This information hasn’t just been ignored. It’s been suppressed, as information on cigarettes and cancer was suppressed for decades.

Meanwhile, fat people are relentlessly blamed and shamed for their weight. They’re called lazy. They eat too much; they don’t care about themselves; they’re a burden on society. And the chemical companies that are doing this to us and to every person and animal on Earth aren’t blamed. They’re making billions. It’s a perfect example of what corporations are doing to our planet.

This doesn’t mean diet and exercise don’t matter. They do. But chemicals do too.

None of which is to say that people who get fat, whether from chemical or other causes, are bound to get sick. Lots of heavy people are quite healthy. The stigma and discrimination they suffer may be worse than any physical effects and may cause physical harm.

And it’s all unjust; it’s all wrong. It’s all based on lies like the “calories in/calories out” theory of weight that ignores the effects of chemicals, stress, bacteria, and genes.

We have to stop destroying our environment. We have to stop blaming victims. I guess for me, the place to start is by telling the truth. Governments and corporations probably won’t. So we have to.

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  • Redneck Angel

    “Fat Chance”?!? You jest!

  • jim snell


    What a most interesting article and comments. The part about lab animals and zoo animals being affected is very disconcerting in what we would assume would be very controlled and regulated environments is extremely worrying.

    Thank you for sharing with us.

  • chet

    Living s healthy life is what all people like. I don’t know that those things can cause or trigger diabetes. Thanks for this article, now I know what are the things I should avoid. Nice article!

  • Laurie Klipfel

    Wonderful article David!!
    It is important to expose this kind of information. The big business that profits by having this under the rug may have the money, but we have the numbers. Way to go!! And thanks to Diabetes Self Management for publishing!!

  • rene

    This is a tragically misinformed argument that negates sound science disproving such chemical fears. Remember, our environment has never been cleaner while obesity and diabetes rates are supposedly increasing. I would urge the author to seek more credible sources of information and research.

  • David Spero RN


    I almost never reply to negative comments. But your criticism is so instructively wrong. You say, “Our environment has never been cleaner.” The reality is that our environment has never been so filled with chemicals, most of which have never been evaluated for human health effects.

    You ask me to seek “more credible sources of information.” But there is tons of science on the obesogenic effects of many of the chemicals I mentioned. I cited some of it. Your criticism, on the other hand, cites no science at all, but repeats chemical industry marketing themes.

    Rene, please read some of the sources I linked to, and maybe their sources. You will be amazed.


  • Cheri

    We would like to think that being in a first world industrialized nation that we would have the opportunity of being healthier. Lately our water sources have been attacked by for profit corporations. Our food sources are no longer safe and the very environment of our houses are toxic. this is a great informative article. Sooner than later I will be eating only my own organic vegetables and chickens just to make my few remaining years a bit easier.

  • Ferne

    Farmers can’t afford to overfeed their animals. Pork is leaner than it used to be. With the drought there has been a shortage of feed for cattle.

  • Lorraine Starsky

    I am a public health nurse who grew up on a livestock farm. I know from first hand experience that the pigs that were raised were routinely given antibiotics to promote weight gain. Ditto for the the cows. It was added to the feed mixture, which was produced at the farm from grain that was grown in fields laced with chemical fertilizers and weed killers. Given that almost all pork in this country in produced in massive pig factory farms, I am willing to wager that the pork Ferne is consuming has been raised with antibiotics. Compared to world of my small farmer grandparents, we are now living in a chemical stew. In addition to the long term toxic effects of this hodgepodge of chemicals that may be responsible for cancer and obesity, we need to be concerned about the alarming growth of antibioitc resistance. This has long been blamed on individuals misusing antibiotics. The real origin of this crisis has been swept under the rug. We need to hold the responsible corporations and the politicians who receive lavish contributions from them accountable. Our children’s lives depend on us beforming informed and taking action.