Scientists investigate chemicals’ ties to obesity
David Epstein | 10/17/2013, 6 a.m.
Everyone knows Americans are fat and getting fatter, and everyone thinks they know why: more eating and less moving.
But the “big two” factors may not be the whole story. Consider this: Animals have been getting fatter too. The National Pet Obesity Survey recently reported that more than 50 percent of cats and dogs — that’s more than 80 million pets — are overweight or obese. Pets have gotten so plump that there’s now a National Pet Obesity Awareness Day. (It was Wednesday.) Lap dogs and comatose cats aren’t alone in the fat animal kingdom. Animals in strictly controlled research laboratories that have enforced the same diet and lifestyle for decades are also ballooning.
In 2010, an international team of scientists published findings that two dozen animal populations — all cared for by or living near humans — had been rapidly fattening in recent decades. “Canaries in the Coal Mine,” they titled the paper, and the “canaries” most closely genetically related to humans — chimps — showed the most troubling trend. Between 1985 and 2005, the male and female chimps studied experienced 33.2 and 37.2 percent weight gains, respectively. Their odds of obesity increased more than 10-fold.
To be sure, some of the chimp obesity crisis may be caused by the big two. According to Joseph Kemnitz, director of the Wisconsin National Primate Research Center, animal welfare laws passed in recent decades have led caretakers to strive to make animals happier, often employing a method known to any parent of a toddler: plying them with sugary food.
“All animals love to eat, and you can make them happy by giving them food,” Kemnitz said. “We have to be careful how much of that kind of enrichment we give them. They might be happier, but not healthier.”
And because they don’t have to forage for the food, non-human primates get less exercise. Orangutans, who Kemnitz says are rather indolent even in their native habitats in Borneo and Sumatra, have in captivity developed the physique of spreading batter.
Still, in “Canaries in the Coal Mine,” the scientists write that, more recently, the chimps studied were “living in highly controlled environments with nearly constant living conditions and diets,” so their continued fattening in stable circumstances was a surprise. The same goes for lab rats, which have been living and eating the same way for thirty years.
The potential causes of animal obesity are legion: ranging from increased rates of certain infections to stress from captivity. Antibiotics might increase obesity by killing off beneficial bacteria. “Some bacteria in our intestines are associated with weight gain,” Kemnitz said. “Others might provide a protective effect.”
But feral rats studied around Baltimore have gotten fatter, and they don’t suffer the stress of captivity, nor have they received antibiotics. Increasingly, scientists are turning their attention toward factors that humans and the wild and captive animals that live around them have in common: air, soil, and water, and the hormone-altering chemicals that pollute them.
Hormones are the body’s chemical messengers, released by a particular gland or organ but capable of affecting cells all over the body. While hormones such as testosterone and estrogen help make men masculine and women feminine, they and other hormones are involved in a vast array of functions. Altering or impeding hormones can cause systemic effects, such as weight gain.