What Fat Animals Tell Us About Human Obesity

"No one who understands the ironclad laws of thermodynamics disputes why people gain weight: calories in > calories out. But the reasons for that inequality are almost certainly more complicated than PlayStation replacing tag and Froot Loops replacing oatmeal, or even the fattening school lunches that will be given a whole-grain-and-fruit makeover under a new federal law. For instance, fascinating new research shows that bacteria in our gut affect how many calories we extract from foods; with more calorie-extracting microbes, more of that cheeseburger winds up on your hips, while with more nonmetabolizing bugs, your annoying friend can gorge without breaking a size 6. Even Weight Watchers recognizes that not all calories are equal, and has revamped its points system. By focusing only on obvious explanations, we risk missing what might be more powerful (and interesting) influences on the caloric imbalance—influences that might bring a bigger payoff.
Which brings us to the pudgy pets, lab rodents, and wild animals Allison has chronicled. In macaques living in research colonies, average weight rose about 10 percent per decade. Chimps in labs had a 14-fold increase in obesity, with weight increasing 34 percent per decade. Pet cats: a 38 percent increase in obesity, with weight up 10 percent per decade. Pet dogs: a weight gain of just 3 percent per decade. (Good boy, Spot!) Those alley rats: a 21 percent increase in obesity. Government lab mice: weight gain of 12 percent per decade.
Food marketing, more TV, and less phys ed can no more explain these fatter animals than they can the epidemic of obesity in babies under 6 months. All these creatures live near or with people, however, which raises the intriguing possibility that common factors might explain their obesity as well as ours. Such as? Sleep debt, which increases blood levels of the appetite-stimulating hormone ghrelin and reduces levels of satiety-causing leptin. (Average sleep among U.S. adults has fallen from nine hours per night to seven.) Endocrine-disrupting chemicals such as BPA, which bind to receptors that trigger proliferation of fat cells. More central heating and AC, which means we burn fewer calories to stay warm in winter and don’t get the appetite-killing effects of sweltering in summer. Infection with adenovirus-36, which causes obesity in lab animals and is correlated with it in people.
There are numerous others. Controlled trials have already failed to show that more phys ed reduces kids’ weight (they seem to compensate by being more couch-potatoey at home). It’s time to expand the net of possible suspects in our expanding girths before it’s too late."

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