Pity the experimental subjects in a new paper out of Johns Hopkins: they're "sedentary, obese, glucose intolerant, and on a trajectory to premature death." They very rarely exercise. They eat near constantly, snacking throughout the day with food always at the ready. In short, they sound like victims of the obesity epidemic. But you won't find them chowing down at the local McDonald's or sheepishly buying ever-bigger pants at the mall: they're lab rats. Think about it: if you were in a cage all the time with almost nothing to do except eat, and you could do that whenever you wanted, wouldn't you be a bit chubby too?
The authors of the new paper say that many lab rats may be overweight (theirs weighed up to two pounds, or twice what they should). Laugh if you want, but that's a real problem for science. Researchers are supposed to ensure that their animal models are as closely analogous to the average human as possible so they'll be able to smoothly translate their experimental results into people. If there's something "off" about the animals, the results won't be as trustworthy.
For example, as we reported last year, scientists studying the stress response did their work exclusively with male rats for decades, not realizing that they were missing something major: female rats respond to stress differently than males do. Similarly, if rats are abnormally heavy, their bodies will respond differently than healthy animals' in many situations, as Nature explains:
Beneficial effects of a potential drug or behavior could simply result from its effect on the consequences of an animal's unhealthy lifestyle, they say, and studies showing that caloric restriction can extend lifespan may have to be reinterpreted. "A major reason the lifespan of rats and mice is extended by caloric restriction is they started from an unhealthy baseline," argues [Mark] Mattson, [chief of the National Institute on Aging's Laboratory of Neurosciences and a co-author on the paper]. He and his co-workers identify areas as diverse as immune function, cancer and neurological disorders that could be affected by the problem.
On the other hand, if you want to study Americans, maybe these rats are fairly representative. As the Hopkins paper puts it, "the standard overfed sedentary control animal is a good model for an increasing fraction of human subjects who are overweight and sedentary."
The Johns Hopkins researchers suggest that other scientists should impose a little healthy discipline in their labs: make the rats run on exercise wheels, feed them only every other day. That's the most obvious way for the rest of us to lose weight, too: exercise more, eat less.