Scientists studying human health may be getting bad information from an unlikely source — their own lab rats. Many rats and mice used for research are fat, out of shape, and "on a trajectory to premature death," according to a report from Johns Hopkins University and the National Institute on Aging. That's a problem, because animals used for research are supposed to be reasonable stand-ins for the average human — when they're chubby and unhealthy, results of experiments designed to shine light on everything from Alzheimer's to cancer can be distorted. Are overfed lab rats useless, or is there still something humans can learn from them?

It's shocking scientists didn't realize using fat rats was stupid: Lab rats eat all day and have little incentive to exercise, says "Naturally, these furry versions of coach potatoes balloon." They end up with a skewed metabolism — obviously, a promising drug that works on them "may fail to work, or perform worse on healthy animals."
"Obese lab animals may fudge biology research, experts warn"

Time for the rats to start exercising: This scandal "casts suspicion on an entire body of research," says Stuart Fox in Popular Science. It's especially outrageous because the solution is so simple: "Get these rodents a personal trainer," or at least an exercise wheel. "I don't want to potentially miss out on a cure for cancer because Mickey and Minny didn't want to run some laps."
"Lab rats' pampered lifestyles found to skew research results"

The rats aren't the only ones that are fat. The Johns Hopkins researchers didn't exactly say chubby rats and mice are useless, says Mary Carmichael in Newsweek. In fact, with the U.S. in the grips of an obesity epidemic, "overweight and sedentary" rats might be precisely the animals scientists should be studying. Sure, lab rats could stand to exercise more and eat less, but so could we.
"Rats! Science has a weight problem"