Poor diet is a factor. Lack of exercise doesn't help. But America's rapidly growing problem with childhood obesity might also be tied to a certain virus that causes the common cold, according to new research published in the journal Pediatrics. It's important to recognize that "body weight is more complicated than it’s made out to be," and is not just "one's own fault or the fault of one's parents or family," says Dr. Jeffrey Schwimmer at U.C. San Diego, the lead author of the report. Still, how could a cold virus be to blame?

What did the researchers find?
Schwimmer and his colleagues studied 124 children ages 8 to 18, including 67 obese subjects, for signs they had been infected with adenovirus 36 (AD36). The children with antibodies to AD36 — 22 percent of the obese kids and 7 percent of the non-obese ones — were an average of 50 pounds heavier than those who hadn't been infected. Among just the obese kids, those who tested positive for AD36 were 35 pounds heavier.

What's adenovirus 36?
AD36 is one of 55 known strains of adenovirus that cause a range of respiratory, gastrointestinal, and other ailments (everything from diarrhea to sore throats) in humans. It has previously been linked to obesity in adults and animals.

How is it tied to obesity?
While AD36 hasn't been proven to cause obesity, laboratory animals infected with AD36 have gained a significant amount of weight. And, in petri-dish experiments, immature fat cells (pre-adipocytes) infected with AD36 can develop and reproduce more quickly, and become capable of storing more fat. "This might be [a] mechanism for obesity," Schwimmer says, "but more work needs to be done."

Is this good news or bad news for fighting obesity?
Potentially good news, if further research proves that AD36 causes obesity and researchers manage to develop a vaccine to counteract its effects. In the shorter term, say researchers, this finding could help reduce the criticism corpulent kids face. "Obese children suffer severe stigmatization, contributing to feelings of social rejection and lessened self-worth," the report says. "The possibility that excess weight gain in some children may be due to a viral infection could alter the public debate and perceptions regarding childhood obesity."

So, no more badgering to eat better and exercise?
Hardly. Healthy food and "regular, fun physical activity" will always be important, says Schwimmer. Other experts are more blunt. "People want a magic solution, but unfortunately we don't have one" says Dr. Goutham Rao at Children's Hospital of Pittsburgh. Instead of getting their kids tested for the virus, he says, parents should encourage key behaviors that combat obesity, like limiting juice, soda, and fast food, and engaging in physical activity rather than watching TV or playing video games: "If you can change these behaviors, you'd reduce most childhood obesity."

Sources: Washington Post, U.S. News, BusinessWeek/HealthDay, ScienceBlog, Health News, MSNBC