Earlier this month, a federal agency tried to ban an American lawyer infected with tuberculosis from re-entering the country after he traveled abroad. In light of a new study published in tomorrow’s New England Journal of Medicine, public health quarantines for contagious diseases like TB or influenza may have to be extended to obesity. Yes, obesity. Today, the lead researcher of the study, Dr. Nicholas A. Christakis, told The Washington Post:

It’s almost a cliché to speak of the obesity epidemic as being an epidemic. But we wanted to see if it really did spread from person to person like a fashion or a germ. And the answer is, ‘Yes, it does.’ We are finding evidence for a kind of social contagion.

The authors isolated participants’ weight as the basis for their calculations-implying that numbers on a bathroom scale are somehow independent of a person’s lifestyles. But they’re not. Children in overweight families are often raised to spend nights and weekends in front of the television, rather than at a park. So it’s not surprising that later in life, they would seek out friends with similar sedentary interests. When this population gains weight, it happens as a result of choosing sedentary hobbies, rather than fat friends.
Conversely, the study claims that people can "catch" obesity from their family and friends — even if the corpulent acquaintance lives 500 miles away. The researchers also allege that "infection" is possible through three degrees of separation (an obese friend of a friend). With this incessant threat of "contamination" from siblings and spouses, Christakis told the Los Angeles Times that strategies for tackling obesity should abandon the focus on individual willpower: "The truth is almost no one can do it own their own."

Removing the notion of personal responsibility from the obesity debate, this study could act as a springboard for lawsuits and government regulation. At a press conference Christakis explicitly stated that "these findings reinforce the idea that obesity is not just an individual problem, but a collective problem." This notion gives credence to public officials who want to ban "junk foods" or health activists who campaign to zoning laws against certain restaurants.

Preventing "second-hand obesity" will be their justification.
But while the researchers maintain that "there is a direct causal relationship" between having obese friends and gaining weight, the data also show that people with skinny friends are more likely to be thin. Accordingly, there is another more plausible way to look at the study’s observations. The Law of Attraction stipulates that like attracts like. People with similar interests, ideologies, or lifestyles are drawn to one another. Case in point: high school cliques.

Though adult social networks may be more nuanced than the jock clique or the chess team, adults form their relationships based on shared interests. A person who spends his or her free time training for a triathlon probably won’t gravitate to an overweight video gamer as a best friend. Remembering that birds of a feather flock together, the so-called "groundbreaking" news that overweight friends gain more weight over time is really just old hat … or better said, old fat.