Are Your Friends Making You Fat?

That question was on the cover of today's New York Times magazine. The article was titled Is Happiness Catching? and was by CLIVE THOMPSON.

This article touches on somethings that have already come up in my classes this semester. One has to do with tastes and preferences. This article, although very long, gives us at least one way tastes can be formed, through friends and social networks (as I said in class, economists don't normally try to explain where tastes come from but the article does quote an economist). The other has to do with correlation (or association) vs. causality. As you will see below and in the article, there is some disagreement over whether or not the researchers found a causal link (for example, my friend getting fat caused me to get fat) or if it was just an association (or correlation) if both friends lived near a McDonalds that just opened up (one friend did not cause the other to get fat-they both got fat for the same reason). Also, my last post raised the question of why we have been getting more obese.

Social scientists Nicholas Christakis and James Fowler found that

"...good behaviors — like quitting smoking or staying slender or being happy — pass from friend to friend almost as if they were contagious viruses... [friends] influenced one another’s health just by socializing. And the same was true of bad behaviors — clusters of friends appeared to “infect” each other with obesity, unhappiness and smoking."

Here are some examples:

"A 2000 study of dorm mates at Dartmouth College by the economist Bruce Sacerdote found that they appeared to infect each other with good and bad study habits — such that a roommate with a high grade-point average would drag upward the G.P.A. of his lower-scoring roommate, and vice versa."

"When a Framingham resident (whose residents were part of a long term health study) became obese, his or her friends were 57 percent more likely to become obese, too. Even more astonishing to Christakis and Fowler was the fact that the effect didn’t stop there. In fact, it appeared to skip links. A Framingham resident was roughly 20 percent more likely to become obese if the friend of a friend became obese — even if the connecting friend didn’t put on a single pound. Indeed, a person’s risk of obesity went up about 10 percent even if a friend of a friend of a friend gained weight."

It is not just weight or obesity that can be affected this way. Drinking, smoking, how altruistic you are and how happy you are might also be due to social networks. Gender has an impact. How men and women affect each other can be different. Also, how co-workers affect you can be different from how friends or relatives affect you.

More key exerpts:

"...the simple peer-pressure explanation doesn’t work as well with happiness or obesity: we don’t often urge people around us to eat more or implore them to be happier. (In any case, simply telling someone to be happier or unhappier isn’t likely to work.) Instead, Christakis and Fowler hypothesize that these behaviors spread partly through the subconscious social signals that we pick up from those around us, which serve as cues to what is considered normal behavior."

"...[it] might be driven partly by “mirror neurons” in the brain that automatically mimic what we see in the faces of those around us — which is why looking at photographs of smiling people can itself often lift your mood. "

"...a behavior can skip links — spreading to a friend of a friend without affecting the person who connects them."

"But they theorize that people may be able to pass along a social signal without themselves acting on it. If your friends at work become obese, even if you don’t gain weight yourself, you might become more accepting of obesity as a normal state..."

"This might all be due to "evolutionary roots" "Tribal groups that were tightly connected were likely more able to pass along positive behaviors than those that weren’t.""

Not everyone agrees with the study's findings. Some scienticists say that maybe fat or happy people like to hang out together because in general, we like to be around people who are like us, so it might just be correlaton (or association), not causation. Also, it could be the environment that causes friends to get fat at the same time. Maybe they all live to close to a McDonalds that just opened up. One counter study found that if a high school student was tall, his or her friends were more likely to be tall. You can't catch height from someone else.

But Nicholas Christakis and James Fowler have an answer for that. They say other studies used a "looser" mathematical model (not sure what that means here). But they also found that if person A considered person B a friend but not vice-versa, if person B got fat, then it increased the chance of person A getting fat. But if person A got fat it did not affect the chances of person B getting fat. So if something in the environment caused one person to get fat (like a new McDonalds), it should affect both people. But it did not always do so. That means there has to be another reason. Maybe what you do is affected by what you think other people think is okay.