T Nation

Contagious Habits: How Obesity Spreads


A few years ago, Nicholas Christakis and James Fowler made a striking discovery about obesity: it spreads from person to person, much like a contagious virus. They were able to demonstrate this by mining the data sets of the Framingham Heart Study (FHS), a longitudinal survey that has revealed many of the risk factors underlying cardiovascular disease. Because the FHS noted each participantâ??s close friends, colleagues, and family members, Christakis and Fowler were able to recreate the social network of the town, to see how everyone was connected to everyone else.

And this is when they made their remarkable discovery about weight gain. According to the data, if one person became obese, the likelihood that his friend would follow suit increased by 57 percent. (This means that the network is far more predictive of obesity than the presence of genes associated with the condition.) If a sibling became obese, the chance that another sibling would become obese increased by 40%, while an obese spouse increased the likelihood that the other spouse would become obese increased by 37%.

The Christakis/Fowler work is an important reminder that Donne was right: No man is an island/entire of itself. Instead, we are all plugged into a vast network of social contacts and cultural norms. While we think ourselves as autonomous individuals, that autonomy is severely constrained by those around us.

But this longitudinal data â?? itâ??s a birdâ??s eye view of human life â?? still begs the question: How do other people influence us? Why does an obese friend make us so much more likely to gain weight? Why do the habits of others influence our own habits?

A brand new paper by researchers at the University of Colorado at Boulder helps answer these important questions. The scientists begin their paper with a compelling hypothetical:

Consider the following: Your friend Lucy, who is about 25 pounds overweight, e-mails you pictures from her recent vacation. After you look at Lucyâ??s pictures, the ofï¬?ce secretary comes by with a plate of cookies. Will exposure to someone who is overweight inï¬?uence how many cookies you eat?

When asked this question, a majority of people insist that the picture of Lucy would reduce their consumption of cookies. (31 percent believed that Lucy would inspire them to abstain entirely from the sweet treat.) This is how we like to think ourselves: independent minded creatures, able to learn from the unflattering photographs of others.

Alas, our responsible self-image is entirely divorced from reality. The Colorado researchers demonstrated that, in several situations, the exact opposite occurred: When people were exposed to pictures of someone who was overweight, they ended up consuming far more calories.

In one of their experiments, researchers asked random strangers walking through a lobby at the University if they would take a quick survey. The surveys had photos of an overweight person, a person of normal weight or a lamp. After completing the survey, the researchers asked the subjects to help themselves from a bowl of candy. Those who were exposed to the picture of the overweight individual took, on average, 3o percent more candies than those exposed to the control pictures.

In a second study, subjects were invited to do a cookie taste test. Those who were first exposed to pictures of overweight individuals ate twice as many cookies as those were exposed to images of trees, fishbowls and non-overweight subjects. This effect held when participants said they had a goal to maintain a healthy weight. As the researchers write, â??Exposure to a negative stereotype [seeing someone who is overweight] can lead to stereotype conducive behavior.â?? Even when we are determined to maintain our diet, we are still subtly undermined by the choices and habits of everyone else.

This research builds on a 2010 paper by Northwestern psychologists that demonstrated that people anchored their own portion sizes to the portions around them. If weâ??re surrounded by people eating a supersized Big Mac meal, then weâ??re much more likely to do the same; our hunger is influenced by the hunger of others.

Taken together, this research begins to explain how obesity moves through a social network. It turns out that the habits of others shape our own, that we unconsciously regress to the dietary norms around us. Because weâ??re not particularly good at noticing when weâ??re sated and full â?? the stomach is a crude sensory organ â?? we rely on all sorts of external cues to tell us how much to eat. Many of these cues from other people, which is why our eating habits are so contagious.


You can't have a supersized Big Mac meal in 2010 seeing how it was discontinued years ago.


Choice and will paper is an individual trait, and it doesn't spread, unfortunately.


The problem I have with this study is that it seems to be saying that what you eat is what determines your size. I have thought this before but have read books and studies that claim it is not that simple. First thing I read about this was "Rethinking Thin" by Gina Kolata(sp?).

But I am willing to check out this book these guys wrote based on this study "Connected" right?


Eating is generally seen as a social act. As such, it is of little surprise that friends/family influence what each other eat, even if it is unintentional. What is interesting is what friend's size is more important than spouse or sibling (if I read that right).

Interesting about the other studies, would like to read more.


When I see my friends getting fat, it motivates me more to keep training.
In fact, meeting up with an old (and I do mean looking old and fat) friend was what inspired me to get back in the game after 8 years of sitting on my ass.


The cure is one blue peanut M&M.....but it only works if taken after 45 minutes of hard exercise.


Glad to be of service.



I went to a get together not long ago, where I found some old teammates of mine who used to be stellar athletes resemble something along the lines of people who never exercised a day in their lives. I had some of their girlfriends and wives come up to me asking what it is that I did to stay in shape. I sat and looked at them, pounding away beer after beer, eating cake/cookies/chips and all sorts of shit that made me want to be sick. I sat there and thought, my God, how ashamed would I be if I was with a girl who had to ask someone else to find out how to get me back in shape.


anyone know where I can watch the full episode of this: http://www.youtube.com/watch?v=bOkWTLKI3FU


Yes hijack


There are similar findings for other behaviors also, alcoholism for e.g., even amongst identical twins.


I don't hate fat people, but I really do hate that one in that clip.

She would be the worst wife, nit because of her body, but the way she quickly twists whatever people say.
Comparing the instances of obese people being asked to pay for two seats and segregation on buses is inane. The thing about two seats may be good for some late night talk show jokes, but it does stem from the simple fact that this person is too large for one airline seat. Not everything has to have some ulterior racist/sizeist angle.
Bringing in the KKK was just stupid.


hahaha =D

Theory busted in one fell swoop!


I can see how the reverse could be true also. Me seeing how it could be true doesn't make it Scientific Fact obviously but in my HUGE social network I do see alot of peer influence on working out in general. As in... alot of us exercise, those that do encourage each other, exercise together, like each others gym checkins on facebook (LOL!) etc.


I remember reading somewhere along time ago that our personality is made up mostly of the 3 closest people to us. Basically it said how we take our own personal thoughts and influences and combine that with the traits of the 3 peole we spend the most time with to form our own behaviors.

I'm not sure I agreed with it to much but I do notice how even dumb shit that some of my friends say and do has rubbed off on me from time to time.


From the perspective of a guy who once was a giant fatty I can see how these results came to be. When I didn't care about what I ate, how I looked or how often I need to buy jeans, the way others ate and looked gave me an excuse.
For instance, seeing someone who was really fat gave me the excuse that "well they're fat, it's becoming the norm so F it, I don't care" Or when eating out, someone orders a giant pile of crap food my thought was "well they're eating like that I can too".
Folks remember we're the 1%ers when it comes to training and eating habbits, most of us don't think like the normal person in that regard.


^^^These are Bullocks and they have no Bollox...

carry on!


It wears at you. I'm at college and I have no social life if I don't eat meals at dining halls or go out drinking or stay up too late with others. Now where's the tradeoff to staying moderately healthy? I don't know, but I guess as a collegiate athlete it's a hard balance.


My mom use to tell me, if I want to see how I am, look at my friends.


I do believe this..

Alas, our responsible self-image is entirely divorced from reality. The Colorado researchers demonstrated that, in several situations, the exact opposite occurred: When people were exposed to pictures of someone who was overweight, they ended up consuming far more calories.

maybe because we train all of us, we are different when we see a fat person
but i'm assuming the people they tested are average, average is maybe has a gym membership and walks on treadmill or has none.