Are your friends making you fat?
While doing some research for an essay on social psychology, I came across a fairly recent article about a paper1 which reported on a study of how social networks influence obesity. The paper’s authors Nicholas Christakis and James Fowler found that friends have the greatest influence, followed by siblings, followed by spouses, with neighbours showing no significant effect. They also found that friends and siblings of the same sex seemed to influence each other’s obesity more than did those of the opposite sex. However, spouses did not seem to have as much influence as mutual friends, suggesting that the opposite-sex and friendship influences may cancel each other out.
One conclusion which may be of further interest to you my loyal readers is that, rather than being the result of behavioural imitation, the spread of obesity may be more closely related to the perceived acceptance of obesity in those we hold in high esteem. That is, it seems that your belief about whether or not being obese is ok, is influenced more by your level of esteem for a friend, and how much you think they accept their obesity, than it is by what they actually eat. So it’s not that one obese person eats hamburgers all the time and so their friend starts doing it too. No, it seems that the obese person believes it’s ok to be obese, so the friend’s beliefs shift to be in agreement. They may not eat the same things but they are both likely to put on weight.
Thankfully the study also showed that thinness is contagious too. Perhaps not equally so, but none-the-less the effect is there. So if you want to lose weight the usual good advice still applies, but you’re more likely to be successful if you have healthy skinny friends whom you hold in high esteem.
Amusingly the study shows that distance is irrelevant, so it’s basically a nice piece of evidence in favour of being my friend, where ever in the world you may be. 
1: Christakis N. A., Fowler J. H. (2007, July). The Spread of Obesity in a Large Social Network over 32 Years. The New England Journal of Medicine, 357(4), 370-379
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August 13th, 2007 at 4:39 pm
Happy Birthday, my esteemed skinny friend!
August 14th, 2007 at 1:21 am
That makes me wonder how much that is the case with other beliefs… I know that we pick up filters to our perception from those we are around, but I wonder to what extent we also pick up their “under the surface” beliefs, ie ones you aren’t generally vocal about, unlike religion and politics.
August 14th, 2007 at 7:56 am
I read the linked article and those statistics are crazy! Increases of 57%, 171% and even 40% if a sibling becomes obese. It’s funny to me just how much of social creatures we obviously are.
Nice selling point on your friendship for all the ladies in particular!
I wasn’t on the fence before, but now I’m a friend for life… 
August 14th, 2007 at 8:56 am
Thanks Claire
That probably happens a lot Jason. For example most of my male friends don’t talk about fashion much, yet a lot of them wear similar clothes. I guess that’s as visible an indicator as weight.
Thanks Jenny. Just don’t pay any attention to my breakfast plate piled high with scrambled eggs and bacon
August 16th, 2007 at 12:18 pm
August 16th, 2007 at 12:20 pm
I think it’s sibling competition for food. Even with friends, I think.
It’s like instinct, or something.
Like if there are 3 siblings and a plate of fried chicken, they try to get more than the other sibling.
I heard it from this psychological documentary or something.
August 16th, 2007 at 12:29 pm
People say “you are what you eat.” People also say you may be evolving into characteristics or qualities of the 5 people you spend the most time with. Ask yourself if you’re a leader (trendsetter) or a follower. Think back to elementary school and your habits and friends then. Compare your history to how you feel now and whether your current friends share your values and eating habits. Some people may be drawn to you because they seek to make positive changes in their lives and you represent a great role model.
August 16th, 2007 at 12:54 pm
No doubt that does happen Claireanne. And for me it was also about being the guy who could eat anything and not put on weight, so many of my friends would regularly give me their leftovers whenever we’d go out for dinner together. If someone with a slower metabolism than mine tried that they’d probably be huge
Liara, I think I’ve been both a follower and leader at different times in my life. Leading got some of my friends into trouble because I could eat anything without putting on weight and so I ate anything without concern for its effects on my health. And following lead me to adopt healthier eating habits before my poor habits lead to any serious illnesses.
August 24th, 2007 at 12:02 pm
Mark, I read this post almost two weeks ago and I still find my head returning to it. A sure sign of a good post. What keeps me coming back is that same sex friends have such a larger impact than spouses. I would have thought the opposite because you eat and recreate so much with your spouse. Followed by the fact that this is the person you are intimate with, which would further lead me to believe that you hold each other to the same standards as yourself. Shows you how much I know!
August 24th, 2007 at 1:30 pm
The researchers suggest that same sex friends have more influence because we’re influenced more by those we resemble (though I’d say even more so by those we’d like to resemble). No such effect for most spouses I suppose. I’d have thought the same as you (especially since I have one friend who put on a lot of weight after he got married. His wife was already overweight. But in their case I think it was just that she’s an awesome cook).
August 25th, 2007 at 1:03 am
Actually, I’m not surprised about the same sex thing… like Mark said it’s who you are concerned with comparing yourself. It’s also probably who you can relate to in that area more… different things have different impacts on men and women when it comes to physical fitness.
Oh, and getting married tends to make people put on weight, though it’s generally not because of the quality of the cooking of the new spouse (although that can certainly make a difference… my wife is an excellent cook!), but rather because they lose some of the drive to maintain their appearance for the benefit of the opposite sex. If you’re no longer looking to capture the attention of a special someone, because you already have it, you don’t worry quite as much about your appearance (at least, that’s usually the case).
August 25th, 2007 at 3:58 am
The other piece with same sex friends is the competitive nature, even in close friendships. For example, I have a very strong competitive streak. So if Jenny is running a mile in 8 minutes, you better believe I’m working my hardest to run it in 7 1/2 minutes. The great thing about Jenny is that she just watches me and laughs (and then proceeds to pass me again). It’s a lovely balance - and keeps us both motivated.
I think Mark nailed it for the other end of the spectrum.
August 25th, 2007 at 6:05 am
hah, hah! Speak for yourself E! The thrill of a challenge - my specially chosen and most humbly offered gift to you
You do realize it is in no way fair though, right? (the huge difference in stride length and all…you’re actually working much harder than me, so see? you win!
)
Sorry for the personal conversation… I have nothing of substance to add to the discussion.
September 7th, 2007 at 4:17 pm
Before you decide to attribute blame for something you don’t like about yourself, you first must perceive something is wrong. To feel this way is to discover reason to distance yourself from baseline self-acceptance. Notice how the question that started this posting encourages readers to step further away from the real issue that may beg for attention…
September 7th, 2007 at 5:48 pm
Very true Liara, though I hope no-one would consider the title anything less than tongue-in-cheek. But you are right, the research does show what we already know; that some people are more willing to accept the attitudes they see in others, rather than addressing their own attitudes, and themselves as a whole, in a more positive way.
September 9th, 2007 at 4:52 am
But, blaming others (rather than my decision just to polish of the carton of icecream-oops!) is so much more fun! I guess that is something we all have to contend with. Personal responsibility is hard, in most facets of life.