"You are the average of the five people you spend the most time with." -Jim Rohn Have you ever heard this quote? If you haven't you would probably tend to agree with the statement as a lot of other people have as well. I mean it only makes since people, right. Other influence us in our choices of actions, thoughts, and words. And in many cases we probably allow others to influences without them even trying.

For example, if you are aware that your neighbor is a christian than you are probably going to watch your language a bit closer when you interact them without being asked. Or  how about when you visit your grandmother you have a tendency to dress a bit more conservatively. These people do influence and they aren't even the ones you spend the most time with. So it's only natural to think that those closest to us do influence us in a variety of ways.

But one thing you might not have thought about is that this influence does not only manifest in psychological aspects, but also physical ones. This is what this week's "Study of the Week" shows us. That others health choices or health status may actually influence our own choices related to health. It is wildly unbelievable, but the data is clear that it does happen.

Imagine that you may be the best parent, sibling, or mentor, but because you live an unhealthy lifestyle you are indirectly having a negative affect on your children, sister, brother, or student. This is definitely a phenomenon we need to be aware of and considering that there are more overweight adults than underweight just the fact that we are constantly surrounded by overweight people may be contributing to the growing number of obese people.

Read on. . .and have your mind blown away!


The Spread of Obesity in a Large Social Network Over 32 Years

by Nicholas A. Christakis and James H. Fowler

published 2007 in The New England Journal of Medicine


Researchers note that the level of obesity has increased from 23 to 31 percent and that 66 percent of adults are considered overweight. Proposed explanations for this obesity epidemic include societal changes which have led to inactivity and surplus food consumption. Researchers note that genetics cannot be used as a broad explanation for this obesity growth because it has occurred over a variety of ethnicities and also many socioeconomic categories. Which means that this epidemic is being spurred on by a number of social and environmental explanations.

Researchers note that obesity has been stigmatized in the past, but that this stigma may be lessening. Obesity is becoming seen as a product of voluntary choices or behaviors. Researchers states that people who are embedded in social networks are influenced by the appearance and behaviors of those around them which suggests that one individual gaining weight may influences others to do the same. For example having friends that are obese may make someone more tolerant of being obese or perhaps influence you to adopt certain behaviors. In addition researches note that it is plausible that physiological limitations occur in which areas of the brain corresponding to certain actions may be stimulated by seeing others doing that certain action, for example eating. Finally researchers note that infections causes of obesity are possible.

The researchers wanted to evaluate a network of 12,067 people who were repeatedly measured over a 32 year period. Examining aspects related to the spread of obesity that included existence of clusters of obese people in the network, association between a person's weight gain and weight gain among his or her social contacts, dependence on this association and nature of social ties, and the influence of sex, smoking, and geographic distance.


Researches used data from the Framingham Off Spring Study which began in 1971. Researchers state that there has been minimal follow up loss from the 5,124 subjects other than that due to death and 10 people who left the study electively. In 2002, another group of individuals was introduced to the study consisting of 5,124 subjects. Participants in the Framingham Offspring Study undergo physical examinations and written questions regularly.

Researchers labeled the 5124 subjects as egos. Any person the ego was linked to serve as alters. There was 12,067 living egos and alters connected during the study. Researchers entered information about this group into a computer which was obtained via tracking sheets used during the study period. These sheets provided information about relatives, a close friend, and home addresses at each examination that took place every three years. The researchers then placed parameters on their data to limit the data to significant social ties.

Researchers then used Kamada-Kawai algorithm in Pajek software to graph the network data. They also checked whether the data conformed to theoretical network models. Obesity was defined as a BMI of 30 or more. The researchers used a variety of statistical analysis methods to analyze the data (frantically I could list them all for you, but some are over my head and probably serve little significance to type them out).


Researchers reported that in all examinations of the subjects took part in the risk of obesity among alters who were connected to an obese ego at one degree of separation was 45% higher in the observed network than a random network. The risk of obesity was 20% higher for alters who were two degrees of separation from the obese ego and 10% higher for alters with three degrees of separation. Researchers note that by the fourth degree of separation there was no relationship between an ego's obesity and the alter's obesity.

Researchers reported that results suggest that social distance plays a stronger role than geographic distance in the spread of behaviors and norms of associated obesity.

Researchers reported that an ego who stated that an alter was his or her friend the ego's chances of becoming obese increased by 57% if the alter became obese. But the type of friendship also played a significant role. If the alter and ego were mutual friends the ego's risk of obesity increased by 171% if the alter became obese. There was no statistically meaningful relationship when friendship was not perceived by the ego.

Researchers note that the sex of the ego and alter was important. Same-sex friendships increased the probability of obesity in the ego by 71% when the alter became obese. But no positive association was seen with opposite sex friends.

Researchers report that one siblings change of becoming obese increased by 40% when another sibling became obese. Again this association was more significant between same sex than opposite sex siblings.

Researchers report that in married couples if the alter became obese the spouse was 37% more likely to become obese.


The researches do propose several explanations for the findings of their analysis, but can not definitely explain the phenomenon. The researchers conclude that the spread of obesity in social networks appears to be a factor in the obesity epidemic. They also note that it suggests that it may be possible to harness the same force to slow the obesity epidemic. It also highlights the need for addressing obesity both clinically and socially.


Well wasn't that an awesome read!!! I couldn't believe it myself when I read the paper for the first time. It absolutely changed the way I think about obesity and why people become obese. It adds another psychological layer to this growing problem.

But I need to be going so I can work on that physics homework so I'll keep this wrap up short.

Simply this study shows us that our relationships and whether or not those who we have relationships with are obese may in fact contribute to our own weight gain!

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