Are Your Friends Making You Fat?

Oct 21, 2013 7:21:24 AM

causes of weight gain

While there’s no doubt that the people we spend our time with play an important role in our lives, research shows that when it comes to obesity, our friends are significantly more influential than any other people in our lives, including spouses. In fact, much like a virus, obesity is described as being ‘contagious’ among groups of friends, to the extent that an individual has a 171 percent increased chance of becoming obese if they have an obese close friend. Here, we explain the connection between friendship and obesity, and how we really are the company we keep.

The Spread of Obesity Within Social Networks

It has been known for years that the likelihood of being overweight increases among family members, in part due to a combination of sharing the same genes and living together. Similarly, spouses tend to gain weight together as a result of often sharing the same lifestyle. However, the Framington Heart Study, a longitudinal investigation into a large social network, showed that people were most likely to become obese when a friend became obese.

The study involved a detailed analysis of a large social network of 12,067 people, closely followed for 32 years from 1971 to 2003, and included data about who was friends with whom, as well as who were spouses, siblings and neighbors, and how much people weighed at various times over three decades. The participants’ chances of becoming obese increased by 57 percent if a friend became obese, whereas there was no effect if a neighbor became obese, and family members had less of an influence than friends. The greatest influence of all was between mutual close friends, where if one became obese, the other had a 171 percent increased chance of becoming obese too.

Why do Friends Have Such an Impact?

The first conclusion might be that the shared environmental factors between friends' results in shared obesity, however the researchers point to how obesity spreads from one person to another, rather than becoming evident in friends simultaneously. Furthermore, spouses share much more of their physical environment than friends, so the connection must be explained by another factor.

The researchers explain how pairs of friends and siblings of the same sex had more influence on the weight gain of the other, compared to the pairs of friends and siblings of the opposite sex. This finding also provides support for the social nature of the induction of obesity, since it seems likely that people are more influenced by those they resemble than those they don’t. The key difference is that friends identify with each other, more so than they identify with their family and spouses, therefore friends affect each other’s perception of fatness. Essentially, when a close friend becomes obese our perception of obesity changes - you change your idea of what is an acceptable body type by looking at the people around you, and those you identify with the most are your mutual friends of the same sex.

Similar analyses of friendship groups and weight have also been carried out amongst groups of adolescents, which show that the social ‘contagion’ of obesity may start from adolescence, when individuals are keen to disassociate themselves from their parents and begin to identify more with their friends. A study in the Journal of Adolescent Health found that overweight adolescents were more likely to have overweight friends than their normal weight peers, and another study by Loyola University Chicago showed that school students were more likely to gain weight if they had friends who were heavier than they were. The second study also addressed the possibility that initial friendship selections were made on the basis of weight - that is, that overweight people chose overweight friends and thinner people chose thinner friends. However, even when taking this into account, there was still a significant link between weight changes and a student’s circle of friends.

exercise with friends

Social Networks & Weight Loss

However, before you start avoiding your overweight friends, these same studies show that social networks can have a positive effect on your health too. Firstly, friends are good for your overall health and secondly, healthy habits can be contagious too. So, while you’re on your weight loss journey and becoming healthier, do not underestimate the positive effect this can have on your friends. While the Framington Heart Study established strong links between social relationships and obesity, the authors state that the opposite is just as likely to happen. This was shown in the Loyola study, whereby if a borderline overweight student had leaner friends, there was a 40 percent chance that the student’s BMI would drop in future. So, you could be helping your friends as well as yourself by adopting a new healthy lifestyle. Furthermore, many other studies show that people are more successful at losing weight and keeping it off when they do so with a friend or family member, so you’re more likely to succeed if you do inspire a friend to lose weight alongside you.

These findings therefore show that while obesity can spread among social networks, the opposite is also true, as weight loss and adopting a healthier lifestyle can also have a ripple effect among social circles. However, with positive changes there is the added motivation effect; people can inspire and encourage each other, providing support and setting goals, and holding each other accountable to enhance weight loss outcomes. So, just as friends affect each other’s perception of fatness, they can affect each other’s perception of weight loss capability. When someone loses a significant amount of weight, this changes their friends’ ideas of what they, themselves, could be capable of too. So, while you’re on your weight loss journey and becoming healthier, remember that you’re also inspiring your friends right now!


Do you think obesity is contagious? What about healthy behavior – have you already inspired others to pursue their own weight loss journey? Please share your thoughts with us on this topic below!

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