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The role of society in shaping our view on weight loss

Our propensity to gain weight now seems, at least partly, to be determined by the genes inherited from parents, and some research even suggests that viruses and gut bacteria may also play a role. Now, researchers around the world are investigating whether obesity is contagious, not transmitted through viruses or bacteria, but through our social networks.

This was first used to describe the power our peers and close circle have in shaping our outlook and behaviours, but has increasingly been turned to as a possible explanation for the tripling of obesity rates across the world since 1975.

Globally, around two billion adults are overweight or obese. And if the people around us are heavier, we are more likely to be heavier. Self-guided weight loss was just as effective as the Weight Watchers intervention, however. According to the authors, changing our eating and exercise behaviours can affect those around us both positively and negatively. In a landmark study that brought the idea of obesity as a social contagion to the public, investigators found that it was friends, and even friends of friends, who could lead to you adding on the kilos.

In fact, the magnitude of the effect seemed to be even larger than the role of genes. The study, published in the New England Journal of Medicine, applied advances in mapping theory and technology to the public health sphere. Using the three decades of data from the Framingham Heart Study, the US researchers tracked the relationship between weight gain and friends and family among the 12,000 participants.

Unsurprisingly, the entire network became heavier over the course of the study. But after controlling for potentially confounding factors such as socioeconomic status, gender and predicted weight gain with age, the authors concluded that obesity seemed to be spread through social ties.

Because participants were asked at the start of the study to nominate friends at the outset, and the investigators had access to medical data from three generations of families, they were able to map out the social connections and examine where obesity clustered over the generations. When trying to understand whether weight gain is socially contagious, it is important to note that friends and family members often share the same environment. If this environment has little access to grocery stores, poor pavements for walking and few outdoor areas to do activities, then it would be no surprise that these friends and families tend to put on weight together.

Interestingly, the study revealed that physical proximity was not particularly significant. Even more compellingly, they found that if both participants nominated the other as a friend, the risk of one becoming obese was threefold higher if the other became obese. Could the explanation be that birds of a feather flock together? Humans have a tendency to be drawn towards people who are similar to them, whether it is in values, behaviours or appearance.

A study of 617 US adolescents found that teens who were overweight were twice as likely to have overweight friends, and it is quite plausible that people who are overweight are drawn to other people who are overweight because they enjoy the same activities, eating habits or the subconscious familiarity. Given the spread of obesity through the social network regardless, the authors suggest that the explanation may lay in our friends changing our perception of what is normal.

This was further illustrated by the finding that weight gain was greater among friends of the same sex, presumably because they are more likely to be models for our own behaviour.

Investigators asked the women, who had moved countries within the last month, about their perception of their current weight and their ideal weight at the start of the study and again two months later. After only two months of living in the United States, where body weight is higher than their home country, the women perceived their bodies as smaller and at the same time, their ideal body size increased.

The shrinking gap between current and ideal body size was also correlated with an increase in BMI, suggesting that being around bigger people makes you more comfortable with being bigger On the flip side, a 2005 study of 119 young women found that being around a thinner than average person increased body dissatisfaction, even among those who had high self-esteem and were perceived by others to be attractive. The potential for social networks to help us become a healthier weight was emphasised by Professor Fowler and Professor Christakis.

For starters, replication is vital in science, and yet the uniqueness of the Framingham Heart Study, both in terms of its size, duration and information about friendship ties, meant that it would likely be too expensive to repeat. Follow up analyses have suggested that the impact of friends and family on weight gain may have been less than the authors originally found.

Other critiques argued that it was not possible to differentiate social contagion from homophily based on their observational data. Then in January this year, Californian researchers published a unique paper in JAMA Pediatrics, which tracked the weight of military families as they moved across the country.

The economists explained that if obesity was contagious, then policies should lean to targeting social networks, specifically targeting well-connected individuals to make the most of their wide-reaching effects. Social contagion would also favour interventions that interfered with potentially harmful changing norms and attitudes, they wrote. On the other hand, if obesity is spread through a shared environment then money and resources should be aimed at the built environment or policies.

Luckily, the way military families move across the country offered a natural experiment. The fact that the decision to move areas is in the hands of the military, not the families themselves, makes the case that any correlations between weight and the surrounding area are not due to self-selection and homophily.

Moreover, the investigators were able to factor in how much time the families spent living on the installation or within the community, as a proxy for how much they were exposed to the obesity rate in the community. Among the 1500 military families who participated in the study, those who were sent to live in a county with a higher obesity rate were more likely to be overweight or obese than those sent to counties with lower obesity rates.

But while this type of study appears to control for homophily, it is possible that there was something about the environment that caused both the native population and the new families to gain weight. To account for that, Dr Datar and Dr Nicosia tracked both objective and subjective measures of the shared built environment.

They found that the association remained regardless of how close the population was to a park, grocery store or recreational facility, their incomes and whether the area was perceived as being safe, easy to move around in and be active in.

Can you catch obesity from your social network?

One explanation for social contagion is that individuals mirror the behaviours of those around them. However, the authors noted that mirroring was more common when individuals admired those whose behaviours they were emulating. However, for endocrinologist Emeritus Professor Joseph Proietto it is important to not overstate the role that others have in our own weight gain.

The obesity expert stresses the importance of genes and epigenetics as the predominate factor behind weight-loss. Her own research into this revealed that women who perceived others as having a healthy diet and lifestyle were more likely to engage in those behaviours themselves. Be the First to Comment! Notify of Notify of new replies to this comment Notify of new replies to this comment Stay connected with the Medical Republic.