Social Networks Do Not Explain Physical Activity Levels and Obesity in Younger Adults

Previous studies have suggested that obesity is ‘transmitted’ in social networks.

A study by Janette Leroux (Canadian Obesity Network Bootcamper, class of 2012) and colleagues from the Queen’s University, Kingston, ON, published in PLoS One, now explores the relationships between ‘perceived’ physical activity, obesity, and social networks in about 2,000 participants in the Montreal Neighborhood Networks and Healthy Aging study.

In younger adults (<55 years old), although physical inactivity increased the odds of obesity and of having a higher number of perceived exercising close ties (alters), physical activity did not appear to mediate the association between obesity and the exercising behavior of alters.

Among adults older than 55 years, physical inactivity likewise increased the odds of being obese while having a higher number of exercising alters slightly reduced an older adult’s chances of being obese. However, in contrast to the younger adults, in this older population, a small part of this physical inactivity did appear to be ‘mediated’ by the association between exercising alters and obesity.

Based on these findings, the authors suggest that at least for older adults, social networks may be important determinants of physical inactivity, a finding that may suggest the usefulness of community interventions to promote physical activity and reduce obesity in this population.

However, the authors are also careful to point out that, given the cross-sectional nature of this study, one should not make inferences about causality. Thus, the study cannot answer the question, whether or not active people simply tend to hang out with other active people or whether active people actually ‘transfer’ their higher activity levels to their inactive friends? Nor does it answer the question, whether hanging out with inactive people slows down folks who would otherwise be active – after all, this relationship, if it indeed exists, could well work in either direction.

The authors also note that because of the self-reported nature of activity levels, this study has more to do with ‘perceived’ rather than actual activity levels (hence the title of the paper). After all, it may well be that skinny folks are over-reporting their activity levels, whereas, obese individuals are perhaps underestimating the amount of work it actually takes to move their larger bodies around.

The implications of the association between inactivity and obesity are also unclear – after all, is it (perceived) inactivity that leads to obesity or does obesity lead to (perceived) inactivity?

Thus, it may be fair to conclude from this study that social networks are unlikely to account for any relationship between physical activity (or inactivity) and obesity levels in younger adults and that in older adults, although such relationships may exist, causality remains to be determined.

My take away from this study, is that the relationship between physical activity (or inactivity) and obesity, whether in social networks or otherwise, remains far more complex and less straightforward, than many of us would like to think.

This is not to say that increasing physical activity and reducing inactivity does not have its health benefits. But questions certainly remain whether a) social networks can indeed be harnessed to promote physical activity and b) an increase in activity (or reduction in inactivity) would in fact translate into lower obesity rates.

Perhaps, none of this matters, as greater physical activity and less sedentariness can certainly promote health at any size.

Edmonton, Alberta

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