Obesity, Thinness: Often Shared

Craig Stoltz Health Guide
  • You've probably read or seen news reports by now saying that obesity has been found "contagious." This is based on a fascinating study appearing in the New England Journal of Medicine. It's very well-done and one of the more significant findings in recent obesity research. 


    But "contagious"? No need to strap on one of those N49 surgical masks if you wind up sitting next to a big guy or gal on the plane. Let's dig in.


    Bottom line first


    People tend to take subtle cues from their friends and family, and appear to determine acceptable body weights and health behaviors based on observation and modeling.

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    This study in around 50 words

    Researchers studied about 12,000 people connected in social networks (spouses, siblings, freinds, neighbors, etc.) over three decades. They compared body mass index changes among members of these groups. Both obesity and thinness changes were shared by closely related people, regardless of geography or genetics.

    Yes, but. . . 

    Not many caveats here. The group studied was big and followed a long time, the researchers controlled very well for potential "confounders," the results are published in a major peer-reviewed journal, and there was no behind-the-scenes funding that could distort the findings.

    As usual, however, finding links does not prove cause and effect. 


    Useful observations

    A person's risk of becoming obese was 57 percent higher if a close friend became obese, 40 percent higher when a sibling did, 37 percent higher with a spouse. 

    Similar numbers apply to those who lost rather than gained weight.

    The links weakened but continued for both one degree of separation (friends of siblings, say) and two degrees (friends of spouses' siblings, say). Beyond that, the association of changes in body mass disappeared. 

    With mutual friendships, the link was even more pronounced--the chance of BMI linkage when one friend lost or gained weight was 171 percent higher. 

    The links were stronger by gender: men seemed to be influenced more by men, and women by women. This could explain why the spousal links were not as strong as the friend links. 

    So what are you going to do about it?

    The researchers speculate that there may be useful public health implications: Changing health behaviors and weight in one well-connected individual can have positive ripple effects through the community. (Of course, the reverse would be true too.)

    For individuals, however, the findings dovetail nicely with something that other research has found: People trying to lose weight and live healthier are more likely to succeed when they have social support.

    Learn more 

    Check out our Diet and Exercise center, where an active community provides support for members trying to eat healthier and get more exercise.

    Calculating your body mass index (BMI) is a useful (if rough and flawed) way to raise awareness about this one aspect of your health.

Published On: July 26, 2007