Women & heart disease: is obesity contagious?


by Carolyn Thomas  @HeartSisters

Having a tough time losing weight as part of your heart-healthy lifestyle? Take a look at your friends.

Close friends can influence your weight even more than genes or your family members, say researchers reporting in The New England Journal of Medicine. The study, co-authored by longtime collaborators Dr. Nicholas Christakis and Dr. James Fowler suggests that obesity isn’t just spreading – it may be as contagious between close friends as the common cold.

Researchers followed over 12,000 “densely-connected” people (families and friends of participants in the Framingham Study, a major American heart study between 1971 and 2003).

913342852_111ae68b5c_mHere’s what they found: in pairs of people in which each identified the other as a close friend, when one person became obese, the other had a whopping 171% greater chance of being obese too. Study co-author Dr. James Fowler f  the University of California at San Diego wrote:

“You are what you eat isn’t the end of the story. You are what you – and your friends – eat.”

Researchers were particularly interested in these findings:

  • people who share similar lifestyles tend to become friends
  • geographic distance between friends in the study seemed to have no impact
  • friends who saw each other infrequently were just as influenced by each other’s weight gains as those who  shared frequent meals
  • people were much more likely to pattern their own behaviour on the actions of people they considered to be close friends
  • friendships had to be mutual to show weight gain influences: if you had named another person as a friend, and your friend became obese, than you were more than 50% more likely to get fat too. But if your friend had not named you as a friend, and you became obese, it would have no significant impact on your friend’s weight.

What if your spouse gains weight?  Hubbies may share a bed and a kitchen table with you, but the researchers found a much smaller risk of gaining weight — a 37% increase — when one spouse became obese.  And your siblings share genes, but their influence, too, was smaller, increasing each other’s risk by 40%.  Dr. Fowler believes the effect has much more to do with social norms: having fat friends makes being fat seem more acceptable.

The impact extends not just to your friends, it turns out — but also to your friends’ friendsand even to their friends.  This study found that the ripple effect of a weight gain was significant to three degrees of separation!

Fowler and Christakis also speculate that the contagion effect could hold just as much for weight loss as it does for weight gain.

“A weight-loss plan may be more effective if your closest friends are also on board. And, if you’re successful, your good health will help others achieve a healthy weight too. Helping one person lose weight can have a snowball effect through an entire social network, affecting social norms among the target person’s friends and acquaintances.”

Dr. Christakis, who is that rare combination of both physician and sociologist at Harvard, claims that because people are so inter-connected, their health and even levels of happiness are inter-connected, too. His work explores two aspects of social networks:

  • connection: the process by which social networks form
  • contagion: the way they operate to influence behaviours and attitudes

Most of us recognize that smoking and drinking behaviours are influenced by group standards. But such thinking is relatively new for obesity – still so often thought of as an individual’s moral failing or clinical condition.

Watch this video clip about social network and obesity from the New England Journal of Medicine.  And find out why being overweight is so damaging to our hearts.

Interested in learning more about social networks and contagion?  Fowler and Christakis have written Connected: The Surprising Power of Social Networks and How They Shape Our Lives.  

See also:



 because people are inter-connected, their health is inter-connected. This work explores two aspects of social networks: the process by which they form (“connection”) and the way they operate to influence behavior (“contagion”). Related work examines the health benefits of marriage and the consequences of spousal illness and widowhood. Other ongoing investigations consider the effects of neighborhoods on people’s health, the biodemographic determinants of longevity, and the genetic bases for human behaviors. His past work has examined the accuracy and role of prognosis in medicine and ways of improving end-of-life care.

Along with his long-time collaborator, James Fowler, Dr. Christakis has authored a general-audience book on social networks that will appear in late 2009: Connected: The Surprising Power of Social Networks and How They Shape Our Lives

3 thoughts on “Women & heart disease: is obesity contagious?

  1. Sadly, I’m embarrassed to admit that this appears to be true with me and my girlfriends. We used to joke that we were like “The Golden Girls” who always dug into a whole cheesecake while debating their problems in life! We need to stop this way of “socializing”. I’m forwarding them this article. Thanks for ruining my day…;-(


  2. Pingback: Twitted by PLACTest

Your opinion matters. What do you think?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s