How your friends make you fat—the social network of weight

Christine Junge

Former Editor, Harvard Health Publishing

One of the big health news stories of 2007 was a study showing that your friends influence the size of your waist (and the rest of your body). Like any study, it raised as many questions as it answered, including why this happens. A new study from Arizona State University looked into that question by testing three pathways by which friends might influence one another’s body size:

  1. Collaboration. Over time, you might start to share the ideas of the people close to you after talking with them about what the proper body size is. Then you might choose your food and exercise habits in order to reach that body size, whether that means eating more food to look like your plus-sized friends, or less food to look like your thin ones.
  2. Peer pressure. You feel bullied into trying to look like your friends and family members. They make you feel bad about your body, so you go about eating and exercising to look like them.
  3. Monkey see, monkey do. You change your habits to mirror those of your friends without necessarily thinking or talking about an ideal body weight. Alexandra Brewis Slade, PhD, one of the Arizona State researchers, gave an example of this pathway that most of us can relate to: You’re at a restaurant with friends and the waiter brings over the dessert menu. Everyone else decides not to order anything, so you pass, too, even though you were dying for a piece of chocolate mousse cake.

All three of these pathways are based on the idea that loved ones share social norms, the implicit cultural beliefs that make some things okay, others not.

To test which if any of these pathways affect weight, the researchers recruited 112 women between the ages of 18 and 45 years; half of them were overweight or obese. The researchers then contacted male and female friends, spouses, family members, and coworkers of these women, and ended up with 812 pairs. All of the people were asked about their weight and their feelings about and perceptions of body weight.

The results confirmed the 2007 study’s conclusion that if you have heavier friends, family members, and colleagues, it is more likely that you will be heavier, too. The stronger the relationship between the two people, the stronger the link between their weights. But only one of the pathways—number three—explained why people of the same size clustered together. The study was published in the American Journal of Public Health on May 9, 2011.

“I was surprised,” Dr. Brewis Slade told me during a phone interview. “I would have thought that pathway number two was the most powerful, since it’s really about your struggle to meet other people’s expectations, but it turns out it’s not the best explanation. The key message is that behavior and what people do together is important. So parents might want to go bicycling with their kids, go to a salad bar with kids, focus on what they do together.”

There are, of course, many reasons why people gain weight, and the Arizona State study provides only one possibility. But it also provides another motivation for each of us to make healthy choices—they help not only our own waistlines, but those of our friends and family, too.

If you want to lose weight and would rather not rely on your friends, take a look at Lose Weight and Keep It Off, a new Special Health Report from Harvard Health Publishing.



    Hey, that’s an excelent post and this blog is very interesting too. congratulations!

  2. Daniel

    As they say, you are the average of 5 people who you surround yourself with.


  3. Jon

    I love this post. Friends make such an impact on how much i work out and what i eat. here is a nice site about running to lose weight for beginners.
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  4. Marc Azada

    I absolutely agree with you. Friends/families can definitely influence weight. Thanks for sharing your knowledge about this sensitive issue. I’ve learned a lot from you!

  5. Beryl

    I too would agree that having friends company can be of an influence when it comes to eating. When i was at Uni, i remember a group of us friends would catch up after classes and have lunch at the Chinese Restaurant simply because we loved the food there. Every day, well try a new dish because we wanted to make sure that we tasted everything on their menu list. I can say that had my friends not been round, though i like chinese food ta that restaurant, I alone would not have been tempted to go there everyday!!
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  6. Robin

    I agree. My fiance and I tend to stay in similar shape. When we were overweight, it was at the same time. When we lost weight, I started and he quickly jumped on and we both lost weight.
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  7. Waist to Hip Ratio

    Your health is affected not only by how many overweight body you have, but also by where most of the obese is located on your body. People tend to gain weight especially in the hips and buttocks are almost a pear shape, while those who tend to gain weight especially in the abdomen are more a form of body apple.
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  8. Anonymous

    Is it true that excessively overweight women have a high chance of memory loss down the road?

    • Christine Junge
      Christine Junge

      You know, I’m not sure about that. But I am currently researching the topic of Memory, so I will try to let you know what I find in a future post.

  9. Adz

    I agree with what your saying ” You feel bullied into trying to look like your friends and family members. They make you feel bad about your body, so you go about eating and exercising to look like them.”
    On an even more extreme note look at celebrities. They have the most extreme diets known to man! They always always seem to fail mentioning what happens after their diet….What they dont tell you is what happens to their bodies and what will happen to your body after such radical weight loss programs….e.g. the typical no carb diet….after which you will usually put on more weight because when you do start eating carbs again your body does not know what to do with itself…
    Its not only your friends that affect you its pretty much everywhere you look….

    thanks for the article

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  10. cillio

    I strongly agree with this written statement. if one is not careful friends as a fact can mislead you in many things,hence ending up being like them…birds of the same feathers….flock together…


  11. Stephanie Perez

    I’m impressed with this blog entry because this is exactly some of the things that would happen to me. My girl friends would always want to meet up out for lunch and get desserts & shop together all the time. Needless to say I had a pretty bad weight problem and could never seem to get it under control. I got on a diet called the Scarsdale Diet and it basically gave me good ideas on what to eat when going out. My testimony is on the diet’s Web site and you can see photos of my weight loss. The social norms and the Mexican food that we always ate seriously contributed to my weight gain.

  12. Leonardo

    Thanks for your article. I have often seen that a lot of people are needing to lose weight because they wish to look slim and also attractive. However, they do not generally realize that there are many benefits for losing weight in addition. Doctors claim that obese people come across a variety of health conditions that can be instantly attributed to their particular excess weight. Fortunately that people who definitely are overweight and suffering from diverse diseases can help to eliminate the severity of their particular illnesses by losing weight. You’ll be able to see a continuous but identifiable improvement in health as soon as even a negligible amount of losing weight is attained.

  13. Andy

    I like this topic. Sometimes we are influenced by things that we are not aware of.

    The interesting thing I’ve been noticing is that it’s not just weight. Your friends also influence they type of lifestyle you live including your finances, health, outlook, etc.

    This article is a great reminder of why we should surround ourselves with with people who have traits we want to acquire.

  14. Anonymous

    This post is great especially people who want to reduce body weight..

  15. Anonymous

    i think it happened with me also,i was influenced by my hommies & i began to grow fat:( thank you for this post

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  16. Carolyn Thomas

    Thanks Christine for this fascinating overview of an intriguing phenomenon. Love the ‘monkey see, monkey do’ example here, which likely works powerfully both ways: if all your friends around the table pass on the dessert menu, you will too. But if all your friends order the Triple Hot Fudge Cheesecake Explosion, will you go along, too (despite your previous determination to pass on dessert?)

    I recommend the book “Connected: The Surprising Power of Social Networks and How They Shape Our Lives” by Fowler and Christakis. It explores the impact of connection and contagion in social networks between friends – which in the case of ‘contagious’ obesity appears to be more pronounced among our friends than even our spouses!

    • Christine Junge

      Thanks for the kind words and the book recommendation, Carolyn. I do believe that the Monkey See phenomenon works both ways–so it would be harder to resist dessert if your friends were indulging.

  17. Sondra L Dellaripa

    Conversely the downsize to this discovery is the restrictive or punishing eating habits(anorexia, bulemia). This could fuel an argument against group treatment settings for young girls fighting eating disorders.

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