Can the Company You Keep Make You Fat? (Part 1)


When it comes to weight control[1], it’s probably been ingrained in you by now that eating too many calories without subsequently burning them off can cause you to gain weight. And that not doing enough physical activity can make you gain weight (or at least make it hard to lose weight). You’ve likely also heard theories suggesting that eating too much fat, or too much carbohydrate, or not enough protein can make you gain weight.

But the actual science of weight management is muddied by so many factors, including those that have little or nothing to do with food and activity. For instance, genetics, environment, and hormones all play a role. This helps to explain why you might be able to down 3,000 calories in a day without budging the scale an ounce, yet your spouse might eat half as much and weigh a pound more the next day. And now, another factor in weight control has emerged: your friends!

In 2007, a study was published in The New England Journal of Medicine by Nicholas Christakis, Professor of Medical Sociology at Harvard Medical School, and James Fowler, Associate Professor of Political Science at the University of California, San Diego. What they discovered is that if your friends have gained weight, you’re more likely to gain weight, too. Now, it’s been established that your family or spouse can influence your weight. But your friends seem to have more of an impact on your weight than your family — even if they don’t live nearby.

This study looked at more than 12,000 participants in the now-famous Framingham Heart Study (a long-term study meant to examine the factors associated with the development of cardiovascular disease). The subjects were asked to provide a list of family members and one close friend (many participants listed more than one friend); the patterns of weight gain over time in participants, family, and friends were then analyzed. The findings are interesting: When a person in the study became obese, the risk of his or her sibling becoming obese increased by 40%, and the risk for his or her spouse increased by 37%. If a subject’s friend became obese, the subject’s risk of becoming obese was raised by 57%. Furthermore, if the friends were of the same gender, the subject’s risk of becoming obese increased by 71%. If the friends were particularly close, the risk of obesity in the subject jumped up by 171%!

But there’s more. Even a friend of a friend or a friend’s sibling’s friend who gained weight could affect the subject’s weight.

What might come to mind as an explanation is that overweight people seek other overweight people to pal around with, just as thin people might prefer to hang around with other thin people. But that’s actually not the reason that the authors attribute to these findings. They point out that friends living many miles away can influence one’s weight. So, while genes can and do affect one’s tendency to be thin or heavy, genes haven’t changed enough over the years to explain why more and more people are obese in the U.S.

Certainly, large portions and the increased availability of fatty, processed foods, plus a lack of exercise, are contributors. Yet the authors of the study argue that social networking has had an impact on weight; thanks to e-mail, text messaging, Twitter, Facebook, etc., people are now easily able to stay connected to friends, even if they aren’t physically able to connect. Somehow, social networking seems to “transmit” weight control tendencies from one friend to another.

But it’s about more than just text messaging a friend. It may be that having friends who are gaining or losing weight leads a person to acquire similar attitudes and behaviors, and thus, social norms regarding body weight and what’s deemed as “acceptable” change. Your friends have more of an effect on your weight than you might think. No, friends aren’t going to pin you down and force feed you, or hold you at gunpoint until you run three miles. Rather, it’s what your friends eat and do that seems to influence what you eat and do. So, if your friends eat healthfully and exercise regularly, chances are you will too.

More next week! In the meantime, what are your thoughts on this topic?

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Amy Campbell: Amy Campbell is the author of Staying Healthy with Diabetes: Nutrition and Meal Planning and a frequent contributor to Diabetes Self-Management and Diabetes & You. She has co-authored several books, including the The Joslin Guide to Diabetes and the American Diabetes Association’s 16 Myths of a “Diabetic Diet,” for which she received a Will Solimene Award of Excellence in Medical Communication and a National Health Information Award in 2000. Amy also developed menus for Fit Not Fat at Forty Plus and co-authored Eat Carbs, Lose Weight with fitness expert Denise Austin. Amy earned a bachelor’s degree in nutrition from Simmons College and a master’s degree in nutrition education from Boston University. In addition to being a Registered Dietitian, she is a Certified Diabetes Educator and a member of the American Dietetic Association, the American Diabetes Association, and the American Association of Diabetes Educators. Amy was formerly a Diabetes and Nutrition Educator at Joslin Diabetes Center, where she was responsible for the development, implementation, and evaluation of disease management programs, including clinical guideline and educational material development, and the development, testing, and implementation of disease management applications. She is currently the Director of Clinical Education Content Development and Training at Good Measures. Amy has developed and conducted training sessions for various disease and case management programs and is a frequent presenter at disease management events.

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