How Friends Influence Weight

Studies find we mimic the habits of our closest companions.

By Martina Cartwright, PhD, RD
Jan 26, 2012

Friends may have our backs, but their health and fitness habits can literally shape our backsides.

Multiple studies confirm that enthusiastic friends are essential to developing and sustaining healthier fitness habits. Dieters can lose more weight if partnered with supportive friends, and exercisers get more motivated if paired with positive pals (Bell & Pliner 2003; Hogan, Linden & Najarian 2002; Marcoux, Trenkner & Rosenstock 1990; Verheijden et al. 2005; Wing & Jeffery 1999). But some relationships can have the opposite effect. Either way, it turns out that the company we keep has a profound impact on body size and exercise practices (Burke & Heiland 2007; Gruber 2008; Oygard & Klepp 1996).

Close companions play a powerful role in molding fitness habits through social modeling—our tendency to mimic the actions of those around us. Nutrition and fitness professionals can stimulate the spread of healthy practices by incorporating these social realities into their wellness programs.

The Power of Friendship

Every day, someone strikes up a conversation with a stranger and discovers mutual interests. Flames of friendship ignite and a new alliance forms. Friendships are a valued source of motivation, encouragement and inspiration. Good or bad, friends shape thoughts, emotions, habits—and our physical bodies.

Social support is linked to myriad health benefits ranging from improved mental health to a more robust immune system (Bloom 1990; Jemmott & Locke 1984). The strength of these benefits is tied to the size of the social network, the emotional aspects it provides and the act of lending mutual support. Natural support networks, which include family and friends, have the greatest influence on health because they endure the test of time. Formal support networks that include wellness professionals are less influential but can foster favorable health outcomes (Hogan, Linden & Najarian 2002).

The global Edelman Health Barometer survey (2011) documented the social nature of health influence:

  • Forty-three percent of those surveyed said friends/family have the most impact on personal health lifestyle.
  • Thirty-six percent reported that close social ties have the most impact on personal nutrition.
  • About two-thirds said they had tried to change a negative health behavior, but half failed to sustain the change, citing a lack of ongoing social support as one contributor.

He Who Roams With Wolves Learns to Howl

Research suggests: “He who roams with paunchy pals becomes plump.” Christakis & Fowler (2007) followed 12,067 subjects from the Framingham Heart Study over 32 years. The study results were surprising, demonstrating that a person’s chances of becoming obese increased by 57% if a friend became obese. The type of friendship was also important. Between mutual friends, the subject’s risk of obesity increased by a whopping 171% if the friend became obese.

Gender was also a factor. The probability of obesity increased by 71% if friends were the same sex. All-male friendships resulted in a 100% increase in the chance of becoming obese, while the female-female obesity risk was about 38%. Surprisingly, proximity was not a factor: it didn’t matter if the friend lived nearby or across the country. People were more likely to pack on the pounds if their close pals did too.

This landmark study highlighted social clustering of obesity but failed to identify specific social, cultural, psychological and environmental factors contributing to the spread of obesity, although “social norms” were a suspected culprit.

Social norms are unwritten rules of socially acceptable behavior that govern things like appearance or activities (Oygard & Klepp 1996). Norms regarding acceptable body size, eating habits and exercise are learned from friends and family. Could social norms explain why obesity is contagious among close pals?

Hruschka et al. (2011) interviewed 101 women and 812 of their social ties. The findings confirmed that obesity clusters in friendship groups. However, shared social norms on body size accounted for only 20% of the obesity observed. Similarly, Leahey et al. (2011) reported obesity clusters within groups of young overweight/obese (OW/OB) adults. Although social norms didn’t account for the clustering, norms did influence weight loss intentions. OW/OB adults who had more buddies trying to lose weight had stronger intentions to lose weight.

It seems, therefore, that social modeling—rather than social norms—may play a greater role in the spread of obesity among friendship groups (Herman, Roth & Polivy 2003; Hetherington et al. 2006; Hetherington 2007).

When Dietary Awareness Is Out to Lunch

The desire to mimic those in close proximity is thought to enhance bonding and act as a social super glue (Lakin 2003). When we copy each other’s eating behaviors, we form positive, subconscious bonds with our dining companions. What people do, rather than what they think, may be why obesity flourishes among friends.

The average person makes over 200 food decisions every day (Wansink 2006a). Deciding what and where to eat are just two pieces of the dining puzzle—the other is with whom. Commiserating with pals and engaging in animated conversation over a tasty meal may feel like good therapy, but it can lead to distracted dining. Focusing on the conversation rather than the food often results in overeating (Hetherington 2006; Wansink 2006b).

The number of diners influences individual eating habits, too. If two people dine together, each will eat about 35% more than if they dined alone. If more than seven friends dine together, they will consume 96% more than they would solo (de Castro 1994). Those who eat together subconsciously model each other’s eating styles. Normally light eaters consume more when munching with a group, while heavier eaters eat less when dining with companions (Bell & Pliner 2003).

Eating behaviors are dictated by a tableside “pacesetter” who unknowingly sets the standard for how much is eaten and how fast (Herman, Roth & Polivy 2003). If the pacesetter eats one cookie, dining companions will eat one cookie. But if the pacesetter eats six cookies, then the other diners will eat about the same (Wansink 2006b).

Social modeling may hold the key to spreading healthy behaviors and curbing less-healthy ones. People who decide to adopt better eating habits may unknowingly influence their friends to do the same. The same holds true for exercise behaviors.

Workplace Weight Gain

The workplace can be a minefield for people trying to shed pounds. Co-workers can unknowingly torpedo weight loss efforts. The seemingly endless office celebrations and corporate events provide a steady stream of sugary indulgence that can sabotage the most strident dieter’s efforts. Deskside chats can tempt the most health-conscious employee into mindlessly reaching into the ubiquitous desktop candy jar, spurring weight gain.

Wansink, Painter & Lee (2006) found that secretaries given chocolates in clear jars reached for a sweet treat 71% more often than those given candies in an opaque vessel. As long as the clear dish was visible, the secretary ate 77 more calories a day, which could tack on 5 extra pounds each year (Wansink 2006c). Simply hiding the jar or placing it in a less convenient location quelled temptation. Desktop jars enticed the typical secretary into eating nine chocolates a day, or an extra 225 calories; however,


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Martina Cartwright, PhD, RD

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