And that is exactly where Brewis is hoping to look next. "What we really need to do next is get the behaviors down as well—are they eating together; are they exercising together?" Brewis says. "I think it might be what people do together" and the behavioral cues they follow from those around them—even if they are not related to deep-seated beliefs. "We'll call it the 'Would you like to see the dessert menu?' phenomenon," she says, offering as an example the moment when a waiter arrives to ask if anyone would like to see the dessert menu. In this situation, people often pause to glance around the table and see if anyone is going to ask for it; if no one else asks for the menu, an individual will often pass as well, whereas if one person does ask for the menu, others will be more likely to order dessert.
Fowler and his colleagues are looking into this behavioral side, he says, trying to figure out, "If I start eating more fatty foods, do you start eating more fatty foods?" And Christakis emphasizes that ideas and actions are all part of the complex web of forces that shape us—"Both are part of the story," he says.
In addition to social attitudes and socially determined behaviors, other factors might be at work influencing people in the same social networks.
The environment—from the prevalence of fast food restaurants to the availability of good walking trails—has been shown to play a large role in people's health and BMI. But in their analysis of the Framingham data, Fowler says, his team found that "it's true that your environment has an impact on you, but it doesn't seem to be the reason" for your body weight. Having an obese neighbor did not make a person more likely to be obese, but having a friend or relative who was—even if that person lived hundreds of miles away—did.
Because a large portion of the social relations in the study were listed as family members, genetics could be playing a role, too. And Brewis notes that, "in terms of moving this research forward, that's certainly something to think about."
Winning hearts and minds?
How this and other studies are interpreted could have a large impact on public health messages going forward, determining whether campaigns focus on changing attitudes surrounding healthy body size, zeroing in on directly changing what people eat, or a combination of these.
"We assume that changing the way people think changes how people behave—that's really a core message of public health," Brewis says. "Maybe what people think doesn't really matter that much."
Public health messages have long relied on the notion that by changing attitudes, you can shift behavior. But this and other recent research has shown how this simple notion can be dismantled by a host of complex and still poorly understood factors. People understand that improving their diet and getting more exercise are key to losing weight. "They know, and they want to do it," Brewis says. But that "is really different from being able to do it." Even study-based weight-loss interventions fail to help most people keep weight off—"and we really don't understand why they fail," she says.
And that key disjunction is what Brewis and a host of other researchers are targeting. "If it's not social norms, it's a clue we can start looking for something else," she says.
Fowler says that even if social norms are exerting a minority of influence on weight status, they could still play a powerful role in curbing the rise in obesity. "It still tells you that networks have got to be a key to understanding—and potentially fighting—the obesity epidemic."
Social norms are, after all, an appealing target for intervention. As Fowler points out, they are "very easy to act on. You don't have to change eating or exercise behavior," which are hard habits to alter directly. Instead, "all you have to do is operate on what they think is an appropriate weight" and, at least theoretically, people's weight will follow suit.