A major determinant of human eating behavior is social modeling, whereby people use others' eating as a guide for what and how much to eat. We review the experimental studies that have independently manipulated the eating behavior of a social referent (either through a live confederate or remotely) and measured either food choice or intake. Sixty-nine eligible experiments (with over 5800 participants) were identified that were published between 1974 and 2014. Speaking to the robustness of the modeling phenomenon, 64 of these studies have found a statistically significant modeling effect, despite substantial diversity in methodology, food type, social context and participant demographics. In reviewing the key findings from these studies, we conclude that there is limited evidence for a moderating effect of hunger, personality, age, weight or the presence of others (i.e., where the confederate is live vs. remote). There is inconclusive evidence for whether sex, attention, impulsivity and eating goals moderate modeling, and for whether modeling of food choice is as strong as modeling of food intake. Effects with substantial evidence were: modeling is increased when individuals desire to affiliate with the model, or perceive themselves to be similar to the model; modeling is attenuated (but still significant) for healthy-snack foods and meals such as breakfast and lunch, and modeling is at least partially mediated through behavioral mimicry, which occurs without conscious awareness. We discuss evidence suggesting that modeling is motivated by goals of both affiliation and uncertainty-reduction, and outline how these might be theoretically integrated. Finally, we argue for the importance of taking modeling beyond the laboratory and bringing it to bear on the important societal challenges of obesity and disordered eating.
The consumption of food has implications beyond merely providing nutrients and energy needed to sustain life. Food and eating are also intertwined with our social lives. Most eating takes places in the presence of other people and is often perceived as an enjoyable part of our cultural experience (Rozin, 2005). Therefore, it should not be surprising that one's eating behavior is profoundly affected by social factors. In addition to processes such as social facilitation and impression management (also reviewed in this issue of Appetite), another social influence phenomenon is modeling of food intake, whereby people directly adapt their food intake to that of their eating companion. It was forty years ago that evidence first began to accumulate that modeling 1 is a primary determinant of eating behavior. Nisbett and Storms (1974) demonstrated that young males consistently ate more when their eating companion ate a large number of crackers and less when the other person ate minimally (compared to when eating alone). This so-called modeling effect caught the attention of other researchers and in subsequent years several other attempts were made to identify boundary conditions for the effect. This early modeling research was influenced by the externality hypothesis ( Schachter, 1971), which stated that overweight people are more vulnerable to external food-related cues (such as the social environment) rather than internal cues (such as hunger or satiety). However, and in accordance with the work of Nisbett and Storms (1974), no differences were found between healthy and overweight people, or between restrained and unrestrained eaters, in their extent of modeling ( Conger et al, 1980, Polivy et al, 1979, Rosenthal, Marx, 1979 and Rosenthal, McSweeney, 1979). Researchers therefore concluded that Schachter's externality hypothesis cannot distinguish between healthy-weight and overweight people in the case of modeling, because both groups are influenced by normative external cues ( Herman & Polivy, 2008). Instead, these effects were found to have a strong and pervasive influence on both healthy-weight and overweight individuals' eating behaviors. Although the reproducibility of these effects was easily and repeatedly demonstrated, the question of why modeling occurs has proved more difficult to answer definitively. That is, what purpose does modeling serve, psychologically, that might explain why it is so strongly preserved and generalizable?
Over the decades of modeling research, a variety of explanations have been put forward to understand the effect. The most dominant interpretation, however, is that modeling of food intake is an example of a broader phenomenon of social influence and that general theories of normative behavior might help to understand why people adapt their food intake to that of others. Using a normative approach, Herman and his colleagues proposed that the principal regulatory influence on eating in social contexts is people's beliefs about what or how much is appropriate to eat (Herman, Polivy, 2005 and Herman et al, 2003b). According to this model, people conform to others' eating because they see the amount eaten by others as an indicator of how much one can or should eat without eating excessively.
Although the literature seems to approach consensus on the utility of this normative model, there has not been a systematic review of modeling studies. The lack of a comprehensive review impedes our ability to ascertain from the extant modeling literature: (a) when and why social modeling shapes eating behavior, and (b) how to translate this knowledge to inform applied practice aimed at increasing healthy eating behavior. Therefore, our overarching aim is to review the literature on how people's food choice and intake is affected by modeling and, on the basis of these findings, propose new research directions that might help us to gain insight into the robustness or underlying mechanisms of modeling. We start by reviewing typical methodological approaches to the study of modeling, before summarizing the key findings from our systematic review of 69 modeling experiments. We then discuss theoretical and practical implications of these findings.
