When I was a kid, I used to spend hours listening to Adam Carolla and Dr. Drew Pinsky on their Sunday night call-in radio show Loveline. I listened so often that I began to incorporate one of their catchphrases - "good times" - into my daily conversations. Scientists have a name for this phenomenon: behavioral mimicry.
You've probably experienced this before: after spending enough time with another person, you might start to pick up on his or her little mannerisms or speech quirks. You might even start to mimic your friend without realizing it. There is a large body of literature concerning this sort of phenomenon, and it routinely happens for everything from body postures to accents to drink-sipping patterns. For example, one study found that young adults were more likely to sip an alcoholic drink directly after their same-sex drinking partners, than for the two individuals to drink at their own paces.
And the effect isn't limited to real-life face-to-face interactions. Another study found that the same you-sip-then-I-sip pattern held even when watching a movie! In other words, people were more likely to take a sip of their drinks in a movie theater after watching the actors on the screen enjoy a beverage. At least I don't feel so weird anymore, having picked up on Adam Carolla's "good times."
New research published today in the journal PLoS ONE indicates that the same sort of behavioral mimicry is responsible for social eating, at least among university-age women of normal weight. That's right: the young women were more likely to modulate their eating according to the eating pace of their same-sex dining companion.
Developmental psychopathologist Roel C. J. Hermans and colleagues from the Radboud University Nijmegen in the Netherlands set up a "lab restaurant," comprised of a table for two, complete with water pitcher, glasses, cutlery, plates, and napkins. The chairs were placed at opposite ends of the table, so that the two women could see each other. Each participant was served a full meal, and could eat as much or as little as they liked. This was in contrast to the co-eaters who were instructed to eat a small, medium, or large amount of the food. Despite this instruction, the co-eaters were unaware of the larger purpose of the study, so in a sense, they can be considered experiment participants as well.
Throughout the twenty minute meal, both women could be observed by an experimenter, who had a closed-circuit video on which he had a clear view of each of the diners, thanks to a series of hidden cameras in the lab-restaurant. They took note of the total number of bites per diner, the total amount of food consumed, as well as the exact time at which each participant and co-eater took a bite. Combined across seventy different dining pairs, the researchers had data for 3,888 bites.
The first finding was that the total amount of food eaten, measured in grams, was highly correlated among the eating pairs. What this means is that separate from whether or not the partners' eating pace was similar, the overall amount of food consumed was. More striking was the finding that both women (the participant and the co-eater) were more likely to take a bite while their dining companion was taking a bite, than when their partner was not taking a bite. And that likelihood was three times stronger during the first ten minutes of the meal than the last ten minutes of the meal.
What might explain these patterns? The researchers offer several possible explanations. First, they invoke what is called the "perception-behavior expressway": watching her partner take a bite could have activated, within the participant, the motor system for the same type of action, which may have made it more likely to take a bite as well. Alternatively, it could be that the women were monitoring their partners' eating behaviors in an effort to discern what constitutes "appropriate eating," so that they could modulate their own eating behaviors in accordance. They explain, "adjusting one’s bites to that of others might be another solution (next to adjusting one’s overall intake) to guard against overindulgence and to avoid the negative stereotypes that are associated with eating inappropriately." As with the first explanation, this would occur below the level of conscious awareness.
It is worth noting that this effect works both ways, since the co-eater was always instructed to eat a small, medium, or large portion of their meals. As described above, the participants' food intake was significantly correlated with their partners' consumption. Therefore, some of the participants may have ended up eating less than they might otherwise have preferred (thereby avoiding overindulgence), but some likely ate more than they had initially intended.
One thing that the study did not assess, however, was the impact of mealtime conversation on the women's eating behaviors. It is possible that the natural flow of conversation was itself the main factor driving the synchronized eating.
As with most experiments, these results raise a whole new set of questions. Still, the finding that behavioral mimicry may at least partially account for eating behaviors is important, and has real implications for health. The researchers note that "as long as such important influences on intake are not wholeheartedly acknowledged, it will be difficult to make healthy food choices and maintain a healthy diet, especially in eating contexts in which people are often exposed to the eating behavior of others."
For more on food psychology:
Hermans RCJ, Lichtwarck-Aschoff A, Bevelander KE, Herman CP, Larsen JK, et al. (2012) Mimicry of Food Intake: The Dynamic Interplay between Eating Companions. PLoS ONE 7(2): e31027. doi:10.1371/journal.pone.0031027