Your Fellow Diners' Size May Affect How Much You Eat

By Alison Bruzek

Published October 2, 2014 at 3:34 PM EDT

In one study, people who were in a buffet line served themselves a lot more of an unhealthful pasta dish if they were next to or behind a person perceived to be overweight.

Your dining companion may have more influence over your eating habits than you realize.

We've known that people often have friends with similar body weights, but new research suggests that dining with an overweight companion may make us more likely to eat more unhealthful food.

A study in the appropriately named journal Appetitefinds that undergraduates who were offered pasta and salad while eating near a 5-foot-5-inch, 126-pound woman would eat more pasta when she was zipped into a fat suit adding 50 pounds, or about 8 points, to her body mass index.

"We've long known that what a person [you're with] orders can influence what you order," , director of the Cornell University Food and Brand Lab and one of the study's authors, tells The Salt. "We haven't known as fully how the size of the person who you might be with, how they influence us."

Wansink and his colleagues at Cornell recruited 82 students and one actress from upstate New York to be treated to a pasta and salad buffet lunch. The students were divided into four groups, depending on the look and behavior of the actress: no fat suit and healthful eating; fat suit and healthful eating; no fat suit and unhealthful eating; and fat suit and unhealthful eating. In this case, healthful eating meant the actress served herself a lot of salad, and unhealthful meant she piled on the pasta.

In all groups, the actress was always the first person in the room, and to draw attention to herself, she'd ask out loud, "Do I need to use separate plates for pasta and salad?"

The actress would then gather the appropriate amount of food, and sit down and push the food around (she wasn't actually forced to eat it). After the lunch, the students filled out a questionnaire that included a question on whether they noticed the actress and what her size was.

The results surprised the researchers. The amount of food the actress put on her plate didn't influence the students' behavior, but her perceived weight did. When she wasn't wearing the suit but still took a lot of pasta, the students didn't notice. However, when she was wearing the suit, "if she was next to them or in front of them, they just took a lot of food," says Wansink.

Wansink and colleagues say that this is only one of many factors that influence people to eat certain ways that they're not even aware of. As we've previously reported, even the size of your dinner plate or the type of utensils you use can influence how much you eat and how you perceive the flavor of food.

To fight these subtle powers, he says, "It's really important to commit to what and how much food you want to eat before you get to the restaurant. ... It takes very little to throw us off our game."

The subconscious nature of eating cues, like your companions' size, is what makes it tricky.

"Telling them about it probably won't change the outcome," says Janet Polivy, a psychologist at the University of Toronto, Mississauga who was not affiliated with the research.