The company you keep influences how much you eat

Thin friends who eat a lot could put your waistline in danger. That's the warning from researchers studying how other people's weight and food choices influence how much we eat.

Researchers from Duke University, the University of British Columbia and Arizona State University used snack foods, an obesity prosthesis, and the ruse of a study related to movies to track how students' food consumption was influenced by a companion.

Their findings will appear online this week in the Journal of Consumer Research.

"Obesity is obviously a tremendous public health concern," said Gavan Fitzsimons, F.M. Kirby Research Fellow and professor of marketing and psychology at Duke University's Fuqua School of Business. "Because people often dine in social settings, we decided to investigate how someone's size and food choices could influence how much the people around them order and eat."

The research team recruited 210 college students to participate in a study ostensibly about movie watching. Upon arriving at a research lab, each student was informed that they would be paired with another student taking part in the same study. The other student was in fact a member of the research team whose size was manipulated to make her appear to be either size 0 and 105 pounds (her natural build), or size 16 and 180 pounds (when wearing the obesity prosthesis).

All of the students were offered snacks to enjoy while viewing a film clip. The undercover researcher was served first, and helped herself to either a large or small serving before the student participant was offered the same bowl of food.

In all cases, the amount of food the students took was influenced by the portion size chosen by the undercover researcher, regardless of her size.

"Most participants took a portion similar to what the researcher served herself. However, it is clear that how much food each person took, and how much they ate, depended on whether their companion was thin or obese," said Brent McFerran, assistant professor of marketing at UBC Okanagan, and a member of the research team while completing his PhD at UBC's Sauder School of Business.

Although their serving sizes mimicked those of the researcher, participants dampened the researcher's influence when she was obese but not when she was thin. In other words, if the thin researcher ate a lot or only a little, the participant followed suit. But when the researcher was obese, participants adjusted the amounts they ate and diminished the influence the researcher had on them.

"This indicates that people are influenced, even without being aware of it, by other people's portion choices," said Darren Dahl, the Fred H. Siller Professor of Applied Marketing Research at UBC. "Further, our dining companion's body type can lead us to adjust what we choose and consume ourselves."

"In terms of consumer health, our findings indicate that the size of the person you dine with matters much less than the size of the meal they order," said Fitzsimons. "If a heavy-set colleague eats a lot, you are likely to adjust your behavior and eat less. But a thin friend who eats a lot may lead you to eat more than you normally would."

The research team also included Andrea Morales, associate professor of marketing at the W.P. Carey School of Business, Arizona State University. This research was funded in part by the Association for Consumer Research, the Social Sciences and Humanities Council of Canada, and the Society for Consumer Psychology.

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