Watching Your Weight? Beware Of Skinny Friends With Big Appetites

"Obesity is obviously a tremendous public health concern," write authors Brent McFerran, Darren W. Dahl (both University of British Columbia), Gavan J. Fitzsimons (Duke University), and Andrea C. Morales (Arizona State University). "We decided to investigate how someone's size and food choices could influence how much the people around them eat."

The researchers recruited 210 college students to participate in a study that was ostensibly about movie watching. The participants were told they would be paired with another student taking place in the study. The other student was actually a member of the research team whose natural build was thin (size 0, 105 pounds). But at times this same researcher donned an "obesity prosthesis," which made her appear to be a size 16 and 180 pounds.

All of the students were offered snacks while viewing film clips. 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 accepted 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," the authors explain. "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."

Participants tended to mimic the thin companion's portion sizes. But when they presumed the researcher to be obese, the participants adjusted the amounts they ate. "This indicates that people are influenced, even without being aware of it, by other people's portion choices," the authors write.

"Our findings indicate that the size of the person you dine with matters much less than the size of the meal they order," the authors write. "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."