Research Stories

by Debbie Freeman

Whether your companions are overweight or skinny and how much they put on their plates can greatly influence how much you eat. New research shows if we eat with skinny people, we tend to mimic their food portions, regardless of how much they take. However, if we eat with overweight companions, we generally try to adjust our portions to be different.

“Weight and portion sizes are linked together in people’s minds,” says Associate Professor Andrea Morales of the W. P. Carey School of Business at Arizona State University, one of the authors of the new study in the Journal of Consumer Research. “When our overweight companions take a large portion, we usually take less food to eat. However, it may surprise people to know that when overweight eating partners take small portion sizes, we still try to differentiate ourselves by taking larger portions.”

The research involved three sets of experiments all showing that our food choices are influenced by the body types of those around us.

In one set, college students were invited to a lab supposedly to watch a movie. When they checked in, they were joined by a research assistant who was introduced as just another study participant. The assistant weighed 105 pounds and wore a size 0. However, during some of the sessions, she wore an obesity prosthesis that made her appear to weigh 180 pounds and wear a size 16.

Both the student and the accomplice were offered a snack to enjoy during the movie. When the assistant appeared to be thin, the study participants took a snack amount similar to hers, but when the assistant wore the prosthesis, the students adjusted. If the “overweight” accomplice took 30 candies, then the study participants selected less. If the accomplice took just two candies, then the participants went for a larger portion.

“What makes this interesting is the interaction between the body type and the portion sizes,” says Morales. “It’s not just whether the other person is thin or overweight. In fact, if you frequently eat with skinny people who take large portions, then that could prompt you to gain weight.”

In another set of experiments, conducted at Arizona State University, students were asked to complete a survey about ordering ice cream. They read a scenario about the ice cream-buying experience where the person in line in front of them was described as heavy or thin. Again, the study participants adjusted their ice cream orders away from the portion sizes chosen by the fictional overweight customers.

“This study has a lot of public health implications, given the obesity epidemic in America,” Morales explains. “If you want to encourage healthy behaviors, you should adjust the images involved in those messages accordingly. For example, showing an overweight person eating a smaller portion size will probably not work.”

The other researchers involved in the study are Brent McFerran and Darren W. Wahl from the University of British Columbia and Gavan J. Fitzsimons of Duke University. The full article is available at http://www.journals.uchicago.edu/doi/full/10.1086/644611.