10/06/2014 10:36 EDT | Updated 10/06/2014 12:59 EDT

Your Friends Could Be Making You Overweight

The very presence of an overweight diner can inspire you to order less healthy food and eat more of it than you may have intended, according to researchers at the Cornell Food and Brand Lab.

An actress was enlisted by the researchers to wear a prosthetic flab suit that added 50 pounds to her naturally slender frame and asked to have lunch in four different scenarios with a total of 82 undergraduates who had volunteered for the study.

Lunch was pasta and salad in each of the four scenarios, which varied in how the actress served herself: She ate either more pasta and less salad or the opposite, with and without the prosthetic layer of flab.

Participants viewed her actions and then served themselves. Researchers found their pasta portions and consumption increased 31.6 per cent when the actress wore her fat suit regardless of how much she had served and eaten herself.

When the actress wore the fat suit and helped herself to more salad, participants' salad portions and consumption plunged by 43.5 per cent.

"This finding emphasizes the importance of pre-committing to meal choices before entering the restaurant," says lead author Mitsuru Shimizu, Assistant Professor of Psychology at Southern Illinois University, Edwardsville. "If you go into the restaurant knowing what you will order you're less likely to be negatively influenced by all of the things that nudge you to eat more."

To avoid falling victim to this phenomenon, the researchers advise planning ahead when you know you're going to be dining with others.

"Look up the menu beforehand and select a meal that suits your dietary goals," says Brian Wansink, PhD director of Cornell University's Food and Brand Lab and author of the new book Slim by Design: Mindless Eating Solutions for Everyday Life. "Or, if you're going to a buffet, pre-commit to selecting modest portions of healthy foods and with that goal in mind, those around you will have less of a negative influence over what you eat."

The study was published in the journal Appetite.

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