Portions, such as 8, 12 or 16 ounces, are given different labels -- small, medium or large -- at different restaurants.
The study, published in the journal Health Economics, found consumers use the size labels to dictate how much food they think is a "normal" portion, and then adjust their intake accordingly.
"People are willing to pay more for a portion that sounds larger, but they also are apt to eat more of an enormous portion if they believe it is regular to do so," David R. Just, associate professor at Cornell's Dyson School of Applied Economics, said in a statement.
Just and Brian Wansink, both of the Cornell Food and Brand Lab, served study participants either 1 or 2 cups of spaghetti. For some participants, the small and large portions were labeled half-size and regular, respectively, giving the impression that the larger 2-cup portion was the norm. For other participants, the same portions were labeled regular and double-size -- implying that the smaller one-cup portion was the norm.
"These varying concepts of regular portions made all the difference in how much people would spend and subsequently eat," Just said "Participants ate much more when their portion was labeled regular than when it was labeled double-size. In fact, participants who thought their portion was double-size left 10 times the food on their plate."