I've written a bit here about how portion size can effect how much an individual eats. Turns out, even smaller details can matter: How a food is labeled - whether as a "medium" or "large" cookie, for example - can also alter eating behavior.
NPR's Helen Thompson and Shankar Vedantam report on an experiment from the University of Michigan's Aradhna Krishna, where she labeled the same size cookie as "medium" or "large" for different groups of eaters.
People ate more cookies when they were labeled "medium." Rather than trust what their stomachs were telling them, in other words, people went by the label.
"Just because there's a different size label attached to the same actual quantity of food, people eat more. But also, [they] think they've not eaten as much," says Krishna.
Krishna said the psychological principle at work has big ramifications because a 32-ounce soda at McDonald's is called a large soda, but the same drink at Wendy's is called a medium. A small coffee is 10 ounces at Dunkin' Donuts and 12 ounces at Caribou Coffee. When you trust labels, you could end up eating and drinking a lot more than you thought.