Researchers gave moviegoers stale popcorn in big buckets, and they ate 34 percent more than those given the same stale popcorn in medium-sized containers.
When served fresh popcorn in large tubs, people ate 45 percent more than those given fresh popcorn in medium-sized containers.
"We're finding that portion size can influence intake as much as taste," says researcher Brian Wansink, a professor of marketing and applied economics at Cornell University. "Large packages and containers can lead to overeating foods we do not even find appealing."
The researchers gave 158 moviegoers either medium (4.2 oz) or large (8.4 oz) tubs of free popcorn, either fresh or 14 days old. The researchers asked the moviegoers to describe the popcorn after the movie, and they weighed how much popcorn was left in the containers.
The 14-day-old popcorn was described as "stale" and "it was terrible."
When the moviegoers were asked if they thought they ate more because of the size of the container, 77 percent of those given the large tubs said they would have eaten the same amount if given a medium container.
"This means that the moviegoers were unaware that the exceptional amount they ate was due to the size of the container," Wansink said in a news release.
The study is published in the September/October issue of the Journal of Nutrition Education and Behavior.
