That sick, heavy, queasy feeling you get when you leave the movie theater may not have come from, say, realizing you paid good money to watch 'Conan the Barbarian' in 3D. It may come from having mindlessly shoveled handful after handful of stale popcorn into your mouth.

A new study conducted by scholars at the University of Southern California and published in the journal Personality and Social Psychology Bulletin suggests that moviegoers can't help themselves. If you make a habit of eating popcorn at the movies, you'll keep eating and eating it throughout the picture, regardless of whether or not the popcorn is fresh or even tasty.

In the study, researchers gave movie patrons a bucket of popcorn just before a screening. Some contained fresh popcorn, some contained week-old popcorn. The study found that people who habitually ate popcorn consumed the same amount of popcorn whether fresh or stale, while those who didn't were much less likely to eat the stale kernels. It didn't matter whether or not the moviegoers were hungry before the film.


The study also tried the experiment with modest changes in environment and behavior. A control group was given popcorn before a movie screened in a conference room. Outside the traditional movie theater environment, even frequent popcorn eaters ate much less of the stale popcorn.

Another variation occurred when researchers asked moviegoers at a theater to feed themselves popcorn with their non-dominant hand. Again, popcorn lovers ate much less of the week-old popcorn.

"People believe their eating behavior is largely activated by how food tastes. Nobody likes cold, spongy, week-old popcorn," said study co-author Wendy Wood, a USC Professor of Psychology and Business, in a press release. "But once we've formed an eating habit, we no longer care whether the food tastes good. We'll eat exactly the same amount, whether it's fresh or stale."

'Real Genius' - Too Much Popcorn

The USC study echoes one conducted 12 years ago by Brian Wansink, director of the Cornell University Food & Brand Lab. In his book 'Mindless Eating: Why We Eat More Than We Think,' Wansink wrote that his team gave medium and large buckets of five-day-old popcorn out before a theatrical screening of Mel Gibson's 'Payback.' Not only did people reflexively munch on the stale snack, but they ate 53 percent more if they had the large containers, regardless of how hungry they were or the fact that the popcorn didn't taste very good.

Wansink conducted similar trials at theaters in three states, with a variety of different movies playing, and came up with the same results. He wrote:

Did people eat because they liked the popcorn? No. Did they eat because they were hungry? No. They ate because of all the cues around them -- not only the size of the popcorn bucket, but also other factors... such as the distracting movie, the sound of people eating popcorn around them, and the eating scripts we take to movie theaters with us. All of these were cues that signaled it was okay to keep on eating and eating.

A large bucket of movie theater popcorn can contain as much as 1,200 calories, 980 milligrams of sodium, and 60 grams of saturated fat - and that's before you add your own salt or a squirt of buttery topping. That's according to a study two years ago by the Center for Science in the Public Interest, which likened the nutritional value of a large popcorn-and-soda combo to that of three McDonald's Quarter Pounders topped with 12 pats of butter. "Who expects about 1,500 calories and three days' worth of heart-stopping fat in a popcorn and soda combo? That's the saturated fat of a stick of butter and the calories of two sticks of butter," said CSPI senior nutritionist Jayne Hurley upon the study's release. Addressing those who consider movie theater popcorn a light, healthy snack, she said, "You might think you're getting Bambi, but you're really getting Godzilla."

Air-popped popcorn actually is a light and healthy snack, full of vitamins, minerals and fiber and containing just 31 calories per cup. Movie theaters, however, often pop their corn in oil. Some use heavily saturated coconut oil; others use less saturated but equally caloric canola oil. And then they douse it with salt and oil-based butter flavoring. That brings the calorie count up to 55 calories per cup, and a large tub of popcorn may contain 20 to 22 cups.

So even if you're eating fresh popcorn, it's no wonder you'd leave the theater feeling heavy. At least you now have academic proof that lets you blame the environment. Of course, you could always try to eat with your other hand or order a smaller portion. Or you could follow the recommendation of CSPI's Hurley: "The healthiest snack to buy at the movies is no snack at all."

Follow Gary Susman on Twitter @garysusman.

*Popcorn photos courtesy of Corbis and Getty