At your local movie theater the latest blockbuster isn't the only big thing you may be busting your seams if you hit the concession stand.

"They don't call them tubs for nothing. I mean a tub of popcorn is about a thousand calories," said Dr. Gregory Plemmons of Vanderbilt University.

The Center for Science in the Public Interest recently checked out the fat and calorie content at the nation's three largest theater chains what they found..

"Regal and AMC -- the two largest chains -- are popping in the worst possible oil: coconut oil. Coconut oil is 90% saturated. Lard is 40% saturate. The third largest chain, Cinemark, is popping in a heart healthy oil -- they're using non-hydrogenated canola oil," said the center's Jayne Hurley.

But that doesn't mean it's good for you.

In fact the CSPI claims large popcorns from all three chains were between 910 and 1,200 calories and that's before that buttery topping.

A large soda could add 500 calories.

And with theaters stocking oversized candy some of these could add between 300 and 1,100 calories.

Cinemark and Regal were the only theaters to respond to our interview request and in statements, both said they offer healthier alternatives, but that snack options are driven by patron demand.

The National Association of Theater Owners agreed, pointing out many theaters tried to change to air-popped popcorn after a similar report 15 years ago.

But moviegoers -quote- "made their voices heard and wanted the traditional popcorn back."

Nutrition experts say there really aren't any healthy alternatives to theater snacks but suggest sharing a tub of popcorn between 2 or 3 people.