Forget Freddy Krueger or flesh-eating zombies: the real villain of a night at the movies could be lurking in a bag of popcorn or drinks carton, according to a new US study.

Nutritional analysis of popcorn servings at some of America's biggest cinema chains has found mind-boggling calorie counts that may surprise consumers who think of the snack as a relatively healthy treat.

However the non-profit Center for Science in the Public Interest compared some popcorn and drinks combos to consuming three McDonald's quarter-pounders topped with 12 pats of butter.

The CSPI said in a statement that a medium popcorn and soda combo at Regal, the United States' biggest movie theater chain, contained an eye-popping 1,610 calories and around 60 grams of saturated fat.

At AMC theaters, the second largest theater chain, a large popcorn contained 1,030 calories and 57 grams of saturated fat, equivalent at a pound of baby back spare ribs topped with a scoop of luxury ice cream, CSPI said.

The group said analysis of servings from Regal and AMC theaters showed calorie counts higher than the companies official estimates.

"Regal and AMC are our nominees for Best Supporting Actor in the Obesity Epidemic," CSPI senior nutritionist Jayne Hurley said in a statement.

"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.

"You might think you're getting Bambi, but you're really getting Godzilla."

The study said the high calorie counts could be attributed to the fact that corn was popped in coconut oil.

Popcorn cooked in healthier canola oil showed lower levels of saturated fats but similar levels of calories and higher sodium, the study found.