Experts say consumers make healthier choices when the calories are posted on the menu.
Dr. Susan Roberts and co-authors from Tufts University evaluated the calorie content of several fast food and sit-down restaurant meals countrywide.
Researchers ordered the food and bought it back to the lab, they weighed it, ran it through a food processor, freeze dried it, crushed it into a fine powder, then analyzed that powder to get an accurate calorie count.
"Typically, the foods that were stated as low calorie on the menu contained more calories than they should, which is really bad for dieters," Roberts said. "The high-calorie foods actually contained fewer calories than they should."
The study, which appears in this week's Journal of the American Medical Association, found soups and salads had the biggest discrepancies. Not with fast food salads, but many salads at sit-down restaurants had much higher calorie counts than what was stated on the menu.
"We had one food that came in that contained 1,000 calories more than the amount listed on the menu, which even we were shocked about," Roberts said. "It's really the sit-down restaurants that need to examine their quality control and step up to the plate better."
Researchers also tested pizza.
"Everybody would think is not good food for weight control, actually had the most consistent calories," Roberts said.
Roberts said with at least half of Americans trying to lose weight, accurate calorie counts and portion sizes are important.
"We're expecting consumers to go and look after their own weight and this is really tying their hands," she said.