Weight-watchers who swear by the calorie counts that many restaurants in the United States display on their menus, take heed: the numbers don't always tell the truth.
Researchers at Tufts University's Friedman School of Nutrition Science and Policy found that around half the dishes served in popular US restaurants delivered more calories than stated on the menu, with some packing double the stated energy value.
And the researchers found discrepancies in the portion sizes the restaurants said they were serving and the actual size of the meal that showed up on the diner's plate, the study published in the January edition of the Journal of the American Dietetic Association said.
The researchers analyzed the calorie content of 18 side dishes and main courses from five popular sit-down restaurant chains - Applebee's, Denny's, Olive Garden, P F Chang's and Ruby Tuesday - and 11 sides and main courses from fast food restaurants Domino's, Dunkin' Donuts, McDonald's, Taco Bell and Wendy's.
Ten frozen meals bought at supermarkets were also analyzed.
On average, restaurant foods were found to contain 18 percent more calories than what was stated on the menu, and frozen meals averaged eight percent more calories than stated on their packaging.
But some of the restaurant items contained more than twice the calories listed on the menu.
Frozen dinners fared somewhat better, but even there, three meals - including one each from Weight Watchers and Lean Cuisine - delivered around a quarter more calories than stated on the packet.
"If people use published calorie contents for weight control, discrepancies of this magnitude could result in weight gain of many pounds a year," the study's lead author Susan Roberts said in a statement.
To illustrate the gravity of the problem, imagine ordering a portion of dry toast at Denny's.
The seemingly innocuous side dish is listed on the menu as weighing 28 grams and containing 97 calories.
But the Denny's dry toast analyzed by the Tufts team weighed in at 72 grams and packed 283 calories.Reuse content