In a country where obesity has risen to 34 percent of the population and up to 35 percent of the average person's calorie intake comes from food eaten out
instead of at home, the findings point to a potential source of a nationwide
epidemic.

For instance, with 19 percent of the food coming in at 100 calories higher
than advertised, a person who regularly consumed that additional amount daily
would be projected to gain five to 15 kilos (11-33 pounds) per year, it said.

"The prevalence of obesity remains at epidemic levels and national
recommendations emphasize reducing energy intake to facilitate weight loss and prevent weight gain," said the study.

"However, the extent to which this recommendation can be implemented depends in part on the accuracy of available information on the energy contents of foods that are typically consumed."

Food were sampled from the states of Indiana, Massachusetts and Arkansas from January to June 2010.

Among the restaurants sampled were Arby's, Chuck E. Cheese, Old Spaghetti
Factory, P.F. Chang's China Bistro, Chili's Grill and Bar, and Bob Evans.

At Denny's, a popular chain diner, a sampling of the french fries showed they had 122 more calories than advertised, while the classic hamburger actually had 152 fewer calories than advertised.

Sit-down restaurants tended to show greater differences in actual versus advertised calories when compared to fast-food establishments, possibly due to lack of portion control, the authors said.

The US government is currently finalizing plans to make menu calorie counts mandatory in chain restaurants, a change that comes as part of President Barack Obama's health care law passed last year.