BOSTON — A study of menu items from national chain restaurants found that while stated calories on restaurant menus and websites were accurate on average, 19 percent of individual samples differed from laboratory measurements by more than 100 calories and lower calorie foods tended to contain more calories than listed.

Published in the Journal of the American Medical Association, the study from the Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging (HNRCA) at Tufts University compared laboratory measurements of calories in 269 menu items with the restaurants’ stated calories. Researchers randomly collected the samples from national fast-food restaurants and sit-down chain restaurants in Boston, Indianapolis and Little Rock, Ark.

“On average, the food items measured 10 calories higher than the restaurants’ stated calories,” said Susan Roberts, Ph.D., senior author and director of the Energy Metabolism Laboratory at the HNRCA. “That’s essentially accurate. However, 19 percent of food items contained at least 100 calories more than listed, which suggests calories for individual foods can be unreliable. One item contained 1,000 calories more than listed.”

The study’s laboratory measurements also indicated that lower calorie menu items purchased in sit-down restaurants tended to have more calories than listed. For example, based on the data, the researchers were able to predict a sit-down restaurant item listed as approximately 300 calories, and therefore potentially suitable for weight loss or prevention of weight gain, may contain approximately 90 calories more than listed.

Additionally, menu items often viewed as healthier from both sit-down and fast-food restaurants, such as salads and soups, tended to have more unreliable calorie listings.

“We were pleased to see that average calorie listings are accurate, but we think it is very important that lower calorie foods not contain more calories than listed because such foods are purchased by people trying to control their weight,” Roberts said. “They will find that harder to do if they are eating more than they think.”

Roberts also reported the stated calories listed for fast food tended to be closer to laboratory measurements than the stated calories of items purchased in sit-down restaurants.

“Our data suggests the difference may be related to quality control in the kitchen,” said Roberts, who is also a professor at the Friedman School of Nutrition Science and Policy at Tufts University. “Sit-down restaurants typically rely on workers to prepare food on-site, whereas most fast food is portioned out by factory machinery.”