In a study published in the January 2010 issue of the Journal of the American Dietetic Association, researchers from Tufts University found that some commercially prepared foods contained more calories than indicated in nutritional labeling.

Measured energy values of 10 frozen meals purchased from supermarkets averaged 8% more calories than stated on the label. Over a year’s time for a typical 2,000-calorie daily diet, that would equate to a 10-pound weight gain, researchers noted.

Restaurant foods were similarly tested and also had under-reported calorie values.

The commercially prepared restaurant foods and supermarket frozen convenience meals were obtained in the Boston area. Supermarket purchases focused on frozen complete meals that would be alternative choices to eating out. The calorie content was measured and compared with nutrition data stated by the vendor or manufacturer.

The authors note that the U.S. Food and Drug Administration allows actual calories to exceed the label statement by up to 20%, but weight must be no less than 99% of the stated value. This may lead manufacturers to add more food to the package to insure compliance with the weight standards and thereby exceed the stated calorie content.

Researchers stated that if these samples were indicative of widespread results, it could hamper efforts to self-monitor energy intake to control weight.