With obesity rising markedly, reliance on the accuracy of food labeling is an important weight management strategy. Since people who are trying to reduce their weight are encouraged to choose meals labeled as "lower in calories" or "reduced-energy" in restaurants and supermarkets, it is essential that the listed data are accurate. 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 29 quick-serve and sit-down restaurant foods averaged 18% more calories than the stated values. Likewise, measured energy values of 10 frozen meals purchased from supermarkets averaged 8% more calories than stated on the label.

The commercially prepared restaurant foods and supermarket frozen convenience meals were obtained in the Boston, MA, area. The energy content was measured and compared with nutrition data stated by the vendor or manufacturer. The restaurant chains included both quick-serve and sit-down establishments with broad distribution throughout the United States.

Because the goal of the study was to examine the accuracy of stated energy content of foods typically selected for weight control, specific restaurant menu items were chosen based on three criteria. Selected foods were (1) less than 500 kcal/serving as stated on the label, (2) typical American foods and (3) among those with the lowest stated energy contents on the menu. Supermarket purchases were focused on frozen complete meals that would be alternative choices to eating out.

The authors found a further complication with some restaurant meals. Five restaurants provided side dishes at no extra cost. The average energy provided by these items was 471 kcal, which was greater than the 443 kcal for the entrées they accompanied. Furthermore, some individual foods had discrepancies that were extreme, including three supermarket-purchased complete meals and seven restaurant foods that containing up to twice their stated energy contents.

The authors also note that the US Food and Drug Administration allows up to 20% excess energy content but weight must be no less than 99% of the stated value. This might lead manufacturers to add more food to the package to insure compliance with the weight standards and thereby exceed the stated energy content.

Lead investigator Susan B. Roberts, PhD, director, Energy Metabolism Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, and colleagues write, "These findings suggest that stated energy contents of reduced-energy meals obtained from restaurants and supermarkets are not consistently accurate, and in this study averaged more than measured values, especially when free side dishes were taken into account, which on average contained more energy than the entrees alone. For example, positive energy balance of only 5% per day for an individual requiring 2,000 kcal/day could lead to a 10-lb weight gain in a single year. If widespread, this phenomenon could hamper efforts to self-monitor energy intake to control weight, and could also reduce the potential benefit of recent policy initiatives to disseminate information on food energy content at the point of purchase."