Accuracy of stated energy contents of restaurant foods

Abstract

Context: National recommendations for the prevention and treatment of obesity emphasize reducing energy intake. Foods purchased in restaurants provide approximately 35% of the daily energy intake in US individuals but the accuracy of the energy contents listed for these foods is unknown.

Objective: To examine the accuracy of stated energy contents of foods purchased in restaurants.

Design and setting: A validated bomb calorimetry technique was used to measure dietary energy in food from 42 restaurants, comprising 269 total food items and 242 unique foods. The restaurants and foods were randomly selected from quick-serve and sit-down restaurants in Massachusetts, Arkansas, and Indiana between January and June 2010.

Main outcome measure: The difference between restaurant-stated and laboratory-measured energy contents, which were corrected for standard metabolizable energy conversion factors.

Results: The absolute stated energy contents were not significantly different from the absolute measured energy contents overall (difference of 10 kcal/portion; 95% confidence interval [CI], -15 to 34 kcal/portion; P = .52); however, the stated energy contents of individual foods were variable relative to the measured energy contents. Of the 269 food items, 50 (19%) contained measured energy contents of at least 100 kcal/portion more than the stated energy contents. Of the 10% of foods with the highest excess energy in the initial sampling, 13 of 17 were available for a second sampling. In the first analysis, these foods contained average measured energy contents of 289 kcal/portion (95% CI, 186 to 392 kcal/portion) more than the stated energy contents; in the second analysis, these foods contained average measured energy contents of 258 kcal/portion (95% CI, 154 to 361 kcal/portion) more than the stated energy contents (P <.001 for each vs 0 kcal/portion difference). In addition, foods with lower stated energy contents contained higher measured energy contents than stated, while foods with higher stated energy contents contained lower measured energy contents (P <.001).

Conclusions: Stated energy contents of restaurant foods were accurate overall. However, there was substantial inaccuracy for some individual foods, with understated energy contents for those with lower energy contents.

Figure 1

Sampling Plan Low-stated energy foods had less than 600 kcal/portion and high-stated energy foods had 600 kcal/portion or higher as stated on the restaurant Web site per entire served portion. Four foods were unavailable for resampling and therefore could not be included in the resampling analysis.

Figure 2

Difference Between Measured and Stated Energy for Quick-Serve Foods, Sit-Down Entrees, and Sit-Down Side Dishes Accompanying Entrees A multifactor analysis of variance model was fit for quick-serve foods and sit-down entrees (no side dishes) and included the following predictors: restaurant type, stated energy, and their interaction (model R²=0.10). The interaction was significant (P=.04); thus, the correlation of energy difference and stated energy is presented for each restaurant type separately. Simple linear regression equation for sit-down entrees: energy difference=176−0.28×stated energy.

Figure 3

Difference Between Measured and Stated Energy for a Subset of Repeated Samples (n = 13) The lines connect paired data points. The mean for the original sample was 289 kcal/portion (95% confidence interval, 186 to 392 kcal/portion) and the mean for the repeat sample was 258 kcal/portion (95% confidence interval, 154 to 361 kcal/portion). Both of these were significantly greater than 0 kcal (P<.001 for both) and they were not significantly different from each other (P=.37).