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Nutrition labels have raised awareness of the energetic value of foods, and represent for many a pivotal guideline to regulate food intake. However, recent data have created doubts on label accuracy. Objective: We tested label accuracy for energy and macronutrient content of prepackaged energy-dense snack food products. We measured 'true' caloric content of 24 popular snack food products in the U.S. and determined macronutrient content in 10 selected items. Design and Methods: Bomb calorimetry and food factors were used to estimate energy content. Macronutrient content was determined according to Official Methods of Analysis. Calorimetric measurements were performed in our metabolic laboratory between April 20th and May 18th and macronutrient content was measured between September 28th and October 7th of 2010. Results and Conclusion: Serving size, by weight, exceeded label statements by 1.2% [median] (25th percentile −1.4, 75th percentile 4.3, P = 0.10). When differences in serving size were accounted for, metabolizable calories were 6.8 kcal (0.5, 23.5, P = 0.0003) or 4.3% (0.2, 13.7, P = 0.001) higher than the label statement. In a small convenience sample of the tested snack foods, carbohydrate content exceeded label statements by 7.7% (0.8, 16.7, P = 0.01); however fat and protein content were not significantly different from label statements (−12.8% [−38.6, 9.6], P = 0.23; 6.1% [−6.1, 17.5], P = 0.32). Carbohydrate content explained 40% and serving size an additional 55% of the excess calories. Among a convenience sample of energy-dense snack foods, caloric content is higher than stated on the nutrition labels, but overall well within FDA limits. This discrepancy may be explained by inaccurate carbohydrate content and serving size. [ABSTRACT FROM AUTHOR]