Note: the original title was misleading in that I wrote “on average stated calories are accurate”, but really only 7% were within 10 kcal of what is posted. Averaged together they are accurate, but individually they are not.
Restaurants have been estimated to account for about 35% of american energy intake (USDA data), so it is important that customers are provided accurate information about how many calories they are consuming should they be monitoring their intakes. A previous pilot study by a research group led by Susan Roberts of Tufts suggested lower calorie foods may have more calories than what are listed. One other small study found on average that posted calorie values are accurate. But studies of larger sample sizes and varieties are needed. These are the results of their (Roberts et al.) new study, published today in JAMA.
Foods were purchased from 42 restaurants in 3 different U.S. states, and lab measurements were performed and compared to the stated amounts on their websites.
The restaurants were randomly selected from the top 400 for sales in 2008 and were quick-serve or sit-down. Individual foods from each restaurant were also randomly chosen. The foods were considered low-energy if they had less than 600 kcal per portion and high-energy if they were above. Within each restaurant, 2 foods or low-energy and 2 of high-energy were tested at random.
In total, 269 food items were tested by bomb calorimetry (blended & freeze-dried into a powder, then quantified through combustion). Of these, 108 (40%) were at least 10 kcal/portion higher than the stated value and 141 (52%) were at least 10 kcal/portion lower than the stated value. 20 items (7%) were within + or – 10 kcal of the stated value. The average between all foods was only 10 kcal/portion higher than the stated values. However, 50 items (19%) were more than 100 kcal/portion higher than the stated values. So if you eat at a variety of restaurants and/or have different foods, it may average out over time (if this holds up in different regions as well). But if you repeatedly frequent the same restaurants and choose the same items, you may increase the risk of consuming more (or less) over the long run.
Quick-serve restaurants were on average more accurate than sit-down; for sit-down entrees, as the kcal/portion increased, the stated values tended to be more over-represented. In other words, the items with more calories in them tend to have less calories than what are listed by the restaurant. That doesn’t sound so bad. Howeverexamination of entrees from the sit-down restaurants that had less than 625 kcal/portion found that on average they had more calories than what was stated on the menu. Foods over 625 kcal/portion tended to have less calories than what was stated.
This is important as customer choices may gravitate toward lower calorie choices if calorie values are posted. Those who are tracking their calorie intakes would be more likely to under-represent their calories as well.
Intuitively these results (that quick-serve are more accurate) make sense; quick-serve restaurants are more standardized and require little manual preparation compared to sit-down restaurants. And no doubt there is much more room for “over-plating” to satisfy customers as Yoni blogged about recently.
They authors took the top 10% of foods (17) from both types or restaurants that had the highest (positive) difference between measured and stated energy values (average 289 kcal/portion above) and measured them a second time. 13 were still on the menus, but they found a similar average (258 kcal/portion) difference. With both datasets together, the average was 273 kcal/portion higher than the stated values. This is 48% higher than the average of the stated values.
They also categorized the foods (e.g. desserts, pizza, sandwiches, etc) and found that carbohydrate-rich foods (81 kcal/portion) and desserts (38 kcal/portion) had significantly more calories than stated. Carbohydrate-rich foods and salads had a wider variability in measured energy compared to what the stated values.
Shockingly, 1 side dish contained more than 1000 kcal/portion more than the stated 450 kcal/portion.
The authors note that studying this is important because
“…there are currently no federal regulations specifying acceptable limits of accuracy for stated information of individual restaurant-purchased foods, whereas packaged food regulations require that measured energy content in a random sample of 12 units must average no more than 120% of the stated energy content.”
As calorie posting legislation for sit-down restaurants is still moving slowly in this and other countries, this gives us a better sense of how to begin thinking about future regulations or public health messages.
The authors suggest that more protocols for controlling portions be introduced into sit-down restaurants to better standardize meals. This seems like a good idea, but I couldn’t imagine trying to run a restaurant especially at its busiest- would chefs have time to do this? For a bigger impact, the focus should be to try to get people to cook more and have fewer meals at restaurants, but restaurants will always exist so giving people another tool to aid calorie tracking is important.
Lorien E. Urban, Megan A. McCrory, Gerard E. Dallal, Sai Krupa Das, Edward Saltzman, Judith L. Weber, & Susan B. Roberts (2011). Accuracy of Stated Energy Contents
of Restaurant Foods Journal of the American Medical Association, 306 (3), 287-293 link