A few years ago, New York City required that food service chains to post calorie count on their menu boards. Similar requirements are part of the Affordable Care Act and are growing in popularity. There is a debate as to whether such information does or does not make any notable effect on people's food choices. A study in the July 20 issue of JAMA addresses a different, but very important aspect of the debate. Can you even believe the calorie counts that are posted?
To study this, the researchers went to several sit-down and counter-service chain restaurants (not named) and purchased a variety of entrees, desserts, and side dishes for which there was posted caloric information. They purchased food from three different parts of the country, then freeze dried them and directly measured the caloric content using a bomb calorimeter.
At this point, it might be worth mentioning exactly what a "calorie" is. A calorie is a unit of energy, specifically heat energy. When we talk about calories as laypeople, they are kcals (kilocalories or 1000 calories). A calorie, then, is the amount of energy required to heart one gram of water by one degree (since the density of water = 1, this is also the same as one cubic centimeter or milliliter of water). A bomb calorimeter then is a device for burning a substance to see how much it energy it contains that is released when burned.
For the most part, the research suggests that yes, the calorie content is fairly accurate (within -15 to +54 kcals of the amount stated on the menus). However, they found that about 19% of the products underreported the measured caloric content by at least 100 kcals. There were some other interesting trends I noticed. For example, sit-down restaurant entrees actually were significantly LOWER in calories than reported, and that the more calories an entree reportedly had, the more likely it was being overestimated on the menu. Fruits a vegetables had one of the lowest amount of discrepancy, while salads, soups, carb-rich foods, and desserts had the highest underestimation of reported calories.
The take home message for me is that I do not think this study detected any systematic underreporting of calories to try and fool consumers. That said, there appears to be significant variability between reported and measured calories and it is hard to know if the menu under or over estimates the true calories. I still think the best bet is to take responsibility and make your own food so that you know what goes into it, and if you need to, you can count calories on your own.