In this week's New Scientist, Bijal Trivedi discovers that those calorie labels on food packages are lies, all lies. The typical method used to estimate the caloric content dates back to the 19th century and basically involves burning chunks of food to see how much energy it releases. The problem is that this doesn't account for the energy you spend actually digesting the food, which, it turns out, can be a significant factor. For protein- and fiber-heavy foods in particular, people actually extract anywhere from 5 to 25 percent fewer calories than advertised on the label.
Now, on one level, this is good news for weight-watchers and calorie-counters. If the box for that frozen pepperoni pizza claims 402 calories but the pizza's "really" only serving up 386 calories, then great. Fewer calories than we were led to believe!
But, researchers point out, where this really matters is in comparing foods. Say you're trying to decide between a vegetable curry and a pizza for dinner. The pizza box promises lower calories, so you toss that in the shopping cart. But, in reality, the fiber-filled vegetable curry was actually the lighter option. Small differences in calories can add up over time. (A bonus tip for meat lovers: Having a steak or burger medium rare can lower the calories, since lightly cooked meat is harder to digest.)
Anyway, here's the slightly amusing kicker: Even though scientists increasingly agree that existing calorie labels are all out of whack, they also say it's probably not worth fixing. In 2002, the U.N.'s Food and Agriculture Organization decided to study the issue and concluded that correcting the method for measuring calories was way too burdensome and would outweigh the benefits. What's more, nutritionists point out that consumers are already confused by food labeling, and detailed calorie counts would just baffle them further. So basically, our food labels are scientifically inaccurate and misleading, but living in an imprecise world seems to be good enough.