How Calories Are Really Measured on Labels

You Should Know: If you’ve been following the David protein bar drama, you know a class-action lawsuit alleges tests by a third-party lab found the bars contain significantly more calories and fat than listed on the labels. The brand is pushing back with a defense that comes down to a fairly technical point about how calories get measured. The whole incident raises questions about how exactly calories are measured in the first place.

Going Deeper: Calories can be measured in a lab using a method called “bomb calorimetry” that directly burns the food and measures total heat energy. But most nutrition labels in the U.S. are calculated using the Atwater system. It measures usable energy from food, instead of total energy, by assigning standard calorie values to each macronutrient. 

Takeaway: Not all calories are created equal. How food is processed or cooked can affect how much energy the body actually absorbs, and ingredients like fat substitutes and sugar alcohols, which are minimally digested, use different caloric measurements and values. The FDA also allows up to a 20% variance between what’s declared on a label and what’s actually in a product, meaning even a compliant label has a built-in margin of error.

Bottom Line: Calorie counts are generally reliable — but they are approximations. The David situation is a reminder that calculating nutrition information is more complicated than we might think.