Calorie labels are estimates, not exact numbers, nutrition scientists say
Calorie counts on packaged-food labels are estimates with a typical tolerance of up to 20% due to variations in digestion, absorption, and fiber; bomb calorimetry is the most accurate method but many labels rely on Atwater factors, which approximate calories from fat, carbs and protein. Restaurant and processing differences add to the uncertainty, and insoluble fiber can make actual absorbed calories lower than listed. The takeaway is to treat label numbers as rough guides and compare similar products rather than fixating on precise calories.