Calories Explained: kcal, kJ and Where Food Energy Values Come from
Lo que es una calorías alimentaria, cómo las kilocalorías se relacionan con kilojoules, y cómo se miden o calculan los valores energéticos en FoodFactly.
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This guide is awaiting editorial review.
The "calories" on food labels are kilocalories (kcal). One kilocalorie is 4.184 kilojoules (kJ). Labels in many countries list both values.
Where energy values come from
Food energy is rarely measured by burning food. It is almost always calculated from the amounts of protein, fat, carbohydrate and alcohol using conversion factors, known as Atwater factors. The general factors are about 4 kcal per gram of protein and carbohydrate, 9 kcal per gram of fat and 7 kcal per gram of alcohol. USDA also publishes food-specific factors, which explains why its energy values do not always match the general formula exactly.
On FoodFactly, the energy value of every food is labeled with how it was obtained. When Open Food Facts lists a product's energy only in kilojoules, FoodFactly converts it to kilocalories and marks the result as calculated.
Share of calories
Food pages show roughly what share of a food's calories comes from protein, carbohydrate and fat. This share is an estimate based on the general factors, so it is shown as approximate.
Updated . General information, not medical advice. See the editorial policy.