Typically, speaking of consumers here, when you read a nutritional label it will actually list the number of calories in kilogram calories (or kcal). In fact a calorie is actually an infinitesimal...
The kilogram is a unit of mass. The calorie is the unit of heat energy in the old system CGS. A kilogram of a food has a specific caloric content (expressed in kilocalories or better in kilojoules)...