The amount of heat released is directly related to the amount of energy in the food, allowing a calculation to be made. This method is most commonly used for foods rich in fats and is considered the most reliable method.
However, this method requires detailed knowledge of the ingredients within composite foods — which may reduce accuracy. There is also a margin of error to expect with the Atwater system, because it assumes each ingredient is always the same in composition. Importantly, both methods estimate the amount of energy in food and drinks. But the actual energy our bodies extract from these foods and drinks can vary due to factors such as individual differences in digestion and absorption, as well as food processing and cooking methods.for packaged food items to have a nutrition information panel that displays the number of kcal it contains.
Fresh foods such as fruit, vegetables and meat also don't require a nutrition information panel. To find out the number of kcal in them, you can either run an experiment with a bomb calorimeter or look up an estimated value in an online nutrition database.compile information about the energy and nutrient content of various foods. Dietitians and other health professionals often use these databases to estimate the energy content of foods to inform dietary recommendations.