1, direct measurement method: it is to burn food with a special device and measure the heat released. This method is the most direct, but it is very troublesome and will hardly be used in actual production.

2. Calculation method of measured components: In most foods, calories come from protein, fat and carbohydrates. These three kinds of food ingredients have an average calorie value, protein and carbohydrate are 4 kcal/g, and fat is 9 kcal/g. Dietary fiber in carbohydrates is more complicated. Generally, soluble dietary fiber is calculated at 2 kcal/g, while insoluble dietary fiber is not counted as calories.

As long as the content of these components is measured, the heat can be calculated. However, carbohydrates can't be measured directly, but other components such as water, ash, protein and fat are measured, and the remaining "other components" are subtracted from the total amount as the carbohydrate content.

3, according to the formula calculation method: in food production, most cases are calculated according to the formula. The formula of a product is certain, and the raw materials used have relatively constant nutritional composition. According to the formula, we can also calculate the contents of various nutrients, and then according to their respective calorie values, we can calculate the calories of this food.

Extended data

Daily calorie requirement

1, the daily calories needed by adults = the basic calories needed for basic metabolism of human body+the calories needed for physical activity+the calories needed for digesting food.

2. The heat required for digesting food = 10% x (the minimum heat required for basic metabolism of human body+the heat required for physical activity)

3. The daily calorie required by adults = 1. 1 x (the minimum basic calorie required by basic metabolism of human body+the calorie required by physical activity).

Male: 9250-10090kJ.

Female: 7980-8820 kilojoules?

Baidu encyclopedia-food calories