The calories of general food can be found out from the food composition table, and can also be accurately measured by calorimeter. Put the sample to be measured into the combustion chamber of calorimeter for complete combustion, and all the released energy is absorbed by water.
Under normal pressure, a millilitre of water needs to absorb 4. 187 joules to rise once. The calorie of food samples is defined as: 1 ml (mass: 1 g), and it takes 4. 187 joules to heat.
Extended data:
In the process of human life activities, all life activities need energy, such as the synthetic reaction of material metabolism, muscle contraction, gland secretion and so on. And these energies mainly come from food.
Nutrients contained in animal and plant foods can be divided into five categories: carbohydrates, lipids, protein, minerals and vitamins, and water is six categories. Among them, carbohydrate, fat (fat can also store calories) and protein can release energy through oxidation in the body.