Generally speaking, adults need at least 1500 kcal of energy every day to maintain body function, because even if you lie still, your body still needs energy to maintain body temperature, cardiopulmonary function and brain operation. Basal metabolic consumption varies with individual height, weight, age and gender. Human survival needs energy, which is obtained from food.

Our body "burns" calories in food through metabolism, which breaks down carbohydrates into glucose and other sugars through enzymes, fats into glycerol and fatty acids, and protein into amino acids. Then, these molecules are transported to cells through the blood stream, where they can be absorbed and utilized immediately, or they can enter the final metabolic stage to react with oxygen and release their stored energy.

Extended data:

Calories (Cal for short) are defined as the heat required to raise 1 gram of water to 1 degree Celsius at 1 atmospheric pressure; Calorie is an energy unit, which is still widely used in nutrition measurement and fitness manual. The international standard unit of energy is joule.

As the legal unit of food calories, joules are widely used in Europe, while calories are used in the United States. Although Joule is the legal unit in Chinese mainland and Taiwan Province Province, it is still widely used in Chinese mainland and Taiwan Province Province because of tradition.

References:

Baidu encyclopedia-calories