Calorie (cal) is a physical energy unit, which is widely used in nutrition measurement and fitness manual. This word is transliterated from English calories and is defined as the heat required to raise 1 degree Celsius at 1 atmospheric pressure (10 1.325kPa).
Calories are units of energy. Calories are often associated with food, but in fact they apply to any substance that contains energy. Simply put, 1 calorie of energy or heat can raise the temperature of 1 gram of water by 1 degree Celsius at one atmospheric pressure. 1 calorie is approximately equal to 4. 186 joules (joules are commonly used units of energy in physics).
Most people associate calories with what they eat or drink, such as "This soda contains 200 calories". In fact, the calories listed on food packaging are calories, and the capital letter C is also marked, which is equivalent to the heat required to raise 1 000 grams of water from 14.5 degrees Celsius to 15.5 degrees Celsius at1atmospheric pressure, which is about equal to the internal energy of 4 186 joules.
Metabolism:
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. The calorie content in food is a measure of how much potential energy food produces. 1g carbohydrate has 4000 calories, 1g protein has 4000 calories, and 1g fat has 9000 calories. Food is generally composed of these three substances. Therefore, as long as we know the contents of these three substances in food, we can know how much heat or energy food contains.
The body "burns" calories in food through metabolism. Metabolism 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.