Heat means that when the change of system state comes from the destruction of thermal balance conditions, that is, when there is a temperature difference between the system and the outside world, we say that there is thermal interaction between the system and the outside world, and the result of the interaction is that energy is transferred from a high-temperature object to a low-temperature object. The energy transferred at this time is called heat. Heat and work are two different forms of energy transfer with the change of system state, and they are the measures of different forms of energy transfer. They are all related to the intermediate process of state change, so they are not functions of system state.
In nutrition, the unit of heat is kilocalories. 1 kcal is the heat required for 1000 grams of water to rise from 15 degrees Celsius to 1 degrees Celsius.
There are three main ways to consume heat. The first part is basal metabolic rate, which accounts for about 65% to 70% of the total calorie consumption of human body. The second part is physical activity, accounting for about 15% to 30% of the total calorie consumption. The third part is the thermal effect of food, accounting for at least 10%.